Types of DG: Photovoltaics
Photovoltaics use solid-state materials to produce electricity directly from sunlight. Although the up-front installation costs of photovoltaic (PV) systems can be relatively high, the systems can last 20 to 30 years, and once installed they consume no fuel, their maintenance costs are low, and their operation produces no emissions. Hence, their environmental impacts are very low and their lifetime costs drop dramatically when compared to installation costs. The public appeal of using solar energy to produce electricity results in a positive marketing image for PV-powered buildings and can thereby enhance occupancy rates in commercial buildings.
Photovoltaics are particularly useful for helping to meet peak cooling loads in buildings, since their power output reaches a maximum at midday, when cooling loads are greatest. In commercial applications of PV, building designers should examine the potential savings in terms of both electricity consumption and peak demand. Building designers should also determine if the local utilities offer rebates or credits for installing PV systems.
The best strategy when considering a PV system is to integrate it into the initial design of the building. This can be done in several ways. For example, the system may be integrated into the roof of a building, to become part of the roof's structure as well as providing electricity. Alternatively, PV cells can be laminated into glass being used in the building, such as in the windows of a building or into a daylighting concept, to provide electricity in combination with shade and sunlight. PV systems can also be easily retrofitted onto existing buildings, on rooftops, on added awnings, on solariums, or on nearby land, if it is available. Examples of unique applications that have recently been gaining popularity are included below.
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Photovoltaic Roof
Shingles |
Photovoltaic Window
Shades |
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Photovoltaic Window Panes |
Photovoltaic Awnings |
Whether retrofitting a PV system onto a building or incorporating one into an original design, there are several options on what kind of system could be utilized— systems that track the sun on two axes, that track it on a single axis, or that are installed in a fixed position. For most buildings, the fixed position option has been preferred, especially for those in which the system has been incorporated into the building design.
While conventional PV design has focused on the use of independent applications in which excess electricity is stored in batteries, grid-connected systems are becoming more common. In these cases, electricity generated in excess of immediate demand is sent to the electrical grid and the PV-powered building receives a utility credit. Grid-connected systems are often integrated into building elements.
PV power is being applied in innovative ways. Typical economically-viable
commercial installations include parking lot, pathway, or sign lighting,
emergency telephones and small outbuildings.
A typical PV module consists of 33 to 40 cells and is the basic block used
in commercial applications. Typical components of a module are aluminum,
glass, tedlar and rubber; the cell is usually silicon with trace amounts
of boron and phosphorus. Photovoltaic systems are adaptable, and can easily
be removed and re-installed in other applications. Systems can also be
enlarged for greater capacity through the addition of more PV modules.