Pyranometer specifications explained

Understanding Pyranometer Specifications. 

The world of pyranometer specifications is a tricky one to navigate, and often picking the correct pyranometer for your application is critical. With so many variables in pyranometer specifications, it is important to understand what each is and its effects on your measurements. Without further introduction, we present the ESS Earth Sciences guide to pyranometer specifications. 

Notes:

  1. As we ESS are premier distributors of Kipp and Zonen irradiance sensors we will be primarily focusing on these. However, the specifications are broadly applicable to all makes and models. Many specifications are outlined in the ISO 9060:1990 classifications.
  2. Most specifications apply to all solar irradiance sensors such as pyrheliometers and pyrgeometers. However, this guide focuses on pyranometers. 
SPM10 pyranometer quartz dome for measuring solar irradiance. Choosing the correct pyranometer means obtianing the most cost effective data for your application.
SMP10 Pyranometer with sun shield

Pyranometer specifications, a guide:

Pyranometer Classification

This relates to the overall performance of the pyranometer and how they compare to the ISO 9060:1990 standard. There are 4 classifications although only three are applicable to commercial solar irradiance sensors. Generally speaking solar farms and serious meteorological studies should utilise Class A irradiance sensors, as they offer superior performance which offers better cost-benefit in these sectors.

  • Reference Grade – The gold standard of irradiance sensor to measure all pyranometers against. They are literally world standard. Not commercially viable to own. 
  • Spectrally Flat Class A pyranometer – The highest grade of pyranometer commercially available (SMP and CMP 10, 11, 21, 22 pyranometers). Used to called Secondary Standard)
  • Spectrally Flat Class B pyranometer – High level of performance but does not meet the Class A standard (SMP and CMP 6). Previously, First Class. 
  • Spectrally Flat Class C pyranometer – Good quality performance but does not meet Class B criteria (SMP and CMP 3). Previously called Second Class.

ISO 9060:1990 standards

 Pyranometer Specifications Spectrally Flat Class ASpectrally Flat Class BSpectrally Flat Class C
Response time (95% response)< 15 S< 30s< 60S
Zero off-set
(a) Response to 200 W/m² net thermal radiation (ventilated)

(b) Response 5 K/hr change in ambient temperature
± 7 W/m²
± 2 W/m²
± 15 W/m²
± 4 W/m²
 ± 30 W/m²
± 8 W/m²
Non-stability (change per year, percentage of full scale)± 0.8 %± 1.5 %± 3.0 %
Non -linearity (percentage deviation from the responsivity at 500 W/m² due to  any change of irradiance within the range 100 to 1000 W/m²)± 0.5 %± 1 %± 3 %
Directional response for beam radiation (The range of errors caused by assuming that the normal incidence responsivity is valid for all directions when measuring, from any direction, beam radiation whose normal incidence irradiance is 1000 W/m²) Commonly defined as up to 80° zenith angle.± 10 W/m²± 20 W/m²± 30 W/m²
Spectral selectivity (percentage of deviation of the product of spectral absorptance and spectral transmittance from the corresponding mean within 0.35 µm and 1.5 µm)± 3 %± 5 %± 10 %
Temperature response (percentage deviation due to change in ambient temperature within an interval of 50 K)2%4%8%
Tilt response (percentage deviation from the responsivity at 0° tilt, horizontal, due to change in tilt from 0° to 90° at  1000 W/m² irradiance)± 0.5 %± 2 %± 5 %
ISO 9060:1990 standards for solar irradiace sensors

Sensitivity – analogue pyranometers only

Sensitivity’s units equals microvolts per Watt per metre squared or µV/W/m². It relates to the interpretation of the ourput the overall solar irradiance received. A narrower range will increase resolution.

Impedance – analogue pyranometers only

Relates to the total electrical resistance generated by the junctions, wires and connections within the pyranometer.

Expected output range – analogue pyranometers only

Measured in µV, this is what the output ‘signal’ of the pyranometer will be. Dataloggers record the µV outputs and converted them to W/m² (this occurs either within the logger or elsewhere). The output is directly proportional to solar radiation received by the thermopile sensors.

