# Energy Transition on Sifnos: An Approach to Economic and Social Transition and Development
## 3 The Hybrid Power Plant of Sifnos
### The Hybrid Power Plant's Operation Algorithm  
The operation algorithm of the hybrid power plant is presented below. 1. The calculation data of the overall process are the power production \(\mathrm{P_{RES}}\) from the hybrid power plant's RES unit (namely the wind park) and the power demand \(\mathrm{P_{d}}\). These data are introduced with the annual time series of hourly average values. For every time step, the following calculations are executed. In order to ensure the dynamic security and the stability of the insular grid, the wind power penetration \(\rm P_{\rm RESP}\) for the power demand direct coverage is limited up to a maximum percentage a, equal to 40% over the power demand. This means that the wind park's direct penetration \(\rm P_{\rm RESP}\) will be equal to: \[\rm i.\qquad if\rm P_{\rm RESP}>a\cdot P_{d},\,then\,P_{\rm RESP}=a\cdot P_{d}\] (1) \[\rm ii.\qquad if\rm P_{\rm RESP}\leq a\cdot P_{d},\,then\,P_{\rm RESP}=P_{\rm RES}.\] (2) \[\rm 3.\qquad After the wind power direct penetration, the remaining power demand \(\rm P_{\rm drem}\) will be: \[\rm P_{\rm drem}=P_{d}-P_{\rm RESP}.\] (3) \[\rm 4.\qquad The power available for storage \(\rm P_{\rm RESav}\) will be: \[\rm P_{\rm RESav}=P_{\rm RES}-P_{\rm RESP}.\] (4) \[\rm 5.\qquad The water volume \(\rm V_{P}\) required to be pumped in the PHS upper reservoir, so that the available power \(\rm P_{\rm RESav}\) for a time step of duration \(\rm t\) can be stored, is given by the following relationship (where \(\rm\gamma\) is the water specific weight, \(\rm H_{P}\) is the total pumping head and \(\rm\eta_{P}\) is the pumps' average efficiency) [55]: \[\rm V_{P}=\eta_{P}\cdot P_{\rm RESav}\cdot t/\gamma\cdot H_{P}.\] (5) \[\rm 6.\qquad The water volume \(\rm V_{T}\) required to be supplied from the upper reservoir, so that the remaining power demand \(\rm P_{d}-P_{\rm RESP}\) for a time step of duration \(\rm t\) can be covered by the hydro turbines, is given by the following relationship (where \(\rm H_{h}\) is the total water falling head and \(\rm\eta_{h}\) is the hydro turbines' average efficiency) [55]: \[\rm V_{T}=(P_{d}-P_{\rm RESP})\cdot t/\gamma_{h}\cdot\gamma\cdot H_{h}.\] (6) \[\rm 7.\qquad The remaining water volume \(\rm V_{st}(j)\) in the PHS upper reservoir at the end of the current time calculation step \(\rm j\) will be: \[\rm V_{st}(j)=V_{st}(j-1)+V_{P}-V_{h}.\] (7) \[\rm 8.\qquad If the remaining water volume in the PHS upper reservoir exceeds the reservoir's maximum capacity \(\rm V_{max}\), then: \[\rm i.\qquad If\rm V_{st}(j)>V_{max},\,then\,(where\,P_{st}\,is the power storage,\,P_{sur}\,is the wind power production surplus,and\,P_{h}\,and\,P_{th}\,represent the electricity power production from the hydro turbines and the thermal generators, respectively) [55]: \[\rm P_{h}=P_{d}-P_{\rm RESP}\] (8) \[\rm P_{th}=0\] (9) \[\rm P_{st}=\gamma\cdot H_{P}\cdot(V_{max}-V_{st}(j))/(t\cdot\eta_{P})\] (10) \[\rm ii.\qquad if\rm P_{\rm RESP}\leq a\cdot P_{d},\,then\,P_{\rm RESP}=P_{\rm RES}.\]0 (11) \[\rm ii.\qquad if\rm P_{\rm RESP}\leq a\cdot P_{d},\,then\,P_{\rm RESP}=P_{\rm RES}.\]1 (12) \(\rm ii.\qquad If\rm V_{st}(j)\leq V_{max},\,then\,the remaining water volume in the upper reservoir is checked as to whether it is lower or not than the minimum water volume which is always contained in the reservoir, due to constructive limitations:a. if \(\rm V_{st}(\rm j)<V_{min}\), then the water volume contained in the upper reservoir is not enough to undertake the remaining power demand coverage.