How to Select The Solar Charge Controller

Jun 18, '21

How to Select The Solar Charge Controller

The solar charge controller or solar charge regulator is placed between your solar panel and your battery. It is therefore necessary that its characteristics correspond to your solar panel on one side, and your battery on the other. This is what makes the choice so complicated. Here is our guide and tips to help you make the right choice!

Content

What does a charge controller do?

The charge controller allows you to make the junction between your energy production source (solar panel, wind turbine, hydrogenerator) and your battery. Its role is to protect the battery against too much or too little charge, and to protect your electricity generator from feedback. Depending on the models, the charge controller can also convert the generator voltage into a voltage suitable for the battery bank.

The charge controller stops charging when the batteries are full and evacuates the excess energy produced by transforming it into heat. Depending on the model, it can also analyze the state of charge of the battery park and, if necessary, disconnect the load earlier, so as to recharge the battery to 100% at least once a week.

This device allows you to make better use of your electricity generator while protecting it, as well as your battery bank.

For wind turbines and hydrogenerators, there is usually a recommended charge controller that works just fine. For solar panels, the choice can be more difficult.

MPPT or PWM charge controller?

The PWM charge controller is much more restrictive than the MPPT charge controller. If it has the advantage of being less expensive, it can only work with a single panel of 36 cells in 12V, or a single panel of 72 cells in 24V (or 2 panels 12V in series), of a relatively low power. In addition, for a 12V battery, you will need a 12V solar panel, and for a 24V battery a 24V solar panel.

The MPPT charge controller is much easier to use. It accepts many solar panels in parallel or in series, depending on the cumulative circuit voltage (Voc) and short-circuit current (Isc) of the solar panels. It makes the best use of the capacities of your solar park thanks to advanced technology, to offer you better returns. The MPPT thus makes it possible to recharge a battery with a solar panel having a higher voltage.

BougeRV's opinion:

We recommend that you go for a more efficient and forgiving MPPT charge controller. PWM is less efficient and is only suitable for a specific installation.

How to Choose The Solar Charge Controller?

In this case, you already have one or more solar panels or you already know which solar panel (s) you want to buy. You must then choose the charge controller that will be the most suitable. If you already have a battery and you want to adapt your solar installation to it, the guide and advice on how to choose your charge controller according to your battery fleet will be more suitable.

For an installation with a single solar panel

Choosing a charge controller with a single solar panel is quite simple. There are in fact two data to take into account: the circuit voltage (Voc) and the short-circuit current (Isc). You will find this information in the product sheet, in the manual or directly on the solar panel. It is imperative that the circuit voltage (Voc) and the short-circuit current (Isc) are 10% lower than the maximum accepted by the charge controller.

For an installation with several solar panels

When you have multiple solar panels, choosing the charge controller is a bit more complex. The data to be taken into account are the same: the circuit voltage (Voc) and the short-circuit current (Isc), which you will always find in the product sheet, in the manual or directly on the solar panels. However, these data will be modified depending on the connections and the number of solar panels.

In electricity, there are 3 types of connections:

  • The parallel connection,or the intensities in Ampere (A) add
  • The series connection or the voltage in Volts (V) are added
  • The hybrid connection with solar panels connected in series and others in parallel

Thus the circuit voltage (Voc) will be impacted during a series connection and a hybrid connection. The short-circuit current (Isc) will be affected by a parallel connection and a hybrid connection.

Open Circuit Voltage (Voc)

The open circuit voltage of your solar system must imperatively be 10% lower than that accepted by the solar charge controller. When connected in parallel, it will not be affected by the number of panels, and will be accepted by the majority of MPPT charge controller. On the other hand, when connecting in series, it is necessary to add the circuit voltage (Voc) of each solar panel and check that the sum of the circuit voltages is accepted by the controller. If this is not the case, it will be necessary to choose a charge controller accepting a greater circuit voltage from the solar panel.

For example: 6 12V solar panels with a Voc circuit voltage of 19V connected in series:

Open Circuit Voltage (Voc)

In this situation, the charge controller is a 100/15. This means that it accepts a maximum voltage of 100V for solar panels. The cumulative circuit voltage (Voc) of the 6 panels is 114V. It is therefore too much for the controller, which is not suitable. It will then be necessary either to choose a charge controller accepting a higher voltage Voc, at least 130V to keep a safety margin of 10%, or to change the connections.

Indeed, if we take the same, 6 solar panels, and connect them this time in parallel:

 Open Circuit Voltage (Voc)

This time the cumulative circuit voltage of the 6 panels is 19V. It is therefore well below the maximum 100V that the controller can accept. This controller is well suited for these solar panels, at the level of the circuit voltage Voc. However, it must be seen whether the short-circuit current Isc is not too high.

Short Circuit Current (Isc)

The short-circuit current of your solar system must imperatively be 10% lower than that accepted by the charge controller. When connected in series, it will not be affected by the number of panels, and will be accepted by the majority of MPPT controllers. On the other hand, when connecting in parallel, it is necessary to add the short-circuit current (Isc) of each solar panel and check that the sum of the short-circuit currents is accepted by the controller. If this is not the case, it will be necessary to choose a charge controller that accepts a greater short-circuit current from the solar park.

For example: 6 12V solar panels with a short-circuit current Isc of 6A connected in parallel:

Short Circuit Current (Isc)

By consulting its product sheet, we see that this 100/15 charge controller accepts an Isc current from the solar park of 15A maximum. Depending on the model, this can be marked directly on the controller. Here, the cumulative short-circuit current of the 6 panels is 36A. It is therefore too much for the controller, which is not suitable. It will then be necessary either to choose a charge controller accepting a higher short-circuit current, at least 40A to have 10% of safety margin, or to change the connections of the solar panel.

Indeed, if we take the same, 6 solar panels, and connect them this time in series:

 Short Circuit Current (Isc)

This time, the cumulative short-circuit current of the 6 solar panels is 6A. It is therefore well below the maximum 15A that the controller can accept. This controller is therefore suitable for these solar panels, at the level of the short-circuit current Isc. However, as we saw earlier, the controller will not be matched to the level of the circuit voltage (Voc).

In summary, in this example, for a parallel connection, a charge controller would therefore need to accept a voltage Voc of at least 22V and an intensity Isc of 40A minimum. In the case of a series connection, it is a charge controller which supports a Voc voltage of at least 130V and an Isc current of at least 7A that should be chosen.

Note: To make the most of the capacity of your solar system, you need a battery large enough to store the electricity produced. Once you have chosen your solar panel and your charge controller, you must therefore check that your battery is suitable. For this, it is necessary on the one hand that the voltage of your battery corresponds to the charging voltage of the charge controller. On the other hand, the charging current, or charging current, of the controller must be between 10% and 20% of the capacity in Ah of your battery, as for a charger. For a lithium battery, this can go up to 30%.

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