What should we expect from our battery?

We are PV newbies. We have 10 cells, 8 south facing and two east facing. We also have a 9v battery, which we have just had a switch fitted to so we can use it instead of the grid in power cuts. Up to when we had the switch fitted, the battery charged from the cells to max 10 - 12% on a sunny day with our average usage and then we used that overnight. The two days after the switch was fitted it charged from the cells to 68% - no difference to our usage or the weather - and has now gone back to charging up to 10ish%. It occurred to me I don't know what to expect from the cells or the battery - they could be faulty, inconsistent and I wouldn't know because I don't know what I should expect from them. It's a dark art it seems. Can anyone help? Why would it suddenly charge so quickly then stop?

Maybe you have something in the settings stopping the battery charging or the battery is too cold to charge? Is the battery outside? Why are you not charging the battery from the grid on a cheap tariff at night.... relying totally on solar you will not get much benefit from having a battery this time of year.

It's not quite a dark art, it just seems like it at times. Just for clarity, I'm guessing you mean 10 solar panels and a 9.5kWh battery.

The "Energy graph" and "Energy Graph" on the portal should give you a fair view of what is happening.

Only word of warning is the changeover switch in case of a power cut. Is that limited to just a socket or two?

Sarabuzz Your question sparks more than you're asking. Assuming you have a hybrid inverter connecting your solar panels (aka PV) to your battery (9.5kWh) and the grid via the house consumer unit; this time of year you won't be generating much from the PV. We have 12kWh PV and managed 2.2kWh today but we are almost at the shortest day of the year. The other thing that stands out is the 2 panels mounted East-facing. If they are on their own string, they are unlikely to reach the minimum voltage level other than in the peak season to generate anything. If they are part of one string, or each on different strings with the south-facing, they could pull down the voltage on the south-facing panels and reduce output over the year. If you are confident that your installer has done the due diligence and your installation provides the best output given your circumstances, then you're well placed to harvest a decent amount of PV next year.

Many PV owners have a Time of Use (ToU) tariff such as an EV tariff or Economy 7 which enables them to charge uo their battery off-peak and consume during the peak period. This "load shifting" enables the household to run off PV in summer and off-peak in winter with a blend in between. If you have a large household consumption, a single battery may not fully meet your needs but will go a long way towards reducing your costs. If you have a low consumption, your quids in.

There are issues with battery State of Charge (SoC) being reported incorrectly or simply not working correctly, but there are fixes in the pipeline. Similarly, there are issues with some inverters not reserving battery properly and again there is a fix in the pipeline.

Tim Thank you, Tim. That has given me some really helpful information, and questions to so. Yes, we have the inverter, and I can only assume that the two east facing panels have been connected in the best way - I had no idea they could act against each other. Thanks for the response, and merry Christmas.

SilverArt add far as we know were not limited, but you've given us a quotation to ask the installer! Merry Christmas and thank you for your response.