a NG here. be gentle.

[jaggedben]

I installed a system at my house this past Spring. ~7.5 kWdc / 7.6 kWac SolarEdge system with DC coupled StorEdge inverter. The DC coupled nature of the StorEdge and Solark is a great feature as you only have one grid connected inverter. The Enphase and Tesla systems use dedicated AC coupled batteries if I recall correctly. This makes interconnecting to your house and the grid a bit trickier since both devices can independently dump power to the loads. In our area (National Grid) there is a 10 kW limit on net metered grid tied systems. You could easily surpass this limit with AC coupled solar+storage and the utility could hit you with a price tag of a new transformer at the street.

DC coupled systems also have the inherent benefit of DC clipping recapture, meaning you can safely oversize the PV and have any normally clipped power from the array get dumped into the batteries rather than being curtailed when the inverter reaches nameplate.

Some residential scale energy storage systems are limited to 5 kW of output power meaning you cannot reasonably back up your whole house (an electric dryer is a 5 kW load, for scale). SolarEdge recently rolled out a system called EnergyHub, which essentially is a "smart" transfer switch that gets installed between your utility meter and your main loads center. This 200A rated device allows you to safely island the whole house with a set of StorEdge inverters and up to two batteries (9.8 kWh each) per inverter.

Adding a significant amount of energy storage will raise an eyebrow from a savy local wiring inspector. There are sections in the International Fire Code that will require a 2 hour rated fire room, sprinklered, with a fire alarm and monitoring to a central dispatch. In my research, there seemed to be a threshold at 20 kWh under which these strict and expensive requirements were not not mandated.

Lastly, residential energy storage does not make much financial sense unless 1.) there is an active incentive plan in your area by the utility or the state, and 2.) you lose power once or more per month. The storage equipment for my system was ~$12k.

Interesting comments.

I don't really see more than a marginal benefit to 'clipping recapture.' If your batteries discharged overnight you'll want to start charging them in the morning, before clipping becomes a thing. If your batteries have already charged to full, then the clipped energy still has no where special to go and normal clipping occurs. How often are you actually gonna end up in a window where you're somewhere in between, and how much energy will that amount to? I'm just commenting on my hunch here, but it doesn't seem like it will be that much.

 

[jaggedben]

...

My understanding is that buildings subject to the IRC are exempt from those sections of the IFC, and the IRC has its own, less onerous requirements. But some jurisdictions around here are acting as if they have amended away the IRC exemption (and if they have not actually does so, are acting illegally, in my opinion).

I don't recall it being that way when I read those sections. The exception states something like 'buildings built in accordance with the residential code.' That's not just any residence. Many residences, such as ones that predate the residential code, would not qualify. So I think it would be a hard case to win, even if you were willing to go toe-to-toe on it with an AHJ, which most people aren't. For a given building, it would be up to you to prove it conforms to the residential code, which is probably going to be a tall order except for new construction.

 

[wwhitney]

Adding a significant amount of energy storage will raise an eyebrow from a savy local wiring inspector. There are sections in the International Fire Code that will require a 2 hour rated fire room, sprinklered, with a fire alarm and monitoring to a central dispatch. In my research, there seemed to be a threshold at 20 kWh under which these strict and expensive requirements were not not mandated.

By my reading of the I-Codes (IFC and IBC), the 2 hour rated room requirements do not apply to dwelling units (IBC 509.1 Exception). And the onerous IFC 1206.2.8.3 interior separation requirements (individual arrays not to exceed 50 kWh separated 3 feet from each other and from walls) do not apply to listed preengineered stationary storage battery systems (presumably listed to UL 9540) if they are under 250 kWh, per Exception 2. Although that exception could instead be read to mean only that the individual array limit is increased to 250 kWh for listed systems, not that they are also exempt from the separation requirements.

I don't recall it being that way when I read those sections. The exception states something like 'buildings built in accordance with the residential code.'

The 2018 wording in IFC 102.5 is "where structures are designed and constructed in accordance with the International Residential Code". I would read that to mean "for work permitted under the IRC" rather than as "for buildings fully compliant with the current IRC." [The IFC does not define the word "structure".]

Cheers, Wayne

 

[jaggedben]

The 2018 wording in IFC 102.5 is "where structures are designed and constructed in accordance with the International Residential Code". I would read that to mean "for work permitted under the IRC" rather than as "for buildings fully compliant with the current IRC." [The IFC does not define the word "structure".]

Cheers, Wayne

Are you trying to argue that installing equipment is the same as building a structure? That seems quite a stretch. Note: it doesn't say 'covered by the residential code'. It says what it says. If you're going to argue that a house built in the 1920's was designed and constructed in accordance with a code that didn't exist then, I think you need some other part of the code to back up your interpretation.

 

[wwhitney]

I admit to a somewhat motivated reading. Where there is some ambiguity I prefer to interpret the ambiguity in a way that seems reasonable. If an existing house is non compliant with the current IRC because, say, the porch knee wall is too short, it makes no sense for that fact to have any bearing on whether a newly installed stationary battery storage system in the garage or the basement has to meet certain separation requirements.

In general the codes are written about new buildings, and they apply to existing buildings only to the extent that modifications are occurring. So if I were building an addition to an existing house, with work permitted under the IRC, in my book the addition would qualify as a structure "designed and constructed in accordance with" the IRC. So I would expect the IFC to only apply to that addition to the extent listed in IFC 102.5, regardless of what other deficiencies might exist in the existing house.

