The Six Biggest Myths About Battery Storage

finn's battery system - energy storage myths

If you are buying a solar battery – go in with your eyes wide open.

I’ve been publishing thoughts on the solar industry since 2009. And since Tesla announced their Powerwall battery to great media hype in May 2015, a lot of those thoughts have concerned batteries.

Unfortunately, a lot of the facts I’ve published about batteries, their economics and their environmental impacts have not gone down well with some parts of the solar industry, generally the parts that have bet their future on selling lots of batteries in the short to medium term.

The reason they don’t like what I say (and one battery reseller has even threatened to ‘destroy’ me and my company) is that I (or Ronald) simply point out that home batteries do not currently pay for themselves financially or environmentally. These are not opinions – these are facts based on impartially looking at the numbers and engineering.

So I do have a reputation among some as being ‘anti-battery’. I am not. I have a big-ass battery installed at home (see picture above). I am simply pro-truth.

We have reached a point where big, centralised batteries like the Tesla Big Battery™ can make sense in grids with lots of renewables.  At some point in the nearish future, individual home batteries should make economic and environmental sense (as solar panels do now). When that happens, I’ll be the first to shout about it from the rooftops.

Until then, if you are considering buying a battery to go with your solar power system, here’s what you need to know.

The top 6 battery myths

Myth #1: Batteries improve the economics of solar power

For most homes in Australia, the return on investment from solar is going to vary from good to bloody fantastic.

Unfortunately, many people still look at solar, then look at the feed-in tariff, and mistakenly say:

“8 cents for exported electricity! What a rip-off. Solar can’t pay for itself without a battery; I refuse to virtually give my electricity away to the grid!”

This attitude is stoked by:

  • The mainstream media, who are either too lazy to do the sums or innumerate.
  • Much of the ‘green’ media, who have decided that batteries, and specifically Elon Musk, are the silver bullet that will solve all the world’s energy and CO2 problems.
  • The battery manufacturers who relentlessly gild the lily of battery payback.
  • A psychological condition called ‘inequity bias’ or ‘inequality aversion’. This is a powerful condition where humans hate inequality and will often act in a way that causes them to lose out if it means that it prevents another person (or company) getting what they perceive to be an unfair gain. The result of this very human condition is that people will often buy batteries that will never pay for themselves simply to avoid selling electricity cheaply to the grid, which the ‘evil’ electricity companies can then on-sell to your neighbours at a profit. I would go so far as to say that this is the biggest driver of battery sales at the time of writing.

The truth is that at current prices, for the vast majority of Australian homeowners, batteries will not pay for themselves before the warranty expires. And when buying a solar power system, if you add batteries, you’ll make the payback of the system as a whole worse – not better.

Further reading: Beware of Blended Payback: Solar Pays For Itself But Batteries Don’t Yet.

Myth #2: Grid-connected batteries save you the full cost of buying grid electricity

I occasionally get emails from people who claim I don’t know what I’m talking about when I advise that batteries don’t pay for themselves yet. They then helpfully do the maths for me. And they almost always make the same mistakes in their calculations. The chief one being that they don’t seem to understand the concept of ‘opportunity cost’.

Q. How much do you save, per kWh, if you store your solar energy in a battery and then use it at night?

A. Although you save 30c (or whatever your usage tariff is), by not drawing a kWh from the grid, you are, obviously, not now exporting that kWh to the grid. So you are losing the feed-in tariff on that kWh. Most people, if they shop around, can get at least a 10c per kWh feed-in tariff. So if you are saving 30c per kWh, but losing 10c per kWh. Your net benefit is 20c per kWh. In fact, it’s a bit worse because every time you charge and discharge the battery, you lose ten to thirty per cent of your energy to battery inefficiencies1 .

Further reading: Why Feed In Tariffs Hurt The Economics Of Batteries

But not everyone wants a battery for economic reasons. Many want a battery to reduce the carbon footprint of their home. That brings us onto our third battery myth:

Myth #3: Batteries reduce your carbon footprint

If you have a grid-connected solar power system that exports surplus solar electricity to the grid and you add batteries, you actually increase your home’s carbon footprint. Sound crazy? Bear with me.

If you don’t have batteries, any excess solar energy gets exported to the grid. While you may be disappointed with the feed-in tariff this pays you, the environmental benefits of your exported solar electricity are very real. Each kWh you export means that the grid has to generate a kWh less from fossil fuels. You should feel good about that.

However, if you have batteries on your home, every kWh you put into the battery is one less that goes into the grid. So although your stored solar means that you have to import one less kWh, it also means that you’ve exported one less kWh. So there is no net environmental benefit.

In fact, because a battery system is only seventy to ninety per cent efficient2, you are offsetting ten to thirty per cent less CO2. And you also have to repay the large amount of CO2 emitted in the manufacture, delivery and installation of the battery and battery inverter.

Further Reading: Peer Reviewed Study: Grid Connect Solar Helps Environment But Batteries Harm It

But there is another, non-environmental, non-financial reason for buying batteries: energy security. Which brings us onto myth number 4:

Myth #4: All batteries can provide blackout protection

No one likes losing power to their home. Batteries can power your home during a blackout. So perhaps you are thinking of buying batteries for blackout protection.

There are a few things you need to know if that is the case.

Firstly, many solar battery systems will not work when the grid goes down unless you pay extra for the engineering and electronics to allow this. Running a home without the grid is quite a complicated task, because you need to:

  • Isolate the house safely from the grid, so you don’t send electricity into the grid and kill lineworkers trying to fix it.
  • Balance all the generation and loads so that you match supply and demand at all times.
  • Ensure that the battery is never overloaded by the house loads.
  • Ensure that the battery is never overcharged from the solar.

All this functionality comes at a cost. So if you are buying a battery and want blackout protection, be sure you are getting a system that will actually do that3.

Before you do that, however, you should have a think about how big a problem blackouts are for you, and consider other, much cheaper, solutions.

If blackouts are a major issue for you, the cheapest form of blackout protection is a petrol generator. You can buy one that pushes out 3 kW for about $1,000 at Bunnings. Three kilowatts will power most of your home most of the time, unless you have a particularly large air conditioner, in which case you may want to spend more on your generator. The generator will last as long as you have petrol.

A suitable battery-based solution will cost you about $12,000 at the time of writing.

So, although the generator requires a jerry can of fuel and is noisy and creates exhaust fumes, it is 12 times cheaper. And if it is only used once or twice per year, the overall carbon footprint is likely to be less than a big battery that sits idle ninety-nine per cent of the year.

At some point in the next three to ten years, batteries will become so cheap that it will be crazy not to have them on your home. And if you have batteries on your home, you may as well configure them to back up your home in emergencies. Especially as climate change sends more extreme weather our way.

Further Reading: Does your hybrid solar system really need backup?

So it is important to be able to add batteries to your solar power system in the future. Which brings us onto our last battery myth:

Myth #5: You need a specially designed solar system to add batteries in the future

If you are thinking that a ‘battery ready’ solar system might be a good idea – I agree. That is a great idea. And the good news is that every grid-connect solar power system ever sold in Australia is ‘battery ready’.

Batteries can be added to any existing solar power system using a technique called AC coupling. The batteries’ power simply goes into your home through the standard 230V AC wires. Simple as that.

So don’t worry about buying a special ‘battery ready’ system. Batteries can be fitted to any solar system you buy. The only thing you need to bear in mind is that you have enough panels to charge a future battery. Generally, if you think you’ll add batteries (or an electric car) to your home in the future, I’d err on the large side for your system and buy at least 6kW of solar capacity.

Now, there’s one more myth…

Myth #6: Adding batteries to your solar is sticking one finger up to the electricity companies

Hands up if you like your electricity company?

Thought so. But before we get into the reasons why electricity companies are so hated (the only country that hates them more is the UK), you may not realise there are actually up to four companies that are responsible for getting electricity to your house and they all get paid from your bill. Let’s explore who they are and see which ones we really have the bad feelings for.

electricity companies

The 4 companies that you pay through your electricity bill. Image credit: SAPN

Generators own the power generation fleet, be they coal-fired power stations, wind farms, gas power stations or hydroelectric systems.

Examples are AGL Energy (who are also a retailer), who own lots of coal, gas and wind, Origin (also a retailer), TRUenergy, Macquarie Generation, Snowy Hydro and a handful of others.

For every $100 you pay on your electricity bill, these guys get an average of $22 for generating the electricity. Yes – that’s right – only twenty-two per cent of your bill is paying for electricity to be generated.

When you buy grid electricity, you can have some control of whom you buy your electricity from. If clean energy is important to you (and I personally believe it should be), you can pay more for green power, and the part of your bill that pays the generators will only go to people who have generated enough renewable energy to cover your usage. This is a good thing because it increases demand for green energy, which means more renewable generation will get built.

But bear in mind that many of the largest fossil fuel generators also have the largest fleets of wind and solar, e.g. AGL Energy. So if you really want to ‘stick it to the man’, understand that, even with green power, you may still be lining the man’s pockets.

Transmission networks get about eight per cent of your bill. They are the companies that build and maintain those big pylons that carry electricity from the big generators to the big substations near population centres.4

Their formal name is transmission network service providers or TNSPs to their friends.

Below are the details of local TNSPs:

TNSPs: Transmission Network Service Providers

Are you angry with any of these companies? You may well be – I don’t know. They are a large part of ‘the grid’. They enable coal-fired power stations to distribute their power. But they also make wind and solar farms and the snowy hydro scheme viable. Being angry is your call.

If you decide that a deep dislike of your local transmission network is a reason you want to get batteries, just be aware that they only get eight per cent of your bill. And some of that will come from the fixed ‘service charge’ part. So even if you get your grid imports down to almost zero, as long as you are connected to the grid, you will be giving money to the network companies.

Once the electricity leaves the transmission network, it uses the distribution network to get to your home. The companies that own and operate the distribution network are called the distribution network service providers (DNSPs). These guys get about thirty per cent of your bill.

Below are the details of your local DNSPs:

distribution network service providers in Australia

Again, part of the DNSPs’ income comes from the fixed service charge, so even if you import almost nothing from the grid, these guys will still get paid. Also, they are responsible for administering the premium feed-in tariffs, which are no longer open for new customers, but are still paying really good rates to customers that invested in solar energy many years ago. That was a big part of building the solar industry and a major reason that it became so efficient, meaning Australia now has the cheapest residential solar in the world.

The last company in the line for your cash is the Electricity retailer.

Electricity retailers collect all your money and typically keep thirty per cent of your bill to cover their overheads and profit (these are the guys you can switch easily). These are the brands you probably think of when you think of ‘electricity companies’.

So here are your potential positions:

  1. You hate them all. Then you must go off grid. Even if you draw no energy from the grid, if you are connected, you will still pay the service charge5 of 70c – $2 per day, and every type of company in the list above will get a cut.
  2. You hate the TNSPs or the DNSPs. It’s off grid for you as you can’t avoid paying them.
  3. You hate some of the generators (usually people hate the coal burners or frackers). You can pay extra and specify ‘green power’ with many electricity retailers. The good news is that this will prevent your money going to the generators that don’t have any renewables. The bad news that if you hate the biggest coal generator in Australia (and fan of fracking): AGL, much of your money is still likely to head their way because, ironically, they are also one of the largest renewable generators in Australia thanks to their wind and solar farms. It’s worth noting that any ‘green power’ payment they do get from you has to be for renewable generation, though – so you are encouraging them to mend their ways.
  4. You hate the retailers. Really? All of them? There are some quite nice ones out there who are very pro solar. Two that spring to mind are Diamond Energy and Powershop. You can see how their rates compare with this tool. But again, if you really hate the retailers, you must go off grid to avoid giving them your cash.

So if you have a strong emotional need to stop giving cash to the four types of companies that make up the electricity market, you need to not only get batteries, but disconnect from the grid altogether. This is a much, much more expensive option than adding batteries and staying on the grid. In fact, it is so expensive that you may reconsider quite how much you need to ‘stick it to the power companies’ altogether.

Conclusion: Should you add batteries?

For financial reasons? No. Not for a few years anyway. Don’t worry – I’ll update this post as soon as they make financial sense.

For emotional reasons (sticking it to the man)? No. Batteries only reduce your kWh usage from the grid, you will still be supporting 4 big electricity companies with the daily service charge. If you really don’t want to be part of the grid, then the only rational choice is to go off grid. If you have an average Australian home, a suitable system will start at about $50k6

For green reasons? Hell no. It is better for the environment to reduce your remaining post-solar impact with green power from a friendly retailer like Diamond Energy.

For security? Absolutely. But be aware it adds to the cost, and as I’ve mentioned – many batteries do not come with backup by default, strange as that may seem. So buyer beware.

For nerdy reasons? Go for it. You like new technology and have the cash to spare? Then you can get a big box of batteries and watch the monitoring software to your heart’s content.

