I’ve been thinking about how this could be retrofitted to an existing frame. The generator is too big but it could be mounted in front of the crank shaft under

I’ve been thinking about how this could be retrofitted to an existing frame. The generator is too big but it could be mounted in front of the crank shaft under the frame and then be connected via simple gears or a short chain. This would still have said benefits. I think the possibility to choose when to save energy and when to put it out you mentioned is possible with a conventional e bike but not all bikes support this due to legislation.