Accurate solar radiation measurement is the backbone of solar energy analysis, weather monitoring, and PV performance evaluation. However, not all irradiance sensors measure the same thing. Sensors such as pyrheliometers, pyranometers, irradiance sensors, and albedometers each serve a specific purpose and are designed for different measurement needs.
Why Are Different Solar Radiation Sensors Needed?
Solar radiation reaches the Earth in multiple forms:
- Direct beam radiation
- Diffuse sky radiation
- Reflected radiation from the ground (albedo)
As there isn’t a single sensor that can accurately measure all of these components at once, different sensors exist in the market to fulfill all the measurement requirements.
What Is a Pyranometer?
A pyranometer measures Global Horizontal Irradiance (GHI), which is the total solar radiation received on a horizontal surface.
What the Pyranometer Measures
The Pyranometer measures the Global Horizontal Irradiance (GHI) which includes both:
- Direct radiation
- Diffuse sky radiation
How the Pyranometer Works
We can summarize the working principle of the Pyranometer in the following points:
- Uses a thermopile sensor
- Typically covered by a glass dome
- Measures radiation from the entire sky hemisphere (180°)
Typical Applications of the Pyranometer
The Pyrheliometer is used in diverse applications such as:
- Weather stations
- Solar resource monitoring
- Performance ratio (PR) calculations
- Environmental and climate studies
Pyranometers are widely used because they provide a standardized, meteorological-grade irradiance measurement.
What Is an Irradiance Sensor?
The term irradiance sensor often refers to silicon-based irradiance sensors or reference cells. It is mainly used to measure the Plane of Array (POA) Irradiance.
Key Characteristics of Irradiance Sensors
- Uses reference cells
- Fast response time
- Spectral response similar to PV modules
Typical Applications of Irradiance Sensors
The Irradiance Sensors are mainly used in the following applications:
- PV performance monitoring
- SCADA systems in solar power plants
- IV curve tracing
- Commissioning and O&M diagnostics
Compared to pyranometers, irradiance sensors are often preferred when PV-representative measurement is required rather than meteorological data.
What Is an Albedometer?
An albedometer measures surface reflectivity (albedo) by comparing incoming and reflected solar radiation.
How the Albedometer Works
- Uses two pyranometers or irradiance sensors
- One facing upward (incoming irradiance)
- One facing downward (reflected irradiance)
- Albedo is calculated as:
Reflected Irradiance / Incoming Irradiance
Typical Applications of the Albedometer
- Bifacial PV power plants
- Snow, sand, or high-reflectance surface studies
- Climate and environmental research
- PV system design optimization
Albedometers are especially important in bifacial PV systems, where rear-side irradiance directly affects energy yield.
What Is a Pyrheliometer?
A pyrheliometer is a precision instrument designed to measure Direct Normal Irradiance (DNI), which is the solar radiation coming directly from the sun in a straight line.
How the Pyrheliometer Works
We can summarize the working principle of the pyrheliometer in the following points:
- Uses a narrow field-of-view collimator
- Must be mounted on a solar tracker
- Measures radiation perpendicular (normal) to the sun’s rays
Typical Applications of the Pyrheliometer
The Pyrheliometer is used in many applications such as:
- Concentrated solar power (CSP) plants
- Solar resource assessment for tracking PV systems
- Meteorological and climate research
- DNI-based energy yield modeling
The pyrheliometer is not recommended for fixed installations without solar tracking as it measures only direct sunlight.
Key Differences between the different Sensors measuring Irradiance
| Instrument | Measures | Orientation | Typical Use |
| Pyrheliometer | Direct Normal Irradiance (DNI) | Sun-tracking | CSP, DNI studies |
| Pyranometer | Global Horizontal Irradiance (GHI) | Horizontal | Weather stations, PV monitoring |
| Irradiance Sensor | Plane-of-array or horizontal irradiance | Fixed | PV performance & IV testing |
| Albedometer | Reflected irradiance (albedo) | Up & down | Bifacial PV, surface studies |
Which Sensor Should You Use?
Pyrheliometers, pyranometers, irradiance sensors, and albedometers each play a different role in solar radiation measurement. Understanding what each sensor measures, and what it does not, is essential for selecting the right sensor, whether you are evaluating a PV plant, designing a bifacial system, or conducting climate research.
You can simply choose the correct sensor based on your application:
- CSP or DNI modeling: Pyrheliometer
- Standard weather and resource data: Pyranometer
- PV performance and IV curve measurements: Irradiance sensor (reference cell)
- Bifacial PV or reflectivity analysis: Albedometer
Using the wrong sensor can lead to incorrect conclusions about system performance or energy yield.
For more details about the different types of the Irradiance, you can refer to our previously written article: https://www.sevensensor.com/solar-irradiance-in-pv-systems-poa-ghi-dhi-dni
FAQ: Pyrheliometer vs. Pyranometer vs. Irradiance Sensor vs. Albedometer
1) What are the main Radiation Sensors that exist?
The main sensors used to measure different radiations are: Pyranometer, Irradiance Sensor (Reference Cell), Albedometer, and Pyrheliometer.
2) Which sensor measures DNI for CSP or DNI modeling?
Use a pyrheliometer. It measures Direct Normal Irradiance (DNI) and typically needs a solar tracker to stay aligned with the sun.
3) Which sensor measures GHI for weather stations and standard solar resource data?
Use a pyranometer. It measures Global Horizontal Irradiance (GHI), which includes direct + diffuse radiation from the sky hemisphere.
4) Which sensor is best for PV performance monitoring and SCADA (POA irradiance)?
Use a reference cell when you want PV-representative POA irradiance (fast response, PV-like spectral behavior), especially for commissioning, O&M, diagnostics, and IV curve work.