Calibration of Pyranometer

What is Pyranometer?

The Sun Generate radiation over the different range of wavelength which is known as spectrum. For measurement of radiation which is generated by sun, we need a Pyranometer. Pyranometer is a instrument which is specially designed to measure the Global Solar radiation over a certain range of radiation. Global Radiation is a short wave radiation from the sky falling onto a horizontal surface on the ground. It includes both the direct solar radiation and the diffuse radiation resulting from reflected or scattered sunlight.

Pyranometer is a scientific instrument used to measure solar irradiance on plane finish and even measure the solar flux density in w/sq m. In simple words, it is:

Total Radiation = Direct Radiation (from sun) + Diffused Radiation (scattered by dust, air etc).

Where & What are Pyranometers Used for?

In the Solar energy sector, pyranometers are used to monitor & checking the performance of Solar power Plants. By the comparison of the actual power output from the solar power plant to the expected output based on the Pyranometer reading, the efficiency of the solar plant laid down. The other application of Pyranometer is for climate & weather studies. In such studies pyranometers are used for Global Horizontal irradiance (GHI). In solar plants where the surface often corresponds to the Plane of array (POA) of solar panels, in this case the measured quantity is Global tilted irradiance (GTI).

How Pyranometer Works?

Pyranometrs are grouped in two different technologies i.e:

  • Thermopile Technology &
  • Silicon Technology.

The thermopile pyranometrs are widely used in solar industry. In 1st type of pyranometrs the main components of a Pyranometer are one or two domes, black absorber, thermopile, electronics & body. Dome of the Pyranometer work as a filter that transmit solar radiation & block thermal radiation over long wavelength. Purpose of second dome is to improve the performance of Pyranometer. In Thermopile pyranometer the thermoelectric detection principle is used, whereby filtered radiation is absorbed by the black surface on the Pyranometer & converted into heat. Thermopile converts the heat into electrical energy. 

The resulting increase of temperature is measured via thermocouples connected in series or series-parallel to make a thermopile.

Working of Thermopile Pyranometer

Details of the high-quality pyranometer that uses a thermopile to measure solar radiation:

  1. Outer dome made from a hemisphere of optical-quality glass.
  2. Inner dome made from a smaller hemisphere of optical glass.
  3. Black carbon disk (illuminated by the Sun) absorbs a broad range of wavelengths of solar radiation and acts as the sensing element.
  4. Second, control disk (not illuminated by the Sun) acts as a comparison and compensating element. Any sources of temperature rise other than solar heat (perhaps an air-conditioning unit positioned nearby) will warm both disks equally, so we can be reasonably confident that the difference between the two disks (and the temperature rise we’re measuring) is caused only by the Sun.
  5. Thermopile temperature sensor compares the temperature rise of the two disks.
  6. Output lead (usually about 10m or 30ft long).
  7. Replaceable silica gel cartridge absorbs moisture to prevent dew forming inside on cold nights.
  8. Adjustable screw legs let you level the pyranometer using its built-in, high-precision spirit level, which is sensitive to a fraction of a degree (not shown on this diagram).

Calibration & it’s Importance

Calibration is a part of quality check. Calibration is the act of comparing a device under test (DUT) of an unknown value with a reference standard of a known value. Calibration of your measuring instruments has two objectives: it checks the accuracy of the instrument and it determines the traceability of the measurement. The accuracy of all measuring devices degrade over time.

Pyranometer Calibration Importance & Standards

Pyranometer Calibration

In case of pyranometers, they also need calibration on regular intervals for checking the accuracy. Interval of calibration may vary as per manufacture & type of Pyranometer. Due to regular exposure of sun light Pyranometer Sensitivity is degrade over time. To find the new Sensitivity/Accuracy of Pyranometer, they need calibration as per ISO 9846 & ISO 9847. These are two different standards which are used for calibration.

Why Choose Us?

We ITC India is one of the top laboratory in India, approved by NABL in testing field. We are capable of calibrating multiple brands and work as per established and traceable standards. We follow ISO 17025 Laboratory management System for calibration. Our Reference Pyranometer is directly traceable to World Radiometric reference which is maintained a Davos Switzerland. Pyranometer sensitive is measured in Microvolt, for that we have high accuracy DMM, which is directly traceable to NPL. We follow ISO 9847 Standard for calibration of CMP 10 & CMP11 series of pyranometers. More calibration of pranometer added in future.