In this document
You will learn how to interpret the data acquired from the Solargis Monitor service.
Overview
Solargis Monitor offers a suite of solar resource and meteorological data products, each varying in maturity, accuracy, and intended use. Correct interpretation of these data groups is essential for drawing reliable conclusions in PV system monitoring, performance assessment, and reporting. This guide explains how to interpret Monitor data, clarifies the differences between data groups, and provides best practices for their application in operational and analytical contexts.
Note: This document does not include information about meteorological data.
Key Monitor data groups and their characteristics
Solargis Monitor data is structured into four main groups according to the time frame and data maturity. Each group is generated using different methodologies and input data, which directly affects its accuracy and recommended use.
Nowcast data (current moment)
Definition: Nowcast data provides the most up-to-date estimate of solar irradiance and PV output for the current moment. Although Nowcast is not a traditional monitoring service, it delivers solar parameter values for the present time because of the inherent delay in receiving and processing satellite data. This delay, caused by the time needed for satellite image acquisition, transmission, and processing, means that the latest actual satellite-based observation is always several minutes behind real time. To bridge this gap, Solargis uses its proprietary Cloud Motion Vector (CMV) model to predict solar conditions for the current moment based on recent satellite images.
Every 5, 10, or 15 minutes, depending on geographic location (Fig.1). Meteo data is updated every 6 hours from the IFS forecast model.
Nowcast data is ideal for immediate operational awareness and short-term decision-making. However, as it is based on cloud motion forecasting rather than direct satellite observation, small discrepancies may occur compared to subsequent data updates.
Tip: Use Nowcast for real-time monitoring, but expect values to be refined as more accurate satellite data becomes available.
Figure 1: Data update frequency map for world regions.
Real-time data (today, up to the current moment)
Definition: Real-time data covers the period from midnight to the latest available satellite observation. It is derived from direct satellite imagery using the Solargis satellite model.
Every 10 or 15 minutes (10 minutes for contiguous USA)
Real-time data offers higher accuracy than Nowcast, as it is based on actual satellite measurements. However, there is a short delay due to satellite data processing.
Tip: Use Real-time data for intra-day performance tracking and diagnostics. Be aware that as data transitions from Nowcast to Real-time, values may change due to the shift from forecasted to observed inputs.
Operational data (start of month to yesterday)
Definition: Operational data includes preliminary calculations for recent days. It initially uses forecasted atmospheric parameters (such as aerosols), which are later updated as more accurate inputs become available.
Daily recalculation for the previous two days (DAY-1 and DAY-2), with up to 40 days of data accessible via API.
Operational data is suitable for daily and weekly reporting. Since it may be updated after initial delivery, small changes in values are possible as atmospheric inputs are refined.
Tip: For critical applications, re-evaluate data for the previous two days after updates. When using the API, avoid unnecessary bulk requests for the full 40-day history, as this can complicate data processing without adding value.
Historical data (archive quality)
Definition: Historical data represents the final, homogenized dataset for both solar and meteorological parameters. It is generated using all available observations and reanalyzed atmospheric data (e.g., ERA5), ensuring the highest accuracy and consistency.
Released on the third day of each month for the previous calendar month.
Historical data is the reference standard for long-term performance evaluation, regulatory reporting, and contractual claims.
Tip: Always use historical data for monthly and annual performance assessments. Update any analyses initially performed with operational data once historical data becomes available.
Performance summary
Interpreting Solargis Monitor data correctly requires awareness of data maturity, update cycles, and best practices for application:
Data maturity: Expect values to change as data matures from Nowcast to Real-time, then to Operational, and finally to Historical. Each step incorporates more accurate and comprehensive inputs.
Update cycles:
Nowcast: 5/10/15 minutes (location-dependent)
Real-time: 10/15 minutes (10 minutes for contiguous USA)
Operational: Daily recalculation for last 2 days.
Historical: Monthly, available on the third day for the previous month.
Best practices:
Use Nowcast and Real-time data for immediate operational needs, but rely on Operational and especially Historical data for any formal reporting, benchmarking, or warranty claims.
For warranty or contractual purposes, only archive-quality (historical) data should be referenced, as it reflects the highest data maturity and accuracy.
Regularly update analyses and reports as more mature data becomes available, especially when transitioning from operational to historical datasets.
Data retention: Solargis Monitor retains operational data for up to 40 days (API access) and historical data for the past three months for Monitor Basic and twelve months for Monitor Professional. More data can be acquired through the Solargis Evaluate application.