. Legend: . The first table in Sheet: "Saved money per year(kWh/kWp * Price)" calculates how much money will an PV roof system save (from not buying electricity from the grid) given the kWh one kWp produces per year and the price of electricity. Assuming one uses all the electricity produced by the PV system and the price of electricity stays constant in the following years. . . . . . . . The second table in Sheet "Years for system payback" takes a number from the first table and calculates how many years it will take for one kWp to pay back given the installation cost. . . . . . . Note: It is also interesting to exclude the "soft cost" (non-hardware BoS) of a PV system and make the same calculations only for the hardware. This is helpful when one is installing the PV system by him/her self and not paying for labor or other expenses. . . . . . Hope you find it helpfull. . . Near accurate examples: . Bulgaria: 1250 kWh/kWp with 0.09 eurocents/kWh saves 113 euros per year. With installation cost of 12000-1500 euro/kWp the result is 8-12 years . . . Germany: 900 kWh/kWp with 0.25 eurocents/kWh saves 225 euro per year, 1700 euro/kWp the result is around 7-8 years . . . Italy : 1350+ kWh/kWp and 0.20 eurocents/kWh saves 270 euro and with Germany installation cost - the result is less than 7 years . . . Data taken from (July 2012): . www.energy.eu . http://www.solarwirtschaft.de/preisindex . http://re.jrc.ec.europa.eu/pvgis/ . Same page but in Google Docs for better column/row selecting: . https://docs.google.com/spreadsheet/ccc?key=0Ahl2afL-jL0BdEVGU3dsbllfTzlxMEV0aTNqT0d5Nnc#gid=2 .