Wouldn't the microinverters shut down if the voltage rose? They
wouldn't be able to raise voltage about PUC/DPU limits I would think.
They would shut down on high voltage. I am saying this because of an
experience this fall where our infamous Block Island Power Company
raised the taps on a local xfmr due to their "secret heat pump program"
that was dragging down local voltage. They claimed solar was a burden,
but were quiet on the load building program they embarked upon without
any disclosure. When the cooling loads disappeared, the voltage went
above our grid tied systems set points and they shut down. We told the
utility they had a high voltage problem and they adjusted the taps. Of
course they did not acknowledge or thank us. It seems our little coop
which is now head from a guy from the Vermont Electric Coop is taking an
old utility approach instead of cooperation, integration and
maximization of performance and economics.
I'd think you be able to ask how the supply can raise the voltage when
there is so much diversified load on the same device. Electricians
have to do a diversity calculation, and I know a utility has to conduct
them as part of these studies. Worse case of no load and all generation
is such a low probability that to design for it, when/if it occurred, is
not a danger and of no material consequence makes little sense. But,
we've been dealing with that ever since this person arrived in our neck
of the woods.
Chris Warfel
On 12/25/2022 5:21 PM, Garrison via RE-wrenches wrote:
Hi William,
One possible path forward would be to ask the utility co what AC
inverter capacity would be allowed. Maybe the solution would be to
unplug a micro or two if you are just over the limit. Even better,
maybe they would allow you set an export limit on the micros you have
installed.
I had a recent situation where a 40kW DC system had exceeded a utility
transformer by only 2kW AC, so a simple redesign avoided an $8k
invoice from the utility. The utility was not transparent about this
option at first and only made it clear after some persistence.
Good luck,
Garrison Riegel
Celestar Solar
On Dec 25, 2022, at 3:14 PM, Darryl Thayer via RE-wrenches
<re-wrenches@lists.re-wrenches.org> wrote:
It is common practice for the utility to overload the transformer a
lot for the potential load. They expect no one will use their
service at maximum, furthermore, they expect non coincidence of
loads. Look at the transformer most have a label as to the kW or the
unit, and the utility should give you that number along with the
impedance. Note I have had area engineers not understand that solar
reduces the load on the transformer. They have two concerns, you
will overload and you will raise the voltage to other customers.
Overload is ridiculous; the transformer must be at least 20 kW if a
15 kW concern is valid. However, raising the voltage is not. If all
the customers shut off their power, the voltage would rise to the
inverter limit,and/or feed current back on the distribution line
raising up/downstream customers voltage. I have had this problem, on
three occasions discussions with the utility upper engineering, not
local engineer, i prevailed, one case I did not. In one cast
utility allowed connection and put a voltage monitor on secondary
voltage, then later allowed permanent connection.. Good luck
On Sun, Dec 25, 2022 at 1:16 PM William Miller via RE-wrenches
<re-wrenches@lists.re-wrenches.org> wrote:
Wrenched:
Merry Christmas to those of you that observe such traditions, or
substitute the winter festivity of your choice.
I helped a previous employee install an Enphase IQ8 system on his
home. He applied for the utility approval concurrently with his
building permit The day he got his final inspection the utility
contacted him and claimed "The aggregate generation exceeds the
identified transformer rating" and refused him a Permission to
Operate letter.
Adding up the service ratings of the homes on his secondary we
get about 336 kW of potential consumption. Adding the grid-tied
systems on his secondary we get about 16.5 kW. How is it that
the back-feed exceeds the transformer rating?
I would appreciate any insight on how to consider this situation
and how to fight it.
Sincerely,
William Miller
Miller Solar
17395 Oak Road, Atascadero, CA 93422
805-438-5600
www.millersolar.com <http://www.millersolar.com/>
CA Lic. 773985
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Christopher Warfel
ENTECH Engineering, Inc.
PO Box 871, Block Island, RI 02807
401-466-8978
<http://entech-engineering.com>
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