Client: GL Garrad Hassan
Chris Hornzee-Jones was commissioned together with GL Garrad Hassan to develop a design of support structure and yaw system for a 16 rotor array. Together they delivered a study report for the OWES 5.0 MW Multi-Rotor Support Structure and Yaw System.
In his book "Innovation in Wind Turbine Design" (p.233), Peter Jamieson explains that the "reduction in mass of rotors and drive trains of the multi rotor system as compared [to] a single large wind turbine was enough [so] that all the rotors, drive trains and a frame to support them could be carried on a tubular tower and yaw bearing rather similar to the support structure of an equivalent single large rotor.
This gives a strong indication that the need to yaw a multi rotor array should not greatly erode its potential economic advantage."
A multi rotor array improves on some of the disadvantages VAWT designs have in side-by-side comparison to HAWT, which traditionally shows them to have lower aerodynamic efficiency and higher torque (weight and cost). By counter-rotating alternate rotors, gyroscopic moment can be counter-acted and therefore the loads are reduced.
See here a link to a 2014 presentation by Peter Jamieson, stating the case for multi rotor array systems.