Deep Cycle Battery Better for Solar Battery system

What are deep cycle batteries?

In the context of renewable energy, batteries usually mean deep cycle batteries.

Deep cycle batteries are an energy storage units in which a chemical reaction occurs that develops voltage and results in electricity. These batteries’ design is to cycle (discharge and recharge) many times.

While a car battery’s design to deliver a burst of energy for a short time, a deep cycle battery provides power at a steady rate over a long period.

There are different types of deep cycle batteries such as:

flooded batteries,
gel batteries
AGM batteries (Absorbed Glass Mat); and
more recently – lithium-ion

All have different manufacture processes.

Among conventional deep cycle batteries, the flooded battery is the most common, which is similar to the standard lead acid battery in your car. The gel batteries, as the name suggests, have a gel-like substance in them and the AGM batteries consist of acid suspended in a glass mat separator.

Deep cycle battery ratings

Up until recently there were two ways batteries were generally rated: volts and amps.

Amp hours (Ah) are the rating capacity available in chemical energy inside a battery that is converted into electrical energy. It also refers to the amount of energy that the battery can store, or conversely, it can be seen as the discharge rate, which measures the time it takes to discharge a battery before it needs recharging.

The capacity of the battery reduces if the battery discharges in a shorter period, for instance over 1 hour. The amp hour capacity reduces by about 50% and so will the amount of cycles.

Where the battery discharges at a constant rate of current over a number of hours, this is referred to as the “C” rating. For example, many small batteries rate at the C20 rate, this means that they will deliver their amp hour capacity if discharging over 20 hours. The types of batteries in large stand alone power systems rate at C100 which means that they are designed to discharge over 100 hours or 4 days. This will give you a life span typically of about 15 years.

You can learn about battery voltages and state of charge here.

More recently, with the advent of the home energy storage revolution; batteries for residential applications are often referred to by their kilowatt-hour (kWh) capacity.

Deep cycle battery Discharge cycles

Selecting a battery can be confusing. While all will claim to be particularly well suited to a energy storage purpose, all deep cycle batteries are not created equal, even within their own type such as AGM, Gel or Sealed Lead Acid.

As a deep cycle battery can be quite an investment, you’ll want one that will last the distance.

One of the ways to determine this among conventional types is the cycle rating; that is how many times it can be discharged and recharged. One of the best benchmarks for this is the IEC 896-2, based on a 100% discharge.

While discharging a battery 100% is not recommended as it will significantly decrease the life of any deep cycle battery, the IEC 896-2 provides a good baseline for drawing comparisons between brand X and Y or even different battery lines from the same manufacturer.

How to Choose a Deep Cycle Battery

When you’re shopping for a deep cycle battery, it’s easy to get overwhelmed with the different terms and promises that many manufacturers use to market their product. What is a marine battery? Or a VRLA? But choosing a battery isn’t difficult if you know what to look for. Here are some things to take into consideration:

BATTERY TYPE

There are two categories of deep cycle batteries: flooded and valve-regulated (VRLA). Each has certain advantages and disadvantages. Here’s a brief overview of each:

Flooded Deep Cycle Battery

Flooded deep cycle batteries, also known as wet cell batteries, are characterized by their liquid electrolyte component, which is composed of sulfuric acid and distilled water. Users should regularly open the battery and perform routine maintenance, which includes cleaning and “watering,” or adding distilled water to replace the liquid that evaporates during operation. All deep cycle batteries have thick plates of the active material, which is lead in the case of lead acid batteries, which allow for sustained power generation and deep discharge.

Valve-Regulated Lead Acid Battery

Valve-regulated batteries were created to offer a maintenance-free option for deep cycle applications. There are two main types of VRLA batteries: absorbed glass mat (AGM) and gel batteries. Each uses a different form of electrolyte; for AGM, a fine boron-silicate mat is soaked in electrolyte to around 95% saturation, and evaporated gases are recaptured to eliminate the need for watering. In gel batteries, sulfuric acid is mixed with a gelling agent to form a thick, almost stiff substance. Neither type of VRLA battery will leak electrolyte if the casing is cracked or punctured, which makes them attractive for applications in which the battery will face rough conditions.

