Small Horizontal Axis Wind Turbines: Current Status and Future Challenges

The category of small wind turbines is a rapidly growing market. The U. S., Europe (UK), and China are of particular interest and seeing the most growth. This paper examines the category of small wind starting with the variety of definitions found in the literature. Growth world-wide, with an emphasis on these major markets, is analyzed for trends and predicted development. The focus is on fixed pitch, small horizontal axis wind turbines, with a direct drive DC generator in the 1–10 kW class. To understand small wind turbines it is necessary to discuss design tools available for design. Included in this design discussion is the necessity for computational fluid dynamic models as well as experimentally testing both open rotors and wind tunnel models. In order for small wind turbines to continue to improve, better technologies are necessary. For design, wind turbines must be optimized for peak performance to include startup/cut-in speeds and other modifications. These wind turbines will rely on new and purposely designed airfoils; however, for low Reynolds number conditions actual airfoil data are needed as many of the computational tools do not accurately predict separation. Increasingly, noise is an issue, especially if these wind turbines will be sited in populated urban areas. An analysis of noise generation as well as design techniques for reducing noise is necessary for future designs. Important discussions on the technologies particular to small wind turbines should include the topics of aerodynamics and structures/materials. Future applications of small wind turbines seem bright. Small wind turbines are contributing to the concept of distributed generation and helping to reduce the carbon footprint. Urban environments are becoming more accepted for small wind turbines which lead to studies of flow fields in and around buildings. Of particular note are hybrid systems which combine wind with other energy generation systems such as solar, internal combustion engines, and diesel engines to name a few. These systems are advantageous for the homeowner, small business, cell phone towers, remote locations, and backup emergency power systems (to include lighting). Lastly, the concept of energy storage must be addressed in the context of small wind turbines, especially those turbines used in an isolated application. Permitting and government incentives are critical to the future success of these wind turbines.