UPS batteries.

nobody928

Why are ups batteries a good or bad fit for solar application? MOst of them seem to be agm and have extremly good a.h. ratings.

Cariboocoot

Re: UPS batteries.

nobody928 wrote: »

Why are ups batteries a good or bad fit for solar application? MOst of them seem to be agm and have extremly good a.h. ratings.

Read your own post.

Which UPS batteries are we talking about? "UPS" is in itself not a designation of battery characteristics but of application. It does not define the Voltage, Amp hour capacity, nor construction.

You will often see recommendations to avoid the batteries used in UPS units because they are not AGM but GEL, which have some similar characteristics but are not the same (lower Voltage, not capable of high current).

In general the UPS batteries are not designed for the daily discharge/recharge routine of RE systems but rather meant to sit at 'float' levels for long periods of time and then provide deep discharge occasionally with subsequent recharge from the grid following different parameters than are available with RE.

topper

Re: UPS batteries.

Quote from Enersys concerning my particular batteries. " Factors affecting lifespan of recombination batteries.. cycling or micro-cycling".. Mine are rated at 1200 cycles to 20 % DOD.. Which would be 3 years life on a solar setup at $250 per 12 volt block.
However there are others out there designed for high cyclic lifespan. Do your research.

BB.

Re: UPS batteries.

You have to look at the specs. for the batteries of interest.

Those design for float life (20 years of sitting on a charger) have that long life if they are not discharged below ~15% state of charge (typical telecom battery).

If the battery is deep cycled to 20% SOC (natural disaster, etc.), the Telecom companies will generally do a "mass change out" of the battery bank.

For off grid systems, generally, the maximum discharge is around 25% to 50% in normal operation--"UPS" batteries are not generally designed for that sort of service (short service/cycle life).

Another issue with (at least US) GEL batteries is they only will accept ~5% state of charge. Charge them faster, and they can develop "permanent" gas pockets next to the plates--Which reduces their capacity.

For off grid system, we recommend 5% to 13% rate of charge for solar panels, and you can go as high as 20-25% Rate of Charge with a genset (or when utility power is restored). A 5% rate of charge is usually too slow to "efficiently and effectively" capture the ~4 hours of roughly full sun per day that a typical off grid system sees.

AGMs can be very nice batteries for off grid solar (support very high discharge and recharging rates vs flooded cell lead acid, much cleaner, no water levels to check, etc.). Their main drawback is AGMs are something like 2x the cost of Flooded Cell and AGM may have a few years less service life than similar quality flooded cell.

Also, Flooded Cell tend to be a bit more forgiving with overcharging (miss adjusted charge controller, wrong float voltage, etc.). AGMs can be damaged pretty easily with too high of float/charging voltage.

In the end, if this is your first venture into off grid solar--We usually like to suggest the least expensive battery bank solution first (golf cart deep cycle batteries, etc.). If something goes wrong--much less money out of pocket. Also, many times it is difficult to size an off grid system if you have never lived off grid... We like to recommend erroring a bit on the small side (keep costs low) until you get a year or so of usage under your belt. By then, you will have a better understanding of your needs and any mistakes in operation (teenagers with hair dryers, etc.)--And you can build out your next system that better meets your needs (and buy the more expensive/better quality batteries).

-Bill

westbranch

Re: UPS batteries.

BB. wrote: »

You have to look at the specs. for the batteries of interest.

Those design for float life (20 years of sitting on a charger) have that long life if they are not discharged below ~15% state of charge (typical telecom battery).

If the battery is deep cycled to 20% SOC (natural disaster, etc.), the Telecom companies will generally do a "mass change out" of the battery bank.

-Bill

Also each manufacturer has different test parameters. My old 12V Absolyte AGM was supposed to be discharged tested YEARLY to 10.5V and then recharged immediately, they assumed from the grid, and then all cells were to be assessed for SOC.

Warning this extreme depletion can kill a cell ... or identify a weak one...

I never did the total discharge as it was used, and of unknown health other than failing. I used a 10% discharge rate and monitored the Voltage every 30 minutes till it got to ~ 50% resting SoC voltage, then watched what happened to the resting V over the next 3 hours..

You will learn a lot from a failing battery...
hth