California’s power-grid operators are dealing with a glut of daytime electricity produced by household, government, business and industrial solar installations.

This forces the electricity prices on state’s real-time marketplace to plummet, leading some power-plant operators to shut down until demand catches up with supply later in the day.

And increasing amounts of wind and solar energy are being wasted or “curtailed,” as they call it, because no one can use it, according to data obtained from the California Independent System Operator ( Cal ISO).

Last year 305,241 megawatt hours of solar and wind electricity were curtailed — a loss of enough carbon-free electricity that could have powered about 45,000 California homes for a year. This was almost double the amount of clean power that was lost through curtailment in 2015.

This energy loss coincided with a 28 percent yearly increase in electricity produced from large-scale solar plants on the state’s control grid, according to the data. The grid system, which excludes Los Angeles, Sacramento, and Imperial Valley area utilities, last year got 11.9 percent of its electricity from solar plants, up from 9 percent in 2015 and 6.3 percent in 2014.

The waste could increase unless changes are made. State power officials are pushing to get 50 percent of power from renewable sources by 2030 as required by state law.

Cal ISO officials say the proportion of lost renewable energy is relatively small now.

But they also describe the situation as unsustainable as more big solar plants and rooftop systems come online and create a surge of power late mornings and early afternoons.

The problem is at its worst in springs months, when the sun shines longer reach day, but fewer people are running their air conditioners, the state data shows.

“We need to start finding ways to offset curtailment as we add more renewable sources, or we will be wasting renewable energy,” said Phil Pettingill, Director of State Regulatory Affairs at Cal ISO.

Officials are weighing several ways to harness the midday glut.

One strategy calls for California to buy and sell more power from neighboring states to the east. This would spread out the midday solar surge because the sun rises as much as two hours earlier in Arizona and Nevada, Pettingill said.

Since 2014, limited trade between Cal ISO and utilities in neighboring state have been allowed, but only on an hourly basis.

Not only does expanding the market provide more flexibility to prevent to waste of solar energy, it also allows gives utilities more opportunities to acquire electricity when prices are low, said David Wright, general manager of Los Angeles’ utility during a lecture last week at U.C. Riverside.

Meanwhile, utilities are moving toward time-of-use pricing for home electricity costumers.

This would encourage Californians to set timers on pool pumps, washing machines, dishwashers and other appliances to take advantage of cheaper electricity in the middle of the day while discouraging power consumption in the evening when electricity is more expensive and in greatest demand.

Southern California Edison, for example, already offers time-of-use pricing for the those who sign up for it, said Edison spokesman Robert Laffoon-Villegas. Under rules imposed by the California Public Utilities Commission, Edison will begin next year to phase in time-of-use pricing for all costumers.

Riverside’s publicly owned utility also plans time-of-use prices, and proposals are expected to go before the city’s utility board and council before the end of this year, said Martin Ochotorena, the utility’s manager of contracts, projects, and settlements.

Another strategy is for solar and renewable sources to be located near urban areas where most electricity is consumed. One example is Riverside’s Tequesquite Solar Project built on the city’s former 125-acre landfill. It features enough solar panels to power 2,250 houses.

Situated within the well-populated Inland Southern California, no electricity from this plant has ever been curtailed since it started up in 2015, Ochotorena said.

Battery storage

Another strategy is battery storage, so solar energy can be saved for evening peak demand time.

In January, Edison officials showed off a 1.5-acre, battery-storage facility in Ontario that features 400 modular “powerpack” battery units made by Tesla that can power 15,000 homes for four hours.

Yet the use of this technology on the power grid is still in its infancy and questions linger about the cost and practicality.

Wright, the general manager of the Los Angeles Department of Water and Power, the nation’s largest municipal utility, said in his lecture at UCR that battery-storage systems are too expensive, run out of electricity too fast, and take up too much space.

To illustrate his point, he showed a slide to the audience with a map showing how replacing one natural gas power plant with a battery- storage system would consume more than 200 acres, which would be extremely costly in places like Los Angeles.

Ironically, Wright was speaking in a College of Engineering building at UC Riverside that is powered by a combination of solar panels and a trailer loaded with batteries that keep the lights on and buildings cool after the sun sets.

Sadrul Ula, a UCR engineering professor, said these solar panels and batteries power three buildings at the university’s Center for Environmental Research & Technology, which is working to improve battery-storage technology.

As he showed off rows of yellow batteries in a trailer, he described them as the solution to harnessing peak solar production, storing it for evening and nighttime use.

“We charge these batteries when we have surplus solar, so we don’t waste it,” said Ula, managing director of UCR’s Winston Chung Global Energy Center.

Ula expects batteries to become more cost-effective as more solar comes online and more surplus electricity is available to charge them. Batteries can be stored in big rig truck trailers, so they can be dispatched where needed to ease bottlenecks in the grid. That can reduce land costs, he said.

Electric vehicles

Wright and Ula both see the rise of electric vehicles as a boon for solar energy because cars can be charged when most people are at work and the panels are producing electricity at the peak levels.

Wright said the problem now is a lack of charging stations. He said tax credits and other subsidies are needed, as well as land-use regulations that would require charging stations at new apartment buildings and other locations.

Ula added that technology is being developed that could allow batteries in electric cars and trucks to also store electricity for the grid. This would require smart charging stations that would allow electricity to go in two directions.

Ula envisions a time when car owners could get a cellphone messages asking them if it would be OK to pull power from their car batteries in the evening in exchange for credits to recharge the vehicle during the day when solar energy is plentiful. With millions of cars and trucks in California, such a technology could store to a lot of megawatt hours.

But let’s not forget natural gas power plants, the main workhorses of our power grid that will be with us decades to come, said Sean Gallagher, vice president of state affairs for the Solar Energy Industries Association.

Modernizing fossil fuel plants would allow them to work in better harmony with solar production by allowing them to start up and shut down more quickly, he said.