I have a thought about generating electricity from roof panels with a water underlayment which would create steam and run a turbine.  I suggest water even though it needs a higher temp because it's duh, not flamable.  I guess black metal panels create the most heat, and since hot air rises the generator would need to be mounted on top of the building.  I live in Hawaii where we are 95% dependent on fossil fuels which are imported.

Why not just use photovoltaic panels to generate electricity?

Photovolaic is still very costly, and I'm interested in new ideas. The solar ovens in Africa really inspire me. A simple foil covered box has shown tremendous results. Often villages there are denuded of firewood, and so people travel larger distances every day to get wood to cook with. Now, these inexpensive boxes radiate enough heat to cook bread in and all of that time hunting for wood is eliminated and used in other ways like growing food. With that in mind, I think photovoltaic cells should be implanted in roofing materials. The problem is conversion and storage of energy in an affordable delivery system. Steam engines and turbines could be a less costly alternative, plus, the hazardous waste issue would be more eco friendly.

To generate steam at sufficient temperature/pressure to run turbines requires concentrators- you can't get there under normal glazings & flat panels. You can get close with purpose-built evacuated tube collectors, but it's more commonly (and cheaply & efficiently) done with single-axis tracking parabolic mirrors and an uninsulated solar-absorptive pipe as the collector in commercial solar-steam plants. African solar cooker temps & efficiencies just won't cut it- it's BARELY steam, not useful-power steam.

On a small scale such as a single-family home, photovoltaics are still the only viable option for solar electricity.

That's very interesting! Thanks! I've been on some very hot metal roofs here in Hawaii, and I thought about mirrors. Geothermal is controversial because of the pollution from the gas, although King Kalakaua researched the idea over 100 years ago. So, my thinking is if solar water heaters work, with some engineering why not steam from roofs.

I'm interested in new options and having discussions with smarter and more educated people than I am. I am an architectural drafter and designer, and a lot of people here live off the grid. Windmills are rare here, although we're seeing them more often. Keep those comments coming!

A really "hot" metal roof might hit 220F, but you'd need over 400F to really do much of anything mechanical with the steam produced. The higher the operating temp, the higher the operating losses (==lower efficiency) so it's really a losing proposition. PV works best when you can keep the temps low (well under 150F), which is why hybrid domestic hot water + PV panels are sometimes useful in residential applications. Rather than letting the PV stagnate at high temp, the DWH loop "cools" the panel down to a more reasonable operational temp for the PV, increasing it's average output while utilizing that thermal energy. (eg: http://www.sundrumsolar.com/files/documents/SunDrum_Total_Energy_Data_Sheet_Rev_C.pdf ) It maximizes the solar usefulness of limited roof/collector area.