Solar Panel Facts

For those wanting to know basic fundamentals of PV systems and arrays, here are a few solar panel facts.

| August/September 1991

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    Solar panel facts: The sun strikes a photo-sensitive material (say a solar cell), exciting electrons into a more active state. These electrons then flow through an embedded circuit. The circuit may include a device (say, a light bulb) that uses energy from the electrons or into a battery bank that stores it.

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Here are the basic solar panel facts. To understand photovoltaics, you have to understand electricity. Envision a piece of metal such as the side of a car. As it sits in the sun, the metal warms. This warming is caused by the excitation of electrons, bouncing back and forth creating friction, and therefore heat. Add a mechanism (say a solar cell) to control the flow of electrons and voila! Electricity. Oversimplified, perhaps, but PV boils down to one simple act: the flow of power.

Now that you know electricity, you can understand how PV power flows. First you have the source of PV power, the sun. It's abundant, it's cheap, and it's everywhere. All you have to do is harness it. Enter solar cells. Capable of generating 50 watt-hours of electric power, they sit in the sun and generate power as they warm—simply, quietly, without moving parts or by-product pollution.

This power then flows through a regulator and into the battery bank. Batteries are the heart of a PV system. They store almost all the power the system delivers. The one drawback to this "power storage" unit is the amount of power loss associated with all batteries—roughly 15 to 25%. They "self discharge" a portion of the power they store; for example, if you charge a battery with 1000 watt-hours, you will only receive 800 watt-hours when discharging.

After a battery is charged, though, power can be used day or night, through sunshine and clouds. DC power (the type of power needed to illuminate a light) can be used directly from the battery, traveling via regulator (to control flow to and from batteries) and a fuse box (for overload protection and safety). AC power (used for heavy-duty items such as a dishwasher) can be accessed by means of an inverter. Simply, the inverter converts DC (battery) electricity to 120 VAC electricity. Now you can operate just about any electrical item in the house by means of PV power!

But is PV for you? Maybe. If you live more than half a mile away from a utility line, PV could be cost-effective. The initial cost of a solar electric system is usually less than the power companies charge for line extension. If you are on utility power at present, PV is not a cost-effective move. Utility power is much cheaper than PV power. Why? "Because we have not yet begun to pay for the externalities of fossil fuel and nuclear generating plants," says energy expert Les Clawson, "Power costs will escalate down the road. We are already starting to take a tax hit for damage caused by acid rain, global warming, and nuclear waste disposal. Once you figure in the costs incurred by environmental damage, it's easy to see how costly utility power will be in the future. It'll be more than double your power bill every month."

PV is also competitive when compared to other alternative power sources such as wind- and hydropower. While harnessing wind and tapping a waterfall can be good sources of power (provided you have year-round dependable access to a windy ridge or a river with a healthy flow of water and good vertical drop), solar has the advantage of sunlight being fairly universal and PV arrays having no moving parts to wear and eventually fail.



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