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I know that an ESS (energy storage system) improve power quality issues avoiding interruptions, controlling the voltage and the frequency, injecting reactive power into the grid thanks to the capacitors in their inverters etc... but, inverters produce also harmonics, right? So, is it really correct to say that ESS improve power quality issues?

Samuele Benito Di Gioia
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    Are you confusing harmonics on the inverter input and output? Sine output inverters existed they should have low harmonics on the output. – Transistor May 13 '21 at 16:37
  • @Transistor What do you mean? A storage system can be used also to inject power to the grid to compensate fast transient or to restore the grid from black start for example, so they can inject harmonics into the grid right? – Samuele Benito Di Gioia May 13 '21 at 16:41
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    If the inverter gives a sine output then it won't inject harmonics into the grid - but I haven't studied the topic. – Transistor May 13 '21 at 16:44
  • @Transistor yes, of course, you are right, unfortunately inverters do not create a perfect sinusoid but there will be some harmonics – Samuele Benito Di Gioia May 13 '21 at 16:47
  • Can you provide a reference link where it says that inverter increases power quality? – AJN May 13 '21 at 16:52
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    What is the definition of power quality? – AJN May 13 '21 at 16:53
  • @AJN The energy storage system improves power quality issues, inverters have capacitors that in any case inject reactive power into the grid but creates harmonics. – Samuele Benito Di Gioia May 13 '21 at 16:58
  • If you look at the waveform coming out of your mains socket, you'll see that it isn't a perfect sinusoid due to all the weird loads on the line. Even your bench function generator doesn't produce a perfect sinusoid. What sort of distortion level is acceptable to you? – qrk May 13 '21 at 17:04
  • @qrk I don't know how many harmonics an inverter for energy storage systems produces and how perfect it is, but I know that there are harmonics. So in my question I want to understand if the inverters for energy storage systems produce a lot of harmonics. I know that inverter with PWM modulation do not produce harmonics in practice but not all the inverters have this technology – Samuele Benito Di Gioia May 13 '21 at 17:10
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    The distortion added by an inverter can be mitigated to whatever arbitrary standard is needed. Is 10% total harmonic distortion (THD) acceptable? That is probably easy to achieve. But if 1% THD is needed, then I am sure that can be achieved also. It is just a matter of balancing cost vs power quality etc. Most of the problems on the power line are, I assume, caused by the loads, not the generators/inverters. So having inverters distributed everywhere probably improves the power quality for most people because the disturbances caused by the loads can't propagate as far on the line. – user57037 May 13 '21 at 17:20
  • @mkeith thank you very much! You caught the point!! You can transform your comment into an answer if you want ;) – Samuele Benito Di Gioia May 13 '21 at 17:36

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The distortion added by an inverter can be mitigated to whatever arbitrary standard is needed. Is 10% total harmonic distortion (THD) acceptable? That is probably easy to achieve. But if 1% THD is needed, then I am sure that can be achieved also. It is just a matter of balancing cost vs power quality etc.

But I believe most of the problems on the power line are caused by the loads, not the generators/inverters. So having inverters distributed widely should improve the power quality for most people because the disturbances caused by the loads can't propagate as far on the line. They will be corrected or compensated at the nearest generation source whether it is an inverter or something else.

The one thing about inverters is that some thought has to be given to how they interact with the other generators on the grid. If demand drops suddenly, the inverters need to scale back their output because the big generators can't adjust their output too quickly. I believe what this means is that the inverters must "throttle back" when the voltage and frequency increase, and increase output when the grid voltage and frequency slow down. This should help keep everything stable.

user57037
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