Optimal selection of parallel pumps running as turbines for energy harvesting in water transmission lines considering economic parameters

The need for energy is growing due to concerns about development and well-being, but the traditional methods of energy production harm people and the environment. This impact can be reduced by using renewable energy sources like hydropower. Since the cost of electromechanical equipment in small hydroelectric power plants accounts for a large percentage of the capital cost, applying the pump as turbine (PAT) is recommended. In this research, an effort has been made to select the optimal arrangement of PATs for a water transmission line without the need for control systems. The selection optimization process involves selecting the model of the pump as turbine and the number of turbines in parallel simultaneously. The optimization process relies on economic parameters, aiming to maximize the Net Present Value (NPV) of the power plant. In addition, the financial analysis of the project has been carried out. As a first step to achieve this objective, a database including single and double-suction pumps based on available pumps is needed. To cover a wider range of heads and flow rates, impeller trimming relationships for the pumps are considered. The Brute-Force algorithm has been used for the optimization process and two different objective functions (OF) have been investigated. First, it is based on economic optimization, and the NPV function is used as the OF; then, the Multi-Criteria Decision Making (MCDM) method is used as the second OF. The case study of this research is a water transmission line between two cities in Iran. A MATLAB code has been developed to perform all the steps of this study. The results demonstrate that by considering impeller trimming for pumps in the database and using NPV as OF, the number of pumps used for the power plant decreased from 12 to 6 and the capital cost decreased by about 10%. By implementing impeller trimming, the NPV and energy production of the PAT power plant are increased. Comparing the two desired objective functions leads to the recommended appropriate OF for applications. It is worth mentioning that the harvested energy from this water transmission line is about 9 GWh/year. The economic analysis results show that the PAT power plant payback period (PP) for this water transmission line is less than one year.