What is a Solar Charge Controller?

A charge controller is a current regulator or a voltage regulator. It means it will prevent the batteries from overcharging and keep them safe. A charge controller is also known as a charge regulator.

If a storage battery is installed in a grid-tie home, you do not need a solar charge controller. In general, that solar inverter will do the same job to maintain the battery’s health.

What is a solar charge controller?

The charge controller is an electronic device that controls those powers which are going into a battery from a solar array. A collection of multiple solar panels is called a solar array. And these solar array ensures that the batteries do not get overcharged during daytime and overnight, stored power doesn’t return to the solar array, and does not affect batteries.

Some of the solar charge controllers are also available with different features, like controlling the load and light, but managing the power is the primary job of a solar charge controller.

How does Solar Charge Controller work?

We should keep in mind a basic but important thing is that current or electricity always flows from high voltage to low voltage. During the daytime, when the temperature and voltage will be the highest, at that time, the solar panel produces the highest energy while the combined batteries’ voltage or battery bank voltage will be below. And then a good amount of electricity to get stored in the battery.

During the night, the battery’s voltage is higher than the voltage of the solar panel; since the daytime itself, they are all fully charged. If we want to stop this high voltage from flowing from solar panels, the solar charge controller is used to maintain the electricity balance.

When the battery is about to die, the solar charge controller produces a good amount of power to the battery, and the battery gets charged quickly. If the battery is about to the full, stored enough power, or it is in use, then the solar charge controller sends a low amount of power to the battery, a trickle charge that will keep them always ready to produce power.

Apart from this, if the voltage drops below a certain threshold, the solar charge controllers automatically disconnect in case of non-critical loads across all the batteries, and it is called Low Voltage Disconnect (LVD), which prevents the over-discharging of the battery.

Different Types of Controllers

The Solar Charge Controller is categorized mainly into PWM (Pulse Width Modulation) solar charge controller and MPPT (Maximum Power Point Tracker) solar charge controller. There are some differences as well in these two solar charge controllers.

But before exploring these two, let us see a few terminologies which are going to be helpful to further understanding these solar charge controllers.

The Voltage at Maximum Power (VMP)

When a solar module is connected to a load and operating at its maximum capacity under standard test conditions (STC), that voltage is called VMP or voltage at maximum power. Most solar panel manufacturers specify this voltage on a module-specific sticker or a sheet.

This specific voltage is not easy to measure, and it is also not related to the system’s performance.

When the system is in working mode, it is not common for a battery bank (combination of multiple batteries) or a load to draw down the VMP of an array or a solar module to a few volts lower than VMP.

The Voltage at Open Circuit (VOC)

When the solar module is not connected to any load, energy is not flowing anywhere from the solar panel, and then the voltage is read with a multi-meter or voltmeter; that is called voltage at open circuit (VOC).

It is present on the module’s specification sheet. The voltage at an open circuit is an important parameter if we test it under standard test conditions. If we want to determine the total number of solar panels required for a particular load, we can use the voltage at the open circuit.

Pulse Width Modulation (PWM) Solar Charge Controller

Only a few charge solar charge controllers have PWM, and it is mainly used for float charging. PWM solar charge controller operates by directly connecting the battery bank to the solar array.

When the battery is getting charged, the voltage of that battery increases, which is the main reason for an increase in the solar panel voltage, which is charging the battery. We can use solar panels that will work with the charge controller and voltage of the battery.

Pulse-width modulation sends continuously short charging pulses to batteries which causes a very fast “on-off” switch. The PWM solar charge controller constantly checks the condition of the battery, how wide (long) to send the pulses, and how fast pulses will be.

If the battery is fully charged and there is no load attached to the battery, then in every few seconds, it may just “tick” and sends a short pulse to the battery. If the battery is fully discharged, then in every few seconds, it will send along (wide) pulse and almost continuous mode.

Here, the solar charge controller checks and identifies the state of charge on the battery between the pulses and automatically adjusts itself each time.

With the help of a pulse-width modulation solar charge controller, to charge a 12volts battery, a 12volts solar panel is required, to charge a 24volts battery; a 24volts solar panel is required, and so on.

But if we are trying to charge a 12volts battery with the help of a 48volts solar panel, the pulse-width modulation will not be able to collect that extra energy, and thus it will only collect 12volts.

Maximum Power Point Tracker (MPPT) Solar Charge Controller

An MMPT solar charge controller is a direct electronic current (DC) to DC device that converts and optimizes the match between the battery bank (or utility grid) and solar array (PV panels).

In simple words, MMPT converts the DC output of the solar panels, which is at a higher voltage, to the lower voltage that is required to charge the batteries. Sometimes, in short, we call it “PowerPoint trackers” instead of a maximum power point tracker.

