Sources of Energy
You use energy in many different ways. A car engine transforms the energy stored in gasoline to kinetic energy as you drive. The buildings in which you live and work use electricity for lighting, heating, and operating equipment. The electricity and fuels you use are produced from different energy sources, each having advantages and disadvantages.
Resources are anything on Earth people use to meet their needs, such as minerals, water, soil, and air. You use energy when you tum on a light, cook dinner, tum on the air conditioner, or drive a car. This energy is usually in the form of electricity produced at a power plant or from fuels that are burned.
An energy resource is a natural material people use to meet their energy needs. Energy resources include coal, oil, natural gas, the Sun, and the wind, among others. Most energy resources contain potential energy, often in the form of chemical energy. A power plant transforms the potential energy into electricity. Power plants use coal, water, or another resource to generate that electricity. In most power plants, the potential energy is converted to the kinetic energy of a moving turbine, which is connected to a generator that transforms kinetic energy into electricity.
All energy resources may be classified as renewable or non-renewable. A non-renewable resource cannot be quickly replaced after it is used and, therefore, has the potential to be used up. Fossil fuels, such as coal, or the uranium used in nuclear reactions, are non-renewable energy resources. The supply of these fossil fuels in the world is shrinking. A renewable resource can be replenished. Sunlight, geothermal energy, biomass, wind, and water are renewable energy resources. The Sun’s energy is considered renewable because it can not be used up by humans.
Non-renewable energy resources must be extracted from the ground so they can be turned into usable fuels. Fossil fuels are fuels that formed from the remains of ancient organisms over millions of years. Fossil fuels include coal, oil, and natural gas. They may be found close to Earth’s surface or kilometers underground. Fossil fuels each have distinct advantages and disadvantages, including the ways they can be used, the types of pollution they produce, and how long their supplies are expected to last.
The energy in fossil fuels originally came from sunlight. Photosynthetic organisms that lived in the past used energy from the Sun to produce organic substances that store energy. These organisms died, decomposed, and were covered with layers of rock over millions of years. Under conditions of extreme heat and pressure, the fossil fuels we use today were formed. Today, energy companies may drill several kilometers underground to reach deposits of fossil fuels.
Coal is a solid material formed from the remains of dead plants. Today, most coal is burned in power plants. Oil and natural gas formed from the remains of microscopic marine organisms. Oil is a complex liquid mixture that needs to be separated and converted into useable fuels at oil refineries. Gasoline, propane, kerosene, and jet fuel are all components of crude oil. The relatively recent process of hydraulic fracturing, or fracking, is used to extract, or remove, natural gas that is trapped in rock. Natural gas is used in gas stoves and home furnaces, as well as in some vehicles, such as certain buses.
When fossil fuels are burned, their stored energy is converted to thermal energy, which may then be converted to other types of energy. Fossil fuels are easy to transport and inexpensive compared to other sources of energy. However, burning fossil fuels produces carbon dioxide and other pollutants that may be released into the air.
Radioactive atoms are the source of energy in nuclear power plants. The process of splitting a nucleus into two smaller nuclei is called nuclear fission. A large amount of energy is released during the nuclear fission of very small amounts of elements such as uranium. The energy and particles released during fission, called radioactivity, can generate energy, but it can also harm living organisms.
There are different types of uranium atoms, called isotopes. Uranium-235 (U-235) is an isotope used as fuel in nuclear power plants. While U-235 is non-renewable, there is enough of it to last for thousands of years. U-235 atoms split apart, or decay, when hit by high-speed neutrons in a nuclear reactor. When they undergo nuclear fission, that process produces two more stable atoms and subatomic particles called neutrons. The produced neutrons hit other uranium atoms, causing a chain reaction that must be carefully controlled. Some of the released energy is in the form of thermal energy that is converted to electricity in the nuclear power plant.
A nuclear power plant operates much the same way as a coal power plant. In each, thermal energy is used to produce electrical energy. In the coal plant, thermal energy is produced by the burning of coal in a boiler. In a nuclear plant, thermal energy comes from the fission of nuclei in a nuclear reactor. In each plant, the thermal energy is used to boil water to produce steam. The steam turns a turbine connected to an electric generator. The generator produces electrical power, which then flows down electric power lines.
The use of nuclear energy does not release carbon dioxide or other pollution into the atmosphere. Another advantage of nuclear energy is that a small amount of uranium can produce a large amount of energy. One disadvantage of nuclear energy is that the waste material produced is highly radioactive and must be stored safely.
Think about Science
Directions: Answer the following questions.
- All fossil fuels and nuclear energy share which characteristic? A. They can be replaced quickly. B. They produce carbon dioxide. C. They can release thermal energy. D. They are burned in automobiles.
- What is a potential advantage of fossil fuels over nuclear fuels? A. Fossil fuels do not produce pollution. B. There are vast supplies of fossil fuels. C. Fossil fuels can be easily transported. D. Fossil fuels are used by many people.
Renewable Energy Resources
Some renewable energy resources, such as the Sun, geothermal energy, and wind, are inexhaustible, meaning they cannot be used up. Others, such as biomass, need to be actively replaced in order for them to be renewable.
