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Last updated: 01 April 2019

Solar Batteries

Read about the Advantages of Solar Batteries.

What Are Solar Batteries?

Solar batteries are deep cycle batteries that provide energy storage for solar, wind and other renewable energy systems. These batteries are different from other ones such as a car battery for example. A deep cycle battery is capable of surviving prolonged, repeated and deep discharges which are typical in renewable energy systems that are "off grid".

Off grid photovoltaic solar panel systems are made up of photovoltaic panels, solar charge controllers and batteries. These solar batteries (deep discharge batteries) are a key component in a renewable energy system. Solar batteries require energy storage produced by a wind turbine, a solar panel or a hydroelectric system, which will be connected to the utility grid. Solar batteries are very useful if you want to use an independent electricity network or in case of a power failure.

Without the battery component which can store the harnessed energy from the sun, there would only be power during the daytime or while the generator is running. A solar battery storage system costs between £1,200 and £6,000 based on the battery material, capacity, depth of discharge, and lifespan. Even though the cost is not inexpensive, a good solar battery storage system will pay off in the long run. There are four different basic types of solar batteries which are described further down.

Unlike other batteries, solar batteries are designed to be unloaded and reloaded repeatedly. To maintain solar batteries in good condition and prolong their lifespan, manufacturers recommend limiting depth of discharge to 20%. Do not allow the type of solar batteries to reach a depth of discharge of more than 50%. Monitoring solar batteries helps to have a better maintenance and provides statistics about the general health functioning of the batteries.

Types of Solar Batteries

  • RV/ Marine Solar batteries – Marine solar batteries are suitable for smaller systems and are used for boats and by people who own RV’s. In addition, these types of solar batteries work best whent no other form of electricity can be produced, due to their lower capacity for continuous service.
  •  Flooded type – Flooded type batteries are lead acid batteries which have caps for adding water. These types of batteries are not very expensive to buy and have a good life span compared to the Marine solar batteries. It is recommended that flooded type batteries be used outdoors, as they emit gas when charged. If however, these are installed inside, then it is strongly recommended that a venting system should be used to vent out gases, which can be explosive and toxic.
  •  Gel – As opposed to the flooded type, sealed gel batteries have no vents and do not release gases. Because of this, venting is not important and these batteries can be used indoors without any risks The advantage of this is that the battery will have a more constant temperature indoors, leading to an increase in the maintenance, and therefore performing better than the flooded type.
  • Absorbed Glass Mat batteries (AGM) – A glass mat is used between the plates to hold the electrolyte. These type of batteries are leak proof which means that they do not release gas when charging. In addition to this, Glass Mat batteries also have a superior performance, making them the best types of batteries. They have all the advantages of the sealed gel types but are of higher quality. Other advantages include the fact that they maintain voltage better, they self-discharge slower and finally they last longer. Of course, their superiority does mean that they are the most expensive out of the four types.

Characteristics of Solar Batteries

Sizes of Solar Batteries

Solar batteries vary in size and simply, put can be of small or large proportions. Overall though, size and weight match the solar cell capacity of the battery. To be more specific, the dimension of solar batteries can range from those that weigh less than 4 kg, to solar batteries that weigh over 100 kg. If you need a battery with a large storage capacity, you need to ensure that you have enough space to store one or more these, according to your needs.

Storage Capacity

Storage capacity of electricity in the solar cells varies. Depending on the requirements of each person, a set is designed comprising of one or more batteries. The choice of individual voltage will depend on the total system voltage of the solar panels and on the storage requirements. Often 2V solar batteries offer the highest storage capacity but can take up to 24 pieces if the system is 48 volts.

Connecting Solar Batteries

Solar batteries can be connected through connectors (links) in series, parallel, or a combination of both, depending on the system voltage of solar batteries and on the storage capacity. Although a solar battery system with a considerable capacity can be a big expense, with proper maintenance, it should last anywhere between 5 and 10 years.

Battery Care

Taking care of the batteries is fundamental as it can have a big impact on their lifespan. This means that the temperature and humidity should be monitored, given that as the batteries get colder, their voltage drops making the performance suffer. This is why the AGM batteries have an advantage over the rest, since they can be stored indoors.

Charging the Battery

Another important thing to consider is how deeply you discharge your batteries, known as the depth of discharge, before the next charge cycle. The batteries will last longer if you keep them as charged as possible. In regards to lead acid batteries they work best when fully charged. They will last much longer if you do not discharge them too deeply. However, they can withstand discharges down to 20% or so, with the risk of decreasing their lifespan. Determining the percentage of battery charge can be done with a common voltmeter.

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