PV backfeeding the grid 2

[stevenal]

Situation:
Utility customer meter is occasionally registering reverse power flow and PV panels are visible on the property. The customer has not gone through the net-metering approval process, so the utility has no record of the installation or knowledge if NRTL products were used, what standards were used, or if the AHJ has had a look at it.

The customer claims the PV system is isolated and has no desire to sign up for net-metering. The utility is reluctant to perform any checking on the customer side of the meter.

My first concern is regarding lineman safety, who might think lines were de-energized when not. Utility says the linemen test and ground without fail, so there is no concern here.

My next concern is for the customer. What happens if the inverter continues to operate in island mode during an outage and is out of sync when power is restored? While I’m aware that such occurrences are hard on synchronous machines, what happens to electronic inverters?

Any guidance is appreciated. Happy Independence Day.

 

[davidbeach]

Make sure that the meter records all four quadrants as consumption. A few months of higher than expected billing could bring out the truth.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[Heaviside1925]

OP,
Out of curiosity, where are you in the situation?

Does the utility have the right to pull the meter if the customer is reverse feeding without their knowledge? This would be a scorched earth move and I suspect the utility would warm the customer of the situation so that the customer could remedy on their own. The customer may fully believe that their PV system could in no way cause this but a strongly worded letter from the utility may be enough to convince the customer to hire an electrician to come inspect their system.

 

[stevenal]

I'm on the utility side, and therefore in a position to know that a heavy handed approach is off the table.

 

[waross]

When I was working for a small utility, the default meter parameters were to sum the forward and reverse power.
Note: This was in an area where power theft was common.
Electro-mechanical meters were routinely flipped upside down for one week out of each month.
The electronic meters displayed the sum of forward and reverse power, but the true values ere available in the internal registers.
A well to do business man bought and installed a 60 KW wind turbine.
He had it installed without bothering with any approvals.
The property where it was located was used mostly for storage and normally had little power usage.
When his wind turbine went online he was billed for all of the power that he exported to the grid.

occasionally registering reverse power flow
Utility says the linemen test and ground without fail, so there is no concern here.

I share your concern.
I once had a ride with a one armed, one legged taxi driver.
In a previously he was one of the best linemen who worked for me.
Just one time, but the wrong time, he forgot to;
"Test Before Touch!"
A tragic accident.
He had visual confirmation that the cutout, a span away, was open.
The cutout that should have been opened was two spans away.

Are electrical permits a matter of public record?
A friendly query to the inspection department.
In our area an electrical inspector has a very strongly supported right to investigate the electrical equivalent of "Probable Cause".



--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[cranky108]

How big? In many cases the installation would not even be capable of energizing the pad or pole transformer. If that is the case, why would you worry about it? Don't sweat the small stuff.
I also like the four quadrant meter, and if they have no contract, bill them for the reverse power flow.
Besides I don't like net metering, because it does not allow the utility company to recover the cost of using there equipment, which places that burden on other utility customers.
Also, a customer that does not follow the state or local regulations does have an increased risk of law action, fines and damages. So a nice letter from your legal department, to the customer, installer, town/city, fire department, and inspectors department might be in order.

 

[waross]

which places that burden on other utility customers.

That burden is covered by the demand charges for industrial consumers.
You have a point for residential consumers, but co-generation generally acts to reduce that burden.
And some utilities bill rural customers for a fixed demand.
The demand is limited by a utility supplied and sealed breaker.
A typical rural residential service will be charged for a 5 KVA demand, limited by a 35 Amp breaker.
Yes, they allow 35 Amps times 240 Volts equals an allowed demand of 8.4 KVA on 5 KVA billed.
In the case of a farm or ranch with a shop and/or a barn, the utility mandates a higher demand charge.
By the way, I was only involved in revenue metering in one small country,BUT...
The default setting for new meters in that country was a displayed and reported (via remote meter reading devices) sum of forward and reverse power.
All quadrants were metered and stored in internal registers. Our small utility could not justify the cost of the restricted cost of the software used to change the meter defaults.
Even if we could have justified the costs we may not have been able to meet the security standards.
If we had ever been faced with metering co-generation, we would have special ordered one or two meters with appropriate parameters preprogrammed.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[stevenal]

Thanks for all the responses.
How big? No idea, but big enough to occasionally export.
My real question is toward the end of the post. If customer thought he was installing a stand alone system, he likely installed an inverter not intended for grid tying. What happens when utility power is restored out of synch?

