When California-based Borrego Solar Systems decided to open a regional office in New England, Chris Anderson, the company’s chief technology officer, jumped at the chance to work in the new office. After more than a decade living in the San Francisco Bay Area, he and his wife, Anna Von Mertens, were ready for a change. The couple had wanted to move back east to be closer to family, and the new office location in Lowell, Massachusetts, was just across the state line from Hillsborough County, New Hampshire, Anna’s hometown and where her parents lived.
Years of close-quartered urban abodes had left the couple longing to spread out and build a home that fit their needs and ideals. Not surprisingly, their vision included solar-electric and solar hot water systems. And while living off the grid may not have been on their minds when they went house-hunting, being gifted with 14 acres within a 108-acre parcel that Anna’s mother had purchased to save from development changed their plans.
A conservation easement acquired by Anna’s mother limited construction on the acreage to a maximum of two homes, protecting all the farmland and forestland from additional development for perpetuity—even under new ownership.
Even with the small-town conveniences of Peterborough, New Hampshire, only miles away, Chris admits that the idea of moving off the grid was somewhat intimidating. Although he was confident that the solar-electric and solar thermal systems could be sized appropriately to meet their needs, the transition from city life to country living was a concern.
“We were coming from the city, where we had amenities at our fingertips,” says Chris, “and now we were trying to figure out what it was going to take to live off the grid. We had to learn the ins and outs of septic systems, evaluate the benefits of well water versus town water, and figure out how to get Internet and phone service.”
With power lines a third of a mile from the property, connecting to the grid was an option. And while they liked the idea of feeding excess generation from their solar-electric system back to the grid and capitalizing on the state’s net-metering rules, they didn’t feel comfortable with the idea of running power lines through the adjacent wetlands. The cost of grid connection—close to $50,000, including wetlands mitigation and utility work—seemed wasteful as well. Instead, the couple chose to put that money toward outfitting their home for off-grid living.
Chris and Anna enlisted longtime friend and architect Peter Larsen, of San Francisco, to design the home. The couple, who lived in an industrial loft space in Berkeley at the time, had a tall order. They wanted a home that fit the rural site and respected the local vernacular, yet had open, easily configurable spaces. Since they were planning to start a family, they also wanted room to grow—three bedrooms to accommodate a family of four comfortably. The design needed to be reasonably achievable for novice builders as well, since Chris and Anna planned to do much of the work themselves. Plus, the building design also needed to integrate the home’s solar energy systems gracefully.
The design premise included a roof-mounted photovoltaic system with a battery bank; a solar hot water (SHW) system for domestic water heating and in-floor radiant heating; and a backup pellet-fueled boiler and propane generator. A large south-facing roof sloped to optimize production from the PV modules and SHW collectors, plus enough utility storage space for all of the requisite RE equipment, were among the key design requirements.
Determined to have the exterior of the new structure fit in, the couple studied the design of the area’s original farmhouses and colonial homes. Together with Peter, they explored various ways to combine the modern and colonial influences, from the basic building shape and roof profiles to fine-scale details and finishes.
Months of collaboration gave way to a simple design with a two-and-a-half-car garage and a main house, joined by a mudroom and vestibule, and topped by gabled roofs. Though the expansive use of windows on the south side and a standing-seam metal roof may not strictly adhere to the local aesthetic, the profile takes its cues from the area’s colonial farmhouses. The exterior appears traditional, with rot-resistant cedar shingles left unfinished to weather naturally.
Inside, the layout and materials are modern. The 1,525-square-foot first floor hosts a great room and kitchen to the south, with a den, half bathroom, mudroom, and laundry room, while the second floor is divided into three bedrooms and two bathrooms, with an additional studio space for Anna, who works from home as a textile artist.
The home’s layout was designed for energy efficiency and passive solar gain. Primary living spaces, like the living room and dining area, are laid out along the south side, maximizing natural light in the most occupied portions of the house. In the winter, large south-facing windows capture solar heat until the late afternoon. On the north side, where the building will lose the most heat and needs protection from winter storms, windows are fewer and smaller. Secondary spaces, such as the closets, mudroom, half bathroom, and laundry room, are also clustered to the north.
