Marmora pumped storage project would turn inactive open-pit mine into giant hydro battery

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In eastern Ontario, OPG and Northland Power Inc. are looking to advance a proposed first-of-a-kind project for Canada that would convert a long inactive, open-pit iron ore mine into a hydroelectric battery to help power Ontario’s electrifying future.

The innovative Marmora Pumped Storage Project is a joint-venture between the two power producers. Located in the Municipality of Marmora and Lake, the proposed 400-megawatt (MW) closed-loop hydroelectric pumped storage facility could power up to 400,000 homes at peak demand with clean, renewable electricity for up to five hours.

The Marmora Pumped Storage Project would convert a long inactive, open-pit iron ore mine into a 400 MW hydroelectric battery.

The Marmora Pumped Storage Project would convert a long inactive, open-pit iron ore mine into a 400 MW hydroelectric battery.

The project design would utilize Marmora’s long inactive iron ore mine, now an artificial lake and local attraction, as the facility’s lower reservoir. At night, when demand for electricity is low, water would be pumped into the upper reservoir, formerly the mine’s waste rock pile, in effect charging up like a giant battery. During the day, when demand is high, this water would be released back to the lower reservoir, falling more than 200 metres, or four times the height of Niagara Falls, and pass through turbines to generate power. Repurposing a former mine in this way would be a “first” across Canadian power utilities.

If constructed, the facility’s closed-loop design would recirculate water between its two reservoirs to generate electricity. This approach would avoid drawing water from nearby waterways and lakes, eliminating impacts to fisheries and waterway levels.

The 75-acre mine pit, which reaches a depth of more than 200 metres below ground level, was created for mining operations in the mid-20th century and closed in the late 1970s. Since then, the pit has filled with a combination of rain and ground water.

The Marmora Pumped Storage Project

From a long inactive, open-pit iron ore mine to an innovative clean energy asset.

“The proposed project offers an alternative clean energy storage option to diversify Ontario’s supply resources,” said Scott Nelms, OPG’s Vice President of Corporate Business Development and Strategy. “It would also support growing electrification demands in the province, while strengthening the local economy.”

The project is expected to create up to 3,500 jobs (direct and indirect) over the facility’s lifespan and potentially displace between 70,000 and 140,000 tonnes of greenhouse gas emissions every year.

The inactive open pit mine at Marmora today.
A look at the inactive open-pit mine at Marmora today.
The pumped storage solution also offers many of the same long-term advantages as conventional hydro generating stations, including a long lifespan of more than 90 years of expected service, significantly lower operating costs compared to other technologies, and lower construction-related environmental impacts. The project also supports Canadian investment with more than 70 per cent of the construction costs expected from within the Canadian supply chain.Currently progressing through a gated approvals process managed by the Independent Electricity System Operator, the Marmora Project is one of several initiatives identified by the Ontario Ministry of Energy as potentially helping meet the province’s emerging future energy needs. Marmora is located midway between Ottawa and Toronto, regions with high electrical demand.

OPG and Northland Power kicked-off its public consultation in late 2022 with an open house at the Royal Canadian Legion in Marmora. The project has also been endorsed by several municipal councils and political leaders in the eastern region. Additional engagement activities are expected as project planning work continues.

If approved, the Marmora pumped storage project is expected to be commissioned in late 2029.


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