Dimensional analysis yields an understanding of the power density of the
Sun. All of the power generated within the Sun is radiated from the
photosphere, whose area scales as the radius of the Sun, which scales as
4*Pi*R^2 while the volume scales as 4/3*Pi*R^3. Hence, the power density of
the Sun per unit volume or per unit mass, scales as 3/R. From a human
perspective, since the radius of the Sun R, is almost infinite, the power
density per unit mass is infinitesimal. In fact, when the Sun is active, the
power density of the Sun is less than that of the human body:

http://en.wikipedia.org/wiki/Sun

The power density of the Sun per unit mass could go from infinitesimal of
zero and we would not notice, because we are mortal.