Evaluation
In evaluation against high-quality measurements from SURFRAD and SOLRAD networks, Helios analysis outperforms government models by over 20%. Across all times and locations, Helios has lower error and higher correlation with observations than NOAAʼs High-Resolution Rapid Refresh (HRRR) or Global Forecast System (GFS).
Latency
Helios delivers forecasts sooner than numerical models. Helios forecasts are available in less than 20 minutes, compared with 1.5 to 4 or more hours for traditional models.
| Model | Resolution | Latency |
|---|---|---|
| Helios | 6 km / 1 hour | Minutes |
| HRRR | 3 km / 15 minute | 1.5 hours |
| GFS | 28 km / 1 hour | 4+ hours |
Real-time analysis
Predicting solar irradiance is easy on clear days, but capturing cloud-driven variability is hard for most models. Helios outperforms traditional models in the prediction of real-time actual values, particularly under challenging, cloudy conditions.
- Under clear sky conditions (observed GHI > 0.9 * clearsky GHI; N = 24,255), Helios has 1% lower RMSE than HRRR an 12% lower RMSE than GFS.
- Under cloudy conditions (observed GHI < 0.9 * clearsky GHI; N = 23,687), Helios has 35% lower RMSE than HRRR an 28% lower RMSE than GFS.
| Model | rRMSE (%) | rMBE (%) | R² |
|---|---|---|---|
| Helios V1 | 27.62 | 0.012 | 0.877 |
| HRRR | 38.13 | 10.8 | 0.789 |
| GFS | 36.2 | 5.61 | 0.784 |
Table: All sky condition performance comparison of models versus station observations (N = 47,942). Helios achieves superior Relative Root Mean Square Error (rRMSE), Relative Mean Bias Error (rMBE), and Coefficient of Determination (R²) compared to GFS and HRRR.
6-hour forecast
A more accurate initial state helps Helios perform skillful solar forecasts. For short-term forecasts of solar irradiance, Helios has lower error and higher correlation to station observations than GFS or HRRR.
Figure: Helios delivers greater accuracy than HRRR in analysis and short-term forecasts out to 5 hours, ensuring reliable predictions for intra-day decision-making.
| Model | rRMSE (%) | rMBE (%) | R² |
|---|---|---|---|
| Helios V1 | 34.5 | 5.3 | 0.81 |
| HRRR | 39.97 | 12.14 | 0.77 |
| GFS | 39.83 | 9.06 | 0.79 |
Table: Forecast error metrics versus station observations for a 3-hour lead time.
Additonal validation
Further information and a deeper dive into Helios V1 validation including performance by season and time of day.