How Does a Solar Charge Controller Work?

The advantages of photovoltaic energy are beyond doubt when thinking in terms of environmental sustainability, but this renewable energy still has a great challenge ahead: the optimization of its storage in batteries, which are susceptible to degradation in a short space of time, as a result of voltage drops and repeated charge and discharge cycles. The solar charge controller helps to soften the degradation of the batteries.

How Does a Solar Charge Controller Work

Solar charge controllers are electronic devices used to regulate the energy coming from photovoltaic solar panels, specifically those that have isolated photovoltaic solar installations or those that use batteries to store electricity, but what is and how exactly does a solar panel charge controller work? In order to answer the question, it is advisable to consider how solar panels work and the relationship they have with solar charge controllers.

Solar panels can be used for self-consumption, as well as for large photovoltaic installations. These harness solar energy in the form of radiation to produce electricity. Specifically, they do it through photovoltaic cells or polarized cells with opposite charges so that, through radiation, an electric field is generated.

In short, what happens in this electric field is that photons of light push electrons and generate a flow of current. If the electricity is transmitted directly to the electricity grid, it will not use a battery and will not need a solar panel charge controller. 

Suppose the installation is isolated and uses a battery to store the electricity generated during daylight hours. In that case, the installation will require a solar charge controller to take care of the state of the battery and avoid overloads.

Below, we explain in more detail what a solar charge controller is and how it works and what aspects you should take into account at the time of your choice.

What is a Solar Charge Controller?

A solar panel charge controller is an electronic device placed between the photovoltaic field of the solar panel and the battery field to control the flow of energy that circulates between both systems. The solar charge regulator controls the amount of electricity that comes from the solar panel. It also controls the intensity and voltage of the electricity that goes to the battery. 

solar charge controller diagram

Solar panel charge controllers also ensure the state of charge of the battery so that the charging is optimal – although, in the latter process, electricity can be wasted if the right controller is not chosen, as we will see later.

Solar charge controllers regulate the flow of energy generated in the solar panel according to the charging capacity of the battery and the total energy that has been generated in them. We see it better now.

How Does a Solar Charge Controller Work?

A charge regulator works by controlling the amount of energy that enters a battery and the charging capacity that it has. It adapts to the operation of the battery but prevents it from being overloaded. The battery charging stages work as follows:

Bulk Stage: At this stage, the current that is supplied to the battery passes with maximum intensity. In this mode, voltage increases rapidly and reaches a power of 12.6 V – in general batteries – until it reaches the first voltage limit that the battery has. The battery is charged by approximately 90% until you reach that point. 

At this time, the voltage reached by the battery is around 14.4 V – depending on the battery used – and, although the absorption of current is drastically reduced, the intensity at which it is supplied is still maximum.

Absorption stage: In this case, the charging speed decreases until the battery is fully charged. The voltage at this point is the same as the voltage at the end of the Bulk phase, and the maximum capacity of the battery also called the absorption limit, is reached at this point.

Flotation stage: At this time, the voltage – or voltage – decreases, usually up to 13.5 V. The same happens with the injected current, which is reduced until the battery is completed. It is the last period of charging the battery.

Suppose the solar panel generates too much energy, which is greater than the amount of charge that the battery has. In that case, the solar charge controller ensures that the energy is not injected into the battery avoiding an overload.

This energy is lost by a process known as the “Joule Effect,” which generates heat. Normally, generators must conform to the parameters of the battery. That is, to the load capacity, the voltages at which they operate, and so on, to avoid wasting too much energy.


How to Choose A Solar Charge Controller?

The choice of the solar panel charge controller depends on the amount of energy to be generated through self-consumption with solar panels. Currently, we can find two types of solar charge controllers on the market. These are:

Solar charge controller PWM (Pulse Width Modulation): These controllers may or may not take advantage of the energy generated in the solar panels depending on the state of charge of the battery and the power they offer since they work with the same voltage that the battery has.

They are able to completely fill the battery by voltage pulses in the period of battery flotation. The current is introduced little by little until the battery is filled. These devices are designed, above all, when working with a low-power photovoltaic field – for example, the installation of lights with solar panels in a garden. The advantage of these controllers is that they are cheaper and lighter.

Its most outstanding points are:

  • The average of their prices is cheaper than that of MPPT controllers (next section).
  • They can spend long periods of time with little consumption of solar energy, and therefore, with an excess of energy.
  • They support a wider range of voltages than MPPTs.
  • Greater capture of the energy generated by the panels.

MPPT Solar Charge Controllers  (Maximum Power Point Tracker): These controllers  achieve maximum performance of the solar panel since they take advantage of the maximum power.

This is thanks to the fact that they have a DC-DC voltage converter that transforms the high voltage direct current of the solar panel into a low voltage direct current according to the battery charge. 

There is a proponent of maximum power point in this controller, though. This proponent helps the photovoltaic field run at its highest power. It is, therefore, possible to work with higher voltages in the photovoltaic field and reduce energy losses due to low voltages.

Although they are more expensive, their advantages over PWM are:

  • Greater efficiency in cold climates.
  • They can work with 60-cell panels.
  • They are suitable for systems where the voltage of the panel is different from that of the battery.


Advantages of a regulation system

1. The repetition of charge and discharge cycles is detrimental to the good life of any battery: the main goal achieved by the presence of charge controllers is to cushion the degradation of the batteries, and thus preserve them for longer.

2. In addition, by the simple fact of being able to automatically adjust to the needs of the battery, it manages to prevent it from overheating.

3. By equalizing the load acceptance, it achieves a better balance between the battery cells and prevents the deterioration of their capacity; for example, in the case of lead batteries, when the charge is insufficient, the grids corrode and sulfate crystals (sulfation process) are formed, which damages the battery.

4. Voltage spikes and temperature increases are also degrading factors that are controlled by a regulator.


A solar charge controller must be present in every photovoltaic installation: stopping and rationing the electrical charge is essential to preserve the life and quality of the batteries, and thus maximize the efficiency and durability of the system in the long term.