Coal prices have risen, and they probably have yet to rise because Indonesia has imposed a temporary ban on coal exports, fearing that it could not meet domestic demand.

President Joko Widodo also threatened miners with revocation of their business licenses if they could not supply enough coal for domestic consumption, Reuters reported.

Indonesia is the world's largest exporter of thermal coal, and there are concerns that the ban will undermine global supplies.

Bloomberg said that Indonesia is estimated to export 482 million tonnes of coal, which is far ahead of the world's second-largest exporter, Australia, with 204 million tonnes.

Coal has grown substantially this year amid higher energy demand and limited supplies of natural gas. At the same time, coal exporters have reaped large profits as the world, even Europe changes its negative stance on the most polluting fossil fuels.

China triggered the rally, which effectively banned imports from Australia amid a sharp rise in energy demand, although it was later forced to resume purchases of Australian coal.

However, it also raised concerns about the security of supply. It led to lower-than-normal inventory levels particularly in Indonesia, which prompted the proposed ban as the government is worried about the risk of widespread power outages.

Indonesia already has a protective mechanism to ensure domestic supplies. This is called the internal market commitment policy, which requires coal miners operating in the country to supply 25% of their production to the state-owned Perusahaan Listrik Negara at a maximum fixed price of $ 70 per tonne. For comparison, Newcastle's benchmark coal is now trading at a price above $ 150 per tonne.