Energy Sources You Need to Know for the GED Science Test

By Murray Shukyn, Achim K. Krull

The GED Science test will expect you to have a basic understanding of energy sources. Energy sources are natural resources that can be used or harnessed to provide power for light, heat, and operating machinery. The most common energy sources include the following:

  • Biomass: Wood and other plants contain tremendous amounts of chemical energy formed through photosynthesis. These may be burned directly or converted into other forms of fuel, such as ethanol (commonly added to gas for automobiles) and biodiesel.

  • Fossil fuels: Coal, oil, and natural gas are all fossil fuels obtained from the accumulated remains of prehistoric plants and animals that have been compressed and heated over many thousands of years. Burning these fuels converts chemical energy into thermal energy for heating, into mechanical energy to operate machinery (as in a car), or into mechanical energy to produce electrical energy (such as turning a turbine to produce electricity).

  • Geothermal: The core of the Earth is extremely hot. Geothermal energy harnesses this heat directly for heating homes and businesses and for producing electricity.

  • Hydroelectricity: The movement of water in the form of rivers and waves (mechanical energy) is often harnessed to produce electrical energy to supply homes and businesses.

  • Hydrogen: Hydrogen can be burned or used in fuel cells to produce vast amounts of electricity. NASA has used liquid hydrogen since the 1970s as rocket fuel. It’s a clean-burning fuel that releases only water into the environment. However, hydrogen requires a great deal of energy to produce, so it’s not yet economically efficient to use.

  • Nuclear: Certain chemical elements, especially uranium, have an incredible amount of potential energy. In fact, one gram of the rare uranium isotope U-235 contains approximately the same energy as three tons of coal. Splitting the atoms of these elements releases the energy, or at least a portion of it.

  • Sun: Most of our energy — whether it’s in the form of fossil fuels, biodiesel, biomass (wood, for example), or solar energy — comes from the sun. Solar energy is commonly harnessed using photovoltaic cells that convert the sun’s radiant energy into electrical energy. Solar energy is also used in passive heating systems in homes and businesses to allow energy from the sun to penetrate buildings through windows, where the windows also serve to hold in the heat.

  • Wind: Wind is commonly harnessed in a variety of ways, especially through the use of windmills, to produce electricity.

Using details from the following table, write a short essay explaining the possible challenges of transitioning from fossil fuels to cleaner, renewable energy sources. Write your essay on a separate sheet of paper and spend no more than 10 minutes writing your response.

Energy Source Advantages Drawbacks
Biomass Abundant
Lower emissions than fossil fuels
Can be used as fuel in diesel- and gas-powered vehicles
Air pollutant
Uses fossil fuels in harvest, conversion, and transportation
Coal Abundant
Inexpensive
Reliable
Generates large amounts of power
Emits greenhouse gases
High environmental impact
Dangerous for miners
Geothermal Clean
Efficient
Low cost after initial investment
Limited availability
Expensive to start up
Wells could be depleted over time
Hydroelectric Clean
Reliable
Can generate large amounts of electricity
Output can be regulated to meet demand
Expensive to build
May be affected by drought
Impacts environment and fish migration, if not mitigated
Natural gas Plentiful
Relatively clean fossil fuel
High transportation costs
Emits some pollution
Nonrenewable
Oil/gas Efficient fuel for transportation
Economical
Easy to transport
High greenhouse gas emissions
Environmental impact from drilling and transporting
Nonrenewable
Sun Clean
Abundant
High initial investment
Unreliable, depends on sunny weather
Requires large physical space for solar panels
Uranium No greenhouse gas or CO2 emissions
Efficient
Abundant
High investment costs
Long-term storage of dangerous radioactive waste
Environmental impact of heated waste water released in nearby river
or lake
Potentially harmful to environment and humans
Wind Clean
Affordable
High energy output
Unreliable, relies on presence of wind
Limited availability based on location
High building and maintenance costs
Extensive land use
Environmental impact of bird kill