What Zero-Net Energy Means in the Decarbonization Age
Architect Ben White offered his perspective on zero-net energy (ZNE) and decarbonization during a recent talk at the California Energy Commission.
During the July 31 talk, White, who is a Ph.D. candidate in the Transportation Technology and Policy program at the University of California, Davis, discussed how California’s energy policy is shifting from ZNE to decarbonization.
Under California’s definition of ZNE, carbon emissions can vary from “very high” to “zero,” but White said a distinction should be made between homes that are highly efficient (including ZNE designs) and homes that are responsible for low levels of emissions.
In the “very high” definition there is very little decarbonization. This happens when a home’s energy mix includes natural gas - which adds to a home’s carbon emission footprint. In some cases, a majority of a home’s carbon emissions originate from outside the house, due to methane leakage from the natural gas system.
Official measures of emissions, such as those taken by the California Air Resources Board, often do not account for emissions from leaks that occur when natural gas is imported from other states.
White noted that even highly efficient homes can still be large contributors of greenhouse gas emissions. ZNE homes that use natural gas can lock in high annual carbon emissions for decades due to methane leaks. On a statewide basis, carbon emissions rates from homes built during the current code cycle can be higher than 2 million tons per year if every new home uses natural gas as a fuel source.
There is much higher carbon emission abatement potential with all-electric homes. Statewide, electrifying homes and eliminating methane leaks associated with natural gas use can avoid as much as 90 million tons of carbon emissions over a 30-year timespan.
“Eliminating emissions as soon as possible is a win for everyone, and building electrification is a sensible approach to reducing emissions from the building sector,” White said. “Homeowners benefit from improved affordability, especially when solar generation is used. Eliminating emissions in the short term will make California’s broader climate goals much more achievable at reasonable costs than if we continue to allow high levels of emissions from the built environment.”
Existing homes will be more difficult to decarbonize, compared to new homes that are already highly efficient. White believes that changing views about natural gas use, particularly concerning cooking, will be key to decarbonizing buildings in California.
