The amount of deuterium contained in a planet is a very small fraction of its hydrogen content.

The amount of hydrogen contained in a medium-sized planet like Earth is extremely small in comparison with the amount of hydrogen contained in a star.

The amount of energy that can be produced by fusion per deuteron is smaller than the amount of energy that is produced in stars per proton.

With all these factors multiplied, the amount of energy that could be obtained from all the deuterium contained in Earth is many orders of magnitude smaller than the energy produced by the Sun or by any other star.

Moreover, the energy obtained from fusion could never exceed a very small fraction of the energy received by Earth from the Sun as light, otherwise it would lead to a catastrophic warming of the Earth.

Nuclear fusion reactors are not really useful for solving Earth's energy problems. They could have a crucial importance only for the exploration of the Solar System and for providing energy for human bases established on Moon, Mars or other outer planets.

For Earth the only problems worth solving are how to make better batteries, including very large capacity stationary batteries, how to make other large capacity energy storage devices, e.g. thermal devices, and how to improve the energy efficiency of the methods used to synthesize hydrocarbons from carbon dioxide and water.

Making hydrocarbons at large scale from carbon dioxide would be the best way to sequester carbon dioxide, offering the choice between just storing the carbon in safe products (paraffin like) and using a part of the synthesized hydrocarbons for generating energy in a carbon-neutral way.

Just tie the end of an infinitely long string to the edge of the universe and have it pull on a generator to spin it.