For all the talk of a solar boom in Japan, coal still has a future, and potentially a big one at that. Japan's government and industry are backing emerging coal technologies they say are less damaging to the environment. While they are pushing the most polluting fossil fuel at home and abroad, the government will be trying to burnish its environmental credentials at climate talks that begin at the end of the month in Paris.

Japan is the biggest backer of public coal financing globally, according to a June report coauthored by the Natural Resources Defense Council, a U.S. environmental group, and partners. The country also ranks last among the Group of Seven nations in efforts to move away from coal, according to E3G, a nonprofit group promoting a low-carbon economy, in a statement last month.

By promoting new and advanced coal technologies as cleaner and more efficient, Japan is contradicting environmentalists such as NRDC and WWF, which are seeking to discourage investors from backing fossil fuel. For major Japanese suppliers of power generation systems such as Mitsubishi Hitachi Power Systems Ltd., the national push also offers the opportunity to market their products in countries where coal is still widely used.