Abstract: This invention relates to a low temperature solar thermal power system, which combines the solar hot water collectors with the organic Rankine cycle system using the low critical temperature hydrofluorocarbons (HFC) or hydrocarbons (HC) working fluid for converting solar energy to electrical energy. This invention also relates to systems and methodology for conversion of low temperature thermal energy, wherever obtained, to electrical energy using the low critical temperature hydrofluorocarbons (HFC) or hydrocarbons (HC) working fluid for organic Rankine cycle system to drive an electrical generator or do other work in a cost effective way.