Sun Xtender® Solar Energy AGM Battery vs. Gel Battery ComparisonSun Xtender® Solar Energy AGM Battery vs. Gel Battery Comparison
The review below addresses our Sun Xtender® Absorbent Glass Mat [AGM] Solar Energy Batteries compared with gelled electrolyte batteries.
Concorde Battery Corporation has had years of experience manufacturing quality gelled electrolyte batteries trade named “Gel Power®” before developing the AGM battery technology for Sun Xtender® Series solar energy batteries and is aware of the gel’s inherent limitations.
Prior to 1984 Concorde manufactured wet [flooded] batteries for both US Military and Commercial Aircraft. The US Military requested that we develop a sealed battery with excellent energy density and efficiency. Our sealed gel batteries were not acceptable due the low energy density, and that with heat and vibration, the gel and electrolyte breaks down and separates.
We developed our proprietary AGM battery technology for these applications and Solar / Photovoltaic / Renewable Energy Storage applications. We were very successful in this venture both in military and commercial applications. For instance, we are the world leader in sealed battery technology for aircraft use.
From this excellent start we set forth to develop our AGM technology for “deep cycle” applications. The new AGM batteries outperformed our gel batteries by substantial margins in size/weight reduction, capacity, cycle life and operation in both severe heat and cold climate conditions. Effective in early 1987 we discontinued our gel battery in favor of our superior AGM battery technology for solar energy applications.
Gel technology is old and has been outdated by our AGM battery technology. Concorde is the leading manufacturer to have designed a truly long life, deep cycle AGM product for Solar Energy Storage. Most other AGM manufacturers have concentrated on stand-by [back-up] battery technology which is not suitable for the Renewable Energy / Solar Energy / Photovoltaic Industry’s needs.
With that said there are some serious limitations inherent in the gel technology which affects all past and existing designs. Some of these include:
1. The gel product employs a highly viscous [semi-solid] electrolyte mixture of silica gel/electrolyte. The electrolyte is difficult to keep in a mixture and is not chemically bound. In high temperature applications fissures and voids in the semi-solid electrolyte develop more rapidly which causes the battery to lose capacity faster. Handling and vibration are other operational factors that cause the gel and acid mixture to separate.
2. Electrolyte is necessary for the ionic connection between the anode [negative plate] and the cathode [positive plate]. In short, the discharge and the recharge of a battery is a circuit and it requires a complete connection in order for either charge or discharge to occur. Electrolyte provides this internal connection between the plates. When electrolyte is not present ionic exchange is severely affected. A “dry charged” battery is incapable of providing any electrical energy until activated, thus air is a poor electrolyte.
3. As gel batteries age the semi-solid electrolyte shrinks and dries out. Also, the gel develops fissures which grow into large voids internally by gasses generated during charge. While voids are optimum for oxygen transport, ions cannot span the void gap within the electrolyte and more specifically at the plate surfaces. As a result the internal connection is reduced gradually over repeated cycles causing capacity loss. High temperatures increase the rate.
By contrast in our Sun Xtender® AGM battery for Renewable Energy Storage and Solar / Photovoltaic applications, the microporous glass mat separator holds the liquid electrolyte like a sponge [excellent wicking characteristics] and is not solid. Shrinkage of the electrolyte does not occur. As minimal drying occurs, the ability of the liquid electrolyte to move through the woven glass separator to dryer areas of the plate efficiently maintains a proper connection. Yet, this electrolyte is confined to the battery’s plate areas via the separator material so no electrolyte spillage can occur.
This offers the customer advantages of both a gelled electrolyte battery with no electrolyte spillage [a sealed battery] and a flooded battery with liquid electrolyte, plus many additional advantages over both types. Please refer to “Reasons to Specify Sun Xtender® Batteries”. It describes safety, construction and technical features of the solar energy batteries.
4. It is much easier to fill a container with a liquid versus a semi-solid. Our AGM batteries require less space between battery plates, thus reducing the internal connection length. The shorter distance insures good electrolyte connection and substantially reduces the internal resistance of our Sun Xtender® AGM batteries. As a result the lower internal resistance allows our AGM battery to be far more charge efficient and provides 15 to 30% more available energy than gel batteries.
