Pyranometers are devices used to measure solar irradiance, which is the amount of energy coming from the sun. They are commonly used in climate research, weather stations, greenhouses, building control systems, reflectance studies, and material weathering tests.
What is Solar Irradiance?
Solar irradiance is the amount of solar energy that falls on a surface. It is measured in watts per square meter (W/m²).
Solar irradiance includes more than just visible sunlight. The Sun gives off energy in many forms across the electromagnetic spectrum, including visible light, infrared (IR), ultraviolet (UV), extreme ultraviolet (EUV), and X-rays.
Solar irradiance at the Earth’s surface has two parts: direct irradiance and diffuse irradiance. Direct irradiance comes straight from the Sun in one clear direction. Diffuse irradiance is sunlight that has been scattered by the atmosphere. Some scattered sunlight goes back into space, while some still reaches the Earth’s surface from different directions.
How to measure the Irradiance?
Solar irradiance is measured using sensors placed on surfaces that receive sunlight, such as solar panels or solar collectors.
The amount of sunlight a surface receives depends on its direction, tilt, the position of the Sun, and the weather. Sunlight can reach the surface directly from the Sun, be scattered by the atmosphere, or be reflected from the ground. Because of this, special sensors are used to measure and calculate solar irradiance on flat or tilted surfaces.
Solar irradiance is mainly measured with two devices: pyrheliometers and pyranometers.
A pyrheliometer measures direct sunlight coming straight from the Sun. The sunlight enters through a glass window and reaches a heat sensor, which changes the heat into an electrical signal. This signal is then converted into irradiance values in W/m².
A pyranometer measures the total sunlight received from the sky, including both direct and scattered sunlight. It is usually placed horizontally. It has a thermal sensor and a glass dome that helps control the range of sunlight wavelengths being measured.
Other devices than pyranometers are used to measure irradiation, e.g., the irradiance sensors which are used for measuring the plane of the array (POA) irradiance.
This irradiance sensor is also called a PV pyranometer because it has the same functions as the pyranometer, it measures the POA irradiance, which is defined as the sum of the direct normal irradiance (DNI) and diffuse irradiance (DHI) components incident on a surface with a given inclination and angle of incidence (AOI).
What are the different classes of pyranometers?
Pyranometers can differ in quality. To organize them, the World Meteorological Organization (WMO) and the International Organization for Standardization (ISO) divide them into three classes for different uses.
According to ISO 9060, a pyranometer can be classified as Class A, Class B, or Class C. This classification depends on its technical performance, such as how fast it responds, how stable and accurate it is, how it reacts to temperature, tilt, light direction, and different wavelengths, and how it is calibrated.
SEVEN offers mainly Class A pyranometers. Class B and Class C pyranometers are offered upon request.
Frequently Asked Questions (FAQ)
What is a pyranometer?
A pyranometer is a sensor that measures total solar irradiance (both direct and diffuse sunlight) typically on a horizontal surface.
What are the main components of solar irradiance at Earth’s surface?
Direct radiation: comes straight from the sun in a defined direction
Diffuse radiation: scattered by the atmosphere and arrives from many directions
Why do we measure solar radiation in solar/PV systems?
To understand how much solar energy is available and to support performance monitoring, efficiency calculations, and optimal orientation/tilt decisions.
What instruments are commonly used to measure solar radiation?
Irradiance sensor is used to measure irradiance. On the other hand, pyranometers are used to measure global irradiance (direct and diffuse radiation). Pyrheliometer is also used to measure direct sun radiation.
How does a pyranometer physically work?
It uses a thermal sensor under a glass dome that helps limit the wavelength range and enables the sensor to respond to sunlight coming from all directions.
What is an irradiance sensor (PV pyranometer) in PV plants?
It’s an irradiance sensor used to measure Plane of Array (POA) irradiance—sunlight incident on the PV panel plane (tilted/angled like the modules).
What are pyranometer classes?
ISO 9060 defines pyranometer classes based on performance characteristics (like response time, offsets, stability, non-linearity, directional/spectral response, temperature/tilt effects).
Class A: highest accuracy
Class B: medium
Class C: basic
Higher class generally means better measurement quality for demanding applications.