Nuclear fusion is touted as the next big clean energy source. It works through the fusion of two pairs of light atoms. This releases considerable energy.

Nuclear fusion is the opposite of nuclear fission where heavy atoms are split apart. Fission is the technology used in nuclear power stations and produces dangerous radiation.

Fusion energy is far cleaner and safer than fission and is free of any radioactive fallout. Nuclear fusion is what powers the sun

However, harnessing energy from fusion has a major hurdle — it requires very high temperature and pressure and is not cost effective.

Last December scientists at the Lawrence Livermore National Laboratory, California for the first time produced more energy from a fusion experiment than the input put in.

It was just enough to boil a few kettles of water but is seen as a major breakthrough.