BARCELONA, Spain — The Barcelona subway grinds to a halt, the doors slide open and commuters pour out to go about their daily business.

Little do they know that as they do so, a burst of energy is sent up to street level to help charge an electric car.

Barcelona has put together a package of clean energy technologies to help public transportation go greener while doing its part to combat climate change and aid Europe’s difficult shift to the privately owned electric vehicle market.

Sixteen stations of Barcelona’s subway system are part of its new MetroCharge project, in which the energy from the underground trains’ brakes is used to power the trains and the stations; the remainder is sent snaking through cables to the surface to power plug-in stations for privately owned vehicles.

Bernardo Espinoza, a 49-year-old engineer, commutes daily by subway. He also owns a hybrid car and had just found out that he had a new place to plug in.

“I am pleasantly surprised because I have an electric car and am always looking for where to plug it in,” Espinoza said before catching the subway in a working-class area of southern Barcelona. “And if it is from energy from the metro’s brakes, then even better.”

Regenerative brakes have been in trains for decades and are used in some cars. They consist of an electric motor that captures energy used in the braking action that would be lost as heat by conventional brakes. That energy can be immediately used to accelerate the vehicle or, in the case of the Barcelona subway system, sent along cables to supply electricity for the station or for electric car chargers.

Alvaro Luna, professor of electrical engineering at the Polytechnical University of Catalonia, said the system is innovative in so far as it allows for recycled energy to be redirected to specific local uses — in this case powering electric cars parked nearby. That, he says, boosts efficiency.

“Since the recharging stations are installed nearby, the energy, instead of being put back into the general electric network, goes directly to the charging stations, and that allows the provider to potentially offer lower prices,” Luna said. “We can say that the innovation is one of urban planning, of being able to bring together energy uses within a city.”

Making better use of energy has become a key pillar of reducing rising global temps. Last year, countries at U.N. climate talks and the members of the Group of 20 industrialized and emerging-market nations agreed to double energy efficiency by 2030.

Jordi Picas, head of systems for TMB, Barcelona’s subway, said the public company estimates that it can recover the $7.6 million spent on MetroCharge, which includes European Union funding, in four years, thanks to reduced energy costs.

The system, which includes solar panels, provides all the energy needs of 28 of the 163 subway stations, from the lights to the elevators and ventilation systems, and saves 6% of the total energy spent by the metro, according to Picas.