Use our calculator to easily find the maximum open circuit voltage of your solar array.

### Calculator Assumptions

**Your solar panels are all identical.**I explain below how to calculate maximum open circuit voltage if your solar panels are different.**Your solar panels are rated at 25°C (77°F).**This is the industry-standard temperature at which solar panels are rated.

## How to Use This Calculator

**1. Find the technical specifications label on the back of your solar panel.** For example, this is the label on the back of my Renogy 100W 12V Solar Panel.

**Note:** If your panel doesn't have a label, you can usually find its technical specs in its product manual or online on its product page.

**2. Enter the open circuit voltage (Voc).** My panel's was 22.3V.

**2. Enter the number of solar panels you're wiring in series.** For this example, let's say I'm wiring 4 panels in series.

**3. Enter the lowest temperature you expect your solar array to experience in daylight and select the correct units (°F or °C).** Often, people will use the lowest recorded temperature at their location. For example, I live in Atlanta and did a quick Google search to find out that the lowest recorded temperature here was -9°F (-22.8°C).

**Note:** If your solar panels are mounted on a vehicle, consider the various locations you plan on visiting.

**4. Optional: Enter the temperature coefficient of Voc and select the correct unit (%/°C or mV/°C).** My panel's was -0.28%/°C. If left blank, the calculator uses the appropriate correction factor based on your lowest expected temperature.

**6. Click "Calculate" to get your results.** For this example, I got a maximum solar array voltage of 101.1V.

## 2 More Ways to Calculate Maximum Solar Panel Voltage

Here are a couple more ways to find your max solar panel voltage besides using our calculator. Use one of these methods if your solar panels aren't identical, or if you'd like to understand the math underlying the calculation.

### 1. Use Correction Factors

The National Electrical Code (NEC) provides a table of voltage correction factors for solar panels based on ambient temperature. The correction factors make it easy to calculate your maximum solar system voltage yourself.

Here's the table:

Factor | Ambient Temperature (°F) | Ambient Temperature (°C) |
---|---|---|

1.02 | 76 to 68 | 24 to 20 |

1.04 | 67 to 59 | 19 to 15 |

1.06 | 58 to 50 | 14 to 10 |

1.08 | 49 to 41 | 9 to 5 |

1.10 | 40 to 32 | 4 to 0 |

1.12 | 31 to 23 | -1 to -5 |

1.14 | 22 to 14 | -6 to -10 |

1.16 | 13 to 5 | -11 to -15 |

1.18 | 4 to -4 | -16 to -20 |

1.20 | -5 to -13 | -21 to -25 |

1.21 | -14 to -22 | -26 to -30 |

1.23 | -23 to -31 | -31 to -35 |

1.25 | -32 to -40 | -36 to -40 |

**Note:** The above table has been adapted from Table 690.7(A) from the 2020 edition of the NEC. It applies to monocrystalline and polycrystalline silicon panels, the predominant types on the market today.

For this method, you'll need the table along with the following numbers:

- Voc of each solar panel
- Number of panels wired in series
- Lowest expected temperature

#### Instructions

**1. Find the appropriate correction factor from the above table using your lowest expected temperature.**

**2. Calculate the max open circuit voltage of each solar panel by multiplying its open circuit voltage by your correction factor.**

If your panels are identical:

Max solar panel Voc = Solar panel Voc × Correction factor

If your panels are different:

Max solar panel Voc #1 = Solar panel Voc #1 × Correction factor Max solar panel Voc #2 = Solar panel Voc #2 × Correction factor Max solar panel Voc #3 = Solar panel Voc #3 × Correction factor ...etc

**3. Sum the max open circuit voltages of all your solar panels wired in series.**

If your panels are identical:

Max solar array Voc = Max solar panel Voc × Number of panels

If your panels are different:

Max solar array Voc = Max solar panel Voc #1 + Max solar panel Voc #2 + Max solar panel Voc #3 + ...

*Pretty easy!* For once, the NEC makes life a little easier.

