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The defunct Con Mine in Yellowknife. A study on the feasibility of extracting geothermal energy from the mine is finding wood pellet boilers to be a better option. - Anne Jones/NNSL photo

SOMBA K'E/YELLOWKNIFE - More than a year into research, wood pellet boilers still appear to be a more attractive heat option than geothermal heat, according to the City of Yellowknife.

The city has just completed Phase 2 of a study on the feasibility of extracting a cheap, greenhouse gas-free energy source from the defunct Con Mine: geothermal energy.

Twenty-five Yellowknifers were at city hall Tuesday evening for an update on the geothermal heat research project.

"If we manage the resource properly, it's a very sustainable resource," said Bill Wong of SIC Canada's renewable energy and climate change program, who led the presentation.

To generate geothermal energy from the old Con Mine, warm water would be pumped to the surface by a submerged pump, passed through a stainless heat exchange through buried pipes, and the cooler water would return to the mine, far below the surface. The water would pick up mine heat as it flowed through the extraction pump.

Electricity would need to be used to run a heat pump for thermal energy to be taken from the water.

For an example of what kind of heat the mine is giving off 700 metres below ground, the water is 8 to 18 C. At 1,000 metres below, the temperature is between 13 C and 28 C, and it only gets hotter.

Even if geothermal heat was used, a wood pellet boiler system would still exist as a back-up heat source, also to assist the geothermal heat plant on the coldest days.

One citizen at the information session asked if it would be more feasible to use the heat to warm the town's water supply.

Mark Henry, energy co-ordinator for the City of Yellowknife, said that option was considered in Phase 2 of study, "but it's too far from the mine site and not economical unless diesel fuel becomes significantly cheaper. Extracting heat is very expensive."

There are eight to 10 potential megawatts of sustainable thermal energy available. That's enough to heat 1,600-2,000 households. The energy would be better used in high-density areas and energy-efficient units.

"As long as pellet price stays fairly stable, it's better to stick with pellets. But if it is predicted that the cost of wood pellets will grow at a much faster rate in the future, it would be more beneficial to move to mine heat."