 

[Heaviside1925]

OP,
Concerning your last post.
A couple items in your first post gave me pause to think. They are:

occasionally registering reverse power flow

and

The customer claims the PV system is isolated

The customer may not directly have the two systems combined, ie. at the inverter and does believe they are isolated. I am wondering if it's accidentally crosstied at some point and how it is crosstied would determine the consequences of power being out of phase. Is this a residential service, 120/240 with low side metering?

 

[waross]

The customer may have a system that monitors line current and curtails PV production to the actual facility usage.
I can see such a system responding too slowly to a major load dump to avoid a momentary back feed.
Utility returning out of phase.
Hard to say without more information but I strongly suspect that would be an expensive lesson for the customer.
I suspect that the utility would ride through a relatively minor transient event.
Unless the PV system is massive, I expect that the utility would easily ride through while the customers protection clears what is left of the PV system.

The customer claims the PV system is isolated and has no desire to sign up for net-metering.

It may be time for a Cover Your ASSets letter from the utility legal department to the customer.
Point out that there are documented indications that the PV system is not isolated, and no record of the compliances and protections that should be in place given the data from the revenue meter.
The customer will be held responsible for any damage he may suffer and will be held responsible for any and all damages incurred by the utility.
Given the possible consequences of a back-feed into the utility, the customer may be held criminally responsible for possible injury or death of utility workers as a result of a back-feed into the utility.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[stevenal]

Residential 120/240, and yes I suspect an accidental cross tie.

 

[waross]

I am not sure what is out there now, but at one time, there were some inverters available that monitored the line current from the grid.
They would curtail inverter output depending on the current from the grid.
That is, when the current from the grid dropped, they would lower the inverter output.
I wonder if the removal of a large load such as an electric clothes drier may cause a back-feed transient until the controls could respond.
Do your reverse power events support such an event?
I am thinking like something analogous to a load dump on an automobile electrical system.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[wcaseyharman]

I would set a recorder at the customers meter for starters if you haven’t already. My utility uses products from Power Monitors Inc (PMI) which provide a lot of information. This might be a good starting point to determine what’s going on.

I’ve also found that reading the utility rate tariffs is a really useful exercise for issues like this to understand exactly what the customer is obligated to do. Sometimes there is explicit information in there that is relevant - for example, in my utility’s general rate schedule there is a whole section on the customer impacting the grid, which has come in handy when dealing with customer load issues.

Inverters seem like tricky devices, because so much of their performance seems to be driven by the firmware, which can vary. I would have thought that an islanded inverter would not be capable synchronizing to the grid and if accidentally cross-tied with the utility grid would already be having problems. An inverter designed for islanded operation I think would hold the frequency exactly at 60Hz, and as the grid frequency moves around the inverter would be attempting to regulate the rest of the grid and would trip off all the time - but I can’t be sure of this without knowing the specifications of the inverter.

 

[Heaviside1925]

OP,
Are you focused on inverter damage as a way to convince the customer to fix the issue?
As I am sure you know, it's going to take some detective work to diagnose things just from the utility side. I fully agree with wcaseyharman recommendation of data logging. To add to how much and for how long, I think time of day and the frequency of how often would be helpful as well.
If the customer is being honest that he "knows" his system is not grid/utility connected, then that would indicate, they have an off-grid set-up. If this is the case, then there would be no utility/grid input on the inverter and no syncing of the output with the utility. Any cross-tied connection would already be out of phase and since you haven't had any phone calls from the customer, would lead me to believe that there is no inverter damage. I think there could be a possibility for damage on the line side of the inverter, such as overheating, motors burning up, etc. This could be something you could ask the customer about since if they think their system is isolated, then they are likely blaming the issues on other reasons.
Just from the few residential PV inverter systems I have messed with, my experience has been that manufactures know their products are being purchased by a DYI's or solar installers and many times are not being evaluated at all by a competent electrician. So, the manufactures have made the residential ones fairly bullet proof as far as faulting out or shutting down due to abnormal conditions. Not saying a homeowner still could fry one if they really tried but residential inverters seem to be much more fault tolerant than they used to be.
I have some hypotheses of where the cross-tie could be but before I waste anyone's time with my long-winded ideas, a few more questions. Is this a rural customer? A farm or decent sized property? Is there a barn or machine shed on the property? How old is the account? Do you know if the customer has city/supplied water?

