A method of measuring, monitoring and comparing power generation of at least two renewable power systems, comprising the steps of; providing at least two renewable power systems, at least one data server, at least one generation monitoring device in communication with at least one at premise renewable power system and at least one communication node in communication with at least one of renewable power system, generation monitoring device and data server, determining at least one diagnostic variable for each renewable power system and saving in the data server; determining at least one system coefficient for each renewable power system and saving in the data server; determining the energy generated by each renewable power system; wherein the data server determines comparative information based upon at least one of: background constant, diagnostic variable, system coefficient and energy generated to determine a comparative value of the renewable power system.