Energy and power of a periodic signal

I have read that power of a periodic signal is calculated for a single period (correct me if am wrong). So why can't we calculate energy of a periodic signal for a period and say it has finite energy. Why this is not the case ?

• We can, just by measuring power over a specific interval of time. – EM Fields Nov 24 '16 at 18:34
• Can you elaborate by what you mean by "signal"? – Andy aka Nov 24 '16 at 20:20
• I think what you mean is that power can be correctly calculated only if you know the entire period of a signal. That's the required information to calculate power. Whereas, power can only be calculated if you also know the energy transfer rate. A signal energy is proportional to Vrms^2, so to know it you need to calculate the signal voltage rms, which also means you also need to know the complete period of a signal. – PDuarte Nov 26 '16 at 18:41