2019 was a breakthrough year for non-battery energy storage technologies

This year has been a breakthrough year for non-battery energy storage, with major advances in pumped hydro, power-to-gas and thermal storage technologies. Many industry players are moving from pilot projects to contract projects, which will further scale up and reduce costs.

Pumped Storage

Pumped hydro is a proven, long-term energy storage technology that uses electricity to pump water from a downstream reservoir or lake to an upstream reservoir. When demand for electricity is high, water flows down from the upstream reservoir to power hydroelectric turbines.

Closed-loop pumped hydro uses two artificial reservoirs with no connection to a natural body of water. Under projects planned in Montana and Arizona, a closed-loop system can generate eight to 10 hours of electricity and store energy by pumping water uphill for 10 to 14 hours.

The U.S. has 27 approved pumped hydro projects in 16 states totaling 18.8GW of generating capacity, most of which are at least 30 years old. However, there is also a robust planning program: The Federal Energy Regulatory Commission has approved preliminary permits for 20GW of new capacity, with another 19GW in the pipeline.

There may be more viable pumped storage sites in the United States, as there are an estimated 500,000 pumped storage sites worldwide that are technically suitable, meaning they could potentially be home to both high and low reservoirs.

Pumped hydro is cheap, probably because it has only one modular component — a reversible turbine. All other costs are site-specific, from engineering, moving earth, to building the building that contains the turbine.

A cost forecast concluded that pumped hydro storage has more favourable financing costs than lithium-ion batteries.

Copenhagen Infrastructure Partners appears to support this assessment, as the company invested in a 400MW pumped storage project in Montana last summer. The project has received a construction and operating permit and construction could begin next year.

Pumped Storage Power Station

Electricity to hydrogen (or other fuels)

Electricity-to-hydrogen is another technology that is mature, at least for small-scale installations. Hydrogen produced by electrolysis can be stored and then used to generate electricity through a fuel cell. This is a potential long-term energy storage option.

At least three small industrial installations have been announced in the past year, all of which use proton exchange membrane (PEM) electrolysis technology to produce "green" hydrogen by splitting water into hydrogen and oxygen using solar or wind power. The hydrogen produced can be stored in pressure vessels waiting to be used in a fuel cell. Because the hydrogen storage is separate from the electrolyzer unit, there is no technical limit to the amount of hydrogen that can be stored for a given electrolyzer system.

While PEM and other electrolysis technologies are mature, achieving economies of scale is a challenge. Hydrogen technology will likely need to gain a foothold in a range of markets, increase scale and reduce costs before it can become a cost-competitive energy storage option.

This process of scaling up has already begun. In February last year, Hydrogenics Corp. announced plans to build a 20MW PEM electrolysis system for Air Liquide in Canada. At the time, the system was called the world's largest electrolytic hydrogen project, with an annual hydrogen production of approximately 3,000 tons.

Also in February last year, a unit of Norwegian hydrogen company Nel ASA announced a framework contract for a 30MW electrolyser project in Switzerland. The project will start with a 2MW containerized PEM electrolyser and sell hydrogen to Hydrospider (a subsidiary of H2 Energy) for use in a planned fleet of fuel cell trucks.

Finally, ITM Power announced a 10MW PEM electrolyser in Germany and has designed a 100MW system – a system ITM Power reports growing interest from potential industrial customers. ITM reports that electrolyser costs are currently below €800 per kW and will fall below €500 per kW by the mid-2020s.

Looking further ahead, a group of industry and academics in the Netherlands has set a goal of building a gigawatt-scale electrolysis plant. They aim to produce green hydrogen by 2025 or 2030 at a cost of around €350 million.

Another possible storage method is to use green hydrogen to make ammonia. Japan's JGC has reported an efficient method for converting hydrogen into ammonia, which can then be used to generate electricity. JGC believes it has advantages over hydrogen in terms of safety and cost-effectiveness.

Hydrogen can be obtained from water through electrolysis

Thermal energy storage

A well-known application of thermal energy storage is molten salt energy storage, often associated with the Solana Concentrated Solar Power Plant in Arizona. The heat is used to drive a steam turbine. However, thermal energy storage also includes other ways of storing heat, including storing "cold".

In June 2018, England-based Highview Power began operating a 5MW cryogenic energy storage pilot facility near Manchester. The technology uses electricity to liquefy air at -320˚F and store it in insulated low-pressure tanks, then exposes the liquid air to ambient temperature and rapidly regasifies it, expanding it to 700 times its liquid volume to power a turbine.

Highview Power estimates that for a 200MW/2GWh (10-hour) system, the average cost is $140/MWh. Similar projects are underway. For example, last July, Highview Power announced that it had signed a contract with Nebraska-based Tenaska Power Services to help develop a 4GWh cryogenic energy storage plant in the United States over two years.

Highview Power's cryogenic energy storage system

Cold storage can be used as an alternative to electricity generation, thus shifting electricity demand, especially during peak solar generation times in the summer when the cold air can be used for air conditioning.

California-based Ice Energy is currently installing 1,200 Ice Energy systems under contract with Southern California Edison (SCE). The systems will be centrally controlled to manage peak demand and load shifting.

Siemens Gamesa offers what it calls a cost-competitive technology: electrothermal energy storage. Electricity is used to heat volcanic rocks stored in an insulated container to temperatures of 600°C. The heat is then converted into electricity via a conventional steam turbine, and the system can achieve a round-trip efficiency of 45%. The company says the technology could be used to retrofit retired fossil fuel power plants, and plans to start operating a pilot facility later this year.

Looking ahead

The development of energy storage technology over the past year has shown that battery storage is not the only way forward. Other technologies capable of long-term energy storage are also advancing. Cost projections are beginning to become public, and these technologies should receive more attention in the future.

(Original text from: Global Energy New Energy Network Comprehensive)