Here’s what I tell my friends when they ask for advice on solar and batteries: Unless you need generator-free backup or really, really want a battery for technology’s sake, conserve your cash. Batteries will make sense in a few years, both environmentally and economically. Until then, a big solar power system is a much cheaper way to get tiny bills.  The worst thing you can do is put off getting solar panels because you have an emotional aversion to exporting solar electricity back into the grid at far less than the retail rate. You’ll just be subjecting yourself to more years of high electricity bills and boosting the profits of those electricity companies you dislike so intensely.


  1. People send me their data, and I’m seeing real world battery efficiencies of about 75% due to low discharge power relative to the standby power draw of the battery system
  2. see previous footnote
  3. And if you want multi-day backup, go further and check the system will charge your batteries from solar without the grid
  4. If you are interested, they carry the electricity at 132,000 or 275,000 Volts. The high voltage is to reduce losses due to the resistance of the wires.
  5. yes – even if your bill is zero or a credit, they get paid from the profits made from reselling your solar exports
  6. this is where I get lot of comments from people who use 4 kWh per day telling me they went off grid for tuppence. Try taking a typical 20kWh per day Aussie home reliably off grid for under $50k. It’s not possible.
About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of My last "real job" was working for the CSIRO in their renewable energy division.


  1. Brilliant article, Finn.

    Some typos, the most problematic of which may be:

    “It’s worth nothing that any ‘green power’ payment they do get from you has to be for renewable generation…” Assume you mean ‘noting’, but the typo may suggest the opposite conclusion… .

    Emailed this article to my missus, to help persuade her to wait a while… .

    • Thanks – fixed up now!

    • Steve Charles says

      I agree with the financial argument overall, but if you are going to get a battery, you need one with an inverter that will operate when the power fails. This to me is the whole point in installing a battery.
      Secondly, there are other financial factors too, When the power fails for some time as it has done here in SA, you are without phones, you can lose food in your fridge freezer, and if you are running a business from home, downtime can cost you money. So, what price would you put on a batter.
      Thirdly, a comment about generators and voltage regulation. A generator cannot go from no load to full load without affecting the frequency and output voltage. This can damage equipment in the home such as fridges and pumps – anything that uses a motor. This can be expensive. An electronic inverter, on the other hand, does not have these limitations.

      • Mike Gaskin says

        I live in Mexico where grid electricity fails frequently. I got into solar to protect myself from being without power for weeks at times. What I have now is 4.2 kw of panels, grid tied with a switch box built by my installer that allows either grid tie or battery back up through inverter to power the house.
        It is true that enough batteries to run even my relative low usage for 24 hrs. is cost prohibitive. My answer is battery power used as buffer during the day, turn off the fridges and freezers at night, let them “coast” till the sun comes up, plug them back in while the panels are generating, rinse, repeat.
        I only have 4 deep cycle batteries, which are enough to watch tv and computer at night and led lights. As we normally go to bed at ten we only use the batteries completely for 3 hours or so, we have enough.
        Certainly not elegant but when you are in a grid fail situation and live on very limited retiree income you gravitate to what actually works and can get you by pretty much indefinitely if need be.
        I too am looking towards the future when some serious battery tech becomes available, many charge cycles without damage, light in weight, small footprint, safe, all of it. Lithium Ion latest fill much of this bill, but are very costly in enough storage to run my house.
        I guess my survivalist at core mentality has brought me to the system I have, crude and with drawbacks, but it does work and has gotten me through several extended black outs.

      • Whilst a generator is an option …. there are a few things to keep in mind.

        1/ Unused petrol will deteriorate over time so you’ll need to cycle newer petrol through your storages. Also bear in mind service stations need electricity to run their bowsers, in the event of a long outage, you won’t be able to fill your jerry can.
        2/ Unless you have an automated system, you’ll have to go out and start the generator …. even at 3 in the morning.
        3/ How do you know how long the power will be off ? You might have just started the generator (at 3 in the morning) and the grid power comes back on as you get back into bed.

        There are many reasons why a generator is a good/bad idea as well as the good/bad aspects of having a battery strapped to your wall. The bottom line is the battery will take care of it all for you AS LONG AS you have a system that will continue to operate … and recharge …. even if the mains is down for a long time. Oh … and that won’t come cheap, so of course, do your sums !!

  2. Hi Finn – good summary on reality.

    My two bob’s worth:

    Do NOT buy a hybrid inverter today in view of being able to “simply” add batteries to it tomorrow. If you buy a hybrid inverter today then you need to be serious about adding batteries today Why? #1 Because regulations change with monotonous regularity. It’s very possible someone will dream up a regulation making it “illegal” to add batteries to your battery free hybrid. #2 Because batteries are like computers and they change with monotonous regularity. There is every chance that tomorrow’s batteries will be incompatible with today’s hybrid inverters.

    I haven’t done the hard numbers (yet) but I suspect that people on the Vic PFIT may get an economic return from batteries by using batteries to allow more export of power when the sun is shining and recharging from the grid at off peak rates at night. Finn or Ronald, if you’ve done these numbers, please share 🙂

    • If you go back to nearly the Big-Bang of SolarQuotes you’ll find a comment where I described doing exactly that for 10(?) years ~ ever since I’d moved down from the hills ~ where I’d been living with a stand-alone solar system , including a massive battery bank which more than paid for itself ~ for 20-some years. (and that was when 2nd-hand panels cost $13.80 per watt).

      But the principle is no less sound now than it was then. Think innovatedly, never pay for anything you can do for yourself, and waste nothing.

      • OK. Let’s take these figures for a spin.

        At $13.80 per watt, a 1000W system would cost $13,800. Let’s be generous and say that this caught an average of 5 peak sun hours per day, so 5 kWh per day or 1825 kWh per year. Let’s assume an electricity price of 30c per kWh? That’s $547.50 per year. The simple payback on that would then be 25.2 years and that’s assuming every other component in the system (batteries, regulator, inverters, wire, racking, fuses…) was free and that the system behaved perfectly without any losses.

        Unless a whole ton of this stuff is falling off the back of a truck, or you have a local retailer charging a fortune for electricity, or you live in a world where efficiency factors are all above 100%, or you actually live ON the sun, or you’re working with some very weird maths… I put to you that the figures don’t match the words.

        Your move.

        • A dear old duck I knew for years (probably before you were born) used to say ‘If you assume you make an ass out of u and me’.
          Trite and silly perhaps, but it came to mind irresistibly upon reading your note.
          And your assumptions are wrong, irrelevant or both. Keeping in mind I refer to a time when solar panels had only ever been heard of by inquisitive (and money-free) hippies (and cynics who, even when they were shown a panel-connected globe lighting up, sought high and low for the hidden battery) I can substantiate every doubt you raise. (At this very moment I’m working by the light of a 1st-generation ‘energy-saving light’ which cost about $35… or about 18.% of a week’s wages.

          The point is I CAN demonstrate my claims (more or less, allowing for the passage of time and failing brain-cells) and show you some pretty photos that survived the fire. And in fact tried TWICE to post (here) video of those early panels still at work today in a (mostly tech-free) environment in the mountains.
          But such stuff (anti-commercial and plastic attitudes) doesn’t get printed here, so if you want to get the details you raise (among other good stuff) I can only suggest you inbox me –> [email protected]

          Will look forward to hearing from you.

          ps. Just last week I managed to buy a TV which runs on 7watts dc. ( It replaces the one from back then which ran on 8wattsdc until it died with the advent of digital TV……Judging from your ‘assumptions’ I guess you have one of those wall-size jobs that operate in the kw range?

        • I’m sure you’re aware of the rapidily-falling prices for all the stuff involved. In any case, much of it (cabling/switches/etc/ etc/) can be acqyuired for free: and other things like connectors, etc. I make myself out of boarded bits of stuff.

          But your numbers-game falls on the basis of false assumptions.
          eg. At that time I didn’t have 1000 watts of panels: but a total of (rated) 154watts. (biggest panel available on the market at the time was 64w. (Which can be seen still producing ~ along with a couple of 45w units at that google reference –> Calamity Jill

          And the price of power would’ve been nt unreasonable the time: but the price of getting in onto the property was beyond reason, and certainly beyond me. Had an income-stream of about $120 pw (Centrelink). That was back when price was the only reason the few people who’d heard about solar considered it, despite the price of panels. (And most evrything else was made/adapted.) —->
          Recycled bulldozer/jinker batteries (about 1200 Ah) were available in droves for free. Regulators weren’t needed: the size of the battery-bank and the lack-of-size of panels available made regulation irrelevant. Iverters were of the small crappy car-mounted variety and cost under $20 and so on.

          And of course there were losses ~ even the tiop-shelf omponents back then were inefficient crap. But inefficiencies were tolerable because wastage of some FREE sunlight meant it wasn’t costing you anything.

  3. Nice article! You might want to correct something though: under 3 – you hate some of the generators, it says ” It’s worth nothing ” where the context suggests you mean “It’s worth noting”. Small typo, big difference 🙂

  4. I will keep you informed as my battery system will be installed early next month. I guess I fall into the class where I just want to try it out. I have a 3KW system but unfortunately it is on the ENE side of the house. I looked at adding a second “system” to the other side to cover the evening power use but was offered a battery system for $5271. My thoughts are to see how this works. I read your comum regularly. Unfortunately you normally only comment on eastern states figures and My details do not fit yours so I am going to try it. I am happy to send you details as the system is completed. I did consider installing a second system on the opposite side of the house but I will try this first.


    • I’m in the same camp – I have a battery, it reduces my bill by a modest amount. I bought it to play with. I’m strange like that.

      • Ian Cargill says

        Play? Surely it was purchased to do serious (tax deductible?) research on an important part of your professional activities? 🙂

    • ….. or you could spend about $100 and set up a gazebo, hothouse, workshop, whatever oriented due North and with movable frames to accommodate tracking the sun.
      You can get as simple or expensive as you like….but I see not making the most of your resources as verging on immorality.

      Here’s an old mate of mine who installed (long ago) a manual tracker (!) and who threw out a battery-bank a couple of years ago that she bought, 2nd-hand but hardly used, for either $9 or $15 ~ after using them for 28 years. So much for battery-banks not paying their way.

      Among the solar panels are a few of the first ones I bought all those years ago. They were incredibly expensive, but are still working at about 80% of their rating.

      ps… the water-wheel is an engineering marvel!….. and didn’t require any
      numbers to create the ‘fact’….It not only pumps water to a header-tank 100-odd foot up the hill, it doesn’t scare the fish as some other pumps/weirs probably would.

      • Why was the link not published?? It simply showed a basic hotch-potch of solar-panels and (until recently) used lead-acid batteries that have provided ALL the electrical needs for a house ~ and has done so for over THIRTY years.
        The link was to a short program recorded and broadcast by the ABC, and PROVES ABSOLUTELY THAT A FUNCTIONING SOLAR SYSTEM NEEDN’T COST THOUSANDS OF DOLLARS. ~ which may be why it was black-balled.
        If you have ….um, ‘commercially sensitive’ reasons for not allowing opposing views you might say so.

        ps The water-wheel comment makes no sense without seeing the whole clip.

      • Hell, this blog doesn’t seem to be able to be killed short of a stake being driven through its heart!
        Somebody obviously added a comment recently, and hence I assume updates were sent out to all contributors who opted for notifications at the time of the original blog, four or five months ago.

        Upon re-reading, have just noticed Jackson’s advice of building a hothouse and placing solar panels on it, to get around orientation problems with solar panels.

        Anyhoo . . . . . . . “….. or you could spend about $100 and set up a gazebo, hothouse, workshop, whatever oriented due North”.
        Thanks, Jackson – next time Aldi is running a $100-or-so Special on back yard, 30 square metre hothouses (or a roof for my suburban water-wheel), I’ll keep an eye out for one that will support half a tonne of panels.

        Keep smilin’

        • “…hence I assume updates were sent out to all contributors who opted for notifications…”

          Not sure that this is actually happening. Going back through some topics to which I’ve responded, I’ve noted many replies for which I’ve received no notification… .

  5. Lawrence Coomber says

    1. Finn your’s and before that Ronalds comments about the commercial viability (if of real interest to a prospective purchaser) of current ESS integration with Solar PV systems was accurate and facts based and I endorse in general terms the thrust of your commentary. Well done.

    2. Don’t be at all concerned about abuse from vested interest entities about your factual commentary. Invite them to put up some (facts based) spreadsheet calculations on ROI for example. They won’t respond.

    3. Like yourself I am involved in ESS technology innovation and also battery bank manufacture and have been for many years (Off Grid solutions) and have always only been interested in factual computations that apply to the system technology, and never any fanciful concoctions by nervous vested interest businesses, lobby groups and individuals which at times border on near hysteria.

    Lawrence Coomber

    4. So stick to your guns and don’t fall into the trap of attempting to moderate your facts by moving slightly towards the centre to appease or soften the impact on the vested interest non-facts based critics.

