PV forecasting: what to expect from a solar estimate

PV forecasting is used to set expectations and support planning.

A useful forecast connects a defined roof or site concept to stated assumptions. It helps answer whether detailed design and contractor pricing are worth pursuing; it is not a promise that a particular system will fit, be approved, or produce the estimated amount.

What improves accuracy

• roof orientation and usable area
• shading notes (trees, dormers, nearby structures)
• realistic system size bounds
• a current layout or dimensions for roof features and setbacks
• clarity about whether the project is a new build, retrofit, or future-ready plan

What the forecast should make visible

• the location and geometry used
• the assumed array size and orientation
• material shading or usable-area constraints
• the loss assumptions included in the estimate
• the production range or comparison basis used for the decision

If two concepts are being compared, keep the input basis consistent. Otherwise, a different layout assumption can look like a performance difference.

What you’ll receive

A concise planning summary of estimated production, the assumptions behind it, identified constraints, and the questions that detailed design must resolve. The output should be clear enough to update when a roof layout, shading condition, or system concept changes.

What it does not replace

A planning forecast is not structural review, electrical design, equipment selection, interconnection approval, a contractor quote, or a financial-return guarantee. Weather, equipment, layout, installation, shading, downtime, and future site changes affect actual output.

Before requesting a forecast

Gather the site location, roof plans or dimensions, orientation, useful photos, known shading sources, roof features, planned renovations, and any system-size or energy goal. Missing drawings do not prevent intake, but the scope should state which geometry still needs confirmation.

The right next step is often modest: establish whether the site concept is worth developing, then hand the assumptions and constraints to the qualified designers, installers, and authorities responsible for detailed work.