From Edwin Black's book, Internal Combustion, about the Milwaukee Road, an electric rail system: "Sometimes electrified railways seemed to defy the laws of perpetual motion. For example, when the brakes were applied or the train traveled down a slope, the engine actually returned electricity to the grid. Regenerative braking and similar power returns helped the engines pay for themselves. In some mountain ranges, if timed correctly, a heavy downhill train could actually regenerate enough electricity to the grid to power another train passing it uphill. Thus both trains would travel in a minuet of seemingly energy-free motion. That might have seemed to violate the laws of physics, but not the rules of General Electric's wondrous workhorses, which were designed to observe this maxim: It is better to give than receive when it comes to electrical power. Those engines lasted not for years but for decades. Their endurance was measured in millions of miles. They were monumental vehicles that created economic prosperity and environmental balance everywhere they rolled."
Regenerative braking on electric trains is a technology that is over a century old.
Today, Fortescue Williams, a hard rock mining company, operates an "Infinity Train” in Australia that never needs charging using this idea. Eventually, they want to make all 54 of the trains “Infinity Trains."
Hybrid diesel electric trains with batteries charged by regenerative braking are also now available (https://www.theguardian.com/us-news/2021/sep/16/battery-electric-freight-train-wabtec-rail-transport-emissions) with a present model that reduces fuel use by 11% and a prospective model to be produced within the next two years that will reduce it by nearly a third. Less than 37% of global rail is electrified now (https://www.drawdown.org/solutions/electric-trains/technical-summary) so even without taking full advantage of the energy conservation or exergy maximizing potential of electrified railroads, there is quite a lot of room for improvement.
Some more electric train examples:
Germany’s first battery electric train - 61% of their rail system is electrifiedhttps://www.juancole.com/2022/01/germanys-battery-regional.html
A battery-powered electric train platform: put two together, set a standard shipping container on top of them, and you have an autonomous freight car with none of the emissions of a diesel locomotive.
In addition, companies like ARES North America (https://aresnorthamerica.com) are now designing grid-scale energy storage projects using electric trains as energy storage, "highly efficient electric motors drive mass cars uphill, converting electric power to mechanical potential energy. When needed, mass cars are deployed downhill delivering electric power to the grid quickly and efficiently.”
Regenerative braking can be used on most vehicles including cars, trucks, bicycles, scooters, skateboards, wheelchairs….
One of the largest electric vehicles on Earth, weighing in at 123 tons with a 65 ton payload capacity, is the fully electric eDumper, developed by eMining AG, using regenerative braking to charge the batteries, and in active use since 2018. Roger Miauton, the chief executive of eMining AG, says, “When you have a descent of 10 percent,* from top to bottom, you never need to recharge. You generate enough energy going downhill as you need to get back up again.” (https://cleantechnica.com/2021/04/26/lithium-systems-acquires-123-ton-edumper-project/)
We should keep reminding ourselves that about 2/3rds of the energy we produce each and every year does no useful work, is dissipated as friction, transmission losses, inefficiencies throughout our energy systems. Recovering some of those losses is usually more affordable and easier than building new generation capacity. It is changing the lightbulbs writ large and can be done if we simply recognize that the opportunity is there.
But then, as Pogo says, “We are surrounded by insurmountable opportunities.”
* I wonder if we could use this 10% grade figure to maximize energy generation throughout a regional or national rail system and whether that would equal 100% of the energy needed for rail transportation or, just possibly, generate excess energy to the grid.