• This topic has 42 replies, 24 voices, and was last updated 1 week ago by mulacs.
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  • Is it worth installing a solar battery ?
  • DrJ
    Full Member

    Just had a guy round doing the annual maintenance check on our solar panels. He was strongly pushing the idea of getting a battery so save our excess electrons, but I’m wondering what the right questions to ask are. Right off the bat, the battery he was advocating has a 3.2kWh capacity which seems more or less nothing, considering the power used by our ASHP. At peak rate it’s only about a quid’s worth, so spending 4 grand on a battery seems like a bad idea. So what am I missing? What naive assumptions do I need to rethink?

    alan1977
    Free Member

    you can charge at super low tariffs, and also hold charge to export at super high tariff times

    although I’m not sure about 3.2.. I’ve got 10.4. .which is roughly my daily consumption, so i charge at 16p overnight to whatever amount i need depending on solar, work through until peak export time, and export whatever i don’t need to see me to the evening

    My actual energy cost through January was negative with minimal solar

    bruneep
    Full Member

    what did the annual maintenance consist of?   Failing to see what needs maintained.

    Are you on an export tariff for the excess unused? A battery will allow you to import when price is cheaper at night or to load shift.

    I have 2 x 5 kw of batteries I still pondering adding another one seeing as prices have dropped since I got mine. Batteries fully charged today from sun and exported the excess at .15p a unit

    spyke85
    Free Member

    Also interested in the maintenance check – we have solar panels on a new build (well 7 years old) and they have never been checked for anything.

    Onzadog
    Free Member

    The concept is sound. The capacity and the numbers are very personal. Given the current situation, if you can get in the right tariff, I’m tempted to think that battery only could offer better payback than solar only.

    With EVs, the headline number is range, which relates to battery capacity but little thought is given the charging speeds and curves.

    Similarly, you might like the idea of the 3.2kWh battery, or you might think 10.4kWh is more appropriate. However, don’t forget to look into how quickly you can store or use that energy.

    For example, if your tariff gives you 4 hours really cheap but your battery charges so slowly that you only get half a charge in that time, it has quite an impact on the numbers.

    Similarly, if you want to use your battery as a back up during a power cut, will it allow you to draw the 3kW you need to heat the oven?

    IHN
    Full Member

    Also interested in the maintenance check

    Yup, me three

    footflaps
    Full Member

    Just had a guy round doing the annual maintenance check on our solar panels.

    Had no idea there was such a thing! Sounds like money for old rope….

    He was strongly pushing the idea of getting a battery so save our excess electrons

    Get his commission I think is closer to the truth.

    NB We have a 10KW battery, which cost £5k. I’m not sure it was a particularly shrewd investment, we run off cheap rate leccy in winter, saving £200 a year maybe. And we get to use a bit more of our solar in summer, saving the same again. Pretty long payback…

    We mainly installed it for environmental reasons, although the CO2 cost of the system will take a long time to pay back…

    For example, if your tariff gives you 4 hours really cheap but your battery charges so slowly that you only get half a charge in that time, it has quite an impact on the numbers.

    Yep, our system can nominally charge at 3kWh, so if we have a 3 hour window, that’s 9 kWh. However, it ramps up the charge over about 30 mins when the battery is flat, so you only really get 2.5 hours at 3 kWh. Normally need 4 hours min to fully charge it.

    sharkbait
    Free Member

    Just had a guy round doing the annual maintenance check on our solar panels.

    Hahaha…. funny! 🤣

    Oh wait – you’re being serious! 😬
    Please tell me what that involves (and I haven’t been doing for the last 14 years).

    mattyfez
    Full Member

    Presumably its just to make sure the panels are clean, and the fixtures are sound & not causing any undue stress on the roof…I cant really see what else there is to check, maybe testing the pannels somehow to make sure they are still efficient…but I think newer ones go for about 25-30 years before they start degrading or whatever?

