SolData 80SPC PYRANOMETER
Data and application notes


PURPOSE

The SolData 80SPC pyranometer is designed to measure global solar radiation. The instrument employs a photovoltaic solar cell which has been temperature compensated by means of a thermistor-resistor network. Each instrument is individually calibrated using to agree with secondary standard meteorological instruments. Our calibration reference has been checked against the World Radiometric Reference (WRR) according to World Meteorological Organization (WMO) Technical Regulations by Kipp & Zonen B.V. of Delft, Holland.

OPERATION

Secondary standard devices such as Eppley, Kipp-Zonen or YES instruments are based upon absorption of solar irradiance from 300-3000 nanometers by a blackened surface under one or more glass domes. These instruments measure the temperature difference between the irradiated surface and a reference point as measured by a thermopile to determine the solar irradiance. The SolData photovoltaic instrument depends upon the direct conversion of the solar irradiance on the solar cell to an electric current.

APPLICATIONS

The SolData instrument is useful for projects, laboratory exercises and demonstrations in science education. It has also been used successfully for monitoring solar irradiance on solar thermal and photovoltaic energy systems at locations all over the world. Daily measurements of global radiation using the SolData 80SPC will typically agree with broad band thermopile instruments to within +/-3%.

DESCRIPTION

TYPICAL CALIBRATION


Typical calibration results. The SolData pyranometer reacts instantaneously to changes in irradiance, while the thermopile instrument has a response time of several seconds, so data collected during cloud passages deviate from the straight line.

DAILY SOLAR IRRADIANCE


A SolData pyranometer will typically yield results like the data displayed here for a clear spring day in Denmark (56 N). The area under the curve corresponds to the total daily global solar energy e.g. measured in kWh per square meter.

TECHNICAL SPECIFICATIONS
Mass:400 gram
Size:100 x 100 x 25 mm
Cable:300 cm, 2 lead unshielded
Detector:Photovoltaic silicon cell
Spectral response:300-1150 nm (see note)
Spatial response:cosine to ca. 700
Supply voltage:none required
Output voltage:ca. 160 mV per kW/m2

The price of a photovoltaic instrument is about 10-20% of the price of a thermopile instrument. The high output signal makes is easy to collect data without amplification. Signal conditioning units are available if another voltage range is desired.

TEMPERATURE COMPENSATION


A SolData pyranometer is temperature compensated to within about +/-1% from -5 0C to 50 0C. Temperature compensation is achieved by means of a selected thermistor (NTC resistor)-shunt resistor combination.

APPLICATIONS EXAMPLE:

 A SolData instrument is compared with a Kipp-Zonen CM21. The instruments were mounted on a horizontal surface in Silkeborg, Denmark (56,1 N) a few weeks after the autumn equinox. Data was collected using a Grant type 1023 data logger. The SolData calibration factor is determined by comparing the instruments and correcting to air mass 1.5 (elevation angle 42 0).


Measurements of global irradiance on a horizonal surface using a SolData 80SPC and a Kipp-Zonen. To avoid the deviation visible in the afternoon, it is important that the receiving surfaces of the instruments be perfectly parallel. Any deviation becomes very apparent at high angles of incidence.

Responsivity variations are apparent in the early morning and late afternoon hours due to the high angle of incidence of the direct beam radiation. The error due to spectral shift in the direct beam toward the red due to Rayleigh scattering at high air mass values enhances the silicon detector sensitivity, while the cosine response deviation is of the opposite sign. These two errors tend to cancel. The remaining deviation is usually insignificant, because the radiation levels early and late in the day are small.

The global solar irradiance measured by the two instruments from 8 - 18 local time was as follows:
Kipp-Zonen: 4,307 kWh/m2
SolData 80spc: 4,232 kWh/m2
Deviation: -1,74%


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