Hydro-Québec's brokers work around the clock to buy and sell energy at the most advantageous price. When they buy electricity at a low price, they allow generating stations with reservoirs to cut back production and store more water. When they sell electric power at a time when prices are high, for example during a summer heat wave to American customers, they optimize the profitability of Québec's hydroelectric facilities, since demand is comparatively low in Québec in the summer.