How concerned are you about lightning?

BB.

Re: How concerned are you about lightning?

In general, there is no good reason to add a "surge capacitor" to a generic AC circuit. At a minimum, the capacitors would just add to the inverter's output current without doing anything useful.

Motor Run type capacitors can be added to bring the power factor closer to 0.95 if you have induction motors you are powering (fridge, electric fans, etc.). And there can be some advantage to doing that. However, the capacitors have to be sized to the load, and switched with the load (motor off, capacitors also off). Also, there can be "stability" issues if the capacitors are used to bring the Power Factor to near 1.00 PF.

Surge suppressors work by diverging excess voltage somewhere else. Capacitors just "store" and "release" the excess energy--Not near as useful (again, in my humble opinion).

-Bill

northerner

Re: How concerned are you about lightning?

Cariboocoot wrote: »

I know I'm going to regret asking this but ...
What is a "surge capacitor"?

It is a fast acting surge suppressor that can take care of spikes, but can not handle the heavier surges that a surge arrestor will.

http://www.electrotechnik.net/2009/10/what-are-surge-capacitors.html

http://www.deltala.com/prod04.htm

As for lightning rods, how likely are strikes there? Survey other buildings in the area and see if they have rods. That's usually a good indication of the need and propriety.

I'm more concerned about protecting my equipment. We do get some dandy electrical storms.

Cariboocoot

Re: How concerned are you about lightning?

Hmm. Doesn't exactly look like something ordinarily installed on household wiring, does it?

northerner

Re: How concerned are you about lightning?

Cariboocoot wrote: »

Hmm. Doesn't exactly look like something ordinarily installed on household wiring, does it?

Delta has a specific product (surge capacitor) for protection. Check out he 2nd link I posted.

NorthGuy

Re: How concerned are you about lightning?

Capacitor conducts high frequency AC, such that you say the lightning is. The higher the frequency, the less resistance from the capacitor. If you use a relatively small value capacitor, such as 0.1 to 1 uF accross the lines, it wil not conduct 50-60Hz AC very well, but it'll get much more conductive for high frequency signal. Probably has to be rated for higher voltage - 1kV or more.

I think inverter should already have some capacitors on their AC output, which are supposed to be carefully sized. Adding more capacitors may make things worse.

I've also seen protective varistors on the Xantrex XW AC connections. So the inverter tries to take care of overvoltage by itself.

northerner

Re: How concerned are you about lightning?

Here is some more info on the surge capacitor. Apparently it doesn't cause a waste of electricity. In fact they claim it can actually reduce net power a fractional amount by cancelling some of the inductive load.
http://www.deltala.com/surge.htm

Cariboocoot

Re: How concerned are you about lightning?

northerner wrote: »

Here is some more info on the surge capacitor. Apparently it doesn't cause a waste of electricity. In fact they claim it can actually reduce net power a fractional amount by cancelling some of the inductance load.
http://www.deltala.com/surge.htm

A claim which is eerily similar to that which is often made about whole-house power factor correction capacitors.

I wonder if this isn't a solution in search of a problem? If they were really a valuable addition to a system, would this not be born out by millions of people losing their quality electrical equipment to such surges? A good piece of hardware should have its own relevant protection built-in.

I've only been plugging things in to grid power, generators, and inverters for something like 50 years and so far none of it has ever blown up. Most of my life I've lived in high lightning strike areas too. This sort of experience leads me to question the practical value of such things. Rather difficult to prove they work if installed as the evidence of "no failure" could have occurred without it as well.

As always, everyone is free to spend their money how they see fit.

BB.

Re: How concerned are you about lightning?

I am not sure that a surge capacitor would be that helpful... Many electronic devices already have capacitors and inductors on their AC inputs anyway to suppress conducted radio emissions to meet FCC Class A/Class B requirements. These types of capacitive elements usually have a much better (higher) frequency response vs a capacitor and some 14 awg wiring in a main service panel. On the other hand, if lighting has a typical maximum frequency of ~7.5 kHz, then you don't need to be too serious about wiring/capacitor design.

Adding capacitors to an AC power circuit is always a bit of a shot in the dark. Smaller devices may not do anything other than waste a small amount of current. Larger ones can cause resonance issues (capacitors+inductors=Tank or oscillator circuit).

And, if you have no surge capacitor and have a failure--would a surge capacitor worked or not? And if you have capacitors+surge suppressors and no failures, was it the caps that did anything useful.

