With an estimated total energy load of 13,560 kilowatt-hours per year for each townhome, the combined output of the 3-kilowatt PV array and a 56-square-foot thermal solar collector is expected to supply a little more than 50% of the residence’s energy requirement. Doug Boleyn, consulting engineer for the project, says that’s impressive for an all-electric home on Oregon’s chilly Columbia River Gorge.
But this shouldn’t be surprising, given that the Mosier Creek development was built to the highest energy specification. This LEED-certified project features high- efficiency heat pumps, and Energy Star appliances and lighting. Two-by-six studs framed at 24 inches on center conserve lumber and reduce thermal bridging, and R-21 insulation in walls, R-30 in the floors, R-38 in ceilings, and low-emissivity, high-performance windows throughout help ensure each townhome’s excellent thermal performance. The townhomes are sited in an east–west orientation to maximize solar gain. In all, the buildings use 30% less energy than energy-efficient buildings of a decade ago.
At just under 1,600 square feet, space was at a premium in the two-bedroom townhomes—both inside and on the roof. So the common two-tank solar water heating system—with a solar preheat tank and conventional backup water heater—was abandoned. Instead, a 120-gallon solar tank with built-in heat exchanger and a single upper electric element serves as both the solar preheating tank and backup electric water heater within a single footprint. The tank fits neatly beside the energy-efficient clothes washer and dryer in each townhome’s laundry room.
Twenty-eight individual PV systems, with a total installed capacity of 86.7 KW, were installed by Tod LeFevre, P.E., of Hood River, Oregon-based Common Energy LCC. PV Powered inverters, which are manufactured in Bend, Oregon, were specified to synchronize the output of the PV arrays with the utility grid.
On the roof, keeping the solar collectors and PV modules at a low profile was important to the streamlined architecture of the development. The long side-to-side layout of the Sol-Reliant collectors fits nicely with the roof plan and individual PV arrays.