Well, the quantity alone doesn't point to any one particular process.
I mean, you could get 3.826 x 10²⁶ watts of heat out of a pile of
smoldering charcoal IF the pile was big enough and you kept it
supplied with enough oxygen.
The thing about the sun is that ==> it can churn out energy at that rate
from the mass that it has, ==> it has already been doing that for so many
billions of years, and ==> it will continue doing that for so many more
billions of years in the future.
The only possible process able to accomplish that is nuclear fusion.
