/ Home & Energy

Home batteries: are they the next big thing?

home battery

They claim to save you hundreds of pounds on your electricity bill, help you towards electricity self-sufficiency, and even let you play a part in the National Grid. Are you tempted by a home battery?

Energy storage systems – also known as batteries – store electricity in your home so you can use it when you need it. Usually this is electricity generated by a renewable system, such as solar PV or a wind turbine, but you can also store electricity from the grid.

And it looks as though batteries are moving into the mainstream.

Eon launched its solar and storage offering last month and it claims that installing a battery can help you use 30% more of the electricity you generate than with solar panels alone. Combined, it says you could make £560 a year in savings and earnings.

This week, Nissan also announced it’ll be selling home batteries – customers can choose a battery previously used in an electric car, or the pricier option of buying brand new.

And Tesla, which is more famous for its cars, sells a home battery it claims can power the average two-bedroom house for a day.

It’s early days yet for home battery storage but, with over 900,000 solar PV installations in the UK, its potential to grow is huge.

Battery storage benefits

If you have solar PV, wind or hydro turbine, it may generate most electricity when you’re not at home to use it. Unused electricity is exported to the grid and you’ll probably import electricity in the evenings.

Batteries store excess renewable electricity so you can use more of what you generate and help cut your electricity bills. They range from around 1kWh to 8kWh, which the Energy Saving Trust says is enough energy to boil your kettle between 10 and 70 times.

There’s also the potential, with time-of-use tariffs, to charge your battery from the grid when electricity is cheaper, and use up your store at times of day when electricity is more expensive.

Consumer concerns

Solar PV has the Feed-in Tariff, and heat pumps, solar thermal and biomass boilers are supported by the Renewable Heat Incentive, but there are currently no government incentives for home batteries.

So how much money you could save depends on the system you have installed and how it’s used. Many technologies are too new for there to be independent data to estimate typical savings yet.

Battery storage isn’t regulated either, although the Renewable Energy Consumer Code (RECC) was recently extended to include battery storage systems. Installers signed up to the code agree to abide by high consumer protection standards. RECC said that it has seen ‘increased interest in these products’, but also ‘a rise in complaints citing mis-selling’.

We’ve heard from Which? members with battery systems who have very different views on them. One told us about reducing their energy bill to less than £20 per month, while others have complained about systems not working as expected and installation problems. Some found the cost off-putting.

So, do you have a home battery installed? How do you use it and what do you think of it? Is there anything you wish you’d known in advance?

Comments
Gordon Monk says:
13 May 2017

I have no doubt that the battery systems currently available are built to very stringent safety standards, but my concern is that once these systems become mainstream and are seen along with double glazing, large flat screen TV etc as an essential item to have in a modern household, that lower quality and ‘fake’ systems will flood the market leading to some very nasty fires. We have all been warned about the ‘fake’ mobile phone and laptop batteries and the damage that these can cause – imagine several thousand of them catching fire at the same time, and you know that it’s going to happen! I would hope therefore that the manufacture and supply of these devices is strictly regulated, but not in such a way that will discourage people from fitting good quality units, just to stop the supply of dangerous ones. Assuming that it’s viably and ecologically cost effective, I’ll probably be an ‘early adopter’ of one of these systems, but I will be making absolutely certain that it’s from a trusted source.

David says:
13 May 2017

I sometimes feel Which reviews the easier items to assess, mobile phone, washing machines etc. I have several times urged them to focus more on items of growing significance to readers, flood protection, flood insurance etc. This is another example where Which are collecting “Brownie Points” by publishing an article on battery storage with absolutely no help for anyone considering such a move. Advice on available systems, calculating benefits etc would have been extremely useful.
Thanks to Patrick Taylor for a very useful link to information on battery storage.

