feedback on DOE-sponsored residential Plug and Play PV prototype system

[THCleveland]

I am part of a university team working on a Department of Energy funded project to develop a Plug and Play residential PV system and am seeking feedback regarding a possible roadmap for such a system to eliminate, or significantly automate, both electrical permitting and inspection. Our scope does not cover structural permitting or inspection.

The prototype system is based around what we call the PV Utility Interface (PUI) which is a smart PV receptacle that is installed by the utility between the existing meter socket and residential meter. The PUI communicates to Plug and Play (PnP) inverters and PV modules. This communication allows several features, including auto-authentication that all inverters and modules are properly listed. The PUI also provides AC arc fault and ground fault protection, continuous verification that only approved modules and inverters are generating, DC connector resistance checks, module Voc checks (indicator of module damage/malfunction), and inverter efficiency checks (indicator of inverter damage/malfunction). We believe the ability to conduct a daily AC insulation resistance test could and should be added to the PUI. It may also be possible to add the ability for the PUI to measure the length and resistance of the AC cable between the last inverter and the PUI as a way to validate that it has adequate current carrying capacity. Without this feature, adequate cable capacity is assured by the unique AC PnP connector that is only available on a single capacity cable, which is equal to the capacity of the PUI with that AC PnP connector. The PUI conducts its system auto-inspection every day before startup for the life of the system. The vision is that the PUI would be listed to a yet-to-be-defined UL standard covering these auto-inspection features. The PUI could also potentially determine which AHJ's jurisdiction it is installed in and engage or disengage features depending on if that AHJ allows PnP PV to waive in-person electrical inspection.

For more details about the system, including some photos of the prototype system, please review this PDF presentation.

Click this link to complete an online survey supplying feedback on the PnP PV system. The survey is expected to take between 10 minutes and 30 minutes depending on the depth of answers. Your feedback here is most helpful to the project.

For discussion in the forum, here are some seed questions:

1. Considering the plug and play nature of the system connections and the safety provided by the PUI auto-inspection features, do you think such a system could be safely installed by anyone besides a licensed electrical contractor? Where would you draw the line for a "qualified person" for installing the electrical aspects of this system?
2. Based on the prototype system description in the attached presentation, do you have any safety concerns were such systems to be installed without a traditional electrical inspection? (assuming all features verified with appropriate UL listings, likely including 1 or more yet-to-be-created Plug and Play related standards)
3. As an AHJ, would you consider supporting a policy that would allow this type of Plug and Play system to be installed on homes in your jurisdiction without an electrical inspection? Why or Why not? What information or data would you need to see to consider supporting such a policy?
4. Are you concerned about the safety of the AC cable on the exterior of the building between the last inverter on the roof and the PV inlet on the PUI near ground level if there is no visual inspection of the installation? Why or why not?
5. Do you think that any portion of the AC cable needs to be in conduit? Why or why not? Note that the PUI in the prototype system includes a 6' cord preinstalled in flexible conduit, this allows the AC cable from the roof to plug into this PUI cord at least 8 feet above grade in most, but not all, situations.
6. What is your general reaction to the system and its possibility to eliminate electrical inspections?

Thanks for sharing your expertise and experience!

 

[petersonra]

inspection and permitting is largely about making sure local governments can jack up your real estate taxes if you increase the value of your property and controlling as much of your life as they can. they are not going to give up any of that.

even if none of that were the case, what makes you think any of this will reduce inspection and permitting requirements?

maybe I am missing the point but unless the system is essentially something the HO can go to Walmart and buy and plug in himself like he would plug in a new TV, I see it making the system more complex with little or no benefit.

inspectors hate cord (for mostly no real good reason). you will find that a tough thing to get past.

I would not be adding chunks of conduit to the system. That just gets away from the ease of the HO installing his own system. You will probably have to find some kind of cable that can be installed exposed outside and use that. I don't think there is such a thing recognized in the code. As long as the cable is in a place where damage is iulikely I don't see an issue with finding something suitable, but it will be very hard to convince old timers of this.

ETA: Maybe MC that has been preterminated to some kind of plug. Keep in mind that both ends of the connection can be live so there may not be a safe way to use such a receptacle system.

 

[TommyO]

ETA: Maybe MC that has been preterminated to some kind of plug. Keep in mind that both ends of the connection can be live so there may not be a safe way to use such a receptacle system.

With intelligent electronics on both sides, making it safe to plug in is very doable.
For example, see car EV plugs - very little voltage until the two sides handshake, do some checks, and agree on the power to be delivered.

Un-plugging without arcing I would think is probably a little more challenging - but I *think* EV plugs deal with that as well - that part I'm not as sure about.

The permitting/inspection process for solar also includes the mechanical/fire aspect. ex. that there is access to the roof for firemen, and that the panels and such aren't putting too much load on the structure. I can't see a way to get away from that.

 

[jaggedben]

The whole thing strikes me as ridiculously quixotic.

Perhaps the most salient point, which has already been alluded to, is that the real obstacle to something like this is not technical. It's political and institutional. To begin with, your idea of eliminating inspections will in most cases run afoul of some state or local law that in some way requires them.

Second, if the idea is that amateurs can install PV and that this device of yours will do everything to keep them from setting houses on fire, I think the result will be a lot of systems that your device refuses to turn on. :lol:

...The PUI communicates to Plug and Play (PnP) inverters and PV modules.

Since these don't exist, are you working to get the major manufacturers on board?

The PUI also provides ...DC connector resistance checks, module Voc checks (indicator of module damage/malfunction),

Surely it doesn't do this by itself, right? It must be passed through the inverter.

