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

TL;DR

This study demonstrates that counter-rotating vertical-axis wind turbine arrays can significantly increase land-based wind farm power density, potentially achieving an order of magnitude higher output without higher turbine efficiency.

Contribution

The paper introduces a novel VAWT array layout that exploits wake interactions to dramatically boost power density, offering a new approach to wind farm design.

Findings

Power density can be increased by an order of magnitude.

Closer turbine spacing is feasible without efficiency loss.

Performance relies on wake interactions and turbulence flux.

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 to 3 watts 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.