Maximum Operational Irradiance

Maximum solar irradiance the pyranometer is able to receive before damage is likely to occur. The lowest value for a Kipp and Zonen pyranometer is 2000 W/m2. The solar constant (average received on earth per W/m2)  is approximately 1370 W m-2 so the maximum limit is unlikely to be exceeded during studies performed on earth. Higher grade pyranometer have a maximum irradiance of 4000 W/m-2

Response time (63%) and Response time (95%)

There are a couple of details to break down here. Firstly what is response time, and secondly what’s with the 63% and 95%? For some applications response time is not critical. However, for applications such as concentrated solar power stations, where the ramping up and down of supply to meet demand is dependant on clouds moving, a fast response time of pyranometers and pyrheliometers is paramount. As such, this is one of the more important pyranometer specifications within the solar industry.

Response time refers to the amount of time it takes a radiometer to react to the change in the measured parameter. Think about how your eyes react to a change in light. The response is not always immediate, adjustment is needed sometimes. The response time is a factor of the thermopile and overall radiometer construction. Higher quality materials and components mean a higher quality response time.

The response time (measured in seconds) values are broken down to 63% and 95%. 63% refers to the seconds it takes for the pyranometer’s output to reach 63% of the final value of the step-change in irradiance. Similarly the 95% refers to the time taken to reach 95% of the final output.

Spectral Range (20% point and 50% points)

Again a few things to break down here.

Spectral range refers to the spectrum of electromagnetic radiation. The electromagnetic spectrum broadly ranges from gamma radiation (0.5µm wavelength) to radiowaves (500,000,000 µm wavelength) Standard PV solar panels produce energy (in the form of electricity) from wavelengths roughly between 200 – 700 µm. This range lies somewhere between UV radiation and near Infrared radiation.

Pyranometers produce outputs to a wide spectral range, usually between 210 to 3600 µm. As such they are ideal for measuring UV light, visible light, and near-infrared radiation.

The 50 % points are the wavelengths where the output of the instrument is 50 % reduced with 100 % input.

50% spectral range
50% Point of Spectral Range. Note this is an approximate graph to demonstrate the 50% response time and, not a true logarithmic scale.

Zero offsets (unventilated)

(a) thermal radiation

Up close shot of a Kipp and Zonen SMP10 pyranometer dome. Choosing the right pyranometer is difficult with so many variations.
Note the two domes of the SMP10 pyranometer to minimise heat transfer.

(b) temperature change

Firstly we must understand a little about how a pyranometer functions (click here for an in-depth look). The thermopile sensor of a pyranometer requires a difference in temperature between the hot and cold junctions of the thermopile. This temperature difference creates a very small voltage. The voltage is proportional to the solar radiation received (more radiation = more voltage). Dataloggers measure the voltage output then calculate solar irradiance in W m2 from the mV – this ties in with the expected output range.

But what does this have to do with zero offsets? Well, in some cases the thermopile sensor is warmer than the surrounding atmosphere (specifically the dome). When this happens heat energy moves away from the sensor to the dome and eventually to the atmosphere. In these cases, a negative output occurs, this is called a Zero Offset Type A. This is perfectly normal and experienced mostly during the night. Fitting a ventilator such as the CVF4 will minimise effects. More advanced pyranometers have two domes to reduce radiative transfer as much as possible.

Zero Offset Type B – temperature change, refers to the pyranometers response to temperature changes to the surrounding air. It is to help account for small fluctuations in the air temperature. It is quantified in ISO 9060:1990 as the response in W/m² to a 5 K/hr change in ambient temperature.

Non-stability (change/year)

This is the percentage change in sensitivity over one year. This effect is mostly due to UV radiation degrading the black absorber coating on the thermopile surface. The blacker the sensor the more radiation it is able to absorb, this makes it more accurate. UV radiation will ‘fade’ the black over time as it would any material left in the sun for an extended period.

The lower this % change is, the better. Kipp and Zonen’s SMP22 is 0.5%. It is because of this drift that re-calibration is needed periodically to reset the pyranometer and understand how the measurements have changed over time.

