Renewable energy

Wind power

Windpower harnesses the energy generated by the movement of air in the earth’s atmosphere to drive electricity-generating turbines. Although humans have used wind power for hundreds of years, modern turbines reflect significant technological advances over early windmills and even over turbines from just ten or twenty years ago.

Wind resource potential varies significantly across the United States with substantial resources found in the Midwest and along the coasts.

Winds generally blow more consistently and at higher speeds at greater heights. As wind speed increases, the amount of available energy increases following a cubic function, so a 10 percent increase in speed corresponds to a 33 percent increase in the amount of available energy. Modern turbines continue to grow larger and more efficient--two important factors that allow a single turbine to produce more usable energy.  Improved materials and design have allowed for larger rotor blades and overall improvements in efficiency (measured as total energy production per unit of swept rotor area,given in kilowatt-hours per square meter) and greater gross generation.

Description

Wind technologies come in a variety of sizes (larger turbines can generally produce more electricity), and styles. Since wind is a variable and uncertain resource, wind turbines tend to have lower capacity factors than conventional power plants that provide most of the nation’s energy. A power plant’s “capacity factor” provides a measure of its productivity by comparing its actual power production over a given period of time with the amount of power the plant would have produced had it run at full capacity over that period. Conventional coal- and gas-fired power plants generally have capacity factors between 40% to 60%. Wind turbines generally have capacity factors that are closer to 25 to 40 percent.  Wind turbine capacity factors have improved over time with advances in technology and better siting, but capacity factors are fundamentally limited by how much the wind blows.

SOLAR

Solar power harnesses the sun’s energy to produce electricity as well as solar heating and cooling. Solar energy resources are massive and widespread, and they can be harnessed anywhere that receives sunlight. The amount of solar radiation, also known as insolation, reaching the earth's suface every hour is more than all the energy currently consumed by all human activities each year. A number of factors, including geographic location, time of day, and current weather conditions, all affect the amount of energy that can be harnessed for electricity production or heating purposes.

Solar energy can be captured for electricity production using solar photovoltaics and concentrating solar power. A solar or photovoltaic cell converts sunlight into electricity using the photoelectric effect.  Typically, photovoltaic is found on the roofs of residential and commercial buildings.  Concentrating solar power uses lenses or mirrors to concentrate sunlight into a narrow beam that heats a fluid, producing steam to drive a turbine which generates electricity. Concentrating solar power projects are larger-scale than residential or commercial PV and are often owned and operated by electric utilities.

Biomass

Biomass energy sources are used to generate electricity, provide direct heating and can be converted into biofuels as a direct substitute for fossil fuels used in transportation. Unlike intermittent wind and solar energy, biomass can be used continuously or according to a schedule. Biomass is derived  from wood, waste, landfill gas, crops and alcohol fuels. Traditional biomass, including waste wood, charcoal and manure has been a source of energy for domestic cooking and heating throughout human history. In rural areas of the developing world, it remains the dominant fuel source. 

water 

Water power captures the energy of flowing water in rivers, streams and waves to generate electricity. Conventional hydropower plants can be built in rivers with no water storage (known as “run-of-the-river” units) or in conjunction with reservoirs that store water, which can be used on an as-needed basis. As water travels downstream, it is channeled down through a pipe or other intake structure in a dam (penstock).  The flowing water turns the blades of a turbine, generating electricity in the powerhouse, located at the base of the dam.