← U.S. Residential Solar Fundamentals
Site suitability and production estimates
By the end: Identify the inputs and limits of a solar-production estimate.
A rooftop assessment considers roof condition, structure, orientation, tilt, shade, usable area, access, and electrical suitability. South-facing roofs are often useful in the northern hemisphere, but the best layout depends on the site and goals. East- or west-facing arrays may also be useful. A compass direction alone does not establish annual output or economic value.
PVWatts estimates grid-connected PV energy using a model and location-dependent resource data. A model is useful for comparing assumptions; it is not a guarantee of next year’s weather or a substitute for a site survey. Check system size, orientation, tilt, mounting assumptions, losses, inverter assumptions, and how shade was assessed.
- Proposal A estimates 8,500 kWh/year and B estimates 9,600 kWh/year.
- Ask whether their array sizes, roof planes, shade assumptions, and loss assumptions match.
- Do not choose B solely because its number is larger. Request the modeling inputs and a monthly profile.
- If the roof needs work soon, resolve that before committing to the PV installation schedule.
For practice, compare two supplied hypothetical cases rather than entering personal home information into an unfamiliar site. An AI assistant can organize questions from a proposal, but its invented production numbers or code conclusions are not engineering evidence.
Quick check
Two estimates differ. What is the most useful first comparison?