Yukon Energy is asking for additional emphasis on conservation during a period of transition over the next few weeks, says corporation spokeswoman Janet Patterson.

Patterson explained the Aishihik hydro facility was taken off line last Tuesday for three weeks, in order to carry on with installation of the new $8.5-million third turbine.

To make up for the loss of hydro generation on the Whitehorse-Aishihik-Faro (WAF) grid, diesel generators in Whitehorse and Faro will be required periodically until Aishihik comes back on line, scheduled for June 21, she pointed out.

Patterson said the lower the demand for electricity, the less the diesel generators have to run.

It's expected replacing Aishihik with diesel generators over the three weeks will cost between $400,000 and $500,000 in fuel, she said.

Also at play, Patterson pointed out, is completing the phase-two extension of the WAF grid from Pelly Crossing to Stewart Crossing, and tying in to the Mayo-Dawson grid.

Once the tie-in is complete by June 17, the Mayo hydro facility will be shut down June 21 until the end of September to facilitate further construction of the Mayo B expansion and the addition of two five-megawatt turbines.

Patterson said it's anticipated there'll be enough hydro power available in Whitehorse and Aishihik to provide for the both grids without any diesels while the Mayo hydro facility is off line.

But again, she explained, it will depend on the demand.

The $120-million Mayo B expansion, the $40-million second-phase extension and the third turbine are all outlined in Yukon Energy's long-term plan to meet the territory's rising demand.

Even still, it's expected without any further addition of generating capacity using renewable resources, diesel generation will be required full-time in a couple of years.

Records from this past winter, for instance, show the diesels were running daily in Whitehorse during periods of peak demand in the mornings and evenings.

The diesels in Dawson were running non-stop through the winter, with the additional load of the new mill at Keno City built to process ore from Alexco Resource Corp.'s Bellekeno silver mine.

The Aishihik hydro facility has a current capacity of 30 megawatts.

Adding the seven-megawatts turbine is not designed to increase maximum output because the amount of available water isn't changing.

The turbine, however, is more efficient and will use less water to generate power, resulting in available water for longer periods during the winter.

The Mayo B expansion will add two five-megawatt turbines to the five-megawatt turbine there now.

Though maximum hydro generation will be 15 megawatts, normal output is expected to be 10 or 11 megawatts.

The peak load on the Mayo-Dawson grid this winter required just under seven megawatts of generation.

By comparison, the Whitehorse Rapids Dam has a maximum hydro capacity of 40 megawatts, and another 25 megawatts in diesel generation.

Domestic demand hit a record last January when 70.5 megawatts of generation were required.

Not since January 1996, when the Faro mine was operationing and temperatures were hovering around -47, was demand so great.