**Table 5.** Data used for LCOE calculation for 2030.



**Table 6.** Data used for LCOE calculation for 2050.

In Figure 7, the size of the bubbles corresponds to the amount of energy generated by each type of technology, whereas on the horizontal axis the LCOE of each unit type is presented, and on the vertical axis, the share of the cost of the different types of technologies in the total cost of the system is depicted.

In the current power supply system, the participation of lignite and natural gas units is crucial in order to meet electricity demand. The LCOE of the system is estimated to 107.59 €/MWh, and the largest share of the cost is due to the conventional units. Although CHP and biomass units are characterized by high levelized costs due to their limited nominal capacity, they do not participate significantly to the final composition of the cost of the system.

The weighted average LCOE of the power system in Greece by 2030, according to the calculations, is decreased to 79 €/MWh. This reduction could be attributed to the decommissioning of lignite units, which present a higher LCOE compared to RES (wind and PV installations) in 2019. Natural gas units gradually replace lignite ones by 2030. Carbon dioxide allowances are expected to rise to a higher level by 2030; therefore, the operational expenditures of conventional units are increased, resulting in a higher LCOE for natural gas units. The expected decrease of the CAPEX required for RES installations contribute to the significant decrease of the weighted average LCOE of the system.

By 2050, a further reduction of the system's cost is expected; the levelized cost is approximately 75 €/MWh, reduced by 30% compared to current levels. Increasing the participation of renewable energy sources in the energy production with the simultaneous significant reduction of their CAPEX leads to a decrease in the levelized cost of the system. Hydro-pumped storage is among the technologies presenting the lowest LCOE, following wind and PV. The CO<sup>2</sup> prices are significantly higher compared to 2030 resulting in the increase of the levelized cost of energy of natural gas power plants.

**Figure 7.** Levelized Cost of Energy and contribution to the weighted average cost of the system by technology (the size of the bubbles corresponds to power generation by each type of technology). **Figure 7.** Levelized Cost of Energy and contribution to the weighted average cost of the system by technology (the size of the bubbles corresponds to power generation by each type of technology).

### In the current power supply system, the participation of lignite and natural gas units **5. Discussion and Conclusions**

is crucial in order to meet electricity demand. The LCOE of the system is estimated to 107.59 €/MWh, and the largest share of the cost is due to the conventional units. Although High renewable penetration could lead to a significant reduction of the system's cost, while hydro-pumped storage systems may contribute to the peak demand supply.

CHP and biomass units are characterized by high levelized costs due to their limited nominal capacity, they do not participate significantly to the final composition of the cost of the system. The weighted average LCOE of the power system in Greece by 2030, according to the calculations, is decreased to 79 €/MWh. This reduction could be attributed to the decommissioning of lignite units, which present a higher LCOE compared to RES (wind and PV installations) in 2019. Natural gas units gradually replace lignite ones by 2030. Carbon dioxide allowances are expected to rise to a higher level by 2030; therefore, the operational expenditures of conventional units are increased, resulting in a higher LCOE for natural The size of the reverse hydro units should be proportional to the development of Wind and PV installed capacity. The over-dimensioning of reverse hydroelectric projects may lead to installed hydroelectric pumps and turbines which will be used only for a few hours per year without ensuring their economic feasibility, while under-dimensioning will lead to insufficient exploitation of the potential. Furthermore, the higher integration of renewable sources (wind and PV) across the country (spatial dispersion) results in significant energy surplus and curtailment during the year, therefore energy that could be stored in hydro-pumped storage systems is increased. In this case, hydro-pumped storage units can contribute significantly to the energy balance, as analyzed in the scenarios.

gas units. The expected decrease of the CAPEX required for RES installations contribute to the significant decrease of the weighted average LCOE of the system. By 2050, a further reduction of the system's cost is expected; the levelized cost is approximately 75 €/MWh, reduced by 30% compared to current levels. Increasing the participation of renewable energy sources in the energy production with the simultaneous significant reduction of their CAPEX leads to a decrease in the levelized cost of the system. Hydro-pumped storage is among the technologies presenting the lowest LCOE, following The economic assessment of the future power system of Greece, based on the scenarios examined in this connection, demonstrates that the increase of RES contribution may lead to lower costs for the system. Greater penetration of photovoltaic and wind installations results in a reduction of the levelized cost of energy of the system, since capital expenditures required for wind and PV systems are expected to decrease significantly over the years. The cost of thermal units in reference years 2030 and 2050 is expected to be higher due to the increase in the cost of carbon dioxide emission allowances. The reduction of the energy

production share of the latter in combination with the higher integration of RES prevents the increase of the weighted average LCOE of the power system.

**Author Contributions:** Conceptualization, G.C. and A.Z.; methodology, G.C. and A.D.; software and formal analysis, A.D.; investigation, A.D.; data curation, V.K. and K.L.; writing—original draft preparation, A.D., T.C.; writing—review and editing, A.D. and G.C.; supervision, G.C.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