APPLICATION

Perhaps the most important consideration when choosing a deep cycle battery is what you intend to use it for. Here are some situations that make a difference in the type of deep cycle battery you choose:

Stationary or Level Equipment

If you’re looking for a deep cycle battery for a vehicle that remains level or a stationary application, a flooded deep cycle battery may be your best bet. Flooded batteries are the most common type of deep cycle battery, and as such they are generally easier to find and more cost-effective than other types of batteries. Because they use a liquid electrolyte, however, they can only be used in an upright position. They should also be used in applications which allow easy access for charging, watering, and other maintenance.

Examples: forklifts, renewable energy storage

Variable Conditions

In applications where conditions such as temperature and required power draw vary, a VRLA battery such as an AGM battery may be the best option. Because VRLA batteries are sealed, there is less chance of damage or weathering of the inside components, which helps to ensure a longer lifespan and better performance. VRLA batteries can operate in any orientation, not just upright like flooded batteries, so they’re ideal for situations where they might frequently tip or are installed sideways.

Examples: boats, RVs

Maintenance Capabilities

In addition, VRLA batteries may be better suited in situations where regular maintenance is difficult. All deep cycle batteries need to be charged according to manufacturer specifications, so some amount of maintenance is always required, but if you’re not able to water your battery frequently for whatever reason, you should consider buying a VRLA.

BATTERY QUALITY

This consideration is not just exclusive to deep cycle batteries — all batteries and applications benefit from a high-quality manufacturing process. But because of their specialized applications and long lifespan, deep cycle batteries can entail a significant investment, which may cause buyers to consider a less expensive, lower quality product. For best performance and return on investment, we strongly recommend higher-quality, more respected brands of deep cycle batteries.

Choosing a deep cycle battery can be a confusing process. Start by understanding the different types of batteries and which are best suited for your intended applications, and you’ll be on the right track. Download our complete guide to deep cycle batteries to learn more:

AGM or GEL ? How to choose solar battery for solar power system ?

We can easily understand the difference of AGM and GEL by the following chart :
AGM and GEL’s deep cycle are suitable for solar However, if it is a more extreme climate or outdoor, Gel’s deep cycle will have a longer life span.

ITEM	GEL／AGM	COMPARE
Electrical performance	The pores of the gel structure are narrow, so the ions are more clogged, and the internal group of colloidal sealed lead acid batteries is larger than AGM. Therefore AGM’s high-power discharge performance is better.	AGM is better
Size	GEL electrolyte is 20% more than AGM, and it adopts flooded process, so AGM energy density is high	AGM is better
Ventilation requirements	GEL is flooded battery, The cracks generated by the gel provide oxygen circulation. GEL must be well ventilated. AGM has 8% of the gap in the separator, and no electrolyte is filled.	AGM is better
Thermal runaway	The AGM sealed lead-acid battery adopts a liquid-lean design. In the separator plate, 8% of the porosity must be maintained and the electrolyte is not allowed to enter. Therefore, the internal heat of the battery is poor, and the oxygen generated during charging reaches the negative electrode, which generates heat.If you can’t dissipate heat immediately, the battery temperature will increase.	GEL is better
Operating temperature	GEL working temperature adaptability is better than AGM	GEL is better
Cycle Life	AGM battery cycle life is about 400 times; GEL battery cycle life is about 600 -800 times	GEL is better
Standby Life	Both AGM and GEL can have a long life design.	Both are good

What is GEL battery ?

VRLA GEL battery is valve-regulated lead-acid battery (VRLA ) + Gel electrolyte cell technology battery. This is one kind of lead-acid battery for energy storage.

Gel battery is using gel as electrolyte instead of liquid acid. Gel is usually produced by homogeneous dispersion of pyrogenic silica in diluted sulfuric acid. Pyrogenic silica is a kind of powder of very well dispersed SiO, which absorb more than 10 times of its weight acid liquid to produce gel. Because of the thixotropic property of gel, the agglomerates are connecting themselves together as a network which keeps the liquid inside and become gel structure after a certain gelling time. The Gel battery has no liquid inside, the electrolytes is in gel form and stand solid between positive and negative plate inside battery.

