This morning I woke up, checked the horse was still alive, checked the children were still alive,1 and then checked my email. To my surprise there was one from Finn telling me the price of the Tesla Powerwall 2 had dropped.
I skipped calling the ex-wife to check if she was still alive and immediately went to Tesla’s Australian website to investigate. I found the price of Powerwall had dropped by $650 from the $12,350 it had been:
The drop is almost equal to one-quarter the price increase Tesla gave it in October, just before South Australia’s battery subsidy kicked in.
October’s Price Increase
In October 2018 Tesla increased the price of the Powerwall 2 by $2,750. Because I’m a terribly suspicious person, I think this may have had something to do with the $6,000 subsidy it was set to receive in South Australia, which is Tesla’s number one market for Powerwalls. But I could be wrong. Maybe Tesla just needed the money and the price increase had nothing to do with the subsidy.
But putting the price up last year seemed odd to me, considering Elon Musk — the CEO of Tesla — had boasted they would get the cost of their battery cells down to $143 per kilowatt-hour by the end of last year. While it seems they only managed to get them down to around $159 that’s still a hell of a lot less than what they used to be:
This means with a total battery capacity of 14 kilowatt-hours, there’s around $2,200 worth of battery cells in a Powerwall 2.2 The rest of the cost comes from putting the cells into packs, electronics, a cooling system, the plastic shell, development, marketing, transport, and so on. That stuff’s not cheap. But if you believed Elon’s announcements you’d think it would be a lot cheaper than it turned out to be.
This Price Cut Is 23.6% Of The Last Price Increase
As this latest price decrease is only 23.6% of of the last price increase, it will take three more $650 cuts to get the price to almost as low as it was at the start of October last year. Fingers crossed battery aficionados won’t have to wait 10 months for the next price change. And let’s really hope the next one is also downwards.
Powerwall 2 Still Won’t Pay For Itself
Unfortunately, even with the latest price cut, the Powerwall 2 is still a long way from paying for itself for any family with remotely normal electricity consumption. This is especially true outside of South Australia where it won’t get a $6,000 subsidy.
My boss, Finn, has one and it saves him less than $1 a day. Even if I use optimistic assumptions it’s impossible for the Powerwall 2 to pay itself off while still in warranty. If I make the following assumptions:
- It’s installed in South Australia for the optimistically low price of $8,640.3
- You use a current retail plan from Origin Energy with a solar feed-in tariff of 18 cents and a per kilowatt-hour charge of around 37 cents.
- The Powerwall 2 is only charged from rooftop solar, giving it a 10 year warranty.
- The average round trip efficiency is 85%.4 This requires 1.2 kilowatt-hours of solar energy for each kilowatt-hour of stored energy provided, which otherwise could have received 21.6 cents worth of feed-in tariff.
- Due to battery degradation I’ll assume the average usable capacity over the warranty period will be 90% of its 13.5 kilowatt-hour usable capacity when new. (Its warranty promises a minimum of 70% of original capacity after 10 years.)
- Because of variation in both electricity consumption and solar energy generation normal households can’t use 100% of a Powerwall 2’s usable storage capacity each day, so I will assume the average will be 80%. This is optimistic for a large battery and requires both high household electricity consumption and a large solar power system.
With these assumptions the average amount of stored energy used per day will be 9.72 kilowatt-hours. Over 10 years it will total 35,500 kilowatt-hours.
Using one kilowatt-hour of stored energy will save the family paying for 37 cents worth of grid electricity, but they will forego the feed-in tariff they would have received for sending 1.2 kilowatt-hours of solar electricity into the grid. This makes the savings 37 cents minus 21.6 cents, which comes to 15.4 cents. Multiplying 15.4 cents by 35,500 kilowatt-hours of stored energy use over 10 years gives $5,467. This is more than $3,000 less than my optimistic estimate for its installation price, so it cannot pay for itself within its warranty period.
If the assumptions above are kept the same, including for battery degradation, then the Tesla Powerwall 2 would have to operate for almost 16 years before the savings on electricity bills exceed its installation price. That’s nearly 6 years beyond its warranty. I haven’t bothered to account for capital costs, but if I had the situation would be even worse.
Things Will Change
In my example above I’ve assumed things will stay the same for the life of the Powerwall 2 battery. But this won’t happen because…
- Feed-in tariffs and electricity rates will change.
