The cost of producing renewable energy using solar and wind has been dropping sharply over the years so that it is now comparable and often even cheaper that energy produced using fossil fuels. So why hasn’t it taken over the energy sector completely? The reason is that when it comes to renewable energy, there is an extra cost that fossil-fuel based power plants do not have and that is the cost of storing the energy and this has to be factored in as well.
It is energy in the form of electric current that drives all our devices but the problem with current is that it cannot be stored as current because as it flows in wires, it dissipates its energy as heat. (Superconductors don’t have any resistance and thus do not lose any heat but the commercial applications of that are far off in the future.) The production of current has to exactly match the use of current at every moment. The energy grid is is a true marvel of engineering technology that achieves precisely this. We have various power plants feeding electricity into the grid and this is the sent all over the area covered by the grid to wherever it is needed at that moment. So in the US during the summer months, for example, energy is sent to the hot southern parts of the country to meet the increased demands of air conditioning.
At the beginning of the 20th century, the US had more than 4,000 utilities, each serving a small area. But over time, they got connected so that now the US has two major grids, the eastern and western, with the state of Texas having its own grid that is not connected to the other two. That was what caused Texas problems in February 2021 when the cold snap disrupted its own power supply and large parts of the state lost power and they could not get power from the other two grids to make up for the loss.
In order to achieve the moment-by-moment current balance in the grid between production and use of current, one needs the ability to control the amount of electric current produced, increasing it in times of high demand and reducing it when demand drops. And this is where fossil fuel plans have an advantage. They consist of largely coal and gas (and nuclear) powered plants and one can control the production levels quite easily by simply burning more or less fuel.
Not so with renewables like solar and wind, which are dependent of factors outside our control. During sunny and windy days, they can produce a lot of cheap energy that can exceed the needs but at night or on still days, production drops dramatically. So the extra step needed with renewables is to find ways to store excess energy that is produced during peak production times so that it can be released when production drops. This is a problem that fossil fuel plants do not face since the energy is stored in the coal and gas, to be used only when needed.
Much of research nowadays is focused on finding ways to economically store the energy produced by renewable sources by converting current energy into other forms that can be released as needed. The more one depends upon renewable sources, the more necessary it becomes to find high-volume storage to overcome the inevitable intermittency of supply.
In the April 25/May 2, 2022 issue of the New Yorker magazine Matthew Hutson looks at the many ways storage technology is being pursued, some of which were quite new to me.
The most conventional form of storing energy is to charge up batteries, which is essentially converting electrical energy into chemical energy.
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.
Much effort is being spent on finding was to use gravity as a storage mechanism, such as by using electricity to pump water to a height to create massive reservoirs and then releasing it to drive turbines. More than 90% of the world’s current energy-storage capacity is in this form.
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.
But the geographic conditions under which this can be done are limited.
While Lithium-ion batteries and pumped water are the biggest storage mechanisms, there are other ways of using gravitational potential energy. One way being explored is to raise massive blocks made of special material and then lower them.
Energy Vault’s first attempt at a system was EV1, a looming, Transformer-like tower crane with six arms. The idea was that such a crane would stack blocks in a wall around itself, then unstack them.
In renderings, it resembles a boxy automated warehouse forty stories tall. Elevators will use clean power to lift blocks weighing as much as thirty tons and put them on trolleys, which will move them toward the middle of the structure. When energy is needed, the blocks will be moved back to the elevators. As they descend, the elevators will power generators, producing new electricity. Energy Vault claims that the system will have a high round-trip efficiency, regenerating a great deal of the electricity it consumes. Yet even so EVx will have to move thousands of heavy blocks to store and release significant amounts of energy. Ordinarily, our energy use is an abstraction; Energy Vault’s approach reveals it in stark, physical terms.
Gravitricity, based in Scotland, recently concluded a demonstration that involved hefting a fifty-ton block up a tower, two stories at a time; it now plans to raise and lower single, thousand-ton blocks inside disused mine shafts. Two other companies, Gravity Power, in California, and Gravity Storage GmbH, in Hamburg, aim to place a massive weight at the bottom of a shaft and then pump water underneath to lift it. To withdraw energy, they’ll let the weight push the water down into a pipe and through a turbine. RheEnergise, based in Montreal, has come up with yet another take on pumped hydro, centered on a fluid that the company invented called R-19, which is two and a half times as dense as water; its system will move the fluid between tanks at the top and bottom of an incline.
Another method is to pump water underground to create reservoirs deep below and have it released under pressure, somewhat like how fracking works, and use that to drive generators. Yet another is to use electricity to decompose water into hydrogen and oxygen, store the two gases separately, and then recombine them in a fuel cell when you need energy.
While there is broad support for research into storage because the storage mechanisms do not care where the energy comes from, things may change if the fossil-fuel companies think that better storage capability will tilt the balance against them and in favor or renewables. Then they will unleash their lobbyists to try and kill it.
It’s partly because storage strengthens the whole grid that it has found broad political support. Energy-storage technologies “are neutral as to the fuel source,” Leah Stokes, a political scientist at the University of California, Santa Barbara, told me. They “can store any kind of power—clean or dirty.” Storage may become a partisan issue if it begins clearly helping renewable energy to threaten fossil fuels. “The politicization of climate and energy policy comes from fossil-fuel companies that give enormous amounts to the Republican Party,” Stokes said. “This is not some kind of ideological cleavage. It’s fundamentally a material issue.” For the time being, storage policy exists in what Stokes calls the “fog of enactment,” where technologies are so new that we can’t yet identify their greatest beneficiaries. Inevitably, there will be some losers, even if as a society—and a planet—we come out ahead.
Hutson tries to envisage what the long-term solution might look like and sees a hybrid system in our future.
The grid as a whole may never be perfected. We may never be able to get away from technologies with undesirable by-products; we may always rely in part on fossil fuels and nuclear power, backed up by Li-ion batteries and natural-gas “peaker” plants, used at times of high demand. But it’s equally possible to envision a future in which some of the technology works out, and the globe is reshaped by a combination of renewable energy and renewable storage. In such a world, wind turbines and solar farms will spread over fields and coastlines, while geothermal plants draw power from below. Meanwhile, in caves and tanks, hydrogen and compressed air will flow back and forth. In industrial areas, energy warehouses will thrum with the movement of mass. In rural places, water will be driven belowground and then will gush back up. When the sun comes out and the wind rises, the grid will inhale, and electricity will get saved. During the doldrums, the grid will exhale, driving energy to factories, homes, offices, and devices. Instead of burning dead things, in the form of fossil fuels, we’ll create and store energy dynamically, in a living system.
I hope he is right.