Optimum Solidity on Downwind Thai Sail Windmill

Abstract

Solidity was a significant parameter affecting the efficiency of wind turbines. It is defined as the ratio between the projected area of all blades and the swept area of the rotor. The solidity could be improved by modifying the shape, cord length, or the number of blades. Research studies mentioned that higher solidity seemed to provide more power due to more blade area. However, it can be argued that if the solidity was too high, it would cause the airflow to be more obstructed and disrupted, causing the gained power to drop down instead. Thus, the optimum solidity, which made the wind turbines maximum effective, must be existent in itself and must be in the range between 0 - 100 %. Thai sail windmill is a kind of horizontal axis wind turbine currently used to pump seawater in salt farms in Thailand, where the general solidity is in the quite wide range of about 15 - 60 %. Mostly, the Thai sail windmill was designed by a rule of thumb. Hence, it has quite a low efficiency, which is only about 10 %. This study aims to investigate the optimum solidity of Thai sail windmill in the downwind type to enhance efficiency. The 4-blade and 6-blade rotors of 1-m radii were used as the prototypes for experiments using the tow testing method. The results showed that the optimum solidity of 4-blade and 6-blade rotors was 28 %, respectively, whereby the maximum efficiency of the 2 rotors was 17 and 25 %.