Green Energy Engineering

Solar, wind, and hydropower sources are ultimately all solar. Direct solar includes photovoltaics (PV), solar thermal electric power plants, and solar thermal heat. Hydropower and wind energy are harnessed by hydroelectric dams and windmills, both of which can directly produce electricity. PV uses solar photons provided they are above the bandgap of the photovoltaic collector. The bandgap also limits the efficiency of solar PV. Solar thermal power converts virtually all of the solar infrared energy to heat and uses it to run a conventional heat-to-electricity power plant. A less sophisticated application is for home heating, which requires lower temperatures and leads to proportionally less heat losses. Windmill farms directly convert incoming kinetic wind energy into mechanical energy, restricted only by the Betz limit. Hydropower is the most developed of the indirect solar power producers. It converts almost 100% of the potential energy of water upstream of a dam directly into electric power.