On the back of the federal rebate, huge batteries are on sale for bargain prices. There’s a catch to many of these deals however: you can’t possibly hope to actually charge these monster batteries to capacity as they are paired with completely inadequate inverters. Here’s what to watch out for.
In a bid to make the rebate useful for businesses, the Cheaper Home Batteries Program discounts as much as 50 kWh of the usable capacity of a battery system – much more than most residential households could need.
This in turn has sparked an arms race of advertisements promoting ever-bigger batteries at ever-smaller prices for homes that simply don’t need them. The cheapness however isn’t just down to the rebate discount – there’s something crucial these batteries are missing.
All Capacity, No Power
My old mate Sam had a Landcruiser “shorty” called Daisy. The previous owner had installed an additional fuel tank, more than doubling the total capacity to 183 litres. With a modest 85kW 4 cylinder using 7.8litres/100km (30mpg) Daisy had a ludicrous range of 2300km. That’s almost Adelaide to Perth, 25½ hours straight.
So if you get a 5kW inverter and a 50kWh battery as we’ve seen advertised in one instance, you’ve got the same combination: modest power output and a novelty oversized tank. The trouble is this doesn’t offer the same advantage that it is does for a car’s range. An average full day of sunshine on 6.6kW of solar will only half fill the battery. Or charging from the grid, sweating its arse off, the inverter will take 10 hours straight.
Once filled, you wouldn’t be able to extract the energy particularly fast either: 6kW to run the toaster, kettle and dishwasher would mean you’re still importing energy from the grid despite a charged battery. And the backup capacity from a 5kW inverter isn’t going to run your whole house in a blackout.
A general rule of thumb, subject to your particular needs, is a 2 or 3-to-1 ratio for battery and inverter size: so a 5kW inverter being appropriate for a 10kWh or 15kWh battery.
Be Aware Of Power and Kilowatt Hours
The key is to understand the difference between kilowatts (peak rating) and kilowatt hours (storage units).
For another car analogy:
- Kilowatts is the grunt under the bonnet. Going fast means you need more peak ‘orsepower under your right foot.
- Moving your car means doing work, using litres of petrol in the tank, measured slowly and accurately into the engine, burnt gradually over time.
- In other words, an aerodynamically efficient car might need 15 kilowatts of power to move it through the air.
- So if you’re consuming 15 kilowatts to keep a steady speed for an hour, that’s 15 kWh of energy out of your tank.
The Worst Example Yet
In what is the worst example I’ve seen to date, a crowd that’s been importing 4WD accessories for all of five years has just set up a brand new ABN for an energy business. They’re doing a “group buy” taking your money in advance so they don’t have to carry the capital cost.
50kWh of battery for just $5100 sounds like an unbelievable deal …
Until you see it is paired with a hopelessly undersized 5kW inverter.
The promise is FIFTY kilowatt hours of storage for $5100 installed.
- Do they realise that as the importer, they’re responsible for warranty under Australian Consumer Law?
– I’m not sure the gravity of that obligation has struck them - Are they approved to parallel import when there’s a local office for the battery?
– That’s worth asking - Have they priced in some after-sales support and warranty stock?
– They’re not transparent on prices, but obviously the federal rebate is paying more than the battery costs - Do they care?
– Apparently they’re out to break the solar industry - Have they designed the system properly?
– No. We can say that categorically.
The qualification I’ve done to be a certified solar and battery electrician goes into great detail. We’re trained to examine the customer’s infrastructure, their electrical loads, their peak demand, their potential solar yield and most importantly, the amount of surplus energy they should have available to fill a battery.
Flogging everyone the same massive battery ignores all of this detail.
Not every designer is going to run every calculation, but being trained means knowing the process.
Can’t Huge Batteries Just Export For Huge Profit?
Worse still, expecting a system to perform properly and claiming you can make wads of cash using a retailer that offers wholesale prices like Amber with 70c/kWh for export is not right.
With 10 times more battery than inverter capacity, it’ll take ten hours to export a full battery for a princely $3.50 per hour. Never mind that you’ll need two days of average solar yield to fill the battery first, as the inverter supplied isn’t actually integrated with Amber smart-shift.
