Utility limiting system size. Thoughts on partial-energization.

[pkhosravani]

Project Overview:
The homeowner's goal is to install the largest possible solar PV system on two buildings, totaling 17.160 kW DC / 13.611 kW AC. This system would consist of (39) 440W modules and (39) Enphase iQ8A-72-M-US microinverters.

The city has no size restrictions, only requiring that the system is structurally and electrically sound, but it's the utility that is restrictive.

The Utility's Restriction:
The utility, Ameren (MO), has limited the homeowner's initial solar PV system size to a maximum of 9.715 kW DC. This limitation is based on the last 12 months of the customer's electricity usage, which is standard procedure.

However, the homeowner's future energy needs are expected to increase significantly due to the recent installation of a new hot tub and the planned purchase of two used electric vehicles (EVs) by October 2025.

Proposed Solution:
To bypass the utility's initial size limit while still installing the full system, the following strategy is being considered:

• Initial Interconnection: Submit an interconnection application to Ameren for (22) 440W modules totaling a 9.680 kW DC system. However, the plan set would show the entire (39) module system being installed.
• Partial Energization: Only connect and energize (22) of the (39) solar modules. This will bring the initial system size to 9.680 kW DC, which is just below the utility's 9.715 kW DC limit. The remaining 17 modules will be installed but will remain dormant and non-functional.
• Future Expansion: Once the homeowner's electricity usage increases due to the hot tub and EVs, a new interconnection agreement can be submitted to Ameren to connect and energize the remaining 17 modules.

Your thoughts and advice would be greatly appreciated!

 

[Elect117]

Utility rules are utility rules. They are mostly governed by your state's public utility commission. Each utility meets the state's goal differently. I would confirm that their limit is DC and not AC. It is normal to receive their limit in AC.

I don't suggested exceeding the utility's limit that they put in writing. They will not hesitate to red tag or turn off the homeowner's power or lock out the solar / utility disconnect. You might get paid and walk away but that would be scummy and the homeowner will be left responsible.

Or modify the plans to be 1 inverter and ask them if you can lock it to only put out their 9.7kW as a max in software. That way you will have a better time maintaining that (partial cover, dust, etc.) with the higher amount of modules rather than being limited to the module side. Tell them they can have the login and password to lock it. They might go for it.

 

[pkhosravani]

Utility rules are utility rules. They are mostly governed by your state's public utility commission. Each utility meets the state's goal differently. I would confirm that their limit is DC and not AC. It is normal to receive their limit in AC.

I don't suggested exceeding the utility's limit that they put in writing. They will not hesitate to red tag or turn off the homeowner's power or lock out the solar / utility disconnect. You might get paid and walk away but that would be scummy and the homeowner will be left responsible.

Or modify the plans to be 1 inverter and ask them if you can lock it to only put out their 9.7kW as a max in software. That way you will have a better time maintaining that (partial cover, dust, etc.) with the higher amount of modules rather than being limited to the module side. Tell them they can have the login and password to lock it. They might go for it.

No, I made sure to ask the utility; it's the DC that the utility is restricting, not the AC.

The homeowner is fully aware of the size limitation and is asking that I lobby the utility to go this route.

The issue isn't the amount of power the system can inject into the grid at any one time; it's a matter of kWh generated. Therefore, adding a software limitation on power injection into the grid is moot. It seems more likely that they would accept the installation of the extra modules minus the physical interconnection than accepting a software power limitation. (I'm of the opinion that many utilities, particularly those in the Midwest, have not fully embraced the PCS features provided by inverter manufacturers.)

 

[Elect117]

No, I made sure to ask the utility; it's the DC that the utility is restricting, not the AC.

The homeowner is fully aware of the size limitation and is asking that I lobby the utility to go this route.

The issue isn't the amount of power the system can inject into the grid at any one time; it's a matter of kWh generated. Therefore, adding a software limitation on power injection into the grid is moot. It seems more likely that they would accept the installation of the extra modules minus the physical interconnection than accepting a software power limitation. (I'm of the opinion that many utilities, particularly those in the Midwest, have not fully embraced the PCS features provided by inverter manufacturers.)

Sounds like two sets of plans is the way to do it then.