    Maybe is a bit like a boiler service, £150 quid for half an hours work.

    trail_rat
    Free Member

    Assuming you don’t work from home then the battery makes sense for that most part out with the spreadsheet

    sharkbait
    Free Member

    Presumably its just to make sure the panels are clean, and the fixtures are sound & not causing any undue stress on the roof

    The former is dealt with by the water that regularly falls from the sky – I’m struggling to see how the latter can be tested or checked without scaffold.

    Save your money DrJ.

    (I should add that I have all my generation data uploaded to pvoutput.com and I can see if there’s a dropoff and I get alerted if generation stops for too long.)

    DrJ
    Full Member

    Just had a guy round doing the annual maintenance check on our solar panels.

    Had no idea there was such a thing! Sounds like money for old rope….

    Well me neither but we pay a sort of annual insurance and this was part of that. It’s not actually “annual” – I mis-spoke – this is the first time he’s been. We have an old FIT tariff which is ridiculously lucrative so some insurance makes sense. He didn’t do much except climb into the loft and say “yup, it’s all working”.

    sharkbait
    Free Member

    We have an old FIT tariff which is ridiculously lucrative so some insurance makes sense.

    Does it? What will it do if something goes wrong?

    I’m also on the very old/lucrative FIT scheme but I know that you’re basically not allowed to make any changes to the hardware without potentially losing your FIT payments.

    Sounds like I’m very much in the wrong business if it involves no more than climbing into a roofspace and looking for a green light on the inverter!

    DrJ
    Full Member

    Does it? What will it do if something goes wrong?

    Fix the problem and compensate for lost generation.

    But that was not my question.

    Daffy
    Full Member

    Yes a battery can make sense.  We generated around 6000kWh and used around 5600kWh.  Of that we exported around 1600kWh and Imported the rest.  Without the battery, we’d have likely imported around 3500kWh instead of 1200kWh and would’ve done so during the peak periods.  We might just be around cost neutral for the year give or take £100.

    BUT, on something like a Flux tariff (which didn’t exist when I bought mine) the delta between having a battery and just exporting is now around £500-£600 a year.  So our batteries will take 8-10y to breakeven and that’s assuming 30p/kWh which also doesn’t seem likely to continue.

    other than for off grid, backup power and environmental reasons, I’m not sure I’d do the same again,

    wzzzz
    Free Member

    Check out the octopus agile thread.

    You can charge overnight at low low prices and discharge or export in the early evening when prices are high. Top up from your panels.

    There have been times overnight in the last month where energy price was negative, so they were paying you to charge the battery.

    Easier to juggle if you have a battery inverter that integrates with the octopus API. You’ll need to buy another inverter to wire in parallel anyway as you can’t touch the FiT setup.

    5lab
    Full Member

    If you have a very generous fit, then a battery may not make sense. It’s only economically viable due to the discrepancy between buying and selling electricity, if the gap is smaller for you it may not work out

    sharkbait
    Free Member

    Do you need a different inverter if you have a battery?

    If so, changing your inverter may well jeopardise your FIT payments and I’m fairly sure you don’t want that.

    (Especially seeing as you “sign” to say that nothing has changed each time you give a generation reading)!

    Edit: only just seen the posts above about the inverter and jeopardy.

    trail_rat
    Free Member

    Most of the generous fits are on assumed export so the more you use you can double dip.

    You would need an ac coupled system though.

    minus
    Free Member

    I don’t get the environmental argument; it’s not like any solar you export just disappears, it displaces other generation. Most likely gas, which is most likely what you would be consuming in the evening if you didn’t have a battery.

    Sandwich
    Full Member

    Maybe is a bit like a boiler service, £150 quid for half an hours work.

    At a tangent but someone is pulling your trousers down. Worcester certified chanp does mine for under £100. I think it’s all he does too as he wasn’t interested in a large plubing job involving moving radiators and the boiler/hot water cylinder.

    DrJ
    Full Member

    Yes a battery can make sense.  We generated around 6000kWh and used around 5600kWh.

