Heating, Hot Water With Solar PV

Editor’s Note: EarthTechling is proud to repost this article courtesy of GreenTech Advocates. Author credit goes to Steven Castle.

Can you get all of a home’s electricity, heating and hot water from a solar photovoltaic (PV) electric system?

That’s what Dave and Suzy Enos of Bedford, Mass., are doing with their home and a 1,300-square-foot addition.

Dave Enos of Bedford, Mass., in front of his addition and 10-kw PV array that will provide the energy for all of his home’s heat and hot water. (image via Green Tech Advocates)

The panels for a 10-kilowatt Sanyo solar electric array line the roof over the Enoses’ new three-car garage, which is wired for 220-volt electric vehicle chargers. Also under the roof is a rental apartment in the making, which will be heated by a Fujitsu AOU12RLS air-source heat pump that can also cool the space. The heat pump, which resembles a mini-split air conditioning unit, is powered by the solar electric array—and this is tied to the electric grid to effectively sell power back to the utility, thereby cutting or eliminating the Enoses’ electric bills.

An 80-gallon Kenmore hybrid water heater will heat water with a built-in air-source heat pump and electricity from the solar array, Enos says. The heat pump unit uses warm air around it to help heat the water. An Energy Star-rated hybrid water heater that uses heat pumps and electricity—either from the grid or a solar array—can save users $300 a year or more in energy costs.

The Enoses paid $55,000 for the solar system, $51,000 or which was out of pocket. After federal, and state tax credits and other incentives, they’ll pay about $31,000 and look to pay off the system in six to eight years.

Energy savings will not just result from the solar array. The addition is super-insulated, with a thick, R60 level of insulation under the roof, R40 lining the walls, R20 in the basement and sides of garage walls and R10 under the concrete garage floor. The addition clad in an insulating HardiePlank cement fiber siding that has the weight and feel of tile.

The existing part of the house will undergo a deep energy retrofit, with additional insulation under the roof and in the exterior walls. Once the rental unit is completed, the Enoses will move into that and renovate their existing house. That will be heated and cooled by two more air-source heat pumps.

Using a solar electric system to provide heat and hot water for a home is somewhat unusual, but in the Enoses’ case, it made sense. Solar thermal systems, which produce domestic hot water—and in some cases home heating—by heating water or antifreeze behind glass plate collectors, often provide “better bang for the buck,” and generally cost around $10,000 to $12,000, which is far less than most PV systems. But Enos was concerned about a solar thermal system’s maintenance as a more mechanical system, especially if the couple is traveling or if renters are confronted with system issues. The Enoses have lived abroad for months at a time, though Dave says he pulled the trigger on this big energy renovation because “my wife and I are planning to stay here” and will reap the energy saving benefits from the system after it is paid off.

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