  Japan has committed to carbon neutrality by 2050. Emissions from the
electricity sector amount to 42% of the total. Solar photovoltaics (PV) and
wind comprise three quarters of global net capacity additions because of low
and falling prices. This provides an opportunity for Japan to make large
reductions in emissions while also reducing its dependence on energy imports.
This study shows that Japan has 14 times more solar and offshore wind resources
than needed to supply 100% renewable electricity. A 40 year hourly energy
balance model is presented of Japan's electricity system using historical data.
Pumped hydro energy storage, high voltage interconnection and dispatchable
capacity (hydro, biomass and hydrogen energy) are included to balance variable
generation and demand. Differential evolution is used to find the least-cost
solution under various constraints. The levelized cost of electricity is found
to be USD 86 per MWh for a PV-dominated system, and USD 110 per MWh for a
wind-dominated system. These costs can be compared with the average system
prices on the spot market in Japan of USD 102 per MWh. In summary, Japan can be
self-sufficient for electricity supply at competitive costs.
