I just saw an amazing new photovoltaic product demonstration. NEXT company is selling double pane windows that also harvest solar energy.
The sales demonstation had light passing through a sample of the window. Mind you one can easily see through this window. The window was wired to a little fan. I blocked the light with my hand and watched the fan stop. Impressive!.
The salesman reported the windows cost about 30% more than high quality windows and can pay for themselves within 3 years. In fact-if one counts incentives, the payback can get better.
No welded steel support racks on the roof. No sacrifice of roof area.
The windows have up to a 75% visible light transmission.
Wow! It is great to see innovations like this. The intent of zero net energy buildings without significantly raising building cost is looking more and more realistic.