The mining industry is always looking for ways to rehabilitate their abandoned operations so that there may be a public use for them. This could entail leaving behind recreational lakes, building golf courses, creating nature parks or using empty pits as public landfills. Another rehabilitation idea being studied is using old underground mines as a means of green energy storage. If successful, we do have a lot of abandoned mines in all regions of the country.
Compressed air can store energy
I was at the 2019 Progressive Mine Forum in Toronto and a presentation was given on underground compressed air storage. The company was Hydrostor (https://www.hydrostor.ca/). They were promoting their Advanced Compressed Air Energy Storage (A-CAES) system.
It is a technology that addresses the power grid need for power transmission deferral services. The A-CAES system can theoretically provide low-cost, long duration bulk energy storage (i.e. hundreds of MWs, 4-24+ hour duration).
The idea is to store off-peak or excess power from solar, wind, or other generating source. Then the system can release this power back into the system during peaks or low generation capacity. Solar and wind power normally don’t work as well at night.
Flood the mine
The system uses excess electricity to run a compressor, producing heated compressed air. Initially heat is extracted from the air and retained inside a thermal store. This preserves the heat energy for later use. Next the compressed air is stored in the underground mine, keeping a constant pressure.
While charging, the compressed air displaces water out of the mine, up a water column to a surface reservoir.
On discharge, water flows back down forcing air to the surface where it is re-heated using the stored heat and expanded to generate electricity.
Imagine an underground mine beneath an open pit, and seeing the open pit water level rise and fall daily as the compressed air is recharged underground and then released.
Hydrostor is currently building a $33 million 5-MW project in Australia at the Angas Zinc Mine site. I asked Hydrostor if they had any white papers describing the economics for a typical abandoned mine we might see here in Canada. Unfortunately they don’t have such a case study available.
No doubt there would be capex and opex costs to build and operate the plant, but these would hopefully be offset by the power generation. It just not clear over what time horizon this payback would occur. Many abandoned underground mines are already in place; they are just waiting to be exploited.
Permitting is still an issue
Converting an abandoned mine into a power storage facility will still have its challenges. Cost and economic uncertainty are part of that. In addition, permitting such a facility will still require some environmental study.
At Hydrostor’s proposed Australian operation, a fairly extensive environmental impacts assessment still had to be completed (see the link here).
Noise, vibration, air quality, ecology, traffic, surface water, groundwater impacts, visual impacts, employment, and indigenous consultations are aspects that would need to be addressed. However, given that this would be a green energy application, one might be able to get all stakeholders on board quickly.