I always tell people to get their interconnection agreement before submitting to the building dept. for this reason. Keeps you from needing to resubmit for plan check. You probably need less material and labor too. So hopefully you don't run up the homeowner's bill with a bunch of stuff they can't use. Like the extra 17 modules and inverters.

 

[Fred B]

Utilities have been pushing back on the private PV because of the interconnect and net metering that they have to pay the customer so they want to limit the size and limit their "losses". And then there is an inherent limitation of PV that fluctuates based from cloud cover and seasonally hours of daylight. A partly cloudy day can cause vary wide swings in power generation, and that their system must be able to accommodate the fluctuation to provide the mandated consistent current. The POCO equipment really struggles with rapid fluctuations from multiple private small (non service) PV.
Also with so many homeowners jumping on board with government grants to private grid tied PV the POCO are seeing the hit from the first statement made. So they have been raising the basic rates for all of us, the more efficient we try to be the more they charge so as to cover their costs to give money back for the increasing number PV users.
We can reduce our utilization but never really reduce how much we spend. Had one commercial client we changed out a bunch of lights to LED and saw a significant reduction of power used but without any substantive reduction of costs and now actually an increase in how much they pay. Paying more for less seems to be typical across the board for everything now.

 

[don_resqcapt19]

I would expect that Ameren will deny the connection, if the additional capacity is physically installed at the time of connection.

 

[pkhosravani]

I would expect that Ameren will deny the connection, it the additional capacity is physically installed at the time of connection.

Don, define what you mean by "physically".

 

[don_resqcapt19]

Don, define what you mean by "physically".

I mean exactly as described in the first post of this thread.

 

[jaggedben]

To me it's rather plain the customer asking if they can get away with doing something illegal. What is the point of physically installing the excess modules if they are not interconnected? (Ok, I know, tax credit this year, but the utility does not care.) Surely the customer intends to have you or someone or other hook up the additional modules anyway after the utility gives approval. Do you want us to give you a justification or excuse for doing this that would hold up in court? Not possible, I think.

I would expect that Ameren will deny the connection, if the additional capacity is physically installed at the time of connection.

Assuming they actually send someone out to inspect, I agree. Also they will likely kick it back if the approved building permit does not match the interconnection application. And the building department will likely not final the permit if more panels are installed than are approved on the permit.

Best course of action is to 'future proof' those parts of the installation (e.g. feed to combiner box, space on roof) so as to avoid rework of that conduit and wire when more capacity is wanted later. I don't think they can ding you for stuff like that. You can probably also get away with installing the mounts for additional panels at the same time. I wouldn't do much more than that. Any above-board expansion would have to be under a separate permit and interconnection, later.

The only thing I will say is that around here the building department would not follow up with the utility if you had an approved expansion that never was properly interconnected with the utility. And the utility might take forever to notice, if they ever do. But then you may never be able to legitimize the expansion because the additional load to justify it will not show up in the billing, and your documentation won't have plausible dates.

 

[Elect117]

The only thing I will say is that around here the building department would not follow up with the utility if you had an approved expansion that never was properly interconnected with the utility. And the utility might take forever to notice, if they ever do. But then you may never be able to legitimize the expansion because the additional load to justify it will not show up in the billing, and your documentation won't have plausible dates.

I always thought it was odd that a interconnection agreement wasn't a building dept. requirement for plan check on solar. Even for expansions.

 

[jaggedben]

I always thought it was odd that a interconnection agreement wasn't a building dept. requirement for plan check on solar. Even for expansions.

That would really have gummed up the works, because often that's not the order things happen in, especially for small residential systems. Glad that's not the case. (What business of it is the building dept's?)

 

[Elect117]

That would really have gummed up the works, because often that's not the order things happen in, especially for small residential systems. Glad that's not the case. (What business of it is the building dept's?)

Without a interconnection agreement for the system size the plans are wrong. Without a agreed upon disconnect location / performance meter location, the plans are wrong.

I just thought it was one of those chicken before the egg deals. Like why buy and install all this stuff with plan check approval when the utility can shut it down. Sounds backwards to me. Like the utility application should be the starting point and after all it is worked out then plan review.

It isn't so much that a building dept would care or have a code to reference but that it is like reviewing plans that can't be installed anyway and it could force them to have to re-review for the "same set". Like it is a waste of their time to review it twice. The easiest way to know that this plan set is okay to be built is to have a interconnection agreement started or some utility letter.