One thing that I learned about Alberta was the problem the phone companies had in winter. The air was very dry in winter (very easy to build up static charges) and the folks walking around the central office computers with their down jackets generated enough static energy that the electric field just from a person walking by their computer racks was enough to take systems down/cause ESD damage (electrostatic discharge). In one Georgia (state of) central office, they did not want us to take flash pictures because of the EMI (electromagnetic emissions) from the flash tube could crash their phone/networking control computers.

In general, the problems were made worse when the metal skins were off of the equipment (such as during repairs, or just covers that gets left off/open from frequent servicing).

-Bill

northerner

Re: How concerned are you about lightning?

They may not help much, that I don't know. But I know that the electrical utilities do use them. Also, I notice quite a few reported inverter problems, although, many of them are likely attributed to improper grounding techniques and/or not using an SPD. So you are saying that the inverter output should be sufficiently protected from sharp fast acting spikes through the use of just a good surge arrestor. Surge capacitor not needed.

BB.

Re: How concerned are you about lightning?

In a past life, I used to design computers systems to pass FCC/EU (CE) testing that included surge, ESD, and radio frequency qualification tests. These certainly where not mil-spec EMP tests or Lightning tests used by utilities for exterior lines--But with well designed systems that met FCC Class A or B, I never had any problem with noise injection or RF field testing (simulating somebody with a hand held transmitter).

ESD testing was something else that almost every computer equipment failed if not properly designed and manufactured. Ensuring there was no spray paint on metal chassis joints, lots of metal fingers and copper braid, a mix of small and medium value caps on PC boards, work at ESD control around keyboards/push buttons all took care of those static discharge issues.

Had one vendor that "forgot" to do any ESD design/testing for their backup tape drive. When we got ready to perform our own testing, they asked us to wait while they tried the testing at their offices. (ESD testing was pretty new at that time for office equipment)

First set of tests knocked out every tape drive/computer (including office PCs) withing a couple dozen feet of their first ESD tests (a small esd gun with human body model). After redesign of the front panel buttons, cleaning paint, and replacing the covers on all their lab/office computers, they no longer had any problems.

-Bill

BB.

Re: How concerned are you about lightning?

I would not add any capacitors to the output of an AC Inverter... Many do not like driving capacitive loads (remember, inverters are full of transformers and inductors).

I did not see any value for the AC surge capacitors--They are probably not that large and should not take the the impedance of the AC output from inductive to capacitive phase shifting (i.e., you can add so much capacitance, the inductive current phase lag will actually be corrected to zero or even positive phase lead with enough capacitors).

Also, taking PF to near 1.0 (better than 0.95 PF correction) with capacitors can cause induction motors to "self excite" and when the AC inverter output (or motor+capacitor circuit is turned off), the motors actually turn into AC generators and can generate hundreds or thousands of volts as the motors slow to a stop.

Remember that those "off the scale" energy spikes would need very high frequency current injection (i.e., very sharp square wave, very narrow impulse, etc. have "high" frequency content) to get those high voltage values--And there has to be no loading nearby to draw energy from those spikes.

Between the AC off grid inverter output and the loads (motors, power supplies, resistive loads, etc.)--It would take a lot of high frequency energy to make those types of high voltage excursions. I just don't see that as being a common problem if the rest of the system is designed correctly.

Surge Capacitors on utility poles are there because they are open to direct and indirect lightning energy. I could see them using pole top surge capacitors to reduce the initial current/voltage spikes a bit. But, remember that utilities frequently use banks of switchable capacitors on their distribution circuits to "fix" summer power factor issues (lots of water pumping and A/C compressor motors). And they have to be careful to prevent any sort of resonance/circulating currents from occurring (again, lots of math).

Here is a 35 page PDF paper on three phase power grounding and capacitive issues. It will make your head hurt (did mine).

-Bill

northerner

Re: How concerned are you about lightning?

BB. wrote: »

I would not add any capacitors to the output of an AC Inverter... Many do not like driving capacitive loads (remember, inverters are full of transformers and inductors).

I did not see any value for the AC surge capacitors--They are probably not that large and should not take the the impedance of the AC output from inductive to capacitive phase shifting (i.e., you can add so much capacitance, the inductive current phase lag will actually be corrected to zero or even positive phase lead with enough capacitors).

Ok, thanks for that Bill. Sounds to me like they are not necessary. And I will spare the potential head hurting from the link you posted.:p

BB.

