Optimization of the pipeline diameter for a small hydropower plant: case study

Abstract

The goal of the paper is to find the optimal diameter and pipeline material for a small hydropower plant (SHPP) Kašići on the Jošanica river. The SHPP has nominal flow rate of 5.65 m3/s, the head37.76 m and the total pipeline length 3000 m. The SHPP should be functioning as the second plant in a cascade system when the above SHPP Belci has extremely low flow rates, below 17% of the nominal. During these flow rates the existing turbine in the SHPP Belci has low efficiency, which is improved by bypassing SHPP Belci and implementing two turbines in the SHPP Kašići. One of these turbines is used for low flow rates during which maximal gauge static pressure in the penstock rises from 3.776 bar to 7.23 bar. Based on the known pipeline routing and probability of the river flow rates, friction factors for different pipe materials, total pressure drop, and total electricity production were calculated. Steel, polyester (fiberglass), polyvinyl, and wood were the analyzed pipeline materials. The net present value (NPV), which was calculated as the ratio between the profit from electricity selling and the penstock investment, was used as the selection criterion for optimal diameter. The optimal is steel pipeline with the inner diameters of 1800 mm. The difference between the NPV’s for two optimal solutions for the analyzed period of 12 years, which is the period of validity for incentive measures for power production from renewable resources in the Republic of Serbia, is less than 0.02%