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

Wed Aug 7 07:49:07 PDT 2024

Hopefully the utilities will start to change their policies with more and
more demand for meter socket MIDs. They really make a lot of sense, and
we've found that the process with our local utility PG&E is fairly
straightforward. These socket adapters make sense for emergency generators (
https://www.pge.com/en/outages-and-safety/outage-preparedness-and-support/general-outage-resources/backup-power-transfer-meter-program.html)
and eventually vehicle to grid/home as well.

Just to clarify, for PV only, the Tesla Solar Inverter can do PCS panel
limits without an MID - you just need CTs around the utility side feed.

Anyway, I'm excited for all these changes and hope all manufacturers get
PCS rolling.

On Wed, Aug 7, 2024 at 7:24 AM Jason Szumlanski <
jason at floridasolardesigngroup.com> wrote:

> I spoke to my engineer, and he had a discussion with Enphase about this
> months ago. Apparently, there was a testing issue with PCS, and Enphase was
> looking at retesting, maybe with a new NRTL. I reached out to Enphase
> engineering and will report back if I get any new information.
>
> Regarding the sockets... Florida Power & Light vehemently rejected the
> ConnectDER and, from what I understand, also does not accept the Tesla
> Backup Switch. They do not allow anything connected to the meter socket
> that they do not provide. After all, how are they going to steal $12 a
> month from people for their surge protector otherwise?! And there is no
> more than a snowball's chance that the local municipal electric provider
> will allow it. So meter socket based transfer switches are out around here.
>
> That puts Enphase at an advantage over Tesla here for simple PV only
> systems, since Enphase should be able to implement PCS with their
> relatively low cost gateway, whereas Tesla will need to install a MID,
> which could require a meter disconnect/reconnect, and that can be a
> nightmare to schedule and coordinate here.
>
>
> 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 Wed, Aug 7, 2024 at 10:10 AM August Goers <august at luminalt.com> wrote:
>
>> Hi Jason - I suspect that Enphase is working on the "panel limits" type
>> feature, it really makes a lot of sense as you point out. Tesla has been
>> rolling out PCS features at a rapid pace - their solar inverter now has
>> panel limits whereas it didn't a few months ago. To respond to one of your
>> comments, we can also use panel limits with the Backup Switch which is
>> Tesla's meter socket Microgrid Interconnect Device (MID). The Backup Switch
>> has the site metering built in. Installations with Backup Switch and
>> Powerwall for whole-home backup are nearly as fast as PV-only builds.
>>
>> I heard from our Enphase rep that they are hopefully releasing their
>> meter socket adapter product in Q1 of 2025. Game changer!
>>
>> August
>>
>>
>> On Wed, Aug 7, 2024 at 6:46 AM Jason Szumlanski <
>> jason at floridasolardesigngroup.com> wrote:
>>
>>> I confirmed via this video (
>>> 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
>>>
>>>
>>> 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>
>>>> 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-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> 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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>>>
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