Are there any temperature vs efficiency charts for PV's and are there PV's designed to be efficient at higher temperatures. The idea is to maximize energy capture by circulating a cooling fluid, water for example, that keeps the cells at or about optimum temperature but collects that otherwise wasted heat for CHP purposes. Even if somewhat more expensive the fewer cells needed reduce costs and you have the added benefit of heating your home in cold climates.
PV's get less efficient with increasing temperature, due to fundamental physics. I think there are some photocatalytic systems (solar to chemical: hydrogen and carbon monoxide generation seem to be the two main tracks of research) that remain efficient at fairly high temperatures.
Moderately-high temperatures can also degrade the cells gradually, causing permanent changes that degrade efficiency but don't destroy the cells in one fell swoop.
A cooling fluid is a great idea. I think some PV arrays produce significant voltages, in which case a non-conductive fluid would be in order, in case a leak should develop. This might be a pre-warmer for a solar thermal collector, so that the temperature of water leaving the system of panels can be a higher temperature than you'd prefer for the PV arrays.
In hot climates, it's common to design PV collectors with a gap above the roof, and a slant, such that the thermal draft raws (relatively) cool air over the roof from dawn to well after dusk. This helps keep the cells cool, but has an added benefit in making the building below easier to keep cool.
mtnDon Miller wrote: A concentrator also would need tracking through the day to make it most effective. Even then with the way PV module prices have fallen a tracker is often more expensive than adding PV modules to the system.
It's even worse than that: a typical concentrator makes a tracker absolutely necessary. The better the concentrator works, the greater the need for precision alignment. A slight misalignment will mean part of the cell goes completely dark, which can mean a disproportionate drop in efficiency.