Energy trading relies on being able to respond quickly to 5 minute price fluctuations. So if there’s a “grid event” and the prices go berserk, you need to automatically export a heap of energy during an short window of time.
If the spot price is on fire, a 30kw inverter might occasionally earn a $20 bonus or $200 bonanza in a fleeting half-hour, but with a 5kw inverter, you’ll be fighting a bushfire with a garden hose… and without smart-shift, you’ll have to be on the app to make a manual intervention at just the right time.
Whatever The Question, The Answer Is More Solar
Inverters aren’t the only issue: how much solar you have is also key. I’ve always maintained that the question doesn’t matter, more solar is always the answer, because generating your own energy is cheaper than importing it and “excess” solar isn’t a thing. Even if the networks resort to export charges instead of feed-in tariffs, setting your system for zero export will zero the problem.
You need extra energy, over and above your daytime loads, to charge up a battery. Qualified solar and battery designers can explain how they specify a solar power system to generate “excess” electricity, and how much battery capacity you need to store this surplus.
So you can come at the problem by working out:
- the storage required to cover your dusk till dawn consumption,
- adding some extra capacity to account for degradation,
- then installing enough solar to harvest what’s required to fill the battery
- and enough to satisfy your daytime appetite.
Or you might have a limitation like roof size or budget constraint, in which case it’s a matter of :
- working out your maximum solar yield,
- subtracting the daytime demand,
- arriving at the battery capacity to store the surplus,
- adding some storage if the budget allows,
- charging this extra battery capacity by importing cheap off-peak electricity.
We Should Have A Second Bite
Part of the problem with the oversized battery epidemic is that households can only claim the rebate once, meaning there’s a temptation to go big or go home. This would be addressed if the battery rebate worked more like the solar rebate, which can be had in any number of increments up to 100kW of installed capacity.
Indeed in the early days, many commercial customers started with 10kW, jumped to 30kW the following year and then really bit the bullet for 99.99kW once they were sure the savings were stacking up.
It would be great to see the same logic applied to the battery rebate. People could buy what they can afford without overcapitalising on something out of fear. A lot of quotes I’ve seen mean a lot of battery capacity is going to be installed, but there’s a risk it will be effectively stranded behind a small inverter.
The first 5kWh of battery capacity offers great benefit to the grid by lopping peak demand, but for public infrastructure owners (the electricity network operators) the savings grow smaller as battery sizes increase.
For domestic customers, I expect 10 to 15 kWh will be a sweet spot in terms of value, again with diminishing returns if batteries grow significantly more.
As bad as going too big is, that’s arguably not the worst you can make with this one-shot rebate. That might be going for too small a battery: I’ll cover this in an upcoming article.
For more on battery capacity, read our deep-dive explainer on battery sizing.
About Anthony Bennett
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Exactly the process I went through when considering a second battery under the rebate scheme. Sure there are days when I might fill a battery with excess solar (I have about 12kW, the most we could fit on the roof and the distributor would allow), but on the days that happens I also don’t tend to need the excess power, because it generally means it’s warmer. And heating is our biggest draw, apart from an EV, which isn’t at home during the day on work days so isn’t normally charged from solar anyway, it’s charged from cheaper overnight grid rates.
Using OVO’s 3 free hours during the day does help there, I can recharge the existing battery from that and potentially partially fill a second, but I’m not spending $10K+ on the off chance those cheap rates continue (which I’m sure they won’t, as grid-level batteries begin to mop up that daily excess production). Having one Powerwall 2 seems to be the sweet spot for us, and also seems to be the conclusion of your article, for most people.
Without actually having the time to look into the batteries used 5k for 50kwh isn’t bad it’s everything else that is filled with concerns.
Helps its not actually excessively oversized by too much for where i live as outdated calculations were around 30kwh needed at minimum to cover nights. Preferably dc batteries to enable over sizing on panels to something like 200% to charge them better.
as the the practical limit for inverters on my house is 10kw-15kw with the 15 needing a negotiated connection contract as ergon only has standard contracts for 1-10kw and 30-100kw
Seriously, SolarQuotes is one of few reliable sources of info re things solar.
