Export Limit Lock is now available on EG4 18kpv

rhino said:

What is the underlying reason why a power company like Duke Energy wants this when very few if any others do?

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In my area in Connecticut, there is a hard limit of 25kW of export. I can't parallel two 15k's because of that. The issue is whether the distribution system is able to handle everyone exporting at the same time.

rhino said:

What is the underlying reason why a power company like Duke Energy wants this when very few if any others do?

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In California, people get a reservation for NEM 2.0
If they later add more PV, that bumps them onto NEM 3.0 (which isn't net metering, rather small credit for backfeed.)

Possibly export limit would let them make and use more, while not being able to export more than original agreement.
Something about a new program to allow that.

Meanwhile the system I reserved for my sister has 7.7kW inverter (limit due to 120% rule) but 15kW PV panels. Adding a battery will let the extra kWh be stored for export during peak rates, staying within limit. Considering a 7.7kW hybrid that processes 15kW PV.

mciholas said:

Doesn't the 18KPV already have a user setting for max export? I suspect that would remain and the new setting just hard caps that value and EG4 can attest to the limit for the utility.

Mike C.

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That is correct.

robby said:

I Never heard of that requirement in the USA, maybe their is some power company somewhere that is requiring it.
I think in the UK they require some sort of lock.

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We have gotten several requests from customers that need this option to get their net metering finalized, so we made the option available.

It was odd to me when I first saw the request come in as well, but with the growing solar market, and more Americans adopting it everyday, utility providers are wanting to make sure that their infrastructure is protected.

This is my take on it, I have not spoken with the utility companies that are asking our customers for this document and lock to be put in place myself, but it seems like others are adopting this as well, and I'm sure we will see even more of it in the future.

robby said:

I just see this as another road block in the endless road blocks put up by utility companies to make Solar unattractive to potential buyers.

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At least Net metering..

rhino said:

What is the underlying reason why a power company like Duke Energy wants this when very few if any others do?

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They want to make it as hard and expensive as possible for customers to offset their grid util. So come up with a bunch of arbitrary restrictions to limit hardware choices.

Brucey said:

They want to make it as hard and expensive as possible for customers to offset their grid util. So come up with a bunch of arbitrary restrictions to limit hardware choices.

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I did find out when talking to some utility workers last Friday that at least in some areas some of the utility company equipment simply can't handle it and would require investment on the utility side for a customer to sell power back at a certain level or even at all. So there could be a somewhat valid technical reason.

For those of us in Ontario, Canada, this might also be useful; net metering connections below 10kW are easy enough and have an expedited (and cheaper) review process. Anything over 10kW requires that you go through the "Connection Impact Assessment" (CIA) process, which is a huge pain in the ass and takes 90-ish days. When I went through the process with my Sol-Ark 15k, I was told that the nameplace capacity of the inverter was what primarily mattered, but they might agree to a software limit if the user couldn't change it. I decided to just do the CIA since I want to add more solar down the road anyway, but for a lot of people this will be very welcome if it works

Hedges said:

Oh, I'm pretty sure I could change the perceived current +10% or -10% if I wanted, with passive components. One approach would be another current transformer or split core, turns ratio between it and some loops of wire through the CT being read.

Another, for CT with burden resistor, would be to just parallel another resistor (reduce perceived current.)

Not that I would, for reasons including smart meter could snitch on me.

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My experience in 2014 with an associate's grid-tie installation we did is that APS (Arizona Public Service) - with just a smart-meter, not even a bi-directional meter - was able to detect his experimental back-feeding to the grid, before the bi-directional & solar meter installs and the final APS approval. Needless to say, someone came out and locked-off the back-feed safety switch to put an end to that, if I remember correctly. I told him NOT to fire up his inverter for testing unless he had some good loads in the house to power to prevent the back-feed, but he did it anyway, heh, heh.

andrew-d said:

For those of us in Ontario, Canada, this might also be useful; net metering connections below 10kW are easy enough and have an expedited (and cheaper) review process. Anything over 10kW requires that you go through the "Connection Impact Assessment" (CIA) process, which is a huge pain in the ass and takes 90-ish days. When I went through the process with my Sol-Ark 15k, I was told that the nameplace capacity of the inverter was what primarily mattered, but they might agree to a software limit if the user couldn't change it. I decided to just do the CIA since I want to add more solar down the road anyway, but for a lot of people this will be very welcome if it works

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The utility here, APS (Arizona Public Service), is very conscious of the safety of an installation. When designing a grid-tie system, we must state on our drawings the maximum possible short-circuit current from at several points. This is calculated by knowing the maximum short-circuit current at the utility transformer, and the size and length of the feeder wires to the service entrance.

