Energy Sources

Note: Some of the information on the other Renewable Energy pages comes from "Drawdown", a recent book edited by Paul Hawken that summarizes what can be done to stop climate change. 

The modern era of global warming began around 1970, after a long stretch of relatively flat temperatures, and the past three years mark the first time in that period that three records were set in a row. Of the 17 hottest years on record, 16 have now occurred since 2000. CO2 concentration was 280ppm pre-industrial age and is now 402ppm, increasing by 2ppm per year.


The 5th Assessment Report (AR5) (IPCC, 2013-2014) published by the Intergovernmental Panel on Climate Change (IPCC) revealed that temperatures will continue to rise as long as anthropogenic greenhouse gases (GHGs) are emitted into the atmosphere and that the climate will not stabilize unless GHG emissions can ultimately be brought down to zero.


The IPCC, based on a voluntary commitment signed off last year by almost every government in the world, estimated a remaining carbon budget of 1,000 GT of CO2 with 2011 as a base to give a 66% chance of staying under 2°C. Subtract the roughly 150 GT we’ve already burned since then and that leaves about 850 GT for all sources of CO2. That is a third of the 2,795 GT that would be released if all the world’s proven oil, coal and gas reserves were burned. Therefore two-thirds of the fossil fuel must stay in the ground.

Non-renewable Energy Sources



Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite. Anthracite contains 86%–97% carbon, and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2015. Bituminous coal contains 45%–86% carbon and it accounted for 45% of total U.S. coal production in 2015. Bituminous coal is used to generate electricity and is an important fuel and raw material for making iron and steel. Subbituminous coal typically contains 35%–45% carbon, and it is about 47% of total U.S. coal production in 2015. Lignite contains 25%–35% carbon and accounted for 8% of total U.S. coal production in 2015. Coal was the source of about 30% of the electricity generated in the United States in 2016.


Power plants make steam by burning coal, and the steam turns turbines (machines for generating rotary mechanical power) to generate electricity. Coal can be turned into gases and liquids that can be used as fuels or processed into chemicals to make other products. These gases or liquids are sometimes called synthetic fuels or synfuels.


Several principal emissions result from coal combustion:

sulfur dioxide (SO2), which contributes to acid rain and respiratory illnesses, nitrogen oxides (NOx), which contribute to smog and respiratory illnesses, particulates, which contribute to smog, haze, and respiratory illnesses and lung disease, carbon dioxide (CO2), which is the primary greenhouse gas produced from the burning of fossil fuels, mercury and other heavy metals, which have been linked to both neurological and developmental damage in humans and other animals, and fly ash and bottom ash, which are residues created when coal is burned at power plants.


Crude oil 

Crude oil is a mixture of hydrocarbons that formed from plants and animals that lived millions of years ago. Crude oil is a fossil fuel, and it exists in liquid form in underground pools or reservoirs, in tiny spaces within sedimentary rocks, and near the surface in tar (or oil) sands. Petroleum products are fuels made from crude oil. Crude oil is used to make the petroleum products we use to fuel airplanes, cars, and trucks; to heat homes; and to make products such as medicines and plastics. Although petroleum products make life easier, finding, producing, and moving crude oil may have negative effects on the environment. Very little electricity comes from oil.

The currently applied technology for producing oil and gas from various installations results in two main types of emissions, namely:

  • Combustion gases consisting of carbon dioxides and minor amounts of carbon monoxide, nitrous oxide, N2O, SO2, and un-combusted hydrocarbons (methane and volatile organic compounds (VOCs)).

  • Hydrocarbons consisting of methane and primarily aliphatic VOCs vented to the atmosphere or escaping from the hydrocarbon processes through fugitive emissions.


Natural Gas

Natural gas occurs deep beneath the earth's surface. Natural gas consists mainly of methane, a compound with one carbon atom and four hydrogen atoms. Natural gas also contains small amounts of hydrocarbon gas liquids and nonhydrocarbon gases. We use natural gas as a fuel and to make materials and chemicals. Most of the natural gas consumed in the United States is produced in the United States. Some natural gas is imported from Canada and Mexico in pipelines. A small amount of natural gas is also imported as liquefied natural gas. Natural gas transmission pipelines are wide-diameter pipelines. They are often the long-distance portion of natural gas pipeline systems that connect gathering systems in producing areas, natural gas processing plants, other receipt points, and the main consumer service areas. Storage of natural gas during periods of low demand helps to ensure that sufficient supplies of natural gas are available during periods of high demand. The United States used about 27.5 trillion cubic feet (Tcf) of natural gas in 2015, the equivalent of 28.3 quadrillion British thermal units (Btu) and 29% of total U.S. energy consumption.


Nuclear energy

Nuclear power plants use heat produced during nuclear fission to heat water to produce electricity. In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains uranium, a non-renewable fuel. The United States has 99 nuclear reactors at 61 operating nuclear power plants located in 30 states. Nuclear power has supplied about one-fifth of annual U.S. electricity since 1990.


Unlike fossil fuel-fired power plants, nuclear reactors do not produce air pollution or carbon dioxide while operating. However, the processes for mining and refining uranium ore and making reactor fuel all require large amounts of energy. Nuclear power plants also have large amounts of metal and concrete, which require large amounts of energy to manufacture. If fossil fuels are used for mining and refining uranium ore, or if fossil fuels are used when constructing the nuclear power plant, then the emissions from burning those fuels could be associated with the electricity that nuclear power plants generate. The primary environmental concern related to nuclear power is the creation of radioactive wastes such as uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. 

