I am a retired electronics engineer, educator, businessman and builder of micro hydro installations for fun and sometimes even profit. This one uses a pump/motor as a turbine/generator using a 200 ft waterfall in our back yard. It is currently producing 15KW. I will be tweaking it to take advantage of greater winter flows.
It's not the product, but the process... I enjoy doing the most with the least. So this renewable energy source cost only $2 per watt of capacity not counting any labor and engineering.