Re: How concerned are you about lightning?

And for folks running MSW type inverters (modified square wave)--Adding capacitors to the output is a terrible idea. MSW have very sharp (square wave) which have lots of high frequency content. Adding capacitors to the output of a MSW inverter is like placing a "high frequency short circuit" on the output of the inverter... Causing excessive current, ringing, circulating currents in inverter transformers, and resonance/oscillation issues in the whole system

Or the capacitors are simply just too small of value to do anything (good or bad)... And probably not worth wasting any money on.

Square waves can be thought of a bunch of different frequency sine waves (starting with fundamental 60 Hz sine wave, with a series of higher frequency sine waves declining in amplitude as the frequency goes up) all added together to get the square waveform.

Square wave - Wikipedia, the free encyclopedia

That is one way to relate the frequency of the input wave form to what happens when you add capacitors+inductors to the circuits.

-Bill

NorthGuy

Re: How concerned are you about lightning?

Also, there's a parasitic capacitance between wires already, which, in long runs may be quite significant. And every bend in the wires add to their inductivity. These two factors make wiring difficult for high-frequency signals. That's why it is difficult to pass high frequency digital signals over long distances.

niel

Re: How concerned are you about lightning?

westom,
mostly i guessed at the depth, but if you say it can be overhead then depth requirements are sort of being made to be moot. i do disagree with overhead interconnecting ground rod tie wires as they pick up emp energy from lightning more readily. with the wire buried it adds to the grounded area while the emp is literally attenuated/dissipated by the soil itself. code may say it's ok, but i don't hold much credence for wiles' insight when it comes to some aspects.

you are being overly argumentative on some aspects that i was not saying. ftr, i am always in favor of a single point ground, but when some distances are involved even utilities do not use a single point ground as evidenced by the separate grounds on poles. they have the neutral wire up high between poles and can send most of the lightning energy into the ground, but residual can still extend outward beyond the ground points on the poles and power is also induced in any other wires nearby making the neutral wire being there in the air somewhat of a false sense of protection even though certainly better than nothing. to me any wire not in the ground is not realy ground and the neutral suspended between poles is merely an above ground wire tied to 2 or more ground rods. you look upon this in a textbook kind of way from power electrics, but emp does not follow power electric rules and ground wires above the ground and long in length are negated in their effectiveness for grounding at rf frequencies which lightning is mostly composed of. it is not a rare instance of emp failures on supposedly well installed electrical systems to nec specs.

i am also in total agreement that any wire entering a building needs to be grounded either directly or through some protection device.

as i said, it is very complicated and takes far more insight than wiles has. i also am not the only one to have written him on mistakes he has made. for the most part he gets things right, but when he goofs he does it royally.

northerner

Re: How concerned are you about lightning?

Just pointing out that the NAWS write up about lightning protection does make reference to surge capacitors and recommends their use for fast spikes that certain makes of surge arrestors may not catch.

http://www.windsun.com/Photovolaic_Systems/Lightning_Protection.htm

westom

Re: How concerned are you about lightning?

niel wrote: »

you are being overly argumentative on some aspects that i was not saying.

First, I was never responding to you. I only discussed facts and numbers of the topic. I don’t care whether you agree or not. I only care about facts and numbers concerning the topic. Even this post is only about the topic from many previous posts. Most is irrelevant to your post. Only relevant to the topic.

I am also not sure what you are saying in that last post. Since I can interpret its first paragraph multiple ways. Posted previously were hard facts with numbers and examples. If something is wrong, corrected numbers are in a reply. And appropriate examples provided. Without numbers and examples, I have no idea what that first paragraph says.

Second, EMP was demonstrated previously with an example. An antenna is designed to maximize E-M energy on its lead. A nearby lightning strike (maybe 10 meters away) creates thousands of volts on that wire. An NE-2 neon bulb conducts a only a few milliamps to lower that voltage to maybe tens of volts.

Energy from EMP is trivial. Made irrelevant by a simplest protector such as a tiny neon bulb. EMP is too often hyped as destructive when that energy is quite trivial. Ie a high voltage made irrelevant by conducting only tiny milliamps. A transient made irrelevant by protection already inside electronics. A transient defined irrelevant by numbers.

Another example – a direct lightning strike to a lightning rod connected to earth on a wire only four feet from an IBM PC. Is the PC damaged? Of course not. That PC did not even blink. EMP from an entire lightning strike only four feet away does nothing to an adjacent PC. Protection routinely found in electronics makes such EMP irrelevant.

