Nuts & Volts - April 2005

The earliest known record of the direct conversion of solar radiation into mechanical power belongs to Auguste Mouchout, a mathematics instructor at the Lyce de Tours. Mouchout began his solar work in 1860 after expressing concerns about his country's dependence on coal. “It would be prudent and wise not to fall asleep regarding this quasi-security,” he wrote. “Eventually industry will no longer find … the resources to satisfy its prodigious expansion. What will industry do then?” By the following year, he was granted the first patent for a motor running on solar power and continued to improve his design until about 1880. During this period the inventor laid the foundation for our modern understanding of converting solar radiation into other forms of power.

Where Mouchout left off, a French man by the name of Charles Tellier took over in 1885. Considered by many the father of refrigeration, Tellier actually began his work in refrigeration as a result of his solar experimentation, which led to the design of the first nonconcentrating, or nonreflecting, solar motor.

If you’re concerned about your ever-growing battery bill, you might want to consider using solar power. Although solar cells are not usually as straightforward as batteries, once you get used to their characteristics, they’re easy.

Types of Solar Cells

A solar cell (sometimes called a photovoltaic cell) is basically a large diode. Just as a photodiode (or even, for that matter, a regular glass-walled diode like a 1N914) will produce a voltage when exposed to light, so will a solar cell. The difference is that a solar cell is designed to produce a useful current. Most solar cells, like most diodes, are made from silicon. A few other semiconductors can be used, such as gallium arsenide, but these are found only in very special circumstances, such as satellites that might need to endure large amounts of radiation in space that would damage silicon cells. Copper oxides can be made to act as solar cells, too (and were the first type of cell discovered), but they are very inefficient.

There are basically two types of silicon cells — crystalline and amorphous. Crystalline cells are made from thin wafers of nearly pure silicon, just like those used to make silicon chips (for that reason, they are often circular or curved, having been cut from circular wafers). They are rigid, but light and fragile, and are fairly expensive to make. Rather cheaper are amorphous cells, which are made from silicon deposited onto a substrate. This can be glass, as in the Sunceram cells by Panasonic that are used in many small solar robot projects, or a flexible plastic film, such as the

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