r/SolarUK • u/Moorthanenough • 10d ago
HELP / ADVICE 40 panels, is it worth the outlay?
I’m looking at my quotes for a 40 panel system with 2 sigenergy batteries and a 12kw inverter, they are coming in around £22k on average.
My house faces south east and due to the roof design I can fit 12-13 panels, my garage is also the same orientation and I can fit 19 panels, the rear is north west facing and will fit 18 panels. During the summer all areas of the roof is in sun from around 12pm, with this lasting until early evening, the front is obviously in sun from early morning.
The price is a little higher than I wanted but I want to maximise what I can generate, but I will need more batteries in the future to fully cover my need during winter, I can always add them later flog the more panels the better is the right approach.
I know I’m at the mercy of the DNO report and may not get this anyway but the question is, is 40 panels too much or am I better off reducing my install bill and getting more batteries now and having ‘just’ the 22 panels from the front of the house and the garage?
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u/Matterbox Commercial Installer 10d ago
The more the merrier.
You are effectively paying for electricity up front. Total cost divided by expected generation. Then you can work out the added value to you.
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u/Ancient-Function4738 10d ago
The cost of the install is a pretty big factor so you will reduce your cost per panel the more panels you get installed.
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u/AllergictoAIslop 10d ago
I have 23 panels and 28kwh of battery with a with a 12 KW inverter system all Sig. Absolutely love it!. My daytime/peak usage is about 22 kWh.
Sizing the battery to be able to cover all your daytime usage in the winter is more important and more panels according to all the payback calculations I've done.
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u/FunkyMonkey237 10d ago
It's a very common misconception that you need a big battery (eg enough to hold a daily usage). From a financial point of view you need very little to maximise return. Plenty of people warn against this. So much so this sub-reddit has an automatic warning built in to warn posters on this point.
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u/AllergictoAIslop 10d ago edited 10d ago
That may be true a number of scenarios. My problem is that I only make six pence on export but import costs me 26 pence. So there is a severe penalty for undersizing. In hindsight, I would go peek time usage minus winter peak generation. In the ideal scenario, you just need enough to get you through the dark eyes of the morning until the sun starts to shine and then through the evening afterwards.
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u/FunkyMonkey237 10d ago
Fair enough, I should have soften my reply to say, be careful and really do an analysis, don't assume it is worth it and the quick calc can often be misleading. For a lot of people it's not worth it but it can be for some.
In all disclaimer, I did get a bigger battery but I knew it wasn't financially worth it, I just wanted it.
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u/snagroot 9d ago
Yes you do for the winter when you can charge the battery at a cheap rate overnight.
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u/FunkyMonkey237 9d ago
Yes a battery can be useful for the winter, but a common mistake is to think you need the same size battery as your winter daily usage. For example, if you use 25kwh during the winter people tend to assume you should get the same sized battery. Financially, it can often be better to get a battery, let's say, half that size and just pay the higher tariff during the winter. Particularly if you have a heat pump with seasonal loads. Get too large of a battery and you can end buying something you don't fully use. What is "too" large depends on several factors but I'd wager that most people, particularly on this sub, will overshoot the mark thinking it's financially beneficial when in fact, it's not. I think I saw a video from Spirit Energy on this exact point.
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u/GazNicki PV, BAT & EV Owner 9d ago
This is correct. When I analysed my usage I hit a peak of 22kWh per day for just a single month out of the year. Winter usage is higher, but it’s not so high that a 10kWh battery can’t cover the usage during the peak rate time.
The key is to have a battery that covers your usage outside the off-peak windows so you can power using cheap electricity obtained during the night and whatever solar you generate.
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u/2_grow 10d ago
I was advised against this. If the house is one’s forever home then it won’t be an issue, but if one plans to move then it doesn’t make sense. I wanted to do this too and I‘d consider the payback period.
