NEW YORK, Sept 25 (Reuters) - Fully decarbonizing

California's electrical grid will require more firm clean power

sources, including advanced geothermal and natural gas with

carbon capture, Edison International ( EIX ) chief executive

officer told Reuters on Wednesday.

The most populous U.S. state has set a goal to produce zero

net emissions from its electrical grid by 2045, with renewable

energy sources solar and wind playing the starring role in

California's power generation plans.

"We need not just clean power, we need power that can meet

demand every single minute of the day," said Pedro Pizarro, head

of the major power company whose largest subsidiary is Southern

California Edison, an electric utility covering about 15 million

people.

Using entirely solar, which California uses more than any

other U.S. state, and wind alone wouldn't provide enough

around-the-clock power or be logistically realistic, he said.

In order to hit its goals, the state would need to add 120

gigawatts of renewables with storage between now and its target

date.

"The challenge is that if we were to meet all of

California's needs with just solar and storage, we would need to

blanket an area the size of the entire Los Angeles metropolitan

area with solar," Pizarro said.

Southern California Edison this year entered into a 320

megawatt power purchase agreement with geothermal provider Fervo

in a largest-of-its kind contract for geothermal. The contract

enables Fervo to finance its power generation build-out, with

the electricity to be phased in starting in 2026 and ramp up

through 2028.

In the time between adding enough clean power in California,

Pizarro called for the state's natural gas-fired power plants to

be preserved to keep power flowing.

"We have an insurance policy in California that's our

existing gas generation fleet," Pizarro said, adding that

Southern California Edison doesn't sell natural gas, which

release global warming carbon emissions.

Multiple natural gas-fired power plants along the California

coast were slated to shut in 2020 under climate plans, but state

officials extended their lifespan until 2026 to avoid power

shortfalls that could cause blackouts.