Passive Solar Design
Harnessing the Sun’s Energy
Our passive solar design capitalizes on the building’s orientation to the sun to maximize solar heat gain through super energy-efficient windows. Our goal was to incorporate as many high-performing windows as possible in the home’s south wall to harness the sun’s energy.
Eight 4x6-foot high-performance windows and a glass panel door stretch across our home’s south side. The sun streams through the windows during its low wintertime transit and warms the interior. During the sun’s high summertime transit, the windows are shaded by the foliage of two mature oak trees.
We installed blocking in the south wall’s framing so we could attach horizontal shade trellises, fitted with angled slats, above the two banks of south-facing windows to keep the house from overheating in the summer, but we haven’t needed to add the shade trellises as the trees are doing the job.
North-Facing Lot Challenge
Super-performance south-facing windows are energy gainers, while east and west-facing windows are both gainers and losers. But north-facing windows are strictly energy losers. Ideally, in a northern climate a passive solar home would have no north-facing window and door openings. Since the front of our home faces north, we needed a street-friendly design that would minimize energy-draining openings while maximizing a welcoming visual appeal.
This challenge was compounded by a city ordinance requiring new houses to have a minimum of 15% glazing (windows and doors) on exterior walls facing a street. We applied for a variance to allow 9.4% glazing on our street elevation, appealing to our city’s energy efficiency goals for new construction and the reality that we could not control the direction from which the sun shines.
Thankfully, our neighbors and the Saint Paul Board of Zoning agreed that our proposed facade—with three 4’4”x4’4” windows, a front door with inset window, and an attached front porch—struck a good balance between retaining the integrity of the home’s energy-saving envelope while keeping the neighborhood’s vernacular spirit intact.
The home’s north side.
Grid-Tied Solar Panels
Our city lot’s solar exposure is along the shorter side of the house, limiting the square footage of southern window glazing. We quickly realized that, in order to offset the home’s energy expenditure and reach net zero, we needed to augment the solar energy production by installing photovoltaic (PV) solar panels on the south-facing roof of our detached garage. We installed 7.695 kW, which was the maximum capacity of our roof.
7.695 kilowatt solar array installed on our south-facing detached garage roof.
At the time of our build, we were able to take advantage of two solar panel purchase incentives. The first was a Made in Minnesota Solar Incentive Program that was offered through the Minnesota Public Utilities Commission, which pays 27 cents per kilowatt hour of electricity produced by our solar panels for 10 years. The second incentive was a federal Solar Investment Tax Credit for 30% of the system’s cost, which can be used over 5 years. Incentives like these help pay for solar investments in a relatively short time—in our case, 8 years.
All Electric
The electrical panel in the back entry.
The house is powered completely by electricity. The heat recovery ventilator (HRV), mini-split heating and cooling units, water heaters, and all appliances and lights are electric.
All the appliances—refrigerator/freezer, cooktop/oven, dishwasher, clothes washer and dryer—are Energy Star rated. A tankless on-demand water heater housed in the second-level utility closet services the bathrooms and kitchen sink, while a smaller one under the kitchen sink boosts the dishwasher. The toilets have a dual flush feature offering the choice of either 0.8 or 1.6 gallons per flush. The shower heads and faucets are low flow EPA WaterSense and ADA compliant. All the light fixtures use LED bulbs.
We designed a combustion-free house to avoid burning non-renewable oil and gas and subsequently adding those pollutants into our home and global environment.
Our Utility Bill
Our monthly utility bill reflects the amount of energy the house produces and consumes. We keep the house at a relatively even indoor temperature throughout the year: 74°F in winter and 76°F in summer. During our high energy production summer months our bill is credited. During our high consumption winter months we have a debit on our account. Some months we get a check from the utility, some swing months the balance is zero, and some months we pay. Over a year’s time (for 7 out of 8 years between 2017 and 2024) the house has produced more energy than it consumes.
From 2017 to 2024 we also used our solar array to power a plug-in hybrid car (see chart below). We estimated its consumption from our solar array at around 2000 kW per year. In 2023 we added a fully electric car to the mix.
Solar Production & Home and Car Consumption
Most Often Performing at Net Positive!
In 2017 our PV solar array produced 8,477 kilowatt hours (kWh) of electricity, which was sent to the grid. The house and our plug-in hybrid car (we had the car for the last 8 months of that year) consumed 7,139 kWh. The utility credited us $88.58 from our net metering. Our total electric utility cost was $234.48 ($221.80 of which our utility provider charges for meter fees and city taxes).
In 2018 our solar array produced a total of 8,018 kWh of electricity. The house and plug-in hybrid car consumed 7,576 kWh. The utility credited us $65.32 from our net metering. Our total electric utility cost was $239.78 ($221.80 of which was for meter fees and city taxes).
In 2019 our home consumed more than our solar array produced, as that winter Minnesota experienced record low temperatures—down to -28°F in January! Except for that year, the house has performed at net positive!!