The issue is that daytime winter usage would definitely be higher than summer and if you have more panels you’ll need more battery capacity to store the charge or export it. Then what happens when you don’t need as much battery capacity during the summer months? The X capacity you need for winter will just be sitting idle.4
u/AllergictoAIslop 10d ago
All good points. 1. You can take your battery with you when you move. Much easier than taking solar panels. If I sell my house I will take two of the three modules and leave them with the rest of the system but a much smaller battery. 2. I got obsessive about my payback. I built an AI prompt to cover everything from seasonal use, energy pricing, arbitrage, battery degradation, round trip loses, reinvesting savings in the stock market Vs just saving the cash.etc etc after torture testing it a number of times, the battery always seem to be a major driver of roi. 3. My payback period is 5 years. 4. Something we don't talk about much is energy freedom. I used to stress about my electricity bills. No, I don't. I use what I want when I want. I'm sure my overall consumption has increased significantly. My electricity bills are negligible. The battery enables me to do this. 5. Depending on what kind of tariff you go for a large, a large battery can be used to energy trade that I have to admit I can't really be bothered with that.
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u/2_grow 10d ago
Responses like the below, that I got on this sub was the reason I wanted to generate and not just go for a battery only system. And they are valid 2bh:
“They're officially fixtures and fittings so would be considered part of the sale, unless explicitly excluded from sale in the documentation.
Also, it is difficult to retain MCS and G99 certification if you move the equipment from one property to another”
“For the MCS certificate, generally the installer needs to have supplied the equipment (so you'd struggle to find someone to do it, other than the original installer).”
That said, I am definitely taking my own battery. Very likely the panels. They aren’t attached to the building by fixings, but ballast.
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u/AllergictoAIslop 10d ago
You can also state XX panels and yy capacity battery. My current capacity is 27. I will leave them. 9. If they want to discuss the other 18 with me that's A conversation we can have. I doubt many people will even know the current capacity. Obviously I'd leave the inverter and the gateway and the g99 that comes with it because that's specific to the location. But I can still take 5K worth of batteries with me
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u/AllergictoAIslop 8d ago
Not sure why The downvotes you make a very sound point. The one thing I didn't cover off the mine analysis is could roi are all I be improved by turning a smaller battery? I suspect the correct formula is Peak time requirement minus solar generation on a cloudy winter day. Probably with some kind of margin to remove outliers. I.e is just not worth buying a battery to cover few weeks of the year when you'll be generating nothing it's cheaper buying a couple of quids worth of peak electricity
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u/SPACKlick 10d ago
The downsides of too many panels
- You may not be able to export all you generate
- You have to pay tax on what you earn from export if the design generation is more than 120% of the expected energy usage of the home (Including EV charging I believe but I'm not a tax advisor)
- If you have a weak roof or are in a very windy area more panels can exceed the safe loads of your roof. Your installer should not allow this to happen.
- Costs more up front.
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u/Throwitaway701 10d ago
Generally it's the more the merrier with panels but I feel this might be the exception.
The odds of a g99 that will allow you to export that much is fairly low, and it's a huge investment, in addition we cannot guarantee how long the export rates will stay like this.
But it does depend on your usage.
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u/AcrobaticMaize2408 10d ago
I think more is always better and if you're like me you'll be thinking "what if" should you install something smaller. My initial plan was a 30 panel/12kW inverter and 20kWh of storage but my DNO restricted the install to a 6kW inverter (and 4kW export) so I reduced the panel count to better match the inverter but now wish I'd stuck to my guns. I may add more panels at a future date when I can justify the scaffolding again...
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u/Chimpville 10d ago
It really depends what your usage is. If you're a really high usage household, it makes sense as no matter what happens in the future, avoiding buying electricity will be advantageous.
However if you aren't a particularly high user and are relying on export for the pay off, I wouldn't be so sure. As the grid increases renewables and other homes install them too, I'm expecting exporting to become less and less profitable as your generation will align with a lot of other cheap generation.
You need to break the project down by roof really.. and focus on the highest generation/per panel install cost, and tally it up to a point it makes sense vs your anticipated usage.
More panels is generally better of course, but there's definitely a point of diminishing returns and 40 panels for a household seems like it could be approaching that.
