Solar Stewardship: Page 2 of 4

Solar Hot Water

Cost: $1,000 after $1,500 state tax credit

In 1997, Candace received approval from her neighborhood advisory board to add a 4-by-10-foot solar hot water collector on the south-facing roof of the garage. In the open-loop drain-down system, potable water is directly heated in the solar thermal collector. During cold weather, when temperatures drop below 40°F, an automatic valve drains the water out of the system and into a rainwater collection system. This drain-down system protects the collector and pipes from freezing. Once the temperature on the collector rises above 40ºF, the valve allows water into the collector. Although thousands of these systems were installed in the 1990s, most were abandoned due to their complexity and common failures during freezing—in favor of closed-loop glycol systems. But Candace’s system has worked perfectly through the years.

The 120 VAC controller sends energy to the drainback valve and pump independently, based on three temperature sensors. The system has demonstrated a 50% savings over the former electric-only water heater, depending upon weather.

Two fan-assisted hydronic heaters are connected in line with the solar water heating system—one in the garage apartment and another in her son’s attic bedroom. Hot water from the solar preheat system and gas backup heater is pumped through a water-to-air heat exchanger, and a fan blows room air across it, providing ample warmth to those well-insulated areas.

1.5 kW Photovoltaic System

Cost: $5,800 after $6,200 Energy Trust credit and $1,500 state tax credit

In 2004, Candace installed a grid-tied PV system to offset the household’s utility electricity use. The roof-mounted design was originally approved by the city, but rejected by the neighborhood advisory board. Their concern? That the array would be too visible from the street-side view of the house and set an unacceptable precedent for future design considerations in the historic neighborhood. The alternative pole-mounted design was, however, given the green light—even though the array in the corner lot’s side yard is equally, if not more, visible. The change in plans turned out to be a good thing, as the new site gets better and longer solar exposure.

Candace teamed up with Mr. Sun Solar, the company that also helped install her solar hot water system, to install the solar-electric system—(14) 110-watt BP modules wired in two strings of seven, feeding into a PV Powered 1,800 W inverter. To cut costs, Candace and her student crew did a lot of the grunt work, hand-digging the trenches and the 3-foot-diameter, 9-foot-deep hole for the pole, and pouring the concrete.

The array was mounted on a UniRac rack with an 8-inch-diameter, schedule 40 galvanized steel pole. The pole—with 9 feet underground and 12 feet above ground—was anchored in 2 1/3 cubic yards of concrete, and designed to withstand 100 mph winds.

The energy-aware household—five people living in the three apartments—uses about 5.5 kWh per day during the summer and about 20 kWh in the winter. At 3.95 average daily peak sun-hours, the system averages 4.3 kWh per day.