Solar Charge Controller Types, Functionality and Applications
A solar charge controller is fundamentally a voltage or current controller to charge the battery and keep electric cells from overcharging. It directs the voltage and current hailing from the solar panels setting off to the electric cell. Generally, 12V boards/panels put out in the ballpark of 16 to 20V, so if there is no regulation the electric cells will damage from overcharging. Generally, electric storage devices require around 14 to 14.5V to get completely charged. The solar charge controllers are available in all features, costs, and sizes. The range of charge controllers is from 4.5A and up to 60 to 80A.
Types of Solar Charger Controller:
- Simple 1 or 2 stage controls
- PWM (pulse width modulated)
- Maximum power point tracking (MPPT)
Simple 1 or 2 Controls: It has shunt transistors to control the voltage in one or two steps. This controller basically just shorts the solar panel when a certain voltage is arrived at. Their main genuine fuel for keeping such a notorious reputation is their unwavering quality – they have so not many segments, there is very little to break.
PWM (Pulse Width Modulated): This is the traditional type charge controller, for instance, anthrax, Blue Sky, and so on. These are essentially the industry standard now.
Maximum power point tracking (MPPT): The MPPT solar charge controller is the sparkling star of today’s solar systems. These controllers truly identify the best working voltage and amperage of the solar panel exhibit and match that with the electric cell bank. The outcome is extra 10-30% more power out of your sun oriented cluster versus a PWM controller. It is usually worth the speculation for any solar electric systems over 200 watts.
Features of Solar Charge Controller:
- Protects the battery (12V) from overcharging
- Reduces system maintenance and increases battery lifetime
- Auto charged indication
- Reliability is high
- 10amp to 40amp of charging current
- Monitors the reverse current flow
The function of the Solar Charge Controller:
The most essential charge controller basically controls the device voltage and opens the circuit, halting the charging, when the battery voltage ascents to a certain level. charge controllers utilized a mechanical relay to open or shut the circuit, halting or beginning power heading off to the electric storage devices.
Generally, solar power systems utilize 12V of batteries. Solar panels can convey much more voltage than is obliged to charge the battery. The charge voltage could be kept at the best level while the time needed to completely charge the electric storage devices is lessened. This permits the solar systems to work optimally constantly. By running higher voltage in the wires from the solar panels to the charge controller, power dissipation in the wires is diminished fundamentally.
The solar charge controllers can also control the reverse power flow. The charge controllers can distinguish when no power is originating from the solar panels and open the circuit separating the solar panels from the battery devices and halting the reverse current flow.
In recent days, the process of generating electricity from sunlight is having more popularity than other alternative sources and the photovoltaic panels are absolutely pollution free and they don’t require high maintenance. The following are some examples of where solar energy is utilizing.
- Street lights use photovoltaic cells to convert sunlight into DC electric charge. This system uses a solar charge controller to store DC in the batteries and uses it in many areas.
- Home systems use a PV module for house-hold applications.
- A hybrid solar system uses for multiple energy sources for providing full-time backup supply to other sources.
Example of Solar Charge Controller:
From the below example, in this, a solar panel is used to charge a battery. A set of operational amplifiers are used to monitor panel voltage and load current continuously. If the battery is fully charged, an indication will be provided by a green LED. To indicate undercharging, overloading, and deep discharge condition a set of LEDs are used. A MOSFET is used as a power semiconductor switch by the solar charge controller to ensure the cut offload in low condition or overloading condition. The solar energy is bypassed using a transistor to a dummy load when the battery gets full charging. This will protect the battery from overcharging.
This unit performs 4 major functions:
- Charges the battery.
- It gives an indication when the battery is fully charged.
- Monitors the battery voltage and when it is minimum, cuts off the supply to the load switch to remove the load connection.
- In case of overload, the load switch is in off condition ensuring the load is cut off from the battery supply.
