the value of solar Thermal & electricity

According to the Appraisal Journal, home value increases by $20 for every $1 reduction in annual utility bills. 
So, a solar energy system that saves $200 per year would add $4,000 to the value of your building.
Investments in energy efficient features, such as solar energy systems, have historically been valued based on how quickly the investment pays for itself. But, such investments are home improvement projects that add value, which can be recovered when the house is sold. 

For solar water heating systems, this added value is often equal to or greater than the out-of-pocket investment, resulting in immediate positive cash flow for the owner if the investment amount had been added to the mortgage.

Read - The Solar Journal, October 1998...