Like how does the building department know you are talking to the utility when doing service upgrades? They can ask for fault current letters, service planner's drawing for meter location / service point, a letter telling the city the utility has agreed to power them, etc. Not that all AHJs do ask for this kind of stuff. But they can.

 

[tortuga]

Texas is a pretty low regulation state I wonder if your customer could just form a Power Generation Company (PGC)?
Then your customer is a electric generating facility that produces electricity for wholesale sale.
They might need a ERCOT Registration (Resource Entity - RE).
https://ftp.puc.texas.gov/public/puct-info/industry/electric/forms/pgc/pgc_inst.pdf
Not real serious advice but it would be funny if somone did that.

 

[Carultch]

One possibility is to see if they can selectively operate some of the panels for a small off-grid system, and support loads that are either time-flexible, or can switch sources via a transfer switch that would only allow their off-grid inverter (if there is one) to operate off-grid.

I'd expect utility rules would only govern the scope of modules connected to grid-tied inverters, but I could see that there's suspicion of a motive to connect the initially off-grid panels at a later date.

 

[pkhosravani]

To me it's rather plain the customer asking if they can get away with doing something illegal. What is the point of physically installing the excess modules if they are not interconnected? (Ok, I know, tax credit this year, but the utility does not care.) Surely the customer intends to have you or someone or other hook up the additional modules anyway after the utility gives approval. Do you want us to give you a justification or excuse for doing this that would hold up in court? Not possible, I think.


Assuming they actually send someone out to inspect, I agree. Also they will likely kick it back if the approved building permit does not match the interconnection application. And the building department will likely not final the permit if more panels are installed than are approved on the permit.

Best course of action is to 'future proof' those parts of the installation (e.g. feed to combiner box, space on roof) so as to avoid rework of that conduit and wire when more capacity is wanted later. I don't think they can ding you for stuff like that. You can probably also get away with installing the mounts for additional panels at the same time. I wouldn't do much more than that. Any above-board expansion would have to be under a separate permit and interconnection, later.

The only thing I will say is that around here the building department would not follow up with the utility if you had an approved expansion that never was properly interconnected with the utility. And the utility might take forever to notice, if they ever do. But then you may never be able to legitimize the expansion because the additional load to justify it will not show up in the billing, and your documentation won't have plausible dates.

To me it's rather plain the customer asking if they can get away with doing something illegal. What is the point of physically installing the excess modules if they are not interconnected? (Ok, I know, tax credit this year, but the utility does not care.) Surely the customer intends to have you or someone or other hook up the additional modules anyway after the utility gives approval. Do you want us to give you a justification or excuse for doing this that would hold up in court? Not possible, I think.


Assuming they actually send someone out to inspect, I agree. Also they will likely kick it back if the approved building permit does not match the interconnection application. And the building department will likely not final the permit if more panels are installed than are approved on the permit.

Best course of action is to 'future proof' those parts of the installation (e.g. feed to combiner box, space on roof) so as to avoid rework of that conduit and wire when more capacity is wanted later. I don't think they can ding you for stuff like that. You can probably also get away with installing the mounts for additional panels at the same time. I wouldn't do much more than that. Any above-board expansion would have to be under a separate permit and interconnection, later.

The only thing I will say is that around here the building department would not follow up with the utility if you had an approved expansion that never was properly interconnected with the utility. And the utility might take forever to notice, if they ever do. But then you may never be able to legitimize the expansion because the additional load to justify it will not show up in the billing, and your documentation won't have plausible dates.

No, you are mistaken, if we go the route of attempting to have the bigger system approved now and then energized in phases, the plan has always been to submit the full system to the AHJ/City. Again, the AHJ doesn't restrict the size of the system, they just want to know that whatever is installed is structurally and electrical sound. I thought that information goes without saying, for anyone who has field experience with solar and city inspections. I guess there are times you have to state it out loud. The customer is not asking us to do anything illegal sir, they are asking that we lobby the utility based on a legitimate argument on the coming increase in usage from 2 EVs and 1 hot tub. It’s called putting the customer first - and overall I’m not afraid to ask and find out what is possible. The tax credit is expiring so it’s all hands on deck, do everything and anything you can within the approved bounds, but don't stop trying to push the limit and innovate.

