Feb 25 (Reuters) - Aluminum producer Alcoa Inc said on Tuesday it has reached a deal to renew its existing power supply agreements in Quebec, but no longer plans to build a new potline to replace the two it closed at its Baie-Comeau facility last year. The company said under the deal the Canadian province's power company, Hydro-Québec, will renew supply contracts for Alcoa's Becancour and Deschambault facilities until 2030, and for its Baie-Comeau plant to 2036. Alcoa closed two potlines at Baie-Comeau last year, with combined annual capacity of 105,000 tonnes, and had planned to build a new potline at the site. A potline is a series of containers used to reduce, or smelt alumina, forming aluminum. It now plans to invest $250 million at the three Quebec facilities over the next five years, and shift some of Baie-Comeau's production to make more of the kinds of aluminum used by automakers. Auto manufacturers' demand is growing rapidly as the industry seeks to improve fuel efficiency. Alcoa had warned in October that if Hydro-Québec went ahead with a planned rate hike, the three smelters would no longer be competitive. Smelting aluminum requires large amounts of electricity, so power costs play a big role in where aluminum producers choose to build their smelters.