[RE-wrenches] Convert Grid Tie SW4048 to Backup System; Add New Inverter, AC Coupled

Sun Nov 20 12:10:23 PST 2011

On Sunday, November 20, 2011 9:32am, "Joel Davidson" <joel.davidson at sbcglobal.net> said:

Wrenches,

I answered Richard off-list,  but other wrenches may find this information about old SW4048s and  batteries useful.

The SW4048 is a  solid machine. We've been using one since 1998 and have sold hundreds of them  for both on and off grid systems. We would leave what's working alone and  replace and expand the battery bank to meet the client's expected grid outage  hours. Our system has only 4 kWh of sealed batteries because we live in an area  that gets almost no power outages and did not want to bother watering batteries.  See info and wiring diagram at [http://www.solarsolar.com/oursys.html] http://www.solarsolar.com/oursys.html 

On the other hand, one of our clients in  Malibu on the grid had an off-grid 5 kW PV system for backup power with 75 kWh  of IBE flooded lead-acid batteries (2 parallel strings of 24 each 2-volt cells).  We installed the system in 1993 but no one maintained the batteries properly. So  in 1996 the dead IBE battery bank was replaced with a maintenance-free, sealed  Absolyte battery bank that only lasted 4 years because of 40 F to 90 F  temperature swings in the equipment room. A few years ago, we upgraded the  system with a 31 kW array, 6 Sunny Boys, 2 Sunny Islands, and went back  to a new set of 75 kWh of IBE cells like before. Now the batteries are  inspected and watered every 2 to 6 months. We are still determining the right  service period.

I have learned to buy good batteries, install them where  the temperature stays 60 to 70 degrees F. as much as possible, inspect and water  flooded batteries at least 2 times per year. All things being equal, sealed  lead-calcium batteries cost twice as much and last half as long as flooded  lead-antimony batteries. Most importantly, batteries are electro-chemical things  just like living organisms. Keep them clean, fed (fully charged as much as  possible), properly watered, at 70 degrees F, don't over-work them (deeply  discharged without fully charging promptly), and they will last 6 to 8 years  easily and often 12 years before old-age (high self-discharge) sets in. Battery  bank owners that take care of themselves, their families, their animals, and  their vehicles carry those good habits over to taking care of their battery  banks. It's sad but true that people who are unhealthy and have vehicle problems  all the time almost always have battery problems.

Best regards,
Joel  Davidson

----- Original Message -----
From: [mailto:allan at positiveenergysolar.com] Allan Sindelar
To: [mailto:re-wrenches at lists.re-wrenches.org] re-wrenches at lists.re-wrenches.org
Sent: Sunday, November 20, 2011 8:21    AM
Subject: Re: [RE-wrenches] Convert Grid    Tie SW4048 to Backup System; Add New Inverter, AC CoupledKirk,
I think there are a couple of subtleties that you're    missing in your post. All of the SW series that we installed in grid-tied mode    prior to Trace/Xantrex losing its 1741 listing - mostly Y2K installations -    are still in use legally, as they were grandfathered in. Once Xantrex lost its    listing and went to the GTI models (firmware rev. 4.10 and above), only with a    GTI were they 1741, and the earlier inverters couldn't be retrofit.

So    if Richard's customer's SW4048 is pre-GTI and is currently legitimately    utility-interactive, it could be argued that it's grandfathered in. Of course,    I'd avoid arguing anything that esoteric with any governing body. 

But    it's a moot issue anyway. Reviewing the other Wrenches' suggestions, none    advised continuing to use the SW as an interactive inverter, but only as a    charging source for a battery bank. One Wrench suggested putting the SW's AC    input on a weekly timer, which is a good idea. Jay is correct that the SW was    a terrible inverter for grid-tie. One primary weakness of the SW series was    that as long as the grid was up, it tried to maintain float voltage to the    batteries continuously (this was the "lack of silent sell" issue). This    brought overall sell efficiency down to around 55%, as I recall, rather than    the 93+% efficiency of today's inverters. But if the inverter is only being    used as a charging source, it's not selling and thus neither the poor    efficiency nor the lack of a GTI is relevant.

Personally, I wouldn't    get rid of the SW if the customer wants battery backup. The inverters have    proven generally reliable, and this one is likely to last for decades as an    occasional battery charger. Plus it's already paid for, and does a good job as    both a battery charger and a backup inverter during outages. I'd use sealed    batteries to deal with the customer's maintenance concerns. The Honda 3000i is    a good choice at sea level, as the SW can hard-limit the AC amp draw from an    undersized generator and avoid overloading it (and nuisance-tripping its    output breaker). But note that the SW can take up to about 5,200 watts from an    AC source, and sealed batteries prefer high charging C/rates, so you might    want to use a generator of around 6kW (at 120V) instead for better efficiency    and less runtime.