The technical features of Gel battery technology :

Using gel as electrolyte
Plate thickness tolerance is not critical since the high compression of plates group assembly is not necessary
More electrolytes for better contact with plates and active materials and container walls, it is good for releasing internal heat and cooling battery temperature.
Using the extra microporous separator which can:
a/ reduce the depolarization of the negative electrode and avoid negative plate sulphation
b/ without any liquid, significantly decreases thermal runaway
c/ Help to prevent short circuits by dendrite growth between the positive and negative plates during deep discharge
Better vent valve design to lower gas leaking rate to extend battery lifetime.

Compared to flooded battery, the advantages of Gel battery are :

Maintenance free, no need to add water
Safe operation since no liquid inside
Can be installed sideways ( upside-down is not recommended )
Long cycle life
Low self-discharge makes shelf life longer.
Long standby life due to its ability to keep electrolyte inside and steady
Performance stays high and stable until the end of life
Tolerance to abuse and heat during operation, good for extreme weather

The advantage of Gel battery in application :

Maintenance free
When battery is charging, hydrogen would be absorbed and reversed to electrolyte by plates. It doesn’t need to refill water and balanced charge, which makes maintenance free.

Flexible installation
AGM separator keep electrolyte absorbed in glass mat and still. Battery can be used or positioned in any orientation.

Longer lifespan in extreme weather
Gel cell electrolyte prevent electrolyte being evaporated in high temperature or being frozen in low temperature, which keep battery in high performance in extreme weather. Extremely safe When excessive gas production by inappropriate charging occurs, safety valves will automatically emit the gas to prevent battery cracked.

Long standby life, Better cycle performance
Anti-corrosion lead-calcium alloy plate provides longer float charging life. AGM separator can trap electrolyte and prevent active materials on positive plate dropping at the same time. Moreover, it gives better deep discharge cycle performance.

Longer shelf life
Special lead-calcium alloy plates make lower self-discharge for longer shelf life.

High rate performance
Low inner resistance allows higher discharging and charging current for better performance in high rate application

What is AGM battery ?

VRLA AGM battery is valve-regulated lead-acid battery (VRLA ) + Absorbent Glass Mat (AGM) technology battery. This is one kind of lead-acid battery for energy storage.

The technical features of AGM battery technology :

Sealed with special compound epoxy and using pressure controlled vent valves.
Electrolyte acid is absorbed in special glass mat separators to prevent electrolyte acid leaking or evaporating.
No spilling – can be operated in any position. However, upside-down installation is not recommended.
Using a recombination reaction to prevent hydrogen and oxygen gases escaping and make this two gases into water, which can keep acid water in same level.
Maintenance free. No need to add water like flooded battery.

VRLA AGM battery uses recombinant technology. The oxygen produced from the positive plates of the battery is absorbed by the negative plates. This suppresses the generation of hydrogen at the negative plates. The recombination of oxygen and hydrogen leads to Water, retaining the electrolyte amount within the battery. Water re-filling is never required.

Compared to flooded battery, the advantages of AGM battery are :

Vibration resistance due to sandwich construction
Performance well in cold temperature
Spill-proof through acid liquid encapsulation in glass mat technology
High specific power, low internal resistance
Up to 5 times faster charge than flooded technology
Better cycle life than flooded systems
Water retention (oxygen and hydrogen combine to produce water)
Less sulfation because no need to open and add water

The advantage of AGM battery in application :

Maintenance free
When battery is charging, hydrogen would be absorbed and reversed to electrolyte by plates. It doesn’t need to refill water and balanced charge, which makes maintenance free.

Flexible installation
AGM separator keep electrolyte absorbed in glass mat and still. Battery can be used or positioned in any orientation.

Extremely safe
When excessive gas production by inappropriate charging occurs, safety valves will automatically emit the gas to prevent battery cracked.

Long standby life, Better cycle performance Anti-corrosion lead-calcium alloy plate provides longer float charging life. AGM separator can trap electrolyte and prevent active materials on positive plate dropping at the same time. Moreover, it gives better deep discharge cycle performance.

Longer shelf life
Special lead-calcium alloy plates make lower self-discharge for longer shelf life.

High rate performance
Low inner resistance allows higher discharging and charging current for better performance in high rate application

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