[RE-wrenches] 2KW PCS import/export limit on a 25KW transformer; Oncor in Texas

[Zeke Yewdall]

I do not know how they do it in Texas, but in Colorado, it's pretty typical
to run a 200A (38kW continuous) service from a 10kVA transformer.  Or even
several houses with 100 to 200A services from a single 10 or 15kVA
transformer.  If all even a few of the houses start drawing anywhere
near their full amperage for a long period of the time (grow operations
were the common reason for this) the transformer explodes.  They are
apparently relying on the very low typical load factor for residential
services. Many of these are older services installed in the 70's to 90's,
but some are newer ones and still not a 25kVA transformer for a 200A
service that would seem more reasonable.  A grid tied PV system will often
load the transformer much higher than typical residential loads because of
the long hours of operation.

I've had two ESS/PV systems recently where they required a transformer
upgrade before they would allow me to backfeed at full system capacity.
Both were all in one inverters, not separate PV and ESS inverters.  In one
case I had 10.135kW CEC rating of inverter capacity on a 10kVA transformer,
but in the other case they calculated that I could not go over 6.6kVA of
export on a 10kVA transformer for some reason -- this was on a brand new
service, new construction, so I was quite surprised by this limit.  2kW
seems insanely low for a 25kVA transformer to me.  In both of my cases in
Colorado, they are upgrading the transformers to 25kVA at very little cost
to the customer -- $300, which I figure is 10% or less the actual cost --
so we opted for the transformer upgrade rather than limiting export.
Sounds like Oncor is charging actual cost for the transformer upgrade?

-- 
Zeke Yewdall
PV Engineer
NABCEP #031508-89
zeke at darkforestsolar.com
303-523-3592
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