**4. Discussion**

#### *4.1. Potential and Limitations of Solar PV in Coal Decommissioning*

Although it cannot phase-out coal, the results show that solar energy has enough potential to be the driver for coal decommissioning with LNG's help. It has also been shown that the decommissioning potential is robust against yearly weather-driven demand, and standby-plants could be used for the colder and warmer periods of the year. Although solar power has limitations in reducing coal capacity, it continually decreases the necessary coal generation, thereby reducing the load factor of coal plants and the corresponding CO2 emissions.

In Kyushu's case, given the 10 GW solar capacity along with a 16 TWh complementary LNG quota, 3.5 GW of the 7 GW coal power plants could be decommissioned. This configuration is already achievable by increasing the LF of the combined-cycle plants of KyEPCO from 20% to 44%. Beyond 12 GW installed solar capacity, solar power alone has no impact on reducing the coal capacity, but it could still reduce coal generation. Compared to the reference scenario, it was shown that CO2 emissions could be reduced by 27% through 20 GW of solar power and a 20 TWh annual LNG quota. The reduction could reach 37% if all the LNG plants in the region are utilized at 60% LF. As a related consequence, reducing coal and introducing more LNG reduced solar curtailment. This potential and limitations show that energy planners should take the necessary precautions in adding solar energy to the grid since there is an appropriate balance. Solar can reduce coal capacity, but it alone cannot phase-out coal. As was shown in Kyushu's case, a thorough analysis of the situation that includes complementary energy sources should be considered in evaluating the potential of solar power in coal decommissioning.
