1/19/2015

Net-Zero Living in a High-Performance Home

Greater energy independence, freedom from fluctuating energy prices, and environmentally-friendly living are alluring concepts that motivated my family to examine our housing and our lifestyle. We recently purchased a high-performance home and installed a solar system, making our home net zero. We now produce as much power as we use over the course of a year.

To realize the dream of a net zero home, we bought a super efficient home at Belfast Cohousing & Ecovillage, a 36-unit multigenerational community in Midcoast Maine, with triple-pane windows and doors, virtually airtight construction, a solar orientation, and lots of insulation. The sun, appliances, and occupants provide a majority of the heat needed to keep our home cozy.

On sunny winter days, our heaters remain off, as the sun gradually warms the house. Electric baseboard heaters kick on as needed, primarily at night or on cold, cloudy days. The home is all electric – with an electric range, hot water heaters, and space heaters. Because we don’t use propane, natural gas, or heating oil,  a solar system can produce all the energy that our home consumes.

Our home has a Zehnder heat recovery ventilation system to ensure high indoor air quality and comfort. Because the home is airtight, mechanical ventilation is essential for fumes and moisture from showers and daily activities to exit the building. Just as important, an airtight home needs a ventilation strategy for the incoming air.  By incorporating a heat recovery ventilator, the constant stream of fresh incoming air is filtered and then preheated – pulling the heat from the outgoing air.

Our home does not have exhaust fans. While 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. Our heat recovery ventilation system recovers most of the heat, keeping our energy use down. Zehnder systems are up to 95 percent efficient, allowing our home to achieve a level of energy efficiency and indoor air quality that wouldn’t be possible otherwise.

Before installing a solar system, we examined how we could further reduce our energy use. We swapped out halogen and incandescent light bulbs for LED bulbs, installed a low-flow shower head to reduce our hot water use and removed the screens from the south-facing windows throughout the winter for greater solar gain.

Last summer, we helped organize the largest community solar purchase in Maine for our neighborhood and we installed a solar system on our home. Because the homes are so efficient, a relatively modest solar system can generate all the needed power over the course of a year. Some of our neighbors with similar homes installed solar systems a year or more before us, which helped us size our system. The Grace/Mebee family realized 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% of its power from a 2.6 kW solar system.

Our homes are connected to the power grid, eliminating the need for batteries. Our local power company has a net metering program, making the solar system more cost-effective. On 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.

It’s gratifying to know that we are harvesting the clean solar energy that falls on our property, both passively with large south-facing windows and actively with a solar system.  Even in a 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.

Sarah Lozanova is a regular contributor to environmental and energy publications and websites including Mother Earth Living, Mothering, Energy International Quarterly, ThinkGreen.com, Triple Pundit, CleanTechnica, Green Business Quarterly, Natural Home, GreenBiz, Renewable Energy World, Windpower Engineering, and Solar Today.  She currently lives with her family in the Belfast Cohousing & Ecovillage.