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| A close-up of the PV array. | A 6.9 kW PV system provides enough electricity for the house and electric car. | The house’s grid-tied inverter. |
Although this Nashville, Tennessee, all-electric home does not “officially” qualify as net-zero energy, homeowners Steve Johnson and his family show a financial surplus on their utility bill at the end of the year. The grid-tied PV system was designed with net-billing in mind, so that the annual cost of their energy zeroes out each year. Under TVA’s Generation Partners program, the system generates surplus credit ($480 for 2011). Last year, the Johnsons bought an electric Nissan Leaf, and now they are saving an additional $1,750 on gasoline while recharging the Leaf with solar electricity.
In addition to the home’s grid-tied PV system, the Johnsons use PV technology in other places: on a golf cart (690 W); on their barn (510 W off-grid system); and for a solar-pumped fish pond. A 20-watt PV module powers LED trail lights. They also use a 30-year-old Elec-Trak lawn tractor and employ the simple technology of two 10-watt solar attic fans to help keep the attic (and, therefore, the home) cool.
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| A stand-alone (off-grid) PV system provides electricity for the horse barn. | The large stone hearth provides thermal mass, absorbing passive solar gain and storing heat from the wood stove. | The house’s ground-source heat pump uses PV electricity to gather heat from the earth. | Steve Johnson charges his family’s Nissan Leaf with electricity from the grid-tied PV system. |
