Data Sources & Methodology

This page explains where Suncastic's forecast data comes from, how the main metrics are calculated, and what the results can (and cannot) be used for.

Data sources

Suncastic combines weather forecasts with your location to estimate solar conditions and PV output.

Weather: Forecast values (cloud cover, irradiance, temperature, weather codes, and sunrise/sunset times) are fetched from Open‑Meteo (API docs).

Geocoding: Address search and reverse lookup use OpenStreetMap via the Nominatim service.

Cloud cover

Cloud cover is shown as a percentage from 0% to 100%. A higher percentage generally means less sunlight reaches the ground, but the relationship is not perfectly linear—thin high clouds can still allow meaningful solar production.

Solar irradiance

Solar irradiance represents the amount of solar energy arriving per square meter of horizontal surface (\(W/m^2\)). It is a key driver of PV output: higher irradiance typically produces higher power—assuming the sun is above the horizon and the array is not shaded.

Irradiance values are forecast estimates and can vary from your site due to local micro‑climate, haze, fog, nearby terrain, and short‑lived cloud patterns.

PV output estimation

PV output is an estimate of your system's AC power (\(kW\)) and energy (\(kWh\)) over time. The forecast table uses the weather forecast (especially irradiance) and a simplified PV model.

When you configure panel strings (azimuth and tilt), the model adjusts output based on how well the array is oriented relative to the sun's position throughout the day. This helps differentiate east‑facing vs west‑facing arrays, and flatter vs steeper tilt.

Even with orientation applied, this remains a simplified model. It does not fully model shading from buildings/trees, snow coverage, inverter behavior under all conditions, wiring losses, or site‑specific clipping.

Performance ratio (simple mode)

Performance ratio is a single efficiency factor that roughly captures typical real‑world losses (temperature, inverter efficiency, wiring, soiling, mismatch, etc.). In Suncastic it is used only when you are not configuring a custom panel layout.

If you configure panel strings (power user mode), the estimate relies on your layout inputs and the weather forecast rather than applying performance ratio as an additional user‑tuned knob.

Important disclaimer

Suncastic's PV numbers are planning‑grade estimates. They are useful for comparing days, spotting trends, and understanding how weather may affect output—but they are not a guarantee of actual production. Always use your inverter/monitoring system as the source of truth for measured performance.