<ref>https://en.wikipedia.org/wiki/Betz%27_law</ref>
Vertical turbines are less efficient than horizontal ones, around 30%. In a design with a diameter of 2-3 m (6-9 ft) you can expect a maximum output of around 2.5 kW (3.35 hp). Small (or “residential”) wind energy vertical systems may be suitable for boats. They range from 400 watts to 500 kilowatts.
== Cost ==