• Energy Research

Abstract The hydro energy of the gravity water flow from the coal-fired thermal power plant units to the river in an open cooling system of turbine condensers is determined. On the basis of statistical data for a long time period, the water net head duration curve due to the river annual level change, as well as the reduction of the hydro energy potential due to the thermal power plant overhauls periods, are evaluated in the case study of the Thermal Power Plant “Nikola Tesla B” in Serbia. A small hydro power plant is designed for the utilization of this hydro energy, and the economic benefits of the project are calculated. The internal rate of returns and pay back periods are calculated in dependence of the electricity price and total investment costs. The increase of profitability is assessed, bearing in mind that the plant might be realized as the Clean Development Mechanism project according to the Kyoto protocol. The obtained results show that the project is economically attractive, and it can be carried out with standard matured solutions of hydro turbines available at the market. Even for the relatively low electricity price from small hydro power plants in Serbia of 0.08 €/kW h the internal rate of return and the pay back period are 17.5% and 5.5 years.

The results of long-term groundwater monitoring in the Bileća reservoir adjacent (eastern Herzegovina, Bosnia and Herzegovina) indicate that there is a good hydraulic connection between the reservoir and the karst aquifer located in the right bank of the reservoir. In remote parts of the right-bank karst aquifer, due to complex lithostratigraphic characteristics and a tectonic structure, the influence of the reservoir is very variable and has been insufficiently studied up until now. This paper presents the analysis and synthesis of new, relevant hydrogeological data, as a basis for the creation of a 3D spatial model, i.e., the analysis of the karst system’s behaviour, both under regular and artificial hydrological conditions of surface reservoir construction and its continuous use (filling and emptying). The interactive connection of the model and complex surface and groundwater time series monitoring data of this system is presented through the analysis of its hydrodynamic characteristics, which completes the spatial model of the karst regime caused by low and high groundwater levels and low and high reservoir water levels. The integration of all the data into one model and further multiparametric analyses revealed the different types of hydrodynamic conditions prevailing in the karst aquifer with regard to the influence of the high or low waters of the reservoir.

The complex Krupaja karst system, located in Serbia, which consists of a strong karst spring, a thermal karst spring, and a borehole that captures sub-thermal waters, has been studied. A phenomenon which gives rise to the occurrence of karst waters of three different temperatures within a relatively short distance (about 200 m) led us to assume that these karst waters are formed within the same karst aquifer and circulate through different levels of karst channels that are zonally distributed within a vertical profile; this was confirmed by assessing the groundwater ages. Based on the development of karstification, as presented in this paper, as well as on previous investigations, explanations of four types of circulation within same karst system are provided. The results of measurements of stable isotopes (H, 18O, and 13C) and radioactive isotopes of tritium and T+He and 14C, as well as hydrochemical water analyses, speleogenetic spatial modeling, speleodiving research, etc., confirmed the assumption that these groundwaters belong to the same karst system. However, these karst waters have different residence times, i.e., from only a few days to over several decades and even up to approximately 4000 years, circulating through channels with various distributions along the depth of the karst aquifer.