Solar String Voltage Calculator
How many solar panels can you connect in one string? Enter your panel and inverter datasheet values to check string voltage on the coldest morning and the hottest day, and see the allowed range of panels per string.
For planning only. This tool gives a preliminary estimate. It is not a design, and a qualified professional must check it against the datasheets and your local electrical rules.
Your string check
10 panels pass these checks near Los Angeles. 5 to 11 panels per string fit this inverter.
Preliminary estimate. Must be verified by a qualified professional.
- Pass: Cold-morning voltage is within the limit542 V against a 600 V limit.
- Pass: Hot-day voltage stays in the tracking range352 V against a 150 V minimum.
- Pass: Cold-day working voltage stays in the tracking range464 V against a 550 V maximum.
We used -10°C from climate data with a 5°C margin. Local rules may need a specific value.
Assumptions used
- Lowest temperature
- -10°C
- Hottest air
- 45°C
- Hot panel temperature
- 70°C
- Cold panel Voc
- 54.2 V
What if?
Save this result, change any setting, and compare.
How this is calculated
Coldest morning
Panel voltage rises as temperature falls. The string's open-circuit voltage at the coldest expected temperature must stay under the inverter's maximum input voltage.
Cold Voc = panels × Voc × (1 + coefficient × (temperature − 25°C))
Hottest day
Voltage falls when panels are hot. Panels run about 25°C above the air in strong sun, and the working voltage must stay above the inverter's minimum tracking voltage.
Hot Vmp = panels × Vmp × (1 + coefficient × (cell temperature − 25°C))
Temperatures
By default we use your location's climate data, with an extra 5°C below the lowest value because rare cold mornings can be missed. You can enter your own design temperatures, and local rules may require specific values.
Worked example: 10 panels at -5°C
A panel with 49.5 V Voc and a -0.27%/°C coefficient reaches 53.5 V at -5°C. Ten panels reach 535 V against a 600 V limit.
On a 40°C day, the cells reach about 65°C and the string's working voltage falls to 359 V. For this inverter, 5 to 11 panels per string fit.
How accurate is this?
The temperature formulas are standard, but this is a preliminary check and not a design. Datasheets and local electrical rules take priority. A qualified professional must verify any string design before installation.
Common mistakes
- Using 25°C voltage instead of the cold-morning voltage
- Using the percent coefficient as a volts coefficient
- Taking the average winter temperature instead of a record low
- Forgetting that hot panels can fall below the tracking range
Limits of this tool
- It does not check current limits or how strings share tracking inputs
- Shading and mixed orientations are not included
- Some electrical codes set their own temperature correction method
What to do next
- Check your inverter size with the inverter size calculator
- Check cable size with the cable size calculator
Frequently asked questions
How many solar panels can I put in a string?
Divide the inverter's maximum voltage by each panel's cold-morning Voc and round down. Then check the hot-day minimum as well.
Why does solar panel voltage rise in cold weather?
Cold cells produce a higher voltage. This is why string limits are checked at the lowest expected temperature.
What is Voc on a solar panel?
It is the open-circuit voltage: the voltage with no load connected. You can find it on the datasheet.
What is the MPPT range?
It is the voltage range in which the inverter can find the panels' best working point. Outside it, output may fall.