A plain conical diffuser is optimized to augment the wind speed at the throat of the diffuser. The diffuser is used in the construction of a diffuser augmented wind turbine (DAWT) to augment the power output of a bare wind turbine (BWT). Experiments with empty conical diffusers were done to determine optimum geometrical parameters for the diffuser to achieve maximum wind speed augmentation. Using the obtained optimum geometrical parameters, an optimized plain conical DAWT was designed, constructed, and field tested. A twin decentralized wind energy system which comprised a BWT and the optimized plain conical DAWT was erected. The electrical power output from these systems was measured and compared. The optimized plain conical DAWT reduced the cut-in wind speed of a BWT from 2.5 m/s to 1.6 m/s. The power output was increased by a factor of 2.5. This power output is comparable to that of flanged diffusers. However, flanged-DAWTs are more inert due to the addition of the flange. Its response to wind speed and direction is slow as compared to plain conical DAWT. Thus, it cannot fully exploit the potential of the wind. Also, the addition of the flange increases its production cost. Therefore, plain conical DAWT can replace flanged-DAWT in wind power augmentation.

The encasing of wind turbines in a duct to enhance performance is not new. A ducted wind turbine produces more power than an unducted wind turbine of the same parameters. A number of approaches in studying the effects of diffusers and other wind concentrating devices have been done and have resulted in a number of prototypes produced but without any commercialization. The aim of this paper is to investigate the failure of commercialization of ducted turbines. A technical and economic analysis of a ducted turbine is also presented. The work shows that traditional economic methods used to evaluate ducted wind turbines are erroneous; they do not account for external effects of power generation and individual and community benefits derived from this technology. Failure to penetrate the market is due to negative publicity as a result of the erroneous evaluation undertaken and lack of appropriate engineering techniques to protect ducted wind energy systems in extreme wind conditions.