can you get thermal water heating (CHP) at same time panels make elec?

Is there any reason against putting solar thermal hot water heating under a set of solar panels to try and get combined heat and power out of them at the same time? From what I understand power panels mostly convert visible light and not really thermal...
Do panels have to stay cool on the backside to work efficiently so that even heating an airspace could be counterproductive?
I am wondering if the layout of a roof should have separate areas for power and solar thermal water preheating (or even space heating assisting a greenhouse), or if they can somehow be combined.
Do panels have to stay cool on the backside to work efficiently so that even heating an airspace could be counterproductive?
I am wondering if the layout of a roof should have separate areas for power and solar thermal water preheating (or even space heating assisting a greenhouse), or if they can somehow be combined.
Comments
Sun Drum has panels/kits to do this.
Sun Drum
In general I don't think this gains much for you--Unless you simply do not have any other space where you could do solar thermal.
Anyone Combing PV with Solar hot water?
-Bill
On the 13th and 14th I attended a conference, where one of the speakers gave a presentation on grant projects, where they are testing various greenhouses with opaque PV in the skin / roof. It sounded like, the more PVs that go onto a roof, a proportional amount of sunlight is lost coming into the greenhouses, and with that loss the loss of heat.
As they see it; if you want electricity, then cover a site with PV. If you want heat, then cover a site with thermal-panels.