Pumped Power – Future Hope?

Wind and solar energy face two barriers to greater acceptance: the power they produce is not always available, nor is it predictable. As these renewable energy sources become more important to the world’s future, finding a way to store their power and smooth out the variability in the supply is increasingly urgent.

While the large-scale commercialization of power storage devices such as flywheels and batteries is still years away, pumped power is a proven technology able to meet large-scale demand, providing the flexibility needed to help “green” our power supply.

Pumped power as an energy storage solution goes back over 100 years to Switzerland and Italy, and it is used today in many countries by coal and nuclear power plants to help meet peak demand loads. At low-demand times, surplus electricity is used to pump water from one reservoir to another reservoir at higher elevation. The water flow is then reversed at high-demand times to power a turbine.

The only pumped power installation in Canada dates from 1957 and is at the Sir Adam Back generating station near Niagara Falls. It has a modest elevation differential of less than 10 metres, for a capacity of 174 MW. One reason for the slow adoption of pumped power in Canada is that much of the country, particularly in Quebec and B.C., already meets much of its need for “regulated” power to match demand through hydroelectricity.

But the growing focus on solar and wind power is breathing new life into the old idea of pumped power. Currently there are several proposed and planned projects, with renewed interest in B.C. and Ontario in particular. B.C. plans to add several thousand MWs of wind capacity, and thanks to its mountains the province has the ideal terrain to build pumped storage plants with head differentials as high as 1,000 metres.

Other proposals include adding pumped storage generating units to existing conventional hydro plants. In Ontario, old mines are being considered as potential sites to provide elevation differentials over 150 metres. Hatch has been involved in a number of studies, looking at the Great Lakes, abandoned mines, and adding pumped storage units at an existing power plant in B.C.

Advancements in computer technologies have helped engineers to develop powerful simulation and optimization models to improve the design and operation of future pumped storage plants. The optimal plant capacity and reservoir size can be determined in relation to the wind energy profile. The effect on the existing generation system can also be evaluated in detail before construction is started.

What’s standing in the way?

Competing storage technologies such as batteries and flywheels cannot efficiently store large quantities of energy for long periods of time. Compressed air storage is an off-shoot of the pumped power concept but requires specific geological conditions to avoid excessive losses.

So what’s in the way of more pumped power projects? Often, capital cost. They require large investments in reservoirs, pipelines, pumps and turbines. But then, like wind and solar power, they can operate for decades without major reinvestments.

Then there’s the need to find locations offering a significant difference in height between water bodies. A good elevation difference, even with small reservoirs, is economically more viable than large reservoirs with a lower height differential.

Pumped power is also not without its environmental costs, and presents similar challenges to conventional hydro generation, such as loss of land for the storage reservoir and effects on existing waterways.

On the other hand, the power industry has a century of experience with pumped power projects. To this we can add improvements in variable-speed generators and in the performance of control systems, allowing for quick, precise shifts in power output to compensate for fluctuations in load and demand. Not only can large changes in power output be achieved within seconds, the turbines can be changed between pumping and generation modes in less than one minute. This allows a pumped power plant with a modest size to provide a significant amount of regulating capacity.

Despite some drawbacks, pumped power holds great promise for the future. It is a proven technology that is able to meet large-scale demand, providing the flexibility needed to help “green” our power supply.cce

C. Richard Donnelly, P.Eng., is director for water power, and Francois Welt, P.Eng. is a project manager/optimization specialist, both with Hatch at its Niagara Falls, Ontario office. E-mail rdonnelly@hatch.ca; fwelt@hatch.ca.