Two Types of Energy

There are two types of energy: primary and secondary.


Primary Energy

Primary energy is intrinsic to nature and does not require conversion to another form.

There are nine major primary energy sources:

icon-geothermal

Geothermal

Geothermal energy is heat in the Earth’s deeper layers. In some regions and countries, like Iceland, hot layers are close to the surface and can economically be used to heat water by circulating it through buried pipes. This heated water can then be used to heat homes and businesses or can be used to make steam to turn turbines.


Coal

Coal is made of biological material compressed and heated by the earth over geologic time. It is a solid and is accessed by mining. Coal is now used almost exclusively for electricity generation in the U.S. with a little bit going to industrial applications. There was a time when it was widely used for transportation and home heating. There aren’t too many people running their cars on coal these days but remember, we used to power transportation with coal. Trains used to require a man or two shoveling coal furiously into the steam engine. Even luxurious ships like the Titanic were powered by coal. Coal used to be the state of the art for transportation. This highlights the fact that things in the energy sector are always changing.


Oil

Oil is ancient biological material that has been compressed and heated over geologic time and is found in a liquid or semi-liquid state in nature, usually deep underground. Oil has high energy density and relatively straightforward transportability, making it a valuable resource for the development of advanced civilization. Unlike coal, petroleum is very infrequently used for electricity generation, while the bulk of it is used for transportation. Most people fill up their automobile fuel tanks with petroleum products at this point in history.


Natural Gas

Natural Gas is ancient biological material that has been compressed and heated over geologic time and is found trapped in geologic spaces deep underground. When brought to the surface, natural gas expands into a gaseous state.


Biofuels

Biofuels include any substance that can be burned or economically converted into something that can be burned, like wood or corn. The term biofuel usually refers to an end product made from readily renewable biological sources.


Wind

Wind energy is harnessed by using moving atmospheric air to turn a turbine. Wind turbines are commonly referred to as windmills, though that term is no longer an accurate moniker for the modern turbines in use today.


Solar

Solar is energy from the sun. There are several methods currently being used to capture the sun’s energy with the most common being direct electrical generation through solar panels. The second method involves concentrating the sun’s energy to heat various substances such as water or salt which creates steam to turn a turbine.


Hydro

Hydro power is generated by capturing energy from flowing water. Today, the most common technique for generating hydro power is the use of dams. Dams capture water behind a wall of some sort and use gravity to pull the water through a turbine as it passes through the elevation change. A second kind of hydro power being explored is tidal turbines. These are embedded in deeper ocean waters that typically maintain a natural current. As the water passes through the turbines, they generate electricity. A third kind of hydro power whose usefulness is being explored is wave energy. Tools are being developed to capture and convert the constant rise and fall of the surface of oceans and seas. Wave energy has not yet become a widely used primary energy source.


Nuclear

Nuclear power is generated by using the heat of a nuclear reaction to convert water into steam and using the expanding volume of the steam to turn turbines that generate electricity. There are over 400 nuclear power stations operating in the world currently.

Conversion Examples

All of these energy sources are valuable because they can be converted into secondary resources. For example, coal is burned for heat, which creates steam, which in turn drives turbines to generate electricity. Oil is refined to produce gasoline, diesel, and jet fuel to power our cars, trucks, trains, ships and planes.


Secondary Energy

In contrast, secondary energy resources do not occur naturally but are obtained from one or more of the primary energy resources. Secondary energy sources include electricity and gasoline. Electricity is produced by burning the primary sources of coal and natural gas, while gasoline is created by refining the primary source of oil. While electricity does exist in nature in the form of lightning, it has not been possible to capture and use that energy source in any significant way. Secondary sources are designed to provide reliable power that can be delivered to the places humans need it, like our vehicle fuel tanks and our electrical wall outlets.

Images: “Wind Turbines” by U.S. Fish and Wildlife Service