A lot of finger-pointing is going on in California these days. The rolling blackouts in January were due to deregulation gone awry … or failure to project rapid growth in demand … or permitting delays … or bottlenecks in power transmission. One thing is crystal clear, however: energy is back on the radar screen. People are talking about the oft-ignored commodity of electricity like never before. Some say that California’s problems this past January are a harbinger of things to come—on a much wider level—this summer. Far from unnoticed in all this discussion are the homes and businesses in California that were insulated from the rolling blackouts because they generate their own power with photovoltaic (PV) modules.
While PV power has been around more than 40 years, interest in this power-production technology has mushroomed recently. Production costs have continued to drop, and options have increased for integrating modules elegantly into buildings. This article takes a look at the state-of-the-art with PV power and building-integrated photovoltaics (BIPV) specifically.
Photovoltaics is the direct conversion of sunlight into electricity. To see just how different this form of electrical generation is, you have to understand that virtually all other power generation technologies in use today function with the same basic principle: rotation of a dynamo, or turbine. With coal, gas, oil, and nuclear power plants, the dynamo is turned by high-pressure steam, while hydro plants use falling water, and wind generators use the wind.
There are no moving parts in a PV cell—no turbine or bearings to wear out. All that moves are electrons. PV cells are made of semiconductor materials (semiconductors can be made conductive or nonconductive by altering the charge—a property on which the computer revolution was built). In a typical PV cell, two electrically dissimilar semiconductor materials are sandwiched together, separated by a
junction. Photons of light excite electrons on the
electron-donor side of the cell and cause them to jump across the junction to the
electron-acceptor side. By attaching electrical contacts to both sides of the cell and connecting those contacts with a wire, an electrical circuit is created—electrons want to flow back to their source. In a PV panel (or module), many of these cells are wired together—both in parallel and series—to create current that can accomplish useful work.
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