A closed mine in southern Ontario may be about to see new life helping unblock a stubborn barrier to renewable energy.
The open pit Marmora Iron Mine, located midway between Toronto and Ottawa, was in operation from 1955 until 1979, and since closure has filled with a pit lake over 160 metres deep.
It was the volume and depth of water, plus the waste rock piled next to the pit, that caught the eye of electrical power producer Northland Power Inc. This company, which operates several wind and thermal power sites in Canada and Germany, sees an opportunity for the mine to generate revenue once again, as well as help manage some of the growing challenges facing the Ontario power sector.
Pumped Storage helps make renewable energy practical
Some of these challenges come from what many members of the public think of as a good thing — the growth of renewable energy, mostly solar and wind power. Although non-polluting, solar energy is limited by being available only when the sun shines, and wind turbines do not turn without enough wind.
Energy consultant Bob Stasko, President and CEO of Science Concepts International, says that in utility terms, wind and solar power is “unregulated” —it cannot be easily increased or decreased to match the peaks and valleys of demand. Also, there is no way to store it. So depending on whether the sun shines or the wind blows, the renewable energy that flows into the grid must be balanced by other sources of power such as hydro, nuclear or gas, ramping up or down.
“That becomes a destabilizing element in the energy mix,” says Stasko, adding that as the installed base of renewable energy grows, this effect becomes more pronounced.
Yet the world needs power sources that are renewable and do not contribute to climate change.
The key? An effective way to hold power available until it is needed. “Energy storage is the magic bullet,” says Stasko. He says that entrepreneurs and governments worldwide have been looking for practical means of “utility scale” power storage.
Part of the solution may lie in one of the oldest ways to store power: pumped storage. This involves pumping water from one reservoir to another at higher elevation at times of day when power is plentiful and cheap, and then running the water back down through a turbine at times of peak demand.
The only pumped power installation in Canada, at the Sir Adam Beck generating station near Niagara Falls, was completed in 1957. It has an elevation differential of about 10 metres, for a capacity of 174 megawatts (for comparison, one MW can power about 800 houses in North America).
Success factors for pumped storage include the need for a good differential in elevation, the ability for the penstock between upper and lower reservoirs to have a steep gradient, and a short distance to electrical corridors with capacity to provide and receive power.
What makes Marmora Mine feasible for pumped storage?
John Wright, Executive Director, Business Development for Northland Power, believes that the Marmora Mine site meets these requirements. His company’s plan involves moving the waste rock piled on the surface so it forms an upper reservoir, lined to prevent water release, with the existing pit lake forming the lower reservoir.
Combination pump/generator units, in an underground powerhouse, will use power from the electrical grid to pump water into the upper reservoir during off-peak periods when power prices are low, and then release that water back down into the pit to generate electricity at high-priced peak demand times.
The design provides for an average head — elevation differential — of 140 metres, making it able to produce 400 MW of power for about five hours, until the upper reservoir needs refilling. That will add significantly to the province’s ability to store surplus power so there is less need to sell it at a discount, or even pay other utilities to take it, as sometimes happens.
Wright says that there are several factors that make the Marmora Mine site particularly attractive to Northland:
• Pumped storage depends on a significant height differential between upper and lower reservoirs — and at the Marmora site, the head of water available is about four times the height of Niagara Falls.
• Success also depends on being able to have the two reservoirs close together, so that the penstock between them can be near vertical — a situation rarely found in nature, but available at Marmora.
• The site is close to the Golden Horseshoe — the urban concentration around the west end of Lake Ontario, for more efficiency in regulating the power supply.
• It is within eight kilometres of a major power utility corridor that has the capacity to provide and absorb the power that will be generated.
While there are many other closed open pit mines that might be used to generate power, says Wright, many are located in remote areas and far from the high-capacity power corridors needed to transmit the power, limiting their usefulness for pumped power.
Wright says that the Marmora Mine project has the support of local political leaders. Northland is now working with Ontario’s new leadership to ensure provincial support for the project. If the project receives the necessary support, there would be about a year and a half for the environmental review process, followed by about four years of construction.
Pumped storage in underground mines
Given the depth of some underground mines, it’s perhaps natural to wonder if they could be used for pumped storage, moving water from one level of a closed mine to another.
Doug Morrison, President and CEO of Sudbury-based Centre for Excellence in Mining Innovation, says that this is a question he has investigated in his current and previous roles.
“Underground mines were designed to be temporary,” Morrison points out. Unlike underground structures that have been designed for longevity and built to civil-engineering standards, mines are vulnerable to collapse if not properly maintained. Repeated flows of water in and out of the workings would likely accelerate this.
As well, Morrison says, the depth of mine workings is not necessarily optimal for the appropriate head of water needed for pumped storage — and the mines’ distance from electrical power corridors may also make them impractical.
Morrison advocates specially designed and constructed underground facilities, using excavation technologies that have been proven to work in mining, for purposes of pumped storage.
This means that the mining sector may have a role to play in helping gain greater acceptance for green energy, in Canada and elsewhere.
*Carl Friesen is a Mississauga, ON-based writer specializing in environmental and energy topics.