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Lesson 11-02 - Solar Energy

Page history last edited by debra.krohn@gmail.com 10 years, 6 months ago

Lesson:  EM 1.o2 Energy

Standards:  ES 4.a.  Students know the relative amount of incoming solar energy compared with Earth's internal energy and the energy used by society.

            This lesson will look primarily at the renewable energy used by society.

Introduction:  There’s no doubt that we live in the age of fossils fuels. These nonrenewable resources supply nearly 90 percent of the world’s energy.  But that can’t last forever. At the present rates of consumption, the amount of recoverable fossil fuels may last only another 170 years. As the world population soars, the rate of consumption will climb as well.  This will leave fossil fuel reserves in even shorter supply. In the meantime, the burning of huge quantities of fossil fuels will continue to damage the environment. Our growing demand for energy along with our need for a healthy environment will likely lead to a greater reliance on alternate energy sources. 



Solar Energy

Solar energy is the direct use of the sun’s rays to supply heat or electricity.  Solar energy has two advantages: the “fuel” is free, and it’s non-polluting. While the energy collected is free, the necessary equipment and installation is not.  There are 3 types of solar energy use today.

            Passive solar has been used for hundreds of years.  Your car is a passive solar collector.  The electromagnetic energy from the sun hits the interior of the car and is absorbed.  The car’s interior radiates the energy back as infrared (heat) energy.  The same principal can be used to heat your home by building windows that face the south (in the northern hemisphere) which allows the sunlight to pass through the windows and the home’s interior will re-radiate the energy as infrared (heat).

The second use of solar energy is with an active solar collector.  The heat they collect can be transferred to areas where it is needed by circulating air or liquids through piping.  Solar collectors are also used to heat water for domestic and commercial needs. For example, solar collectors provide hot water for more than 80 percent of Israel’s homes.

The third use of solar power is probably the most familiar to Californians.  Many homes now have photovoltaic systems (PV) on their roofs.  These black panels convert solar energy into direct current.  Direct current is the energy used in iPods, batteries, and cell phones, but it is not the electricity used for most things in your home like appliances or the lights in your room.  These use AC electricity.  The solar panels must be connected to an inverter which will change the DC current into AC current. 



While the sun continuously provides energy, the earth rotates and thus energy from PV systems is only available during the daylight hours with no clouds obstructing the panels.  Batteries can be used to store energy produced by the system, but they are inefficient and a lot of energy is lost. 

Weather will also impact the ability of all solar systems to work successfully.  In California and the southwestern US, solar systems are useful in reducing the fossil fuels used to provide electricity.  However, in other parts of the US solar systems are not as practical. 

Wind Energy

According to one estimate, if just the winds of North and South Dakota could be harnessed, they would provide 80 percent of the electrical energy used in the United States. Wind is not a new energy source.  People have used it for centuries to power sailing ships and windmills for grinding grains.

Following the “energy crisis” brought about by the oil embargo of the 1970s, interest in wind power and other alternative forms of energy grew.  In 1980, the federal government started a program to develop windpower systems. The U.S. Department of Energy set up experimental wind farms in mountain passes with strong, steady winds. One of these facilities, at Altamont Pass near San Francisco, now operates more than 7000 wind turbines. In the year 2000, wind supplied a little less than one percent of California’s electricity.

Some experts estimate that in the next 50 to 60 years, wind power could meet between 5 to 10 percent of the country’s demand for electricity. Islands and other isolated regions that must import fuel for generating power are major candidates for wind energy expansion.

The future for wind power looks promising, but there are difficulties.  The need for technical advances, noise pollution, and the cost of large tracts of land in populated areas are obstacles to development.

            Like solar, wind has the problem of being an intermittent source of power.  Wind turbines only operate in windy conditions.  If there is not enough wind, the turbines will not turn; but if the winds are too high, turbines are also shut down to protect the generators. 

Wind turbines near Palm Springs, CA


There are several youtube videos showing wind turbines exploding.




