|Shining a Light on Solar Panels: The Basics|
|Friday, 06 August 2010 00:00 | Written by Brian Trusseau | Article|
Live in an area with plentiful sunshine? Want to reduce your electric bill and decrease your carbon footprint? Then you may be thinking of installing solar panels. That’s great. But first, why not learn a little about the technology, rather than shopping blindly or relying on a solar-panel salesperson who may have his commission rather than your best interests at heart?
Most of the solar cells used for generation of home power are of two types: photoelectric and solar thermal. Photoelectric (also called photovoltaic) cells convert sunlight directly into electricity, while solar thermal technology employs the sun to create electricity indirectly. This article will deal exclusively with photoelectric solar cells, which are growing in popularity due to their dependability.
The cost of installing solar panels varies greatly depending on your location--and the benefits vary, too, depending on the amount of exposure they will have to the sun. However, there are potential tax breaks and incentives. Find Solar offers a handy solar-panel-system cost calculator to help you estimate the cost of buying, installing and operating a solar panel array. The calculator also factors in tax incentives available to you based on your location.
Over its 35-year expected life, a 10Kw system will provide the equivalent CO2 reduction as planting 1450 trees. (Based on typical utility pollution, it will prevent emissions of 963,125 lbs. of carbon dioxide, 4,237 lbs. of sulfur dioxide, and 1,364 lbs. of nitrogen oxides.) It will produce 575,000 kilowatt hours of electricity, as much as would be generated by burning 583,000 lbs. of coal.
AC/DC: Batteries, Not the Band
Most household appliances are built to run on AC (alternating current), while electricity that comes from your battery will be DC (direct current). You will need an inverter that converts DC to AC. Most of the other necessary hardware is identical to that used in a regular AC home-electric system: junction boxes, wiring, grounding and over-current protection devices, outlets, etc.
The National Electrical Code includes a section that covers installing photoelectric cells. Be sure to follow all local building codes for electric installation as well. It also makes sense to use a licensed electrician with some prior DC-power installation experience.
Are there disadvantages to using solar panels? One significant caveat is that they do not work when covered with five inches of snow! When it snows, one must carefully clear the panels to avoid damaging them. Placing panels on the side of the house instead of the roof can mitigate this disadvantage. Still, it is important to consider how the system will function during a January ice storm; having a wood-stocked fireplace, backup propane system and candles at the ready would be wise.
Basic Solar Cells
In this simple solar cell, light strikes the modified copper. Some of the photons that strike the first piece of copper excite electrons and--voila!--they jump through the salted water to the other side, reaching the second piece of copper. An multimeter (also known as a volt/ohm meter or VOM) will show the electrical current that flows from one piece of copper to the other.
The Science Behind It
Electrical engineers have a common schema called an "N-P junction" (figure 29, from a 1941 patent to R. Oh, the first for a solar cell). The "N" zone is a semiconductor material like silicon, doped with a negative impurity; the "P" zone is doped with a positive impurity. Alternatively, one could just as easily create a solar cell based on a "P-N junction"; the two layers would be flipped, with the "P" layer on top and the "N" on the bottom.
The "N-P" schemata (or "P-N" as the case may be) represents a useful conceptual diagram that electrical engineers use to show an electrical phenomenon. They equally apply to technologies created back in the 1940s as to those of today.
The solar cell’s silicon is produced in a way that improves its capacity for conducting electrical current. Two silicon wafers are placed next to each other, separated only by a junction. One of the silicon wafers (or layers) is ‘doped’ with negative material, while the other is doped with positive material. Such a design facilitates the creation of an electrical current.
Nobel Prize-winner Alan Heeger, Professor of Physics at the University of California at Santa Barbara, announced in March, 2008 that his team had increased the efficiency of solar cells (neither exclusively solar thermal nor photoelectric) by as much as 5.1 percent. Their technique employs alkanedithiols as agents to improve the solar cell’s power-generation capacity, and is expected to be market-ready within a couple of years.
Given the technology’s far-reaching environmental benefits, recent scientific improvements and the inevitable cost reductions associated with wide adoption, solar power represents a clean, efficient and cost-effective way to reduce both pollution and our dependence upon limited oil, gas and coal resources.
Updated 8/6/10; originally posted 2/19/09.