Appliance decarbonization and its impacts on California’s energy transition

Decarbonizing end-use appliances in homes and businesses is essential to meeting net-zero emissions targets. However, determining the best approach – whether through electrification or with net-zero emissions gas supplies – remains complex and highly dependent on regional demand patterns. This study explores optimal pathways for appliance decarbonization in California under various cost, technological, and regulatory constraints. The analysis was conducted using BRIDGES (Building Resilient Integrated Decarbonized Gas Electric Systems), a co-optimized gas and electric capacity expansion and dispatch model. We represented California as 16 interconnected nodes and tracked three key end-use technologies in the residential and commercial sectors for decarbonization (space heating, water heating, and kitchen ranges). We solved for five investment periods with a five-year interval from 2025 to 2045. To reach net-zero emissions by 2045 under current state plan, 92 % of water heaters and 60 % of kitchen ranges are electrified. 61 % of space heaters are electrified, with preferential electrification of coupled space heating and air conditioning. Our results show that the pace and extent of electrification vary by technology and geography, leading to between 45 % and 232 % increase in peak distribution-level demand and 1 %–17 % increase in peak system-level demand depending on the climate zone. Sensitivity analyses reveal that water heater electrification outcomes are largely insensitive to cost, technological, and regulatory constraints. However, policies around refrigerant leakage mitigation and offsets significantly influence electrification outcomes for space heating. These variations in electrification patterns lead to differing impacts on the grid, underscoring the importance of coordinated gas-electric optimization in regional decarbonization planning.