Freedom from fluctuating energy prices, greater energy independence and eco-friendly living are alluring concepts that motivated my family to examine our housing and our lifestyle. We recently purchased an ultra-energy efficient home and installed a photovoltaic solar system, making our home net zero. Our solar system now produces as much power as we use over the course of a year.
To realize the dream of a net zero home, we bought a high performance home in Belfast Cohousing & Ecovillage, a 36-unit multigenerational community in Midcoast Maine on 42 shared acres. Our home has triple-pane windows and doors, virtually airtight construction, a solar orientation, and lots of insulation. Appliances, the sun, and occupants provide a majority of the heat needed to keep our home warm in our cold climate.
During sunny winter days, our heaters remain off, as the sun gradually warms the home. The electric baseboard heaters kick on as needed, primarily at night or on cold, cloudy days. The home is all electric — with an electric stove, hot water heaters, and space heaters. Because we don’t use natural gas, propane, or heating oil, a 4-kW solar system can produce all the energy that our home consumes, for a family of four.
To ensure high indoor air quality and comfort, our home has a Zehnder heat recovery ventilation system. Because the home is airtight, mechanical ventilation is essential for fumes, odors, and moisture to exit the building. Just as important, an airtight home needs a ventilation strategy for incoming air. By incorporating a heat recovery ventilator, a constant stream of fresh incoming air is filtered and preheated — taking the heat from the exhaust air.
Our net-zero home does not have exhaust fans. Although they effectively vent stale air out of a home, they are not energy efficient because the heat is not recovered when the air exits the home. The heat recovery ventilation system recovers most of the heat, keeping our energy use down. Zehnder systems are up to 95 percent efficient, allowing our house to achieve a level of energy efficiency and indoor air quality that wouldn’t be possible without it.
Before installing a solar system, we examined how we could further reduce our energy use. We swapped out halogen and incandescent light bulbs and put in LED bulbs, installed a low-flow shower head to reduce our hot water use, and removed the screens from the south-facing windows during the winter for greater passive solar gain.
Last summer, Belfast Ecovillage organized the largest community solar purchase in Maine for our neighborhood and we installed a solar system on our home. Because all of the houses are so efficient, a relatively modest solar system can generate all the power used over the course of a year. Some of our neighbors with similar homes installed solar systems a year or more before we did, which helped us size our solar system. The Grace/Mabee family met their net zero goal last year with a 4.5-kW solar system for a 1,500 square foot home and the McBride residence generated 95 percent of its electricity from a mere 2.6-kW solar system.
The homes are connected to the electric grid, eliminating the need for batteries. The local utility company has a net metering program, making the solar system more cost effective. During sunny days, our system feeds excess power to the grid, and the credits are banked in our account. When the sun isn’t shining, we pull power from the grid. Most Belfast Ecovillage solar systems bank credits from April through October and use credits the remainder of the year.
It’s fulfilling to know that we are harvesting the free solar energy that falls on our property, both passively with large south-facing windows and actively with a solar system. Even in our cold climate where most homes are heated for 6 or more months of the year, all our energy needs are met by a winning combination of an energy-efficient design and solar energy.