Earlier this year, utility Pacific Gas & Electric faced pushback from environmental and solar and energy storage industry groups to a plan to deploy natural-gas generators to back up communities facing multiday fire-prevention blackouts . The groups argued that California utilities shouldn’t be adding new carbon- and pollution-emitting resources when the state is trying to meet ambitious zero-carbon goals.

Now PG&E is planning to rely on mobile diesel generators instead, at least for this year. But as California regulators grapple with the best way to provide multiday power backup for wildfire and blackout-prone communities, a new report says that solar and batteries can’t do the job alone. The report is from consultancy The Brattle Group and sponsored by Enchanted Rock, a Texas-based developer of microgrids based on natural-gas generators. It indicates that providing two to four days of backup power for a 10-megawatt community microgrid from solar and batteries alone would require far too much redundant battery capacity — up to 350 megawatt-hours of batteries for 10 megawatts of load — and require up to 90 acres of solar PV to reliably charge them over that time.

Natural gas generators, on the other hand, can provide steady power for emergency needs and bid into state resource adequacy and energy markets to cover their costs, the report says. Combining them with solar and batteries, or offsetting their emissions by capturing renewable natural gas (RNG), or methane from dairy farms, landfills and wastewater […]