33. ## D
The Barcelona subway pulls into the station, the doors slide open and passengers 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 also doing its part to tackle 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, whereby the energy from the underground trains' brakes (刹车) is used to power the trains and the stations themselves, while the remainder is sent snaking through cables (电缆) to the surface to power plug-in stations for privately owned vehicles.
Bernardo Espinoza, an engineer who takes the subway every day, owns an electric car. "I am pleasantly surprised, because I 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 trains' brakes, then even better."
Regenerative brakes have been in trains for decades and are also used in some cars. They consist of an electric motor which collects energy used in the braking action that would be lost as heat by conventional brakes. That energy can be immediately used to accelerate (加速) 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, a professor of electrical engineering, said that 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 said, boosts efficiency.
33. What is Espinoza's concern?
D