[RE-wrenches] Low grid voltage fix

Mon Dec 20 10:07:42 PST 2010

No one should put up with grid voltages "out of range". Immediately inform
your utility: tell them where, when and how often you measured (or your
inverter registered) the out of range voltages. It turns out that you are
doing them a favor and they often appreciate the information.

What we measure with a DMM is an average of a second or so, and there are
short term transients on top of this average that often are as much as +/- 5
Volts. Since inverters measure and respond on the order of 10 milliseconds,
they can provide a means of assessing the health of the grid, which goes
beyond DMM measurements.

A couple of stories:

We responded to a "bad inverter call" where the inverter in question kept
shutting down in the AM. We measured Vac = 252 V around 10 AM pretty
consistently, but the transients kept taking out the inverter. SCE traced
the problem to a nearby firm that was throwing a lot of transients onto the
grid from their equipment.

At our home office, we had our inverter trip a couple of times (thanks to a
TED monitor, we saw it happen in real time) and we called LADWP. To their
credit, they had a technician out THE SAME DAY. They also called us the
following day to say that they looked into the situation and discovered that
they had recently bumped the voltage in our neighborhood, and consequently
backed it off a bit. We then got a call a couple of days later to inquire if
everything was okay (it was). I may be critical of some of the things LADWP
does, but in this case I was very impressed.

As for a high or low (but still compliant) average voltage, the utilities
constantly adjust the "taps" on their distribution transformers, sometimes
for seasonal reasons and sometimes for changing demand (imagine a bunch of
apartments complexes being built in a previously single family dwelling
neighborhood).

Again, don't be shy. If (a) your inverters are shutting down and indicating
out of range grid voltages or (b) you measure Vac within five volts or so of
264 or 216 V, let your utility know.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of frenergy
Sent: Sunday, December 19, 2010 4:49 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Low grid voltage fix

Joel,

        Unrelated, mostly.  I got a call from a customer a few weeks ago 
that was claiming his inverter had failed working.  When I arrived it was in

fact not working and gave a code that the grid voltage was too high.  I 
called Fronius and they said they sometimes have had to replace a card to 
fix this sometimes, but also suggested that I check the grid voltage first, 
just in case.

        I was a bit surprised to find 270 VAC L-L, 135VAC L-Gnd.  Out of 
disbelief, I checked it with another meter and got the same readings.  This 
was PG&E, NE Ca.  Service dude came at customer's request and claimed the 
"voltage reg" was not adjusted properly. Problem fixed.

Bill

Feather River Solar Electric
4291 Nelson St.
Taylorsville, CA  95983
530-284-7849/6544 fax

----- Original Message ----- 
From: "Joel Davidson" <joel.davidson at sbcglobal.net>
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Sent: Sunday, December 19, 2010 9:24 AM
Subject: [RE-wrenches] Low grid voltage fix

> Wrenches,
>
> It's Christmas time again in Southern California Edison (SCE) territory 
> which means low insolation and high regional electric consumption. Every 
> night SCE voltage drops to around 105 VAC or lower. Our grid-tie SW4048 
> inverter sees SCE's low voltage as a brownout and switches to autonomous 
> mode which is normal. However, we have only 4 kWh of battery storage so 
> the combination of nightly brownouts and a series of cloudy days 
> eventually depletes our battery bank causing the inverter to do a 
> low-voltage shut down which is normal. Power goes off in our home and we 
> have to switch over to SCE power, reset the inverter, and wait until the 
> battery bank is recharged. How do we set the SW4048 to accept as low as 
> 100 VAC from the grid before switching to autonomous mode?
>
> Joel Davidson
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