Renewable energy is energy that does not get used up. The wind, the sun, and Earth are sources of renewable energy.

Solar Energy

Solar energy comes from the sun. There are two types: active solar energy and passive solar energy.

Active solar energy uses special technology to capture the sun's rays. The two types are photovoltaic cells (PV cells or solar cells) and mirrors. They focus sunlight in a specific spot to generate electricity. PV cells last for a long time and are efficient.

Passive solar energy does not use equipment. This energy comes from natural sunlight. One example is building a house so that it faces the sun more often. More sun means more heat.

Solar power cannot be used as the only power source in a community. It can be expensive to install PV cells or build structures that use passive solar technology.

Also, it is difficult to say when we will get sunshine. The sunlight we get depends on where we live, the season, and the time of the day.

Wind Energy

Throughout history, people have used the wind's energy. Ancient Egyptians made boats powered by the wind more than 5,000 years ago. In 200 B.C.E., people used windmills to grind grain in the Middle East and pump water in China.

Today, we use wind turbines. Turbines are towers with two or three blades at the top. The wind turns the blades. The blades turn a generator inside the tower. The generator creates electricity. Turbines do not release pollutants into the air.

Groups of wind turbines are known as wind farms. Wind farms can be found near farmland, in narrow mountain passes, and even in the ocean.

If winds are steady, we get cheap electricity. But wind speed depends on the location, time of day and weather. So we cannot rely on it fully. Also, wind turbines are dangerous for bats and birds. They can crash into them.

Geothermal Energy

The center of the planet is extremely hot. It's more than 6,000 degrees Celsius (about 10,800 degrees Fahrenheit). Geothermal energy makes use of this heat.

We can access underground geothermal heat in different ways. One way is to use geothermal heat pumps. Hot water from underground is used to heat houses and other buildings. Geothermal heat pumps can be used to heat houses, sidewalks, and even parking lots.

Another way to use geothermal energy is with steam. In some areas of the world, there is underground steam that naturally rises to the surface. The steam can be piped straight to a power plant.

In Iceland, there are large reservoirs of underground water. Almost 90 percent of people in Iceland use geothermal as an energy source. They heat their homes and businesses.

Biomass Energy

Biomass is material that comes from plants or animals. Plants create energy from the sun through a process called photosynthesis. This energy is stored in the plants even after they die.

Trees, branches, bark, and recycled paper are sources of biomass energy. Manure, garbage, and crops, like corn, soy and sugar cane, can also be used for biomass.

We get energy from biomass by burning it.

Biomass can also be made into biofuel. It can power cars and trucks when mixed with gasoline. Biofuels release less harmful pollutants than gasoline.

Biomass can be stored and used when it is needed. However, to grow crops for biofuels, we need large amounts of land and pesticides.

Hydroelectric Energy

Hydroelectric energy is made by flowing water. Most hydroelectric power plants are located on large dams. Dams control the flow of a river.

Dams block the river and create a human-made lake. A small amount of water is forced out through tunnels in the dam. This water turns huge turbines and generates electricity.

Hydroelectric energy is inexpensive and reliable. Water is constantly flowing and so the dam does not depend on the weather and time of day.

But when a river is dammed, it creates a large lake behind the dam. This lake can drown the original river habitat and sometimes entire towns.

Other Renewable Energy Sources

Scientists and engineers are working to make use of other renewable energy sources. Three promising examples use ocean tides, waves in water, and algae.

Tidal energy uses ocean tides to generate electricity. Moving tides turn the blades of a turbine.

Wave energy uses waves from the ocean, lakes, or rivers. They work in the same way as tidal energy.

Algal fuel is a type of biomass energy that uses the chemicals in seaweed to create a clean and renewable fuel. This kind of fuel does not need the acres of cropland that other biofuel sources do.

Renewable Energy
This building uses wind turbines, solar panels, and geothermal heat pumps.
active solar energy

energy from the sun that is increased by the use of electricity or other mechanical equipment.


energy source derived directly from organic matter, such as plants.


living organisms, and the energy contained within them.

biomass energy

renewable energy derived from living or recently living organisms, mostly plants.

biomass feedstock

crop, residue, and other organic material that can be used to produce energy on an industrial scale.


maintaining a steady, reliable quality.


the extremely hot center of Earth, another planet, or a star.


agricultural produce.


structure built across a river or other waterway to control the flow of water.


performing a task with skill and minimal waste.


set of physical phenomena associated with the presence and flow of electric charge.


to give off or send out.


conditions that surround and influence an organism or community.


water that is not salty.


liquid mixture made from oil and used to run many motor vehicles.


to create or begin.


machine that converts one type of energy to another, such as mechanical energy to electricity.


heat energy generated within the Earth.

geothermal heat pump (GHP)

heating or cooling system that pipes water in a continuous loop from wells drilled into the Earth through the space being heated or cooled, and back again.


natural hot spring that sometimes erupts with water or steam.

green roof

top of a residential or industrial building that is wholly or partially covered in vegetation.


energy generated by moving water converted to electricity. Also known as hydroelectricity.


science and methods of keeping clean and healthy.


activity that produces goods and services.


molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.


molten, or partially melted, rock beneath the Earth's surface.


energy resources that are exhaustible relative to the human life span, such as gas, coal, or petroleum.


having to do with facilities or resources located underwater, usually miles from the coast.

passive solar energy

power from the sun that requires no other energy or mechanical system.


natural or manufactured substance used to kill organisms that threaten agriculture or are undesirable. Pesticides can be fungicides (which kill harmful fungi), insecticides (which kill harmful insects), herbicides (which kill harmful plants), or rodenticides (which kill harmful rodents.)


process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.


able to convert solar radiation to electrical energy.


chemical or other substance that harms a natural resource.

radiant barrier

reflective area that prevents heat transfer.

renewable energy

energy obtained from sources that are virtually inexhaustible and replenish naturally over small time scales relative to the human life span.


to supply or refill.


natural or man-made lake.


overflow of fluid from a farm or industrial factory.


marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria.


small sediment particles.


radiation from the sun.


energy produced as ocean waters surge in and out with tides.


rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun.

wave energy

energy produced by ocean waves.


state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

wind farm

area with a large group of wind turbines, used to generate electric power.


instrument that generates power from the force of wind rotating large blades.

wind turbine

machine that produces power using the motion of wind to turn blades.