I just attended a talk on new photovoltaics, and it reminded me of a question I've had before. All of these systems generate a lot of waste heat. Shouldn't there be a smart way to couple these systems to some sort of heat engine and get some added power generation that way? Seems this should be easier than spending millions of dollars to get another 5% in electrical conversion efficiency. I can't be the first one to think of this, so any suggestions for further reading would be appreciated.
photovoltaic panels coupled with solarthermic heating of water already exist, but I guess this more useful for the roofs than for powerplants
My guess is that the relatively low temperature of the waste heat from PV cells would make it extremely difficult to use a heat engine with it. The "low-grade" heat would mean that you'd need a relatively large (and expensive) heat engine to get a relatively small amount of usable power out.
A very direct and powerful way of looking at the problem would be by doing an exergy analysis. I'd highly recommend looking into the concept of exergy if you're not familiar with it. It deals precisely with the quality or usefulness of energy.
In general the PV module needs to be at low temperature ("cold") because the electrical efficiency decreases with temperature. On the other hand, the medium (water, oil) for photothermal application needs to be at high temperature to be useful. That contradiction implies that the optimization of a combined system is at best difficult.
You may consider a thermoelectric converter (Seebeck effect) at the backplane of a PV device. There are quite efficient thermoelectric semiconductors available nowadays. But then you need a cold reservoir. Unless you are on a ship or near a river, you will have to use a fan-driven air cooling system, and this would probably use much of the power you want to generate.
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