Lunar power?

[Dave Schwartz]

A question that I've always had is: can even the brightest moonlight generate enough DC power in my solar panels that my grid-tie inverter will show even the smallest signs of life?

Last night I satisfied myself that the answer is 'no'.

Last night was about 22 hours before a supermoon (common term for 'full moon at perigee', or closest approach, when the moon would appear near the brightest it could possibly be). I had to do this a bit early since it isn't expected to be so clear tonight, however the illuminated surface visibility was 98.6% so I think the result was pretty close to being definitive.

Despite really being bright enough outside to read the proverbial newspaper, being -25C for maximum panel efficiency, the moon being located perfectly on-axis (67 degree elevation to a 23 degree roof-mounted array and right on the array azimuth) and with perfectly clean panels - no sign of life from the inverter.

Myth busted!

Have a great 2018!!

[Rob Beckers]

Dave, solar PV folklore has it that moonlight can be enough to zap you when working on strings of panels. I've not tested it, so no personal experience. This is about unloaded strings of panels, when there is no inverter present (which even when switched off provides a bit of a load to keep the Voltage on the panels down).

The output Voltage of a panel is reasonably independent of the amount of light hitting it, when there is no current flowing. It's the current that changes (for the most part) linearly with the intensity of the light hitting it; twice the light, twice the current etc. So, at least in theory a little bit of light can be enough to set up a Voltage across a panel, all dependent on how much self-discharge there is inside the cells

For power there isn't much to be made from moon light: A little searching shows that at the very most moonlight produces about 1 lux. There's no direct conversion to Watt-per-square-meter, but an approximation is about 0.0079 W/m2 per lux. Compare that with intense sunlight that is 1000 W/m2 (that also happens to be the intensity used for rating panels). So, a 10 kW solar array would put out only 79 milli-Watt (0.079 Watt) under a full moon.

Anyway, to get back to my first point, I do tell people to be careful working on solar panels, even at night. Getting zapped with 400 - 500 Volt is not fun, even if the current is not enough to kill you.

-RoB-

[Joe Blake]

I'd often pondered on this question myself - glad to have a pretty definitive answer.

However, the moon can generate power - by causing ocean tides which can be harnessed appropriately.

https://subseaworldnews.com/wp-content/uploads/2013/03/VIDEO-CPMs-Deployment-of-Tidal-Generator-in-Cobscook-Bay.jpg

So Viva Luna. :D (Pity I live 200 metres above sea level and about 50 km from any sizeable body of water. :sad:)