will there ever be a day when we don't need to use fossil fuels and rely solely on the sun for our power and heat.
Fossil fuels do not remove our reliance on the sun as a source of power, they simply change the timing.
One might classify energy sources thus:
1) Derived from solar power:
a) Direct - e.g. solar panels
b ) Indirect - e.g. wind power
c) Delayed - e.g. fossil fuels
The rest are not dependent upon the sun
2) Gravitational e.g. tides
3) Fission - current nuclear power generation
4) Fusion - arguably the best long term prospect