What Size Solar Charge Controller Do I Need?

A solar panel charge controller, also known as charge regulator, directs and controls the energy that circulates between the battery and the photovoltaic solar modules. In other words, it prevents overloads of the batteries when they are receiving energy from the solar panels of the photovoltaic installation. That’s why it is placed between the solar panel and the battery and, therefore, must correspond to both. This is what makes it difficult to decide which charge controller to choose for your solar panel. In this regard, this article will answer one of the most frequently asked questions, what size solar charge controller do I need?

If you have a photovoltaic installation with batteries, you must know the importance of the charge controller and how it influences your photovoltaic system’s complete performance. Let’s discuss!

Functions of a Solar Panel Charge Controller

The charge controller is an essential component in photovoltaic installations that monitors the state of charge of the batteries and regulates the charge intensity continuously. Therefore, it is necessary for isolated installations as it improves the performance of the photovoltaic system and lengthens the useful life of the batteries.

The charge controller technology is very advanced, allowing it to adapt to the guidelines set by the battery automatically, although you can adjust the different parameters manually. The three main functions of a charge controller are:

• It protects solar batteries against overcharges and undercharges: Overcharging damages batteries. As its name indicates, a charge controller controls the charge accumulated in the battery produced by the solar panel. If the battery is 100% charged, it disconnects it to avoid overcharging. On the contrary, if its charge level is too low, below a certain limit, it disconnects and discontinues it from the consumer network, preventing it from being used. The controller ensures that the battery is at its optimum point.
• It protects the battery against high voltage: When the solar panels do not receive light (night or rainy days), the batteries have more voltage than the panels. Therefore, the controller protects them from blocking the passage of reverse currents and preventing them from being damaged by overvoltages.
• It prevents batteries from discharging overnight: by detecting darkness and disconnecting them to prevent current from the battery to the panels.

In addition, some controllers may perform the equalization process in solar panels that require periodic charges to keep the device in an optimal state.

Types of Charge Controllers

There are two types of solar panel charge controllers: PMW and MPPT.

 PWM Controllers

PWM stands for “Pulse-Width Modulation,” the most common mode for 12V and 24V isolated installations. PWM Controllers’ useful life is quite long since they are manufactured with very simple components, ideal for small and medium installations.

These regulators use the voltage that the battery needs for charging and discharging. If the module produces 16V and the voltage is 12V for charging, the regulator will provide 12V, and the remaining 4V will be discarded to avoid taking full advantage of its performance.

During charging, the PWM regulator passes the current from the board to the photovoltaic battery until the charge is complete and then disconnects it from the board. These regulators usually come with a programmed configuration that makes it possible to connect different types of 12 or 24V batteries.

MPPT Controllers

MPPT stands for Maximum Power Tracking. These regulators use the entire power of the solar panels, regardless of the voltage differences. As the name indicates, there’s always tension at its optimum point. For example, if your installation produces 1 kWp with a voltage of 100V and an intensity of 10A. In that case, the controller will reduce the voltage to 48V and increase the intensity to 20.8A to adapt to batteries. This way, MPPT controllers maintain the power produced.

MPPT controllers are used in installations where the regulator and the solar panels are placed at a distance and have a more complex structure.

What Size Solar Charge Controller Do I Need?

If you need to choose the right controller model for your photovoltaic installation, the first thing to do is determine whether you need a PWM or MPPT regulator. For simple installation with 4 to 6 plates, use PWM. For huge installations, when the distance between the panel and the batteries is considerable, use MPPT.

To determine the size of the controller, remember that PWM controllers should only be used with 12V (36 cells) or 24V (72 cells) panels. Once you decide the type of charge controller to be installed (PWM or MPPT) for your installation, you must determine the right one that fits your solar installation.

It is necessary to know the configuration of the photovoltaic field, whether it will be in series, parallel or a combination of both. If they are in series, increase the voltage without changing intensity. If they are in parallel, increase the intensity without changing the voltage. In parallel combination, increase both.

Calculation of the Voltage of the Solar Panels System

System Vmp = Vmp of a solar panel x number of solar panels in series

System Voc = Voc of a solar panel x number of solar panels in series

Calculation of the Intensity of the Photovoltaic Field

System Imp = Imp of a solar panel x number of solar panels in parallel

Isc system = Isc of a solar panel x number of solar panels in parallel

For example:

An installation with 2 SCL 190Wp 24V panels connected in parallel; the panel characteristics: Vmp = 37.08V; Voc = 45V; Imp = 5.12A; Isc = 5.48A. The connected panel system gives together the following result: Vmp = 37.08V; Voc = 45V; Imp = 10.24A; Isc = 10.96A

Suppose you have opted for a PWM charge controller (only suitable for 36 or 72 cell panels). In that case, you need a regulator whose intensity is greater than the maximum from the set of photovoltaic panels multiplied by a safety coefficient of 1.25. A safety coefficient is applied because the solar panel data given by the manufacturer are measured at STC standard conditions (1000 W / m2, 25ºC and AM 1.5), and would reflect any variation of these conditions in an increase in the power produced, which may exceed the nominal current of the regulator.

For the above example, use a PWM regulator greater than 1.25 × 5.12 = 6.4A. Looking at the technical sheets of commercial controllers, you can choose an 8A regulator, such as 20A solar charge controller or 30 Amp Charge Controller, 30A PWM Solar Controller.

If you opt for an MPPT charge controller, you need to know the maximum limits for your solar panel system: maximum power of the panels in Wp for the design voltage of the system (12V, 24V or 48V), maximum intensity Isc and maximum no-load voltage System Voc. You must check that the voltage is adequate and does not exceed the maximum power of the panels.

Let’s understand this with the same example!

System of 2 panels 190Wp in parallel: Voc = 45V Panels = 190 × 2 = 380Wp Imp = 10.24A V design = 24V. In general, it would be better to connect the 2 190 Wp panels in series since the MPPT controller allows higher panel voltages than the batteries and thus achieve a smaller cable section between panels and MPPT maximizer. Some of the best MPPT options are WZRELB – 60 A MPPT Solar Charge Controller and AMPINVT MPPT Solar Charge Controller.

Our Final Thoughts!

We hope the information above must have answered the question, what size solar charge controller do I need? The calculations seem complex but once you understand the configurations of your solar panel, it’ll be easier for you to decide which size charge controller you need.