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Solar inverter sizing: capacity, MPPT and string config

Capacity, MPPT and string configuration worked out against NEC voltage and temperature requirements, not a rule-of-thumb ratio.

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Inverter Sizing

How the sizing calculator works

  • String sizing against real voltage limits

    Maximum string length calculates against a module's open-circuit voltage and temperature coefficient under NEC 690.7, accounting for the coldest expected temperature at the site rather than a flat assumption.

  • MPPT and DC-to-AC ratio guidance

    Multiple MPPT input configurations and DC-to-AC ratio recommendations factor in based on the specific inverter and module combination, not a generic 1.2-to-1 rule of thumb applied regardless of equipment.

  • Aware of the n-type shift

    Newer n-type TOPCon modules carry different voltage and temperature characteristics than older p-type panels, and sizing calculations account for that shift rather than reusing outdated assumptions.

Code-accurate sizing, equipment-specific ratios

  • Size strings against actual code limits

    Calculations reflect real NEC voltage and temperature requirements instead of a rough approximation.

  • Get ratio guidance matched to the actual equipment

    DC-to-AC ratio recommendations reflect the specific inverter and module pairing, not a one-size default.

Frequently asked

How does string sizing change for n-type modules compared to older p-type panels?
N-type modules often have different temperature coefficients and voltage characteristics than older p-type panels, which affects the cold-temperature open-circuit voltage that drives maximum string length. In practice that can change how many modules fit safely under the inverter's voltage limit. The tool accounts for the n-type shift rather than assuming legacy p-type behavior.
What DC-to-AC ratio does the tool default to?
DC-to-AC ratios for modern systems commonly land in a range around 1.2 to 1.3, with the right figure depending on the inverter, site irradiance, and design goals. The tool gives ratio guidance matched to the actual equipment rather than forcing one fixed number. Treat any default as a starting point you tune to the project.
Does the calculator account for temperature derating on maximum string voltage?
Yes, the calculator sizes strings against real voltage limits, which means applying the record-low temperature to the module's voltage coefficient to check maximum string voltage. That cold-temperature correction is what keeps a string from exceeding the inverter and NEC voltage ceiling. Sizing to actual code limits avoids a string that passes at room temperature but fails on the coldest morning.

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