WASHINGTON — The Energy Department on Wednesday announced a new effort to tackle one of the toughest technical challenges facing President Biden’s push for an electric grid dominated by solar and wind power — namely, what to do when the sun stops shining and the wind stops blowing.

The government is chasing a promising but uncertain solution: a low-cost way to store electricity generated by the sun or wind for hours, days or even weeks at a time, saving it for when it’s most needed. That goes far beyond what current batteries can do. While dozens of companies are working on different ideas for so-called “long-duration energy storage,” most are still too expensive to be useful.

As part of its initiative, the Energy Department wants to drive down the cost of long-duration storage 90 percent below the cost of today’s lithium-ion batteries by 2030. The agency will direct experts at its national labs to focus on improving such technologies while it seeks funding from Congress for early demonstration projects.

The announcement is part of the agency’s Energy Earthshots Initiative, which aims to accelerate the deployment of nascent technologies to fight climate change. The program is an acknowledgment that the United States has not yet fully developed all the technologies it needs to meet Mr. Biden’s goal of zeroing out the nation’s planet warming emissions by 2050.

“If we want to get to net-zero emissions, we not only need to deploy solutions that are already proven, like wind and solar power,” Jennifer Granholm, the energy secretary, said in an interview earlier this year. “We also have to figure out how to take clean-energy technologies that have been demonstrated in a laboratory and scale them up in the world. There’s a real sense of urgency about this.”

Last month, Ms. Granholm announced a goal of reducing by 80 percent the cost of clean hydrogen fuels, which could help curb emissions from factories, trucks or the electric grid. Both programs are modeled after the Obama-era Sunshot Initiative, which is credited with helping to lower the cost of solar power during the 2010s and ushering the technology into the mainstream.

Mr. Biden is counting on increasingly cheap solar and wind power to meet his goal of having the United States get 100 percent of its electricity from power plants that do not emit carbon dioxide by 2035. The White House is currently trying to persuade Congress to enact a clean electricity standard that would require utilities nationwide to meet that target.

The electricity sector is responsible for one-quarter of greenhouse gas emissions in the United States, with roughly 60 percent of electricity still generated by burning fossil fuels, mostly natural gas and coal. The Biden administration sees curbing electricity emissions as central to its climate plans, since it is also trying to convince Americans to buy more electric cars and heat pumps that will plug into the grid.

But cleaning up the power sector will require more than just new laws, experts said. It also poses major technological challenges.

Several recent studies have found that utilities could plausibly get to 80 percent clean electricity using today’s technology, mainly by installing vastly more wind turbines and solar panels and relying on existing hydropower dams and nuclear reactors.

But cleaning up that last 20 percent of emissions could prove trickier. One obstacle: wind and solar farms generate power only when weather conditions are favorable. That means utilities today still rely on gas- or coal-burning plants for backup.

Many utilities are now installing large arrays of lithium-ion batteries, similar to those used in electric cars, to help smooth over fluctuations in supply. But those batteries typically store electricity for just four to six hours at a time, which is insufficient to handle larger seasonal swings in wind and solar power. Some regions of the country can go days or weeks with little wind.

There are plausible solutions, but many still have drawbacks. Grid operators could build massive new transmission lines across the country, on the theory that it’s usually windy somewhere. But some communities have opposed new power lines.

Utilities might also use surplus wind and solar power to produce hydrogen, which can then be burned cleanly for electricity during times of need. This fall, the New York Power Authority will test this kind of “green” hydrogen as a replacement for some of the gas it typically burns at a facility on Long Island. But, for now, this remains pricier than burning fossil fuels like natural gas.

Another possibility is the development of new types of carbon-free power plants that can run at all hours, such as advanced nuclear reactors, geothermal plants or gas plants that can capture and bury their emissions underground. But many of these technologies are still in their infancy.

Long-duration storage offers another potentially useful option. Dozens of companies are experimenting with various devices that could store electricity for extended periods of time.

Some utilities are building pumped storage hydropower facilities, an older technology that draws on electricity when it’s plentiful to pump water uphill, releasing the water to spin a turbine for power in times of need. The Los Angeles Department of Water and Power is exploring ways to inject compressed air or hydrogen into underground salt caverns, which can be used later to generate power.

Other companies are working on new battery chemistries. Form Energy, a start-up backed by Bill Gates, recently announced it would partner with a utility in Minnesota on a pilot project to build an aqueous air battery that could deliver continuous power for 150 hours.

Yet energy researchers say that these long-duration storage technologies need to get drastically cheaper to be viable, in part because they would operate infrequently. One recent study in Nature Energy estimated that capacity costs might need to fall below $50 per kilowatt-hour — roughly one-third the cost of today’s grid-scale lithium-ion batteries — before utilities start using long-duration storage more widely. And such storage may have to get as cheap as $1 to $10 per kilowatt-hour before it becomes a dominant solution.

“Those cost targets won’t be easy to hit, although they’re in line with what many developers are aiming for,” said Nestor Sepulveda, who led the study as a researcher at the Massachusetts Institute of Technology. “One big obstacle right now is that there’s no policy requirement for utilities to build long-duration storage. It’s easier and cheaper to simply burn natural gas.”

Ultimately, it may take years before utilities have a clear sense of which technologies work best to balance large amounts of wind and solar power. Jesse Jenkins, an expert at Princeton University, said that long-duration storage could play a valuable role if it becomes cheap. But in his research, he has found that utilities would likely need to rely on a mix of different solutions for a clean grid, potentially including hydrogen or advanced emissions-free power plants that can run at all hours.

“There’s a lot of focus on energy storage as the Holy Grail answer for wind and solar intermittency,” Dr. Jenkins said. “And we found it can be a solution, but it’s one of many. So we need to be making as many bets as we can today on new technologies, so that when we really need them a decade or two from now, they’re ready to go.”

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