Powerwall Vs. Lead Acid Batteries. Which is best for off grid?

powerwall and a lead acid battery

Does the Powerwall make sense for off grid applications?

I recently wrote about how my parents could save money by going off-grid in sub-tropical Queensland under close to best case conditions, and how it made no sense at all for them to do this as the return from having grid connected rooftop solar is so much better.

The recently announced Tesla Powerwall doesn’t change this. However, it will still be a very useful option for people who have no choice other than to live off grid, and for those who want to go off grid for non-economic reasons. It has a number of advantages over currently used lead-acid batteries, and in my opinion, for many applications the Powerwall knocks lead-acid batteries into a cocked hat, which will soon be squashed very flat, as lead-acid batteries are really heavy.

Powerwall Warranty Versus Lead-Acid

 

The Tesla Powerwall’s internal software carefully monitors its batteries’ rate of charge, discharge, voltage levels, temperature, percentage of world conquered, and so forth, in order to maximise their lifespan which enables it to come with a 10 year warranty with an optional extension out to 20 years. Meanwhile, the makers of lead-acid batteries have no control over how you are going to use their products and so only offer warranties of one year or perhaps two if you are willing to pay for a more expensive brand. This is the Powerwall’s greatest advantage over the competition. Most people, and particularly business people, are simply unwilling to shell out a significant amount of money for a new investment unless they know they won’t be out of pocket if something goes wrong. If lead-acid batteries were my only choice, I know I would pay a huge premium for ones that came with a ten year warranty.

Powerwall Storage Capacity Versus Lead-Acid

 

The capacities of the Powerwall and lead-acid batteries can’t be directly compared because life is confusing. For the $3,800 dollar cost of a 7 kilowatt-hour Powerwall I could buy around 17 kilowatt-hours of decent quality long life lead-acid batteries. However, because they can’t be discharged by more than 80% they really only have about 13.6 kilowatt-hours of effective storage. And if I want them to last 15 years then I’ll need to avoid discharging them by more than around 25% a night, so for the majority of the time they really only have about 4.25 kilowatt-hours of storage. So for day to day use the Powerwall is superior, but when required lead-acid batteries can be more deeply discharged to provide electricity during periods of bad weather and/or high electricity use. But if this is done too often it will destroy them.

Powerwall Efficiency

 

A Powerwall’s energy storage efficiency is 92% which is significantly better than lead-acid batteries at around 85%. In practice this is not a huge difference, but it does help. It will take about one half to two-thirds of a kilowatt-hour less solar electricity to fully charge a Powerwall with 7 kilowatt-hours than lead-acid batteries, which is roughly half the average daily output of one solar panel.

Space Invaders

 

The Powerwall is suitable for inside or outside installation, takes up very little space, and as the name suggests is made to be mounted on walls. When properly installed it should be extremely safe. There are lead-acid batteries that can be installed indoors with suitable precautions, but due to the very small but real chance that a lead-acid battery will decide to transform itself into a hot pile of fuming goo, I strongly recommend putting them outside. The amount of space taken up by enough lead-acid batteries to power an off-grid house is not as great as many people often assume, but is still greater than what Powerwalls require. To take a two person household off-grid might require a bank of lead-acid batteries around the width of a single bed, the thickness of a dinner plate, and about as high as a bar fridge. While a battery enclosure is not strictly necessary for all installations, precautions do need to be taken to prevent children stress testing the system or vice-versa.

Maintenance

 

Sealed long life lead-acid batteries require a small amount of maintenance every six months. The Powerwall requires none.

Powerwall Power Output Versus Lead-Acid

 

A single Powerwall can provide 2 kilowatts of continuous power or 3.3 kilowatts peak. I have no idea how long peak power can be maintained, but hopefully it would be long enough to let me boil the kettle and grill a cheese sandwich while I play Dance Dance Revolution. An off-grid household with a single Powerwall would be limited in what appliances could be run after sunset. Two kilowatts is enough to operate lights, refrigeration, laptops, TVs, and not much else. Air conditioning is not really possible unless it is a very small unit or it can operate in a low energy mode, and even then care will have to be taken with the use of other appliances. Electric space heaters are similarly restricted, but a highly efficient heat pump could still be used. It would be difficult to use an electric stove, and as for clothes dryers and dish washing machines – forget about it.

Two Powerwalls should be enough to provide normal evening appliance use for many households, although care would still need to be taken to avoid running more than one or two power hungry items at a time. And it would still be a very good idea to use the air conditioner to cool the house down before the sun sets to reduce the amount of electricity it draws in the evening.

