Last time I briefly introduced the solar generator and what it entails.I also mentioned that one of the most essential stuff we need for a solar generator is a battery.Battery is very fundamental in a solar power system.Without battery you cannot store energy for a later use especially when there is no sunshine.Today I am going to explain what kind of battery you need and also tackle how to connect the battery to get to the solar panel in order to get a high power output.
There are many types of batteries available outside there in the market.However,the battery that is widely used in Photovoltaic system is the lead acid batteries.Other types of batteries such as nickel-cadmium battery may be used but the advantages of lead acid batteries ensures that it is still the most poplar choice.
Battery types
There are two main types of lead acid battery;starting battery and axillary power battery.The two battery types are constructed in completely different ways; having different plate thicknesses etc. The number of times a battery can be discharged is called cycle life.This is what determine its suitability for use with solar cells.The most common type of lead acid battery is car batteries. A car battery is an example of starting battery.It can survive only 5-10cycles and will be damaged if it is deeply discharged.Therefore not appropriate for use in Photovoltaic system.A car battery is designed to provide a very large amount of current for a short period of time.This surge of current is needed to turn the engine over during starting.Once the engine starts,the alternator provides all the power that the car needs,so a car battery may go through its entire life without ever being drained more than 20% of its total capacity.To achieve a large amount of current,a car battery uses thin plates in order to increase its surface area.On the other hand a deep cycle battery that is highly used in solar cell system is designed to provide a stead amount of current over a long period of time.A deep cycle battery can provide a surge when needed ,but nothing like the surge a car battery can. Deep cycle battery is also designed to be deeply discharged over and over again something that would ruin a car battery very quickly. To accomplish this, a deep cycle battery uses thicker plates.
Leisure battery
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Exide G80 Gel leisure battery 80Ah
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A leisure battery is an auxiliary power battery designed to provide a steady rate of power over a period of time. A deep cycle leisure battery is designed to perform a high number of discharge/recharge cycles without loss of battery health.They are the cheapest deep cycle battery.They look similar to a car battery but have a different plate construction. Their capacity is normally in the range of 60 to 120 Ah at 12 Volts, making them most suitable for smaller systems.
Essentially,the higher the Ah the longer it will last between charges.The higher the Ah figure,the physically larger the battery.To main capacities are the 85Ah leisure battery and the 110Ah leisure battery.The cycle life of leisure batteries is limited to a few hundred cycles, meaning that they are most suitable for systems which will not be used every day, such as those in caravans or holiday homes.The vast majority of leisure batteries are
wet lead acid/flooded type batteries as they are cheaper to produce and extremely easy to look after.They are Lead acid batteries that have caps to add water. Many
manufacturers make these types for Solar Energy use. Trojan, Surrette,
and Deka are probably the most well known. All flooded batteries release gas when
charged and should not be used indoors. If installed in an enclosure, a
venting system should be used to vent out the gases which can be
explosive.You also have to handle wet lead acid batteries carefully due to their acid content;you have to keep them upright for example.
Gel batteries such as the Exide G80 80Ah Gel leisure Battery have no liquid content so can be stored in any orientation and are safe to handle.The picture of
Exide G80 Gel leisure battery 80Ah is shown above.
Gel Leisure batteries are extremely low gassing so can be safely installed inside the cabin of a motorhome. Downsides to gel are that they can be expensive and you have to be very careful not to overcharge them.
AGM(Absorbed Glass Mat) batteries are the latest technological development in leisure and caravan batteries that blurs the distinctions of the various types, combining all the best features.IT IS THE BEST AVAILABLE BATTERY FOR SOLAR POWER SYSTEM USEHL.Instead of using gel, AGM batteries use a fibreglass type material to hold the electrolyte in place, making them spill-proof and extremely vibration resistant. The AGM battery can be constructed with extremely
thin separators which keep the internal resistance low. This means that you can
leverage high power from a small volume which makes the AGM battery ideal as a starter
battery as well as auxiliary battery. The AGM battery has one drawback which is that the amount of acid is limited.
All acid must be absorbed by the separator paper and when the small amount of acid
has been converted into lead sulphate, this signals that the "petrol tank" is empty.
To deal with this problem, the AGM battery often have a somewhat higher acid weight.
This means that an AGM battery can, and often should, be charged using a voltage
that is a little higher.