A solar panel is a collection of solar cells. The solar panel converts solar energy into electrical energy. The solar panel uses Ohmic material for interconnections as well as the external terminals. So the electrons created in the n-type material passes through the electrode to the wire connected to the battery. Through the battery, the electrons reach the p-type material. Here the electrons combine with the holes. When the solar panel is connected to the battery, it behaves like other battery, and both the systems are in series just like two batteries connected serially. The solar panel has totally consisted of four process steps overload, under charge, low battery, and deep discharge condition. The out from the solar panel is connected to the switch and from there the output is fed to the battery. And setting from there it goes to the load switch and finally at the output load. This system consists of 4 different parts-over voltage indication and detection, overcharge detection, overcharge indication, low battery indication, and detection. In the case of the overcharge, the power from the solar panel is bypassed through a diode to the MOSFET switch. In case of low charge, the supply to MOSFET switch is cut off to make it in off condition and thus switch off the power supply to the load.
Solar energy is the cleanest and most available renewable energy source. Modern technology can harness this energy for a variety of uses, including producing electricity, providing light and heating water for domestic, commercial or industrial applications.
What is a solar charge controller and why are they important?
As the name suggests, a solar charge controller is a component of a solar panel system that controls the charging of a battery bank. Solar charge controllers ensure the batteries are charged at the proper rate and to the proper level. Without a charge controller, batteries can be damaged by incoming power, and could also leak power back to the solar panels when the sun isn’t shining.
Solar charge controllers have a simple job, but it’s important to learn about the two main types, how they work, and how to pair them with solar panels and batteries. Armed with that knowledge, you’ll be one step closer to building an off-grid solar system!
Find out how much you can save by installing solar
- Solar charge controllers allow batteries to safely charge and discharge using the output of solar panels.
- A charge controller is needed any time a battery will be connected to the direct current (DC) output of solar panels; most often in small off-grid systems.
- The two kinds of charge controllers are pulse-width modulation (PWM) and maximum power point tracking (MPPT).
- PWM charge controllers are less expensive, but less efficient, and are best suited for small off-grid systems with a few solar panels and batteries.
- MPPT charge controllers are more expensive and more efficient, and are good for larger off-grid systems that can power a small home or cabin.
- The top off-grid charge controllers are made by brands like Victron, EPEVER, and Renogy, but non-brand-name charge controllers can be just fine if you know what to look for.
Who needs a solar charge controller?
A charge controller is necessary any time a battery bank will be connected to the direct current (DC) output of solar panels. In most cases, this means a small off-grid setup like solar panels on an RV or cabin. If you’re looking for information on how to use solar and batteries off the grid, you’re in the right place!
There are also charge controllers aimed at providing battery backup for an existing grid-tied solar system that is on the roof of a home or business. This application requires a high-voltage charge controller and usually involves rewiring the system to direct a portion of the solar output through the charge controller.
How does a solar charge controller work?
Fair warning before we get started: we’re about to discuss voltage, amperage, and wattage. If you need a refresher on how these things work together, check out our article on watts, kilowatts, and kilowatt-hours.
A solar charge controller is connected between solar panels and batteries to ensure power from the panels reaches the battery safely and effectively. The battery feeds into an inverter that changes the DC power into AC to run appliances (aka loads).
How a charge controller works within an off-grid solar system.
The four main functions of a solar charge controller are:
- Accept incoming power from solar panels
- Control the amount of power sent to the battery
- Monitor the voltage of the battery to prevent overcharging
- Allow power to flow only from the solar panels to the batteries
As a battery charges, its voltage increases, up to a limit. The battery can be damaged if an additional charge is applied past this limit. Therefore, the ability of a battery to provide or accept power can be measured by its voltage. For example, a typical 12-volt AGM lead-acid battery will show a voltage of 11.8 volts at 10% charged to 12.9 volts at 100% charge.
