TODAY’S STUDY: How Community Solar Figures Into Zero Net Energy Homes
Beyond Zero Net Energy? Alternative Approaches to Enhance Consumer and Environmental Outcomes
Ryan Hledik, Bruce Tsuchida, John Palfreyman, June 2018 (Brattle Group)
• Zero net energy (ZNE) initiatives focus narrowly on energy efficiency and clean energy generation at the individual building level, ignoring the advantages of a more inclusive approach. • A broader, system-oriented approach to satisfying decarbonization objectives could improve upon the consumer and environmental outcomes that would otherwise be achieved through ZNE initiatives. The use of community solar to power a development of energy efficient homes is one example of such an alternative approach. • Due to economies of scale and a higher capacity factor, the community solar-based approach could serve a development of 200 energy efficient homes with total solar PV project cost savings of approximately 30 to 35 percent relative to conventional ZNE configurations.
A zero net energy (ZNE) home is designed to produce as much energy from clean on-site energy sources as it consumes each year.1 Policymakers have become interested in ZNE building code initiatives as a way to achieve decarbonization goals. Recently, the California Energy Commission adopted an update to the state’s building code, requiring that new homes offset their annual electricity consumption using solar power beginning in 2020 (though natural gas use does not have to be offset).2
However, the narrow focus of ZNE initiatives on energy reductions and on-site generation at the individual building level presents several often overlooked challenges.
• The potential economic advantages of grid-connected renewable generation are often discounted or ignored in ZNE initiatives.
• A focus on energy conservation overlooks the potential environmental benefits of “beneficial electrification,” which could produce net environmental benefits even if the result does not minimize the home’s total energy consumption.3
• Certain residential building types – including some that are environmentally advantageous, like high-rises – may have difficulty meeting ZNE standards because of site qualities, roof area, or size.
• While ZNE with rooftop solar PV implies energy independence, customers still must rely on the grid for electricity when the sun is not shining, and may export electricity to the grid when solar PV output exceeds the home’s energy demand.
Given the above considerations, there may be attractive alternatives to ZNE initiatives with lower costs, expanded participant eligibility, and improved environmental benefits. Possibilities include expanding the ZNE “boundary” beyond that of the individual home, considering a broader range of zero-carbon generation resources, aligning generation with the timing of the home’s consumption profile, and recognizing the system-wide benefits of new electric end-uses beyond a narrow focus on energy conservation (e.g., accounting for the grid resiliency benefits of appliances with flexible electricity demand).
In this report, we explore just one of many possible ways to improve upon the consumer and environmental outcomes that may otherwise be achieved through ZNE initiatives. Specifically, we analyze the possible impacts of powering a development of efficient homes using “community solar” rather than on-site generation.
The community solar concept allows individual households to purchase a share of the output of a larger solar PV project.4 Community solar programs can be sited in advantageous locations of the distribution grid, benefit from economies of scale in construction, and are capable of greater total electricity production through advanced technical options that are prevalent in larger-scale PV installations, such as tracking or ideal orientation of the panels. Therefore, the inclusion of community solar is one way to ensure that future ZNE initiatives do not ignore opportunities for system-wide environmental and economic improvements.
The National Rural Electric Cooperative Association (NRECA) and the Natural Resources Defense Council (NRDC) commissioned The Brattle Group to quantify the potential economic and environmental advantages of strategies that are more inclusive than current ZNE initiatives.
Rather than producing clean energy from individual rooftop solar installations, our study illustrates the benefits of powering energy efficient homes from a larger solar PV project that is shared by the community.5
Several aspects of the study scope should be noted. First, the study does not endorse or criticize the concept of ZNE buildings, but instead looks for opportunities to improve future policies with similar objectives where they are being pursued. Second, the study takes a system-level view of costs and benefits, rather than the perspective of individual stakeholders. Third, the study focuses on the relative costs and benefits between ZNE homes and other configurations (specifically energy efficient homes with community solar in this analysis), not the costeffectiveness of standalone projects. Fourth, the study focuses specifically on new ZNE housing developments in non-urban locations. Lastly, but importantly, the study is based on a review of publicly available data and should be updated and expanded as additional data becomes available…
Under the specific market characteristics considered in this study, the economies of scale and technological advantages of the homes configured with community solar provide roughly:
• 13% lower total solar PV project expenditures per watt than ZNE homes
• 25 to 30% greater annual energy output per watt than ZNE homes As a result of these advantages, a community solar-based approach could serve a development of 200 homes with total solar PV project cost savings of approximately 30 to 35 percent relative to conventional ZNE configurations.
Viewed an alternative way, the same total expenditure on the community solar-based approach that would have been required in the conventional ZNE approach could produce:
• Enough additional electricity production to power another 80 to 90 efficient homes
• 50 to 60% resource cost savings (i.e., avoided generation from the power grid)
• 40 to 45% reduction in average CO2 emissions (equivalent to 80 to 100 cars off the road, or roughly one car per two ZNE homes)
In addition to these economic and environmental benefits, the inclusion of community solar projects could expand the types of dwellings that may be considered ZNE (e.g., individual tenants of large apartment buildings). Figure ES-1 provides a summary of the 20-year cumulative benefits quantified in this study…