Transforming a coal mine into a pumped hydro storage facility at Tent Mountain

Alberta has made big strides in renewable energy, with wind and solar being added to the grid at a rapid pace. But with these energy sources sometimes unable to deliver when they’re needed, it was difficult to guarantee a steady supply of power, especially during peak demand. The province needed a reliable way to store renewable energy and release it when the grid needed it most.

Tent Mountain, once a coal mine that powered industry in the 20th century, had been sitting idle since the early 1980s. But in 2022, Evolve Power saw something different, an opportunity to transform this legacy site into a clean energy asset. The mining pits, already filled with rainwater and snowmelt, had the potential to become reservoirs in a pumped hydro energy storage (PHES) system — essentially, a giant battery.

It was a compelling vision, but there were real challenges to solve. How could old mining infrastructure be converted into a modern energy facility that’s not only technically sound but also commercially viable? How could grid-scale energy storage be delivered in a way that supports Canada’s energy transition, creates long-term jobs and engages Indigenous communities as meaningful partners?

Shifting government incentives also meant the business case needed regular recalibration. Any solution had to be flexible, future-proof and backed by a solid engineering foundation.

To bring Tent Mountain’s potential to life, our team worked closely with Evolve Power to help shape a bold, integrated energy solution, one that reuses what was already there while planning for what’s ahead.

GHD, Evolve, and other consultants evaluated the site’s natural topography and existing mining infrastructure. The former pits, now water-filled reservoirs, were ideal for pumped hydro storage. By connecting these two reservoirs, one higher up the mountain and one lower down, the project could store and release energy by moving water between them. It’s a tried-and-true method, but on a greater scale. When complete, the system has the potential to store up to 4,955 megawatt-hour (MWh) of energy and supply up to 15 hours of continuous electricity using four 80 megawatt (MW) reversible Francis turbines.

More than just hydro, Tent Mountain has been designed as a fully integrated clean energy hub. GHD supported planning for a 100 MW electrolyser to produce green hydrogen, offering a clean fuel source for heavy vehicles like haul trucks. We also worked to connect the site with a 100 MW wind farm, proposed to be developed and owned by the Piikani First Nation, adding another layer of renewable generation to the mix.

Throughout the project, we helped update the business case to reflect changing tax incentives and regulatory conditions and maximized the potential for funding with relevant Federal applications under Canada’s Clean Fuels Standards programs. We also worked with project partners so Indigenous groups could take on active roles, from equity participation to owning key infrastructure like the wind farm.

We helped shape a solution that combines engineering, environmental thinking and strategic advisory, delivering an approach that’s not only technically sound, but also built for long-term sustainability and financial viability. 

Tent Mountain’s transformation is a story of long-term resilience, community benefit and environmental leadership. Once operational, the project is set to deliver 320 MW of dispatchable clean power and help power approximately 400,000 Alberta homes, providing critical support to a renewable-heavy grid.

Since the initial phase of the project, TransAlta has purchased the asset and continues to drive the development forward. The project is expected to create hundreds of jobs in the Crowsnest Pass region and cut an estimated 400,000 tons of CO₂ emissions annually. It provides a high potential opportunity for investors and stakeholders with economic benefits to the region. It will also help decarbonize sectors like mining and heavy transport through integrated green hydrogen production. The Piikani First Nation’s proposed ownership of the associated wind farm also supports inclusive economic development.

With a lifespan of over 80 years, Tent Mountain stands as a globally recognised model for sustainable energy transition — a reputation reinforced by its 2025 win as Energy Project of the Year at the Sustainability Delivery Awards. It’s a project that shows how smart reuse, strong partnerships and bold thinking can reshape what’s possible for the future of power.