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.

Despite the effects the struggling economy has had on new home construction, interest in supplementing residential power with solar energy is growing. The primary driver is economic. In the United States, for example, state and federal capital rebates help a homeowner ease the cost of installing a photovoltaic system. In Canada, feed-in tariffs mean utilities purchase solar energy from an individual homeowner at a higher rate than the homeowner would pay for grid electricity, which provides an incentive for homeowners to install photovoltaic systems.

Additionally, the cost of a photovoltaic system is dropping. According to USA Today, the cost of a rooftop array, including installation, is expected to fall as much as 20 percent in 2009, which is in addition to the substantial drop that already occurred in autumn 2008. Another factor is that the housing slump means new homeowners are more likely to remain in their homes for a longer period, thus increasing the return on their investment in a photovoltaic system.

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.

But interest in solar power is also being spurred by advances in electrical distribution technologies that allow a homeowner to proactively plan for the future installation of a photovoltaic system. For example, a 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. Once a photovoltaic system is in place, communications gateways help a homeowner track the amount of solar power being generated. They can play a key role in helping homeowners “net zero” their energy use — meaning that, in a calendar year, the solar power produced and used is equal to or greater than the home’s grid power usage.

These technological advances coupled with the many economic incentives make solar energy a more alluring opportunity for electrical contractors and homebuilders alike. Though 90 percent of residential photovoltaic system installations are on existing homes, that trend could be shifting. Some housing developments are demanding that a certain percentage of new homes be solar-ready, while many homebuilders are using solar energy as a market differentiator.

“You need to know how to sell solar,” says Neal Pavletich, who co-owns electrical contracting firm Star Electric in Bakersfield, Calif., with his son Mark. “You have to instill confidence in the customer that what you propose is good for them now, next year and in the future.”

Enlarge this picture A screen shot showing kilowatt hours produced by a Xantrex GT Inverter for the previous 24-hour period. The top portion of the graphic indicates the current amount of power (4.6 kW) being generated by the solar system.

Economics vs. Technology

While a photovoltaic system can create substantial energy savings for homeowners, a typical 3,000- to 5,000-watt system can cost a homeowner tens of thousands of dollars. However, U.S. federal and state capital rebates help reduce that cash outlay. For example, the California Solar Initiative offers residential solar rebates in two formats: One based on actual energy output by the photovoltaic system; the other is based on expected performance, where an upfront lump sum is paid to the homeowner by the state based on factors like equipment ratings and geographic location. From a federal standpoint, the Energy Improvement and Extension Act of 2008 (a component of the Emergency 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 back-fed 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.

Enlarge this picture A screen shot from a Xantrex Communications Gateway showing the lifetime energy generation and cost savings. Note: NOx is nitrous oxide, a greenhouse gas.

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 net-zero 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 with regard to recent technological advances like combination service entrance devices and communications gateways. There are many ways to gather information about these technologies, from conferences and trade shows to the Internet to contacting trusted suppliers of electrical distribution equipment. The next step is to seek opportunities to apply this knowledge.

“We hope that we can up-sell this equipment to our homebuilders to give homeowners the option of putting in a photovoltaic system when they buy,” Mark Pavletich says. “If people can come in and view the system in a model home, it will make sense to them.”