WATER MILLS REFURBISHMENT FOR INCREASING THE HYDROPOWER CAPACITY: AN ITALIAN CASE STUDY

The energy sector is undergoing considerable changes in both energy production and utilization in the view of an optimal management of renewable energy resources. Europe is currently pushing for the deployment of renewables to achieve emissions reduction targets set by 2030. In 2023, Photovoltaics (PV), wind, hydropower, and bioenergy added capacity accounted for 359 GW, 141 GW, 28 GW, and 11 GW, respectively. Focusing on hydropower, the small-scale plants look promising for further enhancing their share, especially considering the so-called hidden hydropower. In this sense, several old water mills in Europe have been abandoned, but they could be an interesting energy resource if properly refurbished. This paper deals with a water mill in the center of Italy that has been converted into a hydropower plant. A rated flow rate of 0.65 m3/s and a gross head of 9 m can be exploited in the site under investigation. In particular, two hydraulic turbines have been analysed and designed for being installed on site: a Cross-flow (Banki) and a Francis one. Finally, the Francis turbine type has been chosen since it reaches a higher power output of 46.48 kW than the Cross-flow (Banki) one and can lead to a yearly energy production of nearly 150 MWh. From an economic perspective, the capital cost for the overall refurbishment was equal to 200 k€ and, considering a yearly expense coming from the Operation and Maintenance (O&M) of the plant along with a revenue of 24 k€ due to the energy sold to the electricity market, a worst-case PayBack Period (PBP) of 10 years might be achieved which is quite long. This result should make government institutions and policymakers aware of providing further incentives for deploying these kinds of interventions, thus being more affordable, profitable, and interesting for attracting potential investors and stakeholders. Furthermore, these interventions might preserve rivers and avoid the accumulation of debris which is the main cause of river floods.