Okay, this maybe dumb but just stay with me here

[Javaman]

and to all the scientists out there please rip this apart if it's a really dumb idea.

Is there a metal or material that expands and contracts in a very high ratio when exposed to sunlight then to night time?

meaning, it expans during the day when the sun is up but then contracts rapidly when the sun is down?

If so, is it possible to construct a power generator based upon this expansion and contraction?

I'm no engineer nor to I play one on TV so I'm just throwing this out there.

[GreenPartyVoter]

1. That's not a lot of time to gather engergy, really. And I am not sure

that there is a lot of energy there to gather.

But I am no scientist either. :)

[AndyA]

2. What we need is something that can make energy out of carbon dioxide.

We have too much of that now. So, we should try to find a way to start using it.

[Fridays Child]

6. Wasn't there just an article about that? Some little microbe critters that...

...eat carbon dioxide and produce methane?

[Sal Minella]

10. Was it convert carbon dioxide to ethanol?

Like yeast does? Think it was a cyanobacter, the same critters that produce the red tide....maybe. The memory gets spottier by the day, here.

Actually I think Yeast converts sugar to ethanol and carbon dioxide. Actually I think I'll go take a nap.

[Fridays Child]

15. I found the article...

http://www.honoluluadvertiser.com/apps/pbcs.dll/article?AID=/20070512/NEWS01/705120347/1001/NEWS

[Sal Minella]

17. Yes, you did. Good. Thanks.

[frogcycle]

12. when carbon and oxygen combine, energy is released

it's an exothermic ("heat goes out") reaction - more commonly known as fire.

getting the molecules to separate is endothermic ("heat goes in") requires an input of energy.

[IDemo]

3. A bi-metal coil such as a thermostat will expand and contract with heating changes

but to produce usable energy even with very large coils, or a large number of them, would be extremely difficult.

[phantom power]

4. There are such materials.

And they have even been proposed for certain specialized power applications, like on satellites. However, they don't really compete with solar thermal (or even PV) in terms of efficiency for converting sunlight into useable energy.

The "nitinol" alloy had 15 minutes of fame back in the 80s:

http://en.wikipedia.org/wiki/Shape_memory_alloy

[Ian David]

7. You beat me to it. I was gonna mention Nitinol, too.

Nitinol and Omni Magazine... ah, remember the 80s?

[phantom power]

13. Those were the days.

When I mostly worried about nuclear winter. My end-of-the-world list was so much shorter then. It was almost cute.

[drm604]

5. I'm not a physicist or engineer

but I think that, compared to what you're suggesting, solar cells or boiling water would be much more efficient at converting sunlight into usable energy.

Although I guess if you use a solar collector to boil water then you would be using a material that expands when exposed to sunlight, but I don't think that's what you're talking about.

[Ian David]

8. How about creating a "Heat Capacitor" that stores heat from your refrigerator or air conditioner...

during the day, and then releases that heat at night to keep your house warm?

[jgraz]

9. I like the solar generator that uses molten salt

Just cuz the thought of red-hot molten salt is cool.

http://www3.iptv.org/exploremore/energy/Features/Fsolar.cfm

[drm604]

18. Cool article and pictures.

Thanks for the link.

[frogcycle]

11. solar cell is much more direct and efficient

it does the same energy collection and converts it real-time

[eppur_se_muova]

14. A gas would have the highest thermal expansion of anything ...

or a liquid/solid that transforms into a gas.

I know that's not what you're asking for, but taking it to its logical conclusion, that would be the most useful. So I think if you follow this idea as far as it leads, it suggests a solar-thermal Stirling engine. I don't know that any of these take advantage of the day/night cycle, but it would seem that a large, cold reservoir underground connected to the usual Stirling engine might *possibly* up the efficiency a little. The reservoir could soak up heat from the Stirlings during the day, and release it through above-ground radiators at night. Don't know if the added cost and complexity would be justified by further energy output.

Buckminster Fuller suggested that a sufficiently large geodesic dome could function as a solar hot-air balloon, rising during the day, and descending at night. Interesting concept, even if it doesn't deliver a big energy kick.

edit to add illuminating illustration:

[skids]

16. Here's the rub...

Say you had such a metal. It heats up to a nice hot temperature within the first few minutes of sunlight, and then stays at that temperature until the sun goes down. All the time in the middle is wasted energy -- only the energy that is necessary to heat the metal to it's equilibrium temperature can be harvested. (Actually somewhat less than that)

Now if you had something that would shade the metal until it cooled, then let the sun hit it again, that would allow you to extract more energy by running the cycles several times in a day. If you had a wheel with spokes made out of the metal, and kept half the spokes in the shade, it would probably turn.

But there are much more efficient ways to go about harvesting heat energy.