A recent article in The Age/SMH went out of its way to explain the terminology “Kilowatt” and “kilowatt HOUR”, got them A-about-F. Even after numerous comments pointing it out, wasn’t unedited.
So, thanks once again SQ and AB.
Additional to issues mentioned is fact that export rates are capped at 5 kW in many if not all jurisdictions, irrespective of size of inverter and whether exporting to grid solar power directly or discharging from battery.
Also, unless your system is compatible with Amber’s tech, you won’t be taken on as a customer to even manually issue command to discharge battery. Btw, I have been paid over $100 for an evening peak time discharge on a few occasions. But that’s rare. Most days the accrued credit is about $2 after ev charging, pool pump. resistive hws, eyc during middle day usually when FiTs are negative.
I suppose how much of a shonk doing this type of greatly under powered install depends on what you are up to
– perhaps planning on replacing the small inverter with a larger/better inverter later on when you can afford it?. Because as you say, only one bite at the battery cherry.
– perhaps you might be a dodgy landlord installing 5kw solar panels and a small inverter to have your massive battery subsidised on your rental, when you fully intend to remove 3/4 of the battery from and use elsewhere where the subsidy wont apply?
Winter Usage the last 7 days :
34.8kwh with 20.40kwh created
36.0kwh with 19.9kwh created
26.5kwh with 17.79kwh created
34.7kwh with 18.60kwh created
33.8kwh 12.0 kwh created
39.8kwh 10.80kwh created
40.5kwh and only 8.0kwh created
Worse in the last 10 days was we used 42kWh and and only 2.50kwh created all day.
8.5kW inverter. – 12 east string and 10 west facing panels on the other string averaging 7.8kw generated during peak summer
Summer time it’s great – winter we will always suck. Retailer is increasing the service charge from 85c a day to $1.12 and dropping 4c to 1c feed in – its obvious that its time to kick the kids out ! lol
Can’t see how a big battery would help with our usage as we couldnt charge the beast when we need it in winter.
Chris, high winter consumption such as yours seems to require a pile of PV, a thumping great battery, and *ample inverter/chargers*, if grid independence is a goal. Admittedly, even with 27 kW of PV and 46 kWh of battery here, this heavily overcast morning’s miserly 0.8 kW was barely breaking even, but the sun’s out now, yielding 8 kW. It is the wide mouthed frog which gobbles what’s going, and my 24 kW of inverters + 10 kW of MPPTs have charged at up to 15 kW, though not in winter. Double the PV would be nifty in winter, but even 27 kW is overkill in summer. As Tony Seba advises, “Size renewable production for the trough.” The roof’s the limit … unless you add ground mounted PV or a carport.
If grid rules obstruct bigger inverters, then a big 48v battery might appeal, as MPPTs can easily add DC coupled solar which adds no export power. Mind you, my brother has 22 kW inverters, 19 kW PV, and only 10 kW export limit, all grid-kosher. Some states are somewhat backward, I fear.
For us the main use for a larger battery in winter is charging off-peak at night and using the battery for peak times in the afternoon and evening. On a Time of use plan in Sydney the peak rate (Red Energy 2pm-8pm) is about twice that of off-peak (10pm-7am). We do watch total power draw in the evening to try and keep it below the battery/inverter limit.
I guess it saves us roughly $40/month. Not much but it helps.
BTW – the Tesla Powerwall app has always had a “storm watch” function that automatically charges the battery if a severe storm is approaching. Recently the app was updated so that the user can start a “scheduled” charge from the grid for a selected number of hours.
So, for example, if I know there will be large consumption in the evening and there will be outcast skies during the day I can elect to charge the battery at shoulder rates (i.e before 2pm weekdays).
Then there is the power draw you require.
It is good to have an inverter that can produce enough power to power whatever your peak draw is. A small inverter will be unable to output enough power back into your house regardless of how big the battery is. If you have an all-electric house, even if you are not silly enough to try to charge your EV off the battery, the inverter output might not be able to handle the output of the kettle if you have the oven or the induction cooktop running.