We believe the ability to conduct a daily AC insulation resistance test could and should be added to the PUI. It may also be possible to add the ability for the PUI to measure the length and resistance of the AC cable between the last inverter and the PUI as a way to validate that it has adequate current carrying capacity.

Maybe you could have it do this for the rest of the house as well? Seriously, holding AC wiring for PV to a higher standard than other AC wiring is an idea I wish would die, not be encouraged.

Without this feature, adequate cable capacity is assured by the unique AC PnP connector that is only available on a single capacity cable, which is equal to the capacity of the PUI with that AC PnP connector.

I don't get it. Someone could just cut your cable in the middle and splice their own wiring product in between the two ends.

Considering the plug and play nature of the system connections and the safety provided by the PUI auto-inspection features, do you think such a system could be safely installed by anyone besides a licensed electrical [or solar] contractor?

No, and the law will agree in most states.

Based on the prototype system description in the attached presentation, do you have any safety concerns were such systems to be installed without a traditional electrical inspection? (assuming all features verified with appropriate UL listings, likely including 1 or more yet-to-be-created Plug and Play related standards)

As I said above, my concern is that systems installed by amateurs would have so many problems that your device would frequently shut them down.

Are you concerned about the safety of the AC cable on the exterior of the building between the last inverter on the roof and the PV inlet on the PUI near ground level if there is no visual inspection of the installation? Why or why not?

For a million reasons, yes.

Do you think that any portion of the AC cable needs to be in conduit? Why or why not? Note that the PUI in the prototype system includes a 6' cord preinstalled in flexible conduit, this allows the AC cable from the roof to plug into this PUI cord at least 8 feet above grade in most, but not all, situations.

Currently we install the entire AC wiring in conduit from the edge of the solar array to wherever it interconnects. So yes, you are proposing something radically different than the way we do it, at least here in the States. With the scant details you've provided, it doesn't sound like it makes a lot of sense.

What is your general reaction to the system and its possibility to eliminate electrical inspections?

As an installer, if it adds hassles to installation itself, or requires more than one post-install visit for trouble shooting, it's not worth it.

 

[jaggedben]

Oh, and finally, the fire departments will really hate it, and some houses roofs may cave in.

 

[ggunn]

IMO, the safe installation of a PV system which will supply enough energy to make an appreciable difference to a household's electric bill is far beyond the ability of the average homeowner. Those cheap illegal single module "plug and play" rigs are not worth the trouble or the risk.

 

[GoldDigger]

IMO, the safe installation of a PV system which will supply enough energy to make an appreciable difference to a household's electric bill is far beyond the ability of the average homeowner. Those cheap illegal single module "plug and play" rigs are not worth the trouble or the risk.

There is currently, AFAIK, only one "plug and play" grid tie system available. The catch is that you plug it into a custom receptacle that has been installed on a dedicated circuit by a licensed electrician, and the electrician still has to worry about the 120% rule and other little gotchas.
But you can call it plug and play once the receptacle has been installed. :angel:

I see this offering as going in the same direction, except that it adds a lot of probably unnecessary communications and bells and whistles and still depends on the fixed wiring side of the interface either being easily installed or being a default part of all new construction. Neither of which I am optimistic about.

 

[SolarPro]

The vision is that the PUI would be listed to a yet-to-be-defined UL standard covering these auto-inspection features.

That sounds like a long and drawn out process, especially since there isn't an existing international standard to copy. If that's a 3 year process (or more), I suspect that state-of-the-art solar technology will be better positioned to provide a low-cost plug & play experience than the system proposed here. Say what you will about the use of conduit in the US, but I believe you'll find that it is far more affordable in practice than the custom connectors and cable assemblies shown here.

What I like about this plug & play proposal as compared to others I've reviewed is that it is geared specifically toward expediting the inspection process. Given how smart the power electronics are becoming, I think this is worthy goal that can reasonably be achieved by setting expectations for the technology and developing new product safety standards.

But I don't foresee customer-installed PV systems being viable in the near term. For one, you'd have to eliminate NEC 690.4(C), which states that PV systems shall be installed and interconnected by qualified persons. I suspect that would be a difficult battle to win. Second, many plug & play proposals seem to underestimate the aesthetic requirements and expectations of US consumers. It doesn't really make sense to install a power system on your largest investment (your home) if doing so reduces its market value. And repairing damage caused by a single roof leak far outweighs the annual energy savings provided by a what I suspect would be a typical owner-installed PV system.

As NEC requirements evolve and downward price pressures increase over time, I expect that the market will develop very smart and streamlined PV systems that are far simpler and more elegant than this particular plug & play proposal. At some point, the systems may be perceived as inherently safe, in which case there may be no need for qualified persons to install the systems. But until we have touch-safe PV modules, I think that's pipe dream.

A more likely plug & play future, IMO, involves next-generation building codes, which include "solar-ready" design standards. Couple these advanced building codes with touch-safe PV modules and a UL auto-inspection standard. Bob's your uncle. Adding PV looks pretty simple.

 

[fmtjfw]

POCO support??

POCO support??

The other thing is that it requires the POCO to roll a truck to your house and add the dongle between the meter and the socket. Given the antipathy more and more POCOs are exhibiting towards solar (It won't become mainstream 'til they figure how to meter sunbeams (and charge for them)) I can't imagine support for such a scheme from them.

 

[petersonra]

The other thing is that it requires the POCO to roll a truck to your house and add the dongle between the meter and the socket. Given the antipathy more and more POCOs are exhibiting towards solar (It won't become mainstream 'til they figure how to meter sunbeams (and charge for them)) I can't imagine support for such a scheme from them.

most pocos no longer sell electricity, so why would they care?