  There is a strong need to reduce greenhouse gas emissions to deal with
climate change. In the power sector, changing the power generation method in
the medium and long term is needed to reduce greenhouse gas emissions. This
paper proposes a long-term energy-mix optimization mod-el to obtain the process
of carbon neutrality in the power system. The proposed model models power
supply and demand at an hourly granularity and determines the generation
capacity that minimizes the long-term energy supply cost. Compared with the
models proposed in previous studies, the proposed model can determine the
installed capacity to maintain the balance of power supply and demand by adding
the capacity of regulation reserve required by fluctuations in the output of
variable renewable energy as a constraint condition. A Japan energy mix
calculation is reported as a case study of the proposed model. This model can
clarify the roadmap to achieving each country's emission reduction target and
support the government's decision-making.