Third, utilities use the single point concept. Their various grounds are consistent with that concept. However, only relevant here is ground from the perspective of one building. A ground from a transformer to earth is single point ground for that part of a distribution system. That protection layer is also a building's “primary” surge protection.

Single point ground at a house service entrance is the “secondary” protection layer. Each layer of protection is defined only by its ground.

Fourth, earthing is an art. Yes, it might become more complicated. We returned to a few locations when earthing failed. But basic rules are provided. And are more than sufficient for most venues.

Fifth, I have no idea what ‘surge capacitors’ are. At least not for surge protection. However others may define as a surge other electrical anomalies that are completely different. For example, a USB device that draws too much current creates a 'surge'. IOW the USB port shuts off for the same reason a fuse might blow. That 'surge' is completley irrelevant to this topic.

Sometimes a motherboard will declare a surge. Only a DC voltage that has changed slightly - just enough to be out of spec. Again, completely irrelevant here.

Filter capacitor found on so many appliances is a 'surge capacitor' because it must fail only in a safe manner. Is only about something that would otherwise threaten human life. That failure is also irrelevant to this topic.

If a surge capacitor exists as that citation claimed, then the part is identified in catalogs from electronic supply houses such as www.digikey.com, www.mouser.com, www.newark.com, etc. Define that capacitor with spec numbers.

Noted earlier is one simple rule that applies to a 'surge capacitor'. Nothing as in nothing can block or absorb a typically destructive surge. If a surge capacitor worked as claimed, then capacitors also collect and use that energy. We don’t for one simple reason found in spec numbers.

Sixth, destructive surges are microsecond events. Recommended protectors from more responsible companies respond in nanoseconds. More than fast enough. Worse, that 'surge capacitor' recommendation has no numbers. It makes subjective claims only using the word 'fast'. No numbers means that citation for a 'surge capacitor' is, at best, suspect.

I have never seen a surge capacitor as described in this thread. So which 'surge' were they really discussing?

BB.

Re: How concerned are you about lightning?

I will also add that single point grounding of the AC Neutral is also shaded with lots of grays...

As I understand, the Neutral is usually grounded at the pole transformer, and at the 5 houses (+/-) down the street, each grounding the Neutral at its main panel via cold water pipe/ground rod (as codes/ages change).

So--From a DC/60 Hz point of view, we are looking at multi-point grounding of the AC Neutral, buy design, by the NEC. Is that a good thing or a bad thing.

From my point of view, it is probably a good thing because--From a DC/60 Hz point of view it probably does not matter. We are looking at 1-29 Ohms or so (DC/60 Hz impedance) to earth and should be looking at zero to a few volts of difference between Neutral and these ~half dozen different earth points--if everything is connected correctly (which does not always happen--but another story).

The second reason for earthing is the Lightning energy dissipation. And, at the frequencies that lightning demonstrate (RF energy a maximum "meaningful" frequency at ~7.5 KHz and below--very roughly), the only earth ground that matters is the short ground from the AC panel/neutral bond to the ground rod at the base of the panel/foundation. The others are (for the most part) irrelevant.

Because of the distributed nature of the neutral/ground bonding--There will be a brief impulse of circulating current in the AC Neutral among the various ground points--But it should not be high enough current to cause the excessive (damaging current/energy) in the neutral wiring circuits (because of the overall impedance of the AC Drops).

But, because each house is at "earth potential" for each of their Main Panels--One layer of lightning protection has been obtained.

So--As I think about this, I said that having a ground bond at the Main panel, and another ac neutral ground bond at an out building 200' away may not be the worst thing in the world--And actually would appear to mimic the standard AC bonding of the utility distribution system.

I am not convinced that multiple grounding of the AC neutral between buildings is the wrong way to go at this moment (i.e., it actually may be the "right" way to go).

The downside is I have seen energize earth before--I drove two ground rods ~100 feet apart and got shocked when I ran a wire between the two rods (about 60 VAC between the two rods)--Probably the earth was energized by big 5-10 HP three phase pumps at an aquarium/theme park. If I had thought more about it, I would have attempted to measure the current (i.e., would have I have seen 2-30 AC Amps between the ground rods?). As it was, I was just trying to get rid of RF energy from a near by radio station from entering a hydrophone/amplifier place in a salt water tank.