P A Turner says:
13 May 2017

There is another use for batteries; convenience and safety in a power cut. We two 80 y.o.s live in an assisted living flat, which is all electric, I believe so that a stay in place fire alarm policy is practical. Please could Which recommend a package of deep draw batteries, inverter, trickle (?) charger and 15 m extension cable that would power a TV and two LED lights until bedtime. Ideally it would cost less than £250. Normal householders might find it useful to keep their gas central heating going.

You may like to bear in mind the BRE article actually mentions some systems do not work in the event of a power cut. Astonishing but it seems so counter-intuitive we must alert people to this , IMO, major flaw.

P A Turner – Gas central heating systems are wired into the mains, so you cannot just plug them into an inverter. If you use batteries and an inverter there must be a switching system that ensures that the house wiring is connected to the mains or inverter (manually or automatically) but never both.

There is no problem with powering the TV and lights as you suggest.

Patrick – The BRE article makes interesting reading, though some of the information is rather misleading and looks as if it’s been written by someone with better writing skills than technical knowledge.

It is not explained why some systems do not automatically maintain a supply in event of a power cut but there may be some benefits. If you have limited battery capacity then it is vital to switch off non-essential loads as soon as possible to ensure that there is sufficient power available for essential purposes.

In the UK, most people don’t usually make provision for power cuts unless they live in rural areas where they are frequent, or power is needed for essential medical equipment, etc.

You are quite right. I happened to inherit the simplest form of this, a SINGLE wall socket and a three pin plug which fed the old oil boiler. The reputable firm that installed gas boiler continued to use this.
P A Turner

Thanks very much. I had wondered if this is legal, but don’t see a problem since other fixed appliances such as gas hobs and cooker hoods are often plugged into mains sockets. I know that my heating draws about 110W when the gas boiler is fired and the circulating pump is on its lowest speed. I use batteries and an inverter to keep some lights on when there is a power cut.

smug_alec says:
13 May 2017

So what’s new? It’s called a UPS.

Graham Dawson says:
14 May 2017

Have SOLA_X battery system, 2 x 2.4KW hour. Have frequent battery cut-out, fault occurs in evening when use 3 KW kettle, a battery unit is likely to cut out, needs manual reset. Installer went out of business,am now relying on 10 year guarantee insurer who has little experience with battery system. SOLA_X will not act directly. When working very effective.

I just don’t see the business case for a battery storage system.

I have a 3.96 kwh solar PV system that has for the last 3 years delivered an average annual output of 3,915 units.

In the summer half of the year, my meter readings show that my average daily purchase of units from the grid is 5.0 units per day; the comparative figure for the winter half of the year is 9.1 units.

Making these assumptions – as indicated by the above 2016 BRE guide:
– My solar panels would probably not generate any meaningful charge for the batteries in the winter half of the year.
– An ac-coupled lithium system has a 75% depth of discharge.
– A 4.8kwh ac lithium battery storage system would probably suit my usage pattern. http://www.eco-cute.co.uk/battery-storage-new/ gives a website quote of £3,995 for installation of this sized-system with a claimed life expectancy of 15 years.
– Allowing for holidays, such a system would reduce my meter consumption by 3.6 units per day for 170 days during the summer half of the year.
– At an assumed price of 18 pence per unit, that gives an annual cost reduction of £110.

At the price of £3,995, the projected simple break-even period is thus 36 years – well beyond the claimed life expectancy of 15 years, and never mind how long I am likely to be at my current address. Although I am in tune with the concept, viability seems a long way off.

Whilst the Which? headline obviously caught my interest, I echo the other comments that the Which? remarks are disappointingly-shallow.

For interest, my average (over 3 years) annual meter consumption before the solar panels were installed (in 2011) was 3,639 units; over the last 3 years my average annual meter consumption has been 2,404 units – thus solar panels have reduced my meter consumption (with no change in occupancy etc) by 34%. Also, my solar panels generate more units (3,915 per year) than my pre-installation meter consumption (3,639 per year).

