API reference & integration guides.
Explore how HelioExpect transforms meteorological data, plant configuration, and machine learning into actionable solar generation forecasts. This guide covers configuration, delivery options, accuracy tracking, and best practices for integrating forecasts into operations.
15-Minute Cadence
High-resolution forecasts with automated aggregations
14-Day Horizon
Day-ahead to two-week outlooks for planning and trading
Multi-Array Modeling
Independent simulations per sub-array before site roll-up
Tracker Support
Accurate POA calculations for fixed tilt and tracking systems
Configurable Losses
Tailor DC, AC, and auxiliary losses per array and scenario
Plant Baseline Modelling
Calibrated site models align forecasts with expected baselines
Automated Accuracy Reports
Daily reconciliation across multiple error metrics
Table of Contents
Methodology
a. Data Inputs
Our forecasting system integrates data from multiple Numerical Weather Prediction (NWP) models, including:
- IFS (Integrated Forecasting System) from ECMWF (European Centre for Medium-Range Weather Forecasts)
- GFS (Global Forecast System) from NOAA (National Oceanic and Atmospheric Administration)
These models provide large-scale atmospheric data, including temperature, pressure, humidity, wind speed, and cloud cover. To enhance forecasting accuracy, we incorporate real-time satellite observations from NOAA and ECMWF satellite systems, which offer high-resolution cloud cover and radiation data.
For short-term forecasts, we employ a nowcasting model, which updates every 6 hours, leveraging geostationary satellite data to track atmospheric variations in near real time.
b. Post-Processing
The raw NWP and satellite data undergo extensive post-processing through our proprietary in-house model, which refines forecast outputs using multiple correction techniques:
Aerosol Reconstruction & Attenuation Modeling
We analyze historical aerosol optical depth (AOD) data and integrate real-time satellite observations to reconstruct aerosol concentration profiles. This enables more accurate estimation of solar radiation losses due to atmospheric particulates.
Cloud Motion Vector (CMV) Analysis
Using high-resolution infrared and visible spectrum satellite images, we compute Cloud Motion Vectors (CMV) to determine cloud cover movement and dissipation patterns. Our CMV model employs optical flow-based cloud tracking to project cloud trajectories and estimate shading effects on solar irradiance.
GraphCast Integration with CMV for AI-Powered Forecasting
We pass Cloud Motion Vector (CMV) data through GraphCast, a graph neural network (GNN)-based weather forecasting model developed by Google DeepMind. GraphCast processes CMV in combination with other meteorological features to enhance cloud movement prediction accuracy, reducing errors in cloud cover and irradiance forecasts.
Unlike traditional NWP models, which rely on physics-based simulations, GraphCast leverages spatiotemporal graph networks to predict weather conditions using historical and real-time meteorological data. This results in:
- Reduced Forecast Update Time: GraphCast generates global predictions in minutes compared to the hours required by conventional models.
- Higher Forecast Resolution: By learning fine-scale meteorological patterns, GraphCast improves cloud cover, wind speed, and solar irradiance predictions with greater spatial precision.
- Adaptive Forecasting: Unlike static physics-based models, GraphCast dynamically updates predictions based on evolving weather trends, reducing forecast error margins.
By integrating CMV tracking with GraphCast AI-driven forecasting, we achieve superior weather prediction accuracy, particularly for short-term cloud movement and irradiance estimation, ensuring improved solar energy optimization.
c. Parameter Calculations
We provide high-resolution forecasts for the following key solar and weather parameters:
Photovoltaic (PV) Output Predictions
Forecasted PV generation is computed for fixed-mount, single-axis tracker, and bifacial setups. Using digital twin model, we integrate solar irradiance models with temperature-corrected PV efficiency factors to estimate energy output under varying meteorological conditions. This pvout is corrected using ML models.
Irradiance Components Calculation
- Global Horizontal Irradiance (GHI): Directly obtained from satellite and NWP model data.
- Direct Normal Irradiance (DNI): Derived using the DISC (Direct Insolation Calculation) model, which decomposes GHI into direct and diffuse components.
- Diffuse Horizontal Irradiance (DIF): Calculated by subtracting DNI from GHI based on cloud cover, aerosols, and Rayleigh scattering models.
- Global Tilted Irradiance (GTI): GTI is computed using site-specific azimuth and tilt angle.
Meteorological Variables
- Air Temperature & Wind Speed: Derived from NWP model outputs and corrected using site-specific terrain-based bias adjustments.
