Roger wrote:
So how do we describe that power if it is
always zero because voltage and current are 90 degrees out of phase?

Here's how power engineers solve the problem.
Voltage and Current are phasors.

V*I = volt-amps

V*I*cos(A) = Watts, real power

V*I*sin(A) = VARS, reactive power
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73, Cecil http://www.w5dxp.com