An energy technology start-up has raised $50 million to turbo-charge its plan to convert waste material from coalmines into low-cost fuels.

It uses a steam engine to convert waste heat energy from an internal combustion engine into supplemental power for the vehicle.

Incinerators convert waste materials into heat, gas, steam and, ash.

Critics say that first-generation biofuels compete with food crops - and converting waste products into diesel could be a more sustainable alternative.

Some proposals include converting it into a waterway for barges, setting up small farms on its banks and introduce biogas plants to convert waste into energy.