Solar DC-to-AC Ratio: Match the Production Model to Your Quote

Write down both capacities before comparing the ratio

Request the module count and rated watts, the inverter model and quantity, and the production report’s DC capacity and ratio. Keep DC and AC labels on every number. If a report combines multiple roof planes or inverter groups, ask how their capacities were represented. A rounded headline system size is not enough to reconstruct the equipment schedule.

Hypothetical example: 30 modules at 400 watts give 12 kW DC. A modeled ratio of 1.2 implies 12 ÷ 1.2 = 10 kW AC. If the actual inverter schedule totals 7.6 kW AC, the corresponding capacity ratio is approximately 1.58. That mismatch calls for an explanation or revised model; it does not alone establish that the proposed equipment is unsuitable.

Do not convert the ratio into an annual loss claim

A ratio compares nameplate capacities, not annual energy totals. A ratio of 1.2 does not mean that 20% of annual generation disappears. PVWatts represents inverter power limiting by capping modeled AC output at the inverter’s rated AC size. [1] Ask for the energy effect over the modeled period, not a guessed percentage obtained by subtracting one from the ratio.

A short period at an output limit and a year-long energy total answer different questions. Likewise, a flat section on an operating system’s chart is not by itself a complete diagnosis. Keep proposal modeling separate from field troubleshooting, and preserve actual device alerts and dates if there is an existing-system concern.

Request a controlled comparison of inverter alternatives

For two equipment options, hold the roof layout, location, weather dataset, module capacity and other assumptions constant unless a change is intentional and disclosed. Ask for annual and monthly modeled AC energy for each option, plus the exact installed scope difference. If both the array and inverter change, label that as a whole-design comparison rather than attributing the entire difference to the inverter.

The V8 API exposes separate capacity, ratio and inverter-efficiency inputs, along with the supplied inputs and weather information in its response. [2] A screenshot of one output number conceals that evidence. Request a readable input summary and revision date; there is no need to share an API key or technical login with the homeowner.

Keep model capacity separate from electrical approval

An energy model does not establish acceptable voltage, current, protective equipment, structural suitability or the utility’s application classification. The responsible designer must verify the equipment combination and the actual connection arrangement. Put any unresolved engineering or utility question next to the model comparison rather than treating a favorable energy result as permission to install.

Do not assume that changing inverter size changes a utility tier in the same way. Some providers use their own gross-rating calculation. Confirm the provider shown on the account and its current method separately. This guide supplies no universal Florida tier rule and does not authorize a homeowner to change inverter settings or open electrical equipment.

Close the comparison with one traceable decision

Save the selected inverter schedule with the matching production report and roof layout. Note which options were compared, the reason for the choice and any remaining site-survey conditions. If an equipment substitution occurs later, ask whether both the model and relevant approvals need updating. Keeping the earlier report as superseded is more useful than deleting the explanation for a changed estimate.

For an Origin review, bring the capacity page and the question you want resolved. A useful response connects the selected equipment to an understandable design tradeoff. It does not promise that the largest inverter is always best, that all clipping is unacceptable, or that a modeled energy increase will translate directly into the same percentage of bill savings.

Primary sources

1. SAM Help: PVWatts System Design

   Checked October 20, 2026 for the explicit rated-inverter-size equation and modeled output limiting. The equation and worked capacity example control this guide; no default ratio is recommended for an individual home.

2. National Laboratory of the Rockies: PVWatts V8 API

   Checked October 20, 2026 for separate capacity, ratio, efficiency, input-summary, weather and AC energy fields. No live API request or product approval is implied.

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.

Related guidance

• Separate nameplate capacity from annual energy
• Review other production-model losses
• Check what a module category can establish