Could Deep Shaft Mines Get a Second Life As Energy Storage Sources?

Finding a way to extend or wring some positives out of abandoned or exhausted mines, particularly deep shaft mines, has become a new challenge for many stakeholders. Startups like Gravitricity have got close to building a business out of using them for energy storage, for instance.

Now Centennial, an Australian mining company which is a wholly-owned subsidiary of Banpu Public Company Limited, has begun a technical feasibility study to ascertain if underground coal mines can be used to build a 600MW pumped hydro energy storage facility. The company supplies coal to domestic and export markets and powers close to 30% of New South Wales (NSW) coal-produced electricity. Additionally, it owns 5 operating coal mines, 2 under “maintenance” mines, and other potential new mining and energy projects. This important study will be funded by the Australian Renewable Energy Agency (ARENA) ($995,000) and NSW Government ($4.16 million) for a technical review and pilot trial, which would reveal important details about the viability of the new concept of underground pumped hydro energy storage. 

Its results would be key in exploring coal’s reaction to water movement and the ‘revival’ possibilities of unemployed brownfield sites and coal mines, this time as energy storage sites. The site in question, for now, is the Newstan Colliery in Fassifern, south-west of Newcastle, which has been on care and maintenance since 2014, that is, it’s been kept by the owner on the off chance of needing to scrape more coal out of it in the future. The whopping $13 million being spent on the study might be worth it since the site seems viable for pumped hydro: it houses an upper and a lower reservoir and is already connected to the grid, with proximity to a secure water source. If successful, the proposed 600 MW PHES plant would not only serve a vital storage need but also provide employment to around 1000 people during construction and a further 50 people in ongoing operational roles. 

ARENA CEO Darren Miller has said, “Through Centennial’s study we aim to discover the factors that could lead to broad commercialisation uptake in repurposing brownfield sites and giving them a second life as energy storage facilities to support the growing share of renewable energy in our system.” The plan is to cause minimum water loss by carrying out a closed-loop operation where water in flooded mined seams about 50 metres underground will be transferred to seams about 250m farther down, or 300m underground. The upper reservoir could also include a traditional ground-level reservoir, other underground coal seams or open cut voids. At the time of abundant and cheap solar energy, the water can be pumped to the upper reservoir, turning the pumped hydro system into a storage of sorts, which can sell stored energy at a profit later on. 

Since the mine is located near the large 2.88GW Eraring coal-fired power station, the two would together form an extensive underground battery to make transmission efficient. “We are excited to be working with ARENA and the NSW Government on this pumped hydro project which represents an important and tangible step in evolving Centennial’s business from one solely based on coal, to a diversified energy company,” said Katie Brassil, Centennial’s Executive General Manager External Relations. If the study’s results are positive, the coal mine turned solar energy storage would be a significant addition to the network of renewable energy storage projects being undertaken by the state’s Electricity Infrastructure Roadmap which could potentially generate 2 GW of pumped hydropower. 

Gravity-based storage (including large Hydropower projects) remains the biggest energy storage option for the world till date, accounting for over 90% of global storage capacity. This old fashioned technology to generate power on demand from the 19th century clearly has a role to play in many ways yet.