The main function of a solar charge controller is to ensure the amount of power that is sent to the battery is enough to charge it, but not so much that it increases the battery voltage above a safe level. It does this by reading the voltage of the battery and calculating how much additional energy is required to fully charge the battery.
Another important function of the charge controller is to prevent current from traveling back into the solar panels. When the sun isn’t shining, the solar panels aren’t producing any voltage. Because electricity flows from high voltage to low voltage, the power in the battery would flow into the solar panels if there was nothing in place to stop it. This could potentially cause damage. The charge controller has a diode that allows power to flow in one direction, preventing electricity from feeding back into the panels.
How solar power gets from panels to batteries
As we mentioned above, power flows from high voltage to low. So, to add energy to the battery, the output voltage of a solar panel must always be a little higher than the voltage of the battery it’s charging. Thankfully, solar panels are designed to put out more voltage than a battery needs at any given time.
Here’s an example: Say you have a single 100-watt solar panel and a 12-volt battery. Remember from above that a 12-volt battery is actually able to charge up to about 12.9 volts. 12 volts is what is called its “nominal voltage,” while the actual voltage of the battery depends on how charged it is. It might sink to 11.8 volts at low charge, and 12.9 volts when full.
The 100-watt solar panel can put out a maximum of 18 volts, which is a little too high for the battery to accept safely. Leaving it connected to the battery too long could result in a dangerous situation, eventually causing pressure to build up inside the battery and vent out the side as chemical steam.
You need a charge controller in between the solar panel and the battery to limit the voltage available to the battery. But it’s not just about the voltage. it also has to withstand a certain amount of current (amperage) flowing through it. That’s where the amperage rating of the charge controller comes in.
Charge controller amperage rating
The number of amps of current a charge controller can handle is called its “rating.” Exceeding the amperage rating can cause damage to the wiring within the charge controller. Let’s consider a charge controller rated to handle 30 amps of current. The single 100- watt solar panel described above puts out 5.5 amps of current at 18 volts. That amperage is much lower than the charge controller’s maximum of 30 amps, so the charge controller can easily handle the output of the singular solar panel.
In fact, it could handle the output of multiple solar panels wired in parallel (which increases current output). But there’s an important rule about charge controller ratings to consider: always make sure your charge controller is rated to handle 25% more amps than your solar panels are supposed to put out. That’s because solar panels can exceed their rated current output under especially bright sun, and you don’t want to fry your charge controller on the rare occasion when that happens.
Keeping that rule in mind, the 30-amp charge controller in our example could accept a nominal output of up to 24 amps. You could wire as many as four of those 5.5-amp solar panels in parallel to create a solar array capable of putting out 22 amps, staying under the charge controller’s rating plus the 25% cushion. If you think you might expand the size of your solar array in the future, get a charge controller rated for 50% more amps than your immediate needs.
Another consideration when choosing a charge controller is the voltage of the battery bank you want to charge. Wiring batteries in series increases the voltage they can deliver and accept. For example, two 12-volt batteries wired in series will operate at 24 nominal volts. There are charge controllers on the market that can pair with battery banks of 12, 24, 36, and 48 volts. You need to make sure the charge controller you purchase can pair with the voltage of the battery bank.
Battery charging stages
There are three stages of charging a battery: bulk, absorption, and float. They correspond to how full the battery is.
- Bulk: When a battery charge is low, the charge controller can safely push a lot of energy to it, and the battery fills up with charge very quickly.
- Absorption: as the battery nears its full charge (around 90%), the charge controller reduces its current output, and the battery charges more slowly until it’s full.
- Float: when the battery is full, the charge controller lowers its output voltage just a bit to maintain the full charge.
Think of it like pouring water from a pitcher into a cup with a very slow leak: when the cup is empty, you start pouring and quickly increase the amount of water being poured until the cup is nearly full. Then you reduce the flow until the cup is full. In order to keep the cup full despite the leak, you pour just a trickle to keep it topped off.
