Inverter Sizing Chart

Use this worksheet after the calculator result to record array power, inverter AC target, string count, cold-weather Voc, MPPT window, and manufacturer follow-up.

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Quick reference table

An inverter sizing chart is a calculator-led PV planning worksheet. It connects module data, cold-weather voltage limits, MPPT operating range, and inverter AC sizing before product selection or permit-level review.

Inverter sizing worksheet

Inverter sizing worksheet
Item	Record from calculator	Follow-up
Array	kWdc, module count, module watts	Confirm module datasheet and assigned inverter
String voltage	Module Voc cold, string Vmp, string Voc cold	Check max DC class and the cold-weather method
MPPT window	MPPT minimum, MPPT maximum, pass or warning	Verify datasheet tracker range and startup behavior
Inverter	kWac target, topology, strings, current	Verify manufacturer data, listing, and utility or AHJ review

Inverter selection review lanes

Inverter selection review lanes
Selection item	Record on worksheet	Why it changes the inverter choice
Array loading	Array kWdc, target ratio, recommended kWac range	DC/AC loading changes clipping, utilization, and product fit
Cold-voltage ceiling	Module Voc, coefficient, cold ambient, max modules per string	Cold weather can limit the safe series count before AC size does
MPPT operating window	String Vmp, MPPT min, MPPT max, pass or warning	A string can clear cold Voc but still miss the working tracker range
PV output path	Parallel strings, 125% Isc current, topology	Current path and topology affect wiring, combiner, and equipment review

Formula basis

Recommended inverter kWac = array kWdc / target DC-AC ratio | Max modules per string = floor(max DC voltage / cold-weather module Voc).

Array kWdc comes from module STC watts multiplied by module count.
Cold-weather module Voc uses the module Voc temperature coefficient and the coldest design ambient.
MPPT minimum and maximum voltage come from the inverter datasheet and screen whether the operating string voltage lands inside the tracker window.
Target DC/AC ratio sets the planning inverter AC nameplate before manufacturer approval.

Worked examples

Rooftop PV string-inverter recordRecord array kWdc, recommended inverter kWac, module Voc and Vmp, cold-weather module Voc, modules per string, MPPT window, and manufacturer follow-up.

Hybrid inverter MPPT checkDocument module count, selected string layout, string Vmp, string Voc cold, MPPT minimum and maximum voltage, and the product review note before freezing the design.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

PV inverter sizing depends on module data, cold-weather voltage behavior, MPPT range, DC/AC loading, topology, and product-specific limits.
The worksheet is a planning screen and does not replace the manufacturer string-sizing tool, listed equipment instructions, or engineered design.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart as a PV inverter calculation record; verify the inverter manufacturer string-sizing tool, approved module pairing, adopted NEC installation requirements, conductor and overcurrent review, utility interconnection limits, and AHJ expectations before installation.

How to use this chart

1Capture the array basisRecord module watts, module count, array kWdc, topology, and the target inverter AC size range.

2Check string voltageDocument module Voc, temperature coefficient, cold ambient, string Vmp, and cold-weather string Voc.

3Route product reviewUse the chart to compare MPPT windows, max DC input class, current path, listing, and utility or AHJ review.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture array inputsWrite module wattage, count, array kWdc, module Vmp, module Voc, and topology.
Capture voltage checksRecord cold-weather module Voc, max modules per string, chosen modules per string, string Vmp, and MPPT range.
Capture selection notesDocument inverter kWac target, current path, product data, utility review, and AHJ follow-up.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Choosing a series count only from the max DC voltage class and skipping the MPPT operating window.
Using generic inverter classes instead of the exact manufacturer datasheet for the final string decision.
Locking the inverter AC size before checking DC/AC ratio, parallel-string current, and utility or AHJ constraints.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Why check MPPT range separately from the cold-voltage limit?

Because a string can stay below the inverter maximum DC voltage in cold weather and still miss the working MPPT window during normal operation. Both checks matter.

Why keep a worksheet after the calculator already gives a result?

The worksheet captures the module and inverter assumptions behind the result so the installer, utility, or plan-review handoff can be checked against the datasheet instead of repeating the first pass from memory.