[RE-wrenches] Power Control System for Main Panel Upgrade Avoidance

Wed Aug 7 06:46:18 PDT 2024

I confirmed via this video
(https://app.gotowebinar.com/unified/index.html#/webinar/6915785636472410201/attend/2085639858551605341
[https://app.gotowebinar.com/unified/index.html#/webinar/6915785636472410201/attend/2085639858551605341])
that Enphase does, in fact, limit backfeed based on the 120% rule when
implementing PCS for main panel upgrade avoidance. That is disappointing.

Based on my reading of 705.13(B), as long as the utility feed is monitored by
the PCS, the PCS only needs to limit the PV source such that the TOTAL current
from all sources does not exceed the busbar ampacity rating. Since Enphase can
implement consumption monitoring with CTs on the line side of the main panel,
they should be able to limit PV backfeed based on how much current is coming
from the utility company rather than the far more limiting 120% rule. This
seriously diminishes the value of Enphase's PCS implementation for main panel
upgrade avoidance.

To be fair, Tesla's PCS, to accomplish what I want, requires a Gateway (MID).
that significantly adds to the cost and complexity, and is really intended for
Powerwall systems. But Enphase should be able to implement PCS this way using
it's IQ Gateway without their System Controller (MID) for grid-interactive PV
systems without batteries. This appears to be a big miss on the part of Enphase.
Maybe they are misinterpreting 705.13(B), or maybe there is a technical reason
that they can't comply in this manner.

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208

[data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=3D]
On Tue, Aug 6, 2024 at 10:36 AM Jason Szumlanski
<jason at floridasolardesigngroup.com> wrote:

> Very interesting. Thanks for this information. It seems like Tesla has
> implemented PCS in the way that I hoped it would be. They can set an
> aggregate current limit from all sources feeding a bus.
> 
> Unless I am mistaken, Enphase can only limit based on a selected
> ampacity of *backfeed* from their System Controller to a main panel.
> It does not measure the incoming utility power and set an aggregate
> output limit from all sources. That results in a 40A backfeed limit on
> a 200A panel, which does not make sense to me.
> 
> I hope I have this wrong.
> 
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida State Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
> 
> On Tue, Aug 6, 2024 at 10:30 AM August Goers <august at luminalt.com
> [august at luminalt.com]> wrote:
> >
> > Hi Jason -
> >
> > There are many options on how a manufacturer can implement Power Control
> Systems (PCS) and based on my experience with Tesla products, I'd say it's the
> best thing since sliced bread. I expect that all major manufactures will be
> implementing more advanced PCS features as soon as they are able to develop
> and list them.
> >
> > But, getting back to your question - one PCS variant is a simple conductor
> limit setting that stops controlled equipment output when a certain set
> current limit is reached. This, as you point out, may not be the best choice
> for large PV/inverter systems. Another PCS setting involves setting a
> controlled "virtual panel" where all inputs are monitored. This PCS setting
> can be, for example, 160 Amps in your 200 A meter/main example. Here is more
> info on how that works: https://service.tesla.com/docs
> /Public/Energy/Powerwall/Powerwall-2-Backup-Gateway-2-Instal
> lation-Manual-NA-EN/GUID-D71DFD63-1414-4915-B7A5-7E48703100DE.html
> [https://service.tesla.com/docs/Public/Energy/Powerwall/Powerwall-2-Backup-Gateway-2-Installation-Manual-NA-EN/GUID-D71DFD63-1414-4915-B7A5-7E48703100DE.html]
> >
> > I'm working on learning more about Enphase systems currently since SunPower
> is filing for bankruptcy, so it's good to learn what Enphase can and can't do
> at this point.
> >
> > Best, August
> >
> >
> > On Thu, Aug 1, 2024 at 10:40 AM Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org [re-wrenches at lists.re-wrenches.org]> wrote:
> >>
> >> Note: This email is written from the perspective of the Enphase
> >> terminology, but the concept and question is the same in a general
> >> sense.
> >>
> >>
> >> I am having a hard time understanding the logic and benefit of a power
> >> control system that is used for avoiding a main panel upgrade in a
> >> typical residence. If you have a 200A main panel bus with a 200A main
> >> breaker, the current limit for a backfed breaker is 32A from the PV,
> >> no matter what. The PCS will artificially reduce the PV output to 32A
> >> when it could be capable of a much higher current for large systems
> >> depending on sunlight availability. That would waste a lot of energy
> >> if the PV system is significantly larger than a 32A output rating.
> >>
> >> The PCS standards seem to have missed the mark. Wouldn't it make more
> >> sense to limit the total current delivered to the bus from all
> >> sources? For example, in the example above, if PV is delivering 40A,
> >> why not allow limiting utility input to 120A for a total of 160A
> >> continuous delivered to the bus before PV is throttled? If the utility
> >> is delivering zero, the PV could deliver all the way up to 160A the
> >> the bus if capable. That way, all of the loads would be powered to the
> >> maximum extent from PV with the excess exported (if allowed via net
> >> metering from the serving utility).
> >>
> >> Am I missing something about how PCS works? I just don't see many use
> >> cases for main panel avoidance that are in customers' best interest.
> >> If we can't meet the 120% rule, we just do supply-side
> >> interconnections so nothing is wasted. But a backfed breaker would be
> >> so much easier if PCS were implemented in the way that I would like it
> >> to work.
> >>
> >> Jason Szumlanski
> >> Florida Solar Design Group
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