We were approached in early 2017 by the owners of a certified Passive House in Surry, Maine to install a solar photovoltaic system to move the home towards net zero, a term that means the home generates as much energy as it consumes.
The Passive House approach sets the table well for a net zero project by utilizing passive solar heating and cooling techniques along with high levels of insulation and air-tight construction. On this project, this includes large, south-facing windows that maximize solar gain during the winter months. The windows have an exceptionally high R-value to minimize heat loss. In the summer overhangs above the windows are designed to let in less direct sunlight when the sun is higher in the sky, which reduces cooling demand.
These approaches significantly reduce the home’s heating and cooling demands, which account for the bulk of a typical home’s energy use. Passive House design standards stipulate maximum heating and cooling energy demands per square foot. These low heating demands maximize the performance of high efficiency heating and cooling devices, such as the mini-split heat pumps used at this residence.
Due to its air-tightness, a Passive House must utilize active systems to maintain indoor air quality. This is accomplished through the use of a ventilator that preheats (or precools) incoming air by transferring heat from the air that is exhausted from the home.
During initial construction, the home was made “solar ready” by installing electrical conduit between the roof to the service panel. Two SolaDecks, junction boxes that are flashed into the roof to seal penetrations in the roof for passing wiring from the solar array through the roof surface, were installed to assist with the home’s solar readiness. This helped to facilitate our later installation and to ensure that penetrations in the building envelope were sealed by the original builder.
The roof construction used in this home required special attention during installation of the array. The roof consists of a monolithic membrane on top of braced roof trusses and capped with strapping to create a vented channel below the roof surface that is watertight and vaportight. The roof penetrations we made for securing the array to the roof needed to be precise to avoid disturbance of the membrane.