The Apogee SP-230 All-Season Pyranometer is a game-changer in the measurement of solar radiation by finally eliminating the problem of snow, frost, and dew accumulating on the sensor—a problem that has been shown to drastically affect the accuracy of many radiometers all throughout the year (Malek, 2008).
We combined a tiny internal heater (0.18 Watt), a dome-shaped head, and an elevated base to keep the SP-230 tracking our expensive heated and ventilated reference pyranometer during the most severe weather—while using 1/80th the power.
The heater can be powered by a small solar panel and battery, even on short days at high latitudes.
SP-230 All-Season Pyranometer
|Power Supply:||Battery or Solar Panel|
|Sensitivity:||0.20 mV per W m-2|
|Calibration Factor:||5.0 W m-2 per mV (reciprocal of sensitivity)|
|Calibration Uncertainty:||± 5%|
|Measurement Repeatability:||< 1%|
|Non-stability (Long-term Drift):||< 2% per year|
|Non-linearity:||< 1% (up to 1750 W m-2)|
|Response Time:||< 1 ms|
|Field of View:||180°|
|Spectral Range:||360 nm to 1120 nm (wavelengths where response is 10 % of maximum)|
|Directional (Cosine) Response:||± 5% at 75° zenith angle|
|Temperature Response:||-0.04 ± 0.04% per °C|
|Operating Environment:||-40 to 70°C, 0 to 100% relative humidity|
|Dimensions:||2.40 cm diameter and 2.75 cm height|
|Mass:||90g (with 5m of lead wire)|
Eliminating the problem of snow, frost, and dew accumulating on the sensor, has allowed the SP-230 to be utilised all year round. It is powered by a small solar panel.
Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength range of 280 to 4000 nm (shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined as global shortwave radiation, or shortwave irradiance (incident radiant flux), and is expressed in Watts per square meter.
Pyranometers are sensors that measure global shortwave radiation. Apogee SP series pyranometers are silicon-cell pyranometers, and are only sensitive to a portion of the solar spectrum, approximately 350 – 1100 nm (approximately 80% of total shortwave radiation is within this range). However, silicon-cell pyranometers are calibrated to estimate total shortwave radiation across the entire solar spectrum. Silicon-cell pyranometer specifications compare favourably to specