Energy Sources

Primary energy sources can be classified in to two groups: nonrenewable and renewable. Secondary sources are derived from primary sources.


Nonrenewable Energy Sources

Energy from the ground that has limited supplies, in the form of gas, liquid or solid, are called nonrenewable resources.


Natural Gas

Natural gas is a nonrenewable fossil fuel formed hundreds of millions years ago from the remains of plants and animals. Not to be confused with gasoline, it is used for heating buildings and generating electricity.

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Petroleum is a nonrenewable fossil fuel made naturally from decaying prehistoric plant and animal remains. It is a mixture of hydrocarbon molecules that exist sometimes as a liquid or a vapor. It's primarily used for power and transportation, as well as household items.

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Coal is a nonrenewable energy source that is part of the fossil fuels family. It is a combustible sedimentary rock composed mostly of carbon and hydrocarbons, it is primarily used to generate electricity.

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Uranium is a nonrenewable source that makes nuclear energy. It occurs in the nucleus, or core, of an atom. Bonds that hold atoms together contain large amounts of energy that is released in the form of heat.

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Renewable Energy Sources

Energy that comes from a source that’s constantly renewed, such as the sun and wind, it can be replenished naturally in a short period of time.



Hydropower is renewable energy captured from moving water. Nature’s water cycle is important to making hydropower work. Hydropower was one of the first sources of energy used for electricity generation.

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Solar energy is the radiant energy (light or heat) that comes from the sun. Only a small amount of the sun’s energy strikes the Earth but is still an enormous amount of energy.

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Wind energy is used to generate mechanical power or electricity. People have used wind energy for hundreds of years to pump water or grind grain. Wind power has a relatively high output, but only a fraction of its potential is currently used.

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Geothermal energy comes from reservoirs of hot water below the Earth's surface. Wells are drilled into these reservoirs to tap steam and hot water that are brought to the surface for electricity generation and other uses.

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Biomass is any organic matter – wood, crops, seaweed, animal wastes – that can be used as an energy source. Biomass has been used longer than any other energy source. Biomass now makes up only a small percentage of total world energy use.

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Secondary Energy Sources

Energy that is converted from primary sources are secondary sources of energy. Secondary sources of energy are used to store, move and deliver energy in an easily usable form. Examples include electricity and hydrogen.



Electricity is a form of energy resulting from the existence of charged particles (such as electrons or protons), either statically as an accumulation of charge or dynamically as a current. It is a secondary energy source because it is converted from another (primary) source of energy, such as coal, natural gas, oil, nuclear or renewable sources.

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Hydrogen is a secondary source of energy. It stores and transports energy produced from other resources. It is a clean-burning fuel, and when combined with oxygen in a fuel cell, hydrogen produces heat and electricity with only water vapor as a by-product. 

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