Environmental Design + Construction - March 2009 - (Page 25) Economic Stabilization Act of 2008 that was passed in October 2008) extended until 2016 a 30-percent-investment tax credit for residential solar installations and eliminated a $2,000 tax-credit cap. For more information, visit www.gosolarcalifornia.ca.gov. But legislation and rebates are a moot point without the technology to facilitate the use of solar energy in a home. In a typical photovoltaic array, solar panels (located either on the roof of a home or the ground nearby) capture the sun’s rays. A solar inverter, located in its own enclosure, subsequently converts the rays from DC to AC power and delivers it to the home’s utility feed. If there is a power outage, the inverter must disconnect from the utility to avoid backfeeding the power grid, which is a key safety issue. Some inverters can interconnect to a battery system so solar energy can be stored and used to power critical loads during an outage. Once DC power has been converted to AC, it is routed through a back-fed circuit breaker contained within the home’s combination service entrance device and ultimately supplements utility power. Current transformers, also located at the combination service entrance device, monitor the home’s electrical system providing information to the photovoltaic system’s metering mechanism so the homeowner can quickly ascertain how much solar power is being generated by the array. Due to the high cost of a photovoltaic system, some homebuilders are opting to proactively install a combination service entrance device and do as much pre-wiring as possible well in advance of installing a photovoltaic system. For example, the Square D Combination Service Entrance Device has space for a backfed circuit breaker and a current transformer mounting for monitoring equipment; these areas can remain unused until the inverter and photovoltaic array are installed. Being proactive regarding solar is a key message electrical contractors and homebuilders should deliver to their homeowner customers due to economics, Mark Pavletich says. “At the time you put in the array — when you pull all your wires from the array to the inverter — you’re saving money because all the pre-wiring and conduit has been done,” he says. A CONTRACTOR INSTALLS A RESIDENTIAL PHOTOVOLTAIC SYSTEM. THIS 8.9-KW INSTALLATION IN CORVALLIS, ORE., USES 48 185-WATT SOLAR PANELS CONNECTED TO THREE XANTREX GT 3.0 GRID TIE SOLAR INVERTERS. Information Gateways The energy and cost savings a photovoltaic array generates can be substantial. A 3,000-watt system, for example, can reduce a typical homeowner’s electric bill by roughly $50 to $60 per month allowing for variations based on utility rates among other factors. But knowing how much energy a photovoltaic system is generating is only half of the equation — managing that energy is the other half. That’s why a communications gateway is so important. A communications gateway, like the Xantrex Communications Gateway from Xantrex Technology Inc., for example, is a small device (6 inches by 4 inches) mounted indoors or in an enclosure outdoors. It’s connected to the photovoltaic system’s inverter using Cat-5 cable and to the home’s wireless network using its built-in Wi-Fi capability. A software application on the home’s personal computer communicates with the gateway via the wireless network to provide the homeowner critical system data such as: ■ How much power the photovoltaic system is generating; ■ Daily, weekly, monthly and even lifetime power generation trending; ■ Energy cost savings; ■ Greenhouse gases saved (e.g., carbon dioxide); and ■ Progress toward return on investment for the entire system. The availability of this data can also suggest courses of action for the homeowner such as augmenting the photovoltaic system with more solar panels to increase the amount of solar energy accrued in order to achieve netzero energy usage. Of course, augmenting the system can translate to lower monthly electric bills and possibly a faster return on investment for the entire system. Seizing the opportunity Solar energy may be a great opportunity for electrical contractors and homebuilders, but there is a learning curve — particularly A SQUARE D COMBINATION SERVICE ENTRANCE DEVICE FEATURES SPACES FOR COMPONENTS NECESSARY TO DISTRIBUTE SOLAR ENERGY THROUGHOUT A HOME, BUT IT CAN OPERATE LIKE A COMMON RESIDENTIAL LOAD CENTER UNTIL THOSE COMPONENTS ARE INSTALLED. www.EDCmag.com 25 http://www.gosolarcalifornia.ca.gov http://www.EDCmag.com
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