Ich hab eigentlich alles gesagt, was ich zu sagen habe. Das ich nicht ganz falsch liege, zeigt dieses Zitat aus dem Datenblatt des ADE7953, gemacht für Stromzähler

The real power calculation is derived from the instantaneous power signal. The instantaneous power signal is generated by a direct multiplication of the current and voltage signals. In order to extract the real power component (i.e., the dc component), the instantaneous power signal is low-pass filtered. Figure 2 illustrates the instantaneous real power signal and shows how the real power information can be extracted by low-pass filtering the instantaneous power signal. This scheme correctly calculates real power for nonsinusoidal current and voltage waveforms at all power factors. All signal processing is carried out in the digital domain for superior stability over temperature and time.
(Hervorhebungen von mir)

MfG Klebwax