Quick Facts
What a met station is
A meteorological (met) station is an instrumentation package that collects weather data at a solar plant site. The data is essential for understanding plant performance, calculating Performance Ratio, forecasting generation, and diagnosing issues.
A typical solar met station includes:
Pyranometer (irradiance measurement).
Ambient temperature sensor.
Module back-of-panel temperature sensor.
Anemometer (wind speed).
Wind vane (wind direction).
Humidity sensor.
Sometimes also:
Barometric pressure sensor.
Rain gauge.
Soiling sensor (measures soiling deposition rate).
Cloud sensor or sky imager.
The sensors are mounted on a met mast (a vertical structure typically 5 to 10 metres tall) or on a dedicated platform near the plant. Data is transmitted to the plant’s SCADA system through standard industrial communication protocols (Modbus RTU, Modbus TCP, OPC UA).
Sensors in a met station
Pyranometer:
Measures solar irradiance in W per sq m.
ISO 9060 classification (Secondary Standard, First Class, or Second Class).
POA pyranometer mounted in the plane of the panels (matching tilt and azimuth).
GHI pyranometer mounted horizontally.
Ambient temperature sensor:
Measures air temperature.
RTD (Resistance Temperature Detector) or thermistor type.
Mounted in a radiation shield to avoid solar heating bias.
Module back-of-panel temperature sensor:
Measures the temperature of the back of a representative module.
Validates cell operating temperature for performance analysis.
RTD or thermistor bonded to a module backsheet with thermal paste.
Anemometer:
Measures wind speed.
Cup or sonic anemometer type.
Mounted at 10 metres above ground for WMO compliance.
Wind vane:
Measures wind direction.
Typically combined with anemometer in a single instrument.
Humidity sensor:
Measures relative humidity.
Capacitive sensor in a radiation shield.
These standard sensors provide the data needed for comprehensive solar plant performance analysis.
Met station data uses
Met station data supports multiple solar plant functions:
Performance Ratio calculation: PR formula uses POA irradiance as the reference. Without met station data, PR cannot be calculated accurately.
Real-time monitoring: SCADA dashboards show real-time irradiance, temperature, and plant output. Operators verify the plant is generating as expected for current conditions.
Forecasting: Combined with weather forecasts, met station data supports next-day generation forecasting for grid integration.
Root cause analysis: When plant performance drops, met station data helps determine whether the cause is weather (cloudy day, low sun) or plant-related (failed inverter, soiled panels).
Long-term resource analysis: Multi-year met station data validates the assumed irradiance in the project’s financial model and supports refinancing or sale.
Lender’s reporting: Lenders require periodic performance reports that include met station data for verification.
Warranty claims: When pursuing performance warranty claims, met station data documents the conditions under which the plant operated.
Met station sizing
For different plant scales:
Residential rooftop (under 10 kW): No met station typically. Inverter data and online sources suffice.
Small commercial (10 to 100 kW): Met station optional. Some EPCs include basic monitoring (temperature, possibly irradiance) but not full met station.
Medium commercial (100 kW to 5 MW): Basic met station with First Class pyranometer typical.
Utility-scale (above 5 MW): Met station with Secondary Standard or First Class pyranometers. Sometimes multiple met stations for spatial coverage.
Large utility-scale (above 50 MW): Multiple met stations distributed across the site. 2 to 5 met stations typical for sites larger than 1 sq km.
Met station installation
Proper installation is critical for accurate measurement:
Location: Free from shadows by panels, buildings, or trees. Representative of typical plant conditions.
Mounting structure: Met mast or platform sized for sensor mounting. Met masts typically 5 to 10 metres tall, depending on the site.
Sensor mounting: Pyranometers properly oriented and levelled. Anemometer at 10 metres above ground. Module temperature sensor on a representative module.
Cable routing: Protected cables from sensors to SCADA system. UV-resistant outdoor cables.
Earthing: Proper grounding for safety and signal integrity.
Power supply: Some sensors need DC power; others are passive. Solar-powered met stations are common.
Calibration: Pyranometers calibrated annually. Other sensors checked at recommended intervals.
The detail in installation pays off in measurement accuracy. Poor installation introduces systematic errors that are hard to detect later.
Met station integration with SCADA
Modern met stations integrate with plant SCADA through:
Modbus RTU or Modbus TCP: Most common protocol for solar applications.
OPC UA: Used in larger plants with sophisticated SCADA.
IEC 60870 or IEC 61850: For utility-grade installations with grid integration.
The SCADA system records met station data at typical 1 minute intervals (with faster sampling for some applications). The data is stored in the plant’s historian database for long-term analysis.
Reports generated from the historian use met station data alongside inverter and meter data to characterise plant performance.
Met station maintenance
Like other instruments, met stations require maintenance:
Annual calibration of pyranometers.
Periodic cleaning of pyranometer domes and sensor housings.
Verification of anemometer rotation (bearing wear can affect accuracy).
Replacement of consumables (radiation shields, gaskets, sensors at end of life).
Cable inspection for UV damage and rodent attack.
Earthing system verification.
Mounting structure inspection.
Annual met station audits are part of comprehensive O&M programmes.
Common met station mistakes
Skipping pyranometer calibration. Drift causes measurement errors.
Mounting met station in shaded location. Shadows contaminate irradiance data.
Not levelling pyranometers properly. Misalignment causes systematic errors.
Using inadequate sensor classes. Second Class pyranometers in a Secondary Standard application.
Failing to integrate with SCADA. Standalone data loggers without SCADA integration limit usefulness.
Not maintaining the station. Dirty sensors, failed components, and broken cables go unnoticed.
Best practices
For new plants, include met station in the initial design and budget.
For sensor selection, match the application: Secondary Standard for utility-scale; First Class for commercial; Second Class for budget monitoring.
For installation, follow WMO and industry best practices for mounting and orientation.
For maintenance, include met station in the O&M contract with defined calibration and inspection schedules.
For data, integrate met station with SCADA for real-time access and historian storage.
For multi-MW plants, deploy multiple met stations to characterise spatial variation.
Standards and references
Met station design follows the WMO Guide to Meteorological Instruments and Methods of Observation (CIMO Guide). Pyranometers comply with ISO 9060. Wind sensors follow related ISO and IEC standards. Manufacturer specifications detail performance and operating limits.
Related glossary terms
- Pyranometer
- Solar Irradiance
- Global Horizontal Irradiance
- SCADA in Solar
- Performance Ratio
- Peak Sun Hours
- Tilt Angle
- Azimuth
Key takeaways
A meteorological (met) station in solar is an instrumentation package that collects weather data at a solar plant site, including irradiance, ambient temperature, module temperature, wind speed and direction, and humidity. The data is essential for Performance Ratio calculation, forecasting, and root cause analysis. Met stations are standard for utility-scale and commercial solar plants. Sensor selection matches the application (Secondary Standard, First Class, or Second Class). Proper installation, annual calibration, and SCADA integration are critical for delivering useful data over the plant’s life.