Tackling the problem of renewable energy storage

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.


  1. Matt G says

    I first heard about gravity batteries a year ago and got excited because the home we just bought has great sun exposure (we are good candidates for solar) and runs entirely on electricity. Then I saw the size of the weight used and got depressed. There was something I saw a few weeks ago about a DIY gravity battery but I lost track of that article.

  2. garnetstar says

    I vote for gigantic superconductors outside of each city, where electricity just runs and runs through them and never wears down, and can be tapped into at any time.

    I’ll take a hybrid of all those other forms of storage, however, while I’m waiting.

  3. mnb0 says

    “an extra cost that fossil-fuel based power plants do not have”
    This is not entirely correct -- storing and transporting fuels also cost money.

    “find ways to store excess energy that is produced during peak production times”
    This problem has been known for decades. Yet another idea is to compress air (or other gasses) in caverns that formerly were exploited for salt or gas. That could be an attractive idea for The Netherlands. Somewhere I’ve read that that’s about 60% effective.

  4. says

    The thing about using gravity for storing potential energy is, since potential energy = mass * g * height, each kilogram and each metre only count once towards the total stored potential energy which will ultimately end up as volts * amps * seconds. If anything in the equation was squared, we could just concentrate on making that as big as possible, knowing each improvement we are making will ultimately count double; but here, everything is just increasing linearly. So there simply isn’t any substitute for size; there has to be a lot of mass, and it has to fall a long way. You really need a hollowed-out mountain with two massive lakes, one at the top and one at the bottom — something the likes of Isambard Kingdom Brunel would have been proud of.

  5. John Morales says

    Plenty of other chemistries for batteries; a lot of research going on right now.
    Many are lower energy density or charge/discharge rate, but made of common materials.

    And other forms of grid storage are being developed, for example, hot rocks.
    Crushed basalt is easier (and cheaper!) to source than, say, cobalt.

  6. davidbrown says

    Just today (Saturday) Quirks and Quarks on CBC had an interview with a scientist involved in the development of a ‘thermal battery’. Use exceess electricity to heat something until it glows white-hot (2400 C or so), and then use the light to generate power from solar panels when you need the power. (They explain it *way* better than this brief synopsis.)


  7. tuatara says

    There certainly is rapid development in progress in the area of grid storage.

    My personal favourite (that I have been keeping an eye on for several years now) is Professor Thomas Maschmeyer’s ZnBr2 gel cell. It came out of research at the University of Sydney. It is a non-flow bromide gel technology. Highly recyclable, fire retardant, can be discharged to zero Volts without incurring damage. The stroke of genius was to redesign the cells so that they can be manufactured at a vehicle battery plant, so no new tooling required, mostly just a simple swap of the raw materials at the input end.

    Of course no one here in Australia was interested but a UK company invested and Gelion was born.


  8. xohjoh2n says

    I had a thought a while back that it would be funny to use a nation’s gold reserves to power a gravity battery, after all the stuff isn’t otherwise doing anything useful. Turns out there’s just not enough gold to make an appreciable dent in anyone’s energy requirements. Though you could get a lot further using lead or tungsten, it’s difficult to appreciate fully just how big a mountain-top lake is, or high it is, compared to any more artificial system we could reasonably construct.

  9. says

    @ xohjoh2n, #11: Exactly. A kilowatt-hour doesn’t sound much, but 1000 watts times 36 seconds is 3 600 000J = 3.6MJ. Now let’s say you’ve got 600 metres of drop. That’s up in the top hundred or so mountains in the UK. That means you need 6000 Newtons of force doing work over that distance, which is 600kg. of water and conveniently also 600 litres — just shy of three of those 210L chemical drums, or enough to flood a three by two metre room to a depth of 10cm. For just one kilowatt-hour. A single day’s supply of coffee, or eight minutes under a 7.5kW shower.

    (Homework question: The specific heat capacity of water is 4200 J.kg-1.K-1. How much hotter would 1 kWh, or 3.6MJ, make the 600kg. of water that would have to descend 600m. to generate it?)

  10. John Morales says

    bluerizlagirl, actually, it sounds like a fair bit. But I prefer to think of it as actual work.

    Even more so since the media storm surrounding Chris Froome’s second Tour victory, which saw Team Sky release his power files to provide greater transparency about his performances.

    Froome’s data reveals an average power output of 414W for 41m28s, equating to 5.78W/kg, with Froome weighing 67kg.

    Team Sky’s head of athlete performance, Tim Kerrison, also revealed that Froome regularly exceeds a 30-minute power output of 419W (6.25W/kg) and for 60 minutes he would expect to ride at or above 366W (5.46W/kg).

    So, an elite cyclist can pump out around 0.42 kW, and would need to be doing so for well over 2 hours to generate that 1 kWh.

    (My slow cooker is rated at 390W)

  11. KG says

    Rob Grigjanis@7,
    Flywheels are very useful for load-balancing second-by-second, not so much for storing large amounts of energy. Cryogenic enegy storage (using electicity at times of surplus to liquify air, then using it to drive turbines at times of shortage) is another promising technology (mentioned in the linked New Yorker article). Efficiency is quite low (c. 25%) in isolation but can be raised to around 50% if the low-grade cold from evaporating the cryogen is stored and reused, and perhaps 70%-75% if the storage facility is located near a source of low-grade heat that would otherwise be wasted. Big advantages are scalability, and the lack of any need for rare or expensive minierals. Liquid air can also be transported at atmospheric pressure. Another technology, briefly mentioned in the New Yorker article, is to use surplus electricity to produce hydrogen (or other fuels such as methane or other hydrocarbons, ethanol, ammonia).

    As the New Yorker article says, it’s almost certain that a combination of multiple storage technologies, with different advantages and disadvantages in different contexts, will be needed. Renewable energy sceptics typically ignore this possibility, insisting for example that “there’s not enough lithium”, as if all energy storage has to be in lithium batteries. Nuclear fanbois also tend to ignore the fact that around 1/4 to 1/3 of total global greenhouse gas emissions come from road and air transportation, where nuclear reactors can only be of use by producing electricity to be stored in batteries, or to produce combustible fuels, just as wind and solar plants can do.

  12. says

    Batteries are not the only means of storing energy. And their preformance decreases in the cold.

    Batteries could (should?) be reserved for portable energy to decrease their use. For stationary use, there are other potential (pun intended) ways of storing energy, such as wound springs, which can be changed back into electrical energy.


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