Panels photovoltaic solar energy

What Is a Solar Battery? Operation and Types

What is a solar battery? Operation and types

Solar batteries are electrical accumulators to store the electrical energy generated by a photovoltaic panel in a solar energy installation. Sometimes they are also known as photovoltaic batteries.

Batteries are electrochemical devices that use chemical energy to store or release electricity. In conventional batteries, reagents are introduced during battery manufacture. When the batteries run out, the voltage must weaken and the battery must be replaced.

Solar batteries are used to store the electrical energy generated by photovoltaic solar panels in the hours of greatest solar radiation. In this way, it can be used later at night or on cloudy days.

The use of batteries also makes it possible to provide a higher current intensity than what a photovoltaic panel can offer in operation. This would be the case if several electrical appliances were used at the same time.

Most of the solar kits offered in the photovoltaic market include batteries.

Not all photovoltaic installations have batteries. Sometimes, it is preferable to supply all the electrical energy generated by the solar panels to the electrical network. In fact, large electrical installations that use renewable energy are connected to the electrical grid.

How Is a Solar Battery Formed?

A battery consists of small 2V electric accumulators integrated in the same element. The batteries supply direct current at 6, 12, 24 or 48V. The accumulator is the cell that stores energy through an electrochemical process.

For example, when we talk about a 12-volt battery, we mean a series of 6 lead-acid cells of 2 volts each. Monoblock batteries are batteries composed of several 2V cells forming a single block.

Stationary batteries, also known as solar accumulators, are batteries made up of 2-volt elements connected in series until reaching the desired working voltage for the solar installation.

6V batteries are used in small and medium-sized photovoltaic installations.

How Do Solar Batteries Work?

The batteries have the function of supplying electrical energy to the system at the moment when the photovoltaic panels do not generate the necessary electricity. For example, at night or in times of low light.

At the moment when the solar panels can generate more electricity than that demanded by the electrical system, all the energy demanded is supplied by the panels and the excess is used to charge the batteries.

Batteries transform the electrical energy they receive from photovoltaic modules into chemical energy. This conversion is carried out from the reaction that occurs when two different materials, such as those of the positive and negative plates, are immersed in the electrolyte. The electrolyte is a solution of sulfuric acid and water.

Electricity flows from the battery as soon as there is an electrical circuit connected between the positive and negative poles.

As the battery discharges, the composition of the lead in the plates is more similar. At this time, the density of the acid decreases and the voltage between terminals decreases. 

The ability to undergo a constant charging and discharging process is known as the cycling resistance of a battery.

What Must Be Taken into Account Before Buying a Solar Battery?

Most important characteristics when choosing a battery or a solar kit:

  • Capacity. The capacity is the intensity of current in amperes (A) that can be obtained from a complete discharge of the electric accumulator when it has a state of full charge.

  • Charging efficiency. Charging efficiency is the ratio between the energy used to fill the accumulator and the energy actually stored. Therefore, the closer to 100% the better.

  • Self discharge. Self-discharge is the process of an electric accumulator that, without being in use, tends to discharge.

  • Depth of discharge. Depth of discharge is the amount of energy obtained during a discharge while fully loaded (%).

What Is the Lifespan of a Solar Battery?

The useful life of a battery for solar installations is usually around 10 years.

However, if frequent deep discharges (> 50%) are made, their useful life plummets. Therefore, it is advisable to install enough capacity so that 50% of the discharge is not exceeded.

Another very important factor is temperature. If the temperature is kept between 20 and 25ºC, the useful life will be around 10 years. On the other hand, if the temperature is altered by 10ºC, the useful life can be reduced by up to half.

What Are the Most Commonly Used Types of Solar Batteries?

Batteries are classified according to the type of manufacturing technology as well as the electrolytes used.

The types of solar batteries most used in photovoltaic installations are lead-acid batteries, due to the price ratio for available energy. Its efficiency is between 85-95%, while Ni-Cad is 65%.

Surely the best batteries would be lithium batteries, the ones used in mobiles. However, the lithium battery is not economically viable for this application.

