# Energy Transition on Sifnos: An Approach to Economic and Social Transition and Development
## 5 Extensions  
### Development Perspectives  
The proposed hybrid power plant can provide a multi-level contribution to the social and economic development of the local society, given that the project is implemented by the local islanders themselves, through the cooperative scheme of the Sifnos Energy Community. The tool for this multi-level contribution comes mainly from the electricity surplus produced by the hybrid plant and, in particular, its potential exploitation for specific activities which will enable full energy transition, on the one hand, and will create strong development perspectives on the other. First of all, a major problem on Sifnos is its maritime connection with the neighboring islands, especially during winter, when the scheduled voyages are not executed on a daily basis. This problem is further intensified given that Sifnos, being a small island, does not have an airport. The produced electricity surplus can be exploited for hydrogen production, in order to be used to power a small passenger ship, with which a daily maritime transportation connection between Sifnos and the nearby islands can be established. The hydrogen production process can be easily simulated following the steps described below. Firstly, the annual power surplus time series P\({}_{\rm sur}\) is introduced as calculated by the executed computational simulation. For every calculation step of duration t (hourly), the following tasks are performed:  
1. If P\({}_{\rm el}\) is the electrolysis device's nominal power, then the absorbed power by the electrolysis device P\({}_{\rm REsel}\) will be: \[\rm i.\qquad if\ P_{\rm sur}>P_{\rm el},\ P_{\rm REsel}=P_{\rm el}\] (18) \[\rm ii.\qquad if\ P_{\rm sur}\leq P_{\rm el},\ P_{\rm REsel}=P_{\rm sur}\] (19) 2. If e\({}_{\rm hyd}\) is the specific electricity consumption per produced hydrogen unit of mass (typically 53.5 kWh/kg [65,66]), the produced hydrogen mass m\({}_{\rm el}\) will be: \[\rm m_{el}=\frac{P_{\rm REsel}\cdot t}{e_{\rm hyd}}\] (20) 3. At the same time step, let m\({}_{\rm cons}\) be the consumed hydrogen mass for the needs of the passenger ship. For a passenger capacity of 100 people, an on the safe side assumption regarding the hydrogen-specific consumption is 3 kg/nm [67]. 4. The mass m\({}_{\rm st}\)(j) of hydrogen which will remain stored in the storage tank at the end of the current calculation time step j equals: \[\rm m_{st}(j)=m_{st}(j-1)+m_{el}-m_{cons}\] (21) where m\({}_{\rm st}\)(j \(-\) 1) is the remaining hydrogen's mass in the storage tank at the end of the precedent time step j \(-\) 1. 5. The new pressure in the hydrogen storage tank is calculated with the relationship: \[\rm P_{\rm tank}(j)=\frac{m_{st}(j)}{V_{st}}\cdot R\cdot T_{\rm tank}(j)\] (22) where V\({}_{st}\) is the volume storage capacity of the storage tank and T\({}_{\rm tank}\)(j) the hydrogen temperature in the tank, which can be considered equal to the ambient temperature. R is the hydrogen's ideal gas constant, equal to 4124.2 J/(kgK). 6. It is examined whether the new pressure in the hydrogen tank is lower than the minimum p\({}_{\rm min}\) (e.g., 5 bar) or higher than the maximum possible p\({}_{\rm max}\) value. The following cases are distinguished: i. \[\rm If\ P_{\rm tank}(j)<P_{\rm min},\ then: \rm m_{cons}=0\] (23)\[\text{m}_{\text{st}}(\text{j})=\text{m}_{\text{st}}(\text{j}-1)+\text{m}_{\text{el}}.\] (24) ii. \[\text{If p}_{\text{tank}}(\text{j})>\text{p}_{\text{max}},\text{ then:}\] \[\text{P}_{\text{REsel}}=0 \tag{25}\] \[\text{m}_{\text{el}}=0\] (26) \[\rm ii.\qquad if\ P_{\rm sur}\leq P_{\rm el},\ P_{\rm REsel}=P_{\rm sur}\]0 (27) iii. \[\rm ii.\qquad if\ P_{\rm sur}\leq P_{\rm el},\ P_{\rm REsel}=P_{\rm sur}\]1  
A circular voyage from the marina of Platis Yialos on the southern coast of Sifnos, to the marina of Pollonia on the northeast coast of Milos and then to the port of Paroikia in Paro and the port of Ermoupoli in Syros (capital of the Cyclades Prefecture) and then back to Platis Yialos (Figure 16) covers a total distance of 110 nm.