Both home owners drive ~10k a year, and assuming they charge their vehicles at home 100% of time, then the rule of 1 to 3 applies. Meaning on average for evergy 1 kWh you get 3 miles out an EV. Assuming 100% charging efficiency that is 20k miles / 3 = 6,666 additional kWhs. All the roofs face directly East and West. Therefore, for this particular site for every 1 kW on the roof you get 1,100 kWhs/yr. 6,666 kWh / 1,150 = 6.0 kW of additional solar PV needed plus a cushion for the hot tub that will be used fall, winter, and spring.

 

[wwhitney]

To me it's rather plain the customer asking if they can get away with doing something illegal. What is the point of physically installing the excess modules if they are not interconnected? (Ok, I know, tax credit this year, but the utility does not care.) Surely the customer intends to have you or someone or other hook up the additional modules anyway after the utility gives approval.

I took the idea to be that after they have 12 months of increased usage from the new EVs, they would reapply to the utility for the increased system size, and if approved, it would just be some paperwork and a change of a couple connections to allow the rest of the PV to generate.

Seem poor for the utility to insist on sizing the PV system based on historical usage, rather than providing an allowance based on known future increases in usage.

Cheers, Wayne

 

[pkhosravani]

I took the idea to be that after they have 12 months of increased usage from the new EVs, they would reapply to the utility for the increased system size, and if approved, it would just be some paperwork and a change of a couple connections to allow the rest of the PV to generate.

Seem poor for the utility to insist on sizing the PV system based on historical usage, rather than providing an allowance based on known future increases in usage.

Cheers, Wayne

Wayne, you are correct, that is the idea. Ideally, we could apply sooner than 12 months later, aiming for 6 months or less.

Fingers crossed that the folks at the utility will accept receipt of the EV purchases, which I was just informed moments ago, one of the EVs was just purchased today! In addition, we will be submitting photos of the recently installed hot tub, hoping that this may be reasonable evidence to allow us to move forward with a larger system.

I here asking if anyone in this group has done something like this and could provide some advice or guidance.

 

[jaggedben]

Without a interconnection agreement for the system size the plans are wrong.

Not necessarily.

Without a agreed upon disconnect location / performance meter location, the plans are wrong.

Not for residential when you know what you're doing.

I just thought it was one of those chicken before the egg deals. Like why buy and install all this stuff with plan check approval when the utility can shut it down.

Because people are allowed to fail badly in this country?

In our state for systems under 30kW the utility generally can't reject your application or charge you more that the application fee. So it's not really so backwards when you know the installation will be interconnected. (There are some very rare exceptions only in certain areas.)

If the system is bigger you'd just be absolutely foolish not to do any interconnection first. I mean, this is kind of self enforcing, the building dept doesn't really need to enforce it. I take your point it could make some sense for bigger systems, but it doesn't seem to be needed.

The utility *does* make you get another approval from the building dept if you end up making utility requested changes after the first AHJ approval of the permit.

 

[jaggedben]

No, you are mistaken, if we go the route of attempting to have the bigger system approved now and then energized in phases, the plan has always been to submit the full system to the AHJ/City. Again, the AHJ doesn't restrict the size of the system, ....

As stated above, I find it unlikely the utility will accept a building permit for a system that is larger than what they'll allow you to interconnect.

I've had the utility suggest partial energization of the system pending an upgrade on *their* end, but that's a different situation. In those cases the building permit still matched.

I think best case, pull two permits for solar, only show one to the utility until you think the new load is justified, then show them the other.

I really just kinda don't understand the point of it all if the later one won't gett he tax credit anyway, hence my skepticism. Sorry if I offended.

...
I here asking if anyone in this group has done something like this and could provide some advice or guidance.

In our area the limit is 150% of load and the customer can sign an affidavit attesting to what they're doing that will increase the load to that much. But different states have different rules so that may be totally irrelevant. I kinda assumed from your OP that you had already exhausted this conversation and the utility is already insisting on past history only. You gotta know the state rules that apply to your utility.

 

[zbang]

I don't think it was mentioned, but other than the cars is battery storage involved? If the PoCo is concerned that the customer can backfeed more then they're expecting, can that be limited with filling up the batteries? (Does get back to the "How much money are we losing?" question from the PoCo.)