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For motorists driving to Yosemite National Park from the Bay Area, Don Pedro Reservoir is a familiar sight. But the massive lake along Highway 120 just west of Groveland has taken on a new role recently: as a flashpoint in the debate over what should — and shouldn’t — count as renewable energy in California.

The outcome of that debate could impact how much solar and wind energy is developed across the state in years to come.

In an effort to combat climate change and reduce smog, former Gov. Jerry Brown last year signed a landmark law that requires California’s utilities to produce 60 percent of their electricity from renewable sources like solar and wind by 2030.

But hydroelectric power from large dams doesn’t qualify as renewable, because of another state law, passed nearly 20 years ago, that aimed to protect salmon and other endangered fish.

That’s not right, says State Sen. Anna Caballero, D-Salinas.

Hydroelectric power, which is generated when water spins turbines in dams, is clean energy, and doesn’t produce smog or greenhouse gases, she notes. Caballero has introduced a bill in the state Legislature that would allow the two government agencies that own Don Pedro Reservoir, the Modesto Irrigation District and the Turlock Irrigation District, to count the electricity their dam produces toward the 60 percent renewable energy target they must meet.

The two utilities say that if they can count the dam’s electricity as renewable, they will save millions because they won’t have to sign as many contracts to buy electricity from solar and wind farms to meet their clean energy targets. And, they contend, they will pass along those savings to their customers, many of whom are low-income residents living in and around Modesto.

“The intent is to provide economic relief and equity to these irrigation districts and their ratepayers,” Caballero said at a hearing in Sacramento last month.

“The goals are laudable and worthy,” she added, “but the current system has inequities that we should not ignore.”

Caballero’s bill, SB 386, however, has drawn stiff opposition from environmental and health groups, from the Sierra Club to the American Lung Association. They argue that if Don Pedro Reservoir’s electricity is counted as renewable, then the owners of dozens of other large dams across the state will want the same treatment. And that will mean that demand for solar and wind power, which have been skyrocketing in California in recent years, will falter.

“It would slow the development of clean renewables,” said Kathryn Phillips, executive director of Sierra Club California. “It will stall us on the progress we’ve been making.”

Under the law Brown signed, after 2030, when the 60 percent renewable target is hit, utilities must produce the remaining 40 percent of their electricity by 2045 from renewable or “carbon-free” sources. That means after 2030, large dams, nuclear power and even natural gas-fired power plants that capture and store carbon in the ground are allowed to count as clean energy. As a result, Phillips and other opponents of Caballero’s bill argue, the current restrictions on large dams make sense because solar and wind only have another decade left to make the most of their preferred status.

California is a national leader in renewable energy. Other states, including Washington and New Mexico, have copied its energy laws requiring 100 percent clean energy in the coming decades. California passed its first law, called a “renewable portfolio standard,” in 2002, when Gov. Gray Davis signed a bill requiring 20 percent of the electricity that utilities generate to come from solar, wind, biomass and other renewable sources by 2017.

Back then, Democratic lawmakers wanted to promote wind and solar power, but they didn’t want to encourage the construction of large new dams on rivers that would kill salmon and other wildlife. So they compromised, and prohibited hydropower from large dams from counting as renewable, even though it doesn’t generate greenhouse gases. But they did allow electricity from small dams — defined as those that can generate 30 megawatts of electricity or less — to count. The dam at Don Pedro, however, generates 200 megawatts.

“We were trying to promote more benign methods of electricity that didn’t cause problems in other ways or other kinds of damage,” said Byron Sher, the former state senator from Palo Alto who wrote the 2002 law.

Sher noted that this goal was achieved because solar and wind have grown significantly since then. Also, the big reservoirs built in California over the past 20 years have been “off-stream” projects that don’t dam rivers.

“If I were still in the Legislature I wouldn’t be supportive” of Caballero’s bill, said Sher, now 91, who is considered one of California’s most influential environmental lawmakers of the past half-century. “We don’t want to promote further damming of free-flowing rivers in California.”

So much new solar and wind power has been installed in recent years, and the prices have fallen so significantly, that last year, 34 percent of the state’s electricity came from renewable sources.

An additional 15 percent of California’s electricity production total last year came from large dams. If it could suddenly count as renewable, environmentalists say, it could significantly cut demand for new solar and wind projects.

Caballero said she isn’t buying it. Regardless of what happens with the law, solar and wind will remain robust industries in the state, she said.

“Solar isn’t going anywhere,” she said last month at a hearing. “Last year the state approved that all new houses must have solar panels.”

In December, the California Energy Commission finalized building codes that require new homes and apartments up to three stories high and built after Jan. 1, 2020, to either have solar panels, which can be bought or leased, or be part of an agreement where the developer purchases electricity from a solar project somewhere else.

The rules will add $9,500 to the cost of a new home, the commission estimated, but will save $19,000 in lower energy bills over a 30-year mortgage.

Caballero’s proposed legislation is making for some awkward politics in Sacramento. Her district, which includes eastern Santa Clara County and much of Stanislaus, San Benito, Fresno and Merced counties, is fairly conservative.

Democratic leaders are working to help Caballero, a former mayor of Salinas who won the Senate seat in November, pass new laws that can help her win re-election in 2022 when Republicans will be trying to win back the district as part of a plan to end the Democrats’ two-thirds majority in Sacramento.

But her hydropower bill is not embraced by many in her party. The measure passed its first committee in a 9-1 vote that insiders considered a personal courtesy. In recent days, when it could have been up for a final vote on the Senate floor, it hasn’t been offered, a sign that it may not have the 21 votes needed for passage in the Democratic-controlled chamber.

Caballero, who did not respond to requests for an interview, might inadvertently be harming Central Valley residents, critics of the bill say. They note that during droughts, when reservoirs are low, hydropower production from dams drops. To make up for that, electricity is often generated by cranking up natural gas-fired power plants, which emit carbon dioxide and increase air pollution in the Central Valley, a region with some of the highest rates of childhood asthma in the nation.

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“Even though climate change is a global issue we will have impacts here — longer droughts, sea-level rise, more extreme weather patterns, fires,” said Fran Pavley, a former state senator who wrote California’s landmark cap-and-trade law in 2006. “A lot of the impacts seem to be coming a lot sooner than I imagined.”

Pavley noted there is already a provision in state law that allows utilities to appeal to the California Energy Commission for a waiver if they feel meeting the state’s renewable energy targets will be overly expensive. Neither irrigation district has done that.

But Melissa Williams, a spokeswoman for the Modesto Irrigation District, said allowing electricity from Don Pedro dam to count as renewable would save the agency’s customers $14 million over the next decade, and the agency would have to apply for a waiver every year, that it may or may not get.

“There is no certainty for our ratepayers,” she said. “There’s no guarantees we would be granted relief.”

A deadline is looming. Next Friday, May 31, is the last day for bills to pass in the chamber where they began.