"Fuel" has been defined as

• a store of chemical energy, or
• a substance that can be burned to produce heat, or
• a substance that can be consumed to produce energy, or
• a combustible substance that provides energy.

Remember that heat is a form of energy. This was first proved by Irish mathematician William Thomson in 1847, in response to a lecture at the British Association by James Joule, who originally formulated the mechanical equivalent of heat. Joule's name is still used by scientists as a measurement of energy.

As you know, we cannot create new energy that is not already present in the Universe. Instead, we must take materials in which energy is stored, change their state and harness the energy that escapes. In particular, energy can be harnessed from fuels.

Many natural processes already convert energy. Through photosynthesis, plants take energy from the Sun and convert it into chemical energy which they store as carbohydrates.

The energy that is used to heat your home and power your TV is not too different from the energy your body gets when you eat a steak sandwich. Your body turns food (actually, it "burns fuel") into usable energy -- the ability to do work -- and eliminates waste byproducts.

A power plant does the same thing. Coal, oil or natural gas goes in and gets burned up to power a generator that sends energy to your home -- with carbon dioxide, other gasses and/or sludge as waste byproducts.

When combustion is incomplete in an automobile engine or anything else, the primary gas that's released is carbon monoxide.

Nuclear Energy

Nuclear reactions -- including fission and fusion -- release the mass energy in atoms. As we told you in our last Instruction, energy can become mass and mass can become energy. The mass energy in even a tiny amount of matter is enormous. Although nuclear energy can be a reliable source of power, problems can occur with disposal of nuclear waste, since it remains radioactive for many years. Many scientists are working to solve this problem.

Fossil Fuels

Today, most of the energy we use comes from fossil fuels. Over millions of years, the remains of plants, dinosaurs and other animals were buried in the Earth and changed -- under pressure -- into oil, natural gas and coal. These fossil fuels are called "nonrenewable" because once they're burned up, they are gone forever.

Unfortunately, it takes millions of years to produce this kind of fuel and we're using it up rather quickly. It is estimated that the United States has enough recoverable oil reserves to supply its needs for 7.6 years, although of course there are extensive oil reserves in other parts of the world. The U.S. has enough natural gas reserves for 153 years and enough coal for 527 years.

Other Energy Sources
 

Fortunately, there are other sources of energy -- although scientists are only now beginning to learn how to use them. Most of these "renewable" energy sources can be used over and over or else they are very easy to make from plentiful raw materials. They include:

Solar Energy
 

Solar Energy is energy from the Sun. We can use the energy in sunshine to warm and light our homes, heat our water and provide electricity to power our computers and other appliances. Solar energy comes from processes called solar heating, solar water heating, photovoltaic energy and solar thermal electric power.

Have you ever sat in a closed-up car on a sunny day? Remember how hot it got inside? That's solar heating. Many homes in United States already use various forms of solar heating, both passive (which doesn't require the use of pumps) and active, which does involve storage tanks and collectors.

The Sun's energy can also be turned directly into electricity using photovaltaic (PV) cells, sometimes called solar cells. These cells are often used in  calculators and watches -- but they can also be used to power light bulbs, household appliances and even whole houses.

Solar thermal systems can change sunlight into electricity by concentrating the sunlight to produce heat. This heat then boils water to make steam, which rotates a turbine attached to a generator. The generator then makes electricity.

One problem with PV and solar thermal power is that the Sun doesn't always shine, so solar systems often rely on natural gas as a backup to heat water.

Wind Power
 

For centuries, wind has been used to sail ships, grind grain and pump water. Now people are using it to generate electricity.

Unlike classic Dutch windmills -- which have many short blades -- today's wind turbines have only three long blades, which can be up to 82 feet long. These blades drive a generator that produces electricity -- much like a steam turbine. The longer the blades and the faster the wind speed, the more electricity.

To produce the most electricity, wind turbines need to be located in parts of the world where the wind blows at a relatively constant speed.

Large groups of wind turbines are called wind farms or wind plants. They are connected to electric utility power lines and provide electricity for many people.

Geothermal Energy

We can also get energy directly from the heat in the Earth. This is called geothermal energy. "Geo" means "earth" and "thermal" means "heat."

Geothermal energy starts with hot molten rock (magma) miles beneath the Earth's surface. The heat rising from the magma warms underground pools of water called geothermal reservoirs. We can drill wells deep below the surface of the Earth to tap into these reservoirs. This is called "direct use" of geothermal energy and provides a steady stream of hot water that is pumped to the Earth's surface and used to produce electricity.

Biomass Energy

When you burn a log in your fireplace, you are using biomass energy -- which isn't, of course, renewable. But it is very easy to produce. Because trees depend on sunlight to grow, what biomass energy actually is is a form of stored solar energy.

There are three ways to use biomass. Biomass can be burned to produce heat and electricity, it can be changed into a gas-like fuel such as methane or it can be changed into a liquid fuel called biofuel. Diesel fuel can be replaced by biofuel made from any vegetable oil -- soybean oil, corn oil, cottonseed oil, peanut oil, sunflower oil or canola oil. Biofuel can also be made from grasses, trees, bark, sawdust, paper and farming wastes.

Increased use of biofuels could be very helpful, since nearly one-third of the U.S. energy is now used for transportation.

The most commonly used biofuel in the United States is ethanol, which is produced from corn and other grains. A blend of gasoline and ethanol is already in use in cities with high air pollution.

Hydropower

The water in rivers and streams can be captured and turned into hydropower, which is also called hydroelectric power. The most common form of hydropower uses dams on rivers to create large reservoirs of water. Water released from these reservoirs flows through turbines, causing them to spin. The turbines are connected to generators that produce electricity.

Hydropower power is one of the largest sources of renewable power in the United States, already accounting for about 10 percent of the country's electricity.

Energy from Trash

Municipal solid waste has the potential to be a large source of energy. In 1993, the Environmental Protection Agency estimated that each year the United States generates 207 million tons of trash -- although little of it is currently being converted into energy. But it is an inexpensive, and almost inexhaustible, source of energy for the future. And we all produce it.

Municipal solid waste can be burned in large power plants to generate electric power. There is also a way to use the energy trapped in landfill garbage. When food scraps and other wastes decay, methane is produced -- which is the main ingredient in natural gas.

Reading List From the California Dept. of Education

To read a description of this book from the California Dept. of Education, click on this address and follow the instructions: http://www.cde.ca.gov/ci/sc/ll/ap/searchlist.asp

for Students, Parents and Teachers

Now let's do Practice Exercise 3-2 (top). Choose printer friendly or online exercises. Printer friendly version requires the Adobe Acrobat Reader 5. Click HERE to obtain a free copy.