The bulk/absorption/float process was developed for lead-acid deep cycle batteries. Some newer lithium batteries allow for higher current up until they’re quite full, meaning a charge controller paired with a lithium battery can be set to shorten or eliminate the absorption stage.
Types of charge controller
There are two main ways to control the flow of power to a battery, and they correspond to the two types of charge controller: pulse-width modulation (PWM) and maximum power point tracking (MPPT).
Pulse-width modulation (PWM)
Pulse-width modulation is the simplest and cheapest automatic way to control the flow of power between solar panels and a battery. There are PWM charge controllers on the market for between about 15 to 40.
A PWM charge controller ensures the battery never charges to more than its maximum voltage by switching the power flow on and off hundreds of times per second (i.e. sending “pulses” of power) to reduce the average voltage coming from the solar panels. The width of the pulses reduces the average output voltage.
Here’s an image to illustrate how the pulses work:
For example, if the charge controller accepts 18 volts from the solar panel, it might adjust the pulses so they’re on 82% of the time, and off 18% of the time. This would reduce the average voltage by 18%, down to about 14.8 volts, which can be used to charge a half-full AGM battery. As the battery gets close to a full charge, a PWM charge controller shortens the pulses even further, down to around 77% of the time, or 13.8 volts, to prevent the battery from overcharging.
Unfortunately, the excess energy produced by solar panels is wasted to reduce the output voltage. In our example, the charge controller would average around 80% efficiency. This means it’s very important to make sure the output voltage of the solar panels is not too much higher than the voltage of your battery bank with a PWM charge controller to minimize wasted energy. If your solar array outputs a much higher voltage, the PWM charge controller will cut that voltage down to what the battery can accept, and waste the rest.
Something like 80% efficiency is fine for small off-grid applications like a few solar panels hooked up to a couple of batteries, especially at the low cost of a PWM charge controller. For larger systems with much higher output, it is generally preferable to use the other kind of charge controller technology known as maximum power point tracking, or MPPT.
Maximum power point tracking (MPPT)
An MPPT solar charge controller operates by converting the incoming power from solar panels to match the theoretical highest-efficiency output at the right input voltage for the battery. The charge controller does this by calculating the point at which the maximum current can flow at a voltage the battery can accept, then converting the solar panel output to that mixture of voltage and current.
The major advantages of MPPT charge controllers are greater efficiency and compatibility with higher voltage solar arrays. This means that you can charge a 12V battery bank with a larger solar array wired in series, as long as you stay within the limits of the controller’s amperage rating. You can calculate this limit by taking the total wattage of the solar array and dividing it by the voltage of the battery bank to get the maximum possible output in amps.
Let’s use the same example numbers as before. The solar panel is putting out 100 watts, or about 5.5 amps into 18 volts. The MPPT charge controller converts the output to 14.8 volts but loses about 5% of the power in the conversion process. So the MPPT controller’s output current is about 6.4 amps, times the 14.8 volts, or 95 watts.
Theoretically, in an hour of full sun, the MPPT charge controller will have delivered 95 amp-hours of energy to the batteries, compared to the PWM charge controller’s energy output of about 80 amp-hours. In practice, it isn’t quite that simple, as solar pro Will Prowse discovered in this video:
Common features and settings on a charge controller
The basic features of the simplest PWM charge controller include the ability to set the type of battery and battery bank voltage, and lights indicating the phase of charging (bulk, absorption, and float). advanced PWM and MPPT models come with a small LCD display for programming and data display, a heat sensor port to monitor battery temperature, and a communications port to connect the charge controller to an external display or computer. The most advanced charge controllers offer Bluetooth connectivity and an app for customizing settings.
There are tons of fine charge controllers available on the market. Search any solar supply or online marketplace like Amazon and you’re bound to turn up dozens of results.