  6. I am so happy that you are telling the truth Finn. I think you are the ONLY person doing so. We have for a long time echoed the very same reasons to our clients looking to install batteries. I mean, its our duty as a CEC Approved Solar Retailer to give clients honest advice. Unfortunately, that honest advice is often NOT what people want to hear and that is because they are being hoodwinked into believing that batteries make good economic sense by unscrupulous solar retailers with clever marketing. Actually, remove ‘clever’ marketing and replace with ‘devious’ marketing!, Anyway, well done on pushing the truth mate. It shows that you are a truly genuine and honest individual with a sole purpose of providing consumers with the facts.

    Footnote, I attended a CEC sponsored talk about warranties on all the current batteries on sale in Australia. It was given by a law professor, and this lady said that her investigations found that ALL batteries currently being sold in Australia (this was last year October) were in breach of Australian Consumer Law.

    • Thanks for the kind words.

      Re: ACL – yes we’ve been banging on about this for a while:

      The battery manufacturers appear to have their fingers in their ears.

      not listening

      • That’s why the current ACL needs to be changed. It is complete rubbish. The whole idea of express/implied warranties is just the legal profession’s wet dream. How about going back to an actual warranty….you know what it is when you buy the product…”2 year warranty”, fine you know what you are getting. If you don’t like the warranty then don’t buy the product, simple. I hate to think of the warranty tail that is going to bite every business in coming years due to the ACL. Any there is no definitive view – ask the ACCC what “reasonable” is. Haha…they cannot provide you with a definition, so is entirely subjective. Most ridiculous piece of legislation ever written.

        • Mark McClurg says

          The biggest problem with the ACCC and ACL is that big industry can write their own terms of trade and warranty terms in defiance of the ACCC. Its like the car industry. They set their own warranties over and above what is deemed a reasonable and expected lifespan. Small and medium business don’t have lawyers on their books to write their own warranty terms. There are double standards in play and often it’s the small business owner having to incur the costs of managing ACL or taking over liability from the big corporations who might decide to shut up shop if trading conditions don’t suit their limited liability Ethos.

          • There can be options. The supplier/installer I engaged to put in a grid-connected system (after a month of research/phone-calls ) recommended some Chinese components for (cheap) price and reliability. Nobody had ever heard of the panels, and the inverter had been generally shitcanned by the online ‘experts’. Manufacturers (inChina!) offered the standard warranties, (in China!)
            In the end I composed what I thought were reasonable warranties, in plain English, and asked him to sign that agreement as being binding on BOTH his company and/or him personally.
            He never hesitated ~ and that’s about as good an indicator as it’s possible to get…..and it worked.
            The panels worked stunningly from start to finish. The inverter developed one (known) fault 6 months later; one phone-call had a replacement on the doorstep at 8am the following morning. There was not another hitch over the next nine years that I lived there.
            Technology these days is so complicated and abundant that all we should be concentrating on buying is an enforceable warranty.
            Try it: you might like it.

    • We’ve been making the same points too in our magazines, website, talks etc.

  7. From reading your posts all you seem to harp on is “payback” and NOTHING ELSE matters to you. But luckily that is not exactly how the world works. People do things for MANY reasons and if someone wants to buy a battery bank or go “off grid” than do not try and come up and say “it will never pay for itself”. Because OVER time it certainly will if all you want to take about is “payback”. People who generally go “off grid” do it for many other reasons and the last on the list is”payback” IMO. In fact when people tart taking “paybacK” 99% of the time they do not buy. Solar to me is a lifestyle choice more than anything else. When it is a lifestyle choice than payback basically does normally is not part of the equation. For example, buying a Mercedes car is a lifestyle choice. Do you think for a second the guy buying one cares about “payback” ?

    Two things to keep in mind:

    1. Yoru service or fixed charge will only go up over time. That means you simply pay for the privilege of being hooked to the grid. With proper planing, and implementing energy efficiency measures an “OFF grid ” system does not have to cost $50K. (please break down those costs) Our compnay can supply most people today with an “off grid ” system that costs half that with proper planning and implementation of energy efficient measures and give the a totally modern lifestyle. 50K sure if it is a energy hog. Most people are unfortunately not and that is one reason more people do not go off grid. For example, virtually every one I know leaves lights on when no one is in a room, has no power strips in their homes to control phantom loads and let phantom loads run wild.

    2. The norm is being tied to the grid. Once batteries become cheap enough (and they will as you state) then people will have absolutely NO reason to hook up to the grid. That is when the current utilities will fail as a business model. To survive they will have to join the party so to speak, but by then it may be to late. BTY on site energy is more environmental friendly. On site power requires little transmission, little distribution, no government, no politics and the middle man asking for a rate hike on a regular bases. And one other thing. YOU OWN SOMETHING. How about that! When you are hooked to a utility all you do is pay for a SERVICE. That is it. Nothing more.

    Going “off grid” is not for everyone, but more people should be doing it, but we are creatures of habit and so many of us have a physiological attachment to the grid that one would never stray. They have you by your balls and pocketbook (for now).

    • Hi John,

      Feel free to read the whole post – especially the bits where I say there are other reasons than financial for buying batteries.

      Like most things, solar panels are much more efficient in a network. Off grid solar wastes lots of solar potential when the batteries are full.


      • Lawrence Coomber says

        Yes Finn I have certainly seen those wasteful Off Grid PV generation systems you are referring to over the last 50 years as an electrical engineer. But I have in more recent times (2010 +) seen those Off Grid and Off Grid (Microgrid) generation solutions that are quite a bit smarter in managing generation; storage and alternative loads distribution strategies.

        Lawrence Coomber

    • GoodonyerJohn. My only problem with what you say is that you agree with me……..What’s wrong with you??

      And as always the proof of the pudding is in the eating. “Because OVER time it certainly will if all you want to take about is “payback”.”. I’ve been living with battery banks since the early 1980s, and have on occasion demonstrated that batteries can and do pay for themselves (barring stupidity or other acts of god).
      The proviso is that you stick with the proven (and still provable) product: Basic Lead-Acid batteries.. .. As the old slogan says: When you’re on a good thing, stick to it.

    • John D, I would be interested to hear the storage capacity of your (presumably ~$25,000) storage system. Or does it involve wind power, and/or generator backup, or what? The point being that disconnection from the grid must involve some extended source of power.

      Wind power is largely impractical in suburbia, as is generator power for anything more than just a couple of hours during daylight.

      If you do disconnect from the grid, where do you get your power after three or four days (plus) of continuous bad weather? Genuine question.

    • Ian Cargill says

      Bit of an over-reaction mate. Finn didn’t say you shouldn’t buy batteries, just that if your reason for doing it is to “save money”, you mostly wont. And he is perfectly correct. There are many reasons to install batteries; that isn’t one of them. (Friend lives in rural Tas. The quote for connecting the mains power to them was about twice the cost of an 8kW hybrid wind/solar system with batteries. That’s justification!)

      • ….until Finn is proven to be wrong.
        I responded in some detail to your and Greg’s assertions about that unsubstantiated nonsense re. battery-banks not being able to pay for themselves/save you money/whatever. Once again the censor wielded the green pen. So will try this:-
        Detail aside:-
        1……… Decent panels (currently Jinko) available on ebay/elsewhere for around 60 cents per watt. (or for 34 cents if you buy a shitload/container-full of them).

        2………… AGM/ SLA/etc-type batteries (with a three-year warranty) available almost anywhere for under $2 per ah.

        3……… Without relying on the ‘generosity’ offered by Scott (above) AVERAGE yearly insolation in Melbourne (according to the Bureau/authority) is 4.8 hours per day.

        Accordingly, 2083.333 ‘produced-watts’ x 4.8 hours produces 10 kw per day.
        A 12-volt battery-bank will store 10kw in 834 ah.
        Brackets/cable/switches/etc. can mostly be acquired for free; but say $500 (including small single-circuit inverters, etc.)

        Price of 2083 watts of panels = $1250
        Price of 10kw of battery-storage = $1668
        Ancillary = $500
        Total ~ generate and store 10kw in round figures = $3500
        To accommodate the variables/contingencies/ DOD considerations/etc., DOUBLE the figure ~ and you STILL come out well ahead of the asserted costs.

        As stated above, the numbers/facts/engineering-assertions can’t be taken as gospel, and the endless variables leave open endless variations on a theme. But my (closely-monitored) 10-year experience with 2140 watts of panels in the Latrobe Valley (same latitude as Melbourne though with rather more air-pollution ) approximately supports those figures…. allowing for the inevitable variations.
        Experiments with a a battery bank (ex-standby ‘Vision’ AGM, 1200ah which I bought for $1400) more or less confirmed my daily/monthly/yearly production-rate as near as I could tell. The first battery-failure occurred after eight years.
        The point is that a battery-bank will easily pay for itself in a reasonable time-frame, assuming due care, and need cost NOWHERE near the figures touted.
        While no price outlaid can be reasonably compared to income from the same amount of money, neither can you run your TV and computer from money invested in a bank/wherever. That whole line of argument is a nonsense. (Presumably it’s one reason why FiT offers are limited.) If you want to use electricity ~ or anything else ~ there’s a price attached. How you can minimise/prioritise that price is a different matter. But always remember:- anybody who sells you ANYTHING is not making a loss. He wants to profit: ie, get more money from you than he paid for it. And if you assume that he paid the ‘right’ price for it you, ipso-facto, are paying too much.

        No doubt you can rationalise into existence the profit you make by sending money off to the Taxman, too. 😉

        • Jackson,

          So if I get a pile of tradie mates together, I can build a basic suburban brick bungalow for the wholesale cost of materials alone – I dunno, but for the purpose of this exercise let’s say $50,000, just for the heck of it.
          That does NOT mean a suburban brick bungalow costs $50,000.

          And another mate is a pretty good mechanic who happens to have all the software and tools to service my modern European set of wheels. So I can service it for the cost of the consumables. Again, just for the heck of it, lets say $40.
          That does NOT mean the cost of servicing a modern European car is $40 plus a slab of beer.

          And so on, and so on.
          (However, without in any way reflecting on your skills/qualifications/whatever, I must admit I’m quite relieved suburbia is not full of the great unwashed running themselves up DIY grid-connected solar systems with parts obtained through eBay.)

          Also, I’m fairly confident there is enough competition around in Australia in the solar power field to ensure there is not some national plot to artificially inflate prices – in other words, sort of (in this field, a very active) Free Market. So presumably that is the current basis of pricing.

          In addition, I’m reasonably confident the majority of the masses today (even my tie-dyed neighbours “up the road” at Mulumbimby) are splurging out on something a little more decadent than 6w battery-operated TVs. My point being, on the question of economic viability of batteries in a domestic solar situation, I think Finn probably had in mind an average, mainstream domestic residence. (Although I do find the concept of the kids having to run the TV and charging their gadgets through a pedal-powered alternator, perversely tempting.)

          Finally, sorry Finn has apparently singled you, and apparently you alone out for black-balling and green penning, for commercially sensitive reasons, but hey, we all have to make a quid!

          Keep smilin’

          • What was the definition of ‘sarcasm’?…Oh yes! ~ ‘the lowest form of Twit’.
            I’ll try to respond as briefly as possible, comment by comment.
            For background:-
            1…….. If you’d taken advantage of my offer of photographs you’d have seem the last house I built in the forest out of Marysville. It IS 26 squares including verandahs ~ mudbrick, and EVERYTHING else except concrete was recycled. Did ALL the work myself ~ including the ‘engineering’/plan-draughting up to Council standards ~ including plumbing, electrical, gas, etc. ~ sans a herd of ‘tradies’ and sans any “qualifications”……. All that was required was an accumulation of experience/skills, a few brains and a modicum of motivation; and that, of course, is why ‘tradies’ were banned from the site: great at gluing plastic and other pre-manufactured crap together but not much else. Working alone the whole job took about 18 months, but I was able to move in after 4 months.
            And “working alone” meant ~ among other things ~ transporting, unloading and standing upright tallow-wood poles (ex-SEC) that weighed up to 3.5 ton each ~ and cost me a slab. (ask your tradie mates how they’d manage that…assuming OHS rules allowed them to even consider it.)

