How does a Pyranometer work

Pyranometer Working Principle and Application

Ever heard of Seebeck Effect if you have then you will have no trouble understanding this. However if you haven't heard about the Seebeck effect then lets have a quick recall. According to Wikipedia, "The Seebeck effect is the electromotive force (emf) that develops across two points of an electrically conducting material when there is a temperature difference between them". 

 

A pyranometer is a type of actinometer(Actinometers are instruments used to measure the heating power of radiation) used for measuring solar irradiance on a planar surface. It can measure the sprectum of 300nm to 2,800nm. Pyranometer should have “directional response” or “cosine response” characteristics i.e zero response when sun is at horizon because θ=90°. A typical pyranometer does not require any power to operate and it is fixed on
horizontal plane.

Pyranometer components:

Components labeling:
1. thermopile sensor with black coating
2. Outer glass dome
3. Inner glass dome
4. radiation screen (acts as heat sink)
5. signal cable
6. gland
7. leveling feet
8. printed circuit board
9. Desiccant (absorbs moisture)
10. level

 

Working Principle

Pyranometer works on the principle of Seebeck effect discussed above.

the glass dome 2 and 3, limit spectral response from 300 to 2,800nm and shields the thermopile sensor from convection.Black coating on thermopile sensor absorbs solar radiation which is converted to heat, that heat flows through the sensor to the Pyranometer housing. Now the Seebeck effect comes into play.

Due to Thermoelectric effect (point between 1 and 4), the thermopile sensor
generates a voltage output signal that is proportional to the solar radiation.

And this is how the pyranometer measures the solar radiation.

Advantages of Pyranometer

1. It exhibits very small temperature coefficient.
2. Show linear response.
3. Pyranometers are calibrated according to ISO standards.
4. Longer response than a photovoltaic cell(hence prefered over PV cells)
5. Integrated measurement of the total available short-wave solar energy
   under all working conditions.
6. More accurate measurements of performance index and performance ratio,
   

 

Applications of Pyranometer

1. For predicting insulation requirements for building structures.
2. For ideally locating commercial greenhouses.
3. Also employed for designing commercial solar power systems.
4. Are also used for meteorological and climatological studies.
5. Measuring of solar intensity data

This was pyranomter in a nutshell. Pyranometers are widely used by energy auditors and researchers.