The effect of surface roughness of the impeller to the performance of pump as turbine pico power plant

Pump as Turbine (PAT) is one of a hydropower plant that applies a pump with a reversed flow, working as a turbine to generate electrical power. It has the advantages of low-cost, widely available in the market and user-friendly. However, like other hydropower plants, PAT technology has low performance in term of power output. The impeller surface roughness is one of critical aspect, which influences PAT performance because poor surface roughness causes losses and cavitation. The objective of the research is to increase the PAT performance by improving the quality of the surface roughness and validate by the experimental tests. A low-cost and customize hand grinding process was applied to produce five impellers with three different levels of surface roughness (average surface roughness of 0.16 mm, 0.24 mm, and 0.40 mm), an edge rounded impeller, and a varnish lacquer coated impeller. All of the impellers undergo performance testing. The performance of the original impeller (without modification) used as a comparison. The experiment result shows that an impeller with a lower surface roughness (lower Ra number) has a higher performance. An impeller with an average surface roughness of 0.16 mm improved 10.9% of its initial performance. Additional edge rounding for a 0.16 mm surface roughness impeller would improve its performance by 13.1%.  The optimum turbine efficiency of 15.45% was achieve-able by implementing an impeller with the lowest surface roughness.