Sustainable Building Technical Manual - Etn-presco.net

P h o t ovo l t a i c s★ S I G N I F I CA N C E .Photovoltaic (PV) technology is the direct conversion of sunlight to electricity using semiconductordevices called solar cells. Photovoltaics are almost maintenance-free and seem tohave a long life span. The photoelectric conversion process produces no pollution and canmake use of free solar energy. Overall, the longevity, simplicity, and minimal resourcesused to produce electricity via PV systems make this a highly sustainable technology.PVs are currently cost-effective in small, off-grid applications such as microwave repeaters,remote water pumping, and remote buildings. While the cost is high for typical applicationsin buildings connected to the electric power grid, the integration of PVs into commercialbuildings is projected to greatly increase over time. In fact, worldwide PVmanufacturing is growing at a healthy annual rate of more than 20 percent, and the focusof research is to reduce the cost of PV systems, and to integrate PV into building design.The most common technology in use today is single-crystal PVs, which use wafers of siliconwired together and attached to a module substrate. Thin-film PV, such as amorphoussilicon technology, is based on depositing silicon and other chemicals directly on a substratesuch as glass or flexible stainless steel. Thin-film PV materials can look almost liketinted glass. They can be designed to generate electricity from a portion of the incominglight while still allowing some light to pass through for daylighting and view. Thin filmspromise lower cost per square foot, but also have lower efficiency and produce less electricityper square foot compared to single-crystal PVs.PV panels produce direct current, not the alternating current used to power most buildingequipment. Direct current is easily stored in batteries; a device called an inverter isrequired to transform the direct current to alternating current. The cost of reliable batteriesto store electricity, and the cost of an inverter, increase the overall cost of a system.With an inverter creating alternating current, it is possible to transfer excess electricitygenerated by a photovoltaic system back into the utility grid rather than into batteriesfor off-grid systems. In this case, the utility grid becomes a virtual storage system. Mostutilities are required to buy such excess site-generated electricity back from the customer.Recently, through what is called a “net-metering law,” a few state legislatures orpublic utility commissions have mandated that utilities pay and charge equal ratesregardless of which way the electricity flows. Building owners in such states will findPVs more economically attractive.. ☛ SUGGESTED PRACTICES AND CHECKLISTIInstallation Sites❑ Consider conventional and remote electrical uses for PV power.– Conventional uses include communications or testing devices that need to operatecontinuously without supervision or require direct current. Park districts and transportationdepartments have installed small PV systems to power emergency telephonestations. Water districts have installed PV systems to power monitoring equipment.– Remote uses include applications in off-grid areas and for small, isolated electricuses. For example, isolated communities can store medical supplies in refrigeratorspowered by PVs. Any appliance that can run off a 12-volt battery with direct currentis a good application for remote PVs because it does not require an inverter to createalternating current.– Recreational areas far from utility service, such as parks, beaches, and campsites, are