 

[JJ_Roy]

We had somewhat the same issues in the early days of residential solar when I worked as a district engineer in the distribution dept. at a local utility. We'd have the legal dept. send out a registered letter that cited the interconnection standards, safety,.... blah, blah, blah, and "subject to penalty up to disconnection of service". We had a good relationship with the local AHJ's so we'd just turn it over to them to chase down. The AHJ didn't like missing out on the permit fees (and increase in property taxes for the towns) so they were happy to investigate. I do remember getting a few disconnect orders for some "bandit" solar installations from the AHJ in the early days.

The letter serves as a documented notice that the utility isn't responsible for damage to customer's equipment as it's not an approved installation.

I don't work in distribution anymore but the company instituted "energized work practices" for almost everything now, even work that would have been considered de-energized work. This is due to the proliferation of distributed generation (solar, batteries, etc..) on the low voltage system and not knowing the status in addition to improperly connected portable generators that would sometimes be on the system during outages. The linemen hated the "everything energized" policy when they first started it, but it's probably saved a few lives even though it sometimes slows down restoration work.

FYI, The solar plant wouldn't work properly if it was only set up for islanded operation but somehow is tied to the grid. They probably would have gotten the mysterious "POP" and funny smelling smoke as soon as they closed the breaker or the first time they had a reclose on the feeder.

BTW: We'd never really investigated any improper installations beyond the meter, that's up to the AHJ (or an electrician). We would due a bit of investigation for power quality issues or theft, but that's about it.

 

[cranky108]

I might be a little more careful about sending a notice to AHJ, as our utility would see this as a breach of customer right to privacy. It is bad enough here that we don't even report suspected grow houses to the police.
We know in that industrial metering, and huge water demand, on a residential property.
But it is within your rights to investigate power quality issues, or suspected issues.
The lawyer letter is a good approach.

 

[stevenal]

Update following this morning's meeting. First order of business will be to replace the meter and test the one removed. Meter Foreman will be voltage testing the load side meter base lugs when the meter is out. The area looks more rural, but I have no information on the water service or lot size.
Any thoughts on this?

 

[waross]

Laughing Out Loud!

That definitely has back feed capability.
If you take time to read the specs:
"No Batteries." vs "Power Source, Battery Powered"

"Includes 4PCS of 160 Watt Solar Panels (total 640Watt)," vs "Maximum Power ‎320 Watts"
They claim anti-islanding protection, maybe.
Anti back-feed is very difficult without monitoring the draw from the utility, which this does not do.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

I know of one entire Country where all the meters that were new in the last 10 or 15 years would add the back-feed to the consumption KWHrs automatically.
Thar was the default programming on all new electronic meters, and also one of the reasons to shift towards electronic meters.
Power theft by turning the meter upside down or reversing hidden connections was very common.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bacon4life]

I agree with Heaviside1925 that any damage is likely to occur on the customer side rather than the utility side. DIYers do lots of crazy things, and installing solar seems a similar level of risk as other kinds DIY projects. At some point the industry may need to align the approach of customers adding load versus solar. Typically adding solar requires orders of magnitude more permitting paperwork than adding the equivalent load. The crazy part is the solar output is fairly predictable, whereas individual customer loads are highly chaotic.

Billing non-net metered customers based on forward + reverse power provides customers motivation not to connect solar without going through the official interconnection process. However, this method does slightly penalize customers who periodically regen excess power from elevators/cranes/drives.

Regarding testing the load side lugs- absence of load side voltage does not confirm absence of future backfeed. Typically inverters capable of both grid tied and islanded operation will keep the grid facing output de-energized until the inverter senses the return of good utility voltage.