The cheapest PWM charge controllers can be had for around 15, and are often rebranded versions of the same design. These lack many features but are relatively reliable for how inexpensive they are. expensive PWM charge controllers built with better quality materials can be had for under 50, while full-featured MPPT charge controllers are priced anywhere from 100 to 200.
Below are a few of our recommended charge controllers at different price points for a medium-sized off-grid setup.
Renogy Wanderer 30A 12V PWM
The Renogy Wanderer 30A PWM charge controller is a solid choice for a smaller off-grid setup. It can handle up to 30A of current at 12V, so it’s not meant for a large system.
It doesn’t have a screen, but it does pair with the three main kinds of lead-acid batteries as well as lithium ones. It has a connector port for an optional temperature sensor and includes an RS232 port that can be used to program the charge controller or even to add Renogy’s BT-1 Bluetooth module for connecting to the Renogy app on your smartphone.
The Wanderer can be had for about 40 from Amazon or Renogy direct.
EPEVER Tracer BN 30A 12V/24V MPPT
The EPEVER Tracer BN MPPT 30A charge controller is not the cheapest MPPT charge controller on the market, but it’s a very good one. With a die-cast aluminum body, sturdy connectors, and a DC output to power loads like DC appliances or LED lights, the Tracer BN is a robust piece of equipment perfect for handling solar charging of lead-acid batteries in 12- and 24-volt banks. It can accept an incoming power output of up to 2,340 watts of solar panels (that’s equal to three parallel strings of four 60-cell solar panels wired in series). The Tracer can be programmed to charge lithium batteries, but it doesn’t come with a preset charging profile for them.
This EPEVER Tracer BN kit at Amazon includes a temperature sensor, mounting hardware, and a separate screen for programming and monitoring the health and state of charge of your battery system. Price at the time of publishing was 179.99.
Victron Energy SmartSolar 30A 100V MPPT
Victron is one of the most trusted solar brands in the world, and its technology is now becoming more widely available in the United States. This 30A, 100V charge controller is known as one of the best on market. Just like the EPEVER controller, it works with 12- or 24-volt battery banks but allows for slightly lower voltage solar input. To stay under this charger’s rating, you could run as many as three parallel strings of three 60-cell solar panels in series to achieve an output of 90 volts at around 20 amps (1,800 watts of solar output).
It’s made with quality components, calculates maximum power point quickly and with high efficiency, and is very easy to use. The SmartSolar line of charge controllers all come with Bluetooth connectivity on board and can connect to the VictronConnect app on Android, iOS, macOS, and Windows for easy programming. Perhaps most importantly, you get a 5-year limited warranty that protects you against defects in materials and workmanship.
The SmartSolar 30A is the most expensive product on our list at around 225 on Amazon, but reading the reviews from its users, you can see why the expense might be worth it.
Solar charge controllers: are they right for you?
All the information above should give you a good basis of knowledge about how solar charge controllers work and how to pair them with solar panels and batteries, but there’s no substitute for practical, hands-on experience! If you have a few bucks to spend, you can set up a pretty simple off-grid solar “generator” using a single solar panel, a charge controller, a battery, and a cheap inverter. Choosing a charge controller that’s oversized for a small application gives you a chance to increase the size of the solar array and battery bank as you gain experience or find new ways to use the stored solar energy.
Now go out there and start making solar and batteries work for you!
Solar Charge Controller: 5 Tips to Help You Avoid Oversizing
Estimated Read Time: 10 minutes
TL;DR: Choose the right-sized solar charge controller by considering your system’s energy needs, operating temperature, battery chemistry, and professional advice. Off Grid Direct offers a range of controllers with free shipping, price match guarantees, and a 30-day return policy.
Table of Contents
When it comes to solar charge controllers, bigger isn’t always better.
Unless you’re planning to fit more solar panels into your system, an oversized charge controller will be underutilised and a waste of money.
