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Old 10-31-20, 07:22 AM   #6
Lurking Renovator
Join Date: Oct 2020
Location: North Lincolnshire, England
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Originally Posted by Robl View Post
I can see a few issues:
If you get a feed in tariff (as it's the UK), they won't like you messing with the DC from panel to inverter. You could inject DC here, and "make" money!
Normally a 2kW string of 8 panels would be at a higher voltage - I'd expect more like 70V per panel, so around 500V.
4kW at 12V is a lot of current - normally people would try and avoid such heavy currents, due to the losses in the copper wiring.

A much simpler option, avoiding the possible legal issues & dangerous side with the high voltage DC, would be to charge up batteries from AC, and then use them for certain loads. You could set a timer to charge the batts at mid-day, so they always get charged, and usually it's free. 12V lighting is a very suitable load, maybe power for a laptop. It won't charge up from PV when there's a power cut, but it's a lot simpler.
I can see that I could inject DC but it would surely cost me more to generate it than I would get paid wouldn't it?
Or am I missing something?

I am surprised that you think the voltage will be so high.
I just checked an ebay listing which shows the following
Solar panels
250 watts

Dimensions (H x W x D) in mm: 1485mm x 992mm x 40mm

Weight in kg: 15.8

Cell type: multicrystalline

Power max .: 250 watts

Open circuit voltage max .: 28.16 V

Max voltage: 33.80 volts

Max current: 8.88 A.

Short-circuit current max .: 9.16 A

Module efficiency: 16.97%
Which is in line with what I expected.

It's interesting that you suggested a timed battery charging regime. I had considered doing that and am in any case going to implement a small system to keep my spare car battery and my wife's mobility scooter battery in reasonable condition seeing as my wife and I are old and in poor health so I am rarely using my car.
Still that's no good for such a time when the grid is off for any length of time as the inverter will not run.
Barrowman is offline   Reply With Quote