Compressed air storage is a technology that increasingly looks like it will be a part of the energy mix as the planet moves to a renewable-dominant power generation infrastructure to achieve net-zero emissions by 2050.
A-CAES stands for advanced compressed air energy storage. It works this way (see schematic above). During periods when power demands are low, surplus electricity produced from the grid or from renewable sources powers the compressor. This produces heated compressed air. The heat gets extracted as the compressed air is pumped to pressure-sealed storage underground. When would the energy be released? When renewable power generation is less than peak and demand is high, the compressed air storage system can be switched on. The underground chamber is flooded with water stored at the surface. That pushes the air up where it is combined with the extracted heat to drive turbines to generate electricity.
The advantages of A-CAES technology are many:
When the company was founded in 2012 it was able to get Toronto Hydro to fund a pilot project. This was a 1.75 Megawatt system that has been operational since 2015 and provides continuous energy for six hours at a time. The stored air lies in an excavated cavern some 300 metres (about 1,000 feet) underground. A natural cavern would be as suitable if not a better choice. A second facility has also been commissioned in the Toronto area. And now Hydrostor has two more projects to build, both for California. One will replace the power lost when the Diablo Canyon nuclear plant in San Luis Obispo County is decommissioned in 2025. The other will provide supplemental power for Los Angeles.
Today there are compressed air power plants in operation at two other sites. These are not Hydrostor builds. One is located in Alabama, and the other in Germany. Both use natural gas to heat the air. Both don’t capture the heat for release along with the compressed air. The result is both contribute waste heat and greenhouse gas emissions during operation. Hydrostor doesn’t let the heat it gets from surplus grid or renewable energy sources go to waste because it is stored.
In California’s latest energy plan, the state’s Public Utilities Commission mandated energy producers to develop or acquire 11,500 Megawatts of new electricity by 2023 to 2026. In the request, long-duration storage is included with a goal to add 1,000 Megawatts from these sources. California already uses a mix of long-duration storage today with a total capacity amounting to 3.7 Gigawatts.
The two Hydrostor facilities represent a modest increase in that total, but this is just the start of what could become a fixture in the near future for the state’s net-zero energy infrastructure.
The following infographic illustrates what the Hydrostor facility will look like and how it will operate.
This first system produces enough power to light and heat 330 homes. Hydrostor has plans to dramatically increase capacity. It has a tentative contract for a 5 megawatt system to be installed in Aruba in the Caribbean. The estimated cost for that project is $15 million CDN. A 100 megawatt system would cost around $200 million. All components come from off-the-shelf parts including the balloons which are marine salvage lift bags (see image below).
Large-scale compressed air energy storage (CAES) is not new. In fact the idea has been around since the 1870s. The challenge has always been finding suitable land-based sites for the technology. That has held back commercial CAES from coming to fruition. In 1978 the first commercial plant was opened in Germany. A second commissioned in Alabama in 1991 illustrates the challenge of land-based CAES. The containment room for the air had to be created underneath an underground salt dome. Since 2007 a number of new CAES sites have received funding but the limitation remains. Find a suitable underground environment capable of absorbing air under pressure without destabilizing its surroundings.
Hydrostor believes they have the answer. Don’t put CAES systems on land. Put the storage medium in the water and let water pressure do the job of containment. The company’s CEO, Curtis VanWalleghem states, “finding places to store the air that’s been the problem….we open it up to thousands more sites because we use hydrostatic water pressure.” In the picture below you can see two inflated bags from the current pilot installation immersed in 55 meters of water in Lake Ontario.
Hydrostor claims its system is better than 60% efficient. That means it loses less than 40% of the energy used to charge and release. Compare that to the efficiency of other forms of power generation as illustrated by the chart below which shows the theoretical efficency of other power generation sources. I think you will agree that Hydrostor is on to something big.