5. Overcharging of gel batteries by allowing the voltage to increase beyond their recommended optimum settings will seriously affect its life. The major reason for this problem is the limited hydrogen/oxygen recombination capabilities of gelled batteries. From the Technical Manual of a major gel battery manufacturer they state that battery life will be reduced by almost 60% by charging at 0.7V higher than the recommended levels. Their recommended charging voltage is 13.7V [2.28 V/cell] at temperatures between 70 and 79°F [21 and 26°C]. By charging at 14.4V [2.40 V/cell], expect a 60% loss in life until the batteries capacities fell below 50% of rated capacity.
The Sun Xtender® AGM deep cycle battery is more forgiving in overcharge conditions and its ability to recombine the hydrogen and oxygen gases back into water is more efficient. The recombination rate is better than 99%. Concorde has tested its AGM batteries to find out the effect on cycle life by overcharging. Our standard recommendation for charge voltage is 14.2 to 14.4V [2.37 to 2.40 V/cell].
We have life cycle tested our Sun Xtender® solar energy batteries with voltages of 14.2 to 15.2 in 0.2V increments until the batteries’ capacities fell below 80% of rated capacity [that’s a full 1 volt difference]. The results were the batteries at 15.2V failed first and, as the applied voltages were lowered in 0.2V increments, these failed but each lasted a longer period. The batteries at 14. 2 and 14.4 V. were the longest life [both these batteries had the same life period]. Even at a difference of 1 full volt of overcharge, for the batteries at 15.2V the cycle life was reduced only 23%.
Therefore, based on overcharging conditions only, if you took a 100 AH Gel battery with an expected life of 1,000 cycles, by increasing the charging voltage by 0.7V, it could be expected that after about 400 cycles it could deliver 50 AH. Conversely, taking a Sun Xtender® 100 AH battery and increasing the charging voltage by 1.0V, it could be expected that after 770 cycles it could deliver 80 AH.
6. Charge acceptance and charge efficiency of gel batteries are less than that of our AGM batteries.
Testing of gel batteries and our Sun Xtender® AGM batteries for charge acceptance included discharging the batteries to a charge regulator’s Low Voltage Disconnect [LVD] setting, which was 11.4V for a 12V battery, and then recharging them until the Load Reconnect point at 12.6V. Our AGM batteries had returned 25% of their capacity while the gel batteries had returned less than 1% of their capacity.
In another test, using a charger/inverter, the batteries were discharged to 50% [fairly common in a PV system] of their capacity and then recharged. The gel battery took 34% longer to reach full charge than our AGM.
SUMMARY
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CONSIDERATIONS | SUN XTENDER® AGM | GELLED BATTERY |
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Electrolyte | 1. Liquid, Absorbed in Glass Mat
2. Remains Fluid Over Life, No Loss of Capacity | 1. Highly Viscous [semi-solid]
2. Gassing on Charge Causes Dry Out, Voids & Loss of Capacity. High temperatures increase dry out and voids. |
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Impedance | Low - Provides Better Charge Acceptance and Operation even at Low Temperatures | Higher - More Difficult to Charge at Any Temperature |
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Capacity Per Lb./Cube | Higher Capacity Due to Less Space Between Plates | Lower Capacity - the Gelled Electrolyte Takes More Space |
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Voltage Overcharge | Tolerant to Overcharge | Causes Extreme Loss of Life |
Charge Efficiency
[AH In to AH Out] | 95%+ Efficient | Less Than 90% Efficient |
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Charge Acceptance | Even When Discharged to 100% the Battery Easily Accepts Charge | When Discharged to 80% orGreater Acceptance is Poor |
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Cycle Life | Concorde Test Standards
20% DOD - 2,800 Cycles
50% DOD - 1,050 Cycles
80% DOD - 550 Cycles | Major US Manufacturer’s Data*
25% DOD - 1,500 Cycles
50% DOD - 650 Cycles
80% DOD - 390 Cycles
*Less Demanding Test Standards than Concorde’s |
The data/information contained in the Sun Xtender official website has been reviewed and approved for general release on the basis that these documents contain no export-controlled information.
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