Alternative Energy Resources (Solar)

Types of Solar Power

There are three methods in common use today to capture the energy of the sun's rays for practical use. The first is through passive or active thermal systems, which use the sun's energy to heat buildings, water, and so on. Passive solar heating requires only that a building or installation be designed to capture the sun's rays through orientation, placement of windows, and so on, and requires no additional energy to operate the system. Active solar heating, which is generally more efficient but also more complex and requires the use of electrical or mechanical equipment, uses collectors to capture the energy of the sun. The captured energy is then transmitted to the building through means such as a pump or fan. Both methods are used to heat water. A simple example of passive solar water heating is a painted black barrel placed on a roof—similar to systems used by some campers to heat water in a black bag for use in bathing and dishwashing—while sophisticated systems involve collectors and pumps. These latter systems are commonly used in Europe and Asia.

Photovoltaic cells, also called solar cells, are used to convert solar energy to electricity. The first working photovoltaic cells were developed at Bell Laboratories in the United States in 1954. Although originally considered a curiosity, solar cells proved useful as a power source for spacecraft in the 1960s and 1970s since they were a nonpolluting alternative to power generated from coal or petroleum. The heart of a solar cell is a wafer of semiconductor material (generally silicon) that has been treated so it is positive on one side and negative on the other. Electrical conductors are attached to both sides to form an electrical circuit to capture the energy created when the sun's rays strike the cell and knock electrons loose from the atoms in the semiconductor material. This creates electricity, [Page 16]which can be used as power such as a light. More electricity may be created by connecting multiple solar cells in a module; multiple modules form an array. Modules and arrays produce direct current and are designed to output electricity at a particular voltage (e.g., 12 volts). In general, the greater the area exposed to the sun, the greater the electricity generated.

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