[viernullvier]

Your calculation is way off. Getting 8kWh a day from a single 400Wp panel would already require 20 hours of operation at theoretical peak power, so under real-life conditions you can only expect a fraction of that per day.

This doesn't invalidate your point though - even if you're one order of magnitude off, your £200 solar panel will buy you about ten times its price worth of electricity.

[pjc50]

Ugh, I did 1kWh = 1000 watt-seconds, which should be 3600 watt-seconds, so the calculations are off by a factor of four.

[ftth_finland]

£0.30 per kWh is also optimistic over the lifetime of the panel.

Around these parts you get the spot price for any solar you generate. Prices can, and do, go negative.

In general prices tend to be low when the sun is shining and/or the wind is blowing.

So, you might even end up paying for the pleasure of providing solar power :)