- New types of electricity plans will appear.
- Virtual Power Plants may make batteries profitable.
- Powerwalls could dramatically fall in price.
If any of these changes cause home batteries to pay for themselves — and your goal is to save money — then the time to get one would be when they start to pay for themselves, not before.
If you’re not concerned whether a home battery will provide a positive return, or you are in South Australia and don’t want to risk missing out on the large subsidy, then please go ahead and get a battery. It’s only if you are hoping to save money by installing one that I recommend holding off.
SA Energy Minister May Have Known About The Price Cut
Last week I spoke with the South Australian Energy Minister, Dan van Holst Pellekaan, who told me $9,300 was “very expensive” for an installed Powerwall 2. Now the price has been cut, $9,300 is around what I’d realistically expect you’d have to pay to get one installed, so I wouldn’t call that price very expensive. But it is possible the Minister said it was because he knew the price cut was coming. Or maybe he just didn’t have a clue about what it really costs to have a Tesla Powerwall 2 installed. I could go either way on this.
What If I Ordered Powerwall 2 At The Old Price?
If you have ordered a Tesla Powerwall 2 at the old price you can ask for the price cut to be passed onto you. I don’t know if you’ll be successful, but it doesn’t hurt to ask.
Well, it doesn’t hurt you. But if you’re running a businesses, I can imagine having people ring up and ask you to lower the price on a product you have in stock and paid the old price for probably hurts a lot.
I would say that if you are getting a Powerwall 2 through a company that isn’t Tesla, don’t get your hopes up about having the price reduced. They’ve probably already paid Tesla for it. If you are thinking of cancelling and then reordering, I’ll point out if you’ve put down a 10% deposit, that will be more than the $650 price decrease.
But if you are getting one through Tesla, I’d say definitely ask if you can have the price reduced by $650. After all, there will have been no real difference between what it cost them to make a Powerwall 2 last week and what it cost to make one this week, so it’s not unreasonable to ask them to give you a break.
A Good Start
I don’t know why Tesla decided to cut the price of the Powerwall 2. But if I was to take a wild stab in the dark — as opposed to the precise and controlled ones I normally take — I would say it’s because Tesla think everyone who wanted to snap up a Powerwall 2 because of the introduction of South Australia’s battery subsidy has now got one and it’s time to start competing on price again before they lose too much market share to other solar battery manufacturers. But that’s just something I came up with while waiting for my cat to move so I can report to the children it’s still alive. It may have no semblance to reality at all.
Okay, the cat just bit me, so I’ll assume it’s alive. But since it’s name is Schrodinger I have to consider it may be a zombie cat that is both alive and dead at the same time.
Footnotes
- I have to do it in this order because if the horse isn’t alive I’ll be all “meh” but if the children aren’t alive I won’t enjoy checking on the horse at all. ↩
- Battery cells used for Powerwalls aren’t the same chemistry as ones used for vehicles, but their cost should be comparable. ↩
- You are only likely to be able to pay this price if your home is already ideally suited for the Powerwall 2. There are usually extra costs, so you can generally expect to pay at least $700 more. ↩
- This figure is an estimate based on Finn’s Powerwall 2. ↩
Thanks Ronald. Great writing, informative and entertaining.
Do you happen to have a spreadsheet with all the calculations that you can share? I want to put in my own numbers, it would be very kind of you if you could save me the trouble of repeating your work!
I had to wait to reply until an appropriate XKCD comic was published:
https://xkcd.com/2180/
Lol. Doesn’t have to be a spreadsheet; happy to get code in any language with variables 😀
Thank you guys, you provide a ray of sunshine as I plough through my email load each day. I mostly crack a smile with each post, sometimes even more than one on a really extended post.
I took your advice when purchasing a Rooftop PV Solar System as opposed to a “Solar System” which probably wouldn’t have fitted on my rooftop anyway.
Another purchase I made was a heat pump hot water system, which has also been one of my wiser and more rewarding decisions in my ongoing fight against “my poverty”.
Gracias
Hi Gordon,
I’ve tried heat pumps myself, but haven’t been too impressed due to the fact that the two brands I tried all karked it within a couple of years, (usually just a few months after the warranty ended), and they are not cheap.
Interested to know how you go. The alternative of evacuated tubes is way too expensive as well.
