If economic long-duration energy storage actually existed (other than pumped hydro), it would already have been deployed by every utility with a decarbonization plan. Long-duration storage can accelerate the retirement of peaker plants, defer upgrades of transmission and distribution infrastructure, and improve the dispatchability of renewables such as solar and wind – theoretically, at least.
A recent paper published in Nature Energy offered up a number of compelling findings on long-duration storage. The research indicates that systems with more than 100 hours of energy storage capacity provide the most benefit to the grid. What's more, the researchers found that long-duration storage can reduce the costs of deeply decarbonized electricity systems by 10 percent if the storage technology's costs are below $20/kilowatt-hour. The savings could reach as high as 40 percent if long-duration storage costs could be reduced to $1/kilowatt-hour.
But economic long-duration energy storage doesn't exist. Yet.
Instead, today’s high-growth, gigawatt-scale energy storage market is absolutely dominated by lithium-ion batteries with short durations ranging from minutes to a few hours and used largely in ancillary, not energy, applications.
A host of startups are trying to change that.
Funding and news in long-duration storage
Noon Energy closed on a $3 million seed round led by Prime Impact Fund along with At One Ventures, Collaborative Fund and Xplorer Capital. The self-described “semi-stealth” company is looking to build what it classifies as an "ultra-low-cost” long-duration battery.
Its system is made with "an electrochemical cell stack from a different industry" and built with off-the-shelf components, according to Chris Graves, Noon Energy’s founder and CEO. In an interview with Canary Media, Graves described the system as "a totally new type of battery based on carbon and oxygen," elements "that cost less than their containers."
Foundational research for Noon came from work at Columbia University and the Technical University of Denmark. These research efforts focused on the development of CO2-to-fuel electrolysis technology to store renewable electricity as hydrocarbon fuel. Graves says the technology can be scaled down to residential size and that the system is "much more energy-dense than other storage technologies."
The CEO noted that initial markets for long-duration storage might not be on the utility grid; they are more likely to be behind-the-meter, large industrial and island applications. SunPower founder Dick Swanson is on Noon’s board, as is Amy Duffuor, a principal at Prime Impact Fund.
Malta, a spinout of Alphabet's moonshot effort X, raised a $50 million Series B round to bring its long-duration thermal energy storage to market. The financing was led by Swiss energy firm Proman, along with earlier investors Alfa Laval and Breakthrough Energy Ventures.
Julian Spector reported in February that "Malta's thermal energy storage uses grid power to compress air for storage in hot molten salts and cold antifreeze liquid. A heat engine later converts the energy back to electricity for consumption."
Ty Jagerson, Malta's VP of commercialization, said in an interview with Spector: "Anyone looking at 4 hours [of energy storage] is starting to look 8 to 10. The market is transitioning rapidly." Malta plans to bring its first commercial project online by 2025.
Ares Nevada broke ground on a 50-megawatt gravity-based energy storage facility at Gamebird Pit, a gravel mine in Pahrump, Nevada, late last year.
According to the company, the project will use “a fleet of 210 mass cars, weighing a combined 75,000 tons, operating on a closed set of 10 multi-rail tracks.” The firm claims that the technology is suited for long-duration storage at utility scale, even though the Gamebird Pit will serve as a short-duration resource, providing ancillary services for the California Independent System Operator.
Azelio stores thermal energy in 600°C molten aluminum. When power is required, the stored thermal energy is transferred to a Stirling engine via a heat-transfer fluid.
The Swedish startup recently won a domestic order for its first commercial project to store surplus energy from a 446-kilowatt rooftop solar PV system and supply electricity and heat from the storage on an "on-demand, around-the-clock" basis.
Pumped hydro news: Pumped storage (which consists of pumping water from a low reservoir to a higher-elevation reservoir, and then releasing that water to spin turbines and generate power) accounts for 95% of all utility-scale energy storage in the U.S., according to the Department of Energy. America's 43 pumped storage plants were mostly built between 1960 and 1990 to support nuclear power and have a total combined capacity of roughly 100 gigawatts of storage. There are a number of new plants in development that are being built, in this case, to help support renewables rather than nuclear.
The 1,200-megawatt/12-hour Goldendale pumped hydro project in the Columbia River Gorge in Washington state is two years from its planned groundbreaking and will be built with union labor, according to reporting in the Northwest Labor Press. It was declared “a project of statewide significance” and granted expedited permitting treatment by Washington Gov. Jay Inslee last year. Copenhagen Infrastructure Partners is the developer of the $2.1 billion project that is expected to create over 3,000 jobs.
As Jeff St. John just reported here at Canary Media, California's Public Utilities Commission found the need for at least 1 gigawatt of long-duration energy storage by 2026. The technology "most likely to be ready by mid-decade is pumped hydro storage."
St. John notes some of the problems with new pumped hydro projects: "They cost billions of dollars and take years to build, and can run afoul of environmental opposition, as is the case with the 2-gigawatt, $2.5 billion NextEra Energy-backed Eagle Mountain project. Another project proposed for the San Vicente reservoir in San Diego County hasn’t encountered the same environmental opposition, but it would still cost between $1 billion and $2 billion to complete."
Long-duration vendors and technology survey
Here’s a quick survey of energy storage vendors and technologies with greater than 4-hour discharge times.
