Pyranometer

A pyranometer is a type of solar radiation sensor that measures the total incoming solar radiation from the sky. It captures both the direct sunlight and the diffuse light scattered by clouds or particles. The data it collects is measured in watts per square meter (W/m²). These readings are essential for determining how much solar energy is available at a specific location.

This makes the pyranometer an important component in solar weather stations, solar energy projects, climate studies, and agricultural systems where sunlight affects growth and yield.

The working principle of a pyranometer is based on how it detects and converts sunlight into an electrical signal. There are two main types based on the sensor used:

1. Thermopile Sensor Pyranometer

This type uses a black-coated surface that absorbs sunlight. As the surface heats up, it creates a temperature difference between the hot and cold junctions. This difference produces a small voltage (Seebeck effect), which is directly proportional to the solar radiation.

2. Silicon Photodiode Sensor Pyranometer

In this version, a silicon photodiode converts light into an electrical current. These sensors are faster and more affordable, making them common in basic weather monitoring systems or portable irradiance meters.

Pyranometers are also classified according to the ISO 9060 standard, which helps determine their accuracy and reliability:

1.  Class A (Secondary Standard)

High-accuracy devices used for scientific research, solar power plants, and professional energy audits. These are commonly installed in utility-scale solar weather stations.

2. Class B (First Class)

Used in commercial solar energy systems and environmental studies where a balance of accuracy and cost is needed.

3. Class C (Second Class)

Budget-friendly instruments used for basic environmental tracking or educational purposes.

These classes help users choose the right solar pyranometer depending on the accuracy needed and the application.

A pyranometer is designed to measure different types of solar radiation. These include:

1. GHI – Global Horizontal Irradiance

This is the total amount of solar radiation (direct + diffuse) falling on a horizontal surface. GHI is the most commonly measured value in solar weather stations and solar energy systems.

2. DNI – Direct Normal Irradiance

This is the amount of sunlight coming directly from the sun, without any scattering. It is measured using a pyrheliometer, not a pyranometer. However, both instruments are often used together in solar studies—referred to as pyranometer and pyrheliometer setups.

3. DHI – Diffuse Horizontal Irradiance

This measures only the scattered light coming from the sky, excluding direct sunlight. It is usually measured with a shaded pyranometer that blocks direct rays from the sun.

Together, GHI, DNI, and DHI provide a full picture of solar radiation and help design efficient solar systems.

Because of their versatility and accuracy, pyranometers are used in a variety of fields:

• Weather monitoring systems for environmental data
• Solar weather stations to monitor and predict energy output
• Scientific research related to the Earth’s energy balance
• Agriculture, to track sunlight for crop growth
• Building design and energy efficiency evaluations
• PV (photovoltaic) performance analysis and diagnostics

In many of these cases, a solar pyranometer is used alongside other tools like the irradiance meter or pyrheliometer for a more comprehensive view.

Though both tools measure solar radiation, they do so differently:

• A pyranometer captures radiation from the whole sky, including direct and scattered sunlight.
• A pyrheliometer focuses only on the direct sunlight and must be mounted on a solar tracking system to stay aligned with the sun.

In solar energy systems, using both gives a better understanding of the site's solar resource.