Mike Hymas says:
14 May 2017

Home battery storage has the following benefits:more generated power is used rather than exported which is a financial benefit; The demand on the grid is reduced at a peak time; electricity use can be maintained during power cuts (subject to approval). The payback can be long time-up to 10 years but this will be much less if electricity prices increase. There are therefore both benefits to the consumer and societal benefits, particularly by cutting demand at the evening peak when electricity generation is usually at its peak capacity.
Western power have a current trial which amongst other things uses smart meters and electric cars to reduce peak demands. See http://www.electricnation.org.uk/

Nick Hartley says:
14 May 2017

I looked at battery storage to add to my 14 panel 3.6 kW solar PV system which has operated since 2011. The promise of reducing one’s electricity bills by importing less is seductive, but, for me, the figures don’t stack up. We pay around £250 p.a. to Ecotricity for 1300 kWh p.a. The panels generate about 2600 kWh p.a. and bring in FIT payment of approx £1100 p.a. So we are “quids in” though not self-sufficient. The battery system on offer (sorry, I forget the company name) cost £4000 and promised 15 years operation, so that’s £267 p.a. The saving would be 80% of our bill or £200 p.a, hence no saving.

From an overall environmental viewpoint, The Centre for Alternative Technology say it is best to continue exporting your excess PV generation to the grid, where it is used immediately and does not require inefficient battery storage (about 85% overall for Lithium batteries, including the charging and inversion). There is also the extra lifetime environmental cost to consider (mineral extraction, processing, manufacture, distribution, disposal/recycling) .

There will come a time, of course, when too much renewable energy is produced for the grid to handle at times when supply exceeds demand. Then storage will become essential. We are some way off that time still.

“There will come a time, of course, when too much renewable energy is produced for the grid to handle at times when supply exceeds demand. Then storage will become essential. We are some way off that time still.”

I believe we already have had instances where that has happened in Scotland.

There have certainly been several days this Spring when across the UK no coal was burned to produce electricity, the grid relying on nuclear, gas, oil and renewables. With its hydro capacity and extensive wind-power schemes Scotland is well placed to be permanently self-sufficient in electricity generation.

We seem to focus on individual energy generation schemes which are inefficient compared to commercial-size schemes – solar panel farms for example. The same applies to storage – small capacity expensive batteries. Most electricity storage is by pumped water between reservoirs at different heights, releasing it for hydro-generation when demand exceed normal supply. However this cost a lot of money. Maybe those who are investing £000’s on relatively inefficient small home installations could be formed into a cooperative to help fund much more efficient large scale generation and storage.

I think your calculations lead to the right answer, Nick. Investing in batteries and their maintenance at present is not an economical proposition and nor is it environmentally sound. The economics will not improve with lower FIT rates than those available to the early adopters.

With regard to your last paragraph, what you say is quite right but whether dispersed battery storage by householders will become essential is open to question. In the first place, surely, if micro-generation of solar energy and major supplies from other renewable sources can provide adequate supplies, in addition to the nuclear and other base loads, the best thing to do would be to switch out some wind turbines in order to prolong their lives and reduce the maintenance cost of transformers.

Unless electricity is needed to provide heating (including water heating), solar panels and batteries are a perfectly viable source of electricity, at least during the summer months. Electric cars are probably not environmentally sound if you look at the overall environmental viewpoint, as Nick sensibly suggests, with the exception that they do make sense in polluted city centres.

Nick quoted £4,000 for a set of batteries and that seems a lot to me to add to the capital costs of solar panels that might only be able to charge them over a short period each year. He also drew attention to the environmental impact of producing batteries. I agree the concept is appealing but does it really make sense?

Value for money is not the only reason why we buy goods, John. Cars are one of the best examples. I accept that there is an environmental impact of using batteries. Traditional lead-acid batteries have a good record for recycling simply because used ones are valuable scrap. I have not seen information for lithium batteries, solar panels and associated electronics but manufacturing practices in the Far East have received adverse publicity. One of the reasons that we enjoy cheap goods in the UK is because of poor environmental standards and treatment of workers elsewhere.