Most of the energy on Earth originally comes from the Sun. People can use sunlight directly to produce electricity using solar cells. Solar cells contain materials that absorb sunlight, similar to the function of chlorophyll in plants. This absorbed light is converted to electricity inside the solar cell. Solar cells may be small, such as those used to charge the batteries in solar flashlights. They may also be combined into large modules placed on the roofs of buildings or into very large arrays used at solar power plants. Solar thermal power plants use sunlight to heat fluids that produce steam, which is then used to generate electricity similar to coal or nuclear power plants. Sunlight may also be used to heat water for homes.
Unlike fossil fuels, solar energy does not produce pollution. However, energy cannot be produced at night ,and less energy is produced on cloudy days. Also, the cost of solar panels may be too high for many people.
Geothermal energy comes from the heat generated inside Earth. The temperature and pressure deep inside Earth are hot enough to melt rock. Some areas near Earth’s surface, called hot spots, are so hot they can transform water pumped underground into steam. Hot spots are good locations for geothermal power plants. Cool water from Earth’s surface is pumped underground and heated by Earth’s interior until it changes to steam. The steam turns a turbine that powers a generator. The generator produces electrical energy. Iceland and the United States are two countries that use geothermal energy. Because geothermal power plants do not bum fuels, they do not release carbon dioxide or particulates into the atmosphere. The major limit on the use of geothermal energy is the number of locations where hot rocks are close to Earth’s surface.
Biomass is matter from living organisms, which means that the ultimate energy source of biomass is the Sun. Com, soybeans, switch-grass, and other crops are grown as biomass to produce fuels. Biomass also includes waste products, such as wood chips from lumber mills and unused leftovers from crops. Biomass, such as wood, may be burned in homes as a source of heat. It is also used in some power plants to produce heat used to generate electricity. Some biomass, such as com and soybeans, are converted into bio-diesel fuel or ethanol. Unlike fossil fuels, biomass can be replaced quickly. However, burning biomass is similar to burning fossil fuels because it releases carbon dioxide and other pollutants into the air.
Wind is also the result of energy from the Sun, as winds are caused by temperature differences in the air. For centuries, people have been using windmills to harness the energy of the wind to pump water or grind grain. Today, wind turbines convert the energy of the wind into electricity. Similar to power plants, each wind turbine uses a generator to produce electricity. However, instead of steam, wind pushes on the blades of the turbine to tum it. Wind energy does not release pollution and it is only efficient in areas with strong, steady winds.
Energy from Water
The Sun drives the water cycle and is a main source of the energy of moving water. Water also has gravitational potential energy that is transformed to kinetic energy as water flows downhill. People have been using energy from water for centuries to grind grain, saw wood, and run textile mills. Modem hydroelectric power plants generate electricity when flowing water turns turbines beneath darns. All darns in rivers store water to be released as it is needed, but only a few are used in the production of hydroelectric power. New ways of generating hydroelectric power, such as using the energy of tides and waves, are also currently being used.
Hydroelectric power is very efficient and creates no pollution. However, water power is limited by the number of rivers present. Darns can also disrupt fish breeding cycles and flood the land behind the darn.
Think about Science
Directions: Answer the following questions.
- How are biomass, wind energy, and hydroelectric power related? A. They have energy that comes from the Sun. B. They all produce pollution. C. They must be replaced as they are used. D. They can be used to meet any energy need.
- Which is a use of energy from biomass but not from geothermal energy? A. producing heat B. producing electricity C. powering cars D. recharging batteries
Choosing Sources of Energy
Many factors determine the energy sources people use, including availability, cost, and environmental impact. Worldwide, fossil fuels provide the majority of the energy used for electricity, heating, and transportation. The current supplies of fossil fuels allow producers to meet demands, making them comparatively cheap. Although advancements are being made with renewable energy resources, the technology is already in place to drill or mine and refine fossil fuels. Fossil fuels also release a large amount of energy when burned and have the advantage that they can be stored and used when needed. This makes them an important energy resource for transportation.
Fossil fuels also have disadvantages as their extraction can cause environmental damage. The carbon dioxide they produce when burned contributes to climate change, and the other pollutants released can cause smog and acid rain.
A large amount of nuclear energy is produced from little fuel and does not produce carbon dioxide, but it does produce radioactive waste. This waste must be stored safely for long periods of time. While accidents at nuclear power plants are rare, they can have devastating consequences.
Geothermal, wind, and water energy resources are available only in certain places. For example, wind can produce electricity only in places where the wind is strong enough to tum the blades of the turbines. Geothermal energy can be generated in areas where there are hot springs. It is currently more expensive to generate electricity by using wind and solar energy than it is by using fossil fuels, however costs are decreasing.
Think about Science
Directions: Answer the following questions.
- Which is a disadvantage of biomass but not of hydroelectric power? A. radioactive waste B. pollution in the atmosphere C. availability at any location D. inability to be replaced
- Which could cause the cost of natural gas to increase but is not likely to affect solar power? A. decrease in supply B. improvements in technology C. out-of-date technology D. increase in supply