Experimental optimisation of a low-head pico hydro turgo turbine

Rural electrification can help to alleviate poverty, providing energy for daily household and income generation tasks. Where appropriate resources exist, pico hydropower is a cost effective method of electrical generation, especially in a rural context. For pico hydropower at low heads, propeller turbines are traditionally used. However, these are very site specific and the efficiency dramatically reduces when not operated at rated conditions. This paper derives six key experimental parameters for a Turgo turbine using two-dimensional fluid equations, which are experimentally varied to find the affect on the efficiency on a scale prototype, obtaining a design that is optimised for efficiency. Test results are presented up to heads of 3.5 m. It is found that the turbine efficiency is very sensitive to jet vertical aim position, with the optimum aim at 12 mm from the top of the cup with a jet inclination angle of 20°. The nozzle diameter is found to have a critical value of 20 mm, above and below which the turbine efficiency reduces. The turbine wheel diameter is reduced from 7.5 times to 5 times the nozzle diameter with minimal effect on the maximum efficiency, however, this provides an increase in the rotational speed from 490 to 750 RPM. The maximum experimental jet-to-mechanical efficiency is found to be over 90% for the scaled turbine, with lower sensitivity to head and flow rate than propeller turbines. This demonstrates that Turgo turbines can be used efficiently at low heads over a range of site conditions.