Cheers, Wayne

 

[BandGap1.1eV]

Interesting comments.

I don't really see more than a marginal benefit to 'clipping recapture.' If your batteries discharged overnight you'll want to start charging them in the morning, before clipping becomes a thing. If your batteries have already charged to full, then the clipped energy still has no where special to go and normal clipping occurs. How often are you actually gonna end up in a window where you're somewhere in between, and how much energy will that amount to? I'm just commenting on my hunch here, but it doesn't seem like it will be that much.

We're seeing industrial and utility scale PV systems in our area being designed with massive DC/AC ratios (anywhere from 3:1-5:1) with DC coupled storage. The design strategy is to stay low on the AC side to get your best chance at avoiding significant grid upgrade costs from the utility and avoid ISO involvement. Then put in enough DC/DC converters and kWhs of storage to absorb the clipped energy during the day for discharge later in the afternoon/evening. Your production curve looks like a square wave.

 

[BandGap1.1eV]

I don't recall it being that way when I read those sections. The exception states something like 'buildings built in accordance with the residential code.' That's not just any residence. Many residences, such as ones that predate the residential code, would not qualify. So I think it would be a hard case to win, even if you were willing to go toe-to-toe on it with an AHJ, which most people aren't. For a given building, it would be up to you to prove it conforms to the residential code, which is probably going to be a tall order except for new construction.

This also requires the inspectors to be educated and open minded about reading and understanding the code. Telling an inspector they are wrong is a non-starter. We had an inspector on a commercial job ask if the EMT already in the wall (building was built as solar ready) had the required reflective labels. We replied, "well, no, but it's clearly not exposed and was installed in the wall cavity years ago" to which he replied "so you're saying it was exposed at one point in the past?"

 

[gadfly56]

We're seeing industrial and utility scale PV systems in our area being designed with massive DC/AC ratios (anywhere from 3:1-5:1) with DC coupled storage. The design strategy is to stay low on the AC side to get your best chance at avoiding significant grid upgrade costs from the utility and avoid ISO involvement. Then put in enough DC/DC converters and kWhs of storage to absorb the clipped energy during the day for discharge later in the afternoon/evening. Your production curve looks like a square wave.

And what do your battery + installation costs look like?

 

[jaggedben]

We're seeing industrial and utility scale PV systems in our area being designed with massive DC/AC ratios (anywhere from 3:1-5:1) with DC coupled storage. The design strategy is to stay low on the AC side to get your best chance at avoiding significant grid upgrade costs from the utility and avoid ISO involvement. Then put in enough DC/DC converters and kWhs of storage to absorb the clipped energy during the day for discharge later in the afternoon/evening. Your production curve looks like a square wave.

I see. That makes a lot more sense than in a residential setting.

 

[jaggedben]

I admit to a somewhat motivated reading. Where there is some ambiguity I prefer to interpret the ambiguity in a way that seems reasonable. If an existing house is non compliant with the current IRC because, say, the porch knee wall is too short, it makes no sense for that fact to have any bearing on whether a newly installed stationary battery storage system in the garage or the basement has to meet certain separation requirements.

In general the codes are written about new buildings, and they apply to existing buildings only to the extent that modifications are occurring. So if I were building an addition to an existing house, with work permitted under the IRC, in my book the addition would qualify as a structure "designed and constructed in accordance with" the IRC. So I would expect the IFC to only apply to that addition to the extent listed in IFC 102.5, regardless of what other deficiencies might exist in the existing house.

Cheers, Wayne

As regards your first paragraph and your comment about the porch knee wall, it is my experience that in existing houses of a certain age almost nothing is compliant with current codes. Not rafter sizes and spans, or wall construction, or firewall ratings, or many other things that could make an energy storage installation in new buildings and older buildings quite possibly a very different risk in a fire or earthquake. In other words you may have no compliant location to install energy storage, unless you remodel the house. I'm not saying that the code should be written this way, just that if the AHJ wants to make that argument I'm not sure what can reasonably be said against it.

Regarding your second paragraph, AFAIK it is entirely the decision of AHJs whether to retroactively apply code to any portion of a building in order to issue a permit or pass an inspection. The codes themselves generally say nothing about it, AFAIK. I've experienced several AHJs policies and a couple state laws that specify certain upgrades required based on certain triggers. As far as I can tell that's perfectly legal, and I'm not sure if there's anything other than convention and reasonableness that prevents AHJs from going further.

 

[wwhitney]

If an AHJ took the position you're describing, I'd continue to argue against it somewhat more, but ultimately I can't point to anything to definitely rebut it.

But I would like to say that my position (based on the earlier arguments) is nicely summarized by saying that as the word "structures" in the quoted part of IFC 102.5 is not defined the IFC, and as the IFC is generally about structures, the word is being used just as a synonym for "construction". I.e. it need not imply any scope expansion to the whole building, as opposed to the project under consideration.

Cheers, Wayne

P.S. I agree with you about the certain triggers, but in my (more limited) experience they are explicit and spelled out in local ordinance. Adding smoke detectors if not present is a very common one. And in my area mandated sewer lateral upgrades/certifications are another (as anti ground water pollution measure).