I expect that home batteries will remain a niche product. My personal experience of being dependent on solar power is limited to summer holidays but they do produce a useful amount of electricity for much of the year.

I think the world might be a better place if value for money and environmental concerns were the principal drivers of spending decisions. Cars and in-home entertainment systems are examples of goods that are acquired by affluent households on the basis of other values. For solar panels and a battery pack I doubt if status symbolism has anything to do with it and in the majority of cases the overriding objective is to save or make money with a bonus of environmental conservation on the side. Actually I am indifferent to whether batteries should be added to a solar panel installation. For some it will be a good idea and for others it won’t. This is largely a lifestyle thing: if a household is out at work all day it could make sense to harness the sun’s energy and use it overnight. For others feeding it into the grid and getting a higher pay-back than the cost of electricity on their chosen tariff might be more important.

As a matter of interest, what would be the weight and volume of a set of batteries to support a twelve-panel solar PV installation? Could the batteries be installed in the roof space? If not, the logical place is a garage or outbuilding if such is available. In many modern houses, like ours, there is no vacant roof space as bedrooms with sloping ceilings have been built on the top floor and there is no usable loft. Not that we have any intention of fitting a solar generation system because the complex gabled roof structure makes it practically impossible with the main aspects either facing in the wrong direction or blanked by the house next door.

To establish likely value for money, consumers will need to know how long their batteries will last, so perhaps it’s better not to be an early adopter. Environmental concerns are notoriously difficult to assess, since the consumer will know little about the impacts of manufacture and subsequent disposal.

Your points about size and weight are well worth considering, John. There is not a fixed size battery bank for a certain number of solar panels. A larger bank costs more but will store more energy. Not all lofts are equal. I used to have a bungalow with masses of usable loft space but the loft of my present house seems to have been designed for contortionists and limbo dancers in mind. I can now understand why some boiler engineers refuse to install or service boilers in lofts. Even if the weight is manageable, I wonder how insurance companies would view installation of batteries in lofts in view of the fire risk.

I’m disappointed that new houses and other buildings are not built with a solar roof or even orientated to take advantage of the sun if solar panels were to be fitted subsequently. With the possibility of feeding electricity into the grid, I don’t see many people opting for batteries so long as the supply companies manage to keep up with demand. However, a repeat of the systematic power cuts of the 70s might make home batteries the next big thing.

A stand-by generator might be the better way of dealing with power cuts. I’d prefer to see the large roofs on commercial and industrial sites used for solar cells where more economic installations and control units could be employed. Saves the eyesore of the nice roofs required by planning being spoiled. You sometimes have to wonder what the function of planning is when it is overridden. Our village has an agreed “plan” which seeks to prevent a number of things such as using, for example, appropriate materials in the restoration or construction of roofs. It did not include solar panels, but so watt…

A proper outdoor standby generator that will start automatically and take over when the power fails is seriously expensive. Portable generators are noisy and have to be stored indoors but used outdoors – which is fun if all the lights have gone off. I’ve been repairing a Honda generator today and I hope the neighbours were at work.

It’s obviously nicer to put solar panels on commercial buildings etc. but I suspect that the owners would prefer to make use of the power for their own purposes.

Using the power for their own purposes is what most solar panels are for, I would think. They relieve the commercial generators.

We rarely have power cuts of any length, but the one thing we miss in the winter is lack of central heating. Arranging the controls and pump to plug into a small generator, with the facility to heat a kettle and plug in a table lamp, would relieve the gloom. A torch will find the generator in the garage or shed and if you think you might annoy the neighbours, make them a hot drink.

I have not had anything other than momentary power cuts despite having moved to an isolated development, but power cuts were quite common where I used to live. I became accustomed to using lighting powered by batteries and an inverter, or a generator for longer cuts. I did invite neighbours in for a coffee, made using a camping stove rather than an electric kettle.

