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The US Department of Energy (US DOE) has published Decarbonizing the U.S. Economy by 2050: A National Blueprint for the Buildings Sector, which contains a link to the full study. The blueprint’s objectives include increasing energy efficiency, reducing on-site emissions and increasing demand flexibility. The following are some thoughts about a new construction decarbonized home.

The average US single family home contains approximately 2300 square feet of living space. The most efficient configuration for such a house is a two-story structure with approximately equal area on each floor. The structure would likely feature foamed-in-place insulation and limited window area. New homes built to match the DOE blueprint would be all-electric to eliminate on-site emissions. and the HVAC equipment and major appliances would be internet connected to maximize opportunities for demand management.

The home would provide approximately 500 square feet of South-facing roof with the roof pitch adjusted to maximize collection of solar energy from approximately 380 square feet of solar collectors or solar roof shingles. The solar system would generate approximately 7.5 kW at peak, or approximately 25-50 kWh per day, depending on location weather and season of the year. Approximately 40 kWh could be stored in on-site batteries. An average single family detached home uses approximately 10,000 – 16,000 kWh per year, depending on location and appliances and equipment, or approximately 25 – 45 kWh per day. Note that all-electric homes in cold climates would experience maximum energy consumption in winter, when the output of the solar collectors was significantly reduced as the result of lower sun angle and shorter days.

The average home would have a 2-car garage, which would be equipped with chargers for 2 electric vehicles. The electric vehicles would add approximately 10 – 15 kwh each to the home’s daily energy consumption. However, the EVs would typically have to be charged from the on-site batteries or the grid, since they would likely be away during the day and require charging at night, when solar collector output is zero.

The availability of electric power from the on-site solar and battery systems would reduce the demand on the electric utility grid. However, the similarity between average daily solar collection and average daily usage suggests that grid backup would be essential to assure power reliability during periods of low solar energy generation, such as cloudy, rainy or snowy days. Therefore, the grid would require substantial storage capacity, since it would likely experience low solar availability during the same times as its customers.

The installed cost of solar collectors is approximately $2.50 per watt. Therefore, the installed cost of the 7.5 kW system described above would be approximately $19,000. The on-site storage batteries would add approximately $42,000. One suggested approach to funding the solar installation is utility ownership of the solar system and inclusion of the system costs in the utility ratebase. System ownership and maintenance costs would be added to the utility’s monthly service charge.

The availability of solar energy from on-site generation would reduce the average load on the “grid edge” facilities, including distribution wiring and transformers. However, the increased demand.imposed by EVs and electric heat pumps would likely increase grid demand during periods of low solar availability.