Cheapest home storage battery options?

Spies

Every time I talk to a solar installer they all keep asking if I've considered battery storage, this easily adds £1000 to the quote but as I'm going down a different route of buying my own equipment and paying an electrician to install it, does it make more sense? 

Should I buy a hybrid inverter even if I can't afford the batteries right now?

Or should I just add an AC coupled battery in the future when funds allow?

Thanks! 

tacpot12

I don't think it makes sense. The battery is likely to cost you £1000 for anything worth having, so I can't see you saving much by going down a seperate route. Do the maths on what will pay for itself over a reasonable time. 

QrizB

I bought a used AC-coupled inverter and built my own battery, photo in this thread. The Sofar ME3000SP was about £450 on eBay. I biult a tiny battery - only 25Ah, 1.28kWh - and the cells were £240 plus £60 for the BMS and probably £30-£40 for other odds 'n' ends (cable, connectors, that sort of thing). Say ~£800 all in.

However, I could've bought much larger cells for not a lot more. 105Ah cells would have cost an extra £200 and would have given me 5.4kWh for £1000. If I'd been confident that everything would work, I would have done that in the first place. Instead I spent a bit less in the short term but it will cost me more overall once I've added more capacity.

The experiment with my small-capacity battery has convinced me that it will work for me and that it's now worth buying more cells to increase the amount of storage.

Fr a new install, a hybrid inverter would add less to the system cost than a standalone AC-coupled system. Because I've got an existing system with a FIT I didn't want to do anything to my existing system that might compromise my FIT payments.

Hope this helps.

Spies

In the last month, I've calculated I'd have used 44% (20% worst day 90% best (dull) day) using PV only, or 79% (40% worst day 130% best day) with a 4.8kwh battery.

>100% calcution is due to charge from the previous day rolling over past midnight as I can't easily adjust for that.

It's so hard to calculate because of many variables, but as a safe bet, I'd say I could use twice as much if I had a 4.8kw battery.

QrizB

I've only had export metering since the 26th of July this year, when my smart meter was fitted. Since that date there has only been six days where my import has exceed my import. Put another way, on all bar six days an adequately-sized battery would have let me import no power at all.

Over the same period, my largest import figure was 5kWh, but that was only one day. My lowest export was zero on a very low generation day when my 1.28kWh battery caught it all.

So 4kWh of battery looks like a sensible minimum amount for me, based on my generation and consumption during July-to-September. Time will tell whether that holds during the darker months.

Spies

So additional costs appear to be +£600 for a solax hybrid over the non hybrid version and £750 per pylon 2.4kwh battery.

Payback time, as long as you're buying your own kit, appears to be the same as pv only due to be able to utilise more of the generated power. 

Still not leaving my mind very clear as to what to do! 

QrizB

For battery storage to pay for itself, each kWh stored needs to cost less than, say, 2000x the cost of a kWh of electricity. If electricity is 15p/kWh that's £300/kWh; if electricity is 20p it's £400/kWh.

(You could argue that 3000x or even 4000x is a more reasonable number; if that works for you, I won't contest it.)

Spies

Which does the 2000 and 3000 number come from? Is it the number of cycles the battery is good for? 

Solarchaser

I think you have to ask yourself seriously why you want a battery.
1. Purely economic
2. Green
3. Satisfaction 

If its 1, I'd say whatever you think you need as a battery. Half it, as you need that battery to cycle every day to definitely justify its cost, so if you think you need a 9.6kwh, then buy 4.8kwh and it will definitely cycle each day.

2. Yeah it's green to have a battery, especially if you are in the middle of England where coal power stations are supplying some of your electricity 

3. Now you are at the other end of the scale from 1 really.
You want to run your house on batteries/ your free solar, as much as possible for the Satisfaction of doing it, knowing you are generating most of what you use and no longer sending it out to the grid during the day to simply buy it back later.
So now if you think you need 9.6kwh, you should probably get 19.2kwh.
You have given up on the cycling every day thing and now just try to buy as little as possible from the grid.... thats where I am at.
My 2-4 year old batteries have cycles less than 200 times.

Due to changing inverters several times my figures are not complete,  but come the end of next month I'll have a full year of figures from the current inverters and will post them up for everyone to judge the roi etc.
I can say I've saved over £400 this year... but for that to mean something you need to add up lots of things, total usage, import, generation and export as well as cost of components.

However only I can judge the satisfaction, and I have to say, I'm very satisfied.

QrizB

Spies said:

Which does the 2000 and 3000 number come from? Is it the number of cycles the battery is good for? 

It's a combination of factors, battery life plus time. If you size your battery optimally you'll be cycling once per day so 2000 cycles is ~5.5 years; 4000 would be 11 years. Current-generation LFP batteries claim to be good for 4000 cycles but there aren't any of them that are already 11 years old. Previous generations claimed 2000 cycles and, from what I read, seemed to last that long.

 A benefit of having any battery at all is that it lets you "top up" your instantaneous solar generation when you eg. switch on the kettle or do a load of laundry, reducing or eliminating the import that would otherwise happen during the day. Solarchaser says he's only cycled his battery 200 times in 4 years. OTOH the BMS on my battery shows 59 cycles since July 26th.

Spies

What about overnight base loads? 2.4kw wouldn't cover mine, 4.8kw almost does, if it charged on cheap energy during the night then it definitely would.