Integrating Weather Foundation Model and Satellite to Enable Fine-Grained Solar Irradiance Forecasting

TL;DR

This paper introduces Baguan-solar, a novel two-stage multimodal framework that combines a weather foundation model with satellite imagery to improve day-ahead solar irradiance forecasting at high resolution.

Contribution

It presents a new fusion-based approach that leverages large-scale weather models and satellite data for fine-grained, 24-hour solar irradiance prediction.

Findings

Outperforms existing baselines with 16.08% lower RMSE.

Effectively captures cloud-induced transients in irradiance forecasts.

Supports operational solar power forecasting in China since July 2025.

Abstract

Accurate day-ahead solar irradiance forecasting is essential for integrating solar energy into the power grid. However, it remains challenging due to the pronounced diurnal cycle and inherently complex cloud dynamics. Current methods either lack fine-scale resolution (e.g., numerical weather prediction, weather foundation models) or degrade at longer lead times (e.g., satellite extrapolation). We propose Baguan-solar, a two-stage multimodal framework that fuses forecasts from Baguan, a global weather foundation model, with high-resolution geostationary satellite imagery to produce 24-hour irradiance forecasts at kilometer scale. Its decoupled two-stage design first forecasts day-night continuous intermediates (e.g., cloud cover) and then infers irradiance, while its modality fusion jointly preserves fine-scale cloud structures from satellite and large-scale constraints from Baguan forecasts. Evaluated over East Asia using CLDAS as ground truth, Baguan-solar outperforms strong baselines (including ECMWF IFS, vanilla Baguan, and SolarSeer), reducing RMSE by 16.08% and better resolving cloud-induced transients. An operational deployment of Baguan-solar has supported solar power forecasting in an eastern province in China, since July 2025. Our code is accessible at https://github.com/DAMO-DI-ML/Baguan-solar.git.