            I say “IS” above because I also designed it to withstand the inevitable bushfires. It survived 2009 without a scorchmark although the bluestone-block house over the road was turned to dust ~ as was every other building in the district/town……mostl of which were built by qualified tradies-sans-brains. (Ever seen a serious bushfire up close? I fought my first major one in 1962: experience/skills.)
            Anyway, the house cost a total of about $9500 in cash…(including the initial solar set-up: a single 64-watt panel (biggest then available), some ex-bulldozer batteries (1140 AH for free) and 12-volt bits from the auto-wreckers. (Also built ~ for free from available bits ~ a hydraulic ram pump which back then retailed for $3000…..and a 92-amp battery-charger from a car-alternator.)
            ….. and the 3.5-acres in the forest, backing on to South Creek, cost me $10k. (the original owner paid 1 pound 3 shillings and ninepence for it at the original government auction. (That’s $2.35 to you) These days you’d be looking at maybe $5 mil. Though the people to whom I sold it ( a huge extended family of Italians) have had the grid connected more recently.
            This (“background” is getting too long. Will address your specifics on a new page. (assuming Finn doesn’t spit the dummy….again)

          • Jackson,
            Can’t seem to get to a “Reply” to your missive (possibly something to do with the blog’s limitations to a “reply to a reply to a reply to a reply etc).

            Anyway, thank you very much for making my case – you did a far better job than I ever could. (Although I suspect you will still miss my point.)

            And PS
            Don’t leap to any conclusions on your age assumptions of the need to explain to me the conversion rate of the pounds, shillings and pence side of things. One of my first tasks as a tender, 20 year old Cadet Patrol Officer in New Guinea was to teach the locals about “dis nupela desimal karansi”.

            And PPS
            BTW, actually, shouldn’t that be $2.40? :> :>

            And again . . . . . . keep smilin’
            . . . . Please.

          • Specifics:- I couldn’t imagine paying $50k for a “basic suburban brick bungalow” (though you’d be lucky to get any change from $200k according to recent insurance quotes.)

            Neither could I imagine living in one, much less deliberately living in suburbia.
            Nor yet buying new materials “wholesale” or any other way.

            Certainly you can spend as much as you like to buy a bucket of shit. (are you familiar with the ‘TulipMania’ history ~ or it’s modern-day version the Bitcoin feeding-frenzy?)

            The same goes for solar systems. But the issue is (or was) whether you actually needed to spend “at least” $50,000 for an off-grid ~ or grid-plus-battery ~ solar system. And the FACT is that you don’t. Anything you CHOOSE to pay is up to you(I don’t suppose you lot send a few extra, voluntary, donations to the ATO as well, do you?
            If not why not, since that seems to flow from the philosophy: increase your neighbourhood status! Show off to the Joneses! Got a trophy wife??

            Whilst up at Marysville I was putting a deer in the freezer every week or two to feed my dogs and take the rest down to a local animal-shelter. At the same time the wanna-be tourists in the town’s “authentic Bavarian restaurant” would loudly order a (150-gram?) piece of ‘venison’ for $45 ~ which was about 25% of a weeks wages for a working man ~ and strolling out a bit taller, superciliously discussing the ‘quality’ and ‘value’ of the dog-food they’d just dined upon.

            When the whole ‘alternative lifestyle’ (including alternative energy) thing started it was an exercise in self-sufficient, minimal-cost, across-the-board conservation. That didn’t include brick shithouses in suburbia or computer-controlled cars over which the individual has no actual control beyond what the chip allows… and cost a mint to ‘maintain’ to preserve the warranty.
            Each to their own, of course, but I won’t be dictated to by some government bureaucrat or sniffy European car-maker. My 2000-model AU Falcon SW can do anything the jumped-up VWs can do (had mine up to 230kmh with some pedal left) can comfortably tow 3 ton, as well as provide sleeping-room. (and has better aerodynamics than some planes.) AND I personally service it myself every year or two, whether it needs it or not, for the cost of the consumables. It’s not European, of course ~ and doesn’t come with venison in the glovebox ~ but I don’t need the status. Anyway, I’m originally from Europe and there are plenty of people not the least bit impressed by that
            ….oh:- and it doesn’t consume that slab of beer you mentioned.

            hehehehe… ” I’m quite relieved suburbia is not full of the great unwashed running themselves up DIY grid-connected solar systems with parts obtained through eBay.”
            1………Q. –> How do you know?
            2………Said ‘great unwashed’ would obviously be too bright to get grid-connected ~ DIY or not. Neither would they waste vast sums of money hiring some pretentious (albeit “qualified”) twit with a hi-tech can-opener to open their baked-beans….nor crack their banshee tinnies. (even if, by Jinko!) they do acquire them from ebay. Incidentally, wouldn’t Finn, for example, be delighted if HIS online business was a fraction as successful as ebay?

            Free Market & artificial prices? Yeah. Right. As demonstrated repeatedly ALL the prices to do with the solar industry services are unnecessary, hence artificial. eg. the requirement that only a CEC-approved ‘operator’ can access the subsidy/FiT. One day, god and Finn willing, I’ll tell you the story of how the CEC/government-fiat ~ came into being . And yep! ~ I was there at the beginning…in the hills of Northern NSW all those years ago, where the community-minded hippies (over time) created the idealistic Rainbow Power Company which later morphed into the CEC. You know, the class of people who want to make a living by selling/controlling a product without actually being productive themselves.
            About as competitive and Free-Market as the Legal Industry….. run by the LIV.

            I’m willing to accept that ‘Finn probably had in mind an average, mainstream domestic residence.” whatever THAT is. But that wasn’t the issue. The issue was ‘Facts’, ‘numbers’ and ‘engineering’…..which were supposed to prove that stand-alone solar systems were unequivocally not viable. Particularly financially.
            Such an ‘authoritative’ statement is noit only untrue, it may well discourage (especially young) people from trying to do better for themselves. (The world they’re facing over the next decades is scary enough without naysaying possibilities. (eg. If they’re prepared to move away from bullshit building rules they can STILL build a useful house for not much more than $10k in which to live and raise a family. Keep in mind that the Blackfellas have been doing that for 60,000 years… though not an “average, mainstream domestic residence.”

            If you contact me I’ll send that link Finn refused, twice, to post, which shows all the above is STILL possible: here in Victoria, what’s more.

            As for Finn having “apparently singled you, and apparently you alone out for black-balling and green penning,” —> my first reaction is how do you know it’s me alone?
            Second reaction is that he hasn’t provided any reasons, but HAS left out several definitively relevant comments, including a link (ABC video) demonstrating, absolutely, that a basic, simple DIY solar system IS feasible, with components that HAVE lasted well over thirty years. (which means that whatever the initial price was they’re financially valid…… ie that the ‘at least $50,000’ claims are false.
            mea culpa inasmuch I assumed, possibly incorrectly, that his reasons were commercially motivated. That’s a matter for him, even if the blog invites every would-be contributor to “Have Your Say”.
            I’ve done remarkably well in the Stock Market (facts/numbers!) so have no commercial/business-focussed bone in my head. And despite a long, difficult life I still have the rubbed-off ideals of the hippies with whom I shared a ‘community-spirit’ for a` lot of years as well as a 2-millennia-long ancestry of peasants who never wasted anything.
            Hence my ‘contrarian’ approach to just about everything.

            Motto:- If at first you don’t succeed get a bigger hammer. 😉

  8. Very informative article. Thanks from me in place of the thanks you won’t get from battery makers/vendors.

  9. Warwick Sands says

    Hi Finn,
    Have you heard about the introduction of super-capacitors into the mix?

    Apparently they’re good for a million charge/discharge cycles which means they should last for a while.

    I haven’t seen anything about self-discharge rates and other losses.

    Interesting times…

    • Yup! Ronald is looking into them as we speak. He keeps getting graphene in his eye because he refuses safety glasses. Something to do with vanity I think.

    • Lawrence Coomber says

      Warwick the cycle life of supercapacitors (life of generation system +) is certainly a compelling attribute when compared to LiFePO4 for example in small scale Off Grid solutions.

      We have been assembling and evaluating supercapacitor ESS strings between a VDC operating range of 480 VDC and terminating at 300 VDC, using 4 VDC x 16000 Farad polymer pouch capacitors, and a custom CMS for 6 months now. We plan to install a small capacity supercapacitor ESS in an Off Grid application for field trialling and limits testing in Q4 2018.

      Despite the (life of system +) cycle life attributes in favour of supercapacitors over VRLA and LiFePO4 for example, they are not commercial viable for ESS consideration alone at this point, but that may change in the near term.

      Lawrence Coomber

  10. Hi Finn,
    I have two strings already 1.5 and 3kw on a 3phase system with one not connected to solar. I want to get another 3kw but .have been told the export must be limited to 2kw. I have been given three choices take off the 1.5 Nth facing and sell it second hand and install 5Kw or put in another 1kw nth and 2kw facing slightlly south of west with a dual inverter. The other is to just install the 3Kw on the slightly south of west roof. I would then have 3 Systems with 3 inverters. I have been told this wouldn’t work with a battery in the future. Any suggestions because I am completely confused.

  11. Steve Fuller says

    Thanks Finn – great analysis.
    So what do you make of the AGL Virtual battery scheme and the SA Gov 50,000 home virtual battery scheme?
    As I understand it both schemes allow the ‘sponsor’ AGL and the SA Gov(?) to access the stored energy during high demand periods to maintain grid stability and prevent blackouts (while pocketing the revenue paid for those services via demand reduction services and the spiking wholesale price of electricity during those periods).
    The services that these aggregated batteries provide should reduce network costs that will benefit us all as well as help to force out the dirty expensive fossil fueled generators.
    So they will benefit us all through lower costs and eventually, emissions reductions.
    Do you think that your myths would apply to domestic batteries if they are part of an aggregation scheme. (Presumably if AGL’s current trial scheme proves to be a money spinner they’ll roll out another commercial version.)

    • I think the Tesla VPP plan is great if it works as promised. It costs the government $2m plus a low interest $30m load and a bunch of homes that couldn’t otherwise afford it get 30% cheaper electricity. Plus a large generator comes on line to increase competition, bringing prices down for everyone.

      Co-ordinating individual batteries makes more sense than running them independently. But a big central battery will be more efficient in terms of utilisation and roundtrip efficiency etc.

      If a company wants to install heavily subsidised batteries in return for aggregation – then they may be able to make it work financially for the homeowner. Unfortunately the leader in battery aggregation, Reposit, is so opaque about their existing customers’ savings that I can only conclude that the savings are not there yet.

      At the end of the day the market will decide the most effective battery deployment strategy to allow more renewable integration. At the moment grid-scale is winning.

      • Hi Finn, I agree with all your comments and assessments, and have linked to SQ articles whenever people ask me about residential batteries.

        However, the VPP concept has the potential to be such a game-changer that it should be well worth mentioning in any future articles on the topic (along with your own reasons for purchasing one despite having so many arguments against them). As soon as the proper infrastructure is in place to allow home owners to gain a much higher FiT in times of extreme demand, the economics of batteries will skyrocket regardless of slow, incremental reductions in installation costs. This is by far the most exciting aspect of emerging battery technology.

        Whilst the large scale ‘big batteries’ might have the best efficiency, the same is likely true of solar farms versus residential or commercial roof-top installations. The fact that individual home-owners can win out is a major detail, and the same could happen with batteries once access to a functional VPP system is available. Of course, we are not there yet, hence all of your arguments stand, but this area of emerging technology is worthy of mention.

    • Sadly the incoming “Liberals” are about to scrap the whole thing. Watch out for a new coal mine in the Adelaide Hills!

  12. Tim Efthymiou says

    Hi Guys and Gals, You might know me from previous posts. I don’t care too much about the economics and calculations as it is way too difficult to work out. What I have worked out is that my electricity bill has dropped from $1200.00 per 1/4 to $11.67 with a $30,000 investment. My next bill I’m expecting a CREDIT. With this calculation in mind I should have my system paid off in 6.5 years, NOT TAKING INTO CONSIDERATION ANY FUTURE ELECTRICITY HIKES AND NOT TAKING INTO CONSIDERATION THAT I SUB SELL ELECTRICITY TO A TENANT OF MINE. If you consider the sub sale then I expect the system to be paid off by 5.5 years. Batteries have a warranty period of 10 years and solar cells 25 years. SO, FOR ME, MY 3 BATTERIES TOTALLING 23 K.W. OF STORAGE (1 POWERWALL 1, 1 LG 6.5 AND 1 LG 10. AND MY 10.4 K.W. SOLAR SYSTEM HAS BEEN GREAT AND WOULD NOT HAVE A PROBLEM IN RECCOMENDING ANYONE TO GO SOLAR/BATTERY STORAGE. I DON’T KNOW YOUR MATHS OR CALCULATIONS BUT MINE MAKE SENSE AT THE CORE OF CALCULATION FACTOR. HOW MUCH I WAS PAYING AND HOW MUCH AM I PAYING NOW. FELL FREE TO ASK ME ANY QUESTIONS AND I WILL TRY TO ANSWER THEM.

    • Hi Tim,

      I’d strongly suggest separating out the savings from solar and the savings from your batteries and comparing the returns as described here:


      • Tim Efthymiou says

        Hi Finn and thanks for your comment. I have read the article on payback etc. you see, for me it’s doesn’t have to be all about payback. I’m in a unique situation that I can afford these expensive systems and like to have the latest and greatest toys, whether they are a good investment or not.

