Top Ten Battery Blunders and How to Avoid Them

Intermediate

Inside this Article

Big battery, big mess. Don’t try this at home.
Big battery, big mess. Don’t try this at home.
These batteries have definitely seen better days.
These batteries have definitely seen better days.
Wrong Battery Type
Starting batteries work great in your car, but will quickly fail if used in deep-cycle applications.
Improper Size
A large battery bank requires a large charging source.
Improper Watering
An extreme result of battery neglect.
Many Small Batteries in Parallel Strings
Use bus bars to parallel multiple series strings.
Failure to Prevent Corrosion
Notice the parallel connections on the left side of the photo—the worst corrosion is at these stacked cable lugs. Batteries with corroded terminals will receive less charge, and will fail early.
Lack of a Protective Environment
A beautifully installed 48 V battery bank—sixteen 6 V batteries connected in two strings of eight. These big Surrette batteries have two holes on each terminal, so cable lugs don’t have to be stacked. The peaked battery enclosure allows for excellent hydrogen venting.
Lack of Proper Charge Control
Proper controller settings are critical for battery longevity.
Modern battery monitor
Example of modern battery monitor (amp-hour meter).
Modern battery monitor
Another example of modern battery monitor (amp-hour meter).
Big battery, big mess. Don’t try this at home.
These batteries have definitely seen better days.
Wrong Battery Type
Improper Size
Improper Watering
Many Small Batteries in Parallel Strings
Failure to Prevent Corrosion
Lack of a Protective Environment
Lack of Proper Charge Control
Modern battery monitor
Modern battery monitor

Batteries allow us to store our renewable energy (RE) for times when the sun isn’t shining and the wind isn’t blowing. They are often called the “weakest link” in renewable electricity systems, but battery problems nearly always are the result of bad equipment choices, installation errors, and lack of attention—the human factor!

In my 27 years as a system supplier, I have seen serious battery-related mistakes made repeatedly, by amateurs and professionals alike (and I’ve made a few myself). The results can be expensive, hazardous, and damaging to the reputation of renewable energy. That’s why I am presenting these classic blunders, and their ready solutions. High-quality batteries can last  ten to twenty years, but they can die in one or two years if abused.

Nearly all battery-based RE systems use lead-acid batteries. So this article applies only to them (not to other battery chemistries). It applies to batteries charged by PVs, wind, microhydro, and engine generators, the utility grid, or any combination of sources. It applies to off-grid independent systems and also to grid-tied systems with battery backup.

BLUNDER #1 Wrong Battery Type

Batteries are built with a variety of structures and materials, according to the application. If you choose the wrong type, you will get poor longevity.

RE applications require batteries to discharge to below 50 percent of their storage capacity, repeatedly. This is called “deep cycling.” A full-time, off-grid home system will typically experience 50 to 100 cycles per year at 30 to 80 percent depth-of-discharge. Always use high quality, deep-cycle batteries in RE applications. Engine-starting (car or truck) batteries are designed for quick, high-power bursts, and will survive only a few deep cycles.

The batteries used in grid-tied, emergency backup (standby) systems will only be deep cycled occasionally when there is a utility outage. Periodically, flooded, deep-cycle batteries need to be actively charged to mix the electrolyte. This prevents stratification of the solution. Because battery cycling/active charging may be very infrequent in standby applications, it’s best to use batteries that are specifically designed for emergency standby or float service. They might not be good for hundreds of cycles, but they will stay in working order through years of light usage.

Another distinction is between “sealed” (maintenance-free) and “flooded” (liquid-filled) batteries. Most deep-cycle batteries are flooded. They require occa­sional watering, but tend to last the longest. Emergency standby bat­teries are often sealed, and they require no regular maintenance. Deep-cycle, sealed bat­teries are sometimes chosen because they eliminate need for a ventilated space and for easy access. Sealed absorbed glass mat (AGM) batteries are designed for float applications, and are a great choice for grid-tied PV systems that include battery backup. They typically cost up to twice as much as flooded batteries, and require more careful recharging regimens, but are the best battery type for standby applications.

BLUNDER #2 Improper Size

To design a stand-alone renewable energy system, you first establish an “energy budget”—the number of watt-hours you will consume per day. Next, you need to determine how many days of stored energy (autonomy) is required. This variable can range between three and six days (or more) depending on your average daily electrical consumption, the output of the RE charging sources and their seasonal availability, and your willingness to use a backup engine generator.

Most home systems grow larger over time. Loads are added, a PV array is enlarged, but a battery bank cannot be readily expanded. Batteries like to work as a matched set. After about a year, it is unwise to add new batteries to an established bank. If you foresee growth in your system, it is best to start with a battery set that is larger than you need. But be sure you have sufficient charging capability, or the battery bank will be chronically undercharged, which will lead to sulfation and premature failure.

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Comments (7)

bob tarzwell's picture

one trick for number 4 ie lots of batteries in parallel strings is to balance the charging with final wire size , I had acquired 80 good golf cart batteries and have 10 parallel strings in a 24 kw system , I balanced by voltage and current so each string gets very close to the same charging /discharge, I did it by reducing down a bit on the wire to higher groups , been 3 years now and still working great ,this year I will do a big charge and rearrange batteries in new strings to continue there life. in my other system its 120 volts 10 kw and two sets of 20 rolls s530's so not much to balance , works great especially when you get the charging right and charge hard.
ps after years of solar install I don't trust anyone's cable crimping I always scrimp and solder my connectors.

Woody Petrea's picture

Cool. Thanks for that. :)

Woody Petrea's picture

Was this article originally posted elsewhere?

Michael Welch's picture

As far as I am aware, only in our magazine. If it is out there elsewhere, it is most likely in violation of our copyright.

Woody Petrea's picture

It was just the way the article read. Under item #3 blunders, it states, "The photo at right shows a system that was ignored for more than two years." I noticed that all the images are at the top of the article.

Good read. Thanks to the author and to HP for posting it.

Scott Russell's picture

Fixed that text, Woody. We normally try to catch those references when republishing articles on the website, but they're easy to miss.

Michael Welch's picture

Ahhh. That's because the articles on our web site mirror the corresponding articles in the print version magazine. We generally try to avoid saying things like "to the right" and "on the next page."

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