Lead Acid Batteries for Solar Applications

Lead acid batteries are the oldest rechargeable batteries. These batteries have the ability to deliver high currents, therefore, their cells have a high power density.

This characteristic and their low price make them suitable for many applications, in particular in solar energy, for solar kits, and for motor vehicles. After all, they are capable of delivering the high intensity that starters need.

Because they are cheaper than any other type of battery, lead-acid batteries are widely used. However, these batteries have a low energy density in terms of volume and weight.

So if you want to accumulate large amounts of energy, the size of the battery will have to be very large. For this reason, it would not be the best choice for applications that require an offset. Typically used in large spaces.

They can be used to store safe food sources such as cell phone towers, hospitals, solar installations, and off-grid electrical systems.

All lead acid batteries fail prematurely when they are not fully recharged after each cycle.

If a lead-acid battery is left discharged (for days) at any time, it will cause a permanent loss of capacity.

Liquid Batteries - Liquid Electrolyte

Liquid batteries store energy using a rechargeable fuel made up of electrodes or nanoparticles. This fuel is in a liquid state.

There are two types of liquid batteries:

  1. Open, with lids that allow the water to change.

  2. In a sealed way, which are closed but with valves that allow possible gases to escape during excessive loads.

Advantages of Liquid Batteries

  • The oldest

  • Its production allows economic prices.

  • They are less problematic at overloads.


  • There is a danger of losing (aggressive) fluid.

  • They tend to have a short useful life, between 400 charge and discharge cycles.

  • Very low temperatures can destroy them quickly.

AGM Batteries - Absortion Glass Mat Battery

They are the most modern batteries and the acid is fixed in fiberglass that absorbs it. In these types of batteries, the acid is absorbed better and faster by the battery's lead plates

Almost all AGM batteries are valve regulated: VRLA (valve regulated lead acid)

They have all the benefits of gel, plus the following:

Advantages of AGM Batteries:

  • Good shelf life.

  • More resistance to cold climates.

  • Its self-discharge is minimal: when it is not being used the energy losses are minimal.

  • Low internal resistance allowing high currents.

  • Deep cycle, that is, they are designed to be repeatedly discharged up to 80% of their capacity.

Disadvantages of Using AGM Batteries:

  • Higher price.

There is an increasing trend towards lead AGM batteries. They have their best life / price ratio. If handling is easier.

For someone who can secure the necessary care, the liquid battery may be the best option. Especially considering the price.

What Does It Mean That a Battery Is Low or Deep Cycle?

There are two types of batteries according to their cycle:

  • Low cycle batteries

  • Deep cycle batteries

Low Cycle Batteries

Low-cycle batteries are designed to supply an amount of current for a short period of time and withstand small surges without losing electrolytes, as in the case of automobiles.

However, these batteries do not withstand deep discharge. If they are repeatedly discharged below 20%, their useful life is shortened considerably. Therefore these batteries are not a good choice for solar photovoltaic systems.

Deep Cycle Batteries

This model of batteries are designed to be repeatedly discharged up to 80% of their capacity. This feature makes them the best option for solar energy systems.

What Impact Do Solar Batteries Have on the Environment?

Batteries are a special, toxic and hazardous waste. Solar batteries should never be thrown away directly. Their collection must be done in a thematic way to take them to a suitable recycling site.

Batteries have a high polluting capacity and recycling involves controlling that capacity. For example, the mercury in a button cell can contaminate two million liters of water; This poses serious risks, even to health. Facilitates the use of raw materials contained in batteries.

After leaving the batteries in laundries and other sets, the batteries are taken to the recycling center; where mercury and other metals (zinc, cadmium, lead, silver) are recovered.


Solar batteries are stores of electricity. They store the electricity generated by solar panels at times of low demand and supply it at times of increased demand.

These elements are capable of transforming electrical energy into chemical energy at the moment of charge. At the moment of discharge, they transform chemical energy back into electricity.


Published: May 13, 2015
Last review: September 10, 2021