Portland, Maine, contractor ReVision Energy started out as a solar energy company, installing solar water heaters and photovoltaic power arrays on rooftops in northern New England. But in the last five years, ReVision has opened up a new niche: along with the solar power, ReVision installs high-efficiency air-source heat pumps that can use the solar-generated juice to heat the house—with a three-to-one multiplier effect.
This month, JLC went to a jobsite in Portland to see a ReVision crew install a 4,000-watt solar array on the south-facing roof, and a pair of one-ton (12,000-Btu) Fujitsu mini-split heat pumps.
The solution depends on a "grid-tied" setup: An inverter in the home's garage converts direct current (DC) from the PV panels on the roof into alternating current (AC) synchronized with the power supplied to the house from utility power lines on the street. On long summer days when the solar panels make more power than the house needs, the house feeds power to the grid. During the winter, the utility supplies the home with power to run its heat pumps and meet other domestic needs. In effect, the house is using the electrical grid as a storage battery. The solar array is sized so that on a net annual basis, the PV supplies about the same amount of current that the heat pumps will use every year, which means that, aside from financing the installation cost of the equipment, the owners get the output of the heat pumps for free. Once the system is paid for, the house will be harvesting free heat from the roof for as long as the heat pumps and the solar panels last.
ReVision sent a crew of five technicians to the house: three to set and wire the solar panels, and two to install the heat pumps, requisite wiring, and refrigerant lines. It took two days for the crew to equip the house.