Using technology not unlike the regenerative braking found in hybrids and electric vehicles, trains in Barcelona are generating some of the power required to supply their trains, the EV chargers in the station’s nearby parking lot, the lights illuminating the station, and the escalators taking passengers to the platforms.

Every time a train rumbles to a stop, the energy generated by friction is converted to electricity, which is fed through inverters and distributed throughout the subway system, reports Grist, a nonprofit media outlet focused on highlighting climate solutions. One-third of that powers the trains.

Each year, residents and tourists take 440 million trips on Barcelona’s subway system, which includes 165 stations. The transit agency has installed three inverters so far; 13 more are in progress. Once they are all in place, the agency expects regenerative braking to provide 41 percent of the energy needed to power the trains, a renewable source of energy