The Gel Battery. Your only Choice for Renewables

The Gel Battery, The Best choice in a Cycling Application for Renewable Energy

We get asked this question all the time, which batteries are the best in a cycling renewable energy application, It’s the Gel battery and I will tell you why. First, I’ll take the floods right out of the equation, although they are the cheapest solution. When you put floods in series or add a parallel string, and them cycle them you’re asking for nothing but problems. Not to mention a potentially dangerous situation. Secondly the required maintenance is expensive and time consuming. Finally, when you factor in the amount of out gassing of hydrogen during the charge cycles your potentially sitting on a hydrogen bomb. Who wants that anywhere near their home or business? So that really leaves two choices AGM or Gel.

Here’s the Facts

Cycle life

If you’re using your batteries in a deep cycling application such in a PV solar energy system or as your house batteries on a boat, Gel batteries are the only way to go. No other battery type delivers the energy cycle life you need for as long as a Gel can. When properly maintained a Gel battery is also going to give you 2 to 3 times the cycle life versus an AGM depending on the battery size. The average cycle life of mono-block batteries using AGM technology is rated at about 250 cycles to 80% DOD (depth of discharge). The Gel series in contrast is rated at 600 cycles at 80% DOD, a factor of 2 ½ times greater in a typical situation. Again when properly maintained the Gel battery cycle life will raise to a factor of at least 2 times greater than its AGM counterpart. Therefore in cycle life cost terms the Gel battery works out at a lower overall cost to the customer.

Stratification

 AGM batteries experience acid stratification. As the acid is liquid, the high specific gravity acid coming out of the plate during recharge will tend to flow to the bottom of the cell creating stratification. Thus reducing the capacity of the battery. As the cycling process continues the stratification effect will happen exponentially creating an even smaller reserve capacity. Using an equalization charge to de-stratify will not work on an AGM battery. Gel batteries do not experience any stratification whatsoever. Because of the structure of the gel, it absorbs the acid produced during recharge, and allows it to diffuse throughout the gel matrix. Thus significantly increasing there cycle life versus the AGM battery.

Cell Sulfation

A very important point is to consider is cell sulfation. Cycling batteries, particularly PV batteries tend to spend a fair amount of time operating in a partial state of charge. This means lead sulfate will exist on the battery plates for long periods of time. Lead sulfate has a nasty tendency to harden with time, and results in a permanent loss of capacity. Over time the sulfate can also grow through the separator, and contact other plates causing a sulfation short. Gel batteries due to the presence of the gel and a separator resist this type of failure exceptionally well. While being very problematic for an AGM or flooded battery.

Recovery from discharge

The Gel battery is also good at recovery from deep discharge. AGM and most flooded batteries can be over discharged to the point where it is almost impossible to recharge them. This is because the electrolyte can be driven to almost pure water by the discharge and this leaves no ions in the solution to conduct current. So when the battery is placed on the charger, no charge current can flow through the battery to recharge the plates. The Gel battery due to tight structure of the gel always has some ions to conduct charge current resulting in excellent recovery from deep discharge.

Battery abuse

Another important advantage of the Gel battery is that it is more tolerant to overcharge abuse than an AGM. Almost any loss of water in an AGM battery results in loss of performance due to the so-called starved electrolyte method of construction. In a Gel battery, there is commonly an excess of electrolyte that migrates into the plate area providing some water reserve. In an abusive situation, this reserve can help extend the life of the battery.

Calcium alloy grids

Another feature of the Gel battery is that it has calcium alloy grids. Calcium alloy batteries require less overcharge to become fully charged than antimony alloy batteries. For PV applications where there is limited time and energy available for recharge, this can be a huge advantage. A typical antimony alloy battery will require at least 10% and sometimes more overcharge to get fully charged. A Gel battery will require only about 4-7% overcharge and for shallow DOD’s even less. A significant point in that it shows the superiority of the Gel battery in cycling applications.

The Right Battery for the Right Application

As you can see the AGM just can not compete with the Gel battery in a cycling application. You must always consider using the right battery for the right application. The AGM’s application is a starting battery offering high CCA’s, but has no place in a cycling application such as in a PV array or as a house bank of batteries on yacht.  However in subtropical and tropical environments a Gel battery will also deliver high CCA’s and can be used in the same starting application as an AGM without worry while receiving all the benefits of the Gel over an AGM. 

Stay Charged,

AW