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Solar again


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It all depends!


If you say 12 hours of daylight and 8 hours of strong sunlight of which say two hours is sort of directly beamed (more or less) at your flat non tracking solar panel then I would guess from a potential for 1200 watts you can expect something like a fraction of that figure!


It it helps, the very best domestic roof solar panels facing due south at an angle towards the sun are generally reckoned to be up to 18% efficient. So 18% of 24 x 100 would be 432 watts - or a bit less as your panel is flat! Then there is the loss in the inverter/ regulator and wiring!


More to the point - don't worry about it - just relax safe in the knowledge that (unless you have diesel heating) you are unlikely to use more than you gain - especially if you have two leisure batteries - and as long as it is wired to charge both leisure and engine battery you will never come out of the house to a flat battery again!

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There's a useful article here:




It's suggested in the article that a 100W solar panel would generate 600-700Wh over a 24-hour summer day - equivalent to 50-58Ah. However, professional advice seems to be that one should realistically expect a panel's output to be no greater than two-thirds of its nominal ouput, say 60-70W for a 100W panel. That would equate to a 100W panel generating 360-490Wh over a 24-hour summer day - equivalent to 30-41Ah.


More information here:







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From experience with a BP 80 watt panel over a several years.

Southern France (or a very good day in the UK)

Standard regulator

Analogue ammeter fitted between regulator and leisure battery.


Midday at best 4 amps, most of the time closer to 2.5 and it tails off towards the evening and rises progressively at daybreak. So lets say 12 hours at an average of 2 amps. That's 24 ampere hours per day.


For a 100 watt panel add 25% to make 30 ampere hours per day.


So I agree that providing you have LED lighting and don,t have diesel heating and a compressor fridge nor watch satellite TV for hours on end you should be OK.


Plan for anything more than this and you have wishful thinking.


Good luck






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