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<\/figure>\n\n\n\nCalifornia set two renewable energy records last week: the most solar power ever flowing on the state\u2019s main electric grid, and the most solar power ever taken offline because it wasn\u2019t needed.<\/p>\n\n\n\n
There\u2019s no contradiction: As California utilities buy more and more solar power as part of the state\u2019s quest to confront climate change, supply and demand are increasingly out of sync. The state\u2019s fleet of solar farms and rooftop panels frequently generate more electricity than Californians use during the middle of the day \u2014 a phenomenon that has sent lawmakers and some climate advocates scrambling to find ways to save the extra sunlight rather than let it go to waste.<\/p>\n\n\n\n
But for ratepayers, an oversupply of solar power might actually be a good thing.<\/p>\n\n\n\n
New research published in the peer-reviewed journal Solar Energy suggests California should embrace the idea of building more solar panels than it can consistently use, rather than treating oversupply as a problem to be solved. It sounds counterintuitive, but intentionally overbuilding solar facilities \u2014 and accepting they\u2019ll often need to be dialed down in the absence of sufficient demand \u2014 may be the best way to keep electricity prices low on a power grid dominated by renewable energy, the research found.<\/p>\n\n\n\n
In a\u00a0study published in March, New York-based researchers Richard Perez and Karl R\u00e1bago argue that solar power has gotten so inexpensive that overbuilding it will probably be the cheapest way to keep the lights on during cloudy or overcast days \u2014 cheaper than relying entirely on batteries. Solar power can meet high levels of daytime electricity demand without energy storage, the researchers say, as long as there are enough solar panels on the grid during times when none of them are producing at full capacity.<\/p>\n\n\n\n
\u201cIt\u2019s not like solar is going to be available all the time,\u201d said Perez, a solar energy expert at the State University of New York at Albany. \u201cAt night you will need storage, and on cloudy days you will need storage. But you will need much less of it.\u201d<\/p>\n\n\n\n
California has set a target of 60% renewable energy on the power grid by 2030, as well as a longer-term goal of 100% climate-friendly energy, a broader definition that could include hydroelectricity or nuclear power. A dozen other states and U.S. territories\u00a0have adopted or are considering\u00a0similar 100% clean energy goals, and they\u2019ll be watching California\u2019s progress as they try to figure out how to make those goals a reality.<\/p>\n\n\n\n
The Golden State\u2019s success depends in part on achieving its goals without sending energy prices soaring. California already has\u00a0some of the country\u2019s highest electricity rates, although low levels of energy use mean monthly bills\u00a0are relatively low.<\/p>\n\n\n\n
Perez and R\u00e1bago coauthored their study with analysts at Clean Power Research, a company with offices in California and Washington state. The study built on an\u00a0earlier Clean Power Research report, which showed that in Minnesota \u2014 a state not known for abundant sunlight \u2014 the cheapest way to run the power grid with solar panels, wind turbines and batteries involved building so many solar panels that their output would have to be \u201ccurtailed,\u201d or reduced below what they\u2019d otherwise be capable of producing, by around 30%.<\/p>\n\n\n\n
Under a range of high-curtailment scenarios, the report found, electricity would be slightly cheaper than it is today in Minnesota \u2014 a conclusion that Perez and R\u00e1bago found to hold true for many power grids.<\/p>\n\n\n\n
Models run by the California Public Utilities Commission, examining the state\u2019s options for reducing planet-warming emissions while maintaining reliable and affordable electricity, have also found that a surplus of solar power makes sense.<\/p>\n\n\n\n
\u201cWhat the models said was dramatically overbuild solar, and either export it when you have excess production or curtailment,\u201d said Edward Randolph, who leads the regulatory agency\u2019s energy division. \u201cCurtailment makes economic sense.\u201d<\/p>\n\n\n\n The argument for overbuilding solar power isn\u2019t new, nor is it especially controversial among researchers who study the logistics of transitioning from fossil fuels to cleaner energy sources. Utility regulators have always built extra power into their planning, requiring enough electric generating capacity on the grid to ensure there will almost always be sufficient power on hand to meet energy demand.<\/p>\n\n\n\n Traditionally, that reserve margin has come from fossil fuels. Overbuilding renewables is a similar concept.<\/p>\n\n\n\n Some experts, though, are skeptical about the sheer scale of overbuilding contemplated by Perez and R\u00e1bago.<\/p>\n\n\n\n Wade Schauer, a Sacramento-based researcher at the energy consulting firm Wood Mackenzie, said Perez and R\u00e1bago didn\u2019t take into account the costly transmission lines that may be needed to accommodate an overbuild of solar, or the landowner opposition that has\u00a0frustrated solar farm developers\u00a0in California and elsewhere. The researchers also assumed energy storage costs will remain \u201claughably high,\u201d Schauer said \u2014 an assumption that makes batteries look less attractive compared with overbuilding solar.