Pumped storage hydro stores electricity by pumping water uphill into a reservoir when power is cheap or plentiful, then letting it flow back down through turbines when power is needed. It's essentially a rechargeable battery made of water, gravity and two reservoirs at different heights. It has been around for more than a century and still accounts for the large majority of the world's grid-scale energy storage capacity.
Key takeaways
- Pumped storage moves water between an upper and lower reservoir to store and release energy.
- Round-trip efficiency is typically around 70–85%, meaning you get most of the stored energy back.
- It can deliver large amounts of power for many hours, longer than most lithium-ion battery installations.
- Projects are expensive and slow to build, and need specific geography.
- Ontario has operated pumped storage at Niagara for decades, and new projects have been proposed in Ontario and Alberta.
How pumped storage works
A pumped storage plant has four basic parts: an upper reservoir, a lower reservoir (which can be a lake or river), a tunnel or penstock connecting them, and reversible pump-turbines in a powerhouse.
- Charging: When electricity demand is low, often overnight or when wind and solar are producing more than the grid needs, the plant uses electricity to pump water to the upper reservoir.
- Storing: The water sits uphill, holding potential energy, for hours or days.
- Discharging: When demand peaks, water flows back down through the turbines, generating electricity within minutes.
The energy stored depends on the height difference (head) and the volume of water. A bigger drop means more energy per litre, which is why ideal sites have steep terrain.
How efficient is it?
Some energy is lost to friction in pipes, turbine and pump inefficiencies, and evaporation. Modern plants typically return roughly 70–85% of the electricity used to pump the water. That's lower than lithium-ion batteries, which often achieve around 85–90%, but pumped storage makes up for it with long life (plants often run 50 to 100 years with refurbishments) and very large capacity.
Pumped storage vs. other storage options
| Feature | Pumped storage hydro | Lithium-ion grid batteries | Conventional reservoir hydro |
|---|---|---|---|
| Typical duration | 6–20+ hours | 1–4 hours (some longer) | Days to seasons |
| Round-trip efficiency | ~70–85% | ~85–90% | Not applicable (no pumping) |
| Lifespan | 50–100 years with refurbishment | ~10–20 years | 50–100+ years |
| Build time | Often 5–10+ years | Months to a couple of years | Many years |
| Site needs | Two reservoirs with a large height difference | Flexible, small footprint | Large river and valley |
For a deeper look at batteries and other storage technologies, see our future of energy page and the glossary for terms like round-trip efficiency and capacity.
Why pumped storage matters for a clean grid
As provinces add more wind and solar, the grid needs ways to shift energy from when it's produced to when it's used. Pumped storage helps in several ways:
- Peak shaving: It covers the highest-demand hours, like cold winter evenings, reducing the need for gas-fired "peaker" plants.
- Absorbing surplus: When there's more renewable power than demand, pumping soaks it up rather than curtailing it.
- Grid stability: Large spinning turbines provide inertia and fast response that help keep the grid's frequency steady.
- Long duration: It can run at full output for many hours, bridging a calm, cloudy evening.
Provinces with big conventional reservoirs, like Quebec and Manitoba, already have much of this flexibility built in, because they can simply hold water back. (We explain that advantage in why Quebec and Manitoba have Canada's cheapest electricity.) Provinces with less storage hydro, like Ontario and Alberta, have more reason to look at pumped storage.
Pumped storage in Canada
The Niagara example
Ontario Power Generation's Sir Adam Beck Pump Generating Station near Niagara Falls has operated since the 1950s. It pumps water into a reservoir at night, when demand is low and water diversion rules allow more water to be taken from the river, and releases it during the day through the generating stations.
Proposed projects
- Ontario Pumped Storage (Meaford, Ontario): A proposed project of roughly 1,000 MW on Georgian Bay, using a Canadian Army training area. As of mid-2026 it was still in the federal impact assessment process, and in July 2026 the proponent and the Municipality of Meaford signed a pre-development agreement to support the community's review. It has not been approved.
- Canyon Creek (Alberta): A proposed pumped storage project of about 75 MW near Hinton, using a former coal mine site, designed to provide up to roughly 37 hours of storage. It has received key provincial approvals but was not yet operating at last update.
Large projects like these face long timelines, environmental review, and questions about impacts on water, shorelines and local communities, including Indigenous rights holders. Some will be built and some won't; following them through your provincial guide is the best way to stay current.
Closed-loop designs
Newer "closed-loop" pumped storage uses two artificial reservoirs not connected to a river, which can reduce impacts on fish and river ecosystems. Old mine pits and quarries are attractive sites because the holes already exist.
Frequently asked questions
Does pumped storage produce clean energy?
Pumped storage doesn't create energy; it stores it, using more electricity than it returns. Its climate benefit depends on what power is used for pumping and what it displaces later, so charging with surplus wind, solar or hydro and displacing gas peakers is the best case.
How long can pumped storage run?
It depends on the size of the upper reservoir. Many plants are designed for six to twenty hours at full output, and some can run longer, which is much longer than most battery installations today.
Why aren't more pumped storage plants being built?
They need specific geography, take many years to permit and build, and require large up-front investment. Falling battery costs have also made batteries the faster choice for short-duration needs, though pumped storage still leads for long-duration storage.
The bottom line
Pumped storage is old technology that has suddenly become very relevant again. It won't fit everywhere, and big projects take years, but for provinces adding lots of wind and solar, a water battery that runs for many hours is a powerful partner. Learn more about how hydropower fits into Canada's grid on our hydro page.
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