If a lead acid battery bank is large enough to have a lifespan of a decade or more, it should be large enough to handle normal appliance use in an evening. However, care should still be taken to limit electricity use after sundown to extend its lifespan.

Powerwalls Plus Extra Solar Panels Beat Lead-Acid Batteries

 

I recently calculated that to take my parents off-grid would require about $6,300 worth of lead-acid batteries with a total capacity of 28.8 kilowatt-hours and hopefully they would have a lifespan of 15 years or more. But if I had the option, I would now prefer to purchase them a single Powerwall and spend the left over money on extra solar panels. And because I would not have to set money aside to cover the possibility of their lead-acid batteries failing early, that would allow me to buy additional panels. So while the Powerwall would only have 7 kilowatt-hours of storage compared to the 23 kilowatt-hours the lead-acid batteries would have with an 80% discharge, the extra solar panels, aided by the better energy storage efficiency of the Powerwall, would let them generate solar electricity equal to their average daily electricity use even on completely overcast days. This option would require my parents to be a little more careful with their appliance use in the evening, and they could still need to conserve electricity and/or use their generator more during periods of bad weather and high electricity use, but I see it as the superior choice because of the Powerwall’s 10 year warranty. For me, the extra peace of mind and financial security is definitely worth it, especially since I know that if something did go wrong, I’d be the one who gets blamed.

Of course, what works for my parents may not work for everyone. Most households have less constant sunshine and greater electricity use. But I’m confident a majority of people will agree with me that for many off-grid applications the Powerwall’s long term warranty makes it superior to lead-acid batteries, even though it is not currently a clear winner on initial costs and gives a smaller maximum usable amount of storage per dollar.

About Ronald Brakels

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.

Comments

  1. Hello emphase is releasing a battery storage
    As well
    Thoughts ?

    • Yes they are. They will come in 1.2kWh increments. The first one will need to be installed by an electrician. Subsequent ones should be able to simply be plugged in.

      I think it makes a lot of sense. You can add to your home bit, by bit and monitor the effect on your bill.

      They should be available early next year.

    • Ronald Brakelsr says

      I think the Tesla Powerwall is very impressive, but it is simply too large to be cost effective when used as on-grid storage for most Australian households. Provided Enphase’s cost per kilowatt-hour is within half a camel spit of the Powerwall’s, it could be exactly what we need to take on-grid energy storage mainstream in this country. Or it could be a horrible mess. I’ll have to wait till I know more to form a solid opinion.

  2. Derrick Nalli says

    Our house is all electric with most of the bells and whistles appliances and gadgets. We also have solar hot water system.

    5 years ago Origin Energy installed a 1.6 KW solar electric system for us, and at that time we qualified for the 48.5 cents per export unit and 8cents for generated units. Total cost 24 payments of $142.12 = $3410.88

    We get the following power accounts per year
    2x$90.00. 2x$120.00 2x$145.00

    With hindsight a 3KW system would have been a real good investment.

    Friends of ours recently installed 18 panels for $17000.00 and their power bills are double ours.

    • 18 panels for $17,000! Who on earth charged them that! A 4.5kW system like that should cost closer to $7,000.

      • Jack Wallace says

        ….or, at the current ($1 per watt) rate……..

        Usage is STILL the key. Anybody who’d even think about using electric space heaters/fridges/etc. through a battery-bank has got more money than brains.
        ……even if their life’s savings amount to 35 cents.

        ‘Efficiency’ can get to the point of inefficiency.
        Even frugality can become extravagant.

        • tell that to a real sailor on a sailing catamaran covered with solar panels)
          I’m thinking about taking at least one diesel engine out and replacing it with a DC motor and even building my own outboard motor with -you guessed it- a small DC motor. If one of the Lithium batteries can be taken out -say, like a briefcase and carried from the mothers-hip to the dinghy… well then I’d be transferring my own solar-fuel around to even charge my iphone on the dinghy… I’m thinking about the scope of the project. Researching options. These kids on youtube or building their own Powerwalls at a fraction of Mr. Musk’s and doing incredible things with electric motors by converting practically ANY car to an EV.
          Costs are no longer as prohibitive as you might think.
          One DIY Powerwall with Tesla (Panasonic Li batteries with whom Mr. Musk -he has my respect- is building these batteries) = $300 US.
          The 2180 -the newest gen battery cell (they really look like slightly larger AA batteries) have twice the capacity as the 18650 cells that are in all Tesla products sold to-date. (as of July 2017)
          Good article… explained simple enough for even me to understand)

  3. VoodooCR says

    ok so your comparing comparing 28,8k(SLA) Vs 7k(TESLA) …. for the same money so to compare like for like in terms of money discharge rates and cycles we get…..

