What is a Pyrheliometer : Working & Its Applications

We know that the sun is the main energy source on earth. So by using this, the production of energy can be done through solar energy harvesting. So life is constant on earth because the sun generates sufficient heat energy for keeping the soil warm, and this energy is in the form of electromagnetic radiation. Generally, it is known as solar radiation. This solar radiation reaches the earth through the atmosphere by absorbing, reflecting, and scattering. So that it results in the energy reduction in the flux density. This energy reduction is very important because above 30% loss will occur on sunshine,  whereas 90% loss will occur on a cloudy day. So the utmost radiation which contacts the surface of the earth through the atmosphere must be below 80%. So the solar energy measurement can be done using an instrument like Pyrheliometer.

What is Pyrheliometer?

Definition: The pyrheliometer is one type of instrument, used to measure the direct beam of solar radiation at the regular occurrence. This instrument is used with a tracking mechanism to follow the sun continuously. It is responsive to wavelengths bands that range from 280 nm to 3000 nm. The units of irradiance are W/m². These instruments are specially used for weather monitoring & climatological research purposes.

Pyrheliometer Instrument
Pyrheliometer Instrument

Pyrheliometer Construction & Working Principle

The external structure of the Pyrheliometer instrument looks like a telescope because it is a lengthy tube. By using this tube, we can spot the lens toward the sun to calculate the radiance. The Pyrheliometer basic structure is shown below. Here the lens can be pointed in the direction of the sun & the solar radiation will flow throughout the lens, after that tube & finally at the last part where the last apart includes a black object at the bottom.

The irradiance of solar enters into this device through a crystal quartz window and directly reaches onto a thermopile. So this energy can be changed from heat to an electrical signal that can be recorded.
A calibration factor can be applied once changing the mV signal to a corresponding radiant energy flux, and it is calculated in W/m² (watts per square meter). This kind of information can be used to increase Insolation maps. It a solar energy measurement, that is received on a specified surface region in a specified time to change around the Globe. The isolation factor for a specific area is very useful once setting up solar panels.

Pyrheliometer Circuit Diagram

The circuit diagram of the pyrheliometer is shown below. It includes two equal strips specified with two strips S1 & S2 with area ‘A’. Here, a thermocouple is used where its one junction can be connected to S1 whereas the other is connected to S2. A responsive galvanometer can be connected to the thermocouple.
The S2 Strip is connected to an exterior electrical circuit.

Pyrheliometer Circuit
Pyrheliometer Circuit

Once both the strips are protected from the radiation of solar, then the galvanometer illustrates there is no deflection because both the junctions are at equal temperature. Now ‘S1’ strip is exposed to the solar radiation & S2 is protected with a cover like M. When S1 strip gets heat radiations from the sun, then strip temperature will be increased, thus the galvanometer illustrates deflection.


When current is supplied throughout the S2 strip, then it is adjusted and the galvanometer illustrates there is no deflection. Now, again both the strips are at equal temperature.

If the heat radiation amount occurred over the unit area within the unit time on S1 strip is ‘Q’ & its absorption co-efficient, so the heat radiation amount which is absorbed through the S1 strip S1 within unit time is ‘QAa’. In addition, the heat generated in unit time within the S2 strip can be given through VI. Here, ‘V’ is the potential difference & ‘I’ is the flow of current through it.

When heat absorbed is equivalent to the heat generated, so

QAa = VI


By substituting the values of V, I, A and a, the value of ‘Q’ can be calculated.

Different Types

There are two types of Pyrheliometers like SHP1 and CHP1


The SHP1 type is a better version compare with CHP1 type, as it is designed with an interface including both improved analog o/p & digital RS-485 Modbus. The response time of this kind of meter has below 2 seconds & independently calculated temperature correction will range from -40°C to +70°C.


The CHP1 type is the most frequently used radiometer used to measure solar radiation directly. This meter includes one thermopile detector as well as two temperature sensors. It generates an utmost o/p like 25mV beneath usual atmospheric situations. This type of device totally obeys the most recent standards which are set by ISO and WMO about the criteria of the Pyrheliometer.

Difference between Pyrheliometer and Pyranometer

Both the instruments like Pyrheliometer & Pyranometer are used to calculate solar irradiance. These are related in their intention but there are some dissimilarities in their construction & working principle.



It is one kind of acidometer mainly used to measure the solar irradiance over a planar surface. This instrument is used to measure direct ray solar irradiance.
It uses thermoelectric detection principle In this, the thermoelectric detection principle is used
In this, the measurement of increasing temperature can be done through thermocouples which are linked in series otherwise series-parallel to build a thermopile.


In this, the increasing temperature can be calculated through thermocouples that are allied in series/series-parallel to create a thermopile.


This is frequently used in meteorological research stations This is also used in meteorological research stations
This instrument calculates global solar radiation. This instrument calculates direct solar radiation.


The advantages of the Pyrheliometer include the following.

  • Very low power consumption
  • Operates from a wide range of voltage supplies
  • Ruggedness
  • Stability

Pyrheliometer Applications

The applications of this instrument include the following.

  • Scientific meteorological
  • Observations of Climate
  • Testing research of Material
  • Estimation of the solar collector’s efficiency
  • PV devices


1). What is the foremost use of the Pyrheliometer?

These devices are used for the measuring direct beam of solar irradiance.

2). Where comes the difference between Pyrheliometer and the pyranometer?

Pyrheliometer is for measuring direct sunbeam whereas pyranometer is for measuring diffused sunbeam.

3). What is a crucial benefit of Pyrheliometers?

They provide extensive reliability and durability

4). What are the uses of the Pyrheliometer?

This instrument used mainly for climatic, meteorological, and scientific measurements or observations.

5). What is the maximum irradiance that this device provides?

It can measure upto irradiance of 4000 W per square meter.

Thus, this is all about an overview of the pyrheliometer that includes construction, working, circuit, differences with a pyranometer, advantages, and applications. Here is a question for you, what are the disadvantages of pyrheliometer?