Solar Harvest in the Rockies
From the outside, with its rows of south-facing windows and its roof covered in solar panels, the Solar Harvest home resembles an ecologically responsible mountain inn or retreat. But instead of being located in a Rocky Mountain resort area, this 4,600-square-foot residence is situated in a typical neighborhood in Boulder, Colo., surrounded by older, more conventionally built homes.
If you have any doubts that this is a single-family home, the pebbled, xeriscaped garden in front might not be a dead giveaway. But if you take a walk around the back of the two-story building, you'll see a spacious flagstone deck, some patio furniture and a commodious solar-powered hot tub that bubbles at the flick of a control. A sturdy swing and climbing set just beyond the deck also lets you know that a family resides here.
Eric Doub, a general contractor and owner of Ecofutures Building Inc., planned and designed Solar Harvest with his wife, Catherine Childs. The couple and their two children, Ariel and Brian, have been living in the house since November 2005 - and since then the home has generated more energy than the family has consumed.
Photos Courtesy Povy Atchison
From the beginning, Doub wanted to rely solely on the sun for the home's energy needs, so his plans called for no backup furnace or boiler in the residence. "In fact, I was so determined that the home's heat supply come only from solar power that I eliminated all fireplaces from the plan," he explains, "so people could not say, "Well of course the house is warm, look at all the fireplaces.'"
At first, a plans examiner for the city of Boulder rejected Doub's proposal because of this lack of a backup-heating source. The chief building official later gave his OK "when our engineering calculations convinced him that the house could maintain a 68-degree temperature through eight cloudy, two-degree days," Doub says. "There are no records of that sort of weather in the entire history of Boulder."
Doub acknowledges that building a furnace- or boiler-free solar home might be more challenging in Michigan or Minnesota, but Colorado usually gets 300 days of sunshine throughout the year, making the sun-powered home possible. Upon its completion and following independent testing, the home was designated by Energy Star to be the most energy-efficient home in the state.
Electricity for Solar Harvest is supplied by a grid-tied 6.84-kilowatt solar photovoltaic (PV) system from Sharp Electronics Corp. The solar panels are mounted in two arrays: half on a first floor roof at a 20-degree tilt and half on an upper roof at a 40-degree tilt. These different tilt angles affect electricity production by only a few percent.
On cloudy days or at night, energy is purchased from the grid. But on sunny days, because the PV system is larger than it needs to be, it feeds excess electricity back into the utility grid, which results in net metering (spinning the home's electric meter backwards).
This was Doub and Childs' primary goal at every stage of the planning and construction of the dwelling - to create a "home power plant" capable of supplying more energy than it consumed, and to sell the excess energy back to the local utility. As of last May, they had not only met but exceeded their goal, as their electric meter showed about minus-400 kilowatt hours.
That same month, the local media gathered on Solar Harvest's front yard to record the moment when Doub reversed the customary cash flow from customer to utility and received an oversized cardboard check for $30,708 from the Colorado president and CEO of Xcel, the local energy company. The check was a rebate for the installation of the home's photovoltaic system and was made possible by Colorado's environmentally savvy voters, who passed Amendment 37 in 2004. This initiative stipulates that Xcel must generate 0.4 percent of its electricity through solar power by 2015. In compliance, the utility, through its Solar Rewards System, now gives customers installing solar systems rebates of about $4.50 per watt of solar power up to 10,000 watts, or 10 kilowatts.
Keeping It Comfortable
"Comfort, health and safety" are the qualities Doub strived to build into his own home, as well as all the homes he builds for his customers. And on the 90-degree summer day I visited Solar Harvest, there was "comfort" in the refreshingly cool air circulating throughout the home, in part because of geo-thermal pre-cooling. Incoming ventilation air is cooled as it passes through 260 feet of 6-inch PVC intake pipe buried 6 to 8 feet underground, where the temperature is a constant 55 degrees. In winter, the cold outside air is pre-warmed by the geothermal system.
Once it enters the house, the air passes through an energy recovery ventilator (ERV), which exchanges energy with the exhaust air. The conditioned air is then circulated throughout the building by a system called the Ultimate RecoupAerator from Stirling Technology Inc., based in Athens, Ohio. The earth-cooled air moves through the home during the day, while in the evening a whole-house fan from Tamarack Technologies pulls warm air up and out through attic vents.
Doub credits the home's insulation for an indoor temperature of 70 degrees on a hot June day. The home's exterior walls have 7 inches of Icynene expandable spray foam insulation, and the insulation in the ceiling is 12 inches thick. Aboveground walls are rated at R-34, while the ceiling is rated at R-45.
Walls were encased with double 5/8-inch sheetrock that provides distributed, indirect thermal mass. For the foundation, Doub used Greenblock insulated concrete forms (ICFs). The home's exterior is finished with GrailCoat SuperFlex Stucco, which breathes like standard stucco but prevents water penetration. Doub selected fiberglass windows from Fibertec, which have Heat Mirror insulated glass from Alpen. The glass blocks summer heat, retains winter warmth, maximizes the passage of natural daylight and reduces the damage to furnishings caused by ultraviolet rays.
Collecting Solar Heat
A sense of not only comfort but also peace and harmony prevails when you enter the home's main floor, which has a sizeable living room, dining room, kitchen, mudroom, half bath and small office. Childs, who designed the home's interior, chose varying shades of earth and neutral tones for the walls and fixtures. Her understated choices throughout the home convey a sense of simplicity and beauty. An abundance of glass and wood, including some floor-to-ceiling art display cases that Childs designed for the dining room and kitchen, add to the clean-lined, airy ambience.
Along the south wall of the main floor is a 275-square-foot "sunspace," resembling a porch or solarium. Many sun-thirsty plants flourish in this windowed area, but its main purpose is to function as a "solar furnace," collecting solar heat, which is then distributed to interior spaces through intake grilles in the ceiling and a series of ducts and fans.
Located on the home's second floor are three bedrooms, two full bathrooms and a guest wing with a bedroom and full bath that extends over the north end of the house. The basement has another guest bedroom and bath, a play and project area for the children, and lots of storage space.
Also located in the basement is a 6,000-gallon super-insulated solar cistern. Designed by Doub, the 18-by-7-by-7-foot tank collects hot water from 12 solar thermal flat-plate collectors mounted on the roof and stores the water at a temperature of 170 to 190 degrees. The cistern's coils of copper tubing act as heat exchangers, transferring heat to the domestic water supply. The cistern also provides hot water to a radiant floor heating system in the winter, and it keeps the 360-gallon hot tub at a therapeutic 103 degrees.
Solar Harvest is not only designed to be green and energy efficient; it's also a healthy place to live. Non-toxic water-based floor finishes and low-solvent construction adhesives were used throughout the home, as were Earth Weave natural wool, formaldehyde-free carpets with mold-resistant hemp cotton backing. Both salvaged oak and high-density bamboo were used for flooring; Marmoleum linoleum flooring was used in the mudroom.
The maple and cherry cabinets in the kitchen were made with wood certified by the Forest Stewardship Council, which indicates the wood was harvested from sustainable forests; the cabinets were finished with linseed oil free of formaldehyde and volatile organic compounds (VOCs). Quartz countertops from HanStone are heat and bacteria resistant, and required no sealing, conditioning or polishing, while the Avonite Surfaces countertops used in the bathrooms were made from recycled materials.
Doub points to the hardwood floors in the kitchen as an example of the "salvaged and second-hand materials" that were used throughout the home. Most of the doors and all of the bathtubs in the house were seconds or misorders as well, acquired from Habitat for Humanity and other local recycled building material vendors.
Doub says he inherited an interest in environmental issues from his energy-frugal, nature-loving parents. "I came by it naturally," he says. "My dad has not driven a car in years. He calls them "pollution waste machines.'"
This combination of family-held values, his own strong interests and early reading in the subject eventually led Doub to Stanford University. While there, he designed his own degree, which he identified as Sustainable U.S. Resource and Security Policies. He left his academic studies for a time and returned to Boulder to learn all he could about solar energy and energy-efficient homebuilding practices, then went back to Stanford to finish his customized degree.
In 1993, he founded his own contracting firm, Ecofutures Building Inc., and for his first project he built a solar greenhouse addition to his parents' home. Since then, Ecofutures has added many green homes to Boulder's eco-friendly landscape and retrofitted existing homes for maximum energy efficiency, converting their fossil fuel systems to renewable energy sources. "Most of the clients I have are filtered by the time they come to me," Doub says. "They are committed to doing everything they can to eliminate waste and toxins in their homes and in the environment."
If you're interested in building a solar home, Doub recommends that you "first educate yourself through books, journals and lectures, and get in contact with people in your area who are interested in building sustainable homes. The AIA [American Institute of Architects] is a good place to start. There is always an architect or designer in a city or town who is committed to green principles and practices." Beyond that, he suggests, "Build tight and insulate right."
After living in their home for nearly a year, Doub notes that "there is a build up of amazement at how comfortable it is." He admits that the five-bedroom, five-bath residence is large by most solar home standards, but adds that he and Childs anticipated that Solar Harvest would become a community resource where students, activists, family and friends would stay from time to time to learn more about solar building. Currently, Solar Harvest opens its doors to frequent tours, which are organized and conducted by Doub and Ecofutures.
Solar Harvest should hold up well despite all the foot traffic through it. Doub built the home to last 200 years, and hopes that in the future it might be used as a type of public center, providing both living space and meeting areas for environmental advocates. His proprietary interest in his home's future extends to details he realizes can do nothing about. "I just hope no one comes in here and considers our countertops to be the avocado green of the future," he says, smiling. After all, he points out, the durability of his chosen materials is only as good as the desirability of those materials to future generations.