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Solar PV String Sizing Calculator

Calculate the maximum number of solar panels that can be wired in series in one string without exceeding inverter/system voltage limits.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Maximum panels per string

13 panels

Check your inputs

The correction factor depends on your site's record low ambient temperature and the panel manufacturer's temperature coefficient — use NEC Table 690.7(A) or the manufacturer's datasheet coefficient for your specific location, not an assumed value.

Temperature-corrected Voc per panel
44.8 V

With the figures above, the maximum panels per string comes to 13. The method behind this is well established, though site conditions and material batches will move it somewhat. This is presented for United States. Building in another market? Change the selector above and the units and terminology follow.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • Maximum panels per string = floor(maximum system voltage ÷ (panel open-circuit voltage × low-temperature correction factor)), per NEC 690.7 which requires PV source circuit voltage calculations to account for Voc increasing in cold temperatures using either the manufacturer's temperature coefficient or NEC Table 690.7(A) correction factors

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Frequently asked questions

Why does cold weather matter for PV string sizing?
A solar panel's open-circuit voltage (Voc) rises as its temperature drops. On a cold morning, an array's actual string voltage can exceed the value measured at Standard Test Conditions, so NEC 690.7 requires correcting Voc upward using a low-temperature correction factor before sizing the maximum string length.
Where does the temperature correction factor come from?
It comes from either the panel manufacturer's published temperature coefficient or NEC Table 690.7(A), applied to your site's record low ambient temperature — not an assumed or default value. Using the wrong factor for your climate can result in a string that exceeds the inverter's maximum voltage in cold conditions.
Why is the result rounded down rather than to the nearest whole number?
The maximum panels per string is floored (rounded down) because any fractional result means that many full panels' worth of voltage would still stay within the limit, while rounding up would push the string voltage over the maximum allowed.