Hi Michael,
Using your figures of 450 MW of installed PV in California, 4.5 sun-hours, and
$0.15/kW-h, I get $1.1 million lost for each 1% of total of downtime. Not
massive in the overall scheme of things, but not insignificant. (My math too
is subject to review...)
4.50E+09 watts of PV in CA
4.5 avg sun-hours/day
2.03E+09 total w-h/day
365 days/year
7.39E+11 watt-hours/year
7.39E+08 Convert to kWh/year
$0.15 Avg $ per kWh
$110,868,750 Annual value of PV energy
$ 1,108,688 Loss for each 1% down time
I deal with UL constantly on the "sensitivity" issue. High line voltage not
withstanding .. it makes even MORE sense to have grid-tied systems stay online
during brownouts .. when they're needed most .. yet grid-tied systems are
required to drop offline around 108/216 Vac (+/-)
Conversations I've had with utility company execs over the years have all been
the same; they feel the UL specs make grid-tie systems "too twitchy".
I'm in complete agreement with William AND the execs....
Unfortunately, there doesn't appear to be any likelihood of relaxation of these
rules any time soon.
Dan
--- On Sun, 8/16/09, Michael Welch <michael.we...@re-wrenches.org> wrote:
From: Michael Welch <michael.we...@re-wrenches.org>
Subject: Re: [RE-wrenches] utility line voltage issues
To: "RE-wrenches" <re-wrenches@lists.re-wrenches.org>
Date: Sunday, August 16, 2009, 12:42 PM
Please check my math, I did it pretty quickly.
CA has over 450 MW of distributed PV systems. At around, say, 4.5 average daily
sun hours (it is probably more, averaged over the state's systems), that would
be 540,000 MWh each year.
If the utilities are dropping out of spec, say, 1% of the time, that's 5,400
MWh of loss each year. At 15 cents a kWh (the average is probably more) that
turns out to be $81,000 worth of losses to us.
That does not seem like a whole lot, but the number will grow as fast as PV
installations are.
Maybe it is time for a class-action lawsuit against the utilities. Or time for
the dream Wrench organization to file with the CPUC for relief in the form of
stricter utility specs, or petition UL for looser inverter specs.
One question, why are inverters required to drop out for out of spec voltage
and frequency? It seems to me that the UL requirements are overly limiting in
that regard. I mean, if the utility can do it with their huge plants, why can't
we with our little ones?
William Korthof wrote at 10:06 AM 8/16/2009:
>I'm beginning to wonder if the allowed voltage range for grid-tie inverters
>(+/-10%) is too sensitive in some networks and contributes more harm than
>benefit. This is close to home.
>
>We actually have a significant number of customers who've had trouble with
>grid voltage causing their systems to go offline at various times. I think
>most or all are SCE customers.
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