Batteries

uk1

In Southern England facing due south with an annual usage of around 7000kwh and a 6k’ish array with for the sake of simplicity normal hourly spread of usage hourly - as a “finger in the air” - what would be the maximum battery storage that one should consider as practically usable, budgetary considerations largely ignored please?  So with a slight rephrasing, at what capacity do others think  “I wish I’d bought a bit more …….!”

Thanks. 

Ectophile

I think you'll suffer from diminishing returns if you buy more.

I have a tiny 3kWh (usable capacity) battery.  For me, a light user, it will keep me powered all evening and night throughout the spring and summer.  So for those months, anything more would be wasted.

But it won't keep me powered all night in the long winter nights.  Perhaps 6kWh would be better.

But in winter, not every day is sunny enough to fully charge the battery, and some are so cloudy that the battery doesn't charge at all - the power generated only covers the base load.  So should I get a battery that will last me several days - maybe 12kWh or 24kWh?

ABrass

What Ectophile said.

My usage is similar to yours as is location, I've got 8kW and a 6.5kWh battery. My battery never makes it through the night at the moment. In the summer it should manage all day and Winter it will be more effective as it'll capture more of my power so proportionally less will be exported.

I think mine is probably the right sort of size for me. But about two days after installation I was checking the price for adding another battery into the system. I suspect that if I'd gone larger I'd have been happier but it would have been a worse financial decision.

Exiled_Tyke

ABrass said:

What Ectophile said.

My usage is similar to yours as is location, I've got 8kW and a 6.5kWh battery. My battery never makes it through the night at the moment. In the summer it should manage all day and Winter it will be more effective as it'll capture more of my power so proportionally less will be exported.

I think mine is probably the right sort of size for me. But about two days after installation I was checking the price for adding another battery into the system. I suspect that if I'd gone larger I'd have been happier but it would have been a worse financial decision.

Absolutely agree.  Two weeks ago I was getting through the night but now I run out mid/late evening (depending on which cooking appliances I use).  I too considered adding another battery but found I couldn't because the specs have changed on them and new ones aren't compatible with my current one and BMS.  However the additional benefits of the extra storage  and of being able to draw a larger current would never have outweighed the cost.

Waywardmike

ABrass said:

What Ectophile said.

My usage is similar to yours as is location, I've got 8kW and a 6.5kWh battery. My battery never makes it through the night at the moment. In the summer it should manage all day and Winter it will be more effective as it'll capture more of my power so proportionally less will be exported.

I think mine is probably the right sort of size for me. But about two days after installation I was checking the price for adding another battery into the system. I suspect that if I'd gone larger I'd have been happier but it would have been a worse financial decision.

This... Exactly this for me! 

I also have a 6.5kWh, and if it's fully charged it will get me through to very early morning currently (~3am), this largely depends upon what the kids are up to, 3 PlayStations with associated big TV's churns through it in an evening.  I think 8-9kWh would have been my sweet spot, adding another 6.5kWh battery would be terrible financially, but I still want one.

Alnat1

Before PV/batteries we used around 3800kWh/yr. Son has now moved out and we've made a few changes so probably around the fabled average user now, 3100kWh.

5.25 on the roof (went with get what you can on while the scaffolding is up) but only 4.8 storage. The battery will just about last overnight at the moment if we've cooked dinner on the gas hob. 

Wish I'd got another couple of 2.4 pylontechs to get us through the morning in the shoulder months as our roof faces SW and doesn't really get going until 10am. As said in the posts above, it wouldn't have really been a good idea financially, but it would have made me happy.

The panels do what you expect them to, but the batteries are the bit of the kit that gives the most (dare I say smug) satisfaction. There needs to be a way of factoring this into the ROI 

uk1

Thanks all,  I have found the opinions helpful.

In the future as electric prices continue to rise, and delivery rates take on newer bands ie “off peak”, has anyone considered buying more battery power than currently seems sensible and charging batteries from the grid on an off peak rate to make more use of the batteries in winter?

ABrass

Yes, if you have a EV and battery system you can join Octopus Go, then the solar charges you up during the day, you top up overnight and virtually never pay higher rates.

I haven't seen another plan as good for just batteries alone, but that would be very good for me.

Octopus Agile does give you some of it, but without the certainty of a fixed price or capped deal.

uk1

Thanks ….

For someone like me who is pretty clueless, is there a simple way to calculate what the optimum level of battery storage would be fully charged at “off peak” rates say during winter to keep us going through the day and night keeping in mind my total annual usage is 7000kwh and ignoring affordability.   I think we might be looking at Pylontech 3000’s. 

Alnat1

That works well if you have an EV and can get on the Octopus Go tariffs. Without an EV maybe an E7 tariff could work? 

For now I've chosen Octopus Agile/Agile Outgoing and made money over summer from the excess going to the grid. Hoping the profit will cover most of our winter electricity costs.

I have played around with the batteries a couple of times when Outgoing was paying crazy high prices. Charging at 35p/kWh (my Agile cap) and sending it back at 80p/kWh was fun but once you factor in the loss in/out of the batteries, it's a faff for a couple of quid. Would take a long time to make back the cost of buying extra storage. Was fun to play though 

ABrass

Pylontechs are very expandable, so if you go too low you can add more easily. Mine is a Growatt 6.5kWh and additional batteries cost at least £2.5k each at the moment.

I'd say half your regular daily use as an upper limit on what will make sense financially. More than that will stop you cycling it frequently which means it's a waste of money.

9kWh as a stab in the dark.