Could the Moon power a solar panel?

Chris put this question to physicist Jess Wade from Imperial College London...

Chris - Jess, Mike’s got an unusual idea for a possible renewable energy source.

Mike - How much energy is in moonlight and could solar panel technology be used to capture this energy?

Chris - So solar powered night lights - feasible?

Jess - This is an interesting question. For a solar panel to work at all you need a material called a semi-conductor. It’s halfway between a metal that conducts all the time and an insulator - like a plastic, which doesn’t conduct. In a semi-conductor you have a gap between conducting and not conducting, and you need enough energy to get the electrons from the not conducting part to the conducting part. And when you put that energy in from the sunlight, it can start working and generate power. If you had the right semiconductor, and enough light intensity from the moon reflected back, you could have a lunar solar panel. But the moon’s not very reflective - about 3% of the sun’s light, so you’d have to have a really efficient concentrator to concentrate all that light coming back from the moon. The other option would be to put solar panels on the moon and send the energy back as microwaves.

Chris - Richard?

Richard - Maybe a mirror in space? The Soviet Union were very keen on this, and planned some experiments in the 1970s to light planes at night with mirrors in space.

Jess - I think these are dreamy blue skies research ideas that either you put solar panels on the moon or you put mirrors in space and shine the light back. Because, obviously the moon has no atmosphere and all these other things that we lose so much of the light intensity coming to Earth wouldn’t happen up there - it’s incredibly expensive and we should probably channel more money into researching - and we’re great it at it now - at researching renewables on Earth before we start playing around in the skies.

Chris - There was some idea about having a giant microwave beam that would gather energy in space and then send that energy down and collect it with a dish on Earth. Obviously there are losses at all the stages but was there not some concern that if was an aeroplane inadvertently flew through the microwave beam it would be cooked out of existence?

Richard - It does seem extraordinary. The big issue with solar energy is storage. It’s the big issue with renewable energy and that’s the thing isn’t it Jess that needs to be sorted?

Jess - We’ve got pretty good at storage now. Lithium ion batteries are a really good way to store it and we’re getting really, really good at that research. We’re really good at in this country and there’s loads of research groups doing. It. So I don’t think it’s storage, I think it’s political the reasons that we haven’t taken it up yet. And also, the cost of doing any of extraterrestrial renewable research is a bit out our range at the moment.

Chris - Kate?

Kate - I just had one other point about the moon being used for a solar panel - the fact that it has phases. And also the light doesn’t decrease linearly as it goes from full, to half phased, to new moon. By half phase it’s only one fifth of the already 3% that you have.

Chris - So once a month you’ve got no light at all?

Jess - Once a month we’re winning and the rest of the time it’s just like urrgh.