When sizing a solar charge controller, the main specification to consider is the Output Current rating of the charge controller. For example, a 10 Amp rating means that the maximum amount of current that the charge controller is capable of delivering at its output is 10 Amps.
The Output Current rating or the “size” of the charge controller that you need for a 200W solar panel will mainly depend on these factors:
- The voltage of your 200W solar panel (12 or 24V)
- The voltage of your battery bank (12 or 24V)
- The type of charge controller you’ll be using (PWM or MPPT)
After reading this article, you’ll know the size of the charge controller that you need, and you’ll also learn about the types of charge controllers, which one you need, and the calculations involved in sizing these charge controllers.
What size charge controller for a 200W solar panel?
In general, if your 200W solar panel and battery bank are both rated at 12 Volts (nominal), the charge controller should be rated at 20 Amps or more. If both the solar panel and the battery bank are rated at 24V, the charge controller should be rated at 10 Amps or more.
However, if your 200W solar panel is rated at 24V, and your battery bank is only rated at 12V, the charge controller should be rated at 20 Amps or more if it’s an MPPT, and at 10 amps or more if it’s a PWM.
Notice that for a 24V solar/12V battery setup, the size of the charge controller needed depends on whether it’s a PWM or an MPPT charge controller. This is because these 2 types of charge controllers operate differently, and are also sized differently.
Let’s see how each of these charge controllers is sized.
What size MPPT do you need for a 200W solar panel?
In order to calculate the – minimum – Output Current rating of the MPPT that you need for your solar panel, simply divide the power rating of the solar panel by the lowest voltage required to charge the battery.
MPPT’s Output Current rating (Amps) should be greater than Solar Panel’s power rating (Watts) ÷ Lowest Voltage Required to charge the Battery (Volts)
The lowest voltage required to charge the battery is:
- 10.5 Volts if your battery is rated at 12V (nominal)
- 21 Volts if your battery is rated at 24V (nominal)
- 42 Volts if your battery is rated at 48V (nominal)
Or, you can let our MPPT calculator do all the work for you.
Since it’s a 200W solar panel, and, for example, if the battery is rated at 12V:
MPPT’s Output Current rating (Amps) should be greater than Solar Panel’s power rating (Watts) ÷ Lowest Voltage Required to charge the Battery (Volts)
MPPT’s Output Current rating (Amps) should be greater than 200 Watts ÷ 10.5 Volts
MPPT’s Output Current rating (Amps) should be greater than 19 Amps
A 20 Amp MPPT for this setup would be a great fit.
If, for example, the battery is rated at 24V:
MPPT’s Output Current rating (Amps) should be greater than Solar Panel’s power rating (Watts) ÷ Lowest Voltage Required to charge the Battery (Volts)
MPPT’s Output Current rating (Amps) should be greater than 200 Watts ÷ 21 Volts
MPPT’s Output Current rating (Amps) should be greater than 9.52 Amps
In this case, a 10-15A MPPT would be enough.
As I explain in my article about how to select an MPPT charge controller and also take into consideration in our MPPT calculator, with larger solar systems where you would have multiple solar panels wired in series, you would also have to pay attention to another specification, which is the Max. Input Voltage rating of the charge controller.
This is because with multiple solar panels in series, the voltage will be higher, and these charge controllers do have a limit on how much voltage is permitted at their input.
However, since we’re only talking about a 200W solar panel here, you won’t really have to in this case. Check out this article for more information on the topic.
What size PWM do you need for a 200W solar panel?
In order to calculate the – minimum – Output Current rating of the PWM that you need for your solar panel, simply multiply the short-circuit current (Isc) of your solar panel by 1.25:
PWM’s Output Current rating (Amps) should be greater than Solar Panel’s Short-Circuit Current rating (Amps) x 1.25
Or, you can use our PWM charge controller calculator.
For example, if your 200W solar panel is rated at 12V, its short-circuit current would be somewhere between 9 and 12 Amps amps depending on the solar panel. The short-circuit current of your solar panel will generally be specified on the label at the back of your panel or in the datasheet provided by the manufacturer.
For the sake of this example, let’s say our Isc is 12 Amps:
PWM’s Output Current rating (Amps) should be greater than Solar Panel’s Short-Circuit Current rating (Amps) x 1.25
PWM’s Output Current rating (Amps) should be greater than 12 Amps x 1.25
PWM’s Output Current rating (Amps) should be greater than 15 Amps
A 20 Amps PWM would be a great fit for this setup.
If, on the other hand, your 200W solar panel is rated at 12V, the short-circuit current would be somewhere between 5 and 6 amps depending on the solar panel. For example, let’s say it is 6 Amps:
PWM’s Output Current rating (Amps) should be greater than Solar Panel’s Short-Circuit Current rating (Amps) x 1.25
PWM’s Output Current rating (Amps) should be greater than 6 Amps x 1.25
PWM’s Output Current rating (Amps) should be greater than 7.5 Amps
In this case, a 10A PWM would be required.
If you haven’t yet decided which type of charge controller to opt for, the next section will clear things up for you.
PWM vs MPPT: what is the difference and which one should you use?
Although a 200w solar panel might be rated at 12 Volts, that’s only its nominal voltage. The actual voltage of the solar panel is generally higher than that.
For example, this 200W solar panel from Renogy is labeled as a 12V solar panel, but if you look at its specifications it says that its Optimum Operating Voltage is actually 22.6 Volts. Its Open-Circuit Voltage is even higher than that (27V).
Solar panels are manufactured with this higher voltage on purpose and in order to be able to charge the battery. However, if left unregulated, the voltage of a solar panel can lead to the overcharging of the battery, which would in turn irreversibly damage the battery.
I explain this thoroughly in my article about the function of charge controllers.
In short, a solar charge controller’s job is to limit the voltage across the terminals of the battery to a certain acceptable value. Both PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking) charge controllers do this. However, each charge controller type achieves this differently.
A PWM charge controller lowers the voltage from the solar panel by connecting and disconnecting the solar panel as required, therefore lowering the average voltage that the battery is subject to.
This works as intended and does protect the battery, however, in those periods when the solar panel is disconnected, any amount of power that could potentially be generated by the solar panel is lost.
The higher the voltage difference between the solar panel and the battery, the longer the solar panel has to be disconnected. In other words, the higher the voltage difference, the more power will be lost, and the less efficient a PWM charge controller is going to be.
A PWM charge controller would only be a good fit for your system if you’re on a budget, and if your solar panel and battery have the same nominal voltage rating.
MPPT charge controllers, on the other hand, are a more advanced charge-controlling technology and are generally more efficient.
An MPPT charge controller will not only lower the voltage of the solar panel to match that of the battery but will also maximize the power production of the solar panel. Read more about this topic here.
And when it does lower the voltage of the solar panel, it does not need to disconnect the solar panel, it has the technology to simply trade the Volts for Amps. In other words, the amount of power coming from the solar panel stays the same, it’s simply transformed to a lower voltage/higher current kind of power.
If the nominal voltage of your solar array is greater than that of your battery bank, you will need an MPPT charge controller. And even if the nominal voltages are matched, you would still get more power out of an MPPT (as opposed to a PWM).
Related Topics:
What can a 200W solar panel run?
What size wire from the solar panel to the charge controller?
What size fuse between the solar panel and the charge controller?