#### Example #1: Identical Solar Panels

Let's say these are the specs for 2 identical solar panels you're wiring in series:

- Solar panel Voc: 19.83V for all panels
- Number of solar panels wired in series: 2
- Lowest expected temperature: -10°F (-23°C)

Here's how you'd find your max solar array voltage:

**1. Find the appropriate correction factor using the above table.** In this example, based on my lowest expected temperature of -10°F (-23°C), my correction factor is 1.2.

**2. Multiply solar panel Voc by your correction factor.**

Max solar panel Voc = 19.83V × 1.2 = 23.796

**3. Multiply the max solar panel Voc by the number of panels wired in series.**

Max solar array Voc = 23.796V × 2 = 47.592V ≈ 47.6V

In this example, the max open circuit voltage of your solar array is 47.6V.

#### Example #2: Different Solar Panels

Let's say instead that your 2 solar panels are different. They have the following open circuit voltages:

- Solar panel Voc #1: 22.6V
- Solar panel Voc #2: 21.4V
- Number of panels wired in series: 2
- Lowest expected temperature: -25°F (-32°C)

Here's how you'd find your max solar array voltage:

**1. Find the appropriate correction factor using the above table.** In this example, based on my lowest expected temperature of -25°F (-32°C), my correction factor is 1.23.

**2. Multiply each panel's Voc by your correction factor.**

Max solar panel Voc #1 = 22.6V × 1.23 = 27.798V Max solar panel Voc #2 = 21.4V × 1.23 = 26.322V

**3. Sum the panels' max open circuit voltages together.**

Max solar array Voc = 27.798V + 26.322V = 54.12V ≈ 54.1V

In this example, the max open circuit voltage of your solar array is 54.1V.

### 2. Use Temperature Coefficient of Voc

For this method, you'll need the following numbers:

- Voc of each solar panel
- Temperature coefficient of Voc (%/°C) of each solar panel
- Number of solar panels wired in series
- Lowest expected temperature (°C)

#### Instructions

**1. Calculate the maximum temperature differential by subtracting 25°C from your lowest expected temperature.** I recommend converting your lowest expected temperature to Celsius. It makes the calculations easier.

Max temp differential = Lowest expected temperature - 25°C

**2. Calculate the maximum voltage increase percentage for each solar panel by multiplying the maximum temperature differential by the panel's temperature coefficient of Voc.**

If your panels are identical:

Max voltage increase percentage = Max temp differential × Temp coefficient of Voc

If your panels are different:

Max voltage increase percentage #1 = Max temp differential × Temp coefficient of Voc #1 Max voltage increase percentage #2 = Max temp differential × Temp coefficient of Voc #2 Max voltage increase percentage #3 = Max temp differential × Temp coefficient of Voc #3 ...etc

**3. Calculate the maximum voltage increase of each panel by multiplying its maximum voltage increase percentage by its open circuit voltage.**

If your panels are identical:

Max voltage increase = Solar panel Voc × Max voltage increase percentage

If your panels are different:

Max voltage increase #1 = Solar panel Voc #1 × Max voltage increase percentage #1 Max voltage increase #2 = Solar panel Voc #2 × Max voltage increase percentage #2 Max voltage increase #3 = Solar panel Voc #3 × Max voltage increase percentage #3 ...etc

**4. Calculate the maximum open circuit voltage of each panel by summing its open circuit voltage and maximum voltage increase.**

If your panels are all identical:

Max solar panel Voc = Solar panel Voc + Max voltage increase

If your panels are different:

Max solar panel Voc #1 = Solar panel Voc #1 + Max voltage increase #1 Max solar panel Voc #2 = Solar panel Voc #2 + Max voltage increase #2 Max solar panel Voc #3 = Solar panel Voc #3 + Max voltage increase #3 ...etc

**5 . Sum the max open circuit voltages of all your solar panels wired in series.**

If your panels are all identical:

Max solar array Voc = Max solar panel Voc × Number of panels in series

If your panels are different:

Max solar array Voc = Max solar panel Voc #1 + Max solar panel Voc #2 + Max solar panel Voc #3 + ...

