- solar energy (light, radiant energy)
- PV cell – electricity
- solar thermal – steam – turbine – generator
- geothermal energy (heat energy)
- heat energy (water/steam) – turbine – generator
- wind, hydropower, wave/tidal (kinetic energy)
- kinetic energy – turbine – generator
- biomass (chemical energy)
- refined to combustible fuels (eg. firewood from trees, ethanol from corn, bio-diesel from vegetable oil)