        I’m a 50 years old self funded retiree that has a fantastic income from investment properties and a lump sum in financial institutions. So for me it’s not all about pay back times etc. I perfectly understand about cost of batteries and their financial return etc. (I didn’t get to where I am but being dumb).

        For most families and I’d suggest this to my kids as well, a good large solar system is adequate enough for most families.
        If you want to look at it strictly from a pay and return point of view on batteries, then you will have to wait for the batteries to fall further in price.

        Cheers, Tim.

    • Paragraphs please, and no caps lock!

      Out of curiosity why did you use different battery’s (models and brands)


      • Tim Efthymiou says

        I used different batteries because I originally had a powerwall 1 installed and was pretty happy with it. So I thought when the powerwall 2 comes out, I’ll go for that to add to my system.
        Well it turns out that I can’t have a powerwall 1 and a powerwall 2 connected to the same property due to one battery running in AC and the other running on DC (don’t remember which is which). So I had to go for an alternative, which was two LG batteries (one 10 k.w. and the other 6.5 k.w. In hindsight, it worked out for the best as I’ve been very happy with the LGs. they’re also smaller and no noisy fans. They say that once they reach a certain temperature (I think its 45 degrees Celsius) they shut down to protect themselves, Well we’ve had some bloody hot days (some as high as 47 degrees) and even though the batteries get morning sun, they have never shut down.


      As Finn has pointed out, it would be an interesting exercise if you would do the sums and work out the alternate cost-benefit if you had invested your battery costs (including installation) at, say, 3% p.a. I suspect a huge proportion of your benefit is coming from your 10kW of panels on your roof and a far, far lesser return from your battery costs.

      Secondly, as I understand it, most single phase residences Australia-wide are only permitted to have 5kW of inverter/s connected to the grid. So in most domestic situations, only half of your system would be permitted to be connected to the grid (or alternatively export-limited by around 50%).

      Thirdly, on your battery warranty calculations, perhaps you should check out the not-so-fine print. You will probably find the warranty is on a sliding scale, and by the time you get to years eight and nine, you’ll be lucky if the warranty value is even 5% of the original cost, plus, without taking in the degrading efficiency of your solar panels.
      Again, YOU’LL BE LUCKY IF THE WARRANTY VALUE IS . . . . . . . . .

      Finally, I am writing this as someone who last had to pay a power bill back in April 2013, and currently has a bill credit of over $1,500. And only added a small (6.5kW) battery system six months ago (just for the heck of it) to 5kW of inverters connected to 6.5kW of existing panels. On a standalone, detailed cost-benefit calculations, I believe the battery will probably pay for itself two to three weeks after hell freezes over.

      Keep smiling. :>

      • Tim Efthymiou says

        Hi Greg (SORRY ABOUT THE EAR ACHE. just kidding. lol). and thanks for your comment. I don’t try to get into too much mathematical calculations as there is way too many variables. Your probably right in saying that most of my advantages are coming from my solar system and not the batteries, BUT keep in mind here in N.S.W. we get charged (if your on a smart meter), 60c per k.w. between the peak times of 2 pm and 8 pm, during this time, because the missus is cooking, washing, air condition on etc. I’m using some solar and batteries. I’m pretty sure that my batteries contribute to about 1/2 of my bill reduction and probable the other 1/2 is from the batteries.

        Down the track in future, I’m expecting batteries to dramatically fall in price, so when they need replacing, the investment won’t be as high.

        BY THE WAY THE BEST INTEREST RATE I COULD GET ON MY MONEY IS 2.85% from ME bank and our money is on call and not locked in to a term deposit. Term deposits offer even less interest and they lock you in.
        I’m now 50 and self funded retiree.

        On you credit of your electricity bill, what will eventually happen?? Can you request to get paid that credit or does it just sit there for ever groining ???

        • Tim,
          You’re obviously not living in a good part of NSW from an electricity charge perspective.

          In Far Far Northern NSW (so far North we have a 07 phone prefix because Telstra doesn’t believe you can reside North of the Tweed River and still be in NSW), my Peak / Shoulder / OffPeak power charges are all in the 20-something cent range. And around 12c FIT. (Up this way, the distributor is Essential Energy.)

          My billing mob then offer a 18% discount off the full bill (of, I suspect the standard EssentialEnergy/Ausgrid/Whoever rate, depending upon your location – subject to provisos of paying monthly in advance on estimated bills, with quarterly actual reads, etc etc.)

          In fact my mob usually offer $75 off the next bill of both the signer-upper and the new customer. And they’ve upped this to $100 but unfortunately the higher offer only to 3 April. If Finn or Ronald is kind enough to let this through I can give you the details if you EMail me at stottstreet at

          On the interest rate side of things, I think you’ll find your bank offers 3% on a five year TD. And realistically, purchasing batteries locks in your money longer than a five year term deposit.

          With regard to the electricity bill credit it could be claimed quarterly, I guess, but my mob offer a (total) 21% discount when making (refundable) bulk purchases in advance, so what the heck!

          Hope that all makes sense.

        • Tim….BUY shares in the major banks. You’ll get a ROI of (approximately) 9% instant get-out options and the security of knowing the government won’t ever let the banks crash.

  13. There is one flaw in your analysis of environmental and economic benefits. To be exporting 100% renewal energy during the day and then buying back 80+% coal power during the night is nett bad for the environment, irrespective of the battery losses. To do a fair comparison you need to use green power rates when buying back, so in effect 8.5 c per kWh more than non-green power, which actually negates most of your feed-in tariff. That way you are comparing like for like – exporting 100% renewables and importing 100% renewables.

  14. Hey Finn,
    With the new VIC FiT rates coming in soon that are supposed to give you 29 cents from 3pm-7pm I think it was, would you be able to do a piece on whether or not this financially brings batteries into the economic sense realm for Victorians after July 1?

  15. Well! I certainly wouldn’t want to ‘destroy your company’ :- ” simply point out that home batteries do not currently pay for themselves financially or environmentally. These are not opinions – these are facts based on impartially looking at the numbers and engineering.”

    BUT…. again….YOU ARE WRONG!

    Numbers (like statistics) and ‘engineering’ (post Egyptian Pyramids) are not impartial. They all have a stated, dedicated purpose and ~ numbers anyway ~ are subject to ‘subjective interpretation’.
    eg. An engineer would tell you that a numeric “fact” is that 2+2=4…..and begin to build a Westgate Bridge on that basis.
    But you’re an engineer, young Finn. Prove to me that 2+2 DOESN’T = 3.
    (or 13 and-a-half for that matter.)
    Point is that numbers are NOT facts per se, nor even accurately define facts. Any more than language does. All that is based on subjective (ie ‘opinionated’) agreement,

    And while everybody and their dog (or favourite politician: a font of unending ‘fact’ and numbers), is entitled to spout whatever nonsense they like ( behold! the factual/numerical facts spewing forth from the Jehova’s Witness on my front step!) the closest we can get to (dare I say) ‘Truth’, is to “ask the man who owns one”.

    Just the other day I did the arithmetic for a bushy-tailed young eager-beaver which clearly demonstrates that ~ at today’s prices for readily available (new) components ~ you can install a 10kwh system for about $4000. (Call it $5K if you’d rather buy than make up mounting frames, and other bits-n-pieces……though anyone keen to DIY outside ‘the system’ would mount their panels on the back lawn, using nothing but dirt.
    As demonstrated elsewhere:- batteries that are guaranteed for 3 years, probably last 5 years, and have been known to last 8 or 10 years can be bought for well under $2 per ah…..otherwise expressed as ( for the numbers-infatuated) about $850 per 10kw.

    But I still say that anyone that actually needs 10kw on hand would need
    to have 14 kids or no brains.. (‘and’???)

    ps…. I’ve just sent a smile engineered to register 3.142 (note the numerical ‘fact’!) on the gloppy-scale….. just so you understand exactly what I mean.

    pps…. anybody with 14 kids doesn’t need a solar-system anyway. Get a few exercise-bikes and have them take turns cranking generators.

    In short,

    • “But you’re an engineer, young Finn. Prove to me that 2+2 DOESN’T = 3”

      If you would like to send me $2 + $2, I’ll happily send you $3 back.

      I’ll repeat this transaction as many times as you like.

      My PayPal address is

      I await the transfer.

      • Excellent response

        • Another 25-watt mathematical whizkid, Rod??? (or is it just that English isn’t your native tongue?)

          You (and Finn the engineer/numbers-cruncher) have obviously overlooked the numbers/facts that:- If I were to send you $2 + $2 and you were happy to send me ‘$3 back as many times as I like’ you’d actually BE proving my contention that 2+2 CAN IN FACT = 3.

          …..and hence prove my basic assertion that many of the ‘numbers/facts’ you push are falsely-based/manipulated.

          Another reality you often seem to overlook/ignore (remarkably since even our ex-PM, a bloody politician!, understood it!) —–> There’s No Such Thing As A Free Lunch.

      • That’s exactly the sort of response I’d expect from a snake-oil salesman protecting his commercial interests: slip in a few unwarranted ‘modifiers’ and shift the goal-posts.
        The issue you raised were ‘numbers’, ‘facts’, and ‘engineering’. Not a mention of ‘$’….nor a mention of confirmation/contradiction of my claims, either Not a Jehova’s Witness in drag are you?

        …and I notice you left out a few other comments you obviously consider detrimental to your claims ~ like the flood of Jinko panels currently flooding the market at a price of 33 cents per watt for a 5kw buy. (try THOSE numbers in terms of setting up a 10kw system.!) tsk tsk tsk….

  16. Bob Johnson says

    Hi Finn,
    Very good article. Very believeable that reported battery efficiency can be down to 70%. My present partner raised her family in a farming area that would often have several days or more of overcast weather. Of necessity solar off grid (with lead acid batteries, of course) with generator back up. When friends get misty eyed about going off grid they very quickly get her opinion. She hates generators (but, by the way, loves being able to walk to our local shops. Hey, she’s easily pleased!)

    • ….and easily confused from the sound of it: obviously not aware that there are a dozen or so options/alternative considerations. A simple example would be to mount some hydro/wind alternatives. (on the assumption that if the
      sun’s not shining the wind is blowing.) And let’s not overlook the reality that there are generators and generators.
      But the bottom line is that while you have daylight you can produce SOME solar power. If one wanted to point out bloody obvious, one would tell you
      to buy a LOT more panels given today’s give-away prices ~ so that if your 200-watt panel was producing, say 50 watts you’d buy another three of them.

      Or you could swap the wife for a decent generator and get the best of both worlds!
      There are plenty of cheap generators around that’ll do the job: put out a ‘pure sine wave at about 2500 watts for 6 hours on a coupla-three litres of petrol ~ or biogas/hydrogen etc etc.; remote start/stop and so quiet you can’t hear them in the shed 15 metres from the house. (One I’d recommend from experience, for a few hundred $, is the Bunnings home-brand model.
      I sometimes wonder how the people of my generation managed ~ often without electricity at all ~ but they did. (I spent my early life in the wilds of Wantirna , about half an hour by car from central Melbourne.)

  17. Myth 3 specifically but the battery argument in general is the reason why electric cars are not the panacea they are made out to be. Every kWh you put into your electric car from any source is one more (or the proportion of that one that is generated by fossil fuels in this country) that has to be generated by fossil fuels. Add to that the cost due to inefficiencies of charging and discharging your batteries while plugged in and driving respectively and all of a sudden hydrocarbons are starting to look pretty good.

    Until we generate most of our electricity from “green” sources the environmental benefits of electric cars are a myth.

    • Look forward, not back says

      That old chestnut. Total rubbish.

    • Ronald Brakels says

      I’ll crunch the numbers for conventional cars, a fuel efficient hybrid such as the Prius, and an electric car and see how they compare on emissions and write about it soon.

      • Look forward, not back says

        Please include in your analysis the ability to (partially/fully) charge your car from your own solar (obviously depends on km driven), and also buying 100% renewable energy for the 8.5c premium. And before the oil lobbyists start saying you “cam’t buy individual electrons from certain power sources”, I’m fully aware of this, but it doesn’t change the fact that you can force your retailer to have buy renewables, or in the case of Powershop they already do.
        So please, please do a thorough analysis which looks at all current options to buy power to recharge electric vehicles.

        • Ronald Brakels says

          I will look into it.

          • Good to see the voice of ‘horse-sense’ back.
            While you’re at it Young Ronald, look into the possibility of getting the RACV out at 3am with a bucket of volts when you’re stuck halfway up the Hume Highway and have run out of power (assuming the battery in your
            phone hasn’t shat itself as well!)……perhaps caused by a fault in the battery or a short-circuit elsewhere in the system, which would mean even several buckets of volts wouldn’t get you going….. Not even with a push-start.

      • Ronald. Not saying that electric cars are worse than cars with combustion engines for greenhouse emissions but at least, in Australia, they are not much better.