I designed a 22.8 kW grid-tie system for a retired physician's new Paradise Valley, AZ, home. The home had 400 A service and a ready-to-go backfeed circuit breaker at its combination service entrance. APS insisted on major upgrades even to properly-sized safety switches. I had to use a 3-phase switch to comply with one of their requirements. Nothing else was readily available at that time for 240 V split-phase.

I cannot complain. The availble current from the utility is tremendous. A friend of mind measured the internal impedance of his utility feed by shorting his utility connection by striking two conductors together with a hammer and tripping his main breaker. That was not a very smart thing to do, but he did measure a very low value, although I forgot what it was.

CharlesWhitlatch said:

I told him NOT to fire up his inverter for testing unless he had some good loads in the house to power to prevent the back-feed, but he did it anyway, heh, heh.

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What I plan to do for my next system. With only some PV strings connected.

CharlesWhitlatch said:

I cannot complain. The availble current from the utility is tremendous. A friend of mind measured the internal impedance of his utility feed by shorting his utility connection by striking two conductors together with a hammer and tripping his main breaker. That was not a very smart thing to do, but he did measure a very low value, although I forgot what it was.

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What measurement device did he use?

I think the proper way is to apply two different impedances, measure change in grid voltage.

SolarAPP+ wanted me to go through additional effort if grid was capable of more than 10kA. My main breakers are 22kA. But I think the neighborhood Pole Pig is only 25kVA or so.

Some 4 ~ 6kA per this site:

Hedges said:

What measurement device did he use?

I think the proper way is to apply two different impedances, measure change in grid voltage.

SolarAPP+ wanted me to go through additional effort if grid was capable of more than 10kA. My main breakers are 22kA. But I think the neighborhood Pole Pig is only 25kVA or so.

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This was around 1981 if I remember. He was a brilliant engineer, very intelligent, but bipolar.

He likely measured (estimated) the resistance of his hammer-induced short-circuit (milliohms), then measured the AC voltage across it with an oscilloscope (at the time of the short). This allows a calculation of the current as a function of the reduced momentary AC waveform. From that, a rough calculation of the source impedance of the power grid at his location can be done. He did the shorting/measurement process several times, he told me - bang!

I had one case where APS was giving us the "run around" because I was told to let the electrician design the interconnect (backfeed) solution, and he came up with something I knew APS would not normally accept. Then, I had to use a special procedure to calculate short-circuit current after APS (additionally) started insisting everything be rated 22 kA, which was not necessary. After my calculations, they dropped that. However, we had to replace the mobile home service with a more-normal 200 A service that would accept a backfeed circuit breaker, which is what APS wanted. Anything esoteric like a line side-tap feed would be impossible with APS. I made four different versions of that drawing. System got installed, finally. Ground mount system, Cave Creek, AZ.

At one point, for some reason, APS would no longer accept a certain model Square D 60 A disconnect switch, even though rated at 10 kA. I understand - none of this stuff can fail or there is disaster.

I had SRP (Salt River Project) come to my TV Transmitter site one night at 4 am (they insisted) to repair some "closers" on our power pole we noticed were sparking - we reported that late at night and were surprised they came in the middle of the night to do the repair (switched to backup generator during repairs). High current and voltage is taken seriously.

SignatureSolarJames said:

Duke Energy is s good example of a 10kw limit for export, or SRP as well, if a person wants 1 or 2 18kpvs they have a problem. a maunfacturer locked export limit certificate with the energy company registered as the decision maker to unlock is a game changer.

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SRP Taking away from their profits which they claim they not suppose to be making any profit.