PATurner has explained how to keep the heating running during a power cut.

On the question of energy relating to Nuclear power stations the Gore-Chernomyrdin agreement ends in -2017 between the USA and Russia who has been supplying the US with nuclear fuel to power its power stations . Russian fuel provides for 10 % of electricity generated in the USA , it is taken from old Soviet missiles but the Ukraine relies 100 % on Russian fuel they stopped payment thinking Russia would be stupid enough to continue to supply -they didn’t , and were forced to pay for it again as Westinghouse Nuclear couldn’t supply it (now sold to Sweden and on the verge of bankruptcy) . The missiles are coming to an end and its down to supply the USA or Ukraine if Russia does not supply the US 40 % of the East coast nuke power generation of electricity will stop . Global enriched uranium = 40/50 thousand tons /year for the 400 nuke power stations in the world meaning a deficit of 20/30 thousand tons , who loses out ?

andrew leng says:
16 May 2017

With all these energy storage / heating comments by Which I never see any mention of Night stores heaters. run on reduced night time tariff.
25 years ago we purchased a simple brick built barn conversion with night stores. There did not seem any sense investing in the capital cost retro fitting of another system. In 25 years our maintenance costs are virtually zero we have replaced one or two elements (in the old days this did not need an electrician) and a thermostat. No leaks. We work form home. No annual maintenance charge or boiler replacement.

Good point, Andrew. Lots of householders have no choice other than to use night storage heaters on economy tariffs but I cannot remember ever seeing a Which? report on them.

Hi Andrew, morning @johnward. You can find detail on storage heaters over on the Which? Reviews pages here: http://www.which.co.uk/reviews/home-heating-systems/article/home-heating-systems/storage-heaters But I take your point that we could certainly comment on them more when talking about conserving energy and saving money on utility bills.

Thanks, Dean – but are there no storage radiator product reviews in the pipeline?

Storage heaters running on off-peak electricity can make sense, especially if mains gas is not available and the house is occupied most of the day. Andrew makes a useful point that storage heaters are maintenance free and rarely need repairs. Even if one fails, the rest of the house will be heated whereas when a gas or oil boiler fails you will have no heating or hot water and have to rely on portable heaters and kettles of hot water until repairs are completed.

Having said that, using home batteries to run any form of heating is either impractical or would need a massive battery bank.

andrew leng says:
17 May 2017

Yes we need considering re utility bills. I dont want to find we are the unintended consequence of the proposed cap on electricity bills and hope the off peak tariff is not somehow caught up and raised to match the limit between the discounted rate and the top rate.

I’ve got to put my hands up, I’m a bit of an Elon Musk fanboy. I can’t wait for the day I’m overseeing the installation of solar panels on my roof (https://www.tesla.com/en_GB/blog/solar-roof) and a home battery in the garage next to my, hopefully somewhat more affordable by then, Tesla. Of course I’m a long way off being able to invest in all this energy and planet saving equipment let alone a house. But, the fact that all this technology comes from a positive place of addressing the environmental issues facing our planet means I’m more than happy to wait and dream and buy the odd energy saving light bulb in the meantime.

andrew leng says:
17 May 2017

Yes and if like our friend your radiator goes you have to replace carpets and floors the insurance might pay but you have all the mess and builders to arrange while you are at work and possible ceiling damage too.

Conventional radiator-based heating systems are a bit of a liability and I know many people who have suffered water damage due to their heating systems. I had contractors in recently and managed to bodge removing a radiator. They had covered carpet with sheet taped to the skirting boards but four days later discovered that the carpet was sodden and had been put in my garage. The company has agreed to replace it and it has gone in the skip. Electric heating certainly has its advantages.

Your radiator can be removed without mess if you take care. Turn off both valves and drain it. I put in my own wet radiator system 35 years ago and had no problem removing radiators when redecorating. If your valves have failed your plumber can freeze the pipes locally to allow the rad to be removed and the valves replaced.

