Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays

TLDR

Horizontal‑axis wind farms require large turbine spacing to avoid wake interference, limiting power density and driving the use of taller, more expensive turbines with greater environmental impacts. This study investigates whether counter‑rotating vertical‑axis turbines can achieve higher power output per land area than conventional HAWT farms. Full‑scale field tests of 10‑m VAWTs in various counter‑rotating configurations were conducted in summer 2010 under natural wind conditions. The tests show that VAWT arrays can potentially deliver an order‑of‑magnitude higher power density by harvesting energy from adjacent wakes and above the farm, without needing higher turbine efficiency, and could reduce cost, size, and environmental impacts.

Abstract

Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require significant land resources to separate each wind turbine from the adjacent turbine wakes. This aerodynamic constraint limits the amount of power that can be extracted from a given wind farm footprint. The resulting inefficiency of HAWT farms is currently compensated by using taller wind turbines to access greater wind resources at high altitudes, but this solution comes at the expense of higher engineering costs and greater visual, acoustic, radar, and environmental impacts. We investigated the use of counter-rotating vertical-axis wind turbines (VAWTs) in order to achieve higher power output per unit land area than existing wind farms consisting of HAWTs. Full-scale field tests of 10-m tall VAWTs in various counter-rotating configurations were conducted under natural wind conditions during summer 2010. Whereas modern wind farms consisting of HAWTs produce 2–3 W of power per square meter of land area, these field tests indicate that power densities an order of magnitude greater can potentially be achieved by arranging VAWTs in layouts that enable them to extract energy from adjacent wakes and from above the wind farm. Moreover, this improved performance does not require higher individual wind turbine efficiency, only closer wind turbine spacing and a sufficient vertical flux of turbulence kinetic energy from the atmospheric surface layer. The results suggest an alternative approach to wind farming that has the potential to concurrently reduce the cost, size, and environmental impacts of wind farms.