        There are a few greenhouse costs associated with them that people tend to leave out when they do calculations.

        An example: Whether you have solar (or any other alternative) energy “dedicated” to charging an electric car does not mean your car is any cleaner than any other electric car living on the grid. The alternative energy generated for this has to be pooled with all the other energy in the community as it could just as easily have been fed back into the grid to offset the burning of fossil fuels.

        Make sure you use figures from Australia where (still) the majority of our generation is based on coal.

    • Joe Blake says

      We seem to have this app in our heads that when we talk about electric “vehicle” it’s immediately translated into “motor car”. On Easter Sunday 2017 I purchased an electric scooter (ZEV, 2012 model) which I have been riding since. I’ve totalled just on 3,000 km. I don’t ride it every day, because I have pedal power for most short trips (say 10-12 km total) and a 14 year old 650CC petrol powered BMW motorcycle for longer trips (50 km+). According to this document

      the average commute distance in Australia is 15.6 km (one way presumably). Now despite the fact that the ZEV is 6 years old and the batteries are not in top condition, I can achieve roughly 40 km on a full charge (I’ve had it up to 80 km/h but traffic conditions did not permit me to go faster). This distance includes a grinding climb up to the Hills behind Perth where I live. Were I on the “flatlands” I’d be looking at 60+ km on a full charge.

      I have 3.2 kW of grid connected solar panels on my rooftop, and an assortment of non-grid panels. Each system has its own batteries, Lead acid, although the scoot has Lithium based storage. It recharges simply by plugging into a standard 240 volt socket and a full charge takes about 3 hours, drawing 1,850 watts, when it cuts back to a trickle of 5 watts. In those 12 months, ALL of my trips on the scoot have been using solar power – total cost – zero.

      As a “civilisation” we are wedded to the motor car, regardless of what powers it. But electric cars do nothing to ease traffic congestion in cities, which causes great time loss that translates into economic loss.

      My BMW 650 gets 26 km/litre and at a cost of $1.40 per litre that works out to be roughly $160 saved in petrol and consequent emissions for that 3,000 km. (I count this cost as coming off my “pay back” time for my house batteries since I use them to charge the scoot overnight if necessary.)

      Back to the myths. Using a generator as a back up instead of a battery. In the early 1980s I had a business which relied upon computers, so I bought a fancy generator which gave out a sine-wave power that computers then needed. I used it a couple of times and it was great, but then there was a fairly serious grid failure and whilst I could I kept my computers going, but I ran out of petrol, and then found that because of the blackout there were huge lines of panicking motorists trying to buy petrol and even on a bicycle I would not be able to keep my business going, for each minute I spent waiting in the queue was a minute lost to my business. (This assumed that I would have been able to buy petrol because some service stations ran dry.) So I decided that relying upon a petrol powered generator was pointless if the petroleum supply was interrupted. I experimented with my non-grid connected panels/ batteries mentioned above (starting in 2006) and since then my computers (and freezers) have never stopped running.

      “So if you are saving 30c per kWh, but losing 10c per kWh. Your net benefit is 20c per kWh. In fact, it’s a bit worse because every time you charge and discharge the battery, you lose ten to thirty per cent of your energy to battery inefficiencies.” This intrigued me as I had never looked at it that way, so I went to my spread-sheet and found that from 1 January 2017 to late May 2018 the difference between importing and exporting power was … $5.66 in favour of the utility. About $0.15 cents per day. (However, ignoring the $’s, in that period for 12 of the 15 months the system has generated more than 100% of my house’s power – 170% for two months, Oct and Nov 2017.)

      I mentioned 1 January 2017 for a specific reason. I’ve had house batteries since late 2013. I’m still on the grid and thus I’m charged for “supply charge” regardless of how much power I import or export, so I sought a way to turn this to my benefit. It’s widely recognised that the life time of batteries is dependent in part upon the depth of discharge, so from 1 January I programmed my system to maintain the state of charge overnight ie off-peak. In other words carry the house load from the grid. (Off-peak on my scheme is 21:00 to 07:00 hours nightly, and I usually have the charge being maintained at between 85 and 87%.) A back of the envelope calculation showed that I could be adding 5 or more years to the useful life of my batteries. So I look at the $0.15 a day I have just mentioned as an investment by delaying the need to purchase more batteries by this time. Just over a 5 bucks a year? Sounds good to me.

      The upshot of all this, Ron, is when you decide to do a comparison of different types of “vehicles” would you also be able to include single person vehicles such as very small cars and scooters/ motorcycles?

      • Ronald Brakels says

        Maybe I’ll mention electric scooters and bicycles but I’ll be focusing on passenger cars and won’t have time to do the topic justice. As for tiny cars we don’t have the “yellow plate” category of small car in Australia as in Japan. They may not be legal here. Anyway, scooters and electric assist bicycles are probably a whole separate article and maybe Finn would be the better person to write it.

  18. “…that has to be generated by fossil fuels…”

    That’s why we’re putting off our Tesla purchase until we can power it with panels.

    “Until we generate most of our electricity from “green” sources the environmental benefits of electric cars are a myth.”

    We have to start somewhere. I’m astonished to note that the _immense_ servo being built at the southern end of our town doesn’t have a single panel on those huge roofs. I guess it would be a capitulation… an admission… that the end of over-reliance on hydrocarbons is coming.

    You’ll disagree… and that’s your right. I imagine carriage-makers scoffed at the ‘horseless’ carriage… and offered plenty of arguments to dispel the ‘myth’ that motor cars would replace the horse. We’ll get to the tipping point more quickly than you imagine, Cynic. Both my sons will purchase EVs soon… before we do, in fact. Already our eBikes have reduced our car use by over 20%*… and I’m deregistering our Honda hatchback next week.

    * Can see that doubling, once my missus retires in January ’19.

  19. Thanks Finn another helpful article direct to point and easy to understand

  20. Tim Efthymiou says

    I just read some people are getting annoyed with the feed in tariff and they should not give their electricity to the grid for pidly money. WELL, I can tell you that pidly money gave me a credit of $275.00 on my last 1/4. This is in N.S.W. which is now 12.5c per k.w. WHAT CAN I SAY, DO I NEED TO SAY ANY MORE. ????????? This is on a 10.4 k.w. solar system with 3 batteries. This feed back is obviously AFTER my batteries are full and ready to use at night time. like I said on my previous post, I’m expecting a credit on my next bill.

    • Lawrence Coomber says

      Well done Tim and your system sounds great.

      Based on face value about your Solar PV in place though, you might like to consider optimising your savings much more and taking the next step by going Off Grid. maybe something worth thinking about.

      Lawrence Coomber

  21. Lawrence Coomber says


    Like most subjects (and certainly power engineering) the devil is in the detail, and Off Grid solutions/designs are a case in point.

    A ‘current best practice’ high voltage DC coupled Off Grid Solar PV + Battery solution design, providing permanent autonomy (for critical services circuits as a minimum 24/7 x 365) can be design guaranteed to provide high quality, reliable and continuous 1-3 Phase AC electricity [24/7] to power whatever your domestic regional or rural premises; business; or industrial/commercial enterprise power demands are, safely, cost effectively, without interruption and maintenance free, whilst being independent of and permanently disconnected from the traditional Utility Grid ‘safety net’ that we are all familiar with.

    You are correct in thinking that rural properties have an advantage over domestic premises because of ‘available space’ particularly as it applies to ground mounted Solar PV opportunities, and it does factor in suburbia, but not to the exclusion of normal domestic premises on the ‘standard aussie ¼ acre’ which is perfectly suited for fully functional and autonomous Off Grid designs using PV mounting technology specifically designed for small area domestic Off Grid solutions.

    What makes domestic Off Grid achievable comes from the excellence of the power plant system design and integration Greg.

    Don’t be spooked by ‘emergency gasoline generation’ in suburbia. This is an important design component for all Off Grid solutions, but remember we are focussing on ‘emergency supply’ here in a domestic scenario, and axiomatic to that of course is ‘critical services circuits’. For most applications that means a 2 – 3 kW Silent Honda Gasoline Generator, and with a well-designed permanent autonomy PV + Battery system it is very rarely required if ever.

    Because Off Grid is a ‘long haul’ customer decision, customer service is a special consideration. As well as having a long and trouble free trading history in Australia that is verifiable, an installer company should demonstrate that they have a long standing and high quality commitment to ongoing customer care and support by coming up with the goods, and provide contact details of previous contemporaneous solutions customers, that potential new customers can contact direct for a chat.

    All the best as you move forward with your Off Grid project Greg.

    Lawrence Coomber

    • Lawrence,

      A couple of observations / comments:
      With respect, your ‘standard aussie ¼ acre’ is trip down memory lane, Lawrence. In the words of “The Castle” – “Tell him he’s dreamin’.
      True, many older blocks are still, for rounding purposes, a whisker over 1,000 square metres (i.e. a quarter acre in the old money). But have a look at your average new development today (and for many of the past few years – the overwhelming majority have block sizes between 500 and 750 square metres – i.e. around half to three quarters of your “standard aussie quarter acre”. And you will find many of your “standard aussie” quarter acre blocks (or thereabouts) are in high demand by investors happily wanting to whack a granny flat in the back yard – especially in the likes of suburban Sydney and other high-cost-land cities.

      Secondly, Lawrence, in many high density areas you would have difficulty running a pool pump late at night – let alone “a 2 – 3 kW Silent Honda Gasoline Generator”. And let’s not even go down the path of suggesting to the neighbours that you are thinking about whacking up a wind turbine next to their bedroom window.

      Lawrence, if I am not mistaken I take it you have a vested interest in people going off-grid, and good on you. But really, with current technology I think you may be trying to push things uphill with a pointed stick at the moment, with the vast majority of your potential client base.

      I appreciate every case is different, but in broad terms (but with some specifics, please) what would your recommendation be for a young family (or to put it another way – a customer wanting to avail themselves of your services) living on a current standard sized suburban block (as per the beginning of my post) to go off-grid in an all-electric household?
      * How many solar panels on the roof? (Not enough room to put them anywhere else, sorry.)
      * What battery capacity?
      * And they have checked with the neighbours who have politely pointed out that if there is any generator noise **at all** at night, or 2/4 stroke fumes entering their dwelling, they will have police, Council and anybody else they can think of down on their neck.
      * They have also approached their local Council who actually fell about laughing when they enquired about installing a wind turbine next to the Hills hoist (which is the collapsible/removable model because their block is so small.
      * And in their neck of the woods, from time to time they can frequently go for three or four days of days where there is insufficient sunshine to effectively run the solar hotwater system by the end of the second day, let alone add a decent top-up to the batteries.
      * Oh . . . . . . . and ball-park cost?

      Lawrence, no doubt there are some suburban premises where it may be practical to go off-grid. I am only trying to elicit from you reasonably broad specifics as to how this can be achieved in today’s “standard aussie” home and at what $$ cost.

      All the best with your business endeavours, Lawrence.

      • Lawrence Coomber says

        Thanks for your comments Greg.

        But please don’t dismissively assume that Australian RE industry engineers are devoid of developing cutting edge technology innovation, and condemned therefore to merely following and adopting imported technologies and trends alone. This has never been the case hitherto; certainly not applicable today; and of course we don’t ever want this notion to represent the limits of Australian engineering know how.

        Of course a fully featured domestic Off Grid solution is not a practical consideration for every Australian premises/apartment/unit/studio/high rise etc; and no experienced RE system designer/integrator would suggest otherwise.

        For the experienced designer/integrator though, a domestic Off Grid solution for the traditional Aussie ¼ acre (it’s a metaphor Greg) style premises, is definitely a practical; achievable; and importantly a cost effective highly reliable option worth considering – today.

        The takeaway point is that a premises’ suitability for deployment of an Off Grid solution is assessed on a case by case basis entirely, and is contingent on the popular Australian axiom “horses for courses”, being completely satisfied. This is the first ‘port of call’ therefore when evaluating the design viability of a particular premises (commercial, rural, regional or domestic) for a domestic Off Grid solution.

        In domestic premises we know that PCE and battery storage hardware is a relatively small footprint easily managed (generally) for both On and Off Grid installations. That leaves the Off Grid Solar PV part which (generally) requires more area than a traditionally sized and mounted On Grid Solar PV installation. In this regard, alternative Solar PV mounting methods in lieu of or in combination with traditional rooftop or ground mount configurations for example, are available as the particular circumstances dictate.

        In summary: Domestic Off Grid with reliable functionality to support a modern energy centric lifestyle 24/7 x 365 is entirely appropriate and cost effective with good ROI prospects – today. It is not however an applicable technology for all domestic premises, and only those where all of the necessary ‘stars line up’ in favour, would be suitable for system design consideration.

        Lawrence Coomber

        • Lawrence,

          You’re welcome.

