Solar Charge Controller

For many people, the price of solar charge controllers is the biggest factor when buying one. But while a cheap model might save some money at first, it’ll cost you thousands of dollars in damaged batteries or worse.

A popular Portuguese proverb says that cheap things often end up being expensive. When you invest thousands of dollars in a solar photovoltaic (PV) system, you want to be sure the most important components are reliable and of high quality.

Solar charge controllers are the brains of every solar installation and play a vital role in the system’s operation. Every charge controller worth its price helps to:

  • Prevent the batteries from undercharging or overcharging, which can damage them
  • Prevent reverse current flow at night or when the sun is not shining, which helps prevent the battery from getting drained
  • Regulate energy usage (also called the load), preventing over-discharging batteries
  • Protect your solar system from overloading and short circuits

You’ve got to go all-in with your solar installation.

The government is now committed to making solar and other renewable energy sources part of Australia’s future. As Prime Minister Antony Albanese said,

“Together we can take advantage of the opportunity for Australia to be a renewable energy superpower.”

That being said, you don’t have to spend thousands on an expensive charge controller. Finding the most economical option is all about striking a balance between costs and technical needs, such as efficiency and durability.

Whether you want a DIY solar installation or are researching your options, it’s vital to understand the role of solar charge controllers.

Here are the four main considerations you should explore before buying a solar charge controller.

1. Choosing Between PWM and MPPT Charge Controllers

Enerdrive Solar Regulator 20A / 12V

The first and biggest decision you’re going to make is choosing between a PWM (pulse-width modulation) and MPPT (maximum power point tracking) charge controller. 

These are two different technologies, and choosing the right one depends on several factors, such as:

  • The size of the installation: High-voltage systems work better with MPPTs.
  • Cost: PWMs are often cheaper compared to MPPTs of the same capacity.
  • Complexity of the system: MPPTs offer more features and safety.
  • Where you live: MPPTs are much more efficient in temperate climates, while PWMs are great for hot, sunny, tropical regions.

For most people, the biggest factor is the price—MPPT charge controllers can be more than double the price of PWM controllers of a similar capacity. 

However, technical considerations must come first, and you may find that investing in a premium charge regulator is the more economical decision in the long run.

PWM Charge Controllers

PWM charge controllers operate by closing and opening a transistor switch very quickly, while varying how long the switch stays open. The amount of electrical energy that passes through into the battery in each pulse determines how quickly it gets charged. 

When the battery is almost full, the switch lets a trickle amount of electricity through to keep the battery topped off. This simple mode of operation makes PWM controllers cheap, robust, and highly versatile.

Victron BlueSolar PWM Charge Controller

However, PWM controllers don’t control the voltage that goes into the battery. You have to match the voltage of the solar panels (array) to that of the battery bank and charge controller. This is done by using solar arrays with a matching nominal voltage.

In reality, most solar panels have a maximum power output that’s well above the battery voltage. For example, a solar array for a 12V battery will have a maximum power voltage (Vmp) of 18–20V. This discrepancy results in lost power and lower efficiency.

MPPT Charge Controllers

MPPT charge controllers are more sophisticated. They first convert the incoming voltage from the solar array into alternating current (AC), then change it back into direct current (DC), whose voltage is matched to the battery charging requirements.

In other words, MPPT charge controllers take the full amount of power from the solar array and adjust it to the battery conditions. This makes the whole system highly efficient, often achieving over 96% efficiency because they take full advantage of the array’s capability.

Morningstar EcoBoost MPPT charge controller

MPPT solar charging regulators don’t require precise matching with the batteries, but their installation is more technical. Some models allow you to program their software (like this one) or select algorithms (like this one) to take full advantage of local weather conditions.

Which Is Better: PWM or MPPT Controller?

MPPT regulators are not always better than PWM models. A solar technician has to consider several factors unique to your installation to figure out which one best meets your needs, such as the size of the installation and local weather conditions.

In the following table, we compare PWM and MPPT solar controllers to help you choose the right one for you.

Controller Type Where It’s Best Used Example
  • Small systems (300–400 Watts)
  • Warm to hot climates with a lot of sunny weather, such as deserts or the tropics
  • Systems where high reliability is desired
  • Where the solar and battery are close, i.e., only short cable runs are needed
  • Systems where battery and solar array voltages are closely matched
  • The battery is not regularly drained of charge, allowing it to operate at near full capacity
  • Installations where budget is a major concern
Victron BlueSolar PWM-Pro Charge Controller
  • Large capacity systems (usually over 300 Watts)
  • Temperate regions with fluctuating weather, temperatures, and lots of shading
  • When higher efficiency is desired—MPPT can be up to 40% more efficient than PWM models
  • High-voltage systems, thus reducing cable costs and maximising efficiency
  • Large, complex solar arrays where advanced monitoring and control is desired, such as when starting a solar farm
Victron SmartSolar MPPT Charge Controller

If you live towards the north of Australia and want to install a small system for your home, chances are that a PWM charge controller will be sufficient for you. In most other cases, an MPPT model is probably the wiser choice.

solar charge controllers are the brains of  every solar installation

2. How to Size Charge Controllers Based on Power Output

In this video, Bob Hopman from Victron Energy explains how you can use the company’s solar calculator to easily find the correct charge controller for your installation.

