Nuclear fusion in the sun is an incredibly powerful process that generates an enormous amount of energy. In fact, the amount of energy produced by fusion in the sun is what makes life on Earth possible.
Scientists estimate that the sun loses about 4 million metric tons of mass every second due to the energy produced by nuclear fusion. This may seem like a lot, but it’s actually a very small fraction of the sun’s total mass, which is about 2 x 10^30 kilograms.
picture from NASA 2014
In the sun, the primary fusion reaction is the fusion of hydrogen nuclei (protons) into helium. This process is known as the proton-proton chain reaction. It occurs in the sun’s core, where temperatures are high enough to overcome the electrostatic repulsion between the positively charged protons.