Again, you must be careful not to overcharge AGM batteries.
Traction battery
The term traction battery relates to all batteries used to power electric vehicles. This can mean anything from a mobility scooter to a fork-lift truck, so encompasses capacities from 30 or 40 Ah to many hundreds. The smaller traction batteries are usually 6 or 12 Volt units, where the largest are single 2 Volt cells. Traction batteries are ideal for solar power applications, as they are intended to be fully discharged and recharged daily. The larger traction batteries can withstand thousands of discharge cycles. There are also batteries known as semi-traction batteries, which can be thought of as higher quality leisure batteries, exhibiting a greater cycle life. Marine,cart golf and RV batteries also fall into this category.Traction batteries generally operate in very harsh operating environments and must withstand wide temperature ranges ( -30°C to +65°C) as well as shock, vibration and abuse.A very popular battery for small systems is the Golf Cart battery. They
are somewhat more expensive than deep cycle recreational batteries but
are probably the least expensive choice for a small system on a budget.
Sealed Lead Acid batteries
There are many types of sealed lead-acid batteries, ranging from those of 1 or 2 Ah to single cell traction batteries of hundreds of Amp-hours. The advantages of sealed batteries are obvious; they need no maintenance and are spill-proof. They do have disadvantages however; they are more expensive than other battery types, they require more accurate charging control and can have a shorter life, especially at high temperatures. Sealed batteries are most appropriate where the solar power system will need to operate for long periods without maintenance.Examples of Sealed Lead Acid Batteries are absorbed glass mat and Gell cell that I explained above.
Battery Maintenance
Deep cycle batteries such as those used in solar power systems have much thicker lead plates to make them last longer. Deep cycle batteries should never really be discharged to below 20% of their full capacity, because internal resistance causes heat and damage when they are recharged. Renewable energy systems usually use a low-charge or low voltage warning light or a low-voltage cut-off switch to prevent the type of damage that will shorten the battery's life.
Battery shelf life can be extended by storing them at a lower temperatures, because the chemical reactions in the batteries are slower. However, in order to reach their maximum voltage, batteries must be returned to room temperature. Therefore, most battery manufacturers do not recommend refrigerating batteries.
Battery safety, explosions and hazards
A battery explosion is caused by the misuse or malfunction of a battery, such as attempting to recharge a non-rechargeable battery or short circuiting a battery. Explosions are most likely to occur when a short circuit generates very large currents. In addition, deep cycle batteries can release hydrogen when they are overcharged (due to electrolysis of the water in the electrolyte). Normally the gas dissipates quickly. However, this gas can be ignited by a nearby spark (for example, when removing the jumper cables).
Attempting to charge a battery beyond its electrical capacity, ie overcharging, can also lead to a battery explosion, leakage, or irreversible damage to the battery. It may also cause damage to the components in which the overcharged battery is used.
When a battery is recharged at an excessive rate, an explosive gas mixture of hydrogen and oxygen may be produced faster than it can escape from within the walls of the battery, leading to pressure build-up and the possibility of the battery case bursting. In extreme cases, the battery acid may spray violently from the casing of the battery and cause injury.
Battery explosions can also occur in maintenance free lead-acid batteries if the valves fail or are blocked. The pressure rises within the cells until a short-circuit ignites the hydrogen-oxygen mixture. Such explosions can cause severe injury. The problem can be detected in most batteries if the sides appear swollen, or if the battery feels hot to touch.
I hope this helps you learn more about batteries to use in you Photovoltaic system!In my next posting I will explain how to build your own large battery bank by connecting the batteries in parallel or series.
typical battery bank
This is a typical of a battery bank by
free sun power . These are 12 volt 105 AmpHour
AGM lead acid batteries wired in parallel. With 1575 total AmpHour
capacity and using 125 to 200 AmpHours per day,He uses around 300 to 350 AmpHours before he recharge to increase the battery life.With this technique the battery can last longer.That means without recharging it can last 2 to 3 days.For people who live in places with less sun supplementing the system with a mid sized AC generator to charge the battery during the period with less sun will be advisable.Replacing power hungry appliances with with alternative energy source of energy such as natural or propane gas.Examples of power hungry appliances include dryers,heaters,electric stoves e.t.c.It is better to replace or buy appliances that consumes less power to around 1,000watts at most.
