Wasted and excess energy in the hydropower sector: A European assessment of tailrace hydrokinetic potential, degassing-methane capture and waste-heat recovery

Abstract

Hydropower is the giant of the renewable energy sector, and a well-established source of energy. In order to reduce the impacts of new barriers in rivers, the retrofitting of existing facilities with new technologies is deserving a great attention, especially when hydropower technologies are hybridized with other energy devices. In this study a European-scale assessment is carried out to quantify the potential associated to the exploitation of the excess (and wasted) energy sources in existing hydropower facilities. Three sources of energy are assessed: 1) the hydrokinetic energy of the tailrace water flow and the potential energy associated to the unexploited head below Pelton units, 2) the thermal energy of the cooling system of the electric generators and 3) the chemical energy of the degassing methane. Considering the available technology, 5.0 TWh/y of heat could be generated by exploiting the thermal energy of the cooling system. 2.4 TWh/y of electricity could be generated by harnessing the hydrokinetic energy at the tailrace; this would correspond to thousands of micro hydropower plants 100 kW each), and would avoid new installations in natural freshwater systems. Degassing methane is relevant at the global scale, especially in tropical reservoirs. In Europe 5,950 tons/year of degassing methane could be theoretically captured, since minor methane emissions from reservoirs occur. R&D activities are ongoing to overcome the current technological limitations and high installation costs. Different novelties are included in this study: for the first time, a continental assessment is carried out on this topic, establishing methodologies that could be implemented at any regional scale. For each technology, a literature review is carried out to collect data and case studies. Data to estimate the number of units and the operating range of Francis, Kaplan and Pelton turbines in Europe, and equations to estimate the degassing methane emissions, are provided. These data can be used for similar large scale assessments.