Efficiency Assessment of Mycro Hydro Power Generation with a Rainwater Harvesting System Under Geometric Variations of the Turbine

Hydro power generation is almost exclusively used at large scale (>10kW). On a micro scale, it is still being assessed as a viable alternative to produce energy, even though this generation process seems to require lower installation and maintenance costs.

The main aim of this work is the performance assessment of a micro hydro power station integrated into a rainwater harvesting system based on the optimal dimensioning of the turbine geometry. This project proposes different heads for a sustainable model that, by means of rainwater harvesting, the system uses that potential energy to generates electrical energy in urban areas. As case of study, the system was set up at an industrial facility in the Toluca Metropolitan Zone, Mexico. Few works have assessed this type of electricity generation as an alternative to meet local energetic demand.

A methodology was developed in order to: a) establish hydraulic setting-up based on the precipitation regime and operational requirements of the generator; b) assess efficiency indicator under sizing variation of main element through Computational Fluid Dynamic (CFD); c) validate prototype throughout a 3D model. This project used 3D printing, an innovative tool for prototype manufacturing.

Due to nature of the rainwater harvesting system, the type or turbine selected was Pelton turbine. Afterwards, hydraulic characteristics were defined, such as the number and diameter of conduit pipes, nozzles, valves and gates used and their diameters and the initial size of turbine (0.78 m). Through CFD, it was possible to analyze fluid behavior (velocity and pressure fields) in the turbine in order to define a suitable geometry. Numerical modeling of the turbine allowed to estimate expected system efficiency according to the variation of coefficients k₂/k1, which measure fluid velocity at inlet and outlet of the Pelton turbine.

By means of an electronic circuit, which measured number of revolutions per minute and power generation (voltage and electrical current) of the system, the efficiency and the energy produced by the system were analyzed under both controlled conditions and real-time rainfall conditions. In general, the hydro power station managed to generate electrical energy using rainwater harvesting system.