As expected from Kris De Decker, it is an excellent overview of the subject, amply referenced.
Generators and batteries and all that goes along with them may cost hundreds or thousands of Euros, perhaps constituting the most significant cost in some systems. So I think it makes sense to try to avoid using them.
What are some ways you can use rotational energy without using a generator?
I am most interested in directly using kinetic energy to heat water, as I think that is the biggest market. What are some products I could buy or make now that would do that and that would end up costing less than using a generator to generate electricity?
As a start: