1.Energy signals are time limited while power signals can

exist over infinite time.

2.Non periodic signals are energy signals while power

signals are periodic.

3.Power of an energy signal is zero and the energy of a

power signals is infinite.

http://www.allinterview.com/showanswers/110486/what-is-the-difference-between-power-signal-and-energy-signal.html

1.Energy signals are time limited while power signals can

exist over infinite time.

2.Non periodic signals are energy signals while power

signals are periodic.

3.Power of an energy signal is zero and the energy of a

power signals is infinite.

http://www.allinterview.com/showanswers/110486/what-is-the-difference-between-power-signal-and-energy-signal.html

 Energy Signals: an energy signal is a signal with finite energy and zero average power ,while the Power Signals: a power signal is a signal with infinite energy but finite average power 

Basics of power and energy signals with derivation is explained in these website links.

http://www.songho.ca/dsp/signal/signals.html

http://www.gaussianwaves.com/2013/12/power-and-energy-of-a-signal/

Power signal: Periodic and exists for infinite time with constant amplitude'. Energy of a power signal is infinite. 

Example: Sinusoidal, Unit step, etc.......

Energy signal: non-periodic, finite and amplitude becomes zero as time tends to infinity. Power of a Energy signal is zero.

Example: Exponentially decaying or increasing signals, etc........ 

Energy Signal : ENERGY will be FINITE and average POWER will be ZERO.

Example : FINITE LENGTH SEQUENCE.

Power Signal :  ENERGY will be INFINITE and average POWER will be FINITE.

Example : PERIODIC SEQUENCE.

I'm struggling with this:

Real world signal-> Finite Energy -> Power=0 -> SNR=0

This line of reasoning means that a Real life signal wille always have SNR=0, which is weird.