So, you also have to consider maximum power draw when designing the system.
Of course, the grid will pick up the excess demand if you do the kettle and oven thing.
Where I live, we have a lot of blackouts, so this is particularly important to factor in.
Ok, 5kW to 50kWh is a bit too big but a ratio of 3 to 1 is great. This gives the option to arbitrage with Amber, and power the house or even refill the EV all in the same 24hr period. My 2020 install of a Tesla pw2 in a 1:1 ratio is ok, but not big enough in an all electric household. Also Tesla pw3 incompatability (with pw2) and price is meaning it’s currently a poor choice.
Good discussion on power generation, and storage. But let’s not forget the other side: consumption.
I used to work for a crusty electrical engineer. When asked for more solar panels, his response was, can’t you instead reduce your consumption?
Some people say they use 30 kWh per day, 40, 50. Maybe they are already super efficient with their energy usage. In that case good on you!
But if not, there’s plenty of energy efficiency tips on this site. So if you think you need more storage and more generation, also remember to try for less energy usage…
I agree with your sentiment, but bear in mind the cost of that energy efficiency compared to the cost of capturing more free energy.
airtightening the house is the cheapest method to save most of our winter energy, covering the windows with blinds/blankets is the next, then start on insulation in the ceiling/walls, working your way to the more expensive for less benefit,….but first put on slippers and a coat and do up the zip.
On the other hand, assuming the inverter is appropriate for the household, doesn’t a still somewhat oversized battery have a longer lifespan due to a reduced C-rate?
Tony, a significantly oversized battery can be good to calendar life, due to low cycle rate. My LiFePO₄ batteries are rated to 6,000 cycles @ 80% SoH, i.e. 20% loss of capacity, or 20 years. At 68 cycles done in 1.5 years, cycle life doesn’t come into it. A smaller battery would do more cycles, with consumption determining whether it’d wear out or rust out.
My take is that battery prices will fall faster than solar panels did, so only economically over-equip now. If on-grid, then enough to fill the morning & evening price peaks might be enough, but black-out resilience and is very nice too. Consider more PV too?
LiFePO₄ is cheaper than Li-Ion, largely fire-safe, and lasts twice as long. If hammering the battery, that’s the one to have. (LTO is even better, but far too expensive for me.)
A bigger battery also safely charges at more kW, allowing an oversized PV array to grab a good bunch of kWh in a couple of sunny hours on an otherwise overcast day: a wide mouthed frog!
Thanks for that. I was thinking more in terms of C-rate affecting cycle life of lithium batteries. Does a 20kWh battery with 10 kW inverter at a potential C-rate of 0.5 have a lower cycle life than a 40kWh battery in the same setup with a potential C-rate of 0.25? Not by a lot, but potentially material?
In an energy-conscious world, isn’t the goal to cycle a battery every day rather than 68 times in 1.5 years? If so, does that make cycle life relevant for more than just the warranty?
Initial development cost amortisation, competition, and economies of scale obviously will decrease battery cost with time. On the other hand, rebates are legislated to fall. As far as input costs go, will there really be enough Lithium mines around to cope for the vastly increased supply and ongoing replacement required?
I don’t think battery prices will fall that much. The history of humanity shows an inexorable rise in required energy, or maybe an unexpected E.V.. Maybe go a bit oversized.
As always, it partly depends. “Automotive Grade” cells, chosen for lower internal resistance, seem to show adequate lifespans at frequent 1C bursts, if you’re a leadfoot. I like to keep Energy Storage cells below 0.33C, but the money saved by making do with a smaller battery, worn out a year early by 0.5C discharge, will buy much more replacement battery by then.
High temperature and internal particle fracturing (showing as cell swelling), reduce lifespan. I feel 0.33C is a sweet spot. Time will tell – maybe more for lower resource utilisation than saving money, if a smaller battery does for now+.
Biggest benefit of a bigger battery is overcast & blackout immunity, & opportunistic quick charge from oversized PV in cloud gaps, at modest C rate.
I.e. less for extra durability than energy yield.
