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Best advice to people thinking of installing a solar array
Best advice to people thinking of installing a solar array
TL;DR My best advice to people thinking of installing a solar array is be cautious as falling export values really impact savings. If you do go ahead see what panels do for you for a full year and then consider your case for a battery.
I’ve had solar panels for three years and thought I’d share some data
My system comprises of 16 panels split 50:50 south and east giving 6kW peak. I am at home during the day and have all the usual appliances
My total electricity use is 5.5 MWh annually and I’m on Octopus intelligent go tariff
Panels supply 1.4 MWh of this so my grid use has fallen to 4.1 MWh
Of this 4.1MWh, 2.75 MWh is used overnight, mainly in the car leaving a total for daytime grid use of 1.47 MWh so panels have cut my daytime usage in half.
My panels also export 5 MWh annually
Overall I save around 1400 * 28p £390 on usage and 5000 * 15p £750 on export a total of £1100 or thereabouts.
Here are some thoughts
1) my usage seems to be tiny compared to some figures I’ve seen on here. I don’t understand why, I don’t scrimp on appliances use nor load shift over night (perhaps I should)
2) my export payments will fall to £600 now that exports are 12p
3) my daytime 1.47 MWh cost £400 so a battery, used perfectly, could save £300 as it would cost £100 to charge on the night rate. But inefficiencies of charging reduce that to £270 or thereabouts.
Would I do the same if I was starting now? Short answer is yes because it is a good thing environmentally imho. If I were doing it to make money, probably not as the export value is highly likely to fall further and this is, for me, the most lucrative aspect. I’ve been fortunate to gain >£1100 for three years but it could fall dramatically if export tariffs fall further. At least panels have a very long lifespan
Should I buy a battery? Well, no based on these figures and the falling export value halving any export income. I’d look at this again if energy prices increase significantly (40p per kWh?) which seems doubtful.
I hope this is useful for anyone about to embark on a solar journey. My best advice is to see what panels do for you for a full year and then consider your case for a battery
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19 Replies
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Tariffs change constantly, 3 years ago you got 4p export! Plan the system for you and treat export as a bonus, my aim was to reduce grid buying so I can’t be affected as much by any future price rises. I was obsessed with ROI when I first started til I realised it can’t be predicted with any accuracy.
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I remember 4p. I never expected the system to pay back like it has. Something new buyers need to be aware of.
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It’s always interesting to hear differing views.
We had solar installed 5 years ago, could only fit 9 panels, south facing so not a massive array.
To be honest we haven’t looked at ROI as our reasoning was really environmental (and I couldn’t be bothered!), we didn’t get a battery as we couldn’t afford it at the time. We have an electric car and charge it via zappi when we have excess solar and top it up overnight on cheap rates when needed.
I know this isn’t the best for ROI but we treat export as a bonus and love that we can get a full charge using our own solar.
We have also applied now for a Libbi battery and the same principle will stand, first off to harvest our own energy.
It’s too hard to predict future tariffs.
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As you have an EV I don’t understand why you didn’t get batteries so that you can run on 7p electricity in Winter & Free in Summer?
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As crazy as it seems people in some countries get charged extra exporting at certain times.
For me my monthly energy charge was nearly £400 and is now £120. My system cost just shy of 11k.
We are a more heavy user ( no heat pump, so this includes gas).
Probably with a drop in export this might go up slightly but this has fluctuated so much ( last year was good, previous year much lower ).
I think the biggest thing for us was when we got access to the cheap rate at night with the car charger. The batteries get charged every night and meet a large part of the usage in winter and until now meant the export was higher in Summer as we didn’t need the solar to fill the batteries.
I actually have a few friends who have no solar and only batteries and up till now have been pretty happy.
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yes, batteries can be more effective in the absence of solar. For me there is the potential to save 2.8 kWh of import or about £600. With panels, this has halved. Ironically, if you have batteries you can make a case for not buying panels. For me, I definitely prefer panels if there is roof space. They last much longer and have green credentials
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Mine is different. We have 16 south facing panels (6.56kw) and 15kWh’s of batteries I fill each night – it was 6.5p, now 8.5p (GE just switched from e.on no EV). My overall usage was 7.1mWh’s for 2025, imported just over 3.8mWh’s, exported 3.2mWh’s (at 16.5p) and generated over 6.6mWh’s of solar. I still have a 15p export rate which could and will likely change. As long as I get more for export than import makes sense to charge my batteries overnight. If not I will charge the batteries more using the solar to avoid import costs for most of the year. I have a big house, no EV so thats my household usage. All cooking electric no mains gas, oil heating which was cheap before the conflict in the middle east. My electricity bill was 240 a month 2023 when I had the install, pretty much zero now.
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I’m not anti battery I’m just suggesting that the effect of panels should be determined first. The good news is that, if you can use every single kWh of your battery every single day, you can save around £800 per year which is getting towards a decent amount.
Having said that, you’d need to be able to use all 15 kWh (some batteries don’t allow 100% dod). Plus account for a 20% loss in capacity over ten years with will reduce your returns on average by 10% over that period so £720.
I might go for that with a cheap battery if I had your usage
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Given that wholesale kWh rates only make up half of the kWh rate we are charged and given that summer afternoon wholesale rates are often buttons, the high all day export rates were never going to be sustainable.
