These external links provide the background to Solar Panels in general and Feed-in Tariffs in particular.
The links were correct as of February 2011.
The regulatory framework: 
(the detailed tariffs are listed on page 48 of the first pdf)
The standard the systems are installed to:
The basis of the calculations are embedded in the above Guide
Real data from across the UK and Europe:
Planning Permission:
Nasa's data on the solar insolation (needs free registration):