# Absorbed energy from the sun, where does it end up?

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1. Nov 27, 2014

### Baconfish

Ok, we had a discussion in class: If we build solar panels all over the earths surface we can collect a good amount of energy. If we use this energy to power el-cars where does the energy end up? The energy law states that no energy can be lost from a system.

2. Nov 27, 2014

### Vagn

Heat, the answer is almost always heat. There's some sound production as well from the motor, but it'll be heat lost in the wiring, heat transferred to the air and any moving part etc. Some will also be radiated away, but most of this will be in the IR part of the spectrum.

3. Nov 27, 2014

### A.T.

From an isolated system. If the Earth was isolated, the Sun's Energy wouldn't get here in the first place, would it? Some energy leaves the Earth on the same way as it got here, as radiation.

4. Nov 27, 2014

### Baconfish

Yes i just thought about the earth as a isolated system afther the energy was taken in. Ok so basically we would heat up the earth since the IR radiation would come back down again. So if kinetic energy usually ends up like heat this means that power production like fission and fusion (in the future :) ) will heat up the planet?

5. Nov 27, 2014

### Staff: Mentor

Yes, although it is a good exercise and somewhat fun to calculate by how much. Try it!

Google will give you some decent values for annual energy production and the mass of the earth, and you can make some reasonable order of magnitude estimate for the specific heat of the earth.

6. Nov 27, 2014

### A.T.

Then no more energy would come in.
Why would it come back? Some of it escapes into space.

7. Nov 27, 2014

### Baconfish

But i should count out wind, wave, water and all kinds of renewable energies right? Since they are in a natural cycle. Or maybe not, as the water in a reservoar for example would naturally not end up as heat, but rather move around some rocks on the natural path down the mountain?

8. Nov 27, 2014

### A.T.

If it moves rocks down, then even more potential energy is released and converted to heat.

9. Nov 27, 2014

### Baconfish

Oh ye! So the i probably should count them out if im interested in a net heating of the earth. I should only count fission and solar.

10. Nov 27, 2014

### Staff: Mentor

Wind, wave, and water are all directly or indirectly powered by incoming solar radiation so power from these sources contributes no heat that wasn't coming in anyways.

Burning fossil fuels does contribute additional heat.

11. Nov 27, 2014

### Baconfish

Ah yes that makes sense. Thanks! :)

12. Nov 27, 2014

### CWatters

Correct. Perhaps see..

http://www.cgd.ucar.edu/tss/ahf/

They suggest that in 2005 this effect accounts for about 1% of global warming.

13. Nov 27, 2014

### Baconfish

This maybe explaines one other thing: Many times i´v wondered why often in cities its wet while its laying snow just outside it eaven though the topography is the same, so its probably just waste heat!

14. Nov 27, 2014

### rcgldr

Angular momentum is conserved. If rocks move down (inwards), then the angular velocity of earth and rocks increases by a tiny amount, and the angular kinetic energy of earth and the rocks increases.

15. Nov 27, 2014

### A.T.

That doesn't contradict what I wrote, does it?

16. Nov 27, 2014

### Baconfish

Hehe thats really cool to think about :) so easy to change the world :p

17. Nov 27, 2014

### DaveC426913

Yes. They are commonly called 'heat islands'.

I live in one, and enjoy that fact immensely.
http://images.slideplayer.us/4/1425045/slides/slide_7.jpg [Broken]

Last edited by a moderator: May 7, 2017
18. Nov 27, 2014

### rcgldr

I'm wondering how much of the decrease in GPE goes into the increase in angular kinetic energy versus heat.

19. Nov 28, 2014

### CWatters

According to wikipedia...

The main cause of the urban heat island effect is from the modification of land surfaces, which use materials that effectively store short-wave radiation.[2][3] Waste heat generated by energy usage is a secondary contributor.

20. Nov 28, 2014

### Baconfish

Aha so basically removal of trees and lots of black asphalt..

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