In Denmark (the country, not the town in W.A.), the small town of Sig on the west cost of Jutland uses a bit over a million dollars worth of PV-powered heat pumps to heat a large insulated tank of water for 63% of the town’s heating. Solar thermal provides another 22% (*1). Quite a few Danish towns have fjernvarme (remote heating) companies which distribute heating to the town’s homes via underground insulated pipes.
The really nifty thing with this setup is that a whopping great insulated tank then substitutes for batteries – and water is a lot cheaper than lithium and cobalt. If 250 L of water heated 34.4°C = 10 kWh, then 250 tonnes = 10 MWh. (I don’t know how big theirs is.) Some people individually do the same here, using heat pumps for slab heating.
Denmark is hell bent on reducing carbon emissions by 70% by 2030, and this technique can win them 5 to 10% points.
With the Alaskan city of Anchorage topping 32C in the last few weeks, and French cities topping 41C, the slow learners are now shifting from denial to panic, and there are thinktank proposals to use up to 300,000 airfreighter flights per year to put one Pinotubo of sulphate aerosols 20 km up in the stratosphere each year. Since we are currently heading for 3C warming, and may struggle to pull that back to 2C (double the mayhem we have now), the extra 0.5C drop by shading may be a game changer – if they use biofuel. 😉
I did worry that the scheme might harm PV production, but I read that one Pinotubo of aerosols amounts to only a 1% insolation reduction. Phew!
(How much do you wanna bet that the yanks don’t have a go at it once they finally, belatedly, wake up?)
(*1) https://www.dr.dk/nyheder/penge/groen-stroem-gaar-til-spilde-men-i-landsbyen-sig-laver-de-den-om-til-varme
Hi Erik,
Would you happen to be the Erik Christiansen ex-Butson St., Hilton WA?
BusBrad
Noooo, I haven;t been to W.A. since our ship called in at Fremantle on the way from Europe to Melbourne in 1958. (If there’s one over there too, that explains why Australian society is so well balanced, I guess.)
I’m getting closer to putting solar on the roof of the off-grid owner-build. Who knew there’d be a million screws in a kit kitchen?
P.S. If you have a little Honda generator that’s no longer new, it’s worth checking the output voltage. My second one was also down below 200 Vac, which is _not_ good for induction motors (e.g. fridge / washing machine / pump)
There’s no regulator electronics in these simple ferroresonant alternators, but replacing the capacitor inside the end cover with one of the same voltage and capacitance values brings the voltage back like a bought one. A quick and effective $10 refurbishment.
Great article. Excell sheet as I live in the Territory 25.5 feed in. Get a lot of outages. Very good Rticle. Hope the horse is OK tomorrow and tomorrow and tomorrow. Thanks. Matt R
Great article. Totally agree with the cost of any of these battery storage products. Take the .money you would have spent on any other of these battery storage solutions and pay it off your .mortgage if you have one or put it into a term deposit account and you would save more 🙂
As Ronald recommended in a earlier blog article, probably best to wait at least 5 years until the supply side of things has settled down a bit, any ‘bugs’ in the manufacturing are fully sorted out, and sufficient Australian installers are trained and brought up to speed.
Great article.. i to would like the spread sheet, as our feed in is only 11 cents, so would vastly effect the final numbers
I don’t actually have a spread sheet, but I believe we will get a battery calculator on the site in the future. Unfortunately, I don’t know when.
So, how does the price of the imaginary Tesla Powerwall 2 compare with the LG equivalent capacity one; installed price?
And, if the cat is named Schrodinger, can it explain the wave equation, which involves second partial derivatives of a function that has no meaniung unless it is squared??
Thev option of owning an electric car should be included in the calculation even if just a small one like a second hand Leaf. Replacing your fuel bills and using nearly all of the battery capacity every day should improve the economics.
I recently wrote about how charging an electric car from a battery doesn’t usually make sense at the moment. But, if you already have a battery it will depend on electricity prices, how much use degrades it, and what you think its replacement price will be:
https://www.solarquotes.com.au/blog/charging-ev-battery-grid/
So, if the installed cost is $11,700 as you say then with the SA $6,000 subsidy the net cost is $5,700 for SA residents. Was the minister correct?
$11.7k is just the cost of the battery. Which is not much more than an oversized paperweight until it is installed. Installation is not free. It’s actually pretty costly (several $thousands) to correctly install a battery.
