To befriend solar panels and batteries in one solar power system, you need a regulator that keeps your whole installation safe. The best thing you can find is a MPPT solar charge controller. What is MPPT, how it works and what are the advantages of such a device — we'll explain in a minute.
Key takeaways
What is a solar charge controller in general? A charge controller is placed between PV modules, batteries and the inverter. Its primary function is to optimize the charging process and protect the system from damage by bridging and isolating it from the batteries. What exactly is it doing?
Photovoltaic panels generate electricity whenever the sun shines. But the batteries have a limit to how much charge they can hold. Continuing to pump electricity into a fully charged battery can overcharge it, causing the battery to overheat, get damaged, killed, or even catch fire. The charge controller prevents it by regulating the flow of electricity from the solar panels to the batteries. When the batteries reach their full charge capacity, the controller reduces or stops the flow of current, preventing overcharging and ensuring the battery’s safety.
Completely draining a battery is also not healthy. It shortens the battery’s lifespan and may even kill it. The charge controller also protects against this. It monitors the battery’s voltage and, if it detects that the charge is getting too low, it disconnects the battery from the load. This prevents the battery from running completely flat.
Pay attention to your battery’s Depth of Discharge or DoD in the data sheet, showing how much the battery can be discharged without being harmed. Say you have a 10 kWh solar battery with a recommended DoD of 80%. This means you should not use more than 8 kWh before charging the battery again.
At night, or when the solar panels aren’t producing enough power, there’s a risk of current flowing back from the batteries to the solar panels. This reverse current flow can drain the batteries and even damage the panels. The charge controller prevents this backflow and ensures that current only flows from the panels to the batteries, and never the other way around.
The voltage of solar panels might not always be perfectly compatible with the battery’s charging requirements. You can't connect a typical 60-cell 32V panel with a 12V battery just like that — the battery is going to break, and the gases inside can even explode and start a fire. Whatever panels you are using, you would always need a regulator of some kind, except for really small panels of 1-5 watts.
Having trouble with solar panels?
Fill out form and compare offers from solar professionals
Get quotesNow that we have figured out what solar charge controllers are designed for, let's take a look at their types. The two main types are: Pulse Width Modulation or PWM and Maximum Power Point Tracker or MPPT.
PWM controllers are the simpler and less expensive option. They act as a switch, connecting the solar panel to the battery. The controller switches this connection on and off, varying the pulse width to regulate the charge. While functional, PWM controllers force the solar panel to operate at the battery voltage, which is often lower than the panel’s optimal operating voltage. This results in wasted power, especially in cooler weather when solar panels tend to produce higher voltages.
MPPT controllers first emerged on the market in 1985 and since then have become very popular.
MPPT controllers are the most modern and efficient ones. An MPPT controller doesn’t just connect the panel to the battery. It works as a smart DC-DC converter – instead of just limiting the voltage of panels to match the one of batteries, an MPPT controller turns it into current and sends it to panels, maximizing the efficiency of the whole system. For that, it uses sophisticated algorithms to constantly track the maximum power point of the solar panels or MPP.
A solar panel’s power output isn’t constant. It varies with sunlight intensity, temperature, and the voltage at which the panel operates. MPP is a specific point on the panel’s voltage-current or IV curve where the power output is at its peak. The MPPT controller is constantly tracking the MPP to ensure the solar panel is always delivering its maximum power output while the battery is safely charged.
How does it work in practice? Say, you have a 60-cell panel. On paper, it has a voltage of 24V – this is their voltage in the middle of a sunny day on a roof somewhere in the continental US. But its maximum operational voltage can go up to 32 V. The panel is connected to a 12 V battery. Without a regulator, the battery will just break, because voltages don't match.
A PWM regulator would just cut the voltage coming from panels to 12 V at any point in time, unless the voltage of panels for some reason drops lower than 12 V and the current would be at approximately 8 A.
On the contrary, the MPPT-controller would use the excessive voltage of panels. When panels reach their peak power voltage or Vpp of 32 V, an MPPT regulator would balance it out: it would decrease the voltage to 12 V for the battery and raise the current coming from panels up to approximately 20 A.
