What a proposal-PDF handoff transfers
When Quote Analyzer has a reviewed first-year production value and a usable DC system size, it can load those two numeric assumptions into this checker. If panel-count × module-wattage arithmetic was independently validated from the proposal text, that calculated DC nameplate can take precedence over a conflicting quoted system size for this production review.
ZIP, roof tilt and array direction are deliberately not transferred from the PDF workflow. Enter or confirm them here so the NREL PVWatts reference is based on location and geometry you intend to review. No street address, installer name, proposal PDF or financing terms are included in the handoff.
What the comparison normalizes
The proposal's first-year annual production is divided by its DC system size to calculate an installer-stated kWh per installed kW. Home Solar Atlas then requests a 1 kW NREL PVWatts V8 reference for the entered ZIP, tilt and array direction and scales that reference to the proposal's DC size.
That makes a 7 kW and a 12 kW proposal easier to reason about without assuming that every roof in the same ZIP performs identically.
Why a PVWatts gap does not automatically mean the proposal is wrong
- A real system may use several roof planes with different tilt and azimuth.
- Nearby trees, chimneys, dormers or neighboring buildings can create site-specific shade.
- Installer software may use a detailed 3D roof model and shade data that this simple reference does not have.
- Module choice, inverter loading ratio and clipping can change expected AC output.
- Soiling, snow, wiring, mismatch, availability and other loss assumptions may differ.
- Weather datasets and the exact production year represented by a proposal may differ from the long-term reference.
What to request when the installer forecast is much higher
Ask for the full production-model report showing the roof planes, shading assumptions, system losses, module and inverter configuration, clipping, weather dataset and first-year degradation treatment. If a salesperson only provides a headline annual kWh number, ask what software and site inputs produced it.
Solar production estimate FAQ
Why can an installer's solar production estimate differ from PVWatts?
An installer may use a detailed roof model, multiple roof planes, site-specific shading, different system-loss assumptions, module and inverter data, clipping assumptions or a different weather dataset. NREL PVWatts is useful as an independent planning reference, but a difference by itself does not prove either forecast is wrong.
Can Quote Analyzer load a proposal's system size and first-year production into this checker?
Yes. When a supported proposal PDF provides a usable first-year production value and a reviewed DC system size, Quote Analyzer can transfer those numeric values into this checker. When validated panel-count × wattage arithmetic is available, Home Solar Atlas can use that calculated DC nameplate instead of a conflicting quoted size. Confirm every transferred value against the original proposal before running the reference.
Why does a PDF handoff not transfer the project ZIP, roof tilt or array direction?
Those location and geometry inputs materially change the NREL PVWatts reference and may not be represented safely by a simple PDF text extraction, especially for multi-plane roofs. The homeowner therefore enters or confirms ZIP, tilt and direction in this checker before a fresh reference is requested. The handoff does not include a street address, proposal PDF, installer name or financing details.
What does kWh per installed kW mean in a solar proposal?
It is the first-year annual production forecast divided by the system's DC capacity. Normalizing production this way makes differently sized proposals easier to compare because total annual kWh alone naturally rises when more solar capacity is installed.
Is a solar proposal more than 10% or 20% above PVWatts automatically unrealistic?
No. A larger gap is a reason to request the installer's production-model report and verify roof geometry, shading, system losses, inverter sizing, clipping and weather data. The threshold in this checker is a review trigger, not a pass/fail rule.
Can PVWatts model a roof with several different directions?
A single lookup in this checker uses one representative tilt and azimuth. If a proposal uses several roof planes, a more detailed model should evaluate those planes separately. Use the dominant roof plane here only as a simplified reference.
What is the monthly PVWatts table showing?
When PVWatts returns a complete 12-month profile, Home Solar Atlas scales each monthly kWh-per-kW value to the proposal's DC system size. The table shows the modeled seasonal shape of the reference year; it is not a monthly production guarantee and it is not an inferred monthly installer forecast.
Why is there no monthly table when the state fallback is used?
The state fallback contains an annual planning yield but no verified 12-month PVWatts profile. Home Solar Atlas therefore hides the monthly table instead of inventing a seasonal distribution from the annual number.
Reference methodology
The ZIP lookup uses Home Solar Atlas location data and the existing solar-resource endpoint. When NREL PVWatts V8 returns a usable value, the reference uses a 1 kW standard-module system with the entered tilt and azimuth and the endpoint's current planning-loss assumptions. If PVWatts is temporarily unavailable, the interface can fall back to the clearly labeled state planning yield.
This tool checks the scale of an explicit first-year production claim. It does not guarantee production, certify an installer design, model every roof plane or replace a shade-aware engineering proposal.