**MPPT** **solar charge controllers**** are rated in amps (Output Current). To select a charge controller, you’ll need to calculate the maximum amount of current (in Amps) that the MPPT should be able to output.**

**This max output current value is calculated by dividing the maximum system wattage (in Watts) by the minimum charging voltage of the battery bank (in Volts).**

In other words, we calculate how much current the solar charge controller needs to be able to put out by using this simple formula:

**MPPT amperage rating = (Max. System Wattage) / (Min. Battery Charging Voltage)**

**However, MPPT charge controllers also have a Maximum Input Voltage rating**, **which indicates the maximum amount of voltage (in Volts) that is acceptable at the input of the MPPT.**

So, when selecting your solar charge controller, you should account for both current and voltage.

But, don’t worry! I got you covered…

To make your life easier, I’ve made an **MPPT size calculator** that will do all the heavy lifting and give you a **direct link to the charge controller best suited for your needs**.

Below the MPPT calculator, I’ll give you 3 examples of different-sized solar arrays and battery banks that’ll illustrate this for you.

Also if you want a more in-depth understanding of how the calculator works, please refer to our MPPT sizing guide.

###### I get commissions for purchases made through links in this post.

## MPPT Size Calculator

The MPPT calculator has 6 input fields that will describe your solar energy system:

**1- Solar panel wattage:** This is the **watts rating** on **each** of your **solar panels**.

**2- Solar panel open-circuit voltage (Voc):** You can find this value in the specification label on the back of your solar panels, or by looking up the specific model. But please make sure that you use the STC (Standard Testing Conditions) rating for this particular input.

**3- Battery bank voltage (Nominal Voltage):** The voltage of each battery is usually written on the casing. If you have more than one battery, the voltage of the battery bank is equal to the voltage from one string of batteries (series).

**4- Lowest temperature during sunlight hours:** In this field, you should enter the lowest value of temperature that you estimate your solar panels are ever going to be exposed to.

**5- Number of strings:** In your solar array, how many parallel strings are there?

**6- Number of solar panels in each string:** In each string, how many solar panels are wired in series?

## MPPT Solar Charge Controller Calculator

As promised, below you’ll find a few examples that’ll clear things up for you.

- In these examples, I’ll use the 100W-12V Monocrystalline Solar Panels from Renogy. The manufacturer specifies 22.3V as an open-circuit voltage for these panels.
- For the batteries, I will use these 100 Ah 12V LiFePO4 Deep Cycle Battery from Battle Born.
- I will also assume the lowest temperature during sunlight hours these panels in the examples will ever be exposed to is
**estimated at -3°F.**

## Example 1: 200W-12V solar array with a 12V battery bank

For the first example, we have 2 100W-12Vwatts solar panels, these panels are wired in series and need to charge a 100Ah-12V Battle Born battery.

Now we need to select the right size MPPT charge controller for this system.

So what do we know so far?

- We have 2 100W-12V solar panels wired in series.
- Our battery bank’s voltage is 12V nominal.

We still need 2 pieces of information:

- The open-circuit voltage (Voc) on these panels.
- The lowest temperature these panels will be exposed to.

As mentioned above, the manufacturer specifies **22.3V** as the open-circuit voltage for each of these panels.

The lowest temperature in our example is **-3°F**.

Now that we have all the information we need, let’s take a look at the results from the MPPT calculator.

The MPPT calculator tells us that our solar charge controller needs to have a maximum voltage input of more than **53V**, and needs to be able to put out **22.5 amps**.

The calculator also gave us links to 2 choices for MPPT charge controllers that meet these criteria.

## Example 2: 400W-24V solar array with a 12V battery bank

For the 2nd example, we have **4 100W-12V solar panels**, these panels are wired in **2S2P** (2 parallel strings with 2 solar panels in each string).

These panels need to charge** 2 parallel wired 100Ah-12V batteries**.

So what we know is:

- We have
**2 parallel strings**. **2**solar**panels****in each string**.- The
**power rating**of our solar panels is**100W**. - The
**open-circuit voltage**of our solar panels is**22.3V**. - The voltage of our
**battery bank is 12V**. - The lowest temperature is
**-3°F**.

For this system, the MPPT calculator suggests a Victron 100V-50A charge controller and an EPEVER 50 amp charge controller.

Both of these charge controllers can handle the anticipated 53 Volts at their input and can put out up to 50 Amps of current.

## Example 3: 200W-24V solar array with a 24V battery bank

For the third example, we have **4 100W-12V solar panels**. And same as the 2nd example, these panels are wired in **2S2P**.

