How solar batteries work

Solar batteries are one of the most important parts of isolated solar installations. These allow us to make use of the accumulated energy at times when electricity is not being generated since it has previously been stored. However, they are also one of the most expensive elements of the installation, therefore, it is important to know how they work, what types there are and how we can configure them in an isolated photovoltaic installation. Pay attention to know more!

Solar batteries: How do they work? 

As we mentioned in the introduction, solar batteries are the devices that allow us to store the surplus energy that is generated in the solar panels of a photovoltaic installation (mainly isolated). In this way, we will be able to use electricity when there is no sunlight —for example, during the night or during a stormy day when our installation is not producing energy or the amount is very low—. The solar battery system of an installation makes it possible to make the most of the installation and improve energy efficiency. They also have a long series of advantages:

• They increase the profitability of the self-consumption solar installation.
• They maximize savings on electricity bills, up to 80%.
• They reduce the carbon footprint in the home —reducing CO2 emissions—.
• They guarantee greater independence from the electrical network (they can even guarantee absolute independence).
• There are subsidies to reduce the total cost of the solar installation.

In general, solar batteries are made up of two electrodes that are immersed in an electrolyte where the charge and discharge reactions take place . Each of the batteries consists of small 2V electric accumulators integrated in the same part. Depending on the quantity, they can supply direct current of 6, 12, 24 and 48V.. The accumulator corresponds to the cell that stores energy through an electrochemical process. For example, a 12-volt battery has a series array of 6 lead-acid cells of 2 volts each. Keep in mind that solar batteries use chemical energy to store or release electricity, so when they run out, the voltage weakens and the batteries must be replaced. That is why it is not recommended to deplete the batteries to the minimum — keep in mind that the different types of batteries for solar panels offer a different discharge capacity from each other. This ability to undergo a process of charging and discharging is known as the cycling resistance of a battery.

Solar batteries: operation within the installation 

The operation within the installation of solar batteries or photovoltaic batteries is to provide energy to the system when the solar panels are not generating electricity. In the opposite case, when the solar panel generates electricity – and there are surpluses – the excess energy is used to charge them. The batteries transform the electrical energy they receive from the photovoltaic modules into chemical energy. To carry out this conversion, a reaction takes place inside it because within the electrolyte, which is a solution of sulfuric acid and water, two different materials are submerged —such as those of the positive and negative plates—. In this way the electricity flows from the battery through the electrical circuit – as long as there is one connected between the positive and negative poles. As the battery discharges, the lead composition of the plates becomes more similar, at which point the density of the acid decreases, as does the voltage between the terminals. 

Types of batteries for solar panels

Now that you have seen what solar batteries are, how they work and their advantages, we are going to briefly talk about the different types that exist; since the benefits that solar batteries can give us, operation and others also depend on it:

• Monoblock battery : Intended for small installations. They are made with acid lead, which supposes an evaporation of gases after heating. They require annual maintenance, although they offer great performance and low cost.
• AGM battery : Also known as Absorption Glass Mat batteries . The technology of these batteries allows them to absorb acid faster, and they also do not require maintenance since they are sealed. They are recommended for large installations as they withstand a large number of cycles —even if they are subjected to a deep discharge—.
• Lithium battery : The characteristic of these batteries is that they charge faster than other types, offer a higher energy density and have a long useful life. They are lighter and do not emit gases, so they can be installed in places without ventilation. In addition, they do not have a memory effect, so they can be discharged 100% without suffering. However, its cost is higher. 
• Stationary battery : They are called stationary because they are constantly charged. They contain a regulator that serves to feed consumption and to charge them. Within this type we can find the stationary OPzV, the OPzS and the TOPzS.
• Gel battery : They contain the gelled electrolyte and are sealed, so they do not give off harmful gases. They usually have about 800 life cycles. Its use is recommended for medium or small-sized installations.

Although we have already summarized the different batteries, in this article you can learn more specifically about the characteristics of the different types of batteries for solar panels .

Configure batteries: in series or in parallel

The way in which the batteries should always be configured, if it is the case that you are going to do the installation on your own, is in series —never in parallel— . You can learn more about installing batteries in this article .