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The majority of our customers still prefer batteryless systems, as
in most parts of the country. Battery-based grid-tied systems are
less than 10% of our residential installations. But I find myself
speaking with more people who inquire about GTWB systems out of a
growing and fundamental lack of confidence in the social
infrastructure in the future. It's very small still, just as
grid-tie in our region was very small ten years ago, and it's the
early adopters, with interest and means to investigate investing in
some type of long-term energy security. These people are looking to
be able to run part of their home on PV for an indefinite period.
The systems are set up as standard GTWB, but with larger backup
energy storage capability. <br>
<br>
The systems aren't necessarily huge. We just completed one on an
urban residence with only 2.2 kW of PV and 600 A/hr @48V of VRLA
Concordes, that the customers carefully calculated would serve their
essential needs if the grid went down permanently. They are
purchasing a sense of security against an uncertain future. These
are by no means the bunker-mentality fringe that we have all read
about; this latest is a retired professor and scientist wife;
another last year was a conservative retired couple with small
livestock and garden on one acre; he was a utility lineman.<br>
<br>
The systems are inherently difficult to design, for two fundamental
reasons. First, they must serve three functions, two of which are
almost mutually contradictory: provide the economic benefit of
grid-tied PV as long as the grid is up, which could (and likely
will) be for the life of the system; provide backup power to
protected loads during a typical short utility outage; and
immediately behave like an off-grid system (but without a backup
generator) in the unlikely event of long-term or permanent loss of
the grid. Second, taking an on-grid home off grid is one of the most
difficult tasks: in 15 years I have never done it, and have turned
it down as impractical numerous times. But if the loads are
carefully selected and moved to a separate panel, and it's
understood what is possible to run and what isn't, and there's a
good monitor in the system, it works. We are very clear with clients
what to expect; this is the place to be very conservative in
explaining how the system works, how long batteries may be expected
to last, the need to go without electricity if there's a week of
cloudy weather, etc. It helps that this is the sunny Southwest, of
course.<br>
<br>
We are very careful not to encourage fear. The desire to install a
system with this capability has to come from the client, and I make
sure that they understand the costs and limitations of this
approach. These systems run in the ballpark of $15-20/W installed -
about 3X a batteryless system. And we also make sure that they
understand that while we can't predict the future any more than they
can, if indeed the worst happens and the grid fails, we likely not
be able to support them, as transportation fuel may also not be
available and social upheaval will be unpredictable.<br>
<br>
For this customer, a generator isn't a solution, as it's limited to
the amount of propane in a tank. And natural gas isn't an option, as
the natural gas distribution system is also dependent on the grid.<br>
<br>
I would think that this approach would also work for medium-term
natural disasters, such as ice storms or Vermont floods, but with a
generator and large propane tank for backup battery charging as part
of the system.<br>
<br>
Are the rest of you Wrenches getting these inquiries? I haven't seen
much on this list about the topic of long-term or permanent loss of
grid power.<br>
Allan<br>
<br>
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<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a href="mailto:Allan@positiveenergysolar.com"><font
color="#000099" face="Times New Roman, Times, serif"><u>Allan@positiveenergysolar.com</u></font></a></small><font
face="Times New Roman, Times, serif"><br>
<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></font>
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<br>
On 9/4/2011 6:28 AM, Christopher Warfel wrote:
<blockquote
cite="mid:20110904122823.47059.qmail@entech-engineering.com"
type="cite">One should also factor in the availability of
generator fuel if an extended outage occurs. In some communities,
the fuel will be scarce or non-existent, especially if significant
damage occurs to fuel transporation and storage infrastructure.
<br>
<br>
<br>
<br>
Original Message -------
<br>
On 9/4/2011 01:18 AM R Ray Walters wrote:<br>Hi Jay;
<br>
<br>
<br>
<br>I agree, for long outages, a generator is the way to go.
It just doesn't make sense to have 5 days of lead acid battery
sitting there for years waiting to be used once or twice in an
epic ice storm.
<br>
<br>On the other hand, many places have very unreliable grid
power with short outages every few days. A battery based backup
system is great in those cases, but I rarely size the bank for
more than a day of storage and I usually use sealed batteries. I
look at it as a big UPS system, that if managed could limp along
for longer in an extended outage.
<br>
<br>I start any system design of this nature with this
question: How often does the power go out?
<br>
<br>RIght there, I talk more than half the folks out of
batteries, while the rest know what they're getting (and not
getting).
<br>
<br>
<br>
<br>R. Walters
<br>
<br>
</blockquote>
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