How a solar roof works
[June 02, 2009]
How Stuff Works: How a solar roof works [BC-HOWSTUFFWORKS:MCT]
(McClatchy-Tribune News Service Via Acquire Media NewsEdge) If you ever travel to Charlotte, N.C., there is an amazing facility there called U.S. National Whitewater Center. The facility is essentially an artificial river where humans have complete control over the flow rate, up to Class IV rapids. People from all over the country travel to Charlotte to train and compete.
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On the roof of one of their buildings they have another amazing facility. They have installed a 5,000 watt photovoltaic solar roof system that is able to generate electricity directly from sunshine. This is the kind of system, and the size of system, that you would need if you wanted to generate all of your home’s electricity using sunshine. Therefore it is a great way to understand how a residential solar power system works.
In addition, the system at the U.S. National Whitewater Center has a real-time monitor that allows you to see exactly what the system is doing right now. You can find it here: http://www.usnwcsolar.com. If you go to that Web site on a sunny afternoon, you will find that the Whitewater Center is producing four or five kilowatts of electricity using free sunlight.
This solar roof system is remarkably simple, and that is one of the things that makes it so appealing. There are three parts: 1) The framework on the roof, 2) the solar panels, and 3) an inverter.
Depending on the type of solar panels you are using, the framework on the roof can be simple or elaborate. There are manufacturers who have integrated solar cells right into shingle-like products. In that case, you nail the product onto the existing roof structure just like ordinary shingles. Sometimes you have to attach an aluminum or wooden framework for the panels.
The solar panels contain the equipment that converts sunlight to electricity. At the U.S. National Whitewater Center they are using lightweight, flexible solar panels that are 15 inches wide. They look like 18-foot-long rolls of flashing. To create a 5,000 watt system, they use 36 panels that produce 136 watts each. Panels like these can be glued to smooth plywood or metal roofs like big stickers.
The more traditional solar panel is made of individual silicon solar cells. The silicon cells are fairly fragile, so they are placed in a frame made of aluminum, plastic and glass. A typical panel produces 100 to 200 watts. These panels tend to be thicker and heavier, and typically mount to an aluminum frame.
The electricity coming out of the solar panels is like the electricity that comes out of a battery. This is called DC or Direct Current electricity. To use the electricity in your home you need to convert it to AC or Alternating Current. A device called an inverter does the conversion. You can use the electricity immediately. Or, if the panels are producing more power than your home needs, you can send the electricity out onto the grid and sell it to the electric company.
This certainly sounds promising. The sunlight is free. The electricity coming out of the panels is therefore “free”. There are no moving parts so the system should last for decades. And a 5,000 watt system will produce all of the electricity a typical home would need. The only question left is, “how much does a system like this cost to install?” The reality is that these systems are still fairly expensive. The 36 panels cost $700 each, and the inverter is $3,000. By the time you add wiring, installation and roofing modifications, a system like this runs in the ballpark of $30,000. If you assume you can produce an average of 30 kilowatt-hours per day, and the electricity is worth 10 cents per kilowatt-hour, that works out to a 10,000 day payback period. And that is about 27 years. If you live in a bright, sunny area, and if electricity is more expensive, and if you can get a big tax credit for doing it, it might make sense. But for the average homeowner, a system like this is hard to justify at today’s prices.
___ (Looking for more? For extra info on this or the scoop on other fascinating topics, go to HowStuffWorks.com. Contact Marshall Brain, founder of HowStuffWorks, at marshall.brain@howstuffworks.com.) ___ (c) 2009, How Stuff Works Inc.
Distributed by McClatchy-Tribune Information Services.
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