Large hydropower

Hydropower from power stations 30mw and larger are considered non-renewable even though they don't emit greenhouse gases. However, large dams can emit methane and do impact fish passage.

Renewable Energy Sources


Small Hydropower (under 30mw)

Hydropower is the largest renewable energy source for electricity generation in the United States. In 2016, hydropower accounted for about 6.5% of total U.S. utility-scale electricity generation and 44% of total utility-scale electricity generation from all renewable energy. Some environmental groups including the Sierra Club do support hydropower, but only in the realm of the “small-scale.” When a dam is constructed to facilitate a hydroelectric project, the biological system which had existed in the formerly free-flowing river prior to a dams construction is disrupted, or in some cases, destroyed.

Some hydro-powered facilities, which include the reservoir powering it, indeed do not meet the “zero greenhouse gas” benchmark either. When a lake or reservoir is created for a conventional hydroelectric project, it results in what is called “reservoir emissions.”


Solar Energy

The amount of solar energy that the earth receives each day is many times greater than the total amount of all energy that people consume. Sunlight is composed of photons, or particles of solar energy. Low-temperature solar thermal collectors absorb the sun's heat energy to heat water or to heat homes, offices, and other buildings. Concentrating solar energy technologies use mirrors to reflect and concentrate sunlight onto receivers that absorb solar energy and convert it to heat. We use this thermal energy for heating homes and buildings or to produce electricity with a steam turbine or a heat engine that drives a generator.


Photovoltaic cells generate direct current (DC) electricity. This DC electricity can be used to charge batteries that, in turn, power devices that use direct current electricity. Nearly all electricity is supplied as alternating current (AC) in electricity transmission and distribution systems. Devices called inverters are used on PV modules or in arrays to convert the DC electricity to AC electricity. PV systems can supply electricity in locations where electricity distribution systems (power lines) do not exist, and they can also supply electricity to an electric power grid.


Passive solar space heating happens when the sun shines through the windows of a building and warms the interior. Building designs that optimize passive solar heating usually have south-facing windows that allow the sun to shine on solar heat-absorbing walls or floors during the winter. Window overhangs or shades block the sun from entering the windows during the summer to keep the building cool.


Active solar heating systems use a collector and a fluid that absorbs solar radiation. Fans or pumps circulate air or heat-absorbing liquids through collectors and then transfer the heated fluid directly to a room or to a heat storage system. Active water heating systems usually have a tank for storing solar heated water.


Solar energy does not produce air or water pollution or greenhouse gases. However, using solar energy may have some indirect negative impacts on the environment. For example, some toxic materials and chemicals are used to make the photovoltaic (PV) cells that convert sunlight into electricity. Some solar thermal systems use potentially hazardous fluids to transfer heat.

As with any type of power plant, large solar power plants can affect the environment near their locations. Clearing land for construction and the placement of the power plant may have long-term effects on habitat areas for native plants and animals. Some solar power plants may require water for cleaning solar collectors and concentrators or for cooling turbine generators. Using large volumes of ground water or surface water in some arid locations may affect the ecosystems that depend on these water resources. In addition, the beam of sunlight a solar power tower creates can kill birds and insects that fly into the beam. For a more detailed explanation, click on button. 


Wind Energy

Wind turbines use blades to collect the wind’s kinetic energy. Wind flows over the blades creating lift (similar to the effect on airplane wings), which causes the blades to turn. The blades are connected to a drive shaft that turns an electric generator, which produces the electricity. In 2016, wind turbines in the United States were the source of nearly 6% of total U.S. utility-scale electricity generation. The amount of electricity generated from wind has grown significantly since 2000. Electricity generation from wind in the United States increased from about 6 billion kilowatthours (kWh) in 2000 to about 226 billion kWh in 2016. Wind turbines can affect the environment near their locations such as birds flying into the blades.


Geothermal Energy

The slow decay of radioactive particles in the earth's core, a process that happens in all rocks, produces geothermal energy. The inner core is solid iron and is surrounded by an outer core of hot molten rock called magma. The mantle surrounds the core and is about 1,800 miles thick. The mantle is made up of magma and rock. The crust is the outermost layer of the earth. The crust forms the continents and ocean floors. The earth's crust is broken into pieces called plates. Magma comes close to the earth's surface near the edges of these plates, which is where many volcanoes occur. The lava that erupts from volcanoes is partly magma. Rocks and water absorb heat from magma deep underground. People around the world use geothermal energy to heat their homes and to produce electricity by drilling deep wells and pumping the hot underground water or steam to the surface. People can also use the stable temperatures near the surface of the earth to heat and cool buildings. California generates the most electricity from geothermal energy. The Geysers dry steam reservoir in northern California is the largest known dry steam field in the world and has been producing electricity since 1960. In 2016, U.S. geothermal power plants produced about 17.4 billion kilowatthours (kWh), or 0.4% of total U.S. electricity generation.



Biomass is organic material that comes from plants and animals, and it is a renewable source of energy. Biomass contains stored energy from the sun. Plants absorb the sun's energy in a process called photosynthesis. When biomass is burned, the chemical energy in biomass is released as heat. Biomass can be burned directly or converted to other useable forms of energy such as methane gas or transportation fuels such as ethanol and biodiesel. Biomass fuels provided about 5% of the primary energy used in the United States in 2016. Of that 5%, about 48% was from biofuels (mainly ethanol), 41% was from wood and wood-derived biomass, and about 11% was from the biomass in municipal waste. Researchers are trying to develop ways to use more biomass for fuel.