Solar Power Electricity and Solar Panels
Photovoltaics -- solar cells -- are a clean way to get free electricity from the sun.
A photovoltaic (PV) system on your roof or in your backyard produces pollution-free power at no cost, although your startup costs will vary. The final cost of buying the solar cells and installing a system depends on the type of solar cell (they vary in cost and efficiency), tax incentives you may receive, whether you can sell excess power to the electric company, and how much the sun shines.
The heart of a PV system is the array of solar cells, which may be rigid panels (most efficient) or thin flexible sheets (least efficient). Some double as roof shingles -- less efficient, but the cost is reduced by what roofing would cost. It might take about 1,500 square feet of PV shingles to provide enough power for a house. Only 500 square feet of more efficient -- but more expensive -- rigid panels might provide the same power.Solar Cells
Solar cells produce direct current, but houses run on alternating current. An inverter will change DC to AC. An inverter is neither complex nor expensive.
Once the sun stops shining, solar cells stop producing power. You can go solar during the day and use power from the electrical utility at night. If you're in one of 35 states that allow it, you can sell excess solar electricity to the power company during the day and buy power at night. Away from utility lines, as in the case of a remote cabin, batteries can store PV power collected during the day for use at night.
Installing a photovoltaic system is not a do-it-yourself project. The wiring is sophisticated, and you may tie into the power company's lines. Siting is crucial to the efficiency of a system.
Solar systems can last 20-30 years with a warranty for perhaps 5 years, if the system is professionally installed. The warranty is one of the standards by which you should judge a system. Given equal costs, efficiency, and experience, choose the system with the best warranty.Types of Photovoltaic Panels
Three basic types of solar cells are used in home photovoltaic systems.
Monocrystalline silicon panels are single large sheets of silicon, with metal strips laid across to collect electricity. They are the most expensive solar cells but also the most efficient, converting 15-18 percent of the available solar energy into electricity. They are often but not always the most cost-efficient.
Polycrystalline silicon panels are made from a block of silicon cut into a series of smaller cells. They are less expensive but are only 12-14 percent efficient.
Thin film panels are made of a thin layer of noncrystalline silicon, which can be sprayed on a variety of backings. They are inexpensive to manufacture and can be used in a variety of ways: Thin film panels are the basis for both photovoltaic shingles and photovoltaic windows. With their versatility and lower price come a drawback -- they are only 5-6 percent efficient.
Group III-V technologies, panels made of materials found in Group III and Group V of the periodic table, reach 25 percent efficiency. But their high price limits them to aerospace applications.Type of Installations
In the Northern Hemisphere, solar panels always face south because there is always at least some sun in the southern sky. The angle of the sun varies in summer and winter, and some systems adjust for the change. Others mount the array at an angle equal to the system's latitude, an angle that, on average, gives the most power. Still other systems are simply placed in a convenient location, with the hope that savings during installation offset the cost of inefficiency. Here are some ways to install solar arrays:
Building integrated photovoltaics (BIPV). These building materials have thin-film photovoltaic surfaces built in. They produce electricity while doubling as an integral part of the building. The most common BIPVs are shingles and windows.
Rack structures. Cells are mounted in a panel angled toward the sun for maximum efficiency year-round. They can be mounted on the roof or on the ground.
Flat mounting. Flat-mounted arrays are mounted on a south-facing roof. Gable roofs may approach the ideal angle of rack structures. Efficiency drops on a flat roof.
Pole mounting. Similar to rack mounting, pole mounting strategically places cells in areas where sunlight is patchy because of trees, terrain, or buildings.
Tracking structures. Tracking structures follow the sun, getting maximum efficiency out of the cells mounted in them.What Does It Cost?
A 5-kilowatt system capable of powering the average home costs from $30,000 to $40,000 and has a life expectancy of 20-30 years. Before incentives, this works out to about 25 cents per kilowatt-hour, double to quadruple what most utilities charge.
Incentives can reduce some of the cost. Among the incentives are one-time grants that pay back part of your initial investment. They're often paid at $4 or $5 per kilowatt, or $20,000-$25,000 on a five-kilowatt system. Some states offer tax incentives, and you may make money selling power back to the electric company. You can take a federal income tax interest deduction if you finance the system through a second mortgage.
Costs, incentives, and economic feasibility of a PV system can vary widely:
- A California study found that after savings and grants, a system providing about two-thirds of a California household's power would cost about $6 a month.
- A study in New York found that a system large enough to power an entire house there would pay for itself in eight to nine years.
- In Philadelphia, half the cost of a $20,000 system providing 70 percent of a household's power is returned in rebates. The system would make about $100 a year above the cost of added electricity. But at $100 a year, paying the $10,000 balance would take 100 years.
You can determine what is available to you through the Database of State Incentives for Renewables and Efficiency (DSIRE) at dsireusa.org. Click on the state you live in to see a list of available incentives.
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