    SLA Battery 50% discharge 1200 cycles (TROJAN batteries) 14.4kWh of usable power
    TESLA/Li-ion 50% discharge 1200 cycles (batteryuniversity,com) 3.5kWh of usable power

    Both batteries would need replacing in 3 years or pehaps 6 if used to 25% discharge or TESLA’s 10 Years Garantee at 16% discharge and 1kWh of usefull power per cycle…..

    How does that make TESLA option superior ?

    • Ronald Brakelsr says

      VoodooCR, the 7 kilowatt-hour Tesla Powerwall has considerably better performance than what you have written down. It will discharge 7 kilowatt-hours a day with a warranty period of 10 years, or over 3,650 cycles. That considerably improves the comparison.

      And just to be clear, the 7 kilowatt-hour Powerwall is only a superior option if one places a significant value on its 10 year warranty. I think the warranty is very useful, particularly with the example of my parents where I generally wouldn’t be around to deal with any problems that might crop up. But if you were supremely confident that lead-acids will operate for many years out of warranty without problem, then the Powerwall’s warranty would be of less value to you. And which type of energy storage is the best will all depend on the individual installation. For example, if one was considering an off-grid installation without a generator backup, that might cause one to lean towards lead-acid. But I do think that, provided they can actually get their hands on them, the Powerwall, or something similar or better from a Tesla competitor, will probably be chosen over lead-acid batteries by a majority of Australians for off-grid use.

      • Jack Wallace says

        Without going into details: it should be remembered that other costs apply to the ‘power-wall’ style of thing. eg the cost(s) of being connected to the grid (currently about $600 pa where I live ~ and increasing geometrically) ~ and therefore the resource/environmental costs of building/maintaining the system. (Including the cost of building/running fleets of vehicles for assorted grid-related purposes, etc.)
        Even just the energy lost in transmitting electricity over long distances (including environmental heating) could probably run a small city.
        And (still within the audit) we have the HUGE cost of bushfires ~and electricity-based house-fires galore.

        The low component-cost these days makes stand-alone (and I favour PROVEN lead-acid storage) alternative energy systems by far the best option.

        Particularly keeping in mind the options of linking wind/water/etc. production to the system. The possibilities are endless, cheap (including DIY) and immensely self-satisfying.
        How would one cost that?

  4. I had a 2Kw solar system installed by Origin Sept 2012 (on the very last day the Premium Feed In Tariff finished here in Victoria – paying 66c/kWh export). Using the highest quality SunTech panels available (supposedly 20% more efficient than their ‘normal’ panels). How has this panned out ?
    Prior to solar, our average power bills were around $1800 per year. No, with solar:
    1Jan13 to 31Dec13 our total expense for power+service charges was $16.53
    1Jan14 to 31Dec14 prices rose to $344.97 which is still less than the service charges. Previously = $1800x2years = $3600 – Bills of (16.53+$344.97=$361.50) = Total saved of $3238.50.

    All this is fine and dandy, but we are about to move to a house with no solar and plan on installing 5Kw in 2 strings – maybe 1Kw facing North, the rest facing West (if this is the most suitable. However the FIT drops to a mere $0.08c/kWh 🙁 This is where the Tesla PowerWall comes into play… It is now better to pump as much power during the day into the PW, then any excess can go to the grid. We will also have to change our power use habits. Instead of dishwashing after 11pm (when off peak cuts in) we will run as much as possible during the day, to utilize excess solar power. Hopefully this will have a marked effect on out bills. Maybe not as good as we have now, and will cost more to install. I will need to crunch the numbers to see if the PW will actually save us anything at all.

    • Ronald Brakels says

      I’m afraid you probably won’t be able to save money with a Powerwall in Victoria, Greg, if that is where your new place is. This is because the state has the lowest electricity prices in Australia. And they have a minimum feed-in tariff rate of 6.2 cents a kilowatt-hour which actually high by current Australian standards. The best states for making money from on-grid Powerwall storage, in order, are: NSW, WA, SA, and QLD. And even then the household will need to be on a time of use tariff and have high electrricity consumption in the evening, so they are unlikely to be worthwhile for two person households.

