[RE-wrenches] Long-term Backup Power; was AC Coupling
penobscotsolar at midmaine.com
penobscotsolar at midmaine.com
Sun Sep 4 10:13:08 PDT 2011
Twenty years ago 100% of our installations were battery based, off
grid. That is all there was, at least here in Maine. Nowadays, we are
installing about 75% grid tie. Of that, about 25% use batteries in
their system with a "critical loads" sub-panel. The remaining 25% of
our clients are off grid and very much reflect the society we live in.
Largely the clients are retired and are looking for a form of security
that can't be had in a worst case scenario such as Allan talks about
below. We also do a lot of work in the Caribbean, where utilities do
not allow for intertie agreements. We just had two large off grid
systems on Cat Island in the Bahamas take a direct hit from Irene (130
mph winds there last week) and beside one charge controller in one
system which was mounted below a leak in one roof, everything in both
installations continued to function well. There is little availability
of generator fuel on Cat Island without electricity and a good part of
the island still has none (electricity), while my clients continue to .
This is a testimony to that independence to which Allan also inferred
his clients were interested in.
We continue in Maine to see "independence driven" systems where the
clients want batteries. It does take considerably more skill and
knowledge on the part of the installer, and more maintenance on the
part of the client, but all things are relative to the value we place
on them. Independence is priceless...every big storm here in Maine
reminds me of that when my battery bank keeps me in power and my panels
keep charging. It is a good feeling that I try to encourage to those
who express interest in battery backup or off grid.
We are currently installing battery backup type systems for on average
about $12-$14 per installed watt, sometimes less, sometimes more
depending on the "down time" load requirements.....
Just two cents from Maine....
Daryl DeJoy
NABCEP Certified PV installer
Penobscot Solar Design
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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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> <title></title>
> <font face="Times New Roman, Times, serif"><b>Allan
> Sindelar</b></font><br>
> <small><a href="mailto:Allan at positiveenergysolar.com"><font
> color="#000099" face="Times New Roman, Times,
> serif"><u>Allan at 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>
> <span style="font-size: 10pt;"><br>
> </span> </div>
> <br>
> On 9/4/2011 6:28 AM, Christopher Warfel wrote:
> <blockquote
> cite="mid:20110904122823.47059.qmail at 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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