Hydroelectric Power

Like wind, moving water has been an energy source for centuries. The mechanical energy that waterwheels produce has powered mills and other machinery. Today, the power that falling water generates, known as hydroelectric power, drives turbines that produce electricity. In the United States, hydroelectric power plants produce about 5 percent of the country’s electricity. Large dams are responsible for most of it. The dams allow for a controlled flow of water. The water held in a reservoir behind a dam is a form of stored energy that can be released through the dam to produce electric power.

Although water power is a renewable resource, hydroelectric dams have finite lifetimes. Rivers deposit sediment behind the dam. Eventually, the sediment fills the reservoir. When this happens, the dam can no longer produce power. This process takes 50 to 300 years, depending on the amount of material the river carries. An example is Egypt’s Aswan High Dam on the Nile River, which was completed in the 1960s. It is estimated that half the reservoir will be filled with sediment by 2025.


            The availability of suitable sites is an important limiting factor in the development of hydroelectric power plants.  A good site must provide a significant height for the water to fall. It also must have a high rate of flow. There are hydroelectric dams in many parts of the United States, with the greatest concentration in the Southeast and the Pacific Northwest. Most of the best U.S. sites have already been developed.  This limits future expansion of hydroelectric power.


Geothermal Energy

Geothermal energy is harnessed by tapping natural underground reservoirs of steam and hot water. Hot water is used directly for heating and to turn turbines to generate electric power. The reservoirs of steam and hot water occur where subsurface temperatures are high due to relatively recent volcanic activity.

            In the United States, areas in several western states use hot water from geothermal sources for heat. The first commercial geothermal power plant in the United States was built in 1960 at The Geysers (http://www.geysers.com/). The Geysers is an important source of electrical power for nearby San Francisco and Oakland. Although production in the plant has declined, it remains the world’s premier geothermal field. It continues to provide electrical power with little environmental impact. Geothermal development is now also occurring in Nevada, Utah, and the Imperial Valley of California.

Geothermal power is clean but not inexhaustible.  When hot fluids are pumped from volcanically heated reservoirs, the reservoir often cannot be recharged. The steam and hot water from individual wells usually lasts no more than 10 to 15 years. Engineers must drill more wells to maintain power production. Eventually, the field is depleted. 

As with other alternative methods of power production, geothermal sources are not expected to provide a high percentage of the world’s growing energy needs. Nevertheless, in regions where people can develop its potential, its use will no doubt grow.


Tidal Power

Several methods of generating electrical energy from the oceans have been proposed, yet the ocean’s energy potential still remains largely untapped. The development of tidal power is one example of energy production from the ocean.

Tides have been a power source for hundreds of years. Beginning in the 12th century, tides drove water wheels that powered gristmillsand sawmills. During the seventeenth and eighteenth centuries, a tidal mill produced much of Boston’s flour. But today’s energy demands require more sophisticated ways of using the force created by the continual rise and fall of the ocean.

Tidal power is harnessed by constructing a dam across the mouth of a bay or an estuary in coastal areas with a large tidal range. The strong in-and-out flow that results drives turbines and electric generators. (http://www.solarpowerwindenergy.org/wp-content/uploads/2010/01/tidal_thumb.gif)

The largest tidal power plant ever constructed is at the mouth of France’s Rance River. This tidal plant went into operation in 1966. It produces enough power to satisfy the needs of Brittany—a region of 27,000 square kilometers—and parts of other regions. Much smaller experimental facilities have been built near Murmansk in Russia, near Taliang in China, and on an arm of the Bay of Fundy in Canada.

Tidal power development isn’t economical if the tidal range is less than eight meters or if a narrow, enclosed bay isn’t available. Although the tides will never provide a high portion of the world’s ever-increasing energy needs, it is an important source at certain sites.



  1.  What are the two main advantages of using solar energy?  What are some of the drawbacks?
  2. In what two ways is geothermal energy used?
  3. What percentage of our energy might be met by wind power over the next 60 years?
  4. What are the advantages and drawbacks of hydroelectric power, geothermal energy, and tidal power?


Take the 11-02 quiz:



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