My batteries will go by calendar life, because I sized for many visitors, but live solo. Full life reduces resource use and emissions, I figure. On-grid options alter the equation, I guess.
Hi Eric,
There’s a similar tradeoff for lead acid too. When sized for off grid you only want to skim 20-30% off the top regularly, but there’s potential to take 60% if you need to once in a while.
Lithium batteries can be economic because you need to buy less. Given a smaller capacity, they can be worked harder, but they simply don’t have days of reserve.
However the higher internal resistance of lead means they can’t be flooded with a burst of sunshine from what are now cheap oversized solar arrays…
But at least the excess solar will meet loads directly and give you plenty of hours at low current for an equalisation charge.
Part 2:
Staggering exponential global growth of gridscale battery deployment has already chopped wholesale LFP prices. 5 yrs of local subsidies will make us resistant to future rip-offs. Cost drops will exceed rebate reductions, so batteries will be cheaper after the rebate ends.
More Li is found every month. There is a glut. Price is *way* down. New mines delayed due to oversupply. >95% recyclability means less mines needed in two decades. Sodium is a poor substitute, but Aluminium could be better, and madly overabundant. Only wholesaling/retailing/tariffs can slow price reductions.
Global solar generation went to 1TWh in 8 yrs, 2 TWh in +3 yrs, 3 TWh about to happen. It pays, & approaches demand increase, but the backlog means CO₂ emissions have yet to go down. Coal & ICE is <30% efficient, 70% energy is wasted. Electricity supplies triple the demand with 0% extra supply!
Yes, 25 kWh+ battery & BEV (magic to drive), to reduce emissions & Kill Coal Now! Buy quality, though.
Thankyou for your thoughful and thorough replies. I beg to differ on Lithium – prices are tumbling at the moment, but likely large shortfalls loom mid next decade based on current approvals versus ever accelerating demand. Given the lag time between new approvals to actual production is seldom less than 10 years, supply may well be in for a tough time when posters here are thinking about their next upgrade or replacement.
Tony G,
You may be right, to the extent that finished battery prices briefly hold up. But the signs are not there. Volume is the driver now. Cheap panels & batteries = sales.
reneweconomy.com.au reports battery rebate uptake trending to 250k x 18 kWh (average) bookings p.a., which is around 6% of existing rooftop solar. IF sustained, and cycled daily, the uptake will equal the Snowy’s annual energy output in a couple of years.
It’s very early days, and demand may slow after the go-getters have thinned out. It’ll take years of escalating demand to raise the price of raw LiCO₃, I expect. But all it takes is hold-ups in gridscale battery approvals, and Chinese production rates will flood-supply our domestic demand – certainly faster than installers can keep up.
Exponential production escalation, needed to meet global demand, accelerates economies of scale at a much faster rate than the much slower adoption rate of PV over past decades. It will be acutely transformational.
Anthony,
Can you do mate a favour and drop a link for that battery deal? Asking for a friend…
A number of studies and anecdotal evidence is pointing towards the fact that calendar age of a battery is as important as cycles.
Signing up to a wholesale energy price retailer means you can charge from the grub when there’s heaps of cheap renewables around and discharge at night when the price typically is more expensive. That’s what I’m doing – my PV system is unlikely to recharge my whole battery in a day. However, I’m quids in from the wholesale price so I say go BIG on the battery and get as much value from your Cheaper Home Battery Rebate as possible.
It’s good in theory, but a trap for the wary. Batteries are still expensive, you need to sell a lot of electricity back into the grid if that’s what people are looking to as a way to amortise the cost. Far cheaper for me to use grid power than buy a second battery, for my needs. A lot depends on the context of each person’s situation.
There’s also the RELE2 plans from SAPN – I’m really only aware of the one I’m on, where I can buy energy @8c/kWh between 10am and 4pm, even in winter. I currently do this with my 19kWh battery, but am about to double that, as winter-time power usage with RC A/C means I’m still having to hit the grid sometime overnight.
8c/KWh is not free, but it’s pretty close.