However, the solar panels in this system need to charge **2 series wired 100Ah-12V batteries**.

So for this example:

- We have
**2 parallel strings**. **2**solar**panels****in each string**.- The
**power rating**of our solar panels is**100W**. - The
**open-circuit voltage**of our solar panels is**22.3V**. - The voltage of our
**battery bank is 24V**. - The lowest temperature is
**-3°F**.

## Related topics:

**What size wire between solar panels and MPPT?**

**What size wire between the MPPT and the battery?**

**Solar panels in series and in parallel – What is the difference?**

i recently bought a 200 amp, 12volt batter with blue tooth, 40 amp Renogy charge controller, 2-100 watt solar panels. from your examples above with 4-100 watt panels, i could add 4 more panels to my system without replacing my charge controller for a 60 amp or higher.

Am i understanding thjis correctly? thanks Steve

Hey there Steve,

Before you make any decisions, I suggest testing the number of solar panels that you intend to add in the calculator.

Thanks Younes you have done a very good job in educating readers about MPPT. However, you have stopped short of explaining the MPPT calculator which I believe will impact on practicing engineers like me. I wish more effort.

Abba

Very comprehensive, thank you! As it turns out, I am already using the Renogy 200W Kit (2 panels w/20A Rover), and now have 6 lead-acid 6V batts in 3banks. I’m having a problem keeping the charge up (52-70%), and thinking that I am not getting enough solar to replenish the batteries over a 4-5day stay. I’m not sure how to look at this, as I am trying to decide if I have too many batteries (to decrease the batts), or not enough solar panels (add panels)!?

Hey there Mike,

From what I understand, you have 6 Lead-Acid batteries each rated at 6V-100Ah, and each 2 of these are wired in series to make a 12V-100Ah battery. This means that you have a 12V-300Ah battery bank in total, making your total rated Energy Capacity 3600 Watt-hours (3.6 kWh).

On the other hand, you only have 200W of solar, which means that at most you’ll be getting 1200 Wh of energy on a daily basis. This is, of course, assuming optimal sunlight.

This means that even if you don’t discharge your batteries at all, you’ll need 3 days to take the battery from 0% to 100%.

So, to answer your question, you need more solar panels.

Hope this helped.

Hi I have 4 200w panels 800w Open Circuit Voltage (Voc): 21.6V is my Victron mppt 150 70 tr over the top and probably would not work 100%

Hey there Brian,

Have you specified the Nominal Voltage of the battery and the configuration of the solar panels (series/parallel/combination of both) to the calculator?

If you do, it should provide a couple of links to appropriate MPPTs.

Thank you very much for prviding this information. have a great day

Hi,

I want to know about the lowest temperature during daytime. Is it the lowest temperature for where I live on yearly basis?

By the way Thanks for your articles. I was looking for these informations.

Hello Tom,

Yes, I’m referring to the lowest temperature possible when the solar panels are capable of producing voltage, which is only possible in daytime hours. If you don’t have an exact data point, just put an estimate.

Glad to have helped.

To keep things simple The figures I am using are just examples.

I plan to use a 5,000 watt hybrid inverter with a MPPT charge controller and 3,000 watts of solar power.

And Im not sure if a MPPT controller is more efficient running input DC voltage at say 150 volts DC or 450 volts DC. since my AC voltage will be 120 volts AC

Hello there Wayne,

Well, I would say higher voltage means less current, so cheaper wires. But in terms of efficiency, as long as the MPPT can handle the voltage, and the output current at that voltage, I’d say it doesn’t really matter. But I still would need to look at the specs of your setup to understand what you’re trying to do.

hello ,i have 2 x 12v 200hah deepcycle batteries,3 off 380w solar panels,42 VOC on panels

panels connect in series

battery bank 12v

Please assist with correct size of controller

Hey there Gideon,

According to the calculator you would need a solar charge controller rated at an input voltage of 150V and output current of 110 Amps. I suggest you wire those batteries in series, making a 24V battery bank. This configuration will allow you to use a 150V 60A charge controller, just make sure it’s compatible with battery voltage (24V), like this controller from Victron or this one from Epever.

Hello,

I have a system withh two solar panels of 450w each (so 900w in total).

The VOC of each panel is 50.2v; current at full power: 10.77 A.

The inverter is a hybrid and includes the charge controller.

It’s specs are 3KW 24v MPPT 50A/100V VPM. The regulator charge current is 50 A.MPPT

and the charger charging current 30A.

