# Determination of Effective Parameters for Hydropower Plants' Energy Generation: A Case Study
## 4 Results and Discussion
### Energy Generation vs. Temperature  
The hydrological cycle is subject to the effect of air temperature, which has a direct impact on the overall water availability within rivers and reservoirs. High or extremely cold temperatures have the potential to induce alterations in precipitation patterns, increase evaporation rates, especially at high temperatures, and alter the timing of snow melting. The alterations have the ability to influence the magnitude and distribution of water discharge, which has a direct impact on the capacity of hydropower facilities to generate energy. Figure 9a-d show the variation in energy generation compared to air temperature for the mentioned years, using daily data. From the outcomes of the comparison of energy generation and temperature data, the adverse effects of air temperature on energy generation can be classified into two categories: effects at high temperatures and effects at extremely low temperatures. The air temperature of the studied area varies between \(-22\)\({}^{\circ}\)C and \(26.8\)\({}^{\circ}\)C. The boundaries of the given temperature interval consist of the highest value in 2018 and the lowest value in 2016. It can be seen from the figure that in the winter season, the cold temperatures were recorded in the range of \(-10\)\({}^{\circ}\)C and \(-20\)\({}^{\circ}\)C, except for the year 2018. Figure 8a-d display the monthly total energy generation, and it is evident that energy generation throughout the winter months, particularly in January and February, was at its lowest levels, comparable to August and September. A circumstance that is quite similar to the one that is shown in Figure 8a-d, which depict monthly energy generations, can be seen in Figure 9a-d, which depict daily energy generations and air temperatures with respect to each other. Figure 9a-d demonstrate that there is no energy generation in the extremely cold (\(<\)\(-20\)\({}^{\circ}\)C) temperature range. Furthermore, the daily energy output reaches its lowest level when the temperature falls between 0 \({}^{\circ}\)C and \(-20\)\({}^{\circ}\)C. The cause of this outcome is the solidification of the water contained in the regulator and river bed as a consequence of the reduced water level. Moreover, based on the mean temperatures recorded in December, January, and February, the lowest mean temperature was \(-6.9\)\({}^{\circ}\)C in 2017, while the highest mean temperature for these months occurred in 2018 at \(-1.8\)\({}^{\circ}\)C. The lowest energy output recorded for December, January, and February of the relevant years was 862 MWh in 2017, while the maximum energy generation was 3796 MWh in 2018. It is observed that higher mean winter temperatures lead to increased energy output during those months.  
The energy generation rate increases with the increase in recorded temperature until its value reaches values around 20 \({}^{\circ}\)C, and it can be seen that the maximum energy generation occurs in the temperature interval of 5 \({}^{\circ}\)C-20 \({}^{\circ}\)C, and the mentioned recorded warmer air temperatures also belong to the time period of the spring season. Beyond 20 \({}^{\circ}\)C, energy generation decreases due to two possible reasons: an increase in temperature that results in high evaporation and a decrease in precipitation during the summer season.  
Figure 9: Alteration in daily energy generation with respect to temperature, (**a**) 2016, (**b**) 2017, (**c**) 2018, and (**d**) 2019.  
The provided figures demonstrate a correlation between the energy output of the HPP and air temperature, indicating that the energy generation of HPPs is directly influenced by air temperature. Moreover, it is crucial to recognize that the influence of air temperature on hydroelectric energy generation may vary depending on variables such as geographical location, type of hydropower system, and local hydrological conditions.