I’m building a house in NE Vic. I’ve put down a deposit on solar PV 14.96kW and a 23.4kWh battery on the following criteria
Average consumption = 18kWh.
Peak consumption (June 2025) = 28kWh.
24 hour blackout protection worst case.
June average solar PV generation = 29kWh.
At year 10, battery capacity = 70% x 23.4kWh = 16.5kWh.
To be able to fully charge the battery in Winter from solar PV alone.
Maximum battery charge/discharge rate = 0.5C = 12kW.
Inverter max output = 43.4A.
Finn would be proud of me as I’ve maxed out my roof space albeit only N and NW. The inverter has extra MPPT’s if more desired later.
I never intended to play tariff arbitrage but for the first 10 years, I’ll have some excess storage capacity should the opportunity arise.
Phil, it does no harm you’re on-grid, if your winter weather is anything like mine in the middle of Gippsland, just a bit to your south. Even the sunny half-days are enough to keep my off-grid system humming, and charge the BEV, but the deep overcast late last week had 27 kW of panels delivering barely 0.8 kW for much of the day. There’s a power of difference between 6.4 kWh for the day, and 36.8 kWh two days later. (A BEV changes consumption dramatically.)
I’m figuring your “fully charge the battery in Winter from solar PV alone” won’t be every day, so the grid is worth keeping for a while yet. 😉
Heating tonight with RCAC, my off-grid system with 46 kWh of battery reports “2d 12h” of autonomy at the current consumption rate. With heating off by 10:30 pm, that’ll jump up to 4d of minimal consumption – much better.
All in all, your system looks well dimensioned for resilient self-generation, grid-backed, but low consumption and partially blackout tolerant.
Hi Erik, I’m not planning to go off-grid. I’m anticipating a tariff inversion in years to come and so expect to export excess power at some stage. The $360+ per year daily service charge is the insurance fee I pay in the event an outage is longer than 24 hours.
As you intimated, there is a danger to design your system based only on averages. It was a surprise but nonetheless instructive to see my June electricity bill at my current home. Even though I’m expecting to fully charge my future home battery in a day based on an average 29kWh of PV output in June, so what if it takes another 1/2 a day? If I was off-grid like you, that could be a problem.
Phil, I imagine that for you, the grid is like my generator – must have, but prefer not to use, at least often. Both cost to use and maintain, and both pollute, but they make the system 24/365 capable.
Here, off-grid, an oversized battery has avoided generator starts – perhaps too much, as it hasn’t run in 1.5 yrs. (I’ll drag it across the paddock to work on the tractor shed.) My big load shifting turns out to be charging the BEV on sunny/cloudy days, not in day-long deep overcast. Delaying a 25 kWh bite three days doesn’t hurt when there’s still range to nip into town. PV oversize (27 kW) keeps the home ticking over, even in overcast – at least with neither wife nor kids to break the hermit mould.
I heard that keeping the battery from being fully charged will protect battery life. Is this also the case for home batteries?
Carfield, the 20% to 80% SoC limits for extended battery life apply to Li-Ion batteries, essentially used only in longer-range EVs. The safer, longer life, LiFePO₄ (LFP) batteries used in static energy storage (and the MG4 base model BEV) are said to be largely unaffected by frequent charging to 100% SoC. But fast charging, at hundreds of kW, does appear to shorten BEV battery life to some degree.
My LiFePO₄ domestic battery charges to 100% every morning – I think most do. I do not rush to bring the BEV up from 76% to 100% after every trip to town, though – but that’s to exercise it through a deeper discharge range, to confirm that I do have the anticipated driving range. It is harder to disable all four charging sources for the domestic battery … but throwing a bunch of breakers should do it … hmmm.
“For domestic customers, I expect 10 to 15 kWh will be a sweet spot in terms of value, again with diminishing returns if batteries grow significantly more.”
That’s the same dilemma has a country energy production and its relation to GDP.
10-15kWh is perhaps the sweet spot today, but what about 5 years from now, when 50% of the new cars are either EV or plug-in hybrid?
Also, if you had more capacity, you could maybe add a split system A/C in the bedrooms… etc.