I have also read about a home that, somewhere, somebody made a miss-connection and earthed one of the Hot wires for a 120/240 VAC home panel. And they finaly noticed it because the snow was being melted around the ground rod (I don't remember where I read that). So, even a miss-wired earth ground is not something that will attract immediate attention (should the utility/electrician/building inspector go around with an AC Current Clamp meter and measure ground currents? May be a good idea--But have no idea how often this ever happens).

-Bill

NorthGuy

Re: How concerned are you about lightning?

westom wrote: »

Fourth, earthing is an art. Yes, it might become more complicated. We returned to a few locations when earthing failed.

May be you could tell us about these examples where earthing failed? That would be very interesting. The best way to learn is by example.

NorthGuy

Re: How concerned are you about lightning?

BB. wrote: »

I am not convinced that multiple grounding of the AC neutral between buildings is the wrong way to go at this moment (i.e., it actually may be the "right" way to go).

I've tried to quantify that somehow. If the piece of neutral between separate "bonding" points is 0.2 Ohms, then even there's a 100A current induced in the wire by the difference in earth potential, it will only produce 100A * 0.2Ohm = 20V difference between the bonding points. So, instead of 120/120V you'll get 100/140V. This may not be very good, but certainly not harmful. If something bad is going to happen, the induced current must be in excess of 100A. To get to your "safe" 1800V, there must be 1800V / 0.2Ohm = 9kA. This is only possible during violent events and is unlikely to be a problem during normal life.

Also, I thought about grounding. If your grounding is really deep and creates a good bond to the deep earth, the path of the lightning is unlikely to be through the neutral to a distant building where there's another ground bond, unless there are some high-impedance anomalies in the earth between the building. But the better your ground, the less chance for that. If, however, the ground is shallow and impedance to ground is high, the part of the neutral may become a dissipation path to a better ground at a different bond. So, good local grounding should make multiple local bonds in multple buildings harmless.

BB.

Re: How concerned are you about lightning?

I agree--But the impedance of the service drop is even higher--So the ability of the lightning to propagate more than a few 10's of feet through the service drop is very low (before the energy attempts to find a different path).

It has been too many years, anyone remember the impedance calculations for a wire 15 feet above the ground (with lightning, a single wire--so impedance would be higher that a twisted pair/coax cable wich is usually in the 50-300 Ohm range).

I believe this should be in the range of hundreds of Ohms--But even this is a bad approximation. Lightning is an impulse so it contains many different frequencies (as discussed earlier) and as the wire length approaches 1/2, 1/4, etc. wave lengths, there is all sorts of interesting reflections that change the impedance dramatically.

Hmm if 7.5 KHz (not kWH) is the maximum "frequency of interest", the 1/4 wave length is around 32,800 feet (10,000 meters)--So reflections and such are not going to matter for the pole transformer to home length of wiring.

Anyway--I will stop here before I embarrass myself even more.

-Bill

westom

Re: How concerned are you about lightning?

NorthGuy wrote: »

May be you could tell us about these examples where earthing failed? That would be very interesting. The best way to learn is by example.

One case study was a Nebraska radio station. Engineers, who had believed myths of lightning attracted by earth ground, compromised the earthing. Resulting in more damage. What averted all damage was to fix the stations earth ground system (secondary protection). And to upgrade the utility earth ground (primary protection).

This example demonstrates a few popular myths and how they corrected the resulting 'damage':
http://www.copper.org/applications/electrical/pq/casestudy/nebraska.html

Apparently resistance and impedance are not understood. To 60 Hz, that wire is maybe 0.1 ohms resistance. To a surge (microsecond spikes) that same wire is maybe 120 ohms impedance. Appreciate a major difference between resistance and impedance. Impedance is why (if I remember) that case study was explicit about wires with no sharp bends. A sharp bend does not increase resistance. And can seriously increase impedance.

Electricity has numerous unique characteristics. For example, connect a 200 watt transmitter to a long wire antenna. Touch one part of that antenna to feel no voltage. Touch another part of the same wire to be shocked by over 100 volts. Many concepts were only summarized at the layman's level. For example, a ground wire cannot be inside a metallic conduit. A connection to earth should be less than 3 meters. Underlying science also explains two completely different voltages on the same wire. All about electricity performing quite differently than at DC or 60 Hz.

inetdog

Re: How concerned are you about lightning?