Non-linearity (100 to 1000 W/m²)

An ISO 9060:1990 definition: As the percentage deviation in the sensitivity over an irradiance range from 100 to 1000 W/m² compared to the sensitivity at the calibration irradiance of 500 W/m².

The non-linear effect is predominantly caused by convective and radiative heat loss at the black sensor’s surface. This makes the conditional thermal equilibrium of the radiometer non-linear.

Directional Response (up to 80° with 1000W/m² beam)

Radiation incident on a flat horizontal surface originating from a point source with a defined zenith position (such as the sun) will have an intensity value proportional to the cosine of the zenith angle of incidence.

Ideally, a pyranometer has a directional response the same as the cosine-law. However, pyranometer’s directional responses are influenced by the detector and by the quality of the dome. The maximum deviation from the ideal cosine-response of the pyranometer is given up to 80° angle of incidence with respect to 1000 W/m² irradiance at normal incidence (0° zenith angle). With thanks to Kipp and Zonen for this explanation.

Pyranometer Directional Response

Spectral selectivity

The variation of the dome transmittance and absorption coefficient of the black detector coating with wavelength. It is commonly specified as % of the mean value.

Tilt Response (0° to 90° at 1000 W/m²)

Deviation of accuracy caused by tilting the pyranometer from between 0° to 90° at 1000 W/m² normal incidence irradiance. The % is very low with Kipp and Zonen pyranometers, the CMP3 for example is 1%, the CMP/SMP 10, 21, and 22 is 0.2%. Information required for calculations of solar irradiance for POA angled pyranometers, although the effect is negligible.

Temperature Response

As defined by the ISO 9060:1990: the percentage deviation due to change in ambient temperature within an interval of 50 K. Given as a percentage, the lower the percentage the lower the deivation. A CMP3 will have a temperature response of 5%, where as an CMP22 has a temperature response of 0.5%.

Field of view

How much can the irradiance sensor ‘see’. This affects the sensor’s maximum exposure possible to incoming radiation. As pyranometers measure Global Horizontal Irradiance (all incoming irradiance on a horizontal plane) when flat they must detect all the incoming radiation from above so a 180° field of view is needed. In contrast, a pyrheliometer only measures direct radiation (a narrow beam), it must have a restricted field of view to approximately 5°.

Solar irradiance direct normal diffuse global horizontal irradiance
Pyranometer and pyrheliometer measuring solar irradiance. The Pyranometer on the left measures GHI (includes DIF and DNI) with its 180° field of view. The Pyrheliometer measures DNI with its 5° field of view.

Detector type

The sensor used within the irradiance instrument. Kipp and Zonen’s CMP and SMP pyranometers use superior thermopile sensors. However, silcone sensor pyranometers are also available.

Operating and storage temperatures

Maximum and minimum temperatures the pyranometers can be exposed to before damage occurs. The operating temperature can be increased with a CVF4 ventilation unit.

Humidity range

Pyranometer cable and connector kipp and zonen
SMP10 Cable and connector

Maximum and minimum exposure levels of humidity a pyranometer can withstand before damage occurs. As pyranometers have desiccant and an ingress protection rating of IP67 they can operate in 100% humidity. In fact, Kipp and Zonen pyranometers can operate underwater. As a result, this is one of the least important of the pyranometer specification.

Mean Time Between Failtures

The predicted elapsed time between inherent failures of a mechanical or electronic system, during normal system operation. source: https://en.wikipedia.org/wiki/Mean_time_between_failures.

Supply voltage – SMP series only

Power supply required for SMP pyranometers to function.

We hope you have found this pyranometer specification guide useful. We welcome ideas for future guides on any of our products, just get in touch and let us know.

