Lesson 5.02 Solar Energy

Solar Energy

Solar energy is an alternative, renewable source of energy that can be used to replace or supplement fossil fuel and nuclear energy sources. Solar energy will never run out or deplete any of the natural resources on earth.

Solar energy is "fuel" that comes from the sun's electromagnetic waves. These waves do not need a medium substance or matter to travel through. This allows them to travel through the vacuum space void of matter of space and reach the earth. The energy that reaches the earth is in the form of both light and heat energy. This energy can be used to heat structures and generate electricity.

Unlike fossil fuels, solar energy does not emit greenhouse gases when it is converted into usable energy.

Can solar energy be the answer to a cleaner earth?

Although solar energy is renewable, it is referred to as an intermittent energy source because it is not always available. When it is night, cloudy, or raining; the sun is unable to supply light, making solar devices unable to generate energy. This makes solar energy less reliable than its fossil fuel counterpart having the same purpose or function as something else .

There are two types of solar energy technology that are used to access the sun's light and heat energy — passive and active solar technologies.

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Passive Solar Energy

Passive solar energy uses the sun's energy simply by the way the structure is oriented, designed, and constructed. Passive solar energy utilizes building characteristics such as walls, floors, roofs, windows, exterior building elements and landscaping to control heat generated by sun. Solar heating designs try to trap and store thermal energy from sunlight directly. Passive solar heating occurs when the sun strikes an object and the object absorbs its heat.

Objects in the building that absorb and hold that heat are referred to as thermal mass absorbers. It is important to have materials that readily absorb light energy: concrete, brick, stone, and tile are example of construction products that are used. Dark colors absorb more heat than lighter colors. So it is important to consider colors of objects when using them as part of passive solar heating.

Passive solar heating can be used in buildings if the windows are oriented correctly. The best window orientation for passive solar heating is south. This allows the sunlight to effectively enter the room through the window. It is important that walls and ceilings are properly insulated to ensure the heat stays trapped within the house. The glass of the window also needs to be insulated to keep the heat from escaping back through it. The glass may need to be insulated with insulating glass spacers or inert gases.

Diagram illustrating passive solar heating

With passive solar heating, there are little to no mechanical devices that are used. Small fans or blowers may be needed to help distribute the heat throughout the building. Some of the distribution will occur naturally through radiation, conduction, and convection.

• Radiation occurs between objects that do not touch.
• Conduction is heat transfer between two objects that touch.
• Convection is the transfer of energy through fluids such as air.

Read about the disadvantages of passive solar heating.

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Active Solar Energy

Active solar energy generates electricity using devices called Solar Photovoltaic (PV) systems. Photovoltaic systems are large panels that are made up of smaller solar cells. These cells are made up of materials known as semi-conductors semi-conductors have a conductivity value between conductors such as copper and insulators: common example of a semi-conductor is silicon . The cells collect or absorb the energy from the sun and then convert it into electricity that can be used for cooking, lighting, and heating. When light hits the semi-conductor in the cell, it creates an electric charge which can then be transferred through a circuit to anything that uses electricity.

Diagram showing the path of active solar energy. View larger version.

To optimize electricity production through active solar energy, panels can be assembled into larger groups called solar arrays. Solar arrays can vary in size and provide electricity for homes, offices, and larger facilities.

An array of solar panels supplies energy for necessities at Marine Corps Air Ground Combat Center Twenty nine Palms, Calif. View larger version.

Solar arrays and panels can also be used to gather solar energy from the sun to heat fluids — water and air — that in turn heat a building. In this type of system, the solar energy captured by the panels is used to heat water. This heated water is then dispensed through a series of pipes in the building. The heated water heats the pipe. Then through conduction and convection, the air within the building is heated.

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Solar Energy vs. Nonrenewable Sources of Energy

Pros

Solar energy has both advantages and disadvantages when compared to fossil fuels and nuclear energy.

• Solar energy is an unlimited renewable resource that will not run out.
• Also, unlike nonrenewable energy sources—fossil fuels and nuclear energy—there are no waste byproducts that result from the energy conversion. In fossil fuels, greenhouse gases are emitted into the atmosphere, and with nuclear energy, harmful radioactive wastes have to be disposed of once they have been used to generate electricity. Therefore, solar energy is much cleaner and safer on the environment since there are no waste byproducts produced.

Cons

Although solar energy presents no environmental risks, there are negative aspects that make it less desirable than fossil fuels and nuclear energy.

• Solar energy is not as efficient as using fossil fuels or nuclear energy to generate electricity. Only about 15% of the energy absorbed by solar panels is able to be converted into electricity. If you will remember for the last lesson, nuclear energy has an efficiency rate of about 91% and coal had an efficiency rate of about 59%.
• Another disadvantage of solar energy is that it is an intermittent source of energy. As mentioned earlier in this lesson, solar energy is not available to be used and converted during the night or on cloudy or rainy days. Therefore it is not as reliable as coal or nuclear energy which can be converted 24 hours 7 days a week into electricity.
• Solar energy technology tends to be more expensive than that of fossil fuels and nuclear energy. Often times the use of passive solar energy means that major renovations to buildings have to be done to make them more capable of using the sun's energy directly. This can often be a costly endeavor. The solar panels and arrays are often very expensive to purchase and install. They also take up a large amount of space.

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