On the first level, a concrete floor made with slag (an industrial by-product that replaces some of the portland cement) provides thermal mass for the radiant heating system and passive solar gain, minimizing backup heating needs in the colder seasons. High-density spray-foam insulation fills the wall cavity (2-by-6-inch studs on 16-inch centers), creating an insulating air seal for the entire home. An additional layer of 1-inch rigid foam board insulation was attached to the exterior framing under the wood shingles, reducing thermal bridges at each stud, resulting in R-24 in the walls. Additionally, wood-to-wood junctions in the framing were caulked to reduce air infiltration.
To insulate the basement floor and walls, 2 1/4-inch thick rigid foam board (R-10) was mechanically fastened to the exterior of the moisture-sealed foundation walls and 2 inches of CFC-free rigid foam board was placed on grade prior to pouring the basement floor. In addition, foam was applied to the junction between the sills and sill-plates and to the entire rim/band perimeter in the basement to reduce infiltration. Eleven inches of blown-in cellulose insulation in the attic (R-40), and triple-glazed windows and insulated doors complete the high-performance building envelope.
An early challenge was siting the proposed 2,900-square-foot house on the 14-acre parcel, which is bound and fragmented by colonial-era stone walls common throughout New England. The way in which the stone walls cut across the most viable site—a hilltop clearing—made a true-south orientation impossible. So the broad side of the house was angled to magnetic south—15° east of true south—only slightly reducing the solar exposure.
The designs for the energy systems evolved over several months alongside the architectural plans. Ultimately, the parameters set forth by the structure—siting, roof angle, roof space, and equipment storage—dictated what was possible for system size and equipment selection. The final architectural plans called for a roof angle of 45° for year-round RE system production and roughly 1,000 square feet of south-facing roof space to mount PV modules and SHW collectors.
Designing the PV system began with a comprehensive load analysis, including the electricity needed for the well pump, refrigeration, water filtration system, and the computer controls and circulating pumps for the heating system.
“Calculating loads is where being the homeowner and system designer is a real advantage. No information gets lost in the exchange,” Chris says. “Because I was closer to the information and I understood our daily use and lifestyle, I knew where we could trim down, and I was able to make realistic choices.”
Among those choices was the decision to put in a propane range and clothes dryer, instead of electric models that can tip the energy scales with even occasional use. As a concession, however, Chris and Anna vowed to line-dry their clothes as much as possible and use the propane dryer sparingly.
Based on a load estimate of 17 kWh per day (including future demands—i.e. children), Chris determined that a 6.8 kW system would slightly exceed their needs, allowing about 3 daily kWh of wiggle room.
Then the work was to maximize the PV system size in the allotted space. Chris ended up pairing 15 new 167 W Sharp modules with 27 used 160 W Sharp modules that he purchased from a system owner who had the other half of their roof-mounted modules stolen. Although the plug-and-play connectors had been cut in the theft attempt, Chris was able to make them work with some jumpers he made. He also ended up modifying the frames of the old modules to make them compatible with the new modules’ rail-mounting clips.
Although the inverter manufacturer does not recommend mixing and matching different module sizes, these modules had almost identical voltage ratings, so the losses were minimal and justified the money saved by purchasing the used modules. Ultimately, the pairing of new and used modules—wired in three 14-module series strings (fourteen 167 W modules, fourteen 160 W modules, and the last string comprised of thirteen 160 W plus one 167 W module)—worked well on the roof.
An architectural engineer and a licensed electrician, Chris has a technical background that trumps the average homeowner. Even still, he faced a slight learning curve when it came to working with the additional equipment that goes into an off-grid PV system. “At Borrego, we specialize in grid-tied PV systems, so it was challenging for me to shift my mind-set, and think in terms of battery banks, chargers, and backup generators,” he says.
The array feeds an SMA America Sunny Boy inverter that is AC-coupled to two SMA Sunny Island inverters wired to the battery bank in the basement. At a depth of discharge of 80%, 24 deep-cycle Surrette S460 batteries provide 840 amp-hours—up to two and a half days of energy with normal usage (about 17 kWh per day) or longer with conservative usage (13 to 14 kWh per day). The Sunny Island inverter system also controls a Kohler 12 kW propane generator to automatically charge the batteries as necessary—usually twice per week in winter and a few times per month the rest of the year, depending on weather patterns. The inverter will also start the generator periodically to equalize the batteries. The two Sunny Island inverters allow 240 VAC input/output to be used for balanced generator battery charging—and will be useful for powering a future workshop and a 240 VAC well pump.