$11,700 divided by 14 kw is $836 per kwh. I’d call this the ‘pre-installation cost’. The Bloomberg chart seems to be from another planet. Am I missing something?
The Bloomberg chart just shows the cost of battery cells and also what those battery cells cost when connected together in a pack. Nothing else that is needed to make either a home battery storage system or an electric car is included.
We bought the powerwall system in May. We live in an inland town on Eyre Peninsula. We paid about 9000 dollars fully installed after the rebate. This included a couple of days tweaking and improving wi fi connections.
You might be right about costs although we only get a 6 cent solar rebate and our electricity is 45 cents /kwh but we do get a 25% reduction for paying on time. Our electricity costs are high. Over 1000 dollars a quarter in winter and 300 in summer.
But we now have guarantveed power supply. This has been very important in protecting us from many minor outages and up to 6 hours while the mains supply was off
Hi Paul
It sounds like you would benefit from a change in your electricity retail plan. There are a number of websites that will let you compare electricity plans, but here’s our own:
https://www.solarquotes.com.au/energy/
I get at least one phone call every week from companies urging me to change providers. Ive changed 3 times this year. ATM I am waiting to see what happens in spring summer but overall given usage patterns, no one has been able to provide a better plan. I can get cheaper power but at a much lower, or non existent, pay on time bonus, so that if I pay on time i have the best deal possible.
So far I am providing no power to the grid,, so that rebate is irrelevant. I am getting about 6 to 8 hours a day free electricity, depending on cloud cover, and this is increasing as the days get longer. The highest expense is night time usage running a heater and reverse cycle. If I have a woodfire going, daily consumption from the grid can be less than 20 kwh, otherwise it can be twice that.
If you are not permitted to export solar electricity than that dramatically improves the return from installing a battery. With the SA battery subsidy you could install a decent sized one for perhaps $10,000 and it could pay itself off within 10 years while also providing backup — although that backup won’t be as reliable as a generator.
PS: Sounds like you may need to go on the Do Not Call list.
Out of curiosity, I read somewhere that a Powerwall has greater than nominal capacity in it. For instance, a Powerwall with a nominal capacity of 13.5-kWh has more than this name plate capacity in the box.
Any truth to this?
The Powerwall 2 has 14 kilowatt-hours total battery cell capacity (maybe give or take a little) and 13.5 kilowatt-hours of usable capacity when new. This means it has a 96% depth of discharge, which is quite low.
I would like to know what company sells kWh at 37cents and buy excess solar at18cents per kWh .i am getting 10 cents per kWh and being charged 55cents per kWh .i am in NSW
That is Origin but in Sydney. Looking up electricity plans for my sister who lives next to the middle of nowhere in NSW I see…
https://fronius.solarconfigurator.de/solar.configurator/quick
It’s even better. She can get a 21 cent solar feed-in tariff while paying 31 cents for grid electricity. However, the daily supply tariff is high, so it may not be suitable for a home with low consumption.
I’m in Brisbane. PowerShop gives me ~22c/kWh effective rate, and it’s all offset by renewable energy production. Feed-in tariff is 9c/kWh. The daily supply charge is 95c/kWh.
Interestingly I received the followint email from Suntrix Solar on the 8th August “Tesla has slashed the price of their Powerwall 2 by $500 – and Suntrix is offering an additional discount for the first 20 customers that sign up for the battery before the end of August.
We’ll take $100 off if you already have solar; and $200 off if you buy a solar system along with your new battery.”
Sounds to me like either Suntrix didnt get the full discount from Tesla passed onto them or that they are using some slick marketing to try not to pass all of the discount onto new customers. I emailed them and asked to explain but I am yet to receive a response
Hi Ronald
Apparently another drop in price for the powerwall.
Can you guys confirm this?
https://www.adelaidenow.com.au/news/south-australia/tesla-cuts-home-battery-price-in-sa-by-more-than-2000/news-story/2dbf9b920b67f18e12d3ffa202c71b37
Thanks for the heads up. We will definitely be investigating this.
Update: Finn has already been on the radio about this.
I also read this in the Adelaide Advertiser today. Says Tesla has cut the price by $2000, and that the powerwall can now be purchased for $3500 plus installation, taking into account a $6000 subsidy. The article claimed the deal was available via retailers including Origin and AGL. Sounded a little too good to be true, so I rang AGL, my supplier. After speaking with the call centre (who asked me what a tesla powerwall was) I was put through to the ‘resolutions centre’. They hung up on me. I rang back, and was hung up on again. The article certainly got my attention, but hard to find actual info on this.
