Another Confirmed Energy-Positive Home
Shortly after I started my new firm devoted to high-performance architecture, Timothy and Lindsey Von Fange tracked me down. They needed help designing their new energy-positive home in rural Bartholomew County, Indiana, near where they both grew up. Among their goals was energy independence with an energy-positive home. They recently sent a year’s worth of energy consumption and production data for their roof-mounted solar photovoltaic (PV) array, showing they produced more energy than they used (see graph). Producing more energy on-site than you use meets the most common definition of an energy-positive home. They are officially part of the solution instead of part of the problem. Their home has negative carbon emissions and a positive impact for generations, including their three children.
One of the discussions on this project was whether it made sense to consider going off-grid since connecting a long electric service line to the local rural electric cooperative would be expensive. They were also concerned that being literally at the end of the power line might mean more outages, and they didn’t want to be without power for extended periods with three children.
You are usually better off connecting to the grid unless the cost is extreme. Assuming that a solar photovoltaic array will provide on-site power production, you will have an overproduction of electricity in summer and underproduction in the shorter days of winter (see graph). Due to the high cost of battery storage and the need for additional backup power in winter, going off-grid would require a significant investment in battery storage that may double the system cost. Off-grid strategies may also include a backup gas or diesel generator, a higher investment in the building envelope, or some non-electric heating source in winter (but then you still need to count that energy consumption in your energy balance). With a grid-tied system, you can sell electricity back to the grid and derive electricity from the grid when your system is not producing electricity. In this case, Jackson County Rural Electric also provided high-speed fiber-optic Internet direct to their home, which became critical during the pandemic.
Like nearly all buildings I design, the Von Fange residence is all electric. Reduced electricity consumption is achieved through good building envelope design, all-LED lighting, energy-efficient appliances, and high-performance heating and cooling via a ground-source heat pump, commonly called a geothermal heat pump. In this case, the geothermal heat exchange piping was installed in vertical boreholes due to an extensive septic field, making horizontal trench installation impractical. Geothermal heat pumps use the earth as a heat source in winter and a heat sink in summer. It is much more efficient to move heat energy than to produce it. Geothermal heat pumps can be twice as efficient as air-source heat pumps, especially in frigid weather, and 3 to 5 times more efficient than a fossil fuel furnace without the associated safety, health, or greenhouse gas emissions risks. You also have no outside condensing unit, which means you can enjoy the sounds of the country without the mechanical noise overcoming birdsong. Tax incentives and utility rebates can significantly reduce the cost differential of geothermal versus conventional or air-source heat pumps. In my home addition project, the cost difference between geothermal and air-source heating and cooling came down to zero with incentives. The recently passed Inflation Reduction Act restores the full 30% Federal tax break for geothermal and solar PV systems for ten years. Utility rebates vary, but you can find that information on the Database of State Incentives for Renewables and Efficiency.
One of the common misconceptions with a PV electric system is that you will have solar power during a grid power failure. With a typical grid-tied system, the solar PV system must shut down during a power failure to reduce hazards to linemen. With a hybrid inverter, however, you can instantly switch to battery backup power, isolate your system from the grid, and recharge those batteries with your solar array or a fossil-fuel generator. Extreme heat events associated with climate change will increase the need for air conditioning and stress the electric grid, potentially leading to blackouts when electricity is most needed. The nonprofit First Street Foundation has an online risk calculator resource, Risk FactorTM, that makes it easy to access environmental risk factors by individual home address. According to Risk Factor, the Von Fange address will experience a 171.4% increase in the number of days with a comfort index over 103 degrees F. From 7 such days a year now to 19 in 30 years. Extreme heat events increase the need for air conditioning that works even when the grid is down. It also speaks to the need for shade, heat-blocking windows, optimal insulation, walkout basements, and reflective roofing. Commercial projects may benefit from covering the parking areas with solar PV to provide power and shade, as with Indiana’s first net-zero-energy medical facility, Orthopedic Associates in Newburgh, Indiana.
With a regulated utility like Duke Energy, net metering makes grid-tied solar pay off faster as those utilities pay you more than wholesale for the power. Senate Bill 309, enacted by the Indiana Legislature in 2017, sunsets net metering in Indiana for regulated utility customers despite a strong protest from a broad coalition of Hoosier voters. Most rural electric cooperatives don’t offer net metering rates on electricity sold back to the grid. Excess clean electricity sold back to the grid is typically credited at the wholesale rate, while the electricity you use is billed at the retail rate.
In addition to the potential for battery backup during power failures, battery storage offers the ability to keep and use more electricity on site instead of sending it back to the grid at a discount. The Von Fange’s priced battery storage for their system but decided to wait for the price of batteries to come down. They futureproofed their solar PV installation by installing a more expensive hybrid battery-ready inverter that works like a regular inverter for now but can work with battery backup in the future. They also look forward to charging their future electric vehicles with their solar PV system. Free fuel from sunlight! At current gas costs, home PV systems pay off even faster than if they were powering only the home. It may become typical for electric vehicles (EVs) to also act as backup power storage for the home in an extended blackout. As used EV batteries become more common, I think we will see those repurposed for home energy storage at a more attractive cost. Electric vehicles are usually charged at night when the sun isn’t shining, which adds to the list of reasons to harvest excess electricity produced in your battery storage for use later in the day and overnight.
Congratulations to Timothy and Lindsey and their family for setting an example for others to follow. Who wants to be next?