Solar plants and energy conservation I'd like to apologise if this question is stupid or if it was asked ten thousand times - I haven't found an answer to it. Quite possibly due to mediocre English or abominable knowledge of physics.
So, let's say that we're able to convert 100% of energy that falls on photovoltaic cell to electricity. This means that NO energy is lost. Now assume that all countries on the planet use these cells. Won't it increase temperature on the Earth? Not that I'm really concerned about it, my guess is that even if we'd cover million square kilometers of Earth with them this change won't be very big (if it would happen), but maybe I'm wrong? Would Earth temperature rise? If yes, why? If not, why? How much?
 A: Running the risk of not understanding your question entirely...
... but solar energy is just converted in electric energy in this scheme. Due to the idealized situation of no energy loss, nothing is in fact converted into heat, so I don't see any reason at all why the temperature would rise. If anything, it would drop.
A: The earth is going to receive an influx of energy (heat) from the sun regardless of whether or not we capture it as electric energy. 
If we don't capture it as electricity, that energy eventually radiates into space.
If we do capture it, once that electricity is used, heat will be released, and that heat will eventually radiate into space.
Thanks, space.
A: Your question is imprecise but I think it can be reduced to "What would be Earth's surface temperature if it would be a blackbody?", because captured energy would be used and radiated as IR.
As you can find on Wikipedia effective temperature of the planet depends on $(1-a)^{0.25}$, where $a$ is albedo ("whiteness") of the planet. Earth's albedo is about 1/3 and in the case of blackbody it's 0. We can estimate that blackbody Earth would have effective temperature $1/(1-1/3)^{0.25}=1.1$ times - from 252K to 277K (4°C) - it's similar to value 5.3°C which can be found on Wikipedia article about greenhouse effect, which is raising Earth's temperature by over 30K. If this greenhouse effect wouldn't change temperature would rise from over ten to about 40°C.
One could think that incredible usage of solar energy would reduce greenhouse effect, but covering the world with black panels would kill all trees, froze ocean and who knows what else, so maybe it's better to cut this speculation here.
