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I understand that multiplying the voltage and amp-hours gives me the watt hours.

I also understand that the volt-ampere is apparent power whereas watts are real power.

What is the difference between watts and volt-ampere when working with inverters that take AC and convert it to DC to charge the battery and from DC to AC again?

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    \$\begingroup\$ This might help you understand the difference between watts and volt-amps. Basically real watts can be volt x amps or, depending on what you multiply, apparent power can also be volt x amps. \$\endgroup\$
    – Andy aka
    Jan 15 at 11:22
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    \$\begingroup\$ Does this answer your question? Why is apparent power not measured in watts? \$\endgroup\$
    – datenheim
    Jan 15 at 11:58
  • \$\begingroup\$ @datenheim I am still confused. Is there a simple explanation for a layman? \$\endgroup\$
    – teebo
    Jan 15 at 12:12
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    \$\begingroup\$ There is no simple explanation for a layman; it's beyond the grasp of a layman without teaching the layman about power factors, RMS vs instantaneous voltages etc.. \$\endgroup\$
    – Andy aka
    Jan 15 at 12:23
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    \$\begingroup\$ Maybe if you give a precise example you stumble upon, one can make it better understandable.... and you still mix Amperes and Ampere*Hours, you should clarify your question/heading, as it are two different things. \$\endgroup\$
    – datenheim
    Jan 15 at 14:23

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If you got pure DC with only a negligible small AC part you may use Watt only. If you got AC or a mix of AC and DC, you should use both Watt for real power and volt-ampere for reactive and apparent power.

For a clean sine wave and a pure resistive load reactive power will be zero and apparent power will equal to real power.

For a load build with resistors, capacitors and inductors, the reactive power will be bigger than zero and apparent power will be bigger than real power. If the load is a water heater, only the real power will heat the water, the reactive power will heat only the cables from the heater to the grid. Of course heating the cables only is not for free, a power plant will burn more fuel to generate the wasted reactive power. A hydroelectric power plant will use more water.

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