Most of the passengers emerging from the station in Bellvitge, a working-class neighborhood outside Barcelona, have no idea how innovative the city’s subway system is. Through technology not unlike the regenerative braking found in hybrid and electric vehicles, the trains they traveled generated some of the power that flowed to the EV chargers in the nearby parking lot, the lights that illuminate the station, and the escalators that take them to the platforms.
Every time a train rumbles to a stop, the energy generated by all that friction is converted into electricity, which is fed through converters and distributed throughout the subway system. One third of that powers the trains; the rest provide juice to station facilities and a growing network of EV chargers.
The ultra-fast charger outside the Bellvitge station is among four electro line shaft – Spanish for “electric gas stations” – which increased in July. The city’s main transport operator, Transports Metropolitans de Barcelona, or TMB, plans to add three more as the project, called MetroCHARGE, expands. “We’re trying to take advantage of the power that’s already in the metro system and use that spare energy to feed EV chargers on the street,” says Marc Iglesias, head of sustainable mobility at Àrea Metropolitana de Barcelona, a regional agency working with TMB on the project.
Each year, residents and tourists take 440 million trips on Barcelona’s subway system, which includes 165 stations connected by 78 miles of track. The transit agency has so far installed three converters; Another 13 are underway. Once they are all in place by the end of September, it expects regenerative braking to provide 41 percent of the energy needed to power the trains, a renewable source of energy it says will save approx. 3.9 metric tons of CO2 emissions annually.
Although many cities, including Vienna, Philadelphiaand São Paulouses regenerative braking to some extent, Barcelona being one of the few to use it so widely and the first to use it for electric vehicle charging infrastructure. Using energy that would otherwise be lost as heat when a train slows down significantly reduce a transit system’s energy consumption. (Other efforts, such as optimizing the settings for Barcelona’s semi-autonomous trains and using AI to optimize the ventilation in each car, further reduced energy needs by double-digit margins.)
With the adoption of MetroCHARGE, 33 percent of the energy used by the trains comes from regenerative braking, or enough to power 25 subway stations, says Jordi Picas, who leads the project and is director of metro systems at TMB. In subway systems that don’t deploy regenerative braking, “there’s so much energy that’s not being used, and it’s not only lost, it’s also generating heat that spreads in the tunnels and raises the temperature,” he said. Since the implementation of regenerative braking, the temperature in Barcelona’s subway system has decreased by 1.8 degrees Fahrenheit.
Last year, transport electrification surpassed renewable energy as the world’s largest category of energy transition investment, receiving around $634 billion worldwide. Although the implementation of MetroCHARGE cost about $8.6 million (7.8 million euros), TMB expects to recoup it in 4 to 5 years through energy savings and income from the charging stations, where drivers pay about 33 cents per kilowatt-hour flowing into their cars.
Metro systems worldwide already have the electrical infrastructure needed to adopt this approach, but not all of them use trains equipped with regenerative braking — and fixing them is expensive, Picas said. All of Barcelona’s trains have featured the technology since the 1980s. Since a single train costs about $6.6 million and has an average lifespan of 35 to 45 years, it’s imperative that transit operators include them in medium- and long-term planning, he said.
There are other challenges beyond cost, such as finding optimal locations for the inverters and charging stations in a dense metropolitan area. “The most difficult challenge was reaching an agreement with the various city halls to access the public space to set up the chargers,” Picas said.
Other cities have expressed an interest in replicating MetroCHARGE, and TMB recently met with a delegation from New Delhi. It also shared information with officials from Vienna and an international consortium of 45 transit systems called The Community of Metros Benchmarking Group. Cities like New York — which has the world’s fifth-largest subway system, with 472 stations and 665 miles of track — could experience significant energy savings from regenerative braking because of the sheer scale of its subway network, says Ahmed Mohamed, director of graduate studies at the Department of Electrical Engineering at the City College of New York.
In a 2018 studyMohamed and his team found that the Metropolitan Transit Authority, or MTA, which runs New York’s subways, could reduce its energy consumption by 35 percent if it widely adopted regenerative braking and used the electricity it generates to power trains and station facilities. As of 2022, only half of the city’s trains will use the technology, according to the New York State Energy Research and Development Authority, although any new trains will be required to have it. “However, there is not necessarily a strategic plan for how they can be used for energy conservation,” Mohamed said, adding that the MTA, who would not make anyone available for comment, favors regenerative braking because it requires less maintenance than conventional friction brakes.
One of the main obstacles to the implementation of regenerative braking is the lack of data indicating how much energy and money can be saved with its adoption, Mohamed said. “When you’re not completely sure about the savings, it’s hard to do a cost-benefit analysis, so decision-making isn’t very easy,” he said. “It’s important to fund pilot projects to get the real numbers.”
Learning from projects like MetroCHARGE can help other cities understand the benefits of regenerative braking, Mohamed said. Improved modeling and encouraging transport systems to share the details of their systems so that others can learn from them will also help.
Another challenge is the number of stakeholders involved – including technology and electricity companies – making it difficult to determine things like who should pay for the project. “Who runs it? Who controls it? And what is the role of different stakeholders?” Mohamed said. He’d like to see the MTA take the lead in adopting this energy-saving technology so that the trains rumbling in its stations might one day power cars on the busy New York City streets above.
