True, nuclear fussion is the answer, problem is they haven't achieved it yet, rather they did, but it requires more energy to run it than what it releases. Even at the Sun nuclear fussion does not occur on the surface, it occurs in the core where the sun cannot stand it's own gravity/pressure thus we get the elements fused into each other.It's very difficult/energy consuming to achieve such pressure on earth considering the Sun is 1 million times bigger.
There are a few good alternatives for example fill the planet with Photovoltaic panels, develop the Hydrogen Engines (by minimizing the risk of handling pure liquid Hydrogen).
At the Uni we learned all the theoritecal clean fission type nuclear reactions, there's a plethora of them and they are all using stable elements, but yet again there's been absolutely no development so far in achieving just one of them.
Main problem seems to be that these damn fossil fuels created an International economic net that -for the moment- is so strong that won't let us go.