Some hybrid and electric cars are equipped with a brake system that collects thermal energy generated in braking and feeds the battery by increasing the range of the vehicle. A similar regenerative braking technology was tested in London Underground.
Based on a capture and reverse energy generated during braking, the system feeds the train with electricity that otherwise would remain untapped. In a Metro system that is so expanded and dense as that of London, the energy savings from such a system can grow to impressive levels.
The first tests of the technology took place onto the Victoria line. Engineers discovered that the system can bind a megawatt hour of electricity per day, which is enough to power 104 households annually.
In economic terms, the London Underground can save up to five percent or six million pounds annually.
During the weekly test, the system froze enough energy to meet the needs of Holborn station for two of the seven days of the week.
There are also indirect benefits beyond the obvious. If the system binds thermal energy that otherwise would go wasted, trains will emit less heat and the air conditioning systems of the Metro stations will operate less.
The new technology is developed within a wider program of energy efficient transportation with reduced environmental footprint.