Here is a new kind of solar cell, using nano scale antennas, that can convert infra read (heat) radiation into electricity.

http://www.sciencefriday.com/program/archives/200808221

Using an antenna tuned to the resonant frequency of IR light is very efficient, theoretically you should be able to get 90% efficiency or more.  Imagine:

1. Putting IR collectors on the interior walls in your house to collect IR radiation, cool the room and generate electricity at the same time.
2. Rooftop IR collectors to collect heat energy from the air, even at night.
3. Lining the engine compartment of your hybrid car with IR collectors to collect waste heat to charge the batteries while the engine is running and even after you turn the engine off.

The waste energy of most machines (and chemical reactions) always comes out as heat.  If you can convert the heat back into useful energy (electricity) you should be able to achieve near 100% efficiency from any kind of machine. 

In fact, if the working part of the machine is kept in a vacuum bottle, like a thermos, the ONLY way it can radiate energy is as IR radiation.  In this way you could capture 100% of the waste energy from any machine.

For example, there is a new catalyst which can be used to extract hydrogen from ethanol.  Just add the catalyst plus heat.  The waste from the reaction comes out as heat, so if you put the whole reactor inside a vacuum chamber (really just a double walled vessel with a vacuum between the walls), now line the inside of the OUTER wall with the IR collector, and 100% of the waste heat is collected as electricity.

Same thing is true of a hydrogen fuel cell.  Hydrogen fuel cells convert hydrogen plus oxygen to electricity, but there is some waste and the waste comes out again as heat.  Again, put the whole thing in a double walled vessel, with a vacuum between the walls, all the waste comes out as heat, which becomes IR radiation, which is collected again using IR collectors (with 90%+ efficiency) and now you have a hydrogen fuel cell with 90%+ efficiency. 

See a trend here?  Any kind of technology can become 90%+ efficiency by collecting waste heat as IR using IR collectors.

Cool stuff.