    May I ask what size battery you have? What I can’t quite figure out is how it can make sense to pay £4K for a 3 kWh battery.  In a simple situation, you charge your battery during the day and discharge it in the evening. One battery holds about £1 worth of electricity, so you save a quid a day. Am I missing something?

    ossify
    Full Member

    How long do these batteries last? Someone up there said 8-10 years payback… do they really last that long at a constant charge/discharge every single day?

    surfer
    Free Member

    I have solar and a home battery. Analysing costs is tricky particularly if like me you change your tariffs at least twice a year and make use of the feed-in tariffs. I did quite a detailed spreadsheet model last year on the 12 month anniversary of installation (I use Home assistant so have access to very detailed data) and, extrapolating, I estimated that total installation (PV and battery) would be paid for in just over 6 years. I am very pleased we did it as finance was only part of the motivation and on good days we are generating up to 4 times our average usage. We are also fortunate that our roof seems perfectly aligned.

    surfer
    Free Member

    One battery holds about £1 worth of electricity, so you save a quid a day. Am I missing something?

    I have an 8.7kW battery and I think it cost about £5.5k. Currently I charge at around 7p per kW overnight so on eaven a cloudy day I can add a small number of kW from the PV meaning I dont buy any from the grid at the higher price. I can count on both hands the days when we have had less than say 3kW per day over the last year and a bit (almost 2 winters) and on most days enough to get through the full day. From spring onwards its pretty amazing and we dont even need to charge the battery overnight and by mid morning it can be full and we are exporting to the grid.

    Its not a simple calculation however its more of a hobby…..

    ossify
    Full Member

    Would like to ask again that those giving income and payback figures/times say roughly where in the country they are… here’s me in soggy Manchester wanting solar but I’m going to be very disappointed if I’m basing expectations on figures from the south of France or something 😆

    surfer
    Free Member

    @ossify I live on the Wirral so not too far from you.

    Use this to estimate your PV

    https://re.jrc.ec.europa.eu/pvg_tools/en/

    This is my estimate and I have found it very accurate:

    .

    alan1977
    Free Member

    ok at its most basic

    if i were paying flate rate electric at 27p a unit, my 10.4 kw saves me approx £1 a day if i were just to charge at my off peak 3 hour window at 16p a unit

    however, that’s not what happens, i charge at 16p and discharge some at 27p depending on what’s in the battery etc, so my daily saving is more like £1.20 simplified.

    Now, add in some saving sessions of which there have been 8 or 9 since november, that’s added around £150 credit

    I haven’t factored in any solar, or more complex tariffs

    on an average day my automation will elect to charge at 16p for the minimum i need based on solar estimates for the day, idea being i want to be fully charged by 4pm peak export. So for example yesterday i think about 2.5 units went in, then a decent 15kwh of solar throughout the day, causing solar export around lunchtime, and then in peak export window some more was dumped out making a thoroughly negative cost day. Myself and my lad are at work/school during the day so battery is a necessity imho as solar generation is more valuable for in home use than it it to export and then import

    I’m not even on agile tariff where i could be charging at 1/3rd the cost, and with more potential charge windows throughout the day.

    I took a big ole loan for my solar plus storage, over 6 years, i reckon it’ll be payed off by the saving/income, leaving 4 years warranty on the battery after that, only installed august so i haven’t got a full year yet to post some complete figures

    flicker
    Free Member

    May I ask what size battery you have? What I can’t quite figure out is how it can make sense to pay £4K for a 3 kWh battery. In a simple situation, you charge your battery during the day and discharge it in the evening. One battery holds about £1 worth of electricity, so you save a quid a day. Am I missing something?

    No, you’re not missing anything. I’d like a battery (4kWh solar installed in 2018) but for our usage the numbers don’t add up.

    We generate 4000 kWh per year and we consume 3900kWh per year. Of that 3900 kWh, 1700 kWh comes from our own generation, meaning we pay Octopus for 2200 kWh.

    If we were able to use a battery to offset that remaining 2200 kWh then @30ppkWh that would save us £660 per year or £6600 over 10 (the warranty period of the battery) that wouldn’t cover the cost of a 10kWh battery, inverter and install costs. It would also be impossible to offset the full 2200kWh especially through winter, which reduces the return even further.