Good thing Richard reposted - the second time got a    bunch of us responding. Kinda fun...

Allan

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
[http://www.positiveenergysolar.com/] www.positiveenergysolar.com

On 11/20/2011 4:33 AM, Kirk    Herander wrote:
PS - Richard, does it have a Trace / Xantrex GTI interface installed? Ifnot, it's not code-legal to be tied to the grid anyway. Get rid of the 4048whatever you do.Kirk HeranderVT Solar, LLCdba Vermont Solar EngineeringNABCEPTM Certified installer Charter MemberNYSERDA-eligible InstallerVT RE Incentive Program Partner-----Original Message-----From: [mailto:re-wrenches-bounces at lists.re-wrenches.org] re-wrenches-bounces at lists.re-wrenches.org[[mailto:re-wrenches-bounces at lists.re-wrenches.org] mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Richard LRaticoSent: Friday, November 18, 2011 6:53 PMTo: [mailto:re-wrenches at lists.re-wrenches.org] re-wrenches at lists.re-wrenches.orgSubject: Re: [RE-wrenches] Convert Grid Tie SW4048 to Backup System; Add NewInverter, AC CoupledJay, Marv, Chris, Ray, Joel & Maverick,Thanks tremendously for your input. Each of you provided interestingsuggestions, all of which I find thought provoking and helpful. I greatlyappreciate your taking the time to share your experience.DickSolarwind Electric--- You wrote:We redid one in a very similar situation recently. In that case the customer wanted super backup and so we put in Grid tie Outbacks and a new battery bank, added modules, and kept the SWs as battery chargers from the generator. He had the option with bypass switches to use the SWs, if the Outbacks went out. This guy wanted a "keep the power going, no matter what" system, but I can't claim that was optimal.  The right answer depends on what the customer wants.I probably wouldn't trash everything though as Jay suggested, since the existing modules are already racked and wired. (unless it's a bogus install, then yep, salvage it all)You could probably easily rewire the parallel 48 v sets of modules all in series in 15 minutes in the combiner box to get the voltage up, and use a small GT only inverter, too. I guess it would also depend on how close the 2 different types of modules are in voltage or current, but it doesn't have to be perfect; as these were modules headed to the scrap heap otherwise.In honor of modules that are well installed and still performing correctly, I do try and reuse them. Being able to brag: "these have been working for 30 years..." is great for the solar industry as a whole, but only if it makes sense.RayOn 11/17/2011 5:51 PM, jay peltz wrote:
HI Richard,I'll chime in, although you won't like it.Dump the system and start over with a new battery less system and a genny
asback up.
Told you, you wouldn't like it.The SW parts are basically gone and it was a terrible  grid tied inverter
anyway.
The modules are usable but why at $1.5 watt keep them?Client doesn't want MX, so that means no batteries.You'll need a genny as back up anyway for long power outages during
storms, soget a natural gas/propane unit as back up instead of batteries.
OK you asked,jaypeltz powerOn Nov 17, 2011, at 4:03 PM, Richard L Ratico wrote:
Hi Wrenches,This is a repost. No replies the first time, so I'm trying one last time.I may be "adopting" an eleven year old, Y2K, grid tie with battery
back-up
system. It consists of 12 - Astro-Power 120 modules, installed in 2000,
12 -
Evergreen  EC-110 modules installed in 2004, only one MX60, which
controlsBOTH
sub-arrays, one SW4048 in SELL mode through a dedicated load sub-panel.Existing, seven year old battery is shot (8-Trojan L-16). Initial bank ofunknown batteries was replaced after only four years.Recent long, nearby, utility outages have the client requesting a
proposal to
include a new back-up generator and to restore the system selling to the
grid.
Client may decide go straight grid tie to eliminate the batteries. They
have
found the maintenance to be a hassle.My thoughts so far:1)To take advantage of most of the existing hardware, I wonder if it
makessense
to try to improve the system efficiency by relegating the SW to a manual
back-up
mode only, where, say, by means of a timer controlling grid availability
through
AC1, it would only charge a smaller battery bank once a week. The battery
bank
would be small,a single string of either, sealed gel units or T-105s with the new Trojanwatering system.2) Provide new grid-tie inverter/s (appropriate string type or Enphase
190s)to
handle the net metering.3) Provide a way to AC couple the new inverter/s to the SW in the event
of an
outage.4) Provide a new Honda 3000 inverter type generator connected to AC2 in
theSW.
5)Provide a way to lockout the grid tie inverter/s when the generator isoperating.Any thoughts or suggestions would be greatly appreciated.Thanks in advance,Dick RaticoSolarwind ElectricBradford, VT
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