You’re better off to purchase a smaller and more affordable controller that suits your setup and performs all the necessary functions, including:
- Solar output monitoring to ensure charge effectiveness
- State of charge monitoring to prevent overcharging
- Auto shutdown in case of voltage spikes to protect your devices
- MPPT Technology (Maximum Power Point Tracking)
We’ve gathered five tips to keep you informed and help you avoid oversizing. As we delve into each idea, you’ll also learn:
- Why battery chemistry matters
- Why it’s important to consider your panel’s current output
- How temperature affects a charge controller
- The best place to find the perfect sized charge controller
Determine Your System’s Energy Needs
To determine a system’s energy needs, you need to compare the maximum power output (wattage) of the solar panels relative to the nominal voltage of your batteries.
The division of these values (wattage/nominal voltage) results in a system’s power rating and an effective way of sizing your charge controller.
This equation accurately predicts the energy level your charge controller will have to cope with, thereby guiding your choice in terms of size and preventing a mismatch.
The best-sized device should be equally rated with an additional 25 percent safety factor for unexpected conditions, such as current-raising temperature drops.
Let’s put this into perspective.
Suppose your panels have a maximum output of 300 watts and your battery has a 12V nominal voltage. What is the optimum size for your charge controller?
- The system’s energy rating will be 25 Amps (from a division of 300 watts by 12 volts).
- The best-sized controller will be equal to 25 Amps plus a 25 percent safety factor.
- A 25 percent safety factor of 25 Amps is 6.25A (from the multiplication of 0.25 by 25 Amps).
- As a result, the optimum size for your charge controller will be 31.25 Amps (from a sum of 25 and 6.25 Amps).
Take Into Account the Operating Temperature
As mentioned earlier, temperature can affect a solar panel’s output current, hence the 25 percent safety factor when calculating the energy level a your controller will be handling.
However, a device’s rated operating temperature range is also important.
When conditions exceed this temperature range, a charge controller will suffer in its ability to regulate panel output.
The transistors within the device that acts as switches malfunction from the heat and experience current leakage. This results in improper energy regulation and charging inefficiencies as is the case with an oversized charge controller.
Take the instance of a 50A charge controller regulating a 10A solar panel. The unutilized 40A charging potential means a longer charge time for your battery and an overall inefficient solar setup.
Similarly, when conditions fall below the specified operating temperature, the components within your controller malfunction from the cold.
The transistors lose conductivity and experience delayed on-off switching times. This creates sensor inaccuracies and impacts the voltage regulation ability of your charge controller. As a result, your solar charging system becomes ineffective.
Choose a solar controller with a wide operating temperature range for optimal results. This ensures resilience and enables your solar system to work efficiently in various environments and conditions.
The Victron BlueSolar MPPT Charge Controller, for instance, has an impressive operating temperature of between.30 to 60°C.
This device can therefore withstand the scorching conditions of the Pilbara region of Western Australia, known to hit 50°C in the summer. You can be confident that it’ll put up with any condition you throw at it.
“It rapidly finds the maximum power point and seems to build local profiles to swap back to in rapidly changing conditions, from direct sun to dark rain and in the middle.”. Neil F. reviewing Victron BlueSolar MPPT
Choose the Right Type of Charge Controller
There are two main types of charge controllers: Maximum Power Point Tracking (MPPT) and Pulse-Width Modulation (PWM).
Both prevent overcharging and undercharging, but they have distinct technologies with size implications that must be considered to avoid oversizing.
A PWM controller uses a simple on-off transistor technology to regulate the voltage sent to your batteries. As such, it’s cheaper and highly robust, but better suited for smaller solar setups.
Its simplicity is such that a PWM controller will always limit energy to its rated voltage, regardless of panel output.
So, a 13V PWM controller will limit charge flow to 13 volts even if you connect it to an 18-volt panel output. The extra energy is simply dissipated as heat, making this controller inefficient for larger solar setups.
An MPPT controller, on the other hand, uses a more sophisticated voltage monitoring technology to extract maximum power from your panels. This makes it pricier, but more efficient for larger solar setups.
