Building-integrated photovoltaics (BIPV), which can replace more traditional building elements while also producing electricity, are now available for most building envelope surfaces. For example, architects can specify photovoltaic shingles, metal standing-seam or exterior insulation systems for the roof. Solar-collecting spandrels, insulated glass units, and sunshade elements are available for curtain-wall systems. And glazing that produces electricity while allowing transparency can be ordered for skylights.
BIPV products fall into one of two categories: crystalline and thin-film. The crystalline technology relies on silicon as the semiconductor material. It is currently available in three types: single-crystal, polycrystalline, and crystalline ribbon.
Both single-crystal and polycrystalline are essentially produced by creating solid blocks from molten silicon. The resulting ingot is sawed into wafers about 5 inches square and .012 inches thick. In the production of crystalline ribbon, the molten silicon flows through a die to form a faceted pipe or flat ribbon, which is then sliced with a laser into similarly sized wafers.
These wafers are processed into cells, which are soldered together in series to achieve the desired voltage. The series is then laminated onto glass. The laminated cells are covered by a plastic backsheet or another sheet of glass.
Single-crystal cells are usually a flat black; polycrystalline cells are a sparkling shade of blue; and crystalline ribbon cells tend toward purple. Custom colors, though possible, decrease the cell's rate of efficiency- the percent of incident sunlight converted into electricity.
Crystalline PV Modules: Generally speaking, single-crystal is the most efficient in terms of electrical output, but it is also the most expensive to manufacture. The sunlight-to-electricity conversion rate is 12 to 17 percent for single-crystal; 11 to 14 percent for both polycrystalline and crystalline ribbon; and 5.5 to 7.5 percent for amorphous silicon. The newer thin-film technologies promise slightly higher efficiencies than amorphous silicon. The average cost for a reasonably sized order of 20 kW (peak) standard factory modules is about $6.50/watt or $78/square foot for single-crystal; $6.25/watt or $71/square foot for both polycrystalline and crystalline ribbon; and $5.50/watt or $28/square foot for amorphous silicon. Actual costs will vary, depending on the modules specific features.
Thin Film: According to one manufacturer, thin film PV technology holds several key advantages over traditional sliced crystal silicon PV technology - it is significantly less expensive, they tend to be more efficient and flexible in a variety of installed environments and they are inherently suited to Building Integrated Photovoltaics (BIPV). While it is true that thin-film solar panels require more area to reach the same nominal wattage as crystalline, new studies suggest that under most real world conditions, amorphous silicon (a-Si) modules produce more energy per-installed-watt than crystalline technology (thin film panels are on average 10% more efficient on a per watt installed basis at low power density levels). In conjunction with the low-cost manufacturing nature of thin-film, this will produce the lowest cost solar power.
Photovoltaics can be one of the most visible components of an energy-efficient building. It should not, however, be the first - and certainly not the only - energy-savings measure considered during design. The building needs to be worthy of a solar array. Architects should first optimize the project‘s site orientation and massing, incorporate passive solar heating and cooling strategies, maximize daylighting opportunities, specify energy-efficient equipment, and consider energy-recovery systems to reduce the building‘s overall energy needs. The benefits of solar energy will not be fully realized until the building is as energy-efficient as possible.
The advent of cost-effective, building-integrated photovoltaics has, however, made sustainable designers rethink the nature of energy-conscious architecture. In the past, people were taught that boxy buildings - those with relatively small surface areas in comparison to their internal volumes - were the most appropriate because they can conserve the most energy. Now buildings can be energy producers allowing buildings with BIPV systems to be slimmer and more elongated to maximize their surface areas. They should reach out to the sun with lots of glassy surfaces, canopies, and pergolas to collect solar energy for electricity.
When calculating payback, BIPV proponents recommend considering variables such as the potential reduction in construction costs when BIPV components replace other building products.
- The federal government offers two incentives to use BIPV products: a 10 percent investment tax credit and a five-year accelerated depreciation.
- Oregon offers a Business Energy Tax Credit through the Oregon Department of Energy of approximately 35% of installed system cost applied over 5 years.
- The Energy Trust of Oregon offers up to $15,000 for homeowners and up to $35,000 for businesses installing photovoltaic systems.
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