Form Energy, a secretive startup backed by Bill Gates’ Breakthrough Energy Ventures and rumored to be developing an aqueous sulfur storage system, recently announced its first commercial project: a 1-megawatt grid-connected storage system with Minnesota-based utility Great River Energy capable of delivering its rated power for 150 hours.
e-Zinc won a $1.3 million grant from the California Energy Commission last year to demonstrate its long-duration zinc battery for the commercial and industrial market. As Julian Spector reported, "The batteries precipitate little bits of zinc out of a solution while charging, using a windshield-wiper-like tool to clear the plate and make room for more charging."
Eos, now public by SPAC, spent 12 years building up a “zinc hybrid cathode” technology it claims can rival the dominant lithium-ion batteries. The technology is capable of discharge times up to 10 hours with minimal impact on cycle life, according to the company.
Flow batteries circulate a liquid electrolyte through stacks of electrochemical cells and have long held the promise of 10-hour durations, tens of thousands of cycles, minimal degradation and no limitations on depth of discharge. This performance promise has lured venture capital investment and research and development — but so far, the investments have yielded few commercial, competitive flow battery products.
Flow battery firms such as ESS, Invinity, Primus Power, Raytheon, Sumitomo, UET and ViZn use materials ranging from vanadium to zinc to iron to sulfur and manganese. Installations are increasing, but the megawatts deployed to date are a rounding error compared to installed lithium-ion batteries.
Mechanical energy storage
Despite some prominent startup failures, compressed-air energy storage remains a contender. The Los Angeles Department of Water and Power selected Range Energy and Mitsubishi Power Systems to develop underground salt caverns to store high pressure air (or someday hydrogen) to replace some of the energy from the soon-to-be retired 1,900-megawatt, coal-fired Intermountain Power Plant in Delta, Utah. Range will build, own and operate the 160-megawatt to 320-megawatt storage project with a generation capacity of up to 54 hours.
Hydrostor, a Canadian startup, is developing massive grid storage in watery caverns. Design work is beginning for a 500-megawatt project that could be online by 2025.
Quidnet Energy won a contract with the New York State Energy Research and Development Authority for a 2-megawatt/20-megawatt-hour demonstration project of its geomechanical pumped storage. Quidnet will use excess renewable energy to store pressurized water underground in dry oil and gas wells.
Thermal storage uses excess or curtailed power to charge a thermal “battery” made of materials such as molten salt or cryogenic liquids.
1414 Degrees stores molten silicon at, yes, 1414 degrees Celsius. The startup acquired the Aurora Solar Energy Project in South Australia (a combination of 70 MW of PV and 150 MW of concentrated solar power), and 1414 is looking to expand the plant and pilot its technology at the site.
Alumina uses a high-temperature, low-cost ceramic material with high thermal conductivity and heat capacity to store and recover thermal energy up to 1,500 °C.
Antora Energy combines high-temperature thermal storage with high-efficiency thermophotovoltaic energy conversion.
Echogen is developing an energy storage system that uses a CO2 heat pump cycle to convert electrical energy to thermal energy by heating a reservoir of low-cost materials such as sand or concrete.
Highview Power uses off-peak or excess electricity to chill and liquefy air at -320°F, storing the liquid air in insulated tanks. When exposed to ambient temperatures, the liquid air expands and powers turbines to generate electricity.
Malta’s storage system operates as a heat pump in charge mode, storing electricity as heat in high-temperature molten salt. In discharge mode, the system operates as a heat engine, using the stored heat to produce electricity.
RayGen’s hybrid CSP-ORC system stores energy as a 90⁰C temperature difference between two reservoirs. When needed, power is dispatched through a thermally-driven Organic Rankine Cycle engine.
Pintail Power's “liquid salt combined-cycle hybrid” integrates thermal energy storage with existing turbomachinery and heat transfer equipment to repurpose existing peaking and combined-cycle facilities as energy storage assets.
“For every complex problem, there is an answer that is clear, simple and wrong”
Long-duration storage seem like an obvious, self-evident solution to intermittent renewables and grid-balancing needs.
Still, commercial, economic and reliable long-duration storage technology remains elusive. Most of the science in this article won't be ready for pilot-testing for years to come, with commercial production years beyond that – and that's if everything goes right with the technology, costs and markets.
Another issue is the state of the regulatory environment and market. A public utility commission can mandate the construction of storage, but the storage asset still has to bid into existing markets. Regulators and utility commissions at the federal and state level are still adjusting to this market reality. For example, long-duration storage technology in California is essentially locked out of the market because of the nature of California’s resource-adequacy requirements.
Lee Kasten, a WECC-based power system operator, suggests that we should rely on software and markets, not hardware: "Where possible, we should use software over hardware. For example, don’t build a battery that costs a billion dollars, only works 2% of the time and only moves around 100 [gigawatt-hours] of electricity. Build an energy-imbalance market or an extended day-ahead market for $50 million or $100 million that moves around hundreds of gigawatts of electricity. Give all consumers price signals, and then watch the flexible consumers adapt to those price signals using software to manage existing loads."
The potential is great and the grid surely needs it, but long-duration energy storage still has a long way to go.
Article image: Mike Steele, The Persistence of Memory (1931) by Salvador Dali, Painting at the Museum of Modern Art, Flickr Creative Commons.
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