Research Shows Solar Thermal Is Essential for Electrification of Water Heating

Sacramento—A new study from Flagstaff Research commissioned by the California Solar & Storage Association (CALSSA) finds that solar water heating with electric backup can reduce greenhouse gas emissions by 90% compared to traditional gas tank water heaters. This surpasses the performance of heat pump water heaters, which reduce emissions by 81% on average across California climate zones.  

For multifamily properties, solar water heating produces more than twice as much bill savings as heat pumps. For residential systems, solar water heating systems reduce monthly bills while heat pumps increase them.

“Solar water heating is a proven technology that fits perfectly with California’s future of all-electric housing and carbon-free energy,” said CALSSA Policy Director Brad Heavner.

California policy makers are intent on electrification of water heating. CALSSA produced this research to demonstrate that solar water heating needs to be part of that effort. In California to date, the majority of solar water heaters installed have used gas backup heaters, but solar water heaters are also very effective when used with electric backup heaters. Solar water heating can be used both for fuel switching from gas to electric and to significantly increase the efficiency of existing water heating.

State agencies are implementing two new programs for water heating electrification. The Building Initiative for Low Emissions Development (BUILD) program targets new construction and will be run by the California Energy Commission (CEC). The Technology and Equipment for Clean Heating (TECH) program will address retrofits and will by run by the California Public Utilities Commission (CPUC). In addition, CEC aims to use Title 24 building standards to encourage the construction of all electric housing. Because heat pumps increase energy costs for homeowners, solar water heating is often a better option.

Flagstaff Research evaluated thirteen water heating technology configurations for cost and performance using detailed simulation models for customer behavior and real world conditions in every region of the state.

Heat pumps are only efficient if they can heat water slowly. Because customers expect hot water to be recharged quickly, heat pumps make heavy use of electric resistance elements. This results in significant electricity usage during TOU peak periods, which increases costs and emissions. Solar water heating systems, in contrast, can almost entirely avoid reliance on electricity during peak periods.

“Heating water is one of the largest sources of greenhouse gas emissions in buildings, and solar water heating can eliminate most of those emissions without adding to electricity consumption during hours when the electric grid is already strained,” said Flagstaff Research Principal Josh Plaisted.

CALSSA makes the following recommendations:

• CEC and CPUC should proceed quickly to implement programs for water heating electrification. Those programs should have a strong focus on solar water heating.

• CEC should incorporate the new research to ensure that appropriate credit under Title 24 building standards is given to homebuilders that install solar water heating.