Manitoba's Crown-owned energy utility announced a deal Monday to sell 100 megawatts of hydroelectric power to its counterpart in Saskatchewan.

The 20-year agreement between Manitoba Hydro and SaskPower starts in 2020 and is big enough to power 40,000 homes. It builds on previous sales, including a 25-megawatt deal signed last year that will run from November 2015 to May 2022.

Interim Manitoba Hydro president Darren Rainkie said the sale is part of the corporation's earlier projected revenues -- the two provinces signed a memorandum of understanding in 2013 for up to 500 megawatts -- and will not affect plans to boost domestic hydro rates by 3.9 per cent a year for the next decade.

"It means that we can continue to deliver reasonably stable rates in the next number of years that is in line with our forecasts. It allows us to firm up the revenue that's in our forecast right now," Rainkie said.

Manitoba Hydro is in the midst of a major expansion, with new generating stations being built in the north and a long transmission line that will bring the energy south. The new sale to Saskatchewan will take up 18 per cent of the energy generated by the Keeyask generation station already under construction, Rainkie said.

The sale to Saskatchewan will require a new 80-kilometre transmission line to be built between the provinces, at cost of roughly $50 million.

Rainkie would not disclose how much SaskPower is paying for the new contract, but said the price is a good one.

"That's a commercially sensitive amount ... we can't compromise future negotiations by releasing it," he said.

"It's fixed price and it becomes then escalated at (the rate of inflation) but it definitely is an attractive price."

Premier Greg Selinger said the deal will help keep domestic hydro rates among the lowest in Canada and will boost the economy.