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

[Jason Szumlanski]

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