Optimal location of micro-turbines in water supply network

Micro-hydropower is currently expanding as a solution to improve the efficiency of water systems by using energy excesses which are typically lost. In the particular case of water supply systems, often excessive pressure exists in zones of the network connected to other areas situated at higher altitudes. Pressure reducing valves are commonly used as a mean for dissipation of this excess energy. In this work, the installation of micro-turbines in a closed water supply network is analyzed as a way to recover the existing surplus of energy by converting it into electricity. The flow in water supply systems is highly variable, with a direct impact on the efficiency of the turbine and, as most water-supply networks are meshed, the optimal location of the energy converters is not straightforward and needs assessment by simulation processes. For this purpose, an optimization tool based on the application of an evolutionary algorithm was developed to select the best location, model and runner size of a selected number of turbines to install in a network. Using the characteristic and efficiency curves of a micro-turbine and a database of flow demand given every hour, a simulated annealing process is applied to maximize the energy production while pressure restrictions imposed by regulation must be respected. The methodology was applied to a case study in a sub-grid of the water supply system of the city of Lausanne, Switzerland, and the considered micro-hydro converter was a five blade tubular propeller. This study is focused on the simulation problem and the convergence to optimal solution is analyzed under different restrictions and number of turbines to install.