Green Energy: Facts

What is Energy?

Bulb Suns

Energy is the ability to do work. Work can be carrying, moving or lifting something, warming something, or lighting something. Energy is needed to make our world work.

Forms of Energy


Energy comes in many different forms — heat (thermal energy), light (radiant energy), mechanical, electrical, chemical, and nuclear energy. These different forms of energy are the result of different physical processes such as the action of photons in light or the combining of molecules in a chemical process.

All matter is a form of energy. Throughout history people have worked to find substances whose potential energy can be converted into a form we find useful. For instance, wood is a useful energy source because it is easily burned, and when burned, it generates both heat (thermal energy) and light (radiant energy).

When we burn wood for energy, we're using up the source. After we've burnt the wood, there's less of it in the world — until we grow some more! Scientists know that some energy sources can be replenished much faster than others. So they've divided them into two groups — renewable (an energy source that we can use over and over again) and non-renewable (an energy source that we are using up and cannot recreate in a short period of time).

Nonrenewable Energy

Nuclear Power

Today we get most of our energy from nonrenewable sources. These include the fossil fuels — oil, natural gas, and coal. Fossil fuels were formed from the remains of dead plants and animals by heat from the Earth's core and pressure from rock and soil applied over millions of years.

Our other major nonrenewable energy source comes from the element uranium. Through a process of nuclear fission we split uranium's atoms to create the heat used to make electricity.

The sites at the links below provide good overviews of each of these energy sources.

Renewable Energy


Renewable energy comes from natural processes such as sunlight, wind, or moving water that are continuously replenished. Solar energy comes from the sun and can be turned into both electricity and heat. Geothermal energy comes from heat inside the earth. Many homes and businesses in the city of Boise, including the Capitol building, get their heat from this source. Wind, biomass, river waters and ocean tides are also sources of renewable energy, mostly to generate electricity.

The sites at the links below provide good overviews of each of these energy sources.

Green Energy

Green Energy

Renewable energy sources are sometimes called Green Energy. The term “Green Energy” describes energy that is produced and used in ways that are considered “environmentally friendly.” So, to be green, energy must be both renewable and non-polluting.

Green energy has two types of benefits. First, because it's renewable, we won't use it up and run out of it. Second, because it's non-polluting, it won't generate harmful emissions or waste products that will hurt our air, land or water.

There are advantages and disadvantages to all sources of energy — green or non-green. Some disadvantages to renewable sources are cost, harmful waste products, danger to wildlife, and sporadic availability. Scientists are always looking for better sources of energy that might limit the disadvantages and make them more 'Green.'


Solar Panel

The sun is the most inexhaustible, renewable source of energy we know. Energy from the sun is called solar energy. We can use solar energy in two ways.

One is for heat. A flat plate, typically on a building roof, collects the sun's radiation. The radiation heats a liquid. The heated liquid travels through pipes to a device with a heat exchanger. If we're trying to make hot water for bathing, cleaning or cooking, the device will be a hot water tank. If we're trying to heat a whole house or building, the device will be a blower so our solar-generated heat can be distributed throughout the building.

We can also use solar energy to create electricity. Again, we need a flat panel to collect the sun's light energy. But instead of heating liquid-filled pipes in the panel, a solar electric panel has a whole lot of small devices called photovoltaic cells that turn the light energy into electricity. Sometimes a building generates more solar electricity than it can use. With the proper equipment, the excess can be passed on to the local electric utility.

Energy.gov has some good illustrations of solar water heating systems. And here are some nice graphics on solar electricity.


Geo Thermal

Geothermal energy comes from the heat inside the earth. Miles below the earth's surface lies hot rock called magma. The heat from this rock rises to the earth's crust in certain spots and warms underground pools of water. In places like Yellowstone National Park, the hot water escapes through cracks in the crust and forms geysers like Old Faithful. In southern Idaho, the underground hot water stays put, and scientists have been able to extract the heat energy and use it to heat homes, commercial buildings, and swimming pools.

Energy.gov offers an animated graphic showing how a geothermal power plant works.


Wind turbines

Windmills have been used for a long time to grind grains and pump water from wells. Modern windmills, called wind turbines, are used to generate electricity. The energy in the wind turns two or three propeller-like blades. The blades are connected to several more parts which spin a generator that creates the electricity.

Wind turbines can be very big and built in groups known as wind farms. Small wind turbines can be used to charge batteries.

Energy.gov has a good animated graphic showing how a turbine works.



The water in rivers can be used for energy. This is called hydropower. A dam across a river creates a large lake behind it. Water from the lake flows through machines called turbines which are connected to generators that make electricity. One large dam with with many turbines can make electricity for whole cities!

Visit Energy.gov for an animated graphic that illustrates how hydropower works.

Ocean Power


Did you know the oceans have a lot of stored energy? We may be able to unlock that potential by using the ocean's tides, waves, and heat. 70% of the earth's surface is covered with water . . . that's a lot of water that can be used for energy!

There are three basic ways to use the oceans for their energy. We can use the ocean's waves, or use the oceans high and low tides, or we can use temperature differences in the water.

We all love watching a sailboat bob on the water or listen to waves crashing on the shore. Scientists are experimenting with different ways to capture the energy in that moving water and turn it into electricity. This Northwest National Marine Renewable Energy Center site shows some of the technologies scientists are developing.

Ocean tides are caused by the gravitational pull of the moon and sun, and the rotation of the earth. They happen twice a day, every day, 365 days a year. Tidal power is generated when a turbine is placed where it can capture the rise and fall of the tidal movements. There aren't many places in the world where this works, because the difference between high and low tides must be more than 16 feet. While tidal power isn't widespread today, it has been used for a long time — when Rome ruled England, tide mills were created to grind grain into flour for bread and other foods.

A third way to get energy from the oceans is by using the difference in temperature between hot water on the surface of the ocean and cooler, deeper waters beneath to drive a heat engine. The heat engine is connected to a generator which makes the electricity. These devices need a difference of at least 20° in order to work well. The best place to find these temperature extremes is in the tropics.



You may be surprised to learn that the countryside can provide excellent sources of energy. Dead trees, left-over crops, sawdust, and clippings can be used to produce electricity and fuel. These sources are called biomass.

There are two basic ways that biomass can be used to generate energy. Biomass such as wood can be burned directly for heat and light. Or, we can use micro-organisms to break down biomass such as grasses and crop residue to create gases or liquid fuels. The gas can be burned to generate electricity. The liquid fuel can be added to oil-based gasoline to power cars and other motor vehicles.

The trash we produce everyday can also be used as fuel. When waste is burned in incinerators it gives off heat which can be used to make electricity or to heat buildings. If waste is buried in a landfill, the gas it gives off as it decomposes can be collected and used. View a graphic (PDF) of how a waste-to-energy plant works.

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