What power factor does AC mains present to solar inverter? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: September 30, 2025, 11:17:22 pm
content: I want to be able to clip an AC current clamp around the inverter connection to the mains and get a rough idea of what the power output is. If the a.c. mains appears as unity power factor and I know the voltage then I’ll know the actual power. But if the a.c. mains doesn’t present unity power factor then obviously that won’t work. So, what does the a.c. mains look like to the inverter?And yes, I know there is a display on the inverter showing power output.

author: Someone
author_rank: Super Contributor
timestamp: September 30, 2025, 11:43:13 pm
content: Quote from: Circlotron on September 30, 2025, 11:17:22 pmPower factor is defined by an energy flow, an inverter sitting on a branch (as the current probe would see) defines its own power factor.Or are you wondering about power quality (harmonics etc) ?

author: bdunham7
author_rank: Super Contributor
timestamp: September 30, 2025, 11:48:34 pm
content: I think what you are asking is what portion of the grid's admittance is due to susceptance.The answer is that the grid as a load will have very high admittance and conductance and will present an almost unlimited sink for the inverter's output. Local consumption might affect this very slightly, but for inverters that do not have a specific power factor adjustment capability you will see the current pretty much exactly in phase with and proportionate to the voltage. The presence of local loads with low power factors won't affect this much as the very low impedance grids supplies the reactive current. The main thing that I think will cause the inverter output to appear to deviate from a 1.0PF would be the distortion of the mains voltage sinewave.Inverters that can be commanded to alter the current phase relationship and PF are another story.

author: Someone
author_rank: Super Contributor
timestamp: October 01, 2025, 12:00:02 am
content: Quote from: bdunham7 on September 30, 2025, 11:48:34 pmAlmost universal on grid connected inverters.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 01, 2025, 01:44:21 am
content: Quote from: Someone on October 01, 2025, 12:00:02 amThe ability to provide reactive power (or harmonic power) is essentially trivial. However afaik the vast majority of small grid tie inverters are not actually set up to do so. They may have the capability internally but they don't have the measurement or communication infrastructure to know what is needed for exactly the reason bdunham7 explained. The grid connection provides such a low impedance that there is no way to tell. That requires an upstream current transformer and probably coordination between multiple inverters.Island capable inverters obviously can and do provide reactive power to support their loads but what I have seen is that when they are in grid mode they revert back to unity power factor.

author: Someone
author_rank: Super Contributor
timestamp: October 01, 2025, 02:27:10 am
content: Quote from: ejeffrey on October 01, 2025, 01:44:21 amGrid synchronised mode is rarely unity power factor, generally a small shift is used to maintain detection of the "low impedance" source (anti islanding). Check what your local gird regulator/operator requires you to set the inverter to.There were some references out to this stuff in one of the stupid/longwinded "but but but inverters can't provide inertia" threads.

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2025, 02:54:27 am
content: Quote from: Someone on October 01, 2025, 12:00:02 amIt may be a common feature nowadays but there is a huge inventory of installed products that don't have this capability. And although the feature may be fully or mostly implemented in the firmware in current versions, many installations won't have it enabled.

author: Someone
author_rank: Super Contributor
timestamp: October 01, 2025, 03:20:45 am
content: Quote from: bdunham7 on October 01, 2025, 02:54:27 amIt has been the most widespread method for anti-islanding, regardless of other proportional /V /W variation (modern additions).

author: bdunham7
author_rank: Super Contributor
timestamp: October 01, 2025, 03:31:30 am
content: Quote from: Someone on October 01, 2025, 03:20:45 am"...that can be commanded..."My inverters may indeed use a small phase shift as part of their grid-detection method--I don't actually know--but I can't command them to do anything. If there is a phase shift, it is small--I've checked!