Electric heating is around 2 times the cost of gas to run and installing decent storage radiators with their wiring will not be cheap. remember on off-peak tariffs your on-peak units cost significantly more than a normal tariff.

I always remove radiators for decorating and never had a problem. I presume that the contractor had forgotten to turn off one of the valves but I was not there at the time. I generally drain the system which empties radiators and makes it easy to collect the water containing corrosion inhibitor. I’m referring to an old system with a header tank rather than a pressurised system.

Robert says:
17 May 2017

I’ve been interested in these since I first came across the idea, but not for cost purposes. We live in an area which is prone to brown-outs, and the occasional complete outage (4-5 in the last three years). Would a system like this act like a computer UPS and see us through problems, or reduce the risk of damage due to a power surge?

Gerry Mewton says:
22 May 2017

I am frequently called by a company that is trying to persude me to have a battery to increase saving from my solar panels. I had a visit but the costings were rubbish. My electricity costs for the last 12 months were about £305. I estimate that I use about 35% of the 3000 kwh produced by the panels, say 1000kwh at 10p, £100. A battery would increase that saving but not by more than about 20%, in other words an additional £20 pa unless it had a really high capacity so it is just not worthwhile as an investment. They quoted me £4,500 all together!

John de Rivaz says:
25 May 2017

I have a Sofar ME3000SP. This has the advantage that it doesn’t require a lot of DC re-wiring, and can even be run on a 13A plug and a couple of current transformers, one one the load and the other on your PV inverters. However if you plug it in rather than wire it in, then you need to shut it down every so often and remove and re-insert the plug. These plugs were not designed for continuous 3kW usage, and can form corroded hot spots if you don’t do this. There is a disadvantage in that the wi-fi reporting doesn’t seem to work, but this is very much a “frill” – it has its own screen where you can check it is working and report per day, week, month or year.

Adam Hill says:
3 May 2018

This thread is a year old now, but I’ve recently had an email conversation with one of these battery suppliers and, frankly, their figures just don’t add up. I think it’s clear that these systems are not ( yet ) cost effective even now, but from a “Which” point of view consumers should at least know what they’re getting into.

Examples of the issues:
– I was told that this 3kWh battery system would save an average of 800kWh a year with a typical 4kWp PV system, “being conservative.” That battery has an 80% depth of discharge, so really 2.4kWh ( on day one at least. ) If it cycled every single day that’s 876kWh, so at first glance 800 looks reasonable. I then looked at our generation figures ( we have a 6kWp PV system ) and IF we didn’t use ANY energy at all, and IF the transfer to/from the battery was 100% efficient, and IF there was no degradation over the year, we’d have saved 826kWh. Suddenly, 800 on a 4kWp system looks like an outrageous claim.
– Even if you assume 800kWh on day one, then 70% of that after 10 years, the saving is 6.8MWh over 10 years. Assuming 25p per unit average cost over that time ( I currently pay less than 14p ) the saving is £1700 for 10 years. The battery costs £3500 ( plus of course the value of the £1700 “return” is itself eroded by inflation. )
– They play the “green” card. There is nothing green about this – the energy is still produced whether you use it or someone else does… having a load of lithium batteries around doesn’t help the environment.

Other adverts I’ve seen from other battery manufacturers quote savings combined with those of the PV itself – you really can’t look at it that way since the investment would be a much better bet without the battery.

This all smacks of mis-selling and is something I think Which should look into in more depth!

I think you are right, Adam. Having a home battery would be a sensible investment for anyone dependent on electrically-powered medical equipment or on computer equipment continuing to operate, for example to power a server.

Adam Hill says:
3 May 2018

I think in those circumstances you’d probably use a UPS, which doesn’t feed power back to the mains and so doesn’t need special approval/additional kit to work when you have a power cut. I already have a couple of UPSs… but they weren’t sold to me on the basis I’d save money or be greener 😀

Fair enough. I had forgotten that home batteries provided the option to feed surplus energy into the grid. As you say a UPS would do the job of maintaining a supply for essential equipment.

