The batteries in your scenario are actually being cycled daily probably somewhere in the 2 to 5% range. Looking at a chart for # of cycles vs. DOD, you see the most efficient use of the battery is usually from 20% to 80% DOD, an FLA battery in perpetual float just doesn't last as long you might think. Depending on the brand of golf car battery, I would give this system a maximum life span of 10 years. Maintenance will eventually be the issue; sometime in the battery's life, it will be over charged, left for weeks under charged, or let the water go dry. A typical scenario I've seen many times: charge controller fails because of lightning, small load is left on, and the battery gets fully discharged. Since no one is there, it sits for weeks and becomes permanently damaged. Scenario 2 is similar: a load is left on (light in a closet) fridge or pump stays on and malfunctions, and the system crashes. Scenario 3 no temp compensation, battery gets over charged in the heat, boils its H20 off a couple of cells, the dead cells pull the rest of the bank down in spiraling failure that can actually do damage to the house: acid spills, corrosion, and exploding cells. I find my off grid systems that fare the best are well designed full time use with one or two people who are very consistent in their use, and maintenance. I've replaced batteries every couple of years on some part time systems, because simple problems are not caught for weeks or months. I have a couple of higher end part time systems that the owner can monitor and contact us, if for instance the power goes out. This keeps it from leading to permanent damage.
Ray Walters On Jul 14, 2012, at 8:58 AM, Jason Lerner wrote: > Hello John, > > Thank you for your helpful explanation. I wonder if there should be a "six" > life, that being time. > > Lets use the small summer cabin analogy that gets used for one month a year. > Let's say the system has Four T105 -RE's, 500 watts of PV, 4 average daily > sun hours. They do one discharge/charge cycle down to 20% DOD and then fully > charge again the same day for a 2 hour absorb. That would be 30 discharge > cycles a year x 8 years = 240 discharge/charge cycles. > > If one was to design and instal a proper battery based system using the > guidelines presented in this email thread with plenty of PV for daily > charging, periodic EQ's, 20% or less DOD, no electrolyte on the battery tops > to cause corrosion, never letting the plates go dry from low electrolyte > level and having them at a cool 60º F year round would you expect this summer > cabin system to last 4000 cycles? In a perfect world would that be 4000 > cycles ÷ summer cabin 30 discharge/charge cycles a year = 133 years ?? > > Of course I am not expecting that, but am just trying to squeeze the longest > life span possible out of batteries that mostly just sit. > > Best, > > Jason Lerner > > Waldron Power and Light Co. > On Jul 13, 2012, at 10:33 AM, John DeBoever wrote: > >> Wrenches, >> >> Forcing a lead acid battery to cycle for the fun of it reduces its cycle >> life. >> >> In a nutshell, lead acid batteries have “five lives”, each varying depending >> their specific intrinsic technology attributes developed by the battery OEM: >> o Cycle life >> o Corrosion life >> o Stratification life >> o Shorting life >> o And… Temperature life >> >> These lives are all inter-connected and temperature is the one that is the >> most influent to all of them. The interesting part is that all of these “5 >> lives” are 90% of the time exacerbated by the system sizing >> (cyclic/non-cyclic, loads, insollation, PV array, battery bank size, wiring >> and power conditioning losses, etc.), the install, the setting points >> commissioning, the maintenance, not to forget the load patterns (perceived >> vs. reality dynamics and growth of the load). Cycling for cycling does not >> increase the battery life. Adequate cycling based on adequate full recharge >> keep the battery in good health. >> >> John >> >> John F. DeBoever >> Global Technical & Projects Director – Renewable Energy >> Trojan Battery Company >> >> 12380 Clark Street >> Santa Fe Springs, CA 90670 >> Tel: +1-562-236-3000 Ext. 3139 >> Cell: +1-845-514-7600 – NY office time zone: USA EST (GMT-5) >> Skype: john.f.deboever >> Fax: +1-562-236-3239 >> jdeboe...@trojanbattery.com >> www.trojanbattery.com >> >> >> From: re-wrenches-boun...@lists.re-wrenches.org >> [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of >> la...@starlightsolar.com >> Sent: Friday, July 13, 2012 12:18 PM >> To: RE-wrenches >> Subject: Re: [RE-wrenches] Battery Experience >> >> Jason, >> >> Forcing a lead acid battery to deeply discharge does not increase capacity >> or life of the battery. It only shortens battery life and may damage the >> battery. This is one of many battery myths. >> >> Larry Crutcher >> Starlight Solar Power Systems >> -------- Original Message -------- >> Subject: Re: [RE-wrenches] Battery Experience >> From: Jason Lerner <wapa...@rockisland.com> >> Date: Fri, July 13, 2012 7:28 am >> To: RE-wrenches <re-wrenches@lists.re-wrenches.org> >> >> Hello John, >> >> This time of year I service off grid summer cabins where people come up once >> a year for a few weeks. The batteries in these systems generally do not die >> from over cycling, but from over/under watering, acid stratification, >> corrosion, and generally being ignored. The more savvy customers I will >> recommend they turn off the PV's when they are there to get a deep discharge >> in. >> >> Could you recommend any thing else they could do to lengthen their battery >> bank lifespan? These systems generally have a small PV charging capability, >> and float charge 350 days a year. It seems ironic that these systems that >> really never get used, and my battery bank at home that gets used (but not >> abused) and cycled daily, will last the same number of years. >> >> Thanks very much, >> >> Jason Lerner >> >> Waldron Power and Light Co. >> >> >> This e-mail message and any attachments that accompany it may contain >> information that is confidential, privileged, or protected from disclosure. >> It is intended solely for the use of the individual(s) to whom it was >> intended to be addressed. If you have received this e-mail by mistake, or >> you are not the intended recipient, any reading, disclosure, copying or >> other use of this communication is strictly prohibited. If you have received >> this communication in error, please immediately advise the sender at their >> phone number listed above, or by electronic mail, and also permanently >> delete the original and all copies of this e-mail and any attachments from >> all locations. 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