The Leicester Mercury in England provided an interesting news item about an aerial photography firm that has a prototype website allowing people to assess if a building is suitable for a PV system. This is a very interesting concept.
Aerial photography firm Bluesky launches Eagle energy website
An aerial photography firm has launched a prototype website allowing people to assess if a building is suitable for solar-powered energy.
Bluesky International, based in Coalville, has set up Eagle, which assesses whether a building can have solar power by using high resolution geographic data.
The information is combined with energy tariffs, expected consumption, cost of installation and available subsidies to calculate the potential return on investment for solar renewable energy systems. James Eddy, technical coordinator for the Eagle project and director of UK aerial mapping company Bluesky, said: “The Eagle platform provides easy to understand, objective yet accurate information about renewable energy systems for a specific dwelling or building.
“This allows for the calculation of return on investment for any given scenario as well as potentially reduced installation costs. “This can then be used to target consumers with information and educational campaigns.”
Energy in Demand - Sustainable Energy - Rod Janssen 
When I was researching installers for my home PV system one of them used Google Maps to make a first quick assessment. Eagle is taking the idea one step further.
I’d still want to do my own NPV and IRR calcs before investing!