How many panels can I put on one string for a 1000 V inverter?

It depends on cold-weather Voc. The calculator computes cold-adjusted Voc and divides inverter max voltage by that value to set the safe maximum module count.

Why does winter temperature reduce max modules per string?

Module voltage rises as cells get colder. A string that is safe at mild temperatures can exceed inverter max DC voltage on very cold mornings if not checked.

Why do I also need a minimum module count?

Hot conditions lower Vmpp. You need enough modules in series so the hot-day string voltage stays above the inverter MPPT minimum and the inverter can track power.

Can I mix different module models in the same string?

It is usually avoided because mismatched electrical characteristics reduce performance and can violate inverter design assumptions. Use matched modules in each string.

Should I use design heating temperature or record low for Voc checks?

Use the site record low (or AHJ-required extreme) for conservative voltage safety checks, not a mild average design temperature.

Solar String Sizing Calculator (NEC 690.7)

Does this replace the inverter manufacturer string tool?

No. Use this as a first-pass sizing screen, then confirm in manufacturer design software and final permit documents.

Run the numbers for your project

Use the Solar String Sizing Calculator (NEC 690.7) to get an exact answer for your inputs.

Open the calculator

Does this replace the inverter manufacturer string tool?

Run the numbers for your project

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