From my understanding, low solidity wind turbines (such as the three blade type) are more efficient due to a higher tip speed ratio, giving a higher coefficient of performance. However, they are not well suited to high torque applications.
Whereas, high solidity turbines have a lower tip speed ratio hence they are less efficient, but they produce more torque, making them better suited for applications like pumping water.
This is what the text books tell me: low solidity for electricity production vs high solidity for pumping water.
My question; why not just use high speed, low solidity turbines and gear them to produce a low speed, high torque output? This makes use of the more efficient turbine design and allows it to be applied to a high torque requirement. There are other factors in choosing a turbine, such as start up speeds but surely in terms of power output gearing can be used to match a turbine to a load?