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Solar lights and the angle of the sun

Peter ScargillHi! You might find this interesting.. it’s not rocket science but plenty of people would argue otherwise.

Have you noticed that NEARLY all garden solar lights have the solar cell FLAT on the top – i.e. not angled to the sun but level. I can only imagine this is for ease of manufacture or style or they’re mainly sold in hot countries where the sun gets high up in the sky.

Either way, not good! You hear people say “ah yes these solar cells work in the shade as well”. The technical term for that is bollocks.

So, here’s the test. I took a typical solar cell (I just happen to have them lying around all over the place) out into the garden this afternoon – just after lunch. Being March in the UK the sun was down near the ankles.

I made sure there were no obstructions and the solar cell was naked – i.e. no glass to add to the confusion. I stuck a meter on the cell and moved it into three positions – firstly JUST out of the sun, secondly in the sun and flat level with the ground and thirdly at 90% to the sun – i.e. pointing at the sun.

solar cell test

Well there it is in plain English… 16ma from the device in the shade, 60ma from the flat device and 100ma from the device when pointing to the sun. The difference is clear and unambiguous.

Put another way… assuming you managed to get the garden light to shine, given the more favourable lighting (3) for, oh, 4 hours at night….. the version with the flat top would only give you 2.4 hours and the one in the shade (only just mind you – I reckon I could have made it give a lot less) would give you 38 minutes at best. Pile more solar cells you get more power – but the ratio remains the same.

I hope that puts that one to rest – there will be minor differences depending on the cell type. Look for garden lights who’s solar cells you can point at typical British sun – set them to the position the sun will be at mid-day – and that’s the best you’re going to get.

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