A new fleet of famous double-decker busses are about to hit the streets of London. Although they may not look much different on the outside, the new busses have one major upgrade: they’re powered by hydrogen. As the capital steps up attempts to tackle its polluted air, London is rolling out 20 hydrogen busses that only emit water as exhaust.

Along with cutting exhaust emissions, the buses will run on green hydrogen produced via North Kent offshore wind farms. The move follows the introduction of the capital’s ultra-low emission zone last month, where the most polluting bus and coaches are charged £100-a-day to drive. One of the major benefits of hydrogen-fuel powered vehicles is that they can be refuelled far more quickly than conventional battery-electric buses can be recharged, requiring only one five-minute refill a day. They also have a longer range than battery buses and can be used on more routes.