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

[Jason Szumlanski]

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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