Renewable Energy Sources

Types of Renewable Energy Sources and How They Work



Solar energy is the most inexhaustible source of energy known to humankind, with an expected life span of at least 5 billion years. Enough clean, renewable solar energy falls from the sky in a day to power the world for 27 years. When the sun is shining, solar cells produce electricity. The energy from sunlight, which is intermittent, can be stored in batteries, as hydrogen, or in many other ways. There are two main ways to harness solar energy:

  • Direct conversion to electricity, known as photovoltaics, which most students have seen as solar cells on calculators, solar walkway lights, or pictures of the space station or space shuttle.
  • Thermal conversion to heat or electricity. Sunlight can be used to heat water and buildings, create steam to turn electric generators, or power industrial processes. Other technologies use the sun to provide natural lighting. Passive solar architecture uses building design and materials to keep buildings warmer in winter and cooler in summer.

Two billion people lack access to electricity. Solar energy can provide power to remote areas.
For more information about Solar Energy, please read our Solar Power Frequently Asked Questions



wind turbines
Wind energy produces electricity by turning blades on a wind turbine, similar to a windmill. It is particularly useful in places with strong, frequent winds. Wind energy can be stored in batteries for later use. It is an ecologically sound alternative because it doesn’t produce waste. Although wind power facilities
can be dangerous to raptors (such as hawks), careful siting away from flight pathways and improvements in wind turbine design have substantially reduced the impact on birds.



Geothermal energy comes from the heat inside the Earth that causes hot springs, geysers, and volcanoes. This natural heat can be captured and used to produce electricity. Geothermal energy is already used in places such as New Zealand, Iceland, and the United States to warm buildings and generate electricity.



Biomass energy is produced from energy crops or from waste materials. Heat, electricity, and transportation fuels can be made from plant materials and wastes such as agricultural residues, forest underbrush, and organic human wastes. While wood is still the most widely used source of biomass fuel worldwide (especially in developing countries), other sustainable biomass sources are being developed. Methane gas from landfills produces electricity, corn is converted to alcohol fuels for cars, and certain vegetable oils can substitute for diesel fuel.



Hydroelectric power harnesses the energy in flowing water to generate electricity. Hydropower production can cause environmental harm by flooding habitat and blocking fish spawning. Increasingly, efforts are being made to obtain hydroelectric power in ways that are less damaging to freshwater habitats and fish.


Ground Source Heat Pumps

Ground source heat pumps are heating/cooling systems that transfer heat to or from the ground. A medium circulates in pipes in the ground to transfer heat between the building and the ground. The GSHP is one of the most efficient residential heating and cooling systems available today, with heating efficiencies 50 to 70% higher than other heating systems and cooling efficiencies 20 to 40% higher than available air conditioners. That directly translates into savings for you on your utility bills.
For more information, check out our Ground Source Heat Pump Frequently Asked Questions


Nuclear energy is produced by the splitting of radioactive uranium atoms. Although it is not a source of global warming pollution, using this type of energy has other environmental consequences. Along with the risk of accidents, radioactive wastes are dangerous to all life for tens of thousands of years. There is no safe way currently to dispose of them.