Why Deep Cycle Battery in PV System

What is a Deep Cycle Battery
This is a device to store electrical energy for later use. They reside under Storage Batteries and are rechargeable. They consist of electrochemical cells which produce electrical energy by converting chemical energy. As chemicals in the battery change, electrical energy is stored or released. In it’s simplest form it consists of a cell with two electrodes, an anode and a cathode and an electrolyte. The electrodes are of different type metal or metal compounds. The electrolyte solution can be acid or alkaline. Deep Cycle is a measure of the number of times you can fully discharge and recharge the battery before it goes dead. For example, if a certain battery has a cycle of say 100, you can fully discharge and fully recharge this battery 100 times. If you repeatedly discharge and recharge this battery to half of its capacity, then you can do this 200 times before the battery is dead.

Why we need Deep Cycle Battery in PV systems.
From the viewpoint of alternative energy systems we use deep cycle battery to collect DC electrical energy produced by the PV System for use at night or on cloudy days when the PV system’s output is low, the batteries should then complement for the shortage of energy.
Start-up power for motors (drawing larger amount of current than produced by the PV system) is primarily drawn from the batteries. Usually motors can draw 4 to 6 times the normal running load amperage or current (surge power). This can be more than the normal producing current of the PV or wind system. For example say the current produce by the system is 5 Amps. This production cannot go higher than that. A 3 Amp motor will start for example with 12Amps or higher for some 3 to 5 seconds, then the battery has to account for the extra 7 Amps otherwise the motor won’t start.

What kind of deep cycle battery can we use for the PV system.
There are different kinds and types on the market. Every one for it’s specific use in variety of conditions. The ones we need, must provide small amount of current for a long period of time (ex. night hours), night hours or cloudy days. And one that can withstand repeating discharge and charge cycles (deep cycle), and still last for years. This kind is a Lead acid deep cycle one and the most commonly used. It comes in two types the Liquid vented and the sealed one VRLA (valve regulated lead acid).The Liquid vented Lead Acid type is made of plates of lead and lead alloy and placed in a electrolyte solution of sulfuric acid and water. To protect it from overcharging, a charge controller is necessary, because when near full charge, hydrogen gas is produced.

Safety Precautions when installing deep cycle battery.
Be aware to the exposure of the following hazards:
- The presence of hydrogen gas, which is highly explosive
- The electrolyte (acid) is very caustic
- High short-circuit potential
- Possibility for electric shock.

How to care and so extend their life.
When we treat them the way we should they can go for years, 4 to 12 years. Those treatments consist of;
- the less % of discharge the better(ex. discharge only to 50% of their capacity) they wear off less
- do not overcharge (and so prevent the formation of hydrogen gas)
- use them in ventilated places
- do not expose them in hot ambient temperature
- do not mix old with new ones
- Since some of the water is lost during recharging, it must be replaced periodically
A battery bank is a combination of several batteries connected electrically together in series, in parallel or in series/parallel combination.

Specifications.
AH (Amp-Hour), is the capacity: meaning the amount of time in which it can deliver a certain amount of current to be completely discharged. Example: 100AH means you can draw 100Amps for 1 hour or you can draw 50Amps for 2 hours, or 200Amps for 0.5 hour. The product of Amps and Hour must equal AH.
RC (Reserve Capacity): is the total of minutes for a fully charged battery at 80 degrees F will discharge 25 Ampere to the point where its voltage reach below 10.5 volts. This is the rate of discharge. The slower the discharge, the greater the capacity.

Other types of Deep Cycle Battery
Gel batteries , the electrolyte (acid) in Gel batteries is not in the liquid form but is like gel. This makes the gel batteries safe to handle. There is no spilling of electrolyte if the battery break. But they have the disadvantage that they cannot be charged at a fast rate otherwise they produce gas that damage the cells of the battery. Extra precaution must be taken to limit the charging current. Loss of capacity in hot climates. Not recommended for hot countries.

AGM battery (Absorbed glass mat) a champion if not for it's price. One of the best among it's counter parts. Has all the benefits of all others plus more. It's internal resistance is very low so it can handle higher current and thus it charge and discharge faster.Very slow self-discharging when not in use.Thus complete discharge will take a long time, when stored away.When discharged it requires no water, thus low maintenance for several years. No spills. They are sealed VRLA (Valve-Regulated Lead-Acid) batteries and can be placed in enclosed areas, for they require no ventilation, because vapors re-combined into the electrolyte. High life cycle, even with deep discharge and recharge. They are used in many applications and can be obtained in many online stores.

When your batteries are nearly dead you can revive them with Recondition Battery and you can go some more years with a reconditioned battery. You can recondition a battery 3 to 5 times before it goes dead.

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