Backed Up in the Rocky Mountains

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Robins Ranch in Colorado’s high country outside of Black Hawk.
Robins Ranch in Colorado’s high country outside of Black Hawk.

When Burnett and Kristin Gunter retired, they decided to pack up their life in northern California and head for Colorado’s high country outside of Black Hawk. Instead of downsizing, as most empty nesters do, the couple built a 5,000-square-foot house on land that has been in Kristin’s family since the 1920s. The house was built to serve a dual purpose—as the couple’s retirement residence but also as a retreat for Kristin’s siblings and cousins, with whom she co-owns the 150 acres.

The couple lives on the main level, occupying 2,000 square feet, while a walk-out basement, roughly the same size, has two bedrooms, two bathrooms, and a large family room to accommodate visitors. “The goal,” Kristin says, “was to build a home that everyone and their families could enjoy—now and for generations to come.”

Thinking about the next generation, and their utility bills, the couple wanted to harness the sun and the open solar window to offset 100% of their electricity use. Their starting point was a 2,400-square-foot workshop where Burnett rehabs cars and trucks, and stores equipment used to maintain the property. The shop was erected about one year prior to home’s construction and built with a south-facing roof pitched at 34°.

The roof accommodates a grid-tied 10.92-kilowatt PV system wired to a 48-volt, 2,490-amp hour battery bank and 20 kW generator housed in the workshop’s electrical room. “The system solves two needs—it generates renewable electricity and provides backup. While the grid in this area is very reliable, big snowstorms can and do happen, and we wanted to make sure we had backup power,” Burnett says.

The system was sized to provide enough electricity for the home’s day-to-day use, but also handle the peak use from multiple visitors. The home features a mix of LED and compact fluorescent lighting. Most of the household appliances are electric, except for a gas dryer and the range. The system also powers an energy recovery ventilator that transfers warmth from inside air that is being exhausted to the fresh air being drawn from outside.

A high-efficiency natural gas boiler with a sidearm water heater supplies the home’s in-floor radiant heating and hot water. Zone heating allows the heat in the home’s lower level to be kept at a minimum when not occupied. The couple supplements radiant heating with a wood-burning masonry heater in the great room on the main floor, which they fire up once in the morning and once in the evening on the coldest days.

Perched on an unprotected hillside 9,000 feet above sea level, the home had to be resilient against inclement weather and cool temperatures. Even in the summer months, day temperatures rarely top 75°F, and night temperatures may dip below 40°F. The main level walls and ceilings are 6.5-inch, R-42 structural insulated panels that are insulated with a high-density urethane foam. In the basement, 8-inch stud-framed walls are filled with closed-cell polyurethane spray foam for R-50. Double-glazed casement windows oriented to the south provide natural light and passive heat gain, while opening the home to panoramic mountain views.

Self-professed tinkerers (and retired engineers), the couple has tested the PV system in several scenarios, disconnecting from the grid and running off battery power for periods of time.

The system started generating in November 2012, providing electricity for the last leg of house construction. As of January 2013, the system has produced 13.5 megawatt-hours. The system was designed by Patty Bruton at The Solar Biz and installed by Namaste Solar in Boulder. The total came to $73,845, with the federal tax credit and a local rebate from United Power bringing the final cost to $49,442.

Kelly Davidson

Comments (4)

Fred Golden's picture

I am a big fan of evacuated tube solar hot water systems and heat pump water heaters. Installing these with a large enough hot water storage tank could allow the boiler to take the summer off, and save a lot of fuel.

The tank could also feed hot water to the floor system, and having dual setpoint thermostats in the lower level, it could be set back to say 45F when not occupied, and 75 - 78F when the solar water storage tank is above 135F.

Andrewl's picture

Heavy snowfall seems like a strange reason to want to have solar panels. Surely snowfall on the panels would stop panels from working at all?

Michael Welch's picture

Utility outages are a concern for these homeowners.

Yes, if covered in snow, PV modules won't put out anything. Fortunately, any part of the PV module that gets exposed to the sun creates some heat, which works to melt more snow, exposing more of the module to the sun for even more heat and more melting.

Even ambient daytime temperatures may warm the modules from behind, and if the tilt is appropriate snow and ice just slide right off. PV modules clear themselves more quickly than many folks realize.

But also note that the system includes a generator, so if there is no access to sun for whatever reason, the generator can be fired up long enough to recharge the batteries.

nick pine's picture

Natural gas??? Looks like a great place for engineers to apply solar air heaters or low-mass sunspaces with heat storage...

Nick

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