Conceptual Hybrid Energy System, Duluth Water Plant
From August through October of 2017, the City of Duluth hosted a German student intern, Max Schuessler. He is doing his masters in mechanical engineering at the University of Siegen, Germany and got the opportunity to do his student internship in Duluth, coordinated through the Climate Smart Municipalities cooperation between Minnesota and the German state of North Rhine-Westphalia. The purpose of this project was to develop a hybrid energy system concept for the City’s water treatment center and main pump house.
Different options were analyzed for each of the main parts of a hybrid energy system – generator, renewable energy, and storage – and were put into the context of a commercial and industrial scale application. It became clear that a diesel generator, a photovoltaic system, and a vanadium-vanadium redox flow battery would be the most feasible components for this particular application. In the comprehensive scenario analysis that followed, three different options for system setup and sizing were derived and compared. The most appropriate scenario would be to install a 1.8 MW diesel generator, 1.5 MW of photovoltaics, and a 2.2 MWh / 600 kW vanadium-vanadium redox flow battery, as this creates a fully integrated hybrid system, with a competitive payback period of 18 years for the photovoltaics and storage.