[RE-wrenches] Shedding ice

Mon Jan 16 10:00:51 PST 2012

I recall a conversation a while back about the possibility of "reversing"
the current in a solar module to increase the cell temp enough to shed
ice/rime.  To follow-up, has anybody been successful at this?  I am
guessing, if so, it would entail, removal of diodes, increasing PV and
battery capacity and some way to sense the ice at the very least. . . It
sounds good in theory, but I am skeptical as to whether it will work in
reality. . .

Best regards,

Mark Dickson,

NABCEP Certified Solar PV Installer T

Oasis Montana Inc.

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan
Sindelar
Sent: Monday, January 16, 2012 10:52 AM
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] Request for Gennie Recommendation

Wrenches,
I very much appreciate this ongoing thread, thank you.

This actually feels like one of those "damned if you do, damned if you
don't" scenarios. The system is six years old, poorly designed and
installed. Two SW5548s, most likely chosen in order to run a 2HP
conventional well pump for this manufactured home. Thirty-two L16s in four
strings, in two unvented battery boxes in an unheated shed at 7800'. 1.66kW
of PV plus an H40? wind generator, in an area not known for great wind
resource. The inverters either were never programmed correctly or lost
programming the first time a battery was replaced, so the batteries never
got above default 57.6V and were never equalized. When the L16s started
failing, the installer instructed the owners to replace individual
batteries, over and over until 17 of the 32 had been replaced, one or two or
four at a time. With a continuing stream of failing cells, each time the
well pump came on the voltage dropped to "must start" and the generator came
on. With default programming, the inverters would charge to 57.6V (if the
batteries would get up there - not sure if they ever did), then go through
the two-hour absorption, then shut off and soon the cycle would repeat.

The installer put a Link-10 in the home, but without a prescaler, so it
couldn't work on a 48V system. So he tapped off of part of one string. All
monitor programming was at default settings, so the system monitor had been
useless to the homeowners since installation. This was designed and
installed by someone in business doing wind and PV since the 1980s. His
website claims he is "the most experienced contracting company in the
Southwest specializing in electric/electronic installation, service and
repair of independent, remote or utility integrated power generation power
supplies. We provide electrical engineering design, specializing in on-site
electrical power generation and related control systems." This is some
mighty poor work.

Our immediate "rescue solution" was to string together 16 of the replacement
batteries, program the inverters to corrective EQ, show the homeowner how to
change inverter settings, and replace the Link-10 with a TriMetric with
prescaler, guessing at 500 amp-hours. At first this appeared to have failed
- the battery voltage rose quickly under charge and then fell just as
quickly. But we later learned that this actually worked, as they told us
that after running a long corrective EQ, the batteries came back and the
generator ran far less. But then the existing generator failed to start;
apparently just worn out, and they're in bad shape.

We plan to add about 2-2.5kW of array, although we have no load profile from
them yet. The existing array is on two poles. The (original) smaller array
of 8 Sharp 80W 12V modules is shaded during winter by the larger array of 6
Sharp 170W modules during the mornings. The larger array is shaded by both a
juniper tree on winter mornings (until after 11 am) and by the power
equipment shed on winter afternoons (after 3 pm). The ground is frozen now,
so we have no easy way to either increase the array of move the existing
arrays out of where they shade each other.

They have two SW5548s, so need around 15kW at 7800' to run the inverters at
full capacity. The unknown is that we don't yet know what size the new
battery bank will be; my SWAG is about 1,000 a-hr in a single string of
industrial cells. Together the SWs can charge at 120A, so 1,000 A-hrs would
be a good match. You are correct that the generator run time will be greatly
reduced once the array is increased, the batteries replaced, and their loads
reduced through customer education. But they need a gennie right away, as
their PV and wind can't keep up and the system is shutting down. I'm
hesitant to recommend a generator of less than industrial quality, given
their experience to date with two residential units. And any good generator
has a 4-6 week lead time. 

What would you do in this situation?
Allan

P.S. Chris Mason, your website doesn't jive...I went to www.cometsystems.co
and got a site that said "Comet Systems Ltd. is a Certified Reseller for
Xorcom PBX products and Ruckus Wireless." Doesn't appear to have anything to
do with either PV or generators. Can you enlighten us?

Allan Sindelar
 <mailto:Allan at positiveenergysolar.com> Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com <http://www.positiveenergysolar.com/>  

On 1/16/2012 9:03 AM, Dave Palumbo wrote: 

Chris,

It would be very helpful if you quote "run hours" rather than "years". 

For example we have seen:

Inexpensive small generators (generally not worth rebuilding) 300 to 500
hours. These are gasoline models of various brands and Generac LP gas
models. 3kW to 10kW in size typically.

Honda gasoline generators 2,500 hours and then rebuild. 

10kW Kohler water cooled diesel gen set still operating within specs at
9,600 hours (rebuilt after 5,500 hrs). This has been in service for 16
years, the first 4 years without inverter/battery system, and another 6
years before the client had us add a PV array to the system. Since adding
the PV array the generator has run 200 hours per year.

All are in off-grid service and loaded at 65% MAX continuous (see some
surges higher than 65%, typically run at 60%, or below, of rated power).

David Palumbo

Independent Power LLC 

462 Solar Way Drive

Hyde Park, VT 05655

www.independentpowerllc.com 

NABCEP Certified PV Installer

Vermont Solar Partner

24 Years Experience, (802) 888-7194 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Comet
Systems
Sent: Monday, January 16, 2012 10:21 AM
To: Howie at catamountsolar.com; RE-wrenches
Subject: Re: [RE-wrenches] Request for Gennie Recommendation

The Generac QT and commercial units do not come with an ATS, you can buy
just the bare machine or have a complete solution designed for your load.

The Generac residential machines are good machines, as long as you
understand the intended use. We install lots of them. They are only designed
to be used occasionally, for residential backup. We get customers who want
to run their business all day on a 10KW residential generator and are
disappointed that the generator won't last ten years. They are a cheap,
lightweight and cost effective solution for people who get occasional
outages.

If your customer has worn out two generators already, then (s)he needs to
pay for a commercial level product. A 22KW QT is not that expensive and will
last ten years at a substantial load factor. If you give me more information
on the location, load factor and loading, I can have engineering recommend a
solution for you.

-- 
Chris Mason

President, Comet Systems Ltd

masonc at cometsystems.co

www.cometsystems.co

Cell: 264.235.5670

Int: +1305.767.2094

Skype: netconcepts

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