#### Example #1: Identical Solar Panels

Let's run through an example using the following numbers:

- Solar panel Voc: 20.2V for all panels
- Number of solar panels wired in series: 3
- Lowest expected temperature: -15°C
- Temperature coefficient of Voc: -0.3%/°C for all panels

**1. Subtract 25°C from your lowest expected temperature.**

Max temp differential = -15°C - 25°C = -40°C

**2. Multiply the maximum temperature differential by the temperature coefficient of Voc.**

Max voltage increase percentage = -0.3%/°C × -40°C = 12%

**3. Multiply the solar panel open circuit voltage by the maximum voltage increase percentage.**

Max voltage increase = 20.2V × 12% = 2.424V

**4. Add the maximum voltage increase to the solar panel open circuit voltage.**

Max solar panel Voc = 20.2V + 2.424V = 22.624V

**5. Multiply the maximum solar panel open circuit voltage by the number of panels wired in series.**

Max solar array Voc = 22.624V × 3 = 67.872V ≈ 67.9V

In this example, the maximum open circuit voltage of your solar array is 67.9V.

#### Example #2: Different Solar Panels

Let's say you have 2 different panels with the following specs:

- Solar panel Voc #1: 19.7V
- Solar panel Voc #2: 22.1V
- Number of panels wired in series: 2
- Lowest expected temperature: -20°C
- Temperature coefficient of Voc #1: -0.28%/°C
- Temperature coefficient of Voc #2: -0.3%/°C

Here's how you'd find your max Voc in this scenario:

**1. Subtract 25°C from your lowest expected temperature.**

Max temp differential = -20°C - 25°C = -45°C

**2. Multiply the maximum temperature differential by each panels' temperature coefficient of Voc.**

Max voltage increase percentage #1 = -0.28%/°C × -45°C = 12.6% Max voltage increase percentage #2 = -0.3%/°C × -45°C = 13.5%

**3. Multiply each panel's Voc by its maximum voltage increase percentage.**

Max voltage increase #1 = 19.7V × 12.6% = 2.4822V Max voltage increase #2 = 22.1V × 13.5% = 2.9835V

**4. Add each panel's maximum voltage increase to its Voc.**

Max solar panel Voc #1 = 19.7V + 2.4822V = 22.1822V Max solar panel Voc #2 = 22.1V + 2.9835V = 25.0835V

**5 . Sum the max open circuit voltages of all the solar panels wired in series.**

Max solar array Voc = 22.1822V + 25.0835V = 47.2657V ≈ 47.3V

In this example, the max voltage of your solar array is 47.3V.

### Common Mistakes When Calculating Max Solar Panel Voltage

Based on my experience -- and lots of reader emails and comments -- here are the most common mistakes I see people make when trying to find their max open circuit voltage:

**Forgetting to correct for temperature.**Solar panel voltage increases as temperature drops. Often, beginners aren't aware of this fact. (I definitely wasn't when I first started.) As a result, they just calculate the Voc of their solar array and use that number to size their solar charge controller. That puts them at risk of frying their charge controller on cold days.**Using maximum power voltage (Vmp or Vmpp) instead of open circuit voltage (Voc).**Many panels also list a maximum power voltage (aka optimum operating voltage), denoted Vmp or Vmpp. Some people mistakenly think they should use Vmp rather than Voc in their max voltage calculations. Always use Voc.**Using rules of thumb without understanding their limits.**A couple times, I've seen people online give a rule of thumb for calculating max Voc -- such as "add 5V to each panel's Voc" or "add 20% to the array's Voc." These can be helpful, but readers often fail to understand that these quick and dirty methods are best suited for certain temperature ranges.

Lastly, it's important to point out that the max solar array voltage you calculate is based on your lowest expected temperature. If your array ever gets colder than that in daylight, there's a chance it could exceed this number.

## How to Size a Charge Controller Using Max Solar Panel Voltage

Now that you know your maximum solar array voltage, it's time to pick a solar charge controller.

When shopping for a charge controller, look for its maximum PV voltage (sometimes called maximum PV open circuit voltage or maximum input voltage).

**Make sure your charge controller's maximum PV voltage is higher than the maximum open circuit voltage of your solar array.**

For example, let's say you calculate your max solar array voltage to be 105V. Then a charge controller with a max PV voltage of 100V is too low. You'll need to instead get one with a max PV voltage of, say, 150V.