I was surprised to discover a little while ago that the London Underground has had energy recovery systems in place for quite some time, based around a short in

I was surprised to discover a little while ago that the London Underground has had energy recovery systems in place for quite some time, based around a short incline on the route into a station, and a descent leading out of it[1]. Energy is then quite neatly stored as gravitational potential over the height difference. The ability to retrofit this new system to existing infrastructure without major engineering works is definitely a huge plus. [1] https://en.wikipedia.org/wiki/Regenerative_brake?s#Electric_railway_vehicle_operation https://en.wikipedia.org/wiki/Regenerative_brake?s#Electric_...