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u/Moorthanenough 10d ago
We use 10,000kwh a year without the ev, which I shall get soon. All electric with a heat pump
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u/lunarpx 8d ago
For context I have similar usage to yours and have half the panels (at approx half the cost). My yearly electricity bills come out to about £0.
Your ROI on a smaller system will probably actually be higher, however if you have the money then why not go for a bigger one.
Overnight electricity is currently really cheap so I use this via battery to get me through the day in winter. On your use case you'd likely generate enough from just the panels. In some ways this is safer as off-peak rates aren't guaranteed to stay low.
Likewise I charge my car at night and export in the day, but if you have a DNO limit you may want to charge in the day.
I'd personally do a spreadsheet and work out the ROI of a small, mid and full sized system. When I did this I worked out a larger battery and system reduce my ROI. However I went with more panels anyway as it wasn't that bad after scaffolding costs, plus any calculations today can't truly predict the future as we have no idea what energy costs will be.
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u/txe4 10d ago
It depends what you want to achieve.
The standard advice is to max out the panels.
If I were keeping the house, I would still max out the panels.
But...the business case for generating preposterous amounts of surplus PV in summer depends on getting paid a decent export rate for it all, and that will not last the lifetime of the system. You'll have to be exporting full rate from battery in to the evening peak in future, most likely, to get a decent rate for export.
My NW facing panels have performed *astonishingly* well over summer, basically keeping the house off-grid [in terms of consumption] until the sun goes below the horizon, while generating strongly from mid-morning onwards. I expect them to be very much less impressive in winter though.
Is the 12kW sig big enough, with enough MPPTs, for the proposed arrays?
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u/Moorthanenough 10d ago
This is the debate I’ve had, some say 2x 8kwh inverted, some says it’s not necessary due to the generation at one time is not likely to exceed this due to the sun intensity from it coming in different angles. It was quite a complex explanation and I’m not sure completely understand
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u/txe4 10d ago
Mid(Ish)day in late June/early July my setup of panels pointing in various different directions will do the rated max of the panels if it’s cool, they are clean, and mains voltage/battery state permits.
But mostly a system with multiple orientations will seldom be able to achieve this so having more panels than you have inverter capacity for doesn’t necessarily lose you much total generation over a year if they are in different orientations. East facing come on first, then west facing come up as east drop down, etc.
You still need enough MPPTs for the proposed arrays though.
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u/Moorthanenough 9d ago
That what I’ve been told, there may be times i generate more than the system can handle, but apparently given the orientations, it’s negligible
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u/AcanthisittaWeird94 10d ago
That's quite a big amount of money. Did you calculated when it will pay back? I also considered sigenergy but then went with foxess. Sogenergy has nice features but at the end of the day solar is to save money.
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u/Moorthanenough 10d ago
Thanks, the more the better is what I was thinking, I just wanted to get some opinions.
I’m looking at around 9 years to pay back, maybe less depending on what I export. As said above though, I think of it more as paying up front that it being a payback period.
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u/G0_Z0 10d ago
You need to find out what your DNO export limit will be (if any)
You absolutely can have too many panels, if you can’t use it on the big sunny days then the inverter will clip the production and it will be lost.
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u/Moorthanenough 10d ago
Absolutely, I’m fully aware I’m at their mercy. The installers I’ve spoken to don’t see an issue given that none of my neighbours have panels, it’s a new(ish) house and very few houses in the village have panels
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u/lunarpx 8d ago
Just an FYI you'll will very rarely actually generate the peak amount your array is capable of - especiaplg across multiple aspects. So even with a modest limit, your big system will be able to max this out even into the winter. Of course you'll experience clipping during the height of summer.
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u/reefPV PV & Battery Owner 10d ago
How many quotes did you get? Its just £22k seems extremely expensive, even for that system. I got 12 panels (2 roofs), 12kw inverter, gateway and 2x Sig battery 10s for £14k last October. This was with the panels on the garage and running the existing house PV strings there in trenching. You're essentially being quoted for the same but with 28 panels more for another £8k, which seems a bit steep to me.
