Explain why solar energy is considered an inexhaustible source of energy

-- The amount of energy radiated by the sun is not affected at all by how much
of it we use or don't use.

-- The sun is not expected to quit shining on us, or to change its rate of energy
output, at any time within the next several many human lifetimes.

Solar energy is going to keep arriving here, continuously, at the same rate,
free of charge, for a long long time, whether we feel like using it or not.  It's
the closest thing to manna from heaven that has been seen around here for
thousands of years.