I only have a small solar system, but I also only use between 2-5kWh per day including aircond. I live by myself, and only pay power bills in the winter months, I get around 52c FIT, but based on the discounted price, I’m thinking I may be further ahead in electricity savings if I have one of these installed. I figure I can always increase my panel capacity later, when I’ve had the opportunity to calculate the actual shortfalls in my current panels.
I’m not sure who is the best to speak to about this new deal. the big retailers, or the small solar shops. It’s nice to see the prices going down though 🙂
Well….on second thoughts, maybe not. The $3500+ installation and conditions, VPP etc. make it a tad less attractive an offer than I initially thought. Why advertise $3500 when the actual cost is more like $7100? Surely install costs could be kept a little lower. Now I’ll wait and see what develops in the market.
What station was it on?
I called up the guys (Kozco) who installed my second solar system, and they hadn’t heard of it yet but was going to check. If it is true, then getting a powerwall might be effective for me.
Over winter we need to import about 8kw a day and have an average export of 10kw.
If the powerwall will cost ~$8,000 to install (minus the SA Gov $6,000 rebate), and you can sign up to the simply energy VPP and get another $5,000 back, then it will cost $3,000, which will save ~$500 a year, paying itself off in 6 years.
These are rough figures but it seems like we are getting close to batteries paying themselves off.
Ron… With the lack of information on costing and using the $11,700 Tesla price from the Internet and with some research it would appear to have a Powerwall 2 installed to an existing system is about $16,000 with full “off the grid” performance.
This would enable us to go off the grid with the solar still charging the battery with throttle back if overcharged.
I’m still waiting for my itemized quotation from one of your top 10 installers who installed my 10.6kWh Enphase LG 345w panels. On good days we are exporting 55kWh and the average this month is 23kWh/day even with the smoke haze.. Our night usage is 12kWh.. Fit 12c and Import at new rates is 21c with discounts.
We definitely need the fallback in an outage situation and need the electric cooking because my wife is sensitive to takeaway precooked food and needs to cook here own. She is reticent to use a camp stove.. Our only gas is the water.
We are already experiencing over-voltage on 1/3 of the panels and the Envoy. Our profile has been changed to top out at 258 V.
In Victoria, United Energy is our provider and AGL my retailer and our postcode doesn’t come up in the Vic Gov rebates yet.
In summary … Cost and if SA are taking all of the Powerwalls what is delivery like in other states.
https://www.domain.com.au/news/the-first-person-in-the-world-to-have-a-tesla-powerwall-battery-924164/?utm_campaign=strap-masthead&utm_source=the-age&utm_medium=link&utm_content=pos5&ref=pos1
A good example of why people need to crunch the numbers to work out how the economic return from a battery system compares to say, a term deposit.
Ron.. In our case the return on a Powerwall 2 is 6.3% after taking a Term Deposit into account and with the loss of the miniscule bank interest, and the gain in our couples part Aged Pension. Great being able to spend some capital and make a gain, plus the unknown electricity gain..
Probably hoping for enough Feedin tariff to cover the service charge and get down to Neil’s 46c/day.
One potato….Two potato…Three potatoes…more!
How silly would you feel if you’d just spent umpteen thousand dollars on a gee-whiz power-wall battery if you could get a similar result from a bag of spuds….. which you could eat afterwards?! –> https://www.google.com/search?q=potato+battery+experiment&oq=potato+battery&aqs=chrome.3.69i57j0l6j69i60.15681j0j7&sourceid=chrome&ie=UTF-8
Is there a Government Solar Battery Sub in W.A.?
There’s no subsidy for home batteries in WA. Not unless there’s a brand new one I don’t know about.
John – depending on where you live, find whether you have a WA Greens party upper house member (MLC), and, if you do have one, send the person an email message, asking what the person is doing about getting financial assistance for householders to get storage batteries connected to rooftop solar systems, to match what other states are doing about it.
And, send an email message to your lower house member (MLA), asking the same question.
Remember; WA has a state election due in March 2021, and, from what has been reported, the outcome is uncertain.
