Renewables and battery storage are only part of the equation leading to meeting California's aggressive decarbonization goals, according to a report presented at a seminar at Stanford University on Wednesday by former Department of Energy Secretary Ernest Moniz.

Moniz's think tank, the Energy Futures Initiative (EFI), recently completed a 300-page report that was sponsored by the gas industry and various business and labor organizations, "but they had no voice in its conclusions," according to the former Obama cabinet member.

EFI officials characterized the report as a "head-on challenge" to the assumptions that California can achieve its carbon-reduction goals mainly by increased wind and solar power, along with battery storage, a so-called "electrification" strategy.

"The suggestion that decarbonization is easy is concerning," said Alex Kizer, EFI's strategic research director and one of multiple authors of the report. "Going out 10 years to 2030, the solutions have to come from today's technology [applying] policies that support near-term actions."

In presenting the report to a gathering of policymakers and stakeholders at Stanford, Moniz agreed that government policymakers need to have "aggressive climate goals, but we have to be really pragmatic in putting together pathways to get as far as we can in the time available." He stressed the need for "optionality, flexibility and innovation."

Among the report's conclusions is the determination that gas is "essential" to fill in when wind and solar power drop off, noting the need for gas backup "swells" in the winter months when wind and solar output drops in half. "Storage options to address the variability -- especially seasonal variability -- do not currently exist," the EFI report authors said.

The report suggested pursuing multiple pathways if the state is to reach its energy goals.

Among them is increasing renewable natural gas (RNG) supplies from landfills, wastewater treatment and other sources of biomethane, along with more research and infrastructure development on expanded uses of hydrogen in transportation, manufacturing and electric generation.

Equal focus on the power generation and transportation sectors is warranted, according to the report, since they account for 16% and 39% of the state's greenhouse gas emissions, respectively. While noting that there is no "silver bullet" technology to achieve decarbonization, technology options and flexibility are critical in reaching the state's goals, the report has identified 31 clean energy pathways.

Although some electrification advocates would not agree, the report underscores that gas-fired generation will continue to "play a key role" in California, and clean fuels, including RNG and hydrogen, are critical pathways. Nevertheless, the report also concluded that reaching the near-term 2030 renewable goal of 60%, relies on wind and solar expansion, some geothermal and increased hydroelectric imports.