Researchers at Delft University of Technology recruited 20 student households in Rotterdam, offering prizes to teams that used the least energy over a month-long period. The teams got an energy meter to tell them their real-time consumption, as well as access to a website where they could see their cumulative usage, and how they fared against each other. The results were striking, at least on the face of it. The winning team cut its energy use by 45%, and the average reduction across the teams was 25%.