It also reminds me of another moment of Australian History:
(Tony Abbott)
“We are absolutely confident 25 megs is going to be enough — more than enough — for the average household” could also end up in the tech world’s Short-sighted Hall of Fame.
Conservatively, I would say that 20-25kWh is the sweet spot for batteries… until builders start to design energy efficient houses.
Yes, Solai, several consumers on these threads have been saying that 10 – 15 kWh is far from sufficient overnight, with RCAC quickly running it flat. OK, it would do overnight for my 50 m² of 6-stars double-glazed, highly insulated living area, but what about deep overcast tomorrow? Overdo panels first (cos they’re cheap), then overdo the battery while the rebate’s on, if there’s the cash for it, I figure, but it’s on for years to come, I understand. There’s only one bite at that cherry though, so back up, have a good, think, and remember that whatever you install, you’ll use most of it.
Admittedly, my 46 kWh for one person has never been below 70% SoC, so 30 kWh would have been fine, except when the old house is full of visitors, all off-grid. I wouldn’t go below 24 kWh for a family, even insulated to the hilt. In a few years, it will be a common minimum, I’m guessing.
It will almost certainly be cheaper for somebody get a single 10-13kWh battery and then use grid power if required in winter overnight, to top up. Definitely the case for us.
I think the grid is a phenomenal resource. It seems quite common to interpret using grid power as some sort of failure.
Nick, our great societal failure is to be 40 years late in reacting to last century’s climate predictions. For now, using the grid at noon is great, at night less so, until gridscale batteries proliferate exponentially, as overseas, and kill coal, as was done in Britain.
The domestic battery rebate fills the gridscale deployment gap, at low cost to taxpayers, with efficiency dividends, as energy is not racing up and back on a limited capacity network, but mostly locally consumed.
In time, all energy will be renewable and emissions-free, but we’re not there yet. A BEV, when the ICE becomes unloved, is maybe a juicier target, offering greater emissions savings, and driving pleasure.
Promised emissions reductions head us to +2.7°C. Unfulfilled, our actions are taking us toward +4°C. We are already above +1.5°C, in denial, and hoping the dying oceans off SA will not be everywhere and much worse in a few years. Hundreds of millions of refugees this century are baked in – literally.
Yes, it’s all rather grim. My fears about the renewables transition is that so much of it has been privatised from the get-go. Both at the grid and domestic level. As an engineer I worry about the long-term viability and stability of the grid, using a market-based approach. We certainly know that electricity provision in Australia went into a pricing explosive spiral from the moment it was substantially privatised, and we seem not to have learned that lesson.
I am confident with my 32kWh coming shortly with a 10kW inverter, even though we only have 6.6kW of PV. My DNSP has a 10kW export limit on single phase, so the inverter is basically maxed out for that and more than any combined loads we could turn on inside. The 32kWh is a lot, maybe 8kWh more than ideal, but the extra cost is only about $1500 with the rebate and becomes 24kWh after 25% degradation. It gets me from full through the longest cloudy spell in winter if desired (and therefore off-grid capable) or gets me a good bite at price spikes that have been known to go over two hours.
“a 2 or 3-to-1 ratio for battery and inverter size: so a 5kW inverter being appropriate for a 10kWh or 15kWh battery”
How does this work withenphase micros limited to around 440w per panel – or is it tge battery inverter that counts
Hi David,
Say you have 14 x 475W panels for 6.6kW of solar on the roof.
If you have 14 x 366W micros that’s 5.1kW of potential generation. ie 5100Watts ÷ 230Volts = 22Amps peak output current to the switchboard.
To charge a battery you’ll need to turn those 22Amps of AC current back into DC, in other words your battery inverter also needs to be 5kW when using AC coupled solar.
If you have a DC coupled hybrid, you can put out 5kW or 22Amps to the loads or grid, plus the additional 1.6kW of DC solar could simultaneously charge the battery directly, under perfect coditions, which isn’t lots of hours per year.
Add up all your micro inverters, eg 10 x 440 = 4.4kW so battery size at 3x would be 13.2kWh
For me the only good reason I can see to not oversize your batteries is the fact that battery prices are dropping.