I know a fair number of people with solar PV but not one has a home battery. They may have done the same calculations as you have done. It’s a year since this Convo was published and time that Which? revisited it.

Nick says:
25 May 2018

There was an article in new scientist sometime ago about an exciting development in aluminium batteries, I’m waiting for those.

Steve says:
24 July 2018

Had solar panels and a Tesla Powerwall II installed in April 2018. As of today 24 July it has generated 2.77 Mw of electricity. Admittedly we have benefited during the peak time of the year so far, but nevertheless I expect that it will beat the forecast generation of 4.497 Mw for the entire year. The Tesla Powerwall allows you to monitor the power you are using, generating, exporting to the grid and recovering from the Powerwall II. Also run two plug-in cars, which in summer take up much of the surplus generation which we can’t store when Powerwall is full. During the last 3 months our electricity bill is down by 95%, not enough to be off-grid, but impressive. Of course this level can’t be sustained in winter, but the Powerwall will allow us to charge up on a Economy 7 type plan, both Powerwall and cars. I reckon the Powerwall will cover more than 90% of the household needs during the winter without drawing from the grid during the day. Overall, our electrical power needs and dependence on fossil fuel is mightily reduced and there are cost savings not only for the household needs but also for motoring. Even paying around 15p/ kW is about 20% of the cost of petrol/diesel – and being able to self generate and store power, amplifies the return. However, the main reason for making the switch is not so much financial as to reduce pollution from fossil fuel. Electric cars are more fun to drive and offer much lower cost of maintenance too – so those factors need to be considered. Since the Which article was written there have been numerous developments in this field which mean the economics are improving all the time. There have to be smarter ways than burning fossil fuels. There are now even Vehicle to Grid systems which allow people to use their cars as mobile battery storage which can be smartly linked to the grid to purchase fuel at the most advantageous times. This offers tremendous scope for cost savings and for balancing the needs of the National Grid. Exciting times. Maybe time for Which to revisit this subject.

I agree it’s an interesting subject, Steve, but when batteries have to be replaced the much lower cost of maintenance might not be a valid argument.

Alan Chapman says:
8 August 2018

Steve, like you I have been an early adopter of battery storrage & like you this summer run for over 90 days without exhausting my batteries.
Operating over 116 days on average consuming 0.67kw per day from the grid.
My system is 7.2 kw & can charge & discharge at 3kw I also heat a thermal store where I can dump a further 5-9kw subject to our hot water ussage.
But this is summer, I ran through last winter & was able to use 98% of the electricity I generated.
But this was only able to meet 40-48% of my winter needs.
You would need a solar array that is about 15kw to even get to 88 ish % to run on solar pv during the shorter light levels in the winter.
My last bill for gas & electricity was £7.48 no gas at all & £6.99 was my standing charge so I paid just 49p for July electricity.
Most people are unable to understand that there are big benifits during the day where batteries work along side solar in supporting users demands that would normally be made up from the grid.
So if you are generating 2kw & switch on a 4kw oven 2kw can come from your batteries.
They can then if sized correctly get you through the night until the pv system can support the houshold needs & start to charge again.
If the battery size is to great not only is it a lot more expensive but if it’s a usable 9kw & you only normally use 6-7kw from it then that is the only space you have to use & fill the next day.
Yes at the begining & end of the winter you may benifit from the extra couple of kw capacity but it’s the bit that stops the costs from stacking up for users.
I estimate that the 6000 cycles that my batteries are warranted for will take me to 16 years & at that they will still be working.
There are already companies starting to rebuild & recycle lithium iron batteries & the mining is not all done by children but by machines & dissolving it into solution.
This year I estimate that with my Fit payments & savings in gas & electricity purchase I will be effectively bill free for the next 17 years when my FIT payments run out.