MPPT controllers are 20-25% more efficient than PWM regulators. They make use of around 90-95% of energy coming from solar panels. PWMs should be used only when the voltages of panels and batteries match. MPPTs can be used at any combination of a panel and a battery and they are more efficient when there is a significant difference between voltages.
Since MPPT controllers make use of the excessive voltage of panels which builds up, for example, in cold sunny weather, it would be fair to say that these regulators pay for themselves best in winter. They let you use around 30% more energy from solar panels at that time of year, so you can be sure your house will be well-heated.
As MPPT controllers have more energy at their disposal during those days, they can charge an empty battery faster. They are the least efficient in summer when it's hot and bring you around 10% more energy than PWM regulators. Judging by that, it makes sense to use MPPT controllers in cold and cloudy states especially.
MPPT controllers seem to be better at literally every single aspect, but are they? Let's take a closer look at the bright and dark spots of this type of regulator.
You’ve got your solar panels, battery bank, and charge controller. Seems the sun's power is yours for the taking, but before connecting everything, you need to ensure your charge controller can handle the electrical load. Let’s check if your charge controller is perfectly suited for your solar panel array, preventing headaches and damage to your system. Here are the main numbers to look for:
Solar panel Voc increases in cold temperatures, so factor in temperature variations in your city when calculating Voc!
The controller’s maximum input voltage must be higher than the solar array’s open-circuit voltage or Voc. When panels are wired in series, their voltages add up. So, calculate the total Voc of your series-connected panels. Be careful with this, as exceeding the controller’s maximum input voltage can cause permanent damage. Don’t forget to ensure the charge controller is compatible with the voltage of your battery bank.
Let's say, you have two 300-watt 24-volt panels with Voc at 42 Volts. The sum of Vocs therefore is 42V*2=84V, so the maximum voltage of the controller should be bigger. However, if the sum of peak voltages (Vpps) exceeds the maximum voltage of the controller it can also be potentially dangerous. Generally, the Vpp of a panel can be calculated by adding 5 Volts to the Voc. In our example the sum of Vpps is 42*2+5*2=94V, so a 100-volt controller should do the job.
The controller’s current rating must be higher than the solar array’s short-circuit current or Isc. When panels are wired in parallel – not in series as with voltage! – their currents add up. So, calculate the total Isc of your parallel-connected panels. It is always good to add a safety margin to the current calculations to account for potential variations and ensure the controller isn’t operating at its maximum capacity.
Say, both of your panels generate 300 W / 24 V =12.5 A*2 =25 Amps in the best-case scenario. For this system, you would need a regulator with a maximum charge of 30 Amps, a maximum voltage of 100 Volts and a 300 amp/hour battery. A 30-amp MPPT charge controller can cost around $200-$300 and the bigger the maximum charge is, the more expensive it gets.
The controller’s wattage rating must be equal to or greater than the total wattage of your solar array. Calculate the total wattage of your solar array by adding up the wattage of each panel.
Most solar charge controllers are equipped with a display that shows the charge of the battery and its current state. Of course, since MPPT-controllers are much more sophisticated than PWM-regulators, they often have more features. Apart from that, many modern charge controllers come equipped with Bluetooth or Wi-Fi modules and can be connected to your laptop or smartphone and controlled that way.
On our website there is a special section for battery charge controllers and you can take a look at models yourself. Follow and check out the models available.
Find your best solar batteries
Keep the sun on 24/7 with a reliable energy storage bank. Don’t let power outages change your plans!
SHOP SOLAR BATTERIES
Andrei has been a news editor and freelance writer for a number of medias before joining the A1 SolarStore. Climate change and its impact on people's lives have always been among his interests and it partially explains his degree in Philosophy and Ethics.
More articles from this authorStay tuned
Learn about the latest arrivals and discounts first!
Backup plan: Best solar batteries in 2025
AC vs DC-coupled solar battery systems: Pros and cons
How do solar panels work on cloudy days and why do electricity prices matter more than the weather