<\/p>\n\n\n\n California got 34% of its electricity from renewable sources in 2018, the state\u2019s Energy Commission\u00a0estimates, not counting production from rooftop solar panels, which would add several more percentage points. Solar power has grown especially fast in recent years, spurred by falling costs, federal tax credits and California\u2019s renewable energy mandate.<\/p>\n\n\n\n The state\u2019s main power grid\u00a0set a record\u00a0for most simultaneous solar generation just before noon on June 1, breaking previous records set in April and May.<\/p>\n\n\n\n The growing amounts of solar power have been accompanied by growing curtailment, according to the California Independent System Operator, which runs the state\u2019s main power grid.<\/p>\n\n\n\n Solar and wind farms on the California grid generated\u00a0223 fewer gigawatt-hours\u00a0than they otherwise would have in May, with solar accounting for the vast majority of the losses. That\u2019s enough electricity to power roughly 400,000 average California households, and more than twice as much curtailment as any month before this year. The numbers are especially high in part because of an influx of cheap hydropower following a wet winter.<\/p>\n\n\n\n On May 27 around 1 p.m., solar plant operators shut off a record total of about 4,700 megawatts of capacity at the same time \u2014 nearly 40% of the entire solar capacity installed on the California grid.<\/p>\n\n\n\n Those numbers sound large, but they\u2019re still relatively small, said Mark Rothleder, the grid operator\u2019s vice president for market quality and regulatory affairs.<\/p>\n\n\n\n In 2018, less than 2% of potential solar generation was curtailed, Rothleder said, a number that may reach 3%-4% this year. The vast majority of curtailments happen through a competitive market, where solar and wind plant operators are paid to ramp down production. In rare instances, the grid operator will manually order certain facilities to ramp down.<\/p>\n\n\n\n Rothleder sees some overbuilding as a good thing, because it creates flexibility for the grid operator. Instead of relying entirely on gas-fired power plants to ramp up and down to match swings in demand, the nonprofit agency can get creative with solar farms, curtailing their production as needed or holding some solar in reserve for times when energy demand might jump unexpectedly.<\/p>\n\n\n\n The key question is how much extra solar power is beneficial, and how much is a waste of money. Rothleder said overbuilding and curtailment are no substitute for the types of steps California will eventually need to take to fully replace fossil fuels with clean energy, such as investing in big energy storage projects, sharing more solar and wind power with neighboring states, and designing electricity rates that encourage people to\u00a0shift their energy use\u00a0to times of day when the sun is shining or the wind is blowing.<\/p>\n\n\n\n \u201cIf [curtailment] starts inching up toward 10%, and greater than 10%, you have to start looking at it and asking what else can you be doing,\u201d Rothleder said. \u201cI don\u2019t think at that point just building more solar is the right thing to do.\u201d<\/p>\n\n\n\n Lawmakers in Sacramento have debated the types of steps described by Rothleder, but haven’t found much consensus.<\/p>\n\n\n\n Last year, for instance, the Legislature once again rejected then-Gov. Jerry Brown\u2019s plan for greater sharing of renewable energy across the West. The proposal\u00a0would have unified the region\u2019s disparate power grids, reducing curtailment by allowing greater sharing of renewable energy across state lines, but lawmakers feared California could lose its sovereignty over its energy supply.<\/p>\n\n\n\n More recently, a bill that would have required huge amounts of large-scale, long-duration energy storage \u2014 a type of storage for which lithium-ion batteries aren\u2019t well-suited \u2014 was pulled from the Senate floor, amid concerns it would burden consumers with steep costs and\u00a0prop up a controversial hydropower project near Joshua Tree National Park.<\/p>\n\n\n\n Those proposals were driven in part by rising alarm over curtailment, and by the revelation that California sometimes\u00a0pays other states to take its excess solar power. The Natural Resources Defense Council\u2019s Ralph Cavanagh, for instance,\u00a0wrote last year\u00a0that lawmakers should support Brown\u2019s regional power grid plan because \u201cwasting growing amounts of our state\u2019s clean energy is no way to advance California\u2019s ambitious energy and climate goals.\u201d<\/p>\n\n\n\n Part of the problem with these debates is that it\u2019s hard to predict what different technologies will cost in the coming decades, said James Bushnell, an energy economist at UC Davis. Maybe solar will keep getting cheaper, and battery costs won\u2019t fall as much as analysts expect. Or maybe not.<\/p>\n\n\n\n \u201cIf you think you know what all the costs and operating characteristics of resources will be 20 years from now, we can write fancy computer models that will optimize all that. But we don\u2019t really know,\u201d Bushnell said. \u201cToo many studies circulate implying that we do.\u201d<\/p>\n\n\n\n<\/figure>\n\n\n\n