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roof-mounted solar power system

solar modules on roof
A solar power system in which solar modules (solar panels) are integrated into, or mounted on top of, the structure of a roof. Usually, the best location for solar modules is a south-facing roof, but roofs that face east or west may also be acceptable. Flat roofs also work well for solar power systems, because solar modules can be mounted flat on the roof facing straight up or fixed to on frames tilted toward the south at an optimal angle (see solar collector orientation and tilt).

So, why would I use PV?

The sun generates enough clean energy in one day to provide a year's supply of energy for your home or office, so it makes excellent sense to tap into this abundant resource of clean energy. Solar energy technology helps preserve the Earth's dwindling fossil-fuel resources – coal, oil, and natural gas – and reduces air and noise pollution associated with these energy sources. Consumers and businesses also benefit from photovoltaic (PV) technology when faced with power outages and future electricity price increases. Recent technological breakthroughs, combined with federal and state programs and incentives, have greatly reduced the costs of PV ownership. Also, PV system reliability and durability are outstanding – typical PV systems may last 30 years with minimal maintenance.

Is my home or office building a good place for a solar system?

A PV system needs unobstructed access to the sun's rays for most or all of the day, throughout the year. Don't worry if you live in an area with a changing climate. PV modules are relatively unaffected by severe weather. In fact, some PV cells actually work better in colder weather. Solar modules are angled to catch the sun, not snow, so any snow that does collect melts quickly. Even hail won't harm them. But you will need adequate roof space to mount your PV system. Most residential systems require as little as 50 square feet (for a small "starter" system) up to as much as 1,000 square feet for larger systems. Whether you are considering a retrofit to an existing roof, or proposing a system in your new construction plans, solar electricity can be a viable source of energy for your home or office. But remember, an energy-efficient building needs a smaller PV system. In other words, the more energy efficient your home or office is, the less energy you will need to produce. A typical one-kilowatt system would occupy from 80 to 360 square feet. The size of your system will depend on your energy needs and usage habits. As part of your purchase process, a solar professional such as a designer or installer, should work with you to assess your needs and the appropriate of size of your system. A PV system can be installed on any type of roof, although some roof types are simpler and cheaper to work with than others. If your roof is older and needs to be replaced in the very near future, you will want to replace it at the time the PV system is installed to avoid the cost of removing and reinstalling your PV system.

What does a typical PV system look like?

A typical photovoltaic system consists of solar cells connected electrically to form a module that can measure two to four feet wide and four to six feet long. Some solar modules look just like traditional roof shingles. Many interconnected PV modules are called a solar array. An array is often mounted on the roof of a building, facing south at an angle, so that the modules receive the maximum amount of sunlight. Other typical features of a PV system are an inverter, which changes your electricity from direct current to alternating current so it can be used by most standard appliances and computers. Batteries may also be added for emergency backup in the event of power outages or in cases where your PV system is not connected to utility power lines.

How can I use PV in my home or business?

Today's photovoltaic systems can be blended into virtually every conceivable structure for homes or commercial buildings. You can find PV being used outdoors for security lighting in gardens, parking lots, and bus shelters. These PV structures can also serve as cover that generates power at the same time. Inside family homes or high-rise office buildings, PV can be used for the operation of all electrical systems, including lights, cooling systems, and appliances. PV systems should be sized according to your electricity needs and budget. In general, PV systems in buildings are sized such that the PV system fully or partially meets the building loads. Those loads will be easier to meet when the building is energy efficient. If your home or building is already connected to a power line, you may be able to get credit for your "net" electricity – the amount of power consumed from the utility minus the power generated by your PV system – through an arrangement with your local electric utility company called "net metering". If your electricity consumption exceeds generation by your PV system, you simply obtain the needed electricity from your utility, as usual.

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