Green Energy

Green Energy Facts

Green Energy ['grēn] ['ĕn-ûr-jē]

Energy that is both renewable and can be produced in a way that protects the natural environment.

What is Energy?

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

9V battery

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


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 atoms to create the heat used to make electricity.

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

men working at an oil field

Renewable Energy

image representing 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 plug

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.'


the sun on the horizon

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.

solar panels has some good illustrations of solar water heating systems.


geothermal collection plant in Iceland

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


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. 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 many turbines can make electricity for whole cities!

Visit for an animated graphic that illustrates how hydropower works.

hydro electric dam

Ocean Power

ocean wave ripples

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 listening 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 Pacific Marine 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.

the gravitational pull of the Moon and the Sun on tides
the gravitational pull of the Moon and the Sun on tides diagram

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, leftover 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.

Cycle of Biomass Energy

The trash we produce every day 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 of how a waste-to-energy plant works.

Top 10 Questions

November 2007

Thanks to Professor Jon Van Gerpen, University of Idaho, and Robert Neilson, Idaho National Laboratory for the answers.

  1. Why is it called "green" energy rather than another color like yellow or orange?

    Green is the color that many people think of when they think of renewable energy and environmentally-conscious efforts. So people just started calling it "green energy." It reflects the idea that this kind of energy is easier on the environment than traditional energy sources. (From Pedro in Mrs. Whitesell's class at Gooding Elementary.)

  2. Does ethanol pollute the air more than gasoline?

    No, basically it's doesn't. The components that go into the air when you burn ethanol are typically friendlier than the components you burn with regular gasoline. The difference with ethanol is that when you burn ethanol, you do get small concentrations of some chemicals going into the air that you don't typically see with gasoline. Is it a significant enough difference in the pollutants that we should all be using ethanol versus gasoline? Well, gasoline is getting harder and harder to find. But since ethanol comes from growing plants, it is basically a way to convert solar energy into liquid fuels. With ethanol, what carbon dioxide comes out into the air while you're driving your car is about the same as the carbon dioxide that the plant took out of the air while it was growing. Carbon dioxide is a greenhouse gas. Because of climate change, we want to reduce the amount of carbon dioxide introduced in the air. That's why some folks are concerned about ethanol. (From Mikayla from Victory Star School.)

  3. How much energy does a regular family use in a year?

    We use a lot of energy in this country. While we've got 5% of the world's population, we use about 25% of the world's energy. So we use a huge amount of energy in that regard. It is hard to say how much an individual family uses each year, but it is easy to say we all use too much. (From Carly in Post Falls.)

  4. How big a difference can changing incandescent bulbs to fluorescent bulbs make?

    A lot. It uses about one-quarter the energy of an incandescent light bulb. People have talk about how much energy you would save if every house just changed one normal light bulb to one compact fluorescent and the amount saved is huge. Compact fluorescent bulbs also last maybe five or six times longer, so you don't have to change the light bulbs as frequently. (From Joan in Boise.)

  5. How do electric cars use or save green energy?

    Electric cars save energy or are more "green" because they typically don't use gasoline or diesel or other fossil fuels. There are at least three different kinds of cars: those that are pure electrics that just use batteries; those that use hybrid electric engines - vehicles that use batteries and also have small gasoline engines; and vehicles that use fuel cells. Fuel cells are a little different because they typically use hydrogen to generate electricity that generates the power that turns the wheels. There is one thing to remember about electric vehicles. The electricity that you use to recharge the batteries has to come from someplace. In most cases, it comes from the electric socket in your house, which comes from a power plant someplace. To make electric cars are truly "green," we have to make sure that the power plants, which create the electricity to charge the batteries, aren't adding to the energy crisis too. (From Veronica in Mrs. Kerr's Class at Roosevelt Elementary in Boise.)

  6. How is sunlight converted into green energy?

    Sunlight is really the source of most of our energy, either directly or indirectly. Sunlight is what powers the wind and it's a source of energy that plants use to survive. Plants are what we use as sources of energy, either directly when we make ethanol or biodiesel, or when we burn wood, or even when we burn petroleum and natural gas that's coming from fossilized plants and biological material that was laid down millions of years ago. But it's still all originating from the sun. Solar panels convert the sun into energy. Photovoltaic, solar cells, use special materials that create electricity when placed in sunlight. The sun causes electrons to move around in the material. Those electrons then are collected and made into an electric current that can be used to power a light bulb, or a radio or television set. (From Shawn in Mrs. Whitesell's class at Gooding Elementary.)

  7. Can we run out of energy?

    Certainly the energy that we get from dams that produce electricity, what we call hydropower, doesn't usually run out because the water used to turn the generators is replenished every time it rains. But sources of energy like petroleum that we pump out of the ground are another matter. We're not really going to pump out every bit of oil that's down there. It just becomes more and more difficult to find the oil and more and more difficult to pump it out. So if we want to pay $15 a barrel for oil, there may not be very much of that kind of oil left. But if we're willing to pay $90 per barrel for the oil, there's more at that price. And if we have to pay $200 per barrel for the oil, then there's quite a bit of that oil available. So you have to look at how much money you're willing to pay to look for and to find and to pump out the oil and then decide how much oil is actually available for us. You also have to consider the cost to the environment to get the oil and decide if are we willing to pay that cost as well. (From Sara in Mrs. Hunt's class at Cynthia Mann Elementary in Boise.)

  8. Where would be the best place in Idaho to put a wind farm?

    Wind farms are found in areas where you have mountains because typically what you're looking for are places where the wind accelerates as it moves past mountains and mountain ridges. So the Snake River Plain, for example, is an excellent conduit for wind blowing west to east. That's why we have some wind farms in southeast Idaho. They pick up the energy as the wind rises up over the mountains in that part of the state. You don't put a wind farm where there isn't much wind, and since most of us don't like to live in windy spots, most wind farms aren't close to populations. (From Hugo in Mrs. Schweitzer's fourth grade class at Riverside Elementary in Boise.)

  9. What is the main cause of air pollution?

    The main cause of air pollution is typically from the burning of fossil fuels. Typically you're looking at hydrocarbons, carbon monoxide and other things that come from petroleum and coal-based products. Cars, factories, and power plants are some of the main sources of burning fossil fuels. Burning wood can add to pollution levels too. (From Evan in Mrs. Hunt's fourth grade class at Cynthia Mann Elementary in Boise.)

  10. What is the cheapest form of green energy?

    The answer is easy. It's conservation. It's always a lot cheaper to not use energy or use less of it than have to create more energy in the first place. But if you want to know what's the cheapest form of energy that we might use, I might vote for wood. Burning wood, if you can do it cleanly, is actually quite inexpensive. It is also renewable, but does have an environmental cost to consider. One other form we are lucky to have here in Idaho is cheap hydropower. But when you think about it, the reason that hydropower is so cheap is that very large, very expensive dams and hydroelectric plants were built 40 and 50 years ago. Now they're paid off, but they're robust in the sense they can operate for many, many, many years. In the same sense the cost of nuclear power may some day be inexpensive. They may be expensive plants to build today, but they may give you cheap power in years to come. (From Brandon in Filer.)