Most everyone is somewhat familiar with a car battery – having had to deal with at least one dead battery in mid-winter.
Well let’s say for simplistic sake that there are two types of batteries, one – the automotive battery and two – the deep cycle battery. So what’s the difference?
The car battery is made to give the starter a lot of energy for a short period of time and then it is ‘dead’ or discharged.
All automotive batteries can be discharged a certain number of times and then you must replace them – probably ½ a dozen or so – depends on what size they are, operating conditions & so on. These batteries have thin lead plates inside which allow for a quick charge & quick discharge but with lots of power (amps).
The deep cycle battery, used in golf carts, floor scrubbers, solar systems are made with thick lead plates that store more power and take longer to charge as well as discharge. They can be discharged to a greater degree and for many more times than a car battery. Battery discharge amounts (i.e. 50% or 30%) along with proper care and conditions can be in the range of 1,000 to 2,000 times! They will eventually ‘die’ also, but it will take an average of 7 to 10 years.
Now, before I go too far, I am only addressing the more common type of deep cycle batteries, the lead acid golf cart, the floor scrubber and the L-16 type. There are batteries in the deep cycle category that last longer, take more abuse, etc. but cost far more. They also require a fork lift to move!!Back to our ‘typical’ deep cycle battery. Brand names like Exide and Trojan are more common. They come in several different sizes. When I say size, I mean AMP/hour more than physical dimensions, even though the higher the AMP/hour rating usually means a larger and, for sure, heavier battery. In order to increase our AMP/hour rating we need to get larger batteries or increase the quantity of batteries.
Some of you are thinking ‘What’s the best battery?’. Well you decide – based on warranty, cost and rating: Thought I’d give you a preference? Well, no, because some people like Fords, some like Chevys, both do the job, but owner care and maintenance determine performance and longevity — just like batteries. If someone tells you that Trojan is best it is because the owner took care of them. ‘Best’ in deep cycle batteries has a lot to do with cost, care and conditions; rather than brand names. I have had clients treat golf cart batteries so well that they last as long as the larger more expensive types.
Deep cycling / Discharge rates
The term deep cycle means a battery can be discharged 50% or more and keep on ‘ticking’. The amount of deep cycle or discharge will be a large factor in how long the battery will last. A simple rule of thumb is if a battery can be discharged 50% it will last ½ as long than if you only discharge it 30%. That translates to sizing your system with more batteries and/or conserve and reduce your energy load. Remember our example of needing 2,344 watt hours/day?
Batteries can be expensive but are far cheaper than other components of a solar system, that is, unless you opt for the $1,000 ++ per battery that are out there!
Care and Maintenance
Batteries are like retired folks in the sun belt – they like 72 Degrees Fahrenheit year round. Keep them this way and they last longer – expose them to very cold or very hot temperatures and it shortens their life
Batteries that are charged & discharged on a regular basis (i.e. used) consume water – actually they boil it off or evaporate it from their cells. Keeping them ‘topped off’ (full) make them last longer (distilled water only). Let one cell go dry and you may have ruined the battery.
Batteries have terminals. These are the ends where the cables are attached. They must always be clean and free from corrosion. Batteries produce hydrogen gas which is explosive and corrosive. This gas attacks clean metal and corrodes it. When this happens electrical contact is jeopardized and your solar panels cannot charge your batteries optimally.
Batteries that are discharged should be recharged within 24 hours. This increases their life span. A process called sulfating happens inside all batteries (lead-acid) and sulfates stick to the plates. During ‘equalization’ this sulfate is broken loose, allowing the battery to accept a more complete charge. Equalizing your batteries on a regular basis increases their longevity.
Batteries should be in an enclosed, vented, protected place and great caution should be used when handling or servicing. Their acid will ruin your clothes, cause severe skin burns and is explosive. The cumulative energy of a battery bank is tremendous. A short can cause serious injury, fire or worse!! Be careful – Be Safe and we will size batteries to our example system next month.
About the Author
Larry LeDue has been designing, installing, and servicing solar systems since 1990. He is an active/certified member/installer with COSEIA; and lives with his wife in an active and passive solar home they built in South Park, Colorado.
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