Primary energy sources take many forms, including nuclear energy , fossil energy -- like oil , coal and natural gas -- and renewable sources like wind , solar , geothermal and hydropower. These primary sources are converted to electricity , a secondary energy source, which flows through power lines and other transmission infrastructure to your home and business.

Clean Energy. Learn more about energy from solar, wind, water, geothermal, biomass and nuclear. Electric Power. Once at the surface, fluids of various temperatures can be used to generate electricity. The technology for electricity generation from hydrothermal reservoirs is mature and reliable, and has been operating for more than years.

Hydropower harnesses the energy of water moving from higher to lower elevations. It can be generated from reservoirs and rivers. Reservoir hydropower plants rely on stored water in a reservoir, while run-of-river hydropower plants harness energy from the available flow of the river.

Hydropower reservoirs often have multiple uses - providing drinking water, water for irrigation, flood and drought control, navigation services, as well as energy supply. Hydropower currently is the largest source of renewable energy in the electricity sector.

It relies on generally stable rainfall patterns, and can be negatively impacted by climate-induced droughts or changes to ecosystems which impact rainfall patterns. The infrastructure needed to create hydropower can also impact on ecosystems in adverse ways. For this reason, many consider small-scale hydro a more environmentally-friendly option , and especially suitable for communities in remote locations.

Ocean energy derives from technologies that use the kinetic and thermal energy of seawater - waves or currents for instance - to produce electricity or heat. Ocean energy systems are still at an early stage of development, with a number of prototype wave and tidal current devices being explored.

The theoretical potential for ocean energy easily exceeds present human energy requirements. Bioenergy is produced from a variety of organic materials, called biomass, such as wood, charcoal, dung and other manures for heat and power production, and agricultural crops for liquid biofuels.

Most biomass is used in rural areas for cooking, lighting and space heating, generally by poorer populations in developing countries. Modern biomass systems include dedicated crops or trees, residues from agriculture and forestry, and various organic waste streams.

Energy created by burning biomass creates greenhouse gas emissions, but at lower levels than burning fossil fuels like coal, oil or gas. However, bioenergy should only be used in limited applications, given potential negative environmental impacts related to large-scale increases in forest and bioenergy plantations, and resulting deforestation and land-use change.

International Energy Agency Renewables. Intergovernmental Panel on Climate Change Renewable Sources of Energy. UN Environment Programme Roadmap to a Carbon-Free Future. Coal, natural gas, and petroleum formed over thousands of years from the buried remains of ancient sea plants and animals that lived millions of years ago, which is why we also call those energy sources fossil fuels.

Most of the petroleum products consumed in the United States are made from crude oil, but petroleum liquids can also be made from natural gas and coal. Nuclear energy is produced from uranium, a nonrenewable energy source whose atoms are split through a process called nuclear fission to create heat and, eventually, electricity.

Scientists think uranium was created billions of years ago when stars formed. Solar energy from the sun Geothermal energy from heat inside the earth Wind energy Biomass from plants Hydropower from flowing water. Renewable energy sources are naturally replenished.

Day after day, the sun shines, plants grow, wind blows, and rivers flow. Throughout most of human history, biomass from plants was the main energy source. Biomass was burned for warmth and light, to cook food, and to feed the animals people used for transportation and plowing. Nonrenewable energy began replacing most renewable energy in the United States in the early s, and by the earlys, fossil fuels were the main source of energy.

Biomass continued to be used for heating homes primarily in rural areas and, to a lesser extent, for supplemental heat in urban areas.

In the mids, use of biomass and other forms of renewable energy began increasing largely because of incentives for their use, especially for electricity generation. Many countries are working to increase renewable energy use as a way to help reduce and avoid carbon dioxide emissions.

Learn more about historical U. energy use and timelines for energy sources. The chart below shows U. energy sources, their major uses, and their percentage shares of total U. energy consumption in What is energy?

Sources of energy. Units and calculators. energy facts. Use of energy. Energy and the environment. Also in What is energy?