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

[August Goers]

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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