CMP SERIES SPECIFICATIONS

Downloadable CMP pyranometer specifications PDF here.
 PYRANOMETER  SPECIFICATIONS CMP SERIES
SPECIFICATIONCMP3CMP6CMP10/CMP11CMP21CMP22
Classification to ISO 9060:1990Class CClass BClass AClass AClass A
Sensitivity5 to 20µV/W/m²5 to 20µV/W/m²7 to 14µV/W/m²7 to 14µV/W/m²7 to 14µV/W/m²
Impedance20 to 200Ω20 to 200Ω10 to 100Ω10 to 100Ω10 to 100Ω
Expected output range (0 to 1500 W/m²)0 to 30mV0 to 30mV0 to 20mV0 to 20mV0 to 20mV
Maximum operational irradiance2000 W/m²2000 W/m²4000 W/m²4000 W/m²4000 W/m²
Response time (63 %)< 6 s< 6 s< 1.7 s< 1.7 s< 1.7 s
Response time (95 %)< 18 s< 18 s< 5 s< 5 s< 5 s
Spectral range
(20 % points)
285 to 3000nm270 to 3000nm270 to 3000nm270 to 3000nm210 to 3600nm
(50 % points)300 to 2800nm285 to 2800nm285 to 2800nm285 to 2800nm250 to 3500nm
Zero offsets (unventilated)     
(a) thermal radiation (at 200 W/m²)< 15 W/m²< 10W/m²< 7W/m²< 7W/m²< 3W/m²
(b) temperature change  (5 K/h) < 5 W/m²< 4 W/m²< 2W/m²< 2W/m²< 1W/m²
Nonstability (change/year) < 1%< 1%< 0.5%< 0.5%< 0.5%
Non-linearity (100 to 1000 W/m²) < 1.5%< 1%< 0.2%< 0.2%< 0.2%
Directional response (up to 80 ° with 1000 W/m² beam)< 20 W/m²< 20 W/m²< 10 W/m²< 10 W/m²< 5W/m²
Spectral selectivity (350 to 1500 nm)< 3%< 3%< 3%< 3%< 3%
Tilt response (0 ° to 90 ° at 1000 W/m²)< 1%< 1%< 0.2%< 0.2%< 0.2%
Temperature response< 5% (-10 °C to +40 °C)< 4% (-10 °C to +40 °C)< 1% (-10 °C to +40 °C)< 1% (-20 °C to +50 °C)< 0.5% (-20 °C to +50 °C)
Field of view180 °180 °180 °180 °180 °
Accuracy of bubble level< 0.2 °< 0.1 °< 0.1 °< 0.1 °< 0.1 °
Temperature sensor outputNANANA10 k Thermistor (optional Pt-100)10 k Thermistor (optional Pt-100)
Detector typeThermopileThermopileThermopileThermopileThermopile
Operating and storage temperature range-40 °C to +80 °C-40 °C to +80 °C-40 °C to +80 °C-40 °C to +80 °C-40 °C to +80 °C
Humidity range0 to 100%0 to 100%0 to 100%0 to 100%0 to 100%
MTBF (Mean Time Between Failures)> 10 years> 10 years> 10 years> 10 years> 10 years
Ingress Protection (IP) rating6767676767
Onsite pyranometer uncertaintyCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty App
Recommended applicationsEconomical solution for routine measurements in weather stations, field testing.Good quality measurements for hydrology networks, greenhouse climate control.Meteorological networks, PV panel and thermal collector testing, materials testing.Meteorological networks, reference measurements in extreme climates, polar or arid.Scientific research requiring the highest level of measurement accuracy and reliability.
Table of CMP pyranometer specifications – Kipp and Zonen Pyranometers.

SMP SERIES SPECIFICATIONS

Downloadable CMP pyranometer specifications PDF here.