For the solar thermal system, Chris turned to Henry Spindler of Optimal Energy Solutions in Keene, New Hampshire. Seven Heliodyne 4-by-10-foot collectors in a closed-loop antifreeze system with a heat exchanger heat water for a 738-gallon storage tank with two output heat exchangers each for the domestic hot water and radiant floor systems.
The domestic hot water system uses a 50-gallon Superstor pressurized tank that is heated through heat exchangers in the larger tanks. A Harman pellet boiler provides backup heating for the radiant floor system and the DHW. The 50-gallon DHW tank is piped to the boiler as a separate zone. This is a typical setup with hydronic heating systems, where the boiler provides heating for the DHW tank through a heat exchanger.
The radiant floor system was designed for minimal power usage, with zone valves to allow individual thermostat control in seven zones of the home. The pellet boiler acts as a backup to the solar thermal system, also providing heat to a 1,200-gallon storage tank. (Additionally, the wood heater in the living room provides supplemental space heating, typically in the shoulder seasons when it is more practical to put another log on the fire than start up the boiler.)
The solar thermal system uses three strategies to prevent overheating in the summer months due to seasonal load imbalances. The control system energizes a zone valve that allows the system to thermosiphon at night until a selected temperature is reached, effectively limiting tank temperature through passive night radiation. Should the tank temperature still be too hot, the controls then circulate water to the larger 1,200-gallon boiler storage tank. In the event that both tanks reach the selected high temperature, the collector loop is energized at night to circulate fluid through the system and dissipate heat through night radiation.
Low-flow faucets and showerheads help conserve water throughout the home. A water recirculation system sends sink and shower water back to the tank—instead of down the drain—until it warms up.
Currently, the AC-coupled PV system generates an average of 12.5 kWh per day. This is well below the designed 20 kWh per day that the system should be able to produce, due to the system being oversized for future needs. When energy production exceeds household consumption (frequent especially in the summer months), the Sunny Island sends a signal to the Sunny Boy inverter to put out less energy to prevent overcharging the batteries. This is the case with any stand-alone PV system that does not use diversion loads. If excess power is available but there is nowhere to send it, available power must be tapered down to avoid overcharging the batteries. When the future loads are added, the system will be able to more fully utilize the existing PV array, and the average daily kWh production will be higher.
The solar thermal system provides all of the DHW and any required heat for the home through early fall. In the dead of winter, the thermal energy generated from the collectors is enough to bring water in the 738-gallon storage tank up to about 92°F—an ample temperature to provide baseline heating through the radiant floor system. For heating performance, Chris says, the system must circulate water that’s at least 10°F warmer than the desired air temperature. Since the DHW generally requires a temperature of 115°F, the backup boiler is usually required in the late fall, winter, and early spring.
Chris estimates that they’re saving approximately $1,700 per year in avoided heating fuel costs—assuming $2,400 fuel costs for fuel oil compared to their actual cost of $700 for pellets. Their solar thermal investment will continue to pay off as heating oil prices rise.
Chris and Anna say that the shift to off-grid living with renewable technologies has been fairly seamless. The real challenges of off-grid living were less tangible—adapting to the seclusion of their new surroundings, for instance, while raising their daughter Hayden, who was born a month after their home’s completion.
“Not having neighbors was a big change. There’s no running next door to borrow a cup of sugar. Our only neighbors are the few houses we can see far across the valley,” Anna says.
That may soon change. Friends from Berkeley, who also plan to start a family, purchased the adjacent 14-acre lot from Anna’s mother and are starting construction on the second home allowed under the conservation easement. The plan is to connect the two homes’ solar-electric systems, using underground conduit Chris already put in place, and someday add a wind turbine between the two properties for additional RE generation.
Associate editor Kelly Davidson and her niece are doing their part to keep New Jersey’s beaches clean by picking up trash on their walks. Even 4-year-old Ava Jade knows that trash on the beach spoils the fun for everyone.
Optimal Energy Solutions LLC • 603-354-7919 • SHW design
Peter Larsen • 415-335-0857 • Architect
PV & Solar Thermal System Components:
Grundfos • www.grundfos.com • Circulation pump
Harman • www.harmanstoves.com • Pellet boiler
Heat Transfer Products Inc. • www.htproducts.com • DHW storage tank
Heliodyne • www.heliodyne.com • SHW collectors
Sharp Solar • www.solar.sharpusa.com • PV modules
SMA America • www.sma-america.com • Inverters
STSS • www.stsscoinc.com • SHW storage tank & heat exchangers
Surrette • www.surrette.com • Batteries