definition of power signals and energy signals
Edit:  some don't understand power and energy signals.  I assume they were never undergrad EEs. I found this definition online:



There is a graphical illustration  here: http://demonstrations.wolfram.com/EnergyAndPowerOfSignals/

But an energy signal has zero power, because energy is power integrated over all time.  When you find the power in an energy signal, you have a finite energy divided by infinity.  Thus zero.

For example, a non-rechargeable battery is an energy signal.  It holds a finite amount of energy.  It can supply some power only for a limited time, but if you compute the average power over your lifetime you will get a very small number.

A power signal is always adding some energy, so integrated over all time (to get energy) will give an infinite result.

For example, the sun is (an approximation of) a power signal.  It radiates at a constant power.  If you add the energy it gives off over your lifetime, you will get a very large number.  For a better example, imagine a sun that exists for all time and never burns out.  This sun would supply infinite energy when you add up its energy over all time.