They do exactly that. They set the current output to be in phase with the grid power. The traditional inverters worked this way. The new ones have the capability to supply vars as well.I could be wrong, but I don't think PV inverters "make" power where the current and voltage are in phase. I think they have ratings based on a unity power factor.
A generator is different because it can vary the phase angle between the voltage and current.Does a 60kW generator with a 0.8 power factor (75kVA) "make" power where the current is 36.9 degrees out of phase with the voltage?
Then the output is all resistive.If so, what happens when all the load on the generator is resistive?
The traditional ones did not. The newer ones can.I would think a 60kW inverter could supply 60kW of power at unity power factor, or 48kW of power at 0.8pf.
You brought up polarity. I was trying to answer in like kind.Current can have a direction. I have no problem with that. Direction and polarity aren't the same.
Yes. It can also take place externally to the meter by running one of the wires backwards through the common CT (you can see this on CT metered high-leg delta banks).I am intrigued by your description of how a power meter works... Are you talking about reversing the direction of the windings of one of the coils inside?
Yes. The inverter will shut down.What happens with the meter stopped when you remove the meter and take the poco out of the picture? Does this reactive load now fail because the inverter can only supply power that is not reactive?
I'm sure the part about not islanding is covered in your text.Perhaps you and mivey have stumbled across something not discussed in our text. I will gladly share the title and author with you. Something of that importance needs to be part of a college text on PV installation, don't you think?
Whether or not the author "concedes" does not change the facts. Perhaps you should base your conclusions on more than one source. Perhaps the author of your text thought the discussion was beyond the scope of the text. I am quite sure the author understands but that does not mean the author covered the subject. This subject is covered in many other places so feel free to expand your knowledge.Let me know how that works out for you. If the author concedes and the text is updated, I'll buy into your allegations. Until then, I fail to see how a PV system can only supply watts and the poco gets dinged for the VArs.
Read my post #12. The correct rate will penalize a customer for an excessive var load. This will happen with larger loads with advanced metering. Residential billing has traditionally not been sophisticated enough to bill for this. The age of smart metering will make that change.Show me where someone or some company has been billed for excess var loads as a result of a PV installation.
I know that industrial customers are penalized for poor power factors. What I am waiting for is any kind of proof that PV systems are detrimental to the power factor in question.
The traditional grid-tied inverter will not run without the grid. An inverter that can run in island mode can supply both the kWs and vars.For example, if one were to connect such an inverter to an inductor (without another source in parallel), what happens with the voltage and current waveforms? Will they be in phase, or will the physics of an inductor still hold?
The author may consider metering and billing to be beyond the scope of the text. I think it is worth a discussion but at what point does the publisher draw the line and not try to be a text on power systems as well? There are other sources that cover this issue. There is no one book/class that covers everything.If those tests confirm that a PV system adversely affects power factor, that needs to be stated in the text. If those tests do not confirm any adverse power factor effect, the text is accurate with proof to support it. If it needs to be stated in the text, rest assured I will be dropping the publisher a line.
I think these micro-inverters can supply vars as well. They should have instructions on how to set the var control if they do.Use a micro-inverter because its size will be smaller.
Search for "var control" at whatever inverter reference you are using.How do I know which switching KVAR bank to look at for the rating of a particular inverter?
Hi Gar, my point wasn't about an ideal current source, it was about a "real-world" PV inverter. Connect an inductor (a "real-world" one) to the output of such a PV inverter, and we will see reactive power being delivered to it. Will the inverter be as efficient as if it was only delivering real power to a real load? Likely not, but I'd place a substantial bet that it will still deliver reactive power. The bottom line is that you can't change the physical properties of an inductor by changing the source, and it will have the voltage/current phase shift through it if a time varying voltage is applied. The real question is how efficiently the inverter will supply power to such a load - not that it either will or won't (it will). That being my thinking, I'd like to see the circuit diagram for a "real-world" inverter that will only deliver power with a unity PF, regardless of the load.110524-2222 EDT
If you connect an ideal current source to any non-zero impedance the result will be infinite voltage across the current source. We have no such real world device. Something will limit the voltage.
I'm pretty sure that absolute values are involved in the power factor formula. I don't have time to look it up right now but I'm sure a web search would show the relevant result.From a purely mathematical standpoint:
If P<0 that puts you in the II and III quadrants which gives you a negative cos ie a negative pf...
The above was from a thread on another site that was locked because the person asking for comments was a guest and not a member.Consider:
a) A house with a solar PV system on it is consuming 1000 W of real power and 400 VAr of reactive power from the grid and generating 0 W. Its power factor is 0.93, 93% or 22? at its service entrance.
b) The solar PV system generates power with a power factor of 1. If the PV system generates 500 W into the house, then the house service entrance is seeing 500 W of real power and the same 400 VAr of reactive power, and thus the electric utility company sees that house has a power factor of 78% and 39?.
c) If the solar PV system generates 1000 W, then the electric utility company sees that the house service entrance has a power factor of 0 or 90?.
d) If the solar PV system generates 1500 W, what is the power factor? The house has a net export of 500 W and it is still using 400 VAr. I would suggest that the power factor becomes negative, not leading or lagging, and that it would be -78% or -39?.
I have several year's worth of 15-minute data on my own PV house that shows this. I suggest that this applies to all electrical services that incorporate their own electricity generator.
May I ask of your comments on this?
Just for mindless fodder, and witty banter that will most certainly follow, I suggest that they are one in the same. when an allen bradley vfd says DC voltage, it is kinda like how you "dowload" to a plc and "upload" from a plc... it's all terminology. If you're on 'you tube' you "upload" from your pc... etc. etc. This 'dc' they are talking about, is much more like "clean dc" it's still ac, make no mistake, but the characteristics (coming from a dude with no college) are strikingly similar to almost flawless DC. I figure the vfd is like the "ANTI-TESLA" woulda been Edison's ultimate weapon. You can control damn near every aspect of the electrical spectrum with a VFD.I have not read the entire thread yet and need to spend some time catching up but my initial thought is that an inverter is basically the same as a VFD. Both an inverter and a VFD have simply a DC bus and 6 output IGBT's that are fired to create a 3-phase voltage at a commanded frequency.
I VFD is obviously capable of supplying reactive power to a motor since ovbiously the motor is running with the output from the VFD. The only difference here is that the input side to the VFD is AC whereas the input to an inverter is DC. I dont see this as mattering however due to the fact that the AC input to a vfd is created to a DC voltage anyway.
So I guess I ask myself why can a vfd provide the reactive current required by a motor but an inverter cannot supply the reactive current required by a motor? I always just thought that the output of a vfd or inverter was a voltage waveform at a given frequency and that the load determined the current and phase angle leaving either of the devices. Never have I heard of a vfd trying to ouput a unity power factor when controlling a motor.