THE SHORT ANSWER
DC module capacity and AC inverter capacity measure different sides of the system. Ask for the ratio, equipment limits and modeled effect for the proposed layout.
Locate both ratings
Record total module watts in kWdc and the applicable inverter or microinverter AC output in kWac. Do not compare one proposal’s rounded marketing label with another proposal’s equipment schedule. For multiple inverters, show how the total was calculated.
Understand why they differ
Modules rarely operate at nameplate output throughout the year. Designers may pair more DC module capacity with a lower AC rating, subject to equipment and design limits, to use inverter capacity across more hours. The relationship is intentional in many systems, not proof of missing equipment.
Model rather than guess
NREL PVWatts includes a DC-to-AC size ratio and reports estimated production from the selected inputs. [1] Ask what ratio the proposal uses and whether the model shows clipping. A ratio alone cannot establish whether the design is appropriate for this roof, climate and equipment.
Check every equipment constraint
Request the module, inverter and optimizer or microinverter model numbers and the proposed string or branch arrangement. The qualified designer should confirm voltage, current, temperature and manufacturer requirements. A homeowner comparison should flag questions without attempting field engineering.
Compare the energy consequence
Ask for a modeled alternative when two proposals use meaningfully different ratios. Compare annual energy, layout, equipment count, warranty responsibilities and scope—not merely inverter kW. Keep the report with the final version so later service teams know which assumptions governed the installed design.
Before your next conversation
- Record total kWdc and kWac.
- Calculate the stated ratio.
- Request modeled clipping context.
- Keep exact equipment and design records.
Primary sources
- National Renewable Energy Laboratory: PVWatts Calculator
Primary source reviewed September 10, 2026. Utility rules, equipment availability, project design and contract terms remain specific to the property and proposal.
Planning examples and questions are Origin’s editorial guidance, not a property-specific diagnosis, engineering design, tax determination or promise of savings. Manufacturer and utility references do not imply an affiliation with Origin.
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