          But . . . . . as originally requested, how about some (even broad) actual specifics for your “Domestic Off Grid with reliable functionality to support a modern energy centric lifestyle 24/7 x 365 is entirely appropriate and cost effective with good ROI prospects – today” . . . . . . . . . . please.

          All I am asking, even for your suitable domestic premises, what exactly is your “practical; achievable; and importantly a cost effective highly reliable option worth considering – today”? . . . . . i.e. within your “limits of Australian engineering know how” – TODAY.

          And BTW, metaphors notwithstanding, surely you agree there are indeed practical issues in this context between your “traditional aussie ¼ acre premises” and my “current traditional aussie one eighth acre premises”? I was merely highlighting those practical issues in exactly the same way if you had used as a standard, premises located on a “traditional aussie two acre hobby farm” just as I would expect you to take exception if I suggested the standard was now a “traditional aussie 10 square home unit”.

          But metaphors aside, again, I am just asking for some broad specifics, actually providing a practical solution to the problem holding back the off-grid option from the perspective of the vast majority of the urban populace, over the issue of a realistic 24/7/52 power supply. Such a suggested solution would include terms including at a minimum: “kWh”, and “dollars” plus a few other specifics mentioning at least “size of batteries”, “number of solar panels” and “backup power source”.

          Otherwise we are reduced to you saying “Trust me, I can probably provide you with a practical off-grid solution” and me responding “I bet you can’t”.

          Exactly what “stars need to line up” today for your scenario to be viable? And if they do, (yet again) what is (or are) your broadly specific solution/s, please?

          • Lawrence Coomber says

            Thanks Greg.

            Please be mindful that Solar Quotes provides the public with a great general interest forum on a variety of technical topics that they choose. It has never been sales pitch or customer/supplier get together discussion platform.

            But I will offer you some general advice as you seem genuinely interested in the subject of domestic Off Grid solutions, and in particular as that might apply to your own situation.

            Customers want prices; system designers/suppliers (generally) require detailed information to determine what it is they might be able to offer a potential customer, and a good ‘starting point’ to work from is a customer’s annual electricity usage profile. Put that annual pack together (both sides of the last 12 months contiguous accounts) Greg with some photos of your property, and I will be happy to provide you with some useful ideas to work from.

            Lawrence Coomber

          • Lawrence,

            I will indeed take you up on your offer, off-blog.
            Talk to you soon.


          • After the recent resurrection of this blog, I just noticed I had not added the outcome of taking up Lawrence’s offer, off-blog, to look at the specifics of the viability of an off-grid solution on my today’s more-or-less-basically-standard-suburban-block.

            Lawrence promptly, courteously and comprehensively responded to the details provided and the “bottom line” was
            “In my job I often mention to energy engineers and others that going Off Grid in a domestic situation is very achievable (today) for those premises where all of the essential ‘stars line up’; and it transpires that your circumstances (as you predicted Greg) are such where the stars do not line up.”
            “. . . . . There is no path forward for an Off Grid solution at your place,”

            A belated “thanks”, Lawrence.

  22. Its interesting reading all of the comments. There are some very passionate battery supporters in the mix. There are comments about ignoring payback which I would say is fine if you are looking for energy security (assuming the grid-tie battery system has back-up capability) and those simply looking to play with the technology. But the reality is that from a economic perspective, if you are looking to save money by buying batteries to connect to your grid-tie solar PV system then it is a foolish investment. You don’t need a maths degree to work out the ROI. The biggest problem I believe is the longevity of the current range Lithium-Ion batteries on the market. Everyone is very foolishly assuming these batteries will last the 10 years that the manufacturers are spruiking and then assuming if they don’t, well they can claim on the warranty and get a new battery? The limited liability warranties offered on ALL batteries are rubbish and they have been written to remove as much as possible any liability over the performance or lifespan of these batteries. Most people don’t know that with some brands, warranty is null and void if the battery has been exposed to ambient temperatures exceeding 35 deg ! Also, if you want to claim, the battery must have been permanently connected to a home network. It reminds me of the solar industry in 2010, there were so many sub-standard products being sold in Australia and the warranties on panels and inverters were crap. Its the same with batteries. Its an emerging technology that is still too young, but it will get better with time and there will be better regulation in place along with consumer protection.

  23. Hello.

    In referring to the use of battery storage for backup protection, the article refers to buying a petrol generator, as being more feasible.

    But, from what I understand, the hybrid (and, dedicated battery storage, such as the Goodwe, and, I believe, SolarEge, add-on) inverters institute the backup electricity supply in about 10 milliseconds or less, (hopefully) avoiding disruption to the electricity supply, thereby minimising the risk of disruptions and damage to computers and whitegoods such as fridges, etcm, where electricty supply failures of less than a minute, can cause loss and damage, against which (from experience) the electricity comp[anies are protected from liability.

    So, I think, a comparison in costinge, needs to be done, between a battery storage backup facility (from memory, a dedicated add-on inverter with the backup facility, costs about $2000, in addition to the price of the battery and installation), and, a generator connection, where the generator provides “transparent” backup – where no loss of electricity supply, is apparent, when the grid supply fails and the generator replaces the grid supply with (up to) 5kW of electricty supply.

    My understanding (and, I am willing to be corrected – quotes from solar installers, are surprisingly difficult to obtain, for any system), is that an add-on battery system with an inverter and around 9-13 (the Tesla powerwall) kWh usable batter capacity, that can output 5kW of power, is about $12,000-15,000.

    And, I understand that, without a hybrid inverter incorporating such backup protection functionality, such an add-on inverter for battery connection, is required, to achieve the specified backup functionality.

    • Tim Efthymiou says

      Hi Bret. I’ll give you exact figures here as I have an extensive array of solar cells, batteries and inverters installed at my place.

      Tesla wants an extra $800 for the battery back up feature. You obviously have to choose which circuits (power points, lights) you want to run of a power outage.
      Their power wall 2 was offered to me for $12,050 (this includes a $1,000 loyal customer discount). This price was fully installed and hooked up to a 5.4 k.w. solar system. (We didn’t go with this as they couldn’t install it at my place due to the pw1 being AC power and the pw2 being DC or the other way around, I don’t remember, and you can’ have both systems. it’s either dc or ac.

      $12,350 got me 2 lg chem resu batteries (one 6.5k.w. and one 10k.w. this is a total price and includes installation and commissioning of the batteries and the hybrid inverter I have can be programmed to use a back up (power outage) for free. Also this system has a great “force charge” feature which I use when I know there will be cloudy days. I’ll charge the batteries, say 2 am to 6 am to have battery power later that evening when I get charged 60c per k.w. peak rate. off peak rate is about 11c

      My whole system has cost about $31,000 which includes:

      1. 5 k.w. solar system with a Tesla power wall 1.
      2. 5.4 k.w. solar system with 2 LG batteries (6.5kw and 10k.w.

      altogether there is 38 solar cells and the system is rated at 10.4 k.w.

      IMPORTANT NOTE: I have my cells facing east (one group, north (two groups and west one group. This way I have solar power as the sun comes up right up to the end of the day as the sun sets.

      My power bill has dropped from $1200 per 1/4 to $11.67 last 1/4, but I’m expecting a credit next 1/4 as we were a 5 member household but now we are 3.

      Cheers, Tim.

      by the way the Tesla power wall 1 can only be discharged at a rate of 3.3 k.w.
      The LG system can be discharged at 5 k.w.

  24. The “add-on inverters” “for battery connection” with backup protection functionality, to which I referred, include the Goodwe GW5000S-BP (“Automatic Switch Time (ms) <10"), and I thought I had seen information for a Storedge equivalent, but I can not now find it.

    The Goodwe product flyer refers to the device, as an "AC-Coupled Retrofit Solution". Unfortunately, it states that "It can effectively upgrade any existing string inverter system by adding battery backup", and so, apparently, is not usable with a Solaredge inverter.

    The Storedge information that I have found tonight (I am sure that I previously found an equivalent Storedge device, to the Goodwe one), appears to not include a single phase equivalent of the Goodwe device, which is single phase. If a Storedge equivalent does exist, Storedge is doing a pretty good job of concealing it.

  25. The Devil is, indeed, in the detail. Just this morning ~ by chance ~ I came across a couple of such ‘details’ of interest:-
    )oops… seems it’s not possible to cut-and-paste here, so you’ll have to take my word ~ and/or check Google)

    1…… Origin charges a top rate of 54 cents per kwh (in the Latrobe Valley where the bulk of Victoria’s power is generated), and charges $1.54 per day in ‘connection fees’.

    2…….. A replacement battery for an electric car ~ after 114,000 MILES of use over 10+ years ~ was cited as just over $3000; and I see Nissan is offering a new battery for one of their vehicles for $5499 plus installation costs (3 hours).

    Hence, if we accept those figures for batter-storage, and check ebay for tier-1 Jinko solar panels @ 60 cents per watt the….er, ‘numbers’ tell us convincingly that we can set up a 10kw solar system ~ which I’d expect to last at least 15 years ~ for WAY UNDER $10,000…. or about the same price as Origin charges for the connection fees alone.

    But you’re right in bringing up the ‘engineering’ issue Finn. Apparently the electric vehicle people engineer the batteries to NOT charge to more than 80% capacity, nor discharge to below 20%. Apparently that makes a huge difference in efficiency and longevity.
    The point is:- It’s VERY practical in ANY terms, including financial, to install a stand-alone solar system for your house….. for a price of LESS THAN 10% OF THE $50,000 – odd you cited above.
    In fact, install a separate back-up system ‘just in case’ would still be a more than worthwhile propositon.
    …..and for my money lead-acid batteries are still a better propositon for aforementioned reasons….. a prominent one being that owners can understand/configure/fiddle-with/etc a battery-bank of decent lead-acid storage. With the Tesla-type stuff one is STILL at the mercy of major industry.

  26. I’m reading all of these comments and repeating a simple mantra:

    Footnote 6
    Footnote 6
    Footnote 6

    It helpa a lot.

  27. Lawrence Coomber says

    Jackson you have rolled many subjects into the one comment and it is impossible to unravel where you focus is:

    1. If you are talking about the global ‘second reuse’ market for EV Batteries for SPS Off Grid Generation ESS purposes, well yes this is already an industry (but not yet so in Australia) but it comes with many application engineering issues, not the least one being only licenced technicians certified with ‘Safe Handling of High Voltage Batteries’ qualifications are permitted to work on them.

    2. EV Batteries are not suited for SPS Off Grid ESS applications without the EV functionality designed BMS being replaced with an SPS functionality designed BMS. They are poles apart in every way including the core operational logic and controls requirements.

    3. If you are talking about an SPS Off Grid System using VRLA Battery ESS that “owners can understand/configure/fiddle with” plus a Solar PV Array to integrate with for under $10,000 all up to power a modern Australian person/family lifestyle. I want one of those.

    Lawrence Coomber

    • Ronald Brakels says

      Lawrence, do you know approximately what kind of depth of discharge Nissan, Tesla, etc. allow on their car battery packs? My possibly flawed understanding is the allowed maximum depth of discharge is very deep, but well before they reach that point the cars get very annoying and start begging for a recharge.

  28. Finn,

    As usual, some thought provoking points..

    However, for me, it is very much a point of defiance to retailers.

    In my case, the following applies:-

    The markup between the distributors and retailers pricing for network tariffs is in the order of about 100%

    I’m on ToU – retailer rates (my contracted rates).
    Peak $0.2584 ex GST
    Shoulder $0.2175 ex GST
    Off Peak $0.1089 ex GST

    The Distributors network rates are (ex GST) for 2017-2018
    Peak $0.14403
    Shoulder $0.94621
    Off Peak $0.055699
    (all units charged per kWh)

    As you can see, there is nearly 100% or more markup in all the usage rates.

    Now, I can use my own electricity instead of exporting, lets say 4000kWh.

    This means, the retailer stands to lose anywhere between $220-450 pa (roughly +/- 10%) profit alone on my avoidance of grid usage. This does not include the daily supply charge fee.

    Not much from a single consumer. Now, let’s multiply this factor by 30,000 customers doing the same thing.

    The retailer now stands to lose something in the order of $6.6M-$13.5M profit markup pa because they did not get to sell electricity. (now imagine if millions of customers instead of thousands did the same thing?).

    Now, this I understand will be the death spiral of retailers, not the distributors because they still get to obtain their money via the daily supply charge because they are fixed fees and are independent of energy consumption. (Like rego and petrol).

    It clearly shows how extortionate the electricity retail market has become in Australia. With 50 or so retailers, it is too crowded for Australia. Why do we need 4 layers of electricity market players? This is worse than politics with 3 layers. Is 4 layers of electricity markets an efficient mechanism? 3 layers would be adding their profit margins at each level. It’s clearly a profiteering scheme.

    So, yes, the battery is my way of defying the retailers. Secondly, reduced bills obviously, thirdly being reducing fossil fuel use. Lastly and eventually self-sufficiency.

