solar panels....Sold a lemon?

[BeeJayEff]

I've just bought another 9.6kw of batteries for mine as even in February on sunny days I was generating more than my batteries can store. I'm very interested about these SEG tarrifs as sofar the buggers have been getting my excess electricity for nowt. I've given up with shell energy they are without doubt the worst company I've ever had the misfortune of dealing with.

How do you judge what size battery/ies to go for ? My installers (in whom I have little confidence) tell me that the inverters dissipate any excess power in the form of heat, but I can see no way that the inverters know how much power is being imported via the main CU ... but are you saying that all excess power is exported but it's only 3.68kW that you can get paid for (if you're on single phase) ?

 

[Jim Gough]

How do you judge what size battery/ies to go for ? My installers (in whom I have little confidence) tell me that the inverters dissipate any excess power in the form of heat, but I can see no way that the inverters know how much power is being imported via the main CU ... but are you saying that all excess power is exported but it's only 3.68kW that you can get paid for (if you're on single phase) ?

I use approx 10kwh a day and had 9.6kwh of batteries which if its sunny every day (hahaha!!!) lasts nicely from one day to the next, but it's rarely sunny every day and after about 3 hours of sunshine my batteries are full and excess power goes to the grid. No idea what your installer is talking about the inverter dissipating heat. Mine is not even slightly warm to touch. I think the 3.68kW reference was to how much you could export when the government scheme was running which ended in 2019. (just shows how much the tory ----ers care about the environment....)

 

[Simon47]

How do you judge what size battery/ies to go for ?

You wet a finger, stick in in the air, then reach down your pants and pull a figure out of your backside
More seriously, there isn't a magic formula. It's a tradeoff.
On the one hand, the more capacity you have, the better you can take advantage of sunny days and store the energy for less sunny days. With a small battery, as noted above, on a really sunny day you'll fill them quickly and then not get the benefit of storing your lecky for later - you'll have to either back off the system or export the excess for a pittance, then buy in when you need it later. With a huge battery, you'll possibly need several really good days to fully charge them and thus get the benefit of keeping all the energy you capture.
The flip side is that bigger batteries cost more, take up more space, and will lose more to self discharge.
I guess you can try and figure out your average usage, how much you could produce from the panels on a good day, and size the batteries to deal with that. But I suspect there's a lot of guesswork involved for that.
Another consideration is that with a small battery you will be working it harder - deeper discharge, higher charge/discharge rates. That's going to age it faster than the same work going into a larger battery. Note that for EVs, they are still advising that for maximum battery life you should go below 30% on discharge or above 80-90% on charge - it tends to be the ends of the charge (the deep discharge, and full charge) that age the cells most.

My installers (in whom I have little confidence) tell me that the inverters dissipate any excess power in the form of heat, but I can see no way that the inverters know how much power is being imported via the main CU ... but are you saying that all excess power is exported but it's only 3.68kW that you can get paid for (if you're on single phase) ?

Your installer is a clueless fu**wit - as are many.
When the inverter reaches its limit, then it'll convert that much and no more - the panel DC voltage will rise higher than it would be with a more powerful converter and the same amount of sunlight.