 PYRANOMETER SPECIFICATIONS  SMP SERIES
SPECIFICATIONSMP3SMP6SMP10/SMP11SMP21SMP22
Classification to ISO 9060:1990Class CClass BClass AClass AClass A
Analogue output V-version0 to 1V0 to 1V0 to 1V0 to 1V0 to 1V
Analogue output range -200 to 2000W/m² -200 to 2000W/m² -200 to 2000W/m² -200 to 2000W/m² -200 to 2000W/m²
Analogue output A-version4 to 20mA4 to 20mA4 to 20mA4 to 20mA4 to 20mA
Analogue output range0 to 1600W/m²0 to 1600W/m²0 to 1600W/m²0 to 1600W/m²0 to 1600W/m²
Serial outputRS-485 Modbus®RS-485 Modbus®RS-485 Modbus®RS-485 Modbus®RS-485 Modbus®
Serial output range -400 to 2000W/m² -400 to 2000W/m² -400 to 4000W/m² -400 to 4000W/m² -400 to 4000W/m²
Response time (63 %)< 1.5 s< 1.5 s< 0.7 s< 0.7 s< 0.7 s
Response time (95 %)< 12 s< 12 s< 2 s< 2 s< 2 s
Spectral range (20 % points)285 to 3000nm270 to 3000nm270 to 3000nm270 to 3000nm210 to 3600nm
(50 % points)300 to 2800nm285 to 2800nm285 to 2800nm285 to 2800nm250 to 3500nm
Zero offsets (unventilated)     
(a) thermal radiation (at 200 W/m²)< 15W/m²< 10W/m²< 7 W/m²< 7 W/m²< 3 W/m²
(b) temperature change  (5 K/h) < 5W/m²< 4W/m²< 2 W/m²< 2 W/m²< 1 W/mm²
Nonstability (change/year) < 1%< 1%< 0.5%< 0.5%< 0.5%
Non-linearity (100 to 1000 W/m²) < 1.5%< 1%< 0.2%< 0.2%< 0.2%
Directional response (up to 80 ° with 1000 W/m beam)< 20W/m²< 15W/m²< 10 W/m²< 10W/m²< 5 W/m²
Temperature response< 2% (-20 °C to +50 °C)< 1.5% (-20 °C to +50 °C)< 1% (-20°C to +50 °C)< 0.3% (-20°C to +50 °C)< 0.3% (-20°C to +50 °C)
 < 4% (-40 °C to +70 °C)< 3% (-40 °C to +70 °C)< 2% (-40 °C to +70 °C)< 0.3% (-40 °C to +70 °C)< 0.3% (-40 °C to +70 °C)
Spectral selectivity (350 to 1500 nm)< 1%< 1%< 1%< 1%< 2%
Tilt response (0 ° to 90 ° at 1000 W/m²)< 1%< 1%< 0.2%< 0.2%< 0.2%
Field of view180 °180 °180 °180 °180 °
Accuracy of bubble level< 0.2 °< 0.1°< 0.1 °< 0.1 °< 0.1 °
Power consumption (at 12 VDC)V-version: 55mWV-version: 55mWV-version: 55mWV-version: 55mWV-version: 55mW
 A-version: 100mWA-version: 100mWA-version: 100mWA-version: 100mWA-version: 100mW
Software, Windows™Smart Sensor Explorer Software, for configuration, test and data logging.Smart Sensor Explorer Software, for configuration, test and data logging.Smart Sensor Explorer Software, for configuration, test and data logging.Smart Sensor Explorer Software, for configuration, test and data logging.Smart Sensor Explorer Software, for configuration, test and data logging.
Supply voltage5 to 30VDC5 to 30VDC5 to 30VDC5 to 30VDC5 to 30VDC
Detector typeThermopileThermopileThermopileThermopileThermopile
Operating and storage temperature range-40 °C to +80 °C-40 °C to +80°C-40 °C to +80 °C-40 °C to +80 °C-40 °C to +80 °C
Humidity range0 to 100%0 to 100%0 to 100%0 to 100%0 to 100%
MTBF (Mean Time Between Failures)> 10 years> 10 years> 10 years> 10 years> 10 years
Ingress Protection (IP) rating6767676767
Onsite pyranometer uncertaintyCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty AppCalculate with Suncertainty App
Recommended applicationsEconomical solution for efficiency and maintenance monitoring of PV power installations, routine measurements in weather stations, agriculture, horticulture and hydrology.Good quality measurements for Solar Monitoring, hydrology networks, greenhouse climate control.High performance for PV panel and thermal collector testing, solar energy research, solar prospecting, materials testing, advanced meteorology and climate networks.Meteorological networks, reference measurements in PV monitoring, extreme climates, polar or arid.Scientific research requiring the highest level of measurement accuracy and reliability under all conditions.
Table of SMP pyranometer specifications – Kipp and Zonen Pyranometers.