String Size Calculator
Enter the panel's open-circuit voltage, maximum power voltage and temperature coefficient from its datasheet, the coldest temperature at your site and the inverter's voltage limits. The calculator gives the range of panels you can put in one string.
- Max for cold mornings
- Min for hot days
- Any inverter
Find Voc, Vmp and the Voc temperature coefficient on the panel datasheet. Use the record low temperature for your area.
Panels in series add their voltages. On a cold, bright morning each panel's voltage rises above its rating, so the string must stay under the inverter's maximum. On hot days voltage drops, so the string must stay above the MPPT minimum.
String size chart
49.5 V Voc panel, −0.27%/°C. Search for a temperature.
| Coldest (°C) | Panel Voc cold (V) | 600 V inverter | 1000 V inverter | 1500 V inverter |
|---|---|---|---|---|
| 10 | 51.5 | 11 | 19 | 29 |
| 0 | 52.8 | 11 | 18 | 28 |
| -10 | 54.2 | 11 | 18 | 27 |
| -20 | 55.5 | 10 | 18 | 27 |
| -30 | 56.9 | 10 | 17 | 26 |
The minimum string length for a 200 V MPPT minimum is 6 of these panels.
Cold and string length
49.5 V Voc panel. Slide the coldest temperature.
The bar under the panels shows the string's cold voltage against a 600 V limit.
How to size a solar string
Cold max, hot min. Step through it.
Cold Voc
Voc × (1 + coef × (25 − Tmin)).
Strings on the same MPPT input must have the same number and type of panels.
600 V, 1000 V or 1500 V
Inverter voltage. Compare them.
Older US residential.
Most homes and businesses.
Large solar farms.
Higher voltage strings carry the same power at lower current, which means thinner cables and less loss.
Before wiring
Design checks. Tick each item.
Tick each item as you go.
Never exceed the inverter's maximum DC voltage. It can destroy the inverter and void the warranty.
What you get
String sizing. Each tile explains one result.
Fewest to most.
At your low.
Summer voltage.
Against the limit.
Min under max.
Check string current too: the panel Isc must stay below the inverter's maximum input current per MPPT.
Frequently Asked Questions
No question matches that search.
How many solar panels per string?
Divide the inverter's max voltage by the panel's cold Voc and round down.
Why does cold raise panel voltage?
Solar cells give higher voltage at lower temperature.
What is a temperature coefficient?
How much panel voltage changes per °C, usually −0.25% to −0.35%.
How many panels on a 600 V inverter?
About 10 to 11 typical 49 V panels.
What happens if a string is too long?
Cold mornings can push voltage over the limit and damage the inverter.
What happens if a string is too short?
On hot days the voltage falls below the MPPT range and output drops.
Can strings have different lengths?
Only on separate MPPT inputs.
Strings that work every day of the year
Check the coldest morning and the hottest afternoon to find the safe range. Your inverter stays protected and runs at its best.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.