Very basic questions about solar, starting now if you don't mind.

[sharpener]

On 27/08/2025 at 14:35, saveasteading said:

Question one. Battery principles.

In principle I assume we want to catch all possible rays on the bright days, to use on the following darker days.

Thus don't undersize the battery.*

So will it be very big? The guy said it's about 0.5 x 0.5 and height is stackable, about 1m if 'oversized'. That felt small.

And is it a fire risk? The video we were directed to last week says one in a million batteries goes on fire.

I had assumed that we would build a block or plasterboard enclosure for it, but the guy said it is enclosed against fire, and weatherproof ? is this so? Keep it in the garage or outside?

 

We have a 190 m^2 barn conversion on two floors. Original panels are 16 x 230W Upsolar with a wonderful pre-Dec 2011 indexed FIT price. Second tranche is 8 x 405W Longi for which we only get the 15p Octopus export rate.

 

Eventually got DNO to allow unlimited inverter output and unlimited export capacity. Facing due South and with a total nameplate capacity of 6.9 kW we get over 7MWh/year (Devon). Of which 5MWh is exported and almost exactly matches total imports (house is not occupied full time.)

 

Original panels have had no maintenance and the rain in Devon keeps them clean, no significant deterioration in output over 14 years.

Battery was originally 2 x 3.55 kWh of Pylontech, quickly increased to 10.65 by adding an extra module. Would ideally add a fourth now that we have a 12kW HP but would mean moving entire stack. Is in rear lobby, not concerned about fire risk beyond getting an "all fires" extinguisher and putting it on the kitchen side of the dividing door. If you are worried then garage would be fine, self-heating will keep the batts warm in winter (we see peak cell temps about 8C above ambient), I would not put them outside in UK climate.

 

@JohnMo's sizing guide is theoretically correct but I think the economics of guaranteeing no import at all during peak tariff periods are questionable, we can achieve this in autumn/spring but not depth of winter. Certainly not worth trying to average over more than 24 hours.

 

We have Victron Multiplus 5kVA/4kW battery inverter (which is excellent if a little bit small, though it does give us whole-house backup) plus a 48V 60A MPPT for the newer panels, and for the others a Solax string inverter (also excellent) replacing the original 2011 Stecagrid one which failed earlier this year.

 

If I were doing it all now I think GivEnergy AIO is worth considering and would go for a 6kW inverter with 15 kWh of batteries and as much solar PV as I could fit.

 

 

 

Edited 22 hours ago by sharpener