2007 год. Даже первые версии Fortius и Magic "умели" это делать.

http://autobus.cyclingnews.com/tech.php?id=tech/2007/reviews/tacx_fortius07

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Incredibly, Tacx also steals a conceptual page from modern hybrid automobiles and their regenerative braking systems which capture otherwise wasted energy to charge the batteries. In similar fashion, the Fortius VR trainer features a "PowerBack System" that actually feeds consumed current back into the system, meaning that the trainer uses relatively little juice.
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Специально для тебя выделил: "consumed current back into the system" ))

И да, это стоит копейки относительно общей стоимости трейнеров.