The analysis can get very deep, but let's use the simplest analysis. Einstein's famous equation is E=mc^2. We create a system of equations with this equation and the definition of power equation: P=E/t.
Replace E with Einstein's famous equation to get P=(mc^2)/t.
This is a simplified version of the God Power Equation, but it works just fine for our purposes.
God is incorporeal, which means he has no mass. This, m=0.
Plug this into the God Power Equation: P=(0xc^2)/t. This zero kills the equation: P=0.
Thus, God's power is zero.