Air Storage: Weatherproofing Renewables- Reliant Grids

Amanda Jasi looks at projects that are compressing air to store energy

STORING energy for later use is becoming increasingly important as the world shifts from primarily fossil fuel reliant energy production to variable, low-emissions renewables.

Research provider BloombergNEF projects that by 2030 energy storage installations will increase 15-fold compared to the end of 2021, to 411 GW / 1,194 GWh. Projects the world over are advancing conventional and novel storage means.

The Chemical Engineer spoke to Curtis VanWalleghem, CEO of Canada-based Hydrostor that plans to weatherproof grids using its advanced compressed air energy storage (A-CAES).

He said: “Our mission is really to have an impact on the energy transition. We want to speed up the decarbonisation of the energy grid.”

Bringing big innovations

Compressed air energy storage (CAES) is a proven energy storage solution that has been operating at commercial scale since the late 1970s. VanWalleghem said a CAES plant has operated “reliably” in Alabama, US for about 40 years, and another in Germany for about 30. The challenges for these plants are that they rely on uncommonly located salt caverns for air storage and must traditionally burn natural gas during a reheating stage ahead of the stored energy being released.

VanWalleghem said Hydrostor’s system instead uses rock caverns, so can be located “anywhere there’s bedrock”. Also, as an adiabatic process it captures and stores heat generated by air compression to later use in expansion, eliminating the need to burn natural gas and reducing emissions while boosting efficiency. It’s these innovations which make Hydrostor’s process advanced.

Explaining operation of a Hydrostor plant in Goderich, Ontario, Canada, he said: “To charge you turn on an electrical compressor which sucks in atmospheric air and pressurises it, and as you pressurise air it gets hot. We then take that hot air – about 250°C, it comes out – we run it through a shell and tube heat exchanger that pulls the heat out of the air and stores it in hot water, which we store at about 200°C in insulated pressure vessels.”

The cooled, pressurised air is then sent underground into the cavern and stored for later use.

“When you want to discharge you open the valve, the air comes out, gets preheated by going in reverse through that shell and tube heat exchanger, and then it drives a turbine which reproduces energy on demand.”

Comparing to established pumped hydro VanWalleghem said a “big advantage” is that Hydrostor’s A-CAES can be located on roughly one-third of Earth’s landmass, “orders of magnitude” more than pumped hydro which can only be located on a fraction of 1%. Hydrostor’s technology is also more compact and uses less land and water and is easier to permit and construct. Though he said pumped hydro is about 10% more efficient than Hydrostor’s A-CAES (about 65% efficiency), he concluded that the advantages “more than outweigh the little bit lower round-trip efficiency”.

He said lithium-ion batteries also offer higher efficiency (about 85%) and can be built quicker and at smaller sizes, but Hydrostor’s solution is more cost competitive for longer duration storage and its assets last more than 50 years and never degrade. According to the US National Renewable Energy Laboratory, lithium-ion batteries last 1,000–2,000 cycles.

By 2030 energy storage installations will increase 15-fold compared to the end of 2021, to 411 GW (1,194 GWh). Projects the world over are advancing conventional and novel storage means