BB. wrote: »

I have also read about a home that, somewhere, somebody made a miss-connection and earthed one of the Hot wires for a 120/240 VAC home panel. And they finaly noticed it because the snow was being melted around the ground rod (I don't remember where I read that). So, even a miss-wired earth ground is not something that will attract immediate attention (should the utility/electrician/building inspector go around with an AC Current Clamp meter and measure ground currents? May be a good idea--But have no idea how often this ever happens).
-Bill

I have a (secondhand) personal connection with a guy who inadvertently grounded a 220 volt hydraulic lift pump motor's 120 volt phase line. It was connected to the lift tower which was bolted to a concrete pier. The result was a constant roughly 30 amp current from a 50 amp breaker. He only noticed it when he got the next months power bill.

waynefromnscanada

Re: How concerned are you about lightning?

BB. wrote: »

I have also read about a home that, somewhere, somebody made a miss-connection and earthed one of the Hot wires for a 120/240 VAC home panel. And they finaly noticed it because the snow was being melted around the ground rod (I don't remember where I read that). So, even a miss-wired earth ground is not something that will attract immediate attention (should the utility/electrician/building inspector go around with an AC Current Clamp meter and measure ground currents? May be a good idea--But have no idea how often this ever happens).

-Bill

Hahaha That could have been a post I made a few years back. Neighbor / friend of mine had completed his electrician training and wired the new house he was building for himself. After running into problems with a couple of breakers kicking out, he asked me to have a look. Tracked down several outlet boxes where the clamps had been screwed down tight enough to cut through the cable insulation. Fixed those. Then he mentioned his entrance meter was always spinning, even when everything was turned off. Yep, the snow was melted around the ground rod. With both my feet very close together, one Fluke lead on the rod and the other stuck in the wet earth, there was voltage measured, and the further out I moved the lead stuck in the earth the higher the voltage. BINGO!!!!! The neutral wire had not been clearly marked, and got interchanged with one of the hots upon entering the main panel. That was probably 20 years ago. The house is still standing, his wife moved out, the zone valves in his baseboard hot water heating system are still installed backwards, resulting in a water hammers every time they close, and as far as I know he never did use his electrician training in his work life.
I'm so thankful I'm perfect. Hahahahaha

niel

Re: How concerned are you about lightning?

"Apparently resistance and impedance are not understood. To 60 Hz, that wire is maybe 0.1 ohms resistance. To a surge (microsecond spikes) that same wire is maybe 120 ohms impedance."

apparently it's not being made clear by you either as i have to correct you here on it. impedance is always applied to ac whereas resistance is to dc. i assume you meant to add that it may be .1 ohm at a dc potential rather than at 60hz?

niel

Re: How concerned are you about lightning?

interesting story on the radio station. one thing they did not address is the fact that as the tower is energized from the strike that this energy can also induct power into the cables carrying the transmitted rf. this is a real problem for many installations and was confirmed by a local guy who does installs + maintenance on many local installations for a living. grounding the outer shield of the cable at the base of the tower (or at whatever point the cable goes away from the tower) often sent the induced spike to ground rather than inside to the equipment. even the center lead of the cable can have some protections incorporated with spark gaps and gas discharge tubes, but with 100kw these will be quite large in their value so as to not ground out their own high voltages from the rf.

in most cases for us the shallower multipoint grounding system works, but i have no argument on driving a rod deeper is actually much better.

ground loops are a real pita when it applies to rf.

ggunn

Re: How concerned are you about lightning?

BB. wrote: »

In general, there is no good reason to add a "surge capacitor" to a generic AC circuit. At a minimum, the capacitors would just add to the inverter's output current ...

How would it do that? A GT inverter's output current is determined by the line voltage and the power input from the PV.

BB.

Re: How concerned are you about lightning?

ggunn wrote: »

How would it do that? A GT inverter's output current is determined by the line voltage and the power input from the PV.

Sorry, I was (apparently) thinking of an Off Grid AC inverter... A capacitor just draws current from the AC inverter--and could cause some stability issues (but a "surge cap" is probably so small as to be almost undetected by the AC inverter).

Adding a capacitor to an AC Utility Line is, in theory, a "don't care". The capacitor draws a little bit of current, but since an ideal capacitor's current is 90% out of phase with the sine wave voltage, there is no "work" being done, so the standard residential meter will never charge for the current.

Of course, there are power factor correction capacitors which are much larger, and can do positive things in certain conditions, but for 99% of the on-grid homes out there, PFC capacitors are not doing anything useful. And be of very limited use for Off Grid systems (if properly sized and connected to the motor loads).

-Bill