Maximum Power Point Tracking:

• MPPT is a digital electronic tracking device. It compares the battery voltage to the charge controller, which is present at the panels’ output. To charge the batteries, it figures out what is the best power that a panel can put out. It takes this power and converts it to the best voltage to the maximum AMPS into the battery. In most of the modern MMPTs, they are able to convert with 93-97% efficiency. And thus, during winter, we get 20% to 40% power gain, and during the summer, we get 10% to 15% power gain. We can see this much difference because the power gain depends on temperature, weather, battery state of charge, etc.
• Maximum power point tracker solar charge controllers are more complicated than pulse-width modulation solar charge controllers. MMPT solar charge controller works by measuring the Solar panel input voltage and then simultaneously decreasing and converting the PV voltage to match the battery voltage.
• With a 20volts solar panel, we can charge a 12volts battery bank, and if we try to charge a 12volts battery with a 24volts solar panel, then half of the solar panel’s power will be thrown. If we try to charge a 24volts battery bank with a 12volts solar panel, then 100% of the solar panel’s ability will be thrown, which could drain the battery.

Which solar charge controller should we use?

A charge controller is critical for a solar system to function correctly, especially when you do not want to lose the system’s quality by simply saving some money. There are multiple options available in the market but getting a high-quality charge controller for battery charging is the best option.

Before selecting a solar charge controller, decide what you are using for and then select one of the solar charge controllers like PWM, MPPT, etc.

1. MPPT and PWM, both solar charge controllers, are designed especially to manage the battery charge current from the solar panels.

2. MPPT solar charge controllers operate above the battery voltage, and due to this, it provides a boost to a low battery while PWM solar charge controllers operate at the battery voltage.

3. In MPPT solar charge controllers, photovoltaic (PV) array voltage can be higher than the battery voltage, while in PWM solar charge controllers, PV voltage and battery voltage must match.

4. The MPPT solar charge controllers work for those systems whose wattage is greater than or equal to 150wattage, while the PWM solar charge controller works for small systems.

5. MPPT solar charge controllers are more efficient with an efficiency of around 95%, while PWM solar charge controllers are less efficient and it can go up to 65% only.

6. MPPT solar charge controllers are designed to support larger solar panels, while PWM solar charge controllers are smaller in size and can support up to 60Amps capacity.

7. MPPT solar charge controllers are expensive, while the cost of the PWM solar charge controllers are half of the MPPT solar charge controllers

8. MPPT controllers can scan the internal resistance of the solar panel and decide which will give maximum output from the solar panel if a load resistance is present.

9. PWM solar charge controllers maximize the voltage by just switching OFF and ON so that they can output maximum power using a maximum voltage during the ON state.

10. If you want to select between PWM and MMT solar charge controllers and prefer efficiency, you should go with MMPT solar charge controller. Here, you just need to control the VOC of the solar panels and to control it to make sure it is under the voltage which is allowed for the MMPT solar charge controller.

Do we always need a charge controller?

A charge controller is not always required but usually. A charge controller is a tool that prevents the batteries from overcharging. These charge controllers ensure that the batteries do not cross a limit that is safe charge current, and thus the charge controller protects the battery from damage and overheating. These charge controllers are generally used to charge batteries with over 20Ah capacity.

Generally, these charge controllers are not required if there is small maintenance.

Check out this post to know if MPPT controllers are worth buying!

Essential Features of Solar Charge Controllers:

• Display – A solar charge controller may display the state of charge, the voltage of multiple batteries that are battery banks, amperes coming in from the solar panel.
• Low Voltage Disconnect (LVD) – A solar charge controller turns OFF the load which is attached to it if the battery is low, and if the battery gets charged, it will back turn ON.
• Multi-stage Charging of Battery Bank – If the batteries are in good condition, the solar charge controllers change the amount of power set to the batteries based on their charge level.
• Lighting Control – Based on sunrise and sunset, a solar charge controller turns the light OFF and ON attached.
• Reverse Current Protection – During the night, when there won’t be any power coming from the solar panels, a solar charge controller will stop the solar panels from draining the batteries.

Conclusion

Now, you have finally decided to select a charge controller, you can add a solar charge controller to an off-grid solar installation, and it will manage the batteries.

A solar charge controller will be able to manage and maintain the batteries by not just over-charging them, and this will help and make sure that the battery’s life gets increased.

In general, a solar charge controller with maximum power point tracker (MPPT) technology is able to control battery charging and handle maximum power tracking. The MPPT solar charge controller is able to manage and utilize the solar module more effectively than another solar charge controller like Pulse-Width Modulation (PWM).