Excerpt from newyorker.com
The German word Dunkelflaute means “dark doldrums.” It chills the hearts of renewable-energy engineers, who use it to refer to the lulls when solar panels and wind turbines are thwarted by clouds, night, or still air. On a bright, cloudless day, a solar farm can generate prodigious amounts of electricity; when it’s gusty, wind turbines whoosh neighborhoods to life. But at night solar cells do little, and in calm air turbines sit useless. These renewable energy sources stop renewing until the weather, or the planet, turns.
The dark doldrums make it difficult for an electrical grid to rely totally on renewable energy. Power companies need to plan not just for individual storms or windless nights but for Dunkelflaute that stretch for days or longer. Last year, Europe experienced a weeks-long “wind drought,” and in 2006 Hawaii endured six weeks of consecutive rainy days. On a smaller scale, factories, data centers, and remote communities that want to go all-renewable need to fill the gaps. Germany is decommissioning its nuclear power plants and working hard to embrace renewables, but, because of the problem of “intermittency” in its renewable power supply, it remains dependent on fossil fuels—including imported Russian gas.
The obvious solution is batteries. The most widespread variety is called lithium-ion, or Li-ion, after the chemical process that makes it work. Such batteries power everything from mobile phones to electric vehicles; they are relatively inexpensive to make and getting cheaper. But typical models exhaust their stored energy after only three or four hours of maximum output, and—as every iPhone owner knows—their capacity dwindles, little by little, with each recharge. It is expensive to collect enough batteries to cover longer discharges. And batteries can catch fire—sites in South Korea have ignited dozens of times in the past few years.
Venkat Srinivasan, a scientist who directs the Argonne Collaborative Center for Energy Storage Science (access), at the Argonne National Laboratory, in Illinois, told me that one of the biggest problems with Li-ion batteries is their supply chain. The batteries depend on lithium and cobalt. In 2020, some seventy per cent of the world’s cobalt came from the Democratic Republic of the Congo. “Unless we have diversity, we’re going to be in trouble,” Srinivasan said. Any disruption to the supply chain can strongly affect prices and availability. Moreover, a lot of water and energy are required for mining the metals, which can cause environmental damage, and some cobalt-mining operations involve child labor. Experts doubt that Li-ion prices will drop more than thirty per cent below their current levels without significant technological advancements—a drop that is still too small, according to the Department of Energy. We need to expand our capacity; by one estimate, we’ll require at least a hundred times more storage by 2040 if we want to shift largely to renewables and avoid climate catastrophe. We may somehow find clean and reliable ways to mine, distribute, and recycle the ingredients for Li-ion batteries. And yet that seems unlikely. Although we usually think about renewable energy in terms of its sources, such as wind turbines and solar panels, that’s only half the picture. Ideally, we’d pair renewable energy with renewable storage.
We already have one kind of renewable energy storage: more than ninety per cent of the world’s energy-storage capacity is in reservoirs, as part of a remarkable but unsung technology called pumped-storage hydropower. Among other things, “pumped hydro” is used to smooth out spikes in electricity demand. Motors pump water uphill from a river or a reservoir to a higher reservoir; when the water is released downhill, it spins a turbine, generating power again. A pumped-hydro installation is like a giant, permanent battery, charged when water is pumped uphill and depleted as it flows down. The facilities can be awe-inspiring: the Bath County Pumped Storage Station, in Virginia, consists of two sprawling lakes, about a quarter of a mile apart in elevation, among tree-covered slopes; at times of high demand, thirteen million gallons of water can flow every minute through the system, which supplies power to hundreds of thousands of homes. Some countries are expanding their use of pumped hydro, but the construction of new facilities in the United States peaked decades ago. The right geography is hard to find, permits are difficult to obtain, and construction is slow and expensive. The hunt is on for new approaches to energy storage.
Quidnet, a Houston-based startup, is one of many companies exploring the possibilities. Last month, I sat in an F-150 King Ranch pickup with Scott Wright, its vice-president of operations, and Jason Craig, its C.O.O., as we drove to one of its test sites, on a farm west of San Antonio. Fields and billboards whizzed by as Craig explained, from the back seat, that Quidnet had patented a new kind of pumped hydro. Instead of pumping water uphill, the company’s system sends it underground through a pipe reaching at least a thousand feet down. Later, the system lets the Earth squeeze the water back up under pressure, using it to drive generators. Wright and Craig are veterans of the oil and gas industry, and Quidnet’s technology is like a green riff on fracking. In that technique, fluid is injected underground, where it builds up pressure that fractures rocks, releasing natural gas. Quidnet uses some of the same equipment and expertise, but with a different goal: the water is meant to be sandwiched between layers of rock, forming underground reservoirs that can be released on demand.