Science and Exploration

[dreadgeek]

Originally Posted by Corkey

Thanks AJ, I was also thinking that the kinetic energy only had to last until the solar cells could re power the batteries, so even if say 5% kinetic energy were lost to friction, 95% of the energy would still remain to energize the batteries/hour of darkness. Now I'm not math minded, but it seems that 5% x 9 or 10/hours of darkness would still mean that there would be at least enough left to power the batteries, and then if solar and kinetic were used in unison, would not the loss of friction be less and therefore power more of the batteries than solar alone? Sorry to be a pest but I'm so removed from physics by age it's a bit daunting.

You're not being a pest at all, brother. Here's the thing (I'm going to try to spare you as much math as I can here) if the solar cells are used to power the propellers and then anything *not* used for that purpose is stored in the batteries that's perfectly legal according to the laws of thermodynamics. If, on the other hand, all of the energy from the solar cells goes to the props and then the turning of the propeller generates its own energy, you're actually getting more energy in. Remember that thrust is work and in *any* system, no matter how efficient you can imagine it being, where work is done some energy is lost.

However, your idea gave me a brainstorm. Imagine a zeppelin where the upper two-thirds was covered in solar panels. Since a lighter than air gas would provide lift, the electric engines would only be needed to provide thrust and internal power. You *still* couldn't get more energy out than you put in, but you would have a relatively cheap means of air travel. It would be slower than jets but I kind of like that idea, actually.

Cheers
Aj