When connected to a large solar array, an MPPT controller will drop the panel output voltage to match your battery while increasing the charging current in the same ratio.
This adjustment allows it to draw maximum power from all your panels, speeding up charge time and enhancing efficiency.
The following table highlights the major differences between PWM and MPPT charge controllers to help you make the right choice.
|Solar Charge Controller||Application||Price|
|PWM||For smaller systems (under 200W) where efficiency isn’t critical such as trickle chargers||From 50|
|MPPT||Essential for larger systems (over 200W) where the extra energy yield from efficiency is worthwhile such as house panels. Still beneficial in smaller systems||From 150|
Consider Your Battery Chemistry
Batteries have different chemistries and a distinct charging profile with implications for your solar charge controller and its size. Therefore, it’s crucial that you understand your battery and its charging requirements to avoid oversizing.
Lead-acid batteries have a complex multistage charging profile requiring various current levels. These stages include a bulk charge, taking up 70 percent of battery capacity, and the absorption and float charge, using the remaining 30 percent.
This chemistry requires a multistage charge controller with a matching current rating (size) to deliver the right charge at each stage—preferably an MPPT controller because of its current adjusting capability.
Lithium-ion phosphate batteries (LiFePO4) have a simpler charging profile and don’t require voltage adjustments. However, they’re incapable of overcharging and only take what they can absorb.
Therefore, a simple on-off PWM controller of the right voltage will be effective at delivering a constant charge and switching off once your battery is full. However for Maximum charge efficiency a MPPT should be used.
Get Professional Advice
Getting professional advice will help you size your charge controller based on the critical aspects discussed above. It also ensures you pick the best model for your specific system and location.
But the biggest advantage is that a solar expert will help you get the most out of the properly sized components through proper installation.
The DIY videos certainly make it look easy, but proper installation goes beyond standard screws and wrenches. It takes specialised equipment to ensure each component is primed to deliver maximum efficiency. For example:
- A solar pathfinder to assess the shading on your rooftop and determine the best placement for maximum solar exposure
- A multimeter to test the overall efficiency of your system by monitoring current flow from panels to batteries and by showing readings on electrical resistance
- A tiltmeter to test the angle placement of your panels to ensure maximum sun exposure
- An infrared camera to spot temperature differences across your panels before they cause system failure
When it comes to solar charge controllers, it’s easier and faster to consult a professional.
Get the Right-Sized Charge Controller From Off Grid Direct
So there you have it. Five tips to help you avoid oversizing your solar charge controller. With these ideas in mind, here’s why we think you should shop at Off Grid Direct.
We’re passionate about bringing value to the marketplace and excited when the customer (you) gets the best deal for bringing sustainability to their home or business.
- Free shipping for orders above 300
- Price match guarantees if you can find a better offer out there
- 30-day easy returns if you’re not happy with your purchase
Contact us today or check out our solar solutions and take advantage of our incredible offers.
What Is An MPPT Charge Controller?
The most basic functionality of a solar power system is solar panels collecting energy from the sun and storing it in batteries so that you can use it whenever you’d like. However, you can’t simply connect your solar panels directly to your batteries and expect them to charge. To get the most out of your solar panels, you’ll need a charge controller to charge your batteries efficiently. The most efficient type of charge controller is the maximum power point tracking or MPPT charge controller.
Let’s take a look at how they work and what benefits they provide.
What is Maximum Power Point Tracking?
Before we dive into how MPPT charge controllers work, let’s explain how they get their name.
The voltage at which a solar panel produces the most power is called the maximum power point voltage. The maximum power point voltage varies depending on environmental conditions and the time of day.
MPPT charge controllers get their name because they monitor the solar panel and determine the maximum power point voltage for the current conditions. This function is called maximum power point tracking, or MPPT for short.
Tip: Refresh on Amps, Volts, Watts and their differences.
