7. The Physics of Starting Process for Vertical Axis Wind Turbines

In recent years there is a renewed interest in both large-scale and small-scale vertical axis wind turbines (VAWT). The development of multi-megawatt floating offshore VAWT is mainly a response to a plateau in the improvement of the aerodynamic performance of horizontal axis wind turbines. The research in small rotors (<100 kW) is motivated by the future demand for a decentralized sustainable energy supply in remote areas. However, such designs have received much less attention than the more common propeller-type designs and the understanding of some aspects of their operation remains, to this day, incomplete. This holds, because after some authors the starting operation is difficult, if not impossible, to induce the self-start capabilities without external assistance. This paper reviews the cause of the inability of the low solidity fixed pitch vertical axis wind turbines to self-start, and investigates the flow physics of dynamic stall in order to comprehend, interpret, understand and explain-all this comprising the problem of start-up.