    Sadly the numbers don’t work and it’d be far better off dumping the money I would have spent in an ISA for 10 years ☹️

    didnthurt
    Full Member

    In-laws have just installed one, I don’t think it’ll make them any profit but their thinking is it will add value to the house and make it more desirable when they come to sell it.

    I’ve asked for the numbers on it but they’re reluctant to do this. I was more intrigued on whether it’d be worth us getting one.

    The last time I did a solar panel calculation on our house, it wasn’t worth the investment. This was a couple of years ago so might be a better investment now as energy prices have increased. It doesn’t help living on the north side of a hill in Scotland.

    I think if you had a spare bit of land with easy access to a power supply then solar would be a great investment. I see a few about especially around holiday lets, where I’m guessing they’re part of the business instead of a private install.

    prettygreenparrot
    Full Member

    Battery? Sure. Though not so sure about a 3kW one. Like you say @DrJ it’s not that much electricity.

    Is VAT charged differently on batteries that are not also part of a contemporaneous solar installation?


    @ossify
    solar in manchester – despite common experience of low grey skies and endless rain, there’s enough sunshine to support solar panels. Our installation started producing late February 2023

    Screenshot 2024-02-13 at 11.12.32

    surfer
    Free Member

    There are a few other things to consider. How much you can shift to overnight usage which makes the lower cost tariffs better value. I dont have an EV yet however being retired means that when we do we have one, for many months of the year we will charge that from excess solar, as we do with our hot water (although opportunity cost of not selling back to the grid of course)

    Each home/family is different and depends on how much you can be bothered making changes (shifting usage etc) but dont discount the fact that your are helping the environment (obvs costs involved with PV/battery production and so on)

    IHN
    Full Member

    Would like to ask again that those giving income and payback figures/times say roughly where in the country they are… here’s me in soggy Manchester wanting solar but I’m going to be very disappointed if I’m basing expectations on figures from the south of France or something

    I’m in Disley with a south facing 4kw array, and we get about 3500 kwh from it and an income of about £5-600 a year.

    DrJ
    Full Member

    I’m in Northumberland, also south facing,  and I generate about 2500 kWh a year, and get about £1500 for it.

    maloney19710776
    Free Member

    I live in the Black Country and yet despite the grim exterior my e/w 3.6kw set up coupled to an 8.2kw (8.5k installed) battery produces:

    2189kWh/annum from solar, sold at 15p=£328.35

    2993 kWh/annum to fill battery every night which lasts the remainder of the day, bought at 7.5p =£224.48

    438 kWh/annum into house direct each night for six hours while battery is charging at 7.5p=£32.85

    730 kWh/annum average per day exported from the battery at 15p=£109.50

    Prior to install the usage was 2700kwh/annum at 30p =£810

    Current set up costs -£180.52

    Neither of these figures included the standing charge.

    aphex_2k
    Free Member

    What are you guys pulling in daily in terms of kWh?

    flicker
    Free Member

    What are you guys pulling in daily in terms of kWh?

    From a 4kW south facing array in Cheshire, anywhere between nothing and 30kWh per day. December/January are the worst months, lowest being 53kWh and highest around 100kWh. May is usually the strongest month, between 550 and 650kWh.

    alan1977
    Free Member

    3.9 kw system, south facing, near portsmouth

    installed mid aug 23, approx month totals

    Aug ~230kwh

    Sep ~400kwh

    Oct ~230KWH

    Nov ~120KWH

    Dec ~50KWH

    Jan ~145KWH

    kcal
    Full Member

    0% VAT on battery systems now as well I think.  That may influence decision.

    Our reasons for thinking battery are multiple; in no real order:

    resilience (power outages)

    seems like right thing to do to utilise roof area

    charge it up off peak (and store solar PV during days) then release at on peak times

    – should be cost negative (although still take a while to pay back)

    flicker
    Free Member

    @kcal

    Not sure if you’re aware but the system will need to be ‘islanded’ otherwise it’ll shut down when there’s a power cut. Extra cost basically.

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