In short, solar charge controllers are sized based on the current output (Amps) and voltage (volts) of the solar array in which they’re installed.

If you’ve settled on a PWM charge controller, all you need to do is match the charge controller to the solar array’s nominal voltage, which in turn is matched to the battery voltage.

For example, a 12V battery bank should only be charged by an array with a 12V nominal voltage. The same goes for 24V and 48V batteries. This is necessary because PWM charge controllers don’t limit the current or voltage flowing to the battery. 

You must also consider local weather conditions. When it’s cold, the solar array can produce up to 25% more than the rated voltage. This requires voltage correction, which is done by multiplying the rated voltage by a specific number supplied by the manufacturer.

For example, a region whose lowest recorded temperature is -250C could have a correction factor of 1.20. Multiply the array’s total voltage by 1.20 in addition to the mandatory safety factor of 1.25 to get the maximum voltage your array can produce.

Sizing MPPT charge controllers is a little more complicated. While MPPTs can handle a high input voltage, you must match the output current and voltage to the battery bank voltage.

Let’s say you have a solar array with two Victron BlueSolar 24V, 330W solar panels connected in parallel. 

Victron BlueSolar 24V, 330W solar panels

From the specifications, each panel produces 8.86 Amps of current for a total of 17.72 Amps. Accounting for the 25% safety margin, you’d need a controller rated for 22.15 Amps minimum.

However, you also need to think about the battery voltage for which the controller is rated. This system will produce a total of 660 Watts, but the charge controller limits the battery voltage to 24V. 

Thus, the current produced could theoretically increase to 27.5 Amps. With a 25% safety factor, you’d need a charge controller that’s rated for at least 34.4 Amps. 

The Victron SmartSolar MPPT Charge Controller shown below is rated for an output of 35 Amps and 12/24/48V, making it perfect for these requirements.

Victron SmartSolar MPPT Charge Controller rated for 35 Amps

In practice, you don’t want the solar array to be too big with respect to the charge controller rating. It’s a good idea to keep the array’s total power at 125% of the charge controller’s maximum power rating. An oversized array is a waste of money and energy.

3. What Extra Features Do You Need?

Victron SmartSolar Charge Controller

This Victron SmartSolar Charge Controller boasts advanced features, such as remote monitoring and control, an optional smart display, and full programmability. It also has a temperature sensor and advanced protection against high temperatures and reverse current.

Such advanced features can increase the price of a charge controller, but the added functionality and protection can give you peace of mind by: 

  • Maximising battery life by monitoring temperature and battery use
  • Keeping track of weather conditions and switching to a more efficient charging algorithm for maximum power harvesting (over 98% efficiency)
  • Maintaining high reliability and durability, usually for more than 20 years
  • Providing remote monitoring and alerts in case of problems in the system

Even if you’re not an expert in photovoltaic (PV) technology, advanced features are often worth the increased cost. For example, if you travel frequently, remote monitoring can help you monitor charging performance or even turn on lights remotely. 

Expert Tip: You don’t always need thousand-dollar charge controllers. Cheaper models, such as this Victron BlueSolar MPPT Charge Controller, offer high-efficiency charging suitable for smaller installations to help you save money.

4. Brand Reputation Is Important

Morningstar SunGuard Charge Controller

This SunGuard solar controller is an affordable but high-quality model. Like the Victron models, it provides reliable protection from overcharging, undercharging, and short circuiting for small systems.

By comparison, generic models may not offer the same protection and reliability. They’re often poorly designed or have low-quality components with a higher risk of failure.

Even when comparing premium brands and models, it’s worth doing some research and talking to experts to find out which brand or model is best suited to your needs.

In the video below, a solar technology expert from Clean Energy Reviews tests four common solar charge controller brands available in Australia.

After testing each model, the expert reviews how accurately each unit measures voltage and current. He also checks performance and power output by measuring how much power each unit delivers to a battery.

From the tests, it’s clear that some brands, such as Victron, are superior in terms of accuracy and performance. The reviewed Victron unit delivered 352 Watts of power, while a Renogy Rover unit delivered 337 Watts under the same conditions.

Better performance, efficiency, and reliability help you to get the most out of your solar installation.

Major brands like Victron and MorningStar might be more expensive, but you can trust the quality of their charge controllers. That’s why we give you five-year warranties on some models, such as this Victron BlueSolar and this Victron SmartSolar.

If you’re in doubt, talk to solar equipment distributors or technicians. The solar experts at Off Grid Direct are here to make it easy for anyone to buy high-quality solar equipment at unbeatable prices. 

We handpick every product at our store for quality and reliability, so you never have to second-guess your purchases. If you’re a DIY solar enthusiast, you can trust us to bring you safe and reliable solar equipment.

Buying Charge Controllers Made Easy With Off Grid Direct

A good solar charge controller is an investment. It helps you maximise the power you harvest with your solar array and keep your system healthy throughout its rated service life.

And now, you can save even more when you buy solar controllers at Off Grid Direct. Thanks to our price match guarantee, you get the most competitive prices on the market. We also offer free shipping for all orders over $300 within mainland Australia.

Explore our collection of solar regulators and controllers and enjoy easy, hassle-free solar equipment purchase and delivery.

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