And, in contacting members of both houses of the state parliament, you could draw their attention to the following, including the news report at
https://www.abc.net.au/news/2020-02-20/law-reform-for-micro-grids-could-revolutionise-electricity-bills/11985388
which includes
”
For years now, politicians on all sides have known the tariff structure which underpins much of the electricity market is fundamentally broken and must be fixed if the right investments are to be made and the system is to be secured.
The reason for this is largely to do with the rampant popularity of rooftop solar, which accounts for more than 1200MW of capacity and is easily the biggest single source of generation in the system.
Solar is now such a large part of the energy mix in WA that it is causing problems only a few people envisaged a decade ago.
Solar upsets the grid’s stability
At the heart of the challenge is the way in which solar output swells in an uncontrolled way during the middle of the day, often displacing other generators such as gas- and coal-fired power plants.
On mild days when solar efficiency is particularly high and demand might be low, solar power can force a significant share of the power generation offline.
That might sound good, and in so many ways it is.
But where the situation becomes problematic is when there is a sharp change in generation, like when clouds blot out a mass of solar panels in Perth at once, or demand changes rapidly — an industrial customer going offline suddenly, for example.
In these circumstances, the so-called firming services provided by conventional power plants, and which keep the system on an even keel, can be stretched thin.
That’s when the Australian Energy Market Operator (AEMO), which runs the wholesale market in WA and is responsible for keeping the lights on, begins to worry.
”
So, it is perceived that the increasing uptake of domestic rooftop photovoltaic systems, poses an increasing threat to the stability of the SWIS grid in WA.
However, also referring to
https://www.sciencedirect.com/science/article/pii/S0306261919302478 ;
”
Abstract
The power system requires an additional amount of flexibility to process the large-scale integration of renewable energy sources. Community Energy Storage (CES) is one of the solutions to offer flexibility. In this paper two scenarios of CES ownership are proposed. Firstly, an Energy Arbitrage (EA) scenario is studied where an aggregator aims to minimize costs and
CO
2
-emissions of an energy portfolio. Secondly, an Energy Arbitrage – Peak Shaving (EA-PS) scenario is assessed, which is based on a shared ownership between a Distribution System Operator (DSO) and an aggregator. A multi-objective Mixed Integer Linear Programming (MILP) optimization model is developed to minimize the operation costs and
CO
2
-emissions of a community situated in Cernier (Switzerland), using different battery technologies in the CES system. The results demonstrate a profitable system design for all Lithium-ion-Batteries (LiBs) and the Vanadium Redox Flow Battery (VRFB), for both the EA and EA-PS scenarios. The economic and environmental performance of the EA-PS scenario is slightly worse compared to the EA scenario, due to power boundaries on grid absorption and injection to achieve peak shaving. Overall, the differences between the EA and EA-PS scenarios, in economic and environmental performance, are small. Therefore, the EA-PS is recommended to prevent problematic loads on the distribution transformer. In addition, the Pareto frontiers demonstrate that LiBs perform best on both economic and environmental performance, with the best economic and environmental performance for the Lithium-Nickel-Manganese-Cobalt (NMC-C) battery.
”
and
https://www.researchgate.net/publication/271462541_Feasibility_of_residential_battery_storage_for_energy_arbitrage ;
”
Abstract
This paper presents the methodology, results and analysis of the feasibility of residential battery storage for energy arbitrage in the context of the Australian retail electricity market. The economic feasibility of a residential battery storage system was determined by its ability to achieve residential cost savings from undertaking energy arbitrage, which is: the implementation of a battery system to buy, store and discharge electrical energy to take advantage of fluctuating electricity prices. Integral to this simulation was the incorporation of the stochasticity of a household’s hourly electricity demand, which is largely determined by consumer behaviour. A Monte Carlo method was used whereby this random household behaviour was simulated with sets of probabilistic household demand. This then allowed accurate and precise statistical inference of the feasibility of various battery storage system configurations. Overall, many of the storage system configurations examined showed high probabilities of being economically feasible within current economic and technical contexts.
”
along with other research, shows that domestic rooftop photovoltaic systems connected to behind the meter battery storage systems, can, with the batteries set to absorb excess electricity generated by the photovoltaic systems, thence to discharge steadily over the period that the photovoltaic systems are not generating, can ameliorate demand and supply peaks, and, can, overall, stabilise the electricity supply grid.