      But a bit of good news is the Powerwall has been uprated at no additional expense. The 7 kilowatt-hour Powerwall will now be able to output 5 kilowatts of continuous power or 7 kilowatts peak. This should more than double the amount of money that can be made from electricity arbitrage using the Reposit software that comes installed on it. This will also have the benefit of reducing the amount of fossil fuel that is burned to provide ancillary services such as spinning reserve. Money from buying and selling electricity may be enough to make the Powerwall profitable for you, although I have to admit I’d be surprised if that turns out to be the case. Currently I think the best thing Victorians can do is install plenty of solar panels and bring closer the day when Victoria’s monster brown coal power stations, such as Hazelwood, start to get shut down.

      • Jack Wallace says

        …and just for the record:- I’ve been using about 2 kwh per day year-round without foregoing anything important to me. (I live alone.)

      • Phil Boyle says

        Hi Ronald Brakels. I live in Rockhampton Qld and selling my house and moving to my property and going off grid. If i bought the new Tesla 2 x2 and 10 kw solar panels could i run a small inverter airconditionor all night.

        Thanks Phil..

        • Ronald Brakels says

          I have heard of people using the Powerwall 2 off-grid, so what you want to do should be possible. When the Powerwalls are new you will have a total of 27 kilowatt-hours of storage and that is far more than what is needed to run an air conditioner for 12 hours. A single room air condition in an might draw 700-800 watts when its compressor is working. So if it operated at full power all night it might use 9 kilowatt-hours. But normally it would not operate at full power and its compressor will switch on and off (or operate at lower power if it’s smart) so unless there is an extreme heatwave I would expect it to use significantly energy than that.

  5. Jack Wallace says

    I’m locked in to a contract until 2024 to receive the 66-cent FiT, but the top going rate for more-recent ‘clients’ is 10 cents per kwh.
    That means that in the Latrobe Valley (close enough to the power-stations to make an extension-cord under the fence a tempting option!) your first 4 kwh of solar-produced energy goes to pay the ‘service-to-property charge’ whether you use ANY energy or not!
    (not including the $2 fee for paying your bill!)

  6. You can’t discharge lead acid batteries more that 50% daily. If you are discharging them to 80% you will shorten the life of the battery.

  7. What are your thoughts about using combine Lithium and lead acid in an off-grid system. Feasible?

    • Ronald Brakels says

      It could be done but I don’t see the advantage of combining lithium with lead-acid. Not unless someone was transitioning away from a lead-acid off-grid system.

  8. Greg Bennett says

    I have a weekender (completely off grid) on a property in the bush.
    There’s usually no more than 2 or 3 of us there each weekend, more often over holidays etc.
    We run a small generator to power the kettle, microwave, fridge, TV etc. which is fine, except we can only run certain appliances together, without straining the genny!
    I’m currently considering a solar system of some kind. (I’m totally new to the idea.)
    Lead acid or Powerwall? I’m leaning lead acid, due to the fact that it WON’T be used more often than it WILL be used.
    Your thoughts?
    Thank you in advance,
    Greg

    • Ronald Brakels says

      Hi Greg,

      The Powerwall 2 is not designed for off-grid use but apparently there are people using it that way. If you wanted to go that route it would cost you perhaps $15,300 installed and you would also need a solar system, although that would not need to be large.

      If you speak to an off-grid installer what they are likely to recommend is a lead-acid battery system. Unless they are trying to up sell, for your needs they’d probably suggest something small. Perhaps just 4 panels and 6 kilowatt-hours of battery storage with a 2.4 kilowatt battery inverter. The small number of solar panels would charge the batteries while you’re away and keep them topped up. While you’re there if skies are cloudy or your electricity use is high you will need to run the generator, but you’ll be running it far less than you are now.

      Because you only spend weekends and holidays there the lead-acid batteries should last a considerable time, but you will have to budget to replace them. They will last longer if the make the effort to treat them gently, such as boiling water in the microwave instead of an electric kettle. If you or others there are don’t want to worry about doing that you may instead want to invest in extra battery capacity from the start so each battery will suffer less strain and so last longer.

  9. Can you also do a comparison of the different battery options (Lithium Ion vs Lead Acid vs flow battery vs any other options) for grid tied solar PV systems?

    • Ronald Brakels says

      Howdy

      For grid tied solar lithium batteries are clearly the most economical option. Lead-acid batteries are a mature technology and have very little room to fall in price. Basically, unless there is a big fall in the price of lead they’re not likely to get much cheaper. But lithium batteries can beat lead-acid on price now and have a lot of room to come down further. While any battery system won’t save the majority of Australian homes at the moment, lithium has a lot of potential for the reasonably near future.

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