To say that a 5 kw Inverter can never charge a 50 kwh battery pack is silly. That would mean no one is ever going to be able to charge their car at home.
I’m waiting on the arrival of a 16 kwh battery pack (Albeit DC connected Sigenergy) and the only thing stopping me adding more battery is knowing that the BYD car that is also arriving soon will one day be able to be DC connected to the same system and will make my virtual battery pack hit 100 kwh. Sure – with my 5 kw inverter I can’t fully charge or discharge that in a day. But I can get through multiple days of poor weather when my consumption is significantly higher than my sunlight recharge. Plus I will be able to keep the batteries away from over charging/discharging.
Must confess to being one of those people oversizing. Have:
– 6.4kw Solar
– NeoVolt 5kw Inverter + 20kWh Battery
Moving GloBird Zero Hero
Wanted to expand to 40kWh to totally cover my usage + 2nd inverter to bump my charge rates, but with current VoltX deals it was actually roughly the same price ($7k) to get 4 extra batteries rather than 2.
So I’ll end up with 2 * 5kw Inverters and 60 kWh of battery. I feel oddly dirty, almost gluttonous being so ridiculously oversized. But it seems idiotic to miss the deals.
Lindsay,
From here, you greatly resemble an early adopter, at least as far as batteries go. If the price is right, the manufacturer known, and the lifecycle warranty in the vicinity of either 80% SoH after 6,000 cycles, or 70% SoH after 8,000 cycles, then there’s probably CATL, EVE, or equivalent goodies inside. (Local retailers may drop the cycle count a bit for derriere cover – I’m talking cell ratings.)
As prices fall, more is better, for the grid, for the consumer, and for blackouts. Perth’s localised tornado this week presages a storm filled future, increasingly violent. A sea surface over 26°C forms tornadoes, and 90% of global heating goes into the oceans – at an *increasing* rate now.
Two 5kW inverters can be better than one 10 kW – for redundancy – still 5kW when one fails. (In disaster, all are off-grid.) Any spare MPPTs on them? 6 kW PV @ 50% = 20 hrs to charge, with zero for consumption meanwhile.
If you export, then you help the impecunious who must import.
The blackout protect is excellent, have auto switchover installed and its flawless, keeps my computers and internet running. Have had several extended outages, one during an online meeting and I never even noticed.
Just a Fronius Primo unfortunately, so no MPPT’s, but between Solar and 3 hour free periods I can fully charge 30kWh.
When I upgrade to two battery inverters and 60kWh it will take longer, but over a period of a couple of days I should be able to fully charge.
Probably explore VPP options towards the end of the year.
Maybe we can label it ‘grid anxiety’, the fear of ever downloading an electron from the grid. It’s very common 😉
Hi there all,
We decided to go with Enphase, in Brisbane.
25 pv, 57 440 panels and 3 5P batteries – 3 phase
Last 7 days were:
All values in kWh
July 20 – 79.7 Produced – 50.6 Consumed – 48.1 Exported – 21.3 Imported – Bat discharged 9.8 – Bat charged 12.1
July 21 – 69.5 Produced – 41.2 Consumed – 41.5 Exported – 15.6 Imported – Bat discharged 10.3 – Bat charged 12.8
July 22 – 62.1 Produced – 44.5 Consumed – 29.9 Exported – 14.7 Imported – Bat discharged 10.3 – Bat charged 12.7
July 23 – 59.6 Produced – 34.8 Consumed – 38.9 Exported – 16.6 Imported – Bat discharged 10.4 – Bat charged 13.0
July 24 – 104.5 Produced – 52.0 Consumed – 60.9 Exported – 19.2 Imported – Bat discharged 10.3 – Bat charged 15.8
July 25 – 90.9 Produced – 58.2 Consumed – 49.3 Exported – 19.2 Imported – Bat discharged 11.3 – Bat charged 13.9
July 26 – 30.7 Produced – 16.3 Consumed – 12.8 Exported – 6.4 Imported – Bat discharged 3.9 – Bat charged 11.9
Would appreciate some advice.