Container cranes at the container-terminal of Bremerhaven in Germany. Photo: Wikipedia, Public Domain.
A Kind of Regenerative Braking
Chances are, a lot of the stuff in the room around you was in a container at some point. Your computer, your phone and most other electronics probably found their way to you after a long journey inside a container (unless you live in Asia). Same for many other household products, clothes, etc. These containers are loaded unto and unloaded from cargo ships by ginormous cranes, like the ones in the photos above and below. They are either powered using electricity from the grid or by big diesel generators. Either way, it is possible to make them much more energy efficient by using the equivalent of "regenerative braking". Read on for more details.
Cranes in the Port of Rotterdam. Photo: Wikipedia, Creative Commons.
The cranes are for moving objects inside the container yard. They are designed with large lithium-ion battery packs that store electricity generated every time a load is lowered by the crane and supply that electricity to a motor that provides supplemental power to move the crane. This reduces the need to run the engine, which in turn helps reduce the crane's carbon dioxide emissions by 60%. (source)
This makes a lot of sense. It takes a lot of energy to lift a container up, but very little to lower it; you just let gravity take car of it and control the rate of descent. But all that energy that you used to lift the container is wasted as heat on brake pads when you lower it. It's much better to use gravity and the weight of the container to spin an electric generator and recharge batteries or send that power back to the grid.
The upfront capital costs might be higher for the ports, but considering how many containers are loaded and unloaded every day and how much energy these cranes use, I bet that the fuel or electric bill reduction would make it worth it after not too long.
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