What Is An MPPT Charge Controller?
Solar panels and batteries have different optimal operating voltages. Not only that, these voltages fluctuate. An MPPT charge controller is a DC-DC converter that maximizes the efficiency of a solar system. It does this by optimizing the voltage match between the solar panel array and the batteries.
For example, depending on the state of charge, a 12-volt battery has a nominal voltage that ranges between just over 10 volts and just under 13 volts. Furthermore, the voltage required to charge a 12-volt battery ranges between 13.5 and 14.5 volts depending on the charging phase.
On the other hand, the optimum output voltage of a solar panel varies depending on the panel’s temperature, time of day, how cloudy it is, and other environmental factors. For instance, under ideal conditions, a 250-watt solar panel may have an optimal operating voltage of 32 volts. As the panel heats up in the sun or on a hot day, the optimal voltage may drop to as low as 26 volts.
The rated panel voltage must be higher than the battery voltage to accommodate for these voltage drops in the panel and the increased required battery charging voltage. Without an MPPT charge controller, this voltage differential leads to a lot of wasted power.
What Is The Difference Between MPPT and PWM Charge Controllers?
To better understand how this voltage difference causes inefficiencies, let’s first examine the other common type of solar charge controller. This controller is the pulse width modulation (PWM) charge controller.
PWM controllers use a transistor switch that rapidly opens and closes as needed to regulate the charge current going into the battery. Since PWM controllers can’t modulate the voltage, they pull the output voltage of the solar panel down to match the battery voltage. Let’s look at an example.
A 250-watt solar panel may have an optimal or max power voltage (Vmp) of 32 volts and a max power current (Imp) of 7.8 amps. (32 volts x 7.8 amps = 250 watts)
Using a PWM controller, your panel will still produce 7.8 amps. But the voltage will drop to match the battery at 12 volts. Now, your panel is only providing 94 watts instead of 250 watts. (12 volts x 7.8 amps = 94 watts)
How MPPT Charge Controllers Work
As we mentioned before, MPPT charge controllers are DC-DC converters. This means they regulate the charge current into the battery like a PWM controller. But, they also convert the voltage coming out of the panel to match what the battery needs. Let’s look at an example of how this drastically improves efficiency.
Using the same 250-watt panel, the MPPT controller allows the panel to operate at the max power voltage (Vmp). Now the power going into the controller is the full rated 250 watts.
The output from the controller to the battery still needs to match the battery at 12 volts. But the current increases to 20.8 amps allowing you to utilize the full 250 watt potential of your panel. (12 volts x 20.8 amps = 250 watts)
For simplicity, these examples assumed a 100% efficient conversion in the charge controllers. In reality, a small amount of power is lost as heat during the conversion.
Benefits of an MPPT Charge Controller
Efficient at Using Power
On a properly sized solar power system, it’s not uncommon to see up to a 30% increase in efficiency by switching to an MPPT controller. This efficiency increase is even more significant on systems where the solar panel voltage is much higher than the battery voltage, like our example above.
Best for Large Systems
Utilizing an additional 20-30% of power out of your system becomes more advantageous as the size of your system grows. For this reason, MPPT controllers are often best used on large systems and may not be worth it on smaller, simpler setups.
Better in Cloudier Environments
The maximum power point tracking feature of MPPT controllers is a huge benefit in cloudy environments where the max power point of the solar panels will be fluctuating all day.
Are MPPT Solar Charge Controllers Worth It?
MPPT charge controllers are more expensive than PWM controllers. The added cost of upgrading your controller may not be worth it on small, basic systems. However, on larger systems or in locations with unstable weather conditions, the increased power and efficiency gained by using an MPPT controller will likely more than makeup for the added cost of the controller.
Nobody likes to waste power. MPPT charge controllers help you get the most out of your solar panels without worrying about changing weather conditions or making sure you perfectly sized your solar panels to your battery voltage.