The obvious answer to this dilemma is cooling the panels and capturing the heat. Several systems use liquids to cool the solar panels and carry off the heat for use elsewhere. But introducing different materials presents problems with heat-related expansion and contraction among the materials.
Berkeley, Calif.-based PVT Solar Inc. has developed an elegantly simple solution to the cooling problem that not only makes solar panels more efficient but uses the heat generated by the sun hitting the panels to make hot water as well as heat and cool the home.
Carl Mulac, a former TOUSA Arizona exec who is now CEO of Joseph Carl Homes, has chosen PVT Solar's system for the CantaMia active-adult community in Newland's Estrella master plan in Sun City, Ariz. The 2-kilowatt Echo™ Solar system will be standard in most every home in the community (some will be smaller due to roof area), which at build-out will include nearly 1,780 homes ranging in size from 1,200 to 2,800 square feet and priced from the $130,000s to the mid-$300,000s.
The solar system is but one element in Joseph Carl Homes' standard green package, which was created under Masco's Environments for Living program. It includes air infiltration and roof radiant barriers, blown-in fiber-glass insulation, Energy Star appliances, low-e vinyl windows, compact fluorescent lighting, a Carrier Puron 14 SEER HVAC system, fresh-air intake filtration, programmable thermostats, jump ducts at all bedrooms, water-saving systems, and a central vacuum.
On opening weekend in mid-February, Mulac said 1,300 prospective buyers showed up, and there was so much interest in the green package on Saturday that the company retooled its sales pitch by Sunday. “The customers could not believe it was standard,” said Mulac.
The Echo Solar system was the prime point of interest.
What it does is circulate air under standard photovoltaic panels, then runs the air through a heat exchanger (usually placed in an attic), which draws off some of the heat and uses it to keep a hot water tank at or around the standard temperature of 120 degrees. It can also provide heating for HVAC systems, or even hot water for swimming pools and/ or spas. The system also draws night air, which is chilled by heat emanating from the photovoltaic panels via a process called radiative night sky cooling, into the home to provide cooling.
This makes the Echo Solar system more than three times more efficient than a standard photovoltaic system. When compared with a standard 2-kilowatt photovoltaic system that provides about 21 percent of a home's energy, Echo Solar would provide about 46 percent given the same conditions.
According to PVT president Gordon Handelsman, the homes at CantaMia, minus the Echo Solar system, would have a Home Energy Rating System (HERS) index between 70 and 80. With the addition of the Echo Solar system, that index falls to 40.5. That is nearly 60 percent more efficient than a home built to the standards of the 2006 International Energy Conservation Code.
Mulac said the anticipated builder's cost for the green package is about $15,000 per home, including utility rebates. There's some major scale involved, given that most photovoltaic systems alone run about $10,000 per kilowatt at retail. That, some would say, is quite a deal, particularly for the home buyer.