Cheapest now a days is Biomass power stations. When natural gas is avaialble plenty, Gas Turbine based power stations also works out. Nuclear based power stations is latest trend. But all these are depending upon fossil fuels. Solar, wind and sea waves generate less power hence not useful for large comunity service. Research is going for using helium gas as alternate resource for electricity production. ISRO struggling in research to establish camps on moon and deep space transport to bring helium from moon to earth. If we succeede our energy needs will be met cheaply.