Highview Power

Technology | Liquid-air energy storage

Levelised cost of storage (LCOS) | About $100/MWh for a 100MW system, with costs falling to $50/MWh by 2030

Storage output (at full capacity) | From three hours to days or weeks

Round-trip efficiency | 60%

First commercial projects | Highview completed a commercial 5MW/15MWh project in Manchester, northwest England, in 2019, and has begun construction of 50MW commercial projects in the US (400MWh) and the UK (250MWh). A further eight projects are expected to begin “execution” this year and next.

Financial backing | The UK-based company has secured more than $145m to date, with $70m raised in a funding round this year, which included a $46m investment from Japan’s Sumitomo Heavy Industries.

Hydrostor

Technology | Advanced compressed-air energy storage

LCOS | No figure provided but company claims if offers the lowest installed cost per MWh for large-scale long-duration energy storage

Storage output | Initial projects are ten hours, but this could be extended with larger storage spaces

Round-trip efficiency | 65%

First commercial projects | Hydrostor has announced two 500MW/5GWh projects in California to be completed in 2024-26. It completed a 1.75MW/pilot project in Ontario, Canada, in 2019.

Financial backing | Raised $37m in 2019 from investors who now sit on Hydrostor’s board.

Siemens Gamesa

Technology | Hot-rock thermal storage

LCOS | As low as €40 ($48) per MWh for its ETES Switch platform, which converts commercial fossil-fuel power plants into storage hubs. Standalone pilot plant LCOS is about €100/MWh.

Storage output | Theoretically unlimited, depends on the amount of basalt used, although the hot rocks lose about 0.5% of their stored heat energy each day.

Round-trip efficiency | 45-50% in 2019, with the aim of increasing this to 70% or higher

First commercial projects | A first system of up to 500MWh is due to be launched in 2022, part of a “vast” commercial pipeline. Siemens Gamesa’s 30MW/130MWh pilot has been running since 2019.

Financial backing | A profitable wind turbine company that is majority-owned by industrial giant Siemens.

Stiesdal A/S

Technology | Hot-rock thermal storage

LCOS: Less than €10/MWh once it is in serial production.

Storage output | Theoretically unlimited, depends on the amount of basalt used, although the hot rocks lose about 0.5% of their stored heat energy each day.

Round-trip efficiency | 55-60%

First commercial projects | A commercial demonstration project of 1MW/24MWh is due to be installed in Denmark in 2022.

Financial backing | Daniwsh pension fund PensionDanmark ploughed a “triple-digit million investment” into the start-up in May this year, giving it all the funds needed “to execute our ambitious growth plans over the coming years”.

Energy Vault

Technology | Gravity-based (brick towers)

LCOS | Not known, but company says it will be 40% lower than competitors’

Storage output | A standard array would be 4MW/35MWh — a nine-hour system

Round-trip efficiency | 80-90%

First commercial projects | A first commercial-scale demonstration unit was completed in July 2020, with testing and optimisation continuing. No further projects have been announced.

Financial backing | Received $110m from Japan’s SoftBank in 2019, with an undisclosed investment from Saudi Aramco Energy Ventures this June.

Zinc8

Technology | Zinc-air battery

LCOS: $100/MWh for a ten-hour system or $180/MWh for a 72-hour system, with costs set to fall as the technology is commercialised

Storage output | Unlimited – hours, days or weeks.

Round-trip efficiency | 65%

First commercial projects | A 100kW/1MWh facility is due to be completed next year, and a second 100kW/1.5MWh system has also been announced.

Financial backing | Zinc8 has raised C$72m ($60m) since 2002, and brought in more than $15m from a sale of new shares earlier this year.

Form Energy

Technology | Aqueous air battery (exact chemistry unknown)

Levelised cost of storage (LCOS) | A tenth of the LCOS of lithium-ion, which would put it around $15-20/MWh

Storage output | Up to 150 hours

Round-trip efficiency | Not known

First commercial projects | A 1MW/150MWh project is due to be built for Minnesota’s Great River Energy before 2023

Financial backing | Form has brought in more than $125m of funding from investors including Bill Gates’ Breakthrough Energy Ventures, Macquarie Capital and Saudi Aramco.

Why new long-duration energy storage technologies will soon replace lithium-ion on grid