- Cloud Cover & Relative Humidity (RH): Processed via CMV-based tracking and GraphCast-enhanced probability distribution models.
Customizable Parameters
Additional weather and atmospheric parameters such as fog availability, visibility, and precipitation probability can be integrated based on site-specific forecasting needs.
Conclusion
Our forecasting pipeline combines physics-based NWP models, real-time satellite data, cloud motion analysis, and AI-powered GraphCast predictions to deliver highly accurate and low-latency weather forecasts for solar energy applications. By integrating Cloud Motion Vector (CMV) tracking with GraphCast, we further enhance short-term and long-term cloud cover predictions, reducing update time while improving forecast accuracy.
Quick Start Guides
Follow these workflows to begin using HelioExpect forecasts in production environments. Each guide references the prediction engine and monitoring platform without exposing proprietary integrations.
Requesting Your First Forecast
Generate an on-demand site forecast using the forecasting engine service.
- 1Collect site latitude/longitude, capacity, module details, and sub-array configuration.
- 2Create a job configuration with the site reference, desired forecast horizon, and preferred aggregation settings.
- 3Store HelioExpect credentials securely so the service can authenticate when it runs.
- 4Trigger the forecasting engine and archive the standard, conservative, and metadata outputs.
- 5Schedule the job via your orchestration tool (e.g., cron, Airflow) to keep data fresh.
Publishing Forecasts to HelioExpect
Expose forecast data inside the HelioExpect forecasting workspace.
- 1Ensure the site is configured in HelioExpect with matching sub-array identifiers.
- 2Trigger the forecasting engine and capture the structured response.
- 3Confirm the forecasting dashboards pick up the latest forecast streams for each sub-array and the rolled-up plant.
- 4Enable scheduled email or FTP delivery if stakeholders require offline reports.
- 5Verify that the Forecasting dashboard displays both standard and conservative curves alongside the expected baseline.
Daily Accuracy Reconciliation
Combine forecasts and actuals to measure accuracy using prediction-ml utilities.
- 1Schedule the reconciliation script after each operations day.
- 2Fetch actual generation from HelioExpect for the relevant window.
- 3Fetch the corresponding forecast time series produced by the forecasting engine.
- 4Merge the datasets with the provided helpers to compute MAPE, MAE, and bias.
- 5Store results in analytics storage or forward them to trading and compliance teams.
Forecast Products & Accuracy
What forecast horizons and resolutions are available?
The HelioExpect Forecasting Engine delivers 15-minute forecasts by default and aggregates them to hourly, intraday, day-ahead, and 14-day horizons. Aggregation happens automatically inside the service so trading, operations, and planning teams can consume the cadence they need without rebuilding time-series logic.
How is accuracy measured and reported?
Forecast accuracy is evaluated daily by pairing predictions with actual generation inside the prediction-ml analytics jobs. The reconciliation pipeline computes MAPE, MAE, RMSE, bias, and capacity-normalized error, storing the metrics alongside each forecast batch so teams can audit performance over time.
How often are forecasts refreshed?
By default the engine refreshes site forecasts every 15 minutes using the latest weather feed and plant telemetry. You can trigger an on-demand run at any time or schedule higher-frequency updates for intraday markets by adjusting the job interval in the orchestration layer.
What is the difference between standard and conservative outputs?
Each response includes a standard forecast, an ML-adjusted prediction, and an optional conservative track that applies configurable buffers for deviation management. The conservative series is useful for scheduling and compliance workflows where under-generation penalties carry higher risk.
Forecast Dashboard Experience
What does the forecasting dashboard include?
The forecasting dashboard inside HelioExpect visualizes standard, ML-adjusted, and conservative forecasts alongside actual generation, deviation bands, and accuracy trends. Users can toggle sub-arrays, inspect contextual metadata, and drill into any interval without exporting.
Can I compare forecasts across multiple sites?
Yes. Use the multi-site selector to view combined generation or switch between individual assets. Saved dashboard layouts remember preferred sites, chart groupings, and metric selections so portfolio managers can monitor different regions side-by-side.
How customizable are the dashboard widgets?
Widgets support per-user time ranges, aggregation levels, and normalization (per MW, cumulative, or raw values). Users can pin deviation histograms, intraday ramp charts, probability cones, and accuracy summaries to create views tailored to trading, operations, or executive reporting.
Are dashboard exports available?
Every chart and table can be exported to CSV, PNG, or PDF. Scheduled deliveries and one-click email sharing allow teams to distribute dashboards without logging into the platform, while secure data feeds provide the same curated datasets for BI tools.