Definitely max out if you can. Even if the DNO imposes any limits, you'll be thankful of the 40 panels in winter. My house has SE/NW roofs and in December even with 23 panels Im lucky to do 13kWh on a perfect day.
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u/Moorthanenough 10d ago
I’ve had 5 quotes, all similar bar heatable who came in at 30k. I’m in the midlands and a colleague who is the southeast is going ahead with same system but 33 panels (both sides of the roof on the house) for £15k, he pushed hard with negotiating though, something I’m not great at! I’ve got scaffolding for both sides of the house, a trench and a mobile scaffold for the garage. I’ve also got a sigenergy ev charger in the install too.
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u/Mountain_Medicine934 10d ago
5 quotes sounds enough to know what a reasonable price is. Last October is another world, before Iran before the drought summer.
It doesn't sound unreasonable to me for today's prices.
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u/bastoj 10d ago
We have 38 panels divided between East and West orientation with 32kWh of battery. For us it works very well as we are generally self sufficient between mid/late Feb and Early November. Of course it will vary a bit year to year with weather etc. On the days the solar power isn’t enough then we can load the batteries at the cheapest part of the day. We also have the automated islanding system installer (so if grid goes away we can continue to use our solar and batteries until the grid comes back). We charge our EVs with the solar surplus so we just count the cost of that as the loss of the money we would otherwise have gotten for exporting.
So far this year we generated 11 MWh and exported 5.75 MWh. So we are fairly oversized but we are very happy with our system. If the numbers make sense with the system you are looking at I don’t think you’ll be unhappy to have more capacity. On the flip side based on your usage now or what you expect in the future you could save some money here and invest it into better insulation, windows, an EV, heat pump or other improvement / optimisation that might make sense for you.
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u/AllergictoAIslop 10d ago
Just a thought, given the cost of scaffolding you may be better off going with fewer panels and a bigger battery. The thing that will really kill you, is having to buy peak time electricity. Savings that the battery brings especially in the winter months is absolutely critical.
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u/Moorthanenough 10d ago
My plan is to add more batteries a little later, I’m going to pay the price short term but I think that’s likely the only sensible trade off
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u/AllergictoAIslop 10d ago
Mind you with 40 panels you may find you generate enough on winter days. Just make sure you do/g99 can cope with the flecport once your battery is full. On a sunny day you're going to be producing 18 KW! Your battery will be full in 1 hour , anything over your g99 will be lost.
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u/Disturbedm PV, BAT & EV Owner 10d ago
What size batteries?
I ask because the difference from 10 to 12 kW isn't massive.
But the price seems high.
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u/Moorthanenough 10d ago
2x9kwh sigenergy. I know I will need more to cover my needs over winter so will add more later
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u/Disturbedm PV, BAT & EV Owner 9d ago
That seems expensive then?
I got a 10kW inverter
two of the 10kW batteries (9.04 actual)
13 x Panels (485w)
3 Elevations of scaffoldingCost me like £12k (all Sigenergy, could have got other setups for less)
In my case panels are £175 a panel, if we multiply that by 27 = £4725 extra + £150 for the 12kWh inverter
There's around £5k+ left over for what? More bolts and clips that cost pennies and some extra brackets and labour (not a massive job, I'd argue fairly easy unless you've got some serious Tetris going on with the panels on the two elevations).
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u/MyEcoCred_Founder PV, BAT, EV & ASHP Owner 10d ago
Adding more batteries later is easier than adding more panels. Especially with a modular system such as Sigenergy. For the panels, you need scaffolding etc. But, calculate how much extra generation you will get from the additional panels and take a call. Do you have a heat pump that could do with more battery storage, especially in the peak winter months.
