This paper reviews some recent advances in the technology of small wind turbines, whose upper power limit we take arbitrarily as 50 kW. Small turbines are used mainly for remote power generation either alone or in conjunction with other energy sources and battery storage. They can be divided into three categories: micro, up to 1 kW; mid-range; and mini-turbines, of 20 kW and larger, intended mainly for wind/diesel mini-grids. The paper discusses a number of issues that are category-dependent; for example, low-wind-speed performance is most critical for microturbines. The starting point for the review is the mature level of large wind turbine technology, and it is demonstrated that this maturity has yet to percolate downwards. Nevertheless, there have been a number of very encouraging recent developments. These include improvements to our understanding of the basic aerodynamics and advances in blade manufacturing, the use of micro-processor controls, and the increasing use of design certification and type approval. The developments are highlighted by two case studies of small turbine design in which the authors were involved. We conclude with a brief discussion of current developments in technology, such as fatigue testing of blades and new methods of blade design, which should further increase the level of small turbine technology towards that of large machines.
Optimizing the NW off-shore wind turbine design
