What panel count does and does not tell you
Panel count multiplied by module wattage gives a simplified DC nameplate capacity. It is a basic arithmetic check, not a final system design. A solar proposal may use different module wattages, string/inverter configurations, optimizers, microinverters or batteries, and the final AC output rating will not necessarily match the DC rating.
Roof area is not all usable
Roof setbacks, fire access pathways, vents, chimneys, skylights, dormers, shading, structural condition, roof age and orientation all affect the number and arrangement of modules. Local codes and utility requirements can also constrain system design. Do not multiply roof area by a generic density and assume that is an installable array.
What to compare in a proposal
- Module make, model, wattage and product warranty.
- Inverter type and the system's DC and AC ratings.
- Annual production estimate and the assumptions behind it.
- Roof layout, shading, setbacks and structural assessment.
- Installed cash price, financing terms, monitoring and service responsibilities.
Use a target based on electricity consumption
Start with annual kWh from your utility bills. Discuss the intended offset with an independent solar professional, while accounting for electric-vehicle charging, heat pumps, household changes and utility export rules. A 100% modeled offset does not necessarily mean a zero electric bill.