Solar panels + battery from Ovo: good or bad?

Hey @SallyWally27,

I’ll couple of our Solar members who can share their insight and opinions - @BPLightlog & @waltyboy.

Let me know if I can help with any questions 😊

Definitely worth doing.

Similarly to @BPLightlog I've had solar panels since 2013, a small array of nominally only 3kW, you’ll do much better nowadays with more productive panels plus being no longer limited to rooftop nominal solar capacity of around 3.6 kW (i.e. 16 Amps at house voltage of 230 volts): modern inverters can handle much larger solar capacity by being designed never to allow export of more than 16 Amps, balancing your home usage and, yes, recharging those crucial batteries in order to help do that.  My ancient and trustworthy Fronius IG has never faltered in over a decade of continuous use, but unlike modern versions isn’t up to that level of software sophistication! Mind you, up here in sunny Sunderland we rarely generate more than 1.3 or 1.4 kWh, even in mid June, and in Winter some (rare) days are zero.

HOWEVER, with the the addition of a very small 24 volt lithium battery a few years ago (nominally 2.4 kW) and a small additional inverter I found we can use every scrap of our low winter production of, say, 1 kW daily, because I use the battery exclusively to run everything in the house between 1600 hours and 0900 hours, recharging with an ordinary 24 volt charger between 0900 and darkness at 1600.  This is not the modern way, as a new system will be able to utilise cheap nighttime tariffs and help with your larger daytime usage, and so be more efficient.  As my wife and I are both retired we watch daytime consumption like hawks, and our evening and nighttime consumption averages only around 100 Wh (and that’s with a small chest freezer and a family-sized upright ‘fridge/freezer) just right for a 2.4 kWh battery so we buy perhaps half a penny’s worth of electricity from the grid hourly overnight. In the summer, of course, much of my rooftop production is exported (“wasted” from the point of view of our household, though not wasted of course in the larger community) because as BPLightlog says you can never use all of what you produce, but with batteries and a sharp eye you can go very close!
 

I would heartily recommend you to go ahead BUT with the usual caveats: seek expert advice, go for as much battery capacity as you can reasonably justify (somewhere between 5 and 15 kWh is normal nowadays, anything bigger requires some very serious thought). I take it you are UK customers of OVO? Our weather will not save you being reliant to some extent on the Grid.  But it’s the “some extent” that can be vastly tweaked with good planning. And then, if you are car drivers, there’s the whole EV side of things which with imaginative tariffs and possibly enabling household or grid usage of the EV’s own batteries (if one has one’s own drive, of course), over the next few years is going to make a panel/battery combo even more attractive (although remember EVs won’t charge solely from your panels without help if your rooftop is producing less than 6 Amps).
 

I would actually suggest that in the very near future, because of increasingly interesting tariffs, that a household battery is almost more relevant than solar panels! 

I can reassure you on one thing: after a decade or two of solar panels becoming ever more widespread in all parts of the UK there are no longer any myths or unanswered questions about productivity, the effect of differing annual solar irradiation figures in different parts of the Country, reliability of the kit, etc. etc. 

Good luck….and get good reputable advice, remember there’s no such thing as daft questions, only daft answers! But ultimately friends, neighbours, colleagues who already have solar panels are a good first port of call….plus the OVO forum of course!

Hi Sally, sounds like your envisaged system is a perfect size…hopefully someone with experience of the OVO Solar offerings will be along shortly.

You and your husband will have a lot of fun exploring the different options and making the final choice: and don’t worry, the process with a good firm is smooth and the disruption nowadays is minimal.

Initially, if you haven’t already done so, ask your local friendly electrician (who probably won’t be a solar installer) to come and have a quick initial look at your meter (is it a smart meter?), consumer unit and your house’s general electric set-up. S/he may well feel confident about pointing you in the direction of one or two local MCS installers who will then chat further about the physical logistics and structural requirements and options…the eventual chosen installer will also liaise with the grid supply people (your local DNO). 
 

All the very best, do let us know how you get on….

 I haven’t gone into any deep calculations about PV arrays and batteries, because I live in a rented property. The cottage has no gas, (inadequate) night storage heaters and an Economy 7 meter/wiring system, but because the NSH became so expensive to run a couple of years ago, I switched them off and switched to a single-rate tariff. I use other means to keep warm. Storing cheaper energy as heat doesn’t work well, but does storing it in batteries work any better?

I could do some sums to see what the return on investment would be for a battery installation designed to charge at the E7 night rate. I assume that it’s 100% efficient in that no energy is wasted (except perhaps in a hot Summer when the proportion that is ‘lost’ as heat would in fact be wasted), but I’m not sure how to determine the required battery specification. I’ve noticed a few recommendations (you know who you are!) to work out how much you think you need, then double it. The variables are:
 

Daily consumption. For the past year, this has been on average 2.800 kWh with considerable deviation. An Excel histogram shows that consumption is less than 3.0 kWh on 70% of days, less than 4.0 kWh on 83% of days and less than 5.0 kWh on 93% of days. Bearing in mind the advice of those who’ve been there, I’d probably say I should go for 5 kWh capacity.

Maximum draw. This is more problematic. Although the meter does register the momentary draw in kW, it doesn’t record it and I know of no way to capture it. It could be that @BPLightlog’s magic machinery could capture, say, the average draw over a minute or two, but that’s an awful lot of data to deal with. However, it would be necessary to go that granular when power-hungry devices may only be operating for a couple of minutes (kettle, toaster, for example). So I’d have to take an empirical approach and arrive at:

I suppose I could go down to 12 kW if I could guarantee that no-one would switch on the kettle while someone was in the shower. I’ve no idea how the system would react if that were to happen, though, and I haven’t looked to see if there is such an animal as a 5 kWh battery that would ever allow for a power draw of 12 kW.

Still, if I could charge the battery each night, consuming say 3 kWh on average, that would cost 3 x £0.1636 per day, or £180 p.a. On the equivalent single-rate tariff, the cost would be 2.8 x £0.2271 per day, or £232 p.a.  (rates from OVO’s E7 plans).

Saving of the order of £50 a year sounds like a 10-20 year payback period. However, a cheaper night rate (like some of those offered to EV owners) might make a much bigger difference.  Octopus’s 8.5p rate, for example, would save £90 a year, bringing the payback period down to perhaps 8 years, which I might just survive.

Do my sums make any sort of sense? Are there other considerations I haven’t taken into account?

Thanks, BP. I’m just not in the market for solar PV, sadly - that would be within the squire’s purview. A compact battery would in theory be portable, with a bit of judicious wiring, so I could take it with me if I were evicted.

I just had a quick look at prices for batteries. I’ve got a lot of rethinking to do ...