From: utzoo!decvax!pur-ee!CSvax:Physics:piner Newsgroups: net.space Title: solar power on the moon. Article-I.D.: pur-phy.483 Posted: Sat Sep 18 16:40:01 1982 Received: Wed Sep 22 07:57:18 1982 There has been some debate on solar power going on, and I would like to add my two cents worth. There are several methods of getting useful energy from sun light on the moon. I will discuss only two. 1) Solar cells. These cells produce electrical power directly when exposed to light. Very nice, but there are problems. Well, on the moon those problems are much easier to overcome. First, directing the cells towards the sun. The sun moves much more slowly across the "sky" than on earth. The mass of the cells is the same, but the weight is much less. So their support system can be built much lighter than would be required on earth. Hence, incredibly small motors can do the task. Indeed, motors may not be needed at all. Since there is no atmosphere very large temperature gradients are possible due to the solar radiation. Mechanical systems using bimetal strips can be designed to point the cells at any source of radiant heat. Thus no energy is used and the alignment is automatic. A side note, some cars use bimetal strips on the engines. On my car, a bimetal strip is linked to the choke and mounted on the manifold. When the manifold gets hot, the strip changes shape and pulls the choke off. Such systems are simple, cheap, and require no logic (other than that used by the designer). Furthermore, since there is no atmosphere, you get the full power of the sun as soon as it comes over the horizon. On earth, the best you can do is about 25 percent and that is only at noon. The other problem is storage. I did some simple calculations and found that the moon has a circumference of 6800 miles. If we are talking about putting a lot of people on the moon, say 100 million or so, one could justify building a superconducting power line around the moon. Bury the cables deep, and they could be kept cold for a fraction of the cost required on earth, and you only lose power during elcipses. Such a project is a large one, but no bigger than current earth bound projects such as the Siberian pipe line. This brings me to my second proposal. 2) Thermoelectric power. The temperature difference from one side of the moon to the other is huge. If you build a thermalcouple around it's circumference electrical power could be generated directly on a continuous basis. Such a system is incredibly simple. A lot of wire, and not much else. Such systems can be used on a local basis too, one side in light, the other side in shade. But then you only have power during light. An only for a fixed system. In any case, if we are talking about a large number of peole on the moon, then solar power is the way to go. The first colony however will probably have to depend on nuclear power, because you have to start somewhere, and nuclear power plants have fairly high energy densities, in other words, if you have to ship fuel to the moon, nuclear is the cheapest. If you want to generate power from what the moon has to offer, solar is the best bet.