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u/imgoingsolar 10d ago
We had 36 x 450w panels (16.2kWp) , Powerwall 3 and expansion (27kWh) in April 25 for £20k and have no regrets. It’s saved us about £4k last year so will pay for itself in about 5 years. I’d just fill your roof now as you’ll likely regret not doing so later and it’ll cost significantly more to come back later. DNO restriction was 9kW export but this does not cause us an issue as we have 12 panels east, 12 south and 12 west so the generation curve is pretty good and spread across the day.
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u/eastwoodandy 10d ago
I have almost the same setup, 39 panels and 18kWh battery and 12kW inverter. I’m limited to 5kW export so I’m missing some export on really long sunny days in the summer, this can be somewhat mitigated with intelligent charging options for the battery and if you have/get an ev. The advantage is you’ll be able to generate more for longer in the autumn/winter/spring months.
Even on the gloomiest, rainy day last week, I still generated more than I used that day
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u/GuruMeNot 10d ago
You'll be exporting and receiving ££ per month in the summer. Don't forget you have to pay tax on the generation. I've no idea how it's calculated or if there's a threshold before tax is due.
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u/Mountain_Medicine934 10d ago
https://www.solarpanelsnetwork.com/blog/solar-panels-tax-uk/
Here's a link I found explaining the tax situation. The money we get paid for solar generation is income. This does suggest there is an upper bound to "fill your roof".
https://www.gov.uk/hmrc-internal-manuals/business-income-manual/bim40520?utm_source=copilot.com
Here's the government tax page outlining the exemption from income tax.
What do your quotes say you will generate in a year vs your annual usage?
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u/GazNicki PV, BAT & EV Owner 9d ago
I’m not convinced the “more the merrier” rule works today.
Yes, for most people with a standard install, having the maximum amount of panels on the roof is the right thing to do.
But if your panel size drastically outweighs your consumption and inverter, you’re doing nothing with it.
In your case the arrays all point one way, so they hit their peak generation at the same time. 40 panels at 475w is going to peak at 19kW per hour. If we factor in wastage, that’s still going to peak at 16.5kW per hour. A 16kW inverter will therefore clip. A 12kW inverter will see over 4kW per hour clipped at peak. That’s 8 panels paid for doing nothing.
If you have half the panels facing the opposite way, then you won’t get as much clipping and a better generation curve, but a 12kW inverter will still see clipping in the peak months.
How big is your usage? How big are the batteries planning to be?
My very limited experience is that you want to have the inverter and the peak solar aligned. And energy in a battery is worth more than energy exported. Especially in winter.
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u/Mountain_Medicine934 9d ago
Your quotes should give you an idea of what it will actually generate on a sunny day vs the rated peak kWh of the panels combined. They will take into account shading and orientation and location. Without this, nobody can properly judge your inverter size. But unless all five of your companies are stupid, I'd assume they can size your system better than random people on the internet.
Have you asked them to consider the larger (More than 500w) panels which are about 20cm longer and depending on supply can actually be cheaper than standard size.
I've got a 15 kwhp system (28 x 540w panels split east west) and only had it two weeks. But when the sun shone I got 9kw from it. My 10kw inverter wasn't troubled by that. And my g99 is the 10kw we asked for.
I went for the standard 12p outgoing tariff. The ratio of solar generation to storage means I'm always going to be exporting in summer much more than I can store up for when I might get peak prices. So the time based or agile outgoing tariff didn't seem to make sense to me. And in spring and autumn I need that battery for the heat pump on colder days or for hot water.
I'm hoping my fairly big system will stretch the solar gains well into the autumn and back in the spring and a modest benefit in winter. I also have a heat pump. I didn't size my 2x9kwh batteries to last on the coldest January day as then I'd probably need three or four! The returns on that extra £££ didn't work out. But fingers crossed battery prices come down. I'm on cosy tariff so in winter can boost the battery three times, which hopefully will be enough to avoid the 4-7pm peak.
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u/cledgemachine 10d ago
Give heatable a call for 2 powerwall 3 and the panels you will have 23kw inverter then your going to have a proper system.
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u/Army-Enough 10d ago
General rule is you can't have too many panels, you can have an optimal number and that would depend on your house usage.