Weather & Irradiance Inputs
Which weather and irradiance sources are supported?
HelioExpect manages licensed irradiance and meteorological datasets on your behalf. Providers can be switched per site configuration, while credential handling remains secured within the platform.
Do I need to upload my own weather data?
No. Standard deployments include all required weather and irradiance feeds. The platform automatically fetches and reconciles the inputs needed for forecast generation.
What granularity options are available?
Forecasts are produced at 15-minute resolution with optional aggregation to hourly, daily, or custom blocks aligned to each site's timezone.
Plant Modeling & Configuration
How do sub-array configurations work?
Each request references HelioExpect site metadata describing capacity, module type, inverter make, number of inverters, and mounting configuration. The engine simulates every active sub-array independently before aggregating to site totals, preserving accuracy for mixed-technology plants.
Do you support tracker sites?
Yes. Single-axis and dual-axis trackers are modeled using the same algorithms that power our monitoring platform. Provide axis azimuth, tilt range, and tracking limits; the engine computes the real-time plane-of-array irradiance before generating power curves.
How are system losses handled?
Losses are configurable via the `lossDiagram` object. You can specify AC and DC wiring losses, soiling, shading, degradation, auxiliary consumption, and other adjustment factors. These values are applied per sub-array so fleet-level and component-level assumptions stay aligned.
Can we enforce export limits?
Use the `grid_power_limit` setting to cap exported generation. The engine respects the declared limit after losses and ML corrections, ensuring the final forecast aligns with grid agreements and interconnection contracts.
Machine Learning Calibration
How does ML calibration improve the physical model?
The forecasting stack pairs physics-based simulations with data-driven corrections. Historical weather, production, and alarm history are featurized inside prediction-ml, which trains gradient boosting and neural models per site. These corrections adjust irradiance-to-power translation while guarding against drift.
What is the role of damping and smoothing?
The engine applies adaptive damping to avoid unrealistic step changes when weather services update. This protects downstream schedules and makes intraday adjustments smoother, particularly when multiple sub-arrays contribute to the same grid node.
How often are models retrained?
Retraining cadence depends on site maturity and data volume. Production sites typically run weekly calibration jobs, while new assets retrain more frequently until the models stabilize. Triggers are orchestrated through prediction-ml and automatically publish updated weights to the forecasting service.
How are accuracy reports generated?
prediction-ml’s consolidated reporting utilities merge actuals from HelioExpect services with forecast outputs, compute day-level error distributions, and export summaries for energy trading, operations, and compliance stakeholders.
Delivery & Integration
What delivery formats do you support?
Forecasts are consumable through the dashboard, scheduled email reports, FTP/SFTP drops, and secure data feeds. The delivery layer can publish CSV, JSON, or Excel outputs, and you can enable automated alerts when deviation thresholds are exceeded.
Can we integrate with external scheduling tools?
Yes. Use automated file drops or secure feeds to push forecasts into ISO submissions, trading desks, or internal scheduling systems. Forecast metadata includes capacity, block identifiers, and timezone-aware timestamps to streamline downstream ingestion.
Operations & Reliability
How are provider credentials managed?
Weather provider keys, HelioExpect service tokens, and delivery credentials live in environment variables or managed secret stores. The engine never logs sensitive data, and the documentation includes guidance on rotating keys without downtime.
What observability is available?
Structured logs capture request metadata, provider responses, and processing durations. Metrics feed into dashboards so you can monitor run time, error rates, and accuracy in real time. Alerts notify operators of upstream weather issues or missing telemetry.
Is there a fallback if weather feeds are delayed?
If a preferred weather feed is unavailable, the engine automatically reuses the last successful run or switches to a secondary provider defined in your configuration, keeping forecasts available without manual intervention.
How do we support compliance audits?
All forecast requests are timestamped with payload hashes and execution logs. Combined with prediction-ml reports, this provides a traceable history for market regulators or investors without disclosing proprietary data sources.
Need Help?
Contact HelioExpect if you need assistance configuring forecasts, tuning models, or integrating with external schedulers.
Forecasting Support
Get help with payload formatting, scheduling jobs, or orchestrating deliveries.
forecast@helioexpect.comIntegration Playbook
Review payload schemas, authentication patterns, and sample configurations.
View Integration GuidesCustom Deployments
Request bespoke data feeds, hybrid modeling, or dedicated instances.
enterprise@helioexpect.com