We’ll see time of export rates with premium paid 4-7pm and I’d hope general export will settle at third to a half of SVT import. But maybe only available to those not using the lowest rate TOU
But I can see brown exports being discouraged
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When we fitted our solar and batteries it wasnt just about saving money, or the environment (it did both though), but the main reason was to gain control over our energy bills, by allowing us take advantage of time of use tariffs, and load shifting.
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I think that you are completely WRONG about not getting a battery straight away !
I have 12 panels, a9.5 Kw battery and a 5Kw hybrid inverter…
Two yrs ago I was paying £175 a month for my energy bill ( I have gas central heating ) one month after my system was installed, I reduced my standing order down to £50 – at the moment I am £450 in credit !
So, thanks to my battery my electricity is just about free and it even gives me a little extra to offset the cost of my gas by about 23%…
You NEED a battery !
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you need to show what proportion of your savings are from panels and what from battery. This is actually quite difficult when you get both together. I am not anti battery, just suggesting a way of working out whether you need one
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you’ve missed out the roi impact achieved by the multiple tariffs that allow one to refill their battery many times a day (Agile, Cosy are the Octopus ones, other providers have similar). You’ve missed out the financial benefit of self utilisation, a well sized battery will be continually topping up and discharging on about 250+ days per year…these savings are harder to measure but equate to ~18p per kWh of sunshine stored and later reused, this is based on rates of 0p import cost, a saving of 30p of unused peak rate netted vs a 12p export rate. Without a battery most of your PV is exported at only 12p per kWh, so it’s a 3rd less valuable. This demonstrates how falling export prices makes getting a battery more attractive for self utilisation. There’s also the value of outage protection for some…thats subjective but very important for some users. In your situation of fairly large array compared to your use a battery is a waste of money, but if folk do their sums properly it’s easy to see how a battery is the right decision and waiting a year isn’t necessary.
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My logic runs a bit like this.
I know my 2011 FIT array more or less halved my electricity bill. That’s just being careful when we could to run the washing machine and dishwasher when the sun shone. But heating and hot water was oil so the electricity bill didn’t start out large. The payback was the FIT. This is in the days before smart meters so happy to take 50% deemed generation as export under the FIT rules. Ah : simpler times.
In 2024, we extended the house, super insulated it, installed MVHR and an ASHP. I added another 4.2kW PV and a 9.5kWh battery. Our import only went up by 1000kWh.
The job of the battery in winter with an HP tariff is to reduce the kWh rate. It does that : 15.1p average Dec to Feb (Good Energy HP tariff two 13p dips a day).
The prime job of the PV is to export production to offset bills. At 13p v 15p arbitrage is pointless.
We generate more than we consume over a year : that was planned as I don’t reckon on continuing to be paid for export at the same rate as import. I’d hope to be paid export at better than 50% of my import.
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FIT is great! Sadly not available for newbies who my post was aimed at really.
I’m thinking of getting ASHP and I’ll be taking my own advice. I’ll run them for a year to see what batteries can achieve. At that point, I’ll know the optimum capacity too
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I have a ‘pre-battery’ solar system and have always wanted a battery. However I can’t justify the cost. I’ve recently bought an EcoFlow stream delta x system which is a small (almost plug and play) (3.84kwh) battery with its own solar inputs and am hoping that’ll work as a low cost (c£1300) means of covering the early morning and evening 28p loads off the 7p IOG overnight rate and then from midday excess solar. It’s still hard to justify on ROI terms and I’m still getting my head around setting it up properly, but it looks to have potential to have a positive impact
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As someone who only came late to batteries I can only say that has been the biggest transformation and I just wish I had done it sooner. The batteries needn’t and shouldn’t cost a fortune, very clearly payback on say a Tesla PW is going to be twice as long as a similar spec system costing half the price. My whole house backup system with 45kWh of battery storage and 15kVA of inverters cost £14k to install (I had to pay VAT) but I went a bit OTT on the specification. Could have done it for around £10k with price reductions since and getting a single contractor in to install so I could get the VAT back. As you are on IOG, with batteries you could charge those fully at 7.5p overnight and use that power during the day in your home, freeing your solar to be exported at 12p. If export prices drop, batteries would enable you to store more of your solar generation and reduce imports. No-one has a crystal ball. Look at how heating oil prices have leapt up, 2 weeks ago it was under 60p/l, now it is 90p. I have an ASHP and my battery is large enough to run my house all day, even in the middle of winter. At current electricity prices heating my home costs £310/year thanks to my battery, and ignoring my solar. If I was to heat it with oil at current oil prices it would be more like £1600, and if I didnt have a battery and just used a tariff like Agile or Cosy the cost would be more like £900. Last Summer when I just installed my batteries and didnt have an export tariff, I was on Agile and tried to charge the batteries whenever electricity was super cheap or even below zero, and also stored everything my solar panels generated. Over a 4 week period the average price of the electricity I imported was just 2p/kWh. Batteries can be so easy to justify if you chose how to use them wisely.
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When I design a system, it is sized to the customer’s needs, rather than the delusion that you think you’ll be able to make a small fortune selling electricity back to the grid
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Totally agree — batteries can be a real game-changer if you size them properly and use smart tariffs. Being able to charge cheaply overnight and run the house during the day makes a big difference. The key is keeping the system cost sensible so the payback actually works.
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