    Numbers are not made up, they are actual published figures by distributors and retailers. Anyone can search for them.

  29. Lawrence Coomber says

    There is no standard answer to this question Ron.

    You will see DOD figures around 80% being published, but it’s in a constant state of flux. When working in Detroit last year with a large team of EV battery stack engineers at SAE, everyone had different ideas. And that’s healthy.

    It goes beyond technical matters alone, and somewhere in the value chain, has to accommodate commercial realities also. From the EV battery design engineers standpoint alone, they understand that in general terms for the standard battery chemistries in service at the moment, very deep discharge should be avoided because the inverse power law dependence of the battery cycle life on DOD, reveals up to a fourfold cycle life gain being possible by moving from very deep discharge (around 100%) to 50% for example. This DOD/cycle life dependency is non-linear as the DOD is reduced.

    CEO’s of EV sales though, have a different view of life and commerce to the more conservative engineering view, and from this point on, they part company usually when DOD is discussed.

    So who should win this argument moving forward?

    I believe that technology must always improve, and pushing harder and being more demanding on the researchers, chemists and engineers is the best strategy to encourage (and in fact demand) technology improvements and even quantum leaps going forward.

    But underneath I am still a simple conservative engineer and guilty of overdesign in most cases, so I will move only 1% point towards the EV salesman’s view of life, and nominate 81% DOD, and put it back on the engineers to design better performing batteries.

    Lawrence Coomber

    • Ronald Brakels says

      Thank you very much for that. I had thought depths of discharge may have been greater than 80% but given how well the battery packs of at least some EVs have held up I guess that’s generally not the case.

  30. Hi Finn

    Some comments on your article:

    Myth 1 and 2: Yep solar on its own will likely offer a higher ROE than batteries and Solar panels, but the question relates to batteries only and I would argue the break even point is quite close for many people. Today I could get the Origin Solar Boost in Sydney which offers a 15c FIT and I pay 14.5 c for off peak power. So no chance their. But my off peak charge is about 53c so there is almost a 40c per kWh spread to be crossed by using the battery to offset peak usage. Add to this some income that maybe could be generated if you could use Reposit and the ROE may beat bank deposit rates (after tax). Whether it beats the after tax cost of a mortgage is a different matter.

    Myth 3 (Carbon Footprint): I don’t buy this argument as presented. A battery can help reduce the duck curve that comes with significant solar (and is visible in the power generation of at least some states). This reduces the need for more fossil fuel peaker power plants – or running coal plants all day to meet a few hours requirement. The carbon footprint argument needs to be based on the the reduction in fixed assets (fossil fuel generators) rather than round trip efficiency.

    Myth 4 (Blackout protection): Yes if you want or need backup from your battery you do need to buy a battery system that will do that. Setting up the solar / battery system from scratch seems cheaper that refitting (by almost a couple of thousand dollars by my reckoning). I do agree that many people don’t need backup, but many people do.

    Myth 5 (Battery Ready system): When I looked into this a couple of months ago it seemed that you could same about $1,500 by buying a ‘battery ready’ system rather than one that would be retro fitted with an AC coupling. I may have got this wrong (and blown $1,000) but it comes from not needing a second inverter. Offsetting this, as others have commented, battery technology changes and a battery ready system now may not support the batteries that will be around in two years time.

    Myth 6 (sticking it to the man): Bringing a rational argument to an emotional response is not a good way to either keep a happy marriage or make friends. Glad you did it and not me…

    Keep up the good work. I love the web site.

  31. Power, power everywhere/ And not a stop to think. (apologies to the Ancient Mariner. (and keep in mind I think grid-connection (unless you can make a LOT of money) is the modern SM flagellator for the Church of Solar Stupidity. eg.

    —-> “Myth 4 (Blackout protection): Yes if you want or need backup from your battery you do need to buy a battery system that will do that. Setting up the solar / battery system from scratch seems cheaper that refitting (by almost a couple of thousand dollars by my reckoning). ”

    Back-up from your battery-bank is no more complicated than:-

    Cable from the array down to some convenient spot. At that spot you wire up an either/or option, (suitable toggle-switch/splitter of some sort), or simply two fuse-boxes with but ONE fuse) so that you can CHOOSE to direct your incoming power to the battery-bank OR the grid-connect inverter.
    On the line that runs to the battery you wire in a regulator (or not, depending on what you want to achieve and how big your battery-bank is). But the diode function in the regulator prevents your battery feeding back into the system, side-stepping other considerations.

    And there ARE a few optional variations possible.
    One of them ….. especially ,er, ‘assuming’ you can make money from the FiT differential…. is to configure a few short cables to provide MANY options which best suit any given requirement.
    One such is to connect batterybank to house-circuits (via inline inverter and fuse-box) and always via an either/or setup so that any risk is obviated.
    And in some cases it might be desirable to run a separate dc circuit to selected power-points around the house directly from the battery.
    Another is to plug a $20 battery-charger into a power-point and leave it attached permanently to the battery-bank, which can produce some useful outcomes. It’s a large subject, so I’ll leave it there, with the stern warning about legality.
    But the point is that such a grid-plus-battery system can cost as little as a coupla hundred dollars over and above the $800-odd dollars 10 kw of battery-storage can be bought for. My email address is posted above somewhere if you want to discuss the matter with a man who owned one.

    • Lawrence Coomber says

      Yes a well explained strategy Jackson for unlicensed DIY integrators of old school inefficient low voltage high current (up to 120 VDC limit) power generation systems.

      Definitely not appropriate for the modern and efficient higher voltage low current LV generation systems around now, who require integrators with a number of professional qualifications and licences to design and install systems safely in this range (up to 1500 VDC).

      Lawrence Coomber

      • Hi Lawrence.
        Being an….what-you-said, it’s true that I don’t understand much of what you say. But I have done all the above ~ and more I wouldn’t go into here ~ quite successfully. And as far as I know grid-power still operates on 240ac, at a ‘standard’ 54 amps. (That’s what all the fuses I know of rate at.)
        As for the vdc side of things, in my experience anything over 24vdc is too restricted in terms of components etc. to be practical; and heavy enough cabling, switches etc. obviates any of the could-be-perceived problems ~ and that stuff (eg 400-amp cabling) can, mostly be found for pennies or free. Nor do I see that it need have any direct interaction with the commercial side of things anyway. The either/or principle doesn’t allow for errors/malfunctions.

        I’m the first to agree that I have no recognised education in this territory. But neither am I bound by ‘professional’, licences/rules, etc. However, I’ve been mucking around with this stuff for a long time (in situations you’d have trouble imagining) and never had a mishap. I sometimes remind the ‘experts’ that over 80% of house-fires are started by electrical faults, almost all of which have been professionally installed and inspected. (But of course the Peter Pedals story ~ sad as it is funny ~ could point out that nothing’s foolproof.)
        Other than conservation (of cash mainly!) one of the major factors in DIY generally is that practitioners almost always ‘overbuild’ to the n-th which, while inelegant, covers most of the bets. For myself I’d rather go without than not have control of every aspect of my life. Unfortunately individuality is a concept fast fading from human existence.

  32. And we have just received notification of this month’s monthly scheduled nine hour daylight hours outage.

    It is unfortunate that it is apparently impossible to get a quote for a new solar system with battery backup.

    • That’s a stir, isn’t it Brett??… or have you been out without your sunhat on?
      Scroll back a few pages and you can have it demonstrated that you CAN get a quote for a “new solar system” ($3500 for 10kw).
      And if you wanted to bother you could use that as a grid-connect backup.

  33. Josie Arnold says

    Hi, I am moving to Canberra and looking into getting solar on whatever property we end up buying. On your quote form you have the options “regular solar system” and ” battery ready system”, but in the above article you state that all solar systems are battery ready, so there is no separate requirement for being battery ready. I may very well have misunderstood your meaning, or the form, but would like some clarification. Thanks for your great website! Also, as a cheeky request, what would you recommend for 2 people on a very limited budget, in a small property (80-100 msquared). We will probably require constant heating in the Canberra winter as my 82 year old mother is VERY cold averse. Thanks again.

    • You are correct of course – any grid connect system is battery ready. The reason we ask the question on the quote form is that it helps the installers understand:

      a) how many panels you should get (you need more to charge a future battery)
      b) where the inverter will go relative to a future battery
      c) ensure they don’t use an inverter that maxes out your inverter capacity for the house making it harder to get permission to add a battery layer.

      If you use constant heating in Canberra winters then:

      First ensure you have an efficient heating system (for example an efficiency reverse cycle air con), second seal up your gaps (most Aussie houses are full of gaps) and then look for a large system. Ideally an 8kW inverter export limited to 5kW if required by your local network, then you can add up to 11kW of panels on a single phase, which will give you a good amount of energy through winter.

      • Josie Arnold says

        Wow, thank you for such a quick and detailed response (on a Sunday!). I have somewhere to start now.

  34. Josie Arnold says

    Edit: I just ask for recommendations as I have no idea as to a starting point, or what I should be looking at (philosophy major). I intend to use your quote system for actual installation.

  35. Hi Finn – we’re about to get solar, and all you’ve said pretty much squares with what our solar company said about batteries. Gratifying to know this – means we’ve got a provider that knows their ins and outs. I think one reason for the appeal of batteries (and the wider appeal of solar generally) is that people feel as though they have more control in their lives (apart from environmental ones if course).
    Re solar rebates: of course a higher rebate would be nice, but I also have no objection to the electricity retailer making some profit from our solar – they do, after all, provide the network. The ultimate point is that, like you said, it means our net carbon footprint is reduced.

  36. Hi Finn, thank you for your article with some enlightening insights.
    I have a question about batteries: in my home power box there are 240 volt circuits for power points and lights. Is it permissible to wire your house so that only the lighting is run from batteries? i.e. leave the heavy lifting of power points separate and drawing from the grid-connected source.
    Also, could the wiring and switches/fixtures that are already there be used for 12 volt lighting with LED globes? I live in Brisbane so sunshine is not a problem, and I’m thinking about batteries charged from solar panels (separate from my existing grid-connected panels).
    In the alternate, is installing new separate 12 volt wiring/ switches/fixtures always required? Looking forward to your views.
    P.S. I am a son of another “electrical engineer, solar and energy efficiency nut” and grew up in the 70’s with solar hot water and some 12 volt lights at home!

    • Ronald Brakels says

      Hi Peter, Ronald here.

      You can definitely wire your home so the light run off batteries. But the economics of this won’t be good given the limited lifespan of the batteries. Of course it would be useful in a blackout.

      If you decide to go ahead the existing wiring won’t be enough for DC powered lights. Every light will need two cables so it will be connected to the positive and negative terminals of the battery. As far as I am aware the existing switches should work without problem. You will need a qualified person to disconnect the lights from the AC power.

  37. Lawrence Coomber says

    Peter yes you can go down this track but there are some essential preliminaries you need to fully understand and deal properly with.

    The best strategy is to start from a clean slate and design a Standalone Power Supply (for selected circuits) system, entirely independent and isolated from the Grid Power Supply.

    In your case and for maximum efficiency and simplicity this means DC coupling your Solar Array (DC Bus) or a part of it, direct to your Battery Bank via a Battery Management Unit. DC Coupling Solar and Battery needs to be design sized and optimised and you will need some professional advice on this point, and it all revolves around what you currently have available to work with (Solar and Batteries) for example if any.

    This Standalone Power Supply (DC coupled Bus) is then connected via appropriate controls and protection to a suitably sized SPS (Off Grid) Inverter supplying AC Power to it’s own MSB for distribution to selected circuits as you choose in the normal manner .

    Note here: that this is a Secondary AC Supply (not DC) and it is derived of course from the DC Coupled Solar Array and Battery Bank functioning as a joint DC Bus supplying an Off Grid type Inverter.

    The selected circuits are then re-routed to the independent MSB that is totally isolated from and has no commonality at all mechanically and electrically with the Grid Supply MSB installation, and this includes having its own MEN. This is a critically important point and one well covered by AS 3000. There is no capability of course to parallel the Standalone Power Supply AC system with the Grid Supply AC system; they are totally separate systems sharing the same address only.

    You can visualize your premises then as one premises with two separate AC Power sources supplying their own respective circuits.

    This is a common design strategy in rural situations connected to the grid, but having a separate and independent Off Grid System installed to supply high current demand (machinery, pumps, multi-phase equipment) etc, as dedicated selected circuits to minimize high maximum demand tariffs being levied.

    Might sound a bit complicated Peter but its straight forward in practice, and a reliable compliant safe solution is the outcome, and in the case of a small demand load circuit such as lighting, can be low cost to implement.

    Good luck with your project Peter.

    Lawrence Coomber

    PS: Running DC switching circuits in any form inside your premises is problematic and should be avoided. That’s what George Westinghouse and Thomas Edison’s stoush was all about 130 years ago. Westinghouse won (AC).

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