Rules on the use of power transmission lines are being reviewed in order to accelerate the expansion of renewable power generation, aiming to shift away from a dependence on coal and reduce carbon emissions amid global criticism, officials said Wednesday.

Under the current rules, distribution of electricity generated by coal-fired thermal power is prioritized and the limited capacity of the cables makes adding new connections for renewable power supplies difficult.

The Economy, Trade and Industry Ministry will allow new connections to power lines at times of lower use by the end of 2021 across the nation. It will also consider ways to avoid the disadvantageous treatment of renewable energy compared to coal power in connections to power lines.

With most nuclear power plants remaining offline since the 2011 crisis at the Fukushima No. 1 complex, Japan currently depends on coal to generate 32 percent of its electricity, compared with just 17 percent by renewable energy sources such as solar and wind power.

The nation's dependence on coal has led to international criticism for not doing enough to tackle global warming. European countries such as the U.K., France and Germany plan to phase out coal in the coming years as part of decarbonization efforts.

In response, Japan's industry ministry said last month the government was aiming to usher out low-efficiency coal-fired power generators by fiscal 2030. It has also set a target of lifting the proportion of energy from renewable sources to around 22 to 24 percent of available electricity by March 2031.

Aside from reviewing the rules on the use of power transmission lines, Japan faces other challenges to the expansion of renewable energy, such as the need to secure storage batteries and reduce costs.