Even so, Gibson estimates that a 1,500-square-foot ecovillage home (without a PV system) uses $300 for heating each year (2,000 kWh at $0.15 per kWh), while a standard Maine home costs more than $2,500 to heat, using an estimated 680 gallons of fuel oil.
What makes the homes so energy-efficient is the attention to details, like insulation and air-sealing. The outer walls are a hybrid system: blown-in cellulose in 2-by-4 framed interior walls and 8.25-inch structural insulated panels (SIPs), achieving R-45. The load-bearing portions of the slab are 12 inches thick, with 4-inch-thick floors. The concrete slab is insulated with 6 inches of EPS rigid foam, slowing heat loss to the ground, and the ceilings have 24 inches of loose-fill cellulose for R-80. The house-wrap seams were taped to complete an air barrier, significantly reducing heat loss due to infiltration.
The triple-glazed wood-aluminum Unilux windows have an SHGC of 0.5 and a U-factor of 0.09. The R-7 windows and doors help keep the homes virtually airtight, and promote ventilation and summer comfort when open. The windows can swing inward on two hinges or be hinged on the bottom to tilt inward, opening at the top. The latter offers draft-free ventilation and prevents rain from entering the home.
Despite being clustered, the ecovillage houses shade each other very little, and only in the early morning and late afternoon. All of the homes are oriented either due south or within 30° of south, making them well-suited for PV and solar water heating systems.
Most of the homes have enough roof space for a grid-tied PV system large enough to offset the home’s electricity using net billing. Some roofs also have room for a couple of solar collectors for water heating. The roof pitches vary—30° on the smaller units and 40° or 45° on the larger units. These angles are well-suited for year-round PV system performance and ease of winter snow removal. All of the homes are PV-system ready, with a junction box on the roof, concealed conduit running from the roof to the load center, and dedicated breakers in the electrical panel. To date, 22 of the 36 ecovillage homes have PV systems installed. One home also has a solar water heating system.
“It was nice to work on a project where there are a large number of folks who are interested in solar power,” says John Luft of ReVision Energy, which installed the first 11 systems. Homebuyers were given the option of a PV system as part of the homes’ feature selection process, and the option of including the system cost in the mortgage. GO Logic provided estimates of energy usage and a variety of solar options drafted by ReVision Energy that were customized to each home based on house size and number of occupants.
In the summer of 2014, residents organized a collective purchase for 11 additional PV systems, which were installed by Capital City Renewables (CCR). To receive wholesale rates on the PV modules and components, all of these systems used Axitec 250-watt PV modules with Enphase microinverters. The systems range in size from 2 to 5 kilowatts. Two BC&E members were trained and helped install the systems with the CCR crew.
With so many PV systems, Central Maine Power was concerned that the transformers couldn’t handle the back-feed, and the utility required BC&E to commission a study. It was determined that numerous PV systems could be supported without upgrading the transformers, although CMP imposed a limit—no more than 150 kW of PV capacity. There was also concern about the “resiliency” of BC&E’s all-electric homes when the utility grid goes down, considering that all the PV systems are grid-tied without battery backup. But so far, residents have—literally—weathered the winter storms with relative ease. Even without mechanical heating during a winter snowstorm and several-day utility outage, indoor temperatures remained relatively constant.
The ecovillage homes are all electric, in part because the 36 units are clustered on 6 acres of a 42-acre site. “There were a lot of discussions of whether or not to have wood heaters,” says Alan Gibson, a principal for GO Logic. Because of air-quality issues and the heating loads of the buildings being so low, it made sense to install inexpensive electric-resistance baseboard heat.
Gibson estimates that using electric baseboards in every room, controlled by individual thermostats, instead of a conventional oil-fired forced-air central furnace, saved $15,000 in each 1,500-square-foot home, although other energy-saving techniques—such as the heat-recovery system ($3,000; see “Heat-Recovery Ventilation” sidebar); increased insulation ($17,000); and triple-pane windows and doors ($8,000)—added to the construction costs.
The mission of the ecovillage includes sustainability, so solar energy was part of the initial vision as a major source of energy for the community. “We didn’t want to truck in deliveries of fossil fuels, so oil and propane were out,” says Gibson. “If you can afford a PV system to meet all of your annual electricity needs, [electric heat in a super-efficient house] can be a greener alternative.”