(https://www.wccsolar.net/product-page/inversor-solar-3kw-24v-h%C3%ADbrido-regulador-mppt-50a-cargador-30a?lang=en)

There are two 12v batteries connected in series.

Would it be possible to add another 450w panel – so have three 450w panels

connected in parallel – and keep using the same hybrid inverter?

I’ve tried using the MPPT calculator but don’t seem to be able to enter 0 for

number of panels in series and am not sure about the results…

Your help would be appreciated!

Hey there Lucy,

On the calculator you should enter “1” rather than “0”. Please try that and it’ll give you your answer.

I’ve entered the specs you provided and seems that you would need a solar charge controller with an output current rating of at least 57.4 Amps to make use of 100% of your solar panels’ power production.

This means that if you do add a 3rd panel, and all 3 solar panels produce 450 Watts each, you’ll lose about 7.4 amps at 24 volts, maybe more if the temperature is colder while sunlight is at its peak.

However, realistically, your solar panel will rarely produce 450 Watts each, and even if they do, that wouldn’t last more than an hour or so, so a little bit of clipping is okay.

What I’m trying to say is, yes, you can add a 450 Watt solar panel in parallel to your array.

Hope this helped!

Thanks very much for your reply, much appreciated!

Hi Younes,

I have 2x100W solar panels with Renogy 30A MPPT with 12V Battery bank. I recently got 2 x 250W panels, according the calculations the 2x250W would require a 50A MPPT.

What would I need if I want to run 2x100W (Voc 22.3) + 2x250W (Voc 37.9) panels? Would it be best to run 2x100w on one string and 2x250w on another string?

Thx

Hey there Derek,

I would suggest you get another MPPT for the 250W solar panels, because you can’t really wire them with the 100W solar panels in the same array (even in separate strings) due to mismatched voltage and current.

Hola Good Sir,

Thank you for all this information and being a fantastic DIY solar resource for all of us newbies out here. I was hoping to get your thoughts on a charge controller sizing query if you don’t mind. I currently have a 1050 W panel array arranged in series (3- 350W panels) and am looking to get a Victron 150/35 controller. I ran a few calculations recommended on other sites for my battery bank of three 12V lead acid batteries, arranged in series, which gave me the figure of ~30 A. Is that enough of a buffer for this system or should I go for the 150/45 model as an added precaution? It’s a little more than I want to spend but if it’s necessary I shall get it.

Kindest Regards

Hey Cam,

Yes I ran the calculations and it seems a 150/35 Amp MPPT would be enough for your setup. The only reason you I would go for a 150/45 model is if you’re planning on adding more panels later.

But even with a 150/35 model, you can still add another panel if you add a battery and upgrade to a 48V battery bank. However, if you do get a 150/45 model, you’ll be able to add up to 3 more panels later if you want, as long as you upgrade to a 48V battery bank.

Good luck!

I have a mishmash of panels some 80 W, some 100 W some 120 w, all 12v.

I have them in 3 strings, parallel wired, connected to pwm controllers.

How much variation would be allowable in voltage and amperage to connect them in series to a mppt controller?

If you were to connect them in series, Voltage wouldn’t really matter. The problem is current, if you connect these solar panels in series, the string current would become equal to that of the current produced by the 80W panel.

I would recommend keeping them wired in parallel.

Younes, thanks for your calculations. I am trying to work backwards into this answer for how many panels I can connect to a controller I already own. I have the renogy rover 60amp. It has Max. PV Input Voltage: 140VDC and charge current of 60amp. I have 2 12 volt lifepo lipo batteries. I asked renogy how many of the 100w panels with 24.3 VOC and they said 6 in parrellel. This seems off to me and using your calculator it appears I should be able to connect 12 panels total, 4 in series and 3 banks of them. Am I missing something, maybe using an incorrect number?? thanks for your page. btw I’m subscribing!

Hey there Chris,

It also depend on the output voltage rating of the MPPT, if its rated at 24V for output voltage and those batteries are going to be wired in series, then yes, you can use 12 solar panels with the configuration you described, you may even be able to do 15 panels (5S3P).

But if your batteries will be wired in parallel, and the MPPT is rated at 12V output, you’ll only be able to do 50% of that.

Hi,

I’m looking to build a solar backup for home. I have a 3500 Watt 12V Pure Sine Inverter. I looking to get a 12V 100Ah lithium battery and MPPT controller. How many 100W solar panels would I need to use the inverter for 24 hours if necessary?

Hey Marshall,

It depends on how much energy (watt-hours) you use in a 24 hours period. I recommend you check out our off-grid solar calculator.