The Atmospheric Radiation Measurement user facility, U.S. Department of Energy (DOE)
Energy, Electronics and Process Laboratory Université de la Réunion, Saint-Denis
- Global (Total) and Diffuse irradiance in W.m-2
- WMO sunshine threshold: 120 W.m-2 direct beam
- DNI (Direct Normal Irradiance) calculations
- Sunshine status
- No moving parts, shade rings or motorised tracking
The SPN1 Pyranometer is a precision solar radiation measurement instrument with a ground glass dome, and is designed for long-term outdoor exposure. It is an affordable and effective alternative to shade-ring pyranometers, pyrheliometers and traditional sunshine recorders.
Video – Introduction to SPN1
The SPN1 Pyranometer is exceptionally easy to use; it needs no routine adjustment or polar alignment and works at any latitude.
An internal heater keeps the pyranometer dome clear of dew, ice and snow down to -20°C (in still air conditions), ensuring reliable readings in difficult climatic conditions.
SPN1 Pyranometer Resource Centre
The Resource Centre contains a wide range of application and technical information for the SPN1 – covering DNI calculation, tilt correction, performance validation, and much more. Visit the SPN1 Resource Centre.
Direct and Diffuse Radiation
The pyranometer uses an array of seven miniature thermopile sensors and a computer-generated shading pattern to measure the direct and diffuse components of incident solar radiation. It computes direct radiation by subtracting the diffuse from the global (total) radiation.
The WMO threshold for bright sunshine is 120 W.m-2 in a plane perpendicular to the direct solar beam. The SPN1 Pyranometer uses an algorithm based on the ratio of direct to diffuse radiation, combined with their absolute values, to estimate sunshine duration to within a few percent of the WMO standard.
The SPN1 Pyranometer does not need to be adjusted or repositioned to track the sun – a distinct advantage over devices with shadow rings. There are no complex electro-mechanical assemblies and no burnt paper tracks to interpret.
Outputs and logging
The SPN1 Pyranometer provides 2 analogue voltage outputs for global and diffuse radiation, and a digital output for sunshine duration, which can be connected to data loggers, such as the Delta-T Devices GP2 and the compact GP1.
Readings can also be obtained directly from the RS232 port and viewed/logged using the SunData software supplied.
The GP1 Data Logger from Delta-T Devices is a powerful general purpose data logger that provides a low cost logging solution for the SPN1 Pyranometer.
The SPN1 Pyranometer is ideally suited to multiple solar radiation measurement application areas, including PV (photovoltaic) efficiency monitoring, air pollution studies, cloud cover research, ET and heat flux studies, canopy analysis, and building energy management systems. For further information please visit the SPN1 Resource Centre.
Evaluation of the SPN1 Pyranometer for measuring Total Optical Depth
Prof Victor Estelle’s Solar Radiation Research group at the University of Valencia has been running an SPN1 Pyranometer alongside Cimel and Prede sun photometers to see how it compares with these higher precision but more complex instruments. Their findings indicate a relatively good correspondence – scientific posters were presented at Skynet Rome 2016 and EGU Vienna 2016.
Direct-Normal Irradiance (DNI) is the amount of solar radiation arriving in unit time at the Earth’s surface on a unit area perpendicular to the direction to the Sun. It is a common practice to compare solar panel efficiency to DNI, particularly in field trials. Output from an SPN1 Pyranometer allows calculation of DNI in sun tracking, horizontal and tilted installations.
Read more about the SPN1 Pyranometer and DNI Calculation in the “SPN1 Technical Fact sheet“.
There are two ways to calculate DNI:
1) DNI Firmware: The SPN1 Pyranometer can calculate DNI (requires firmware version 1.08 or later). The results are only available on the Serial output and requires the use of a Terminal program or similar to send RS232 commands and receive the results. For more information download Use of the DNI Function in SPN1 Firmware. To upgrade the SPN1 firmware to the required version 1.08 contact techsupport@delta-T.co.uk
2) DNI Spreadsheet: You can download an Excel spreadsheet add-in to calculate DNI from the output of a horizontally mounted SPN1 Pyranometer, using data logged from either the analogue or serial outputs. Download the spreadsheet here.
SPN1 Pyranometer – comparison with BF5 Sunshine Sensor
The SPN1 Pyranometer is a precision version of the BF5 Sunshine Sensor and although the two instruments have some features in common, there are important differences. These are explained in the Summary of differences between the SPN1 and BF5 technical note.
Please note that research literature sometimes refers to the SPN1 Pyranometer as the SPN1 Radiometer.
For simultaneous outputs of total radiation, diffuse radiation and sunshine status.
|Overall accuracy: Total (Global)
and Diffuse radiation
±5% Daily integrals
±5% ±10 W.m-2 Hourly averages
±8% ±10 W.m-2 Individual readings
|0.6 W.m-2 =0.6 mV
|0 to >2000 W.m-2
|Analogue output sensitivity
|1 mV=1 W.m-2
|Analogue output range
|0 – 2500 mV
|Sunshine status threshold
|120 W.m-2 in the direct beam
|Accuracy: Sunshine status
|±10% sun hours with respect to the threshold
|Accuracy: Cosine correction
|±2% of incoming radiation over 0-90° Zenith angle
|Accuracy: Azimuth angle
|±5% over 360° rotation
|0.02% per °C (typical)
|-40 to + 70°C
|Recalibration recommended every 2 years
|100 ms (typical)
|400 – 2700 nm
|Spectral sensitivity variation
|< 3 W.m-2 for a change of 5°C/hr in ambient temperature
< 3 W.m-2 dark reading
|-90° to + 90°
|Sunshine status output
|No sun=open circuit
Sun=short circuit to ground
|2 mA (awake ), <30 µA (asleep)
5 V – 15 V DC
|12 V – 15 VDC, up to 1.5 A
|Signal output & power-in connector
|8 pin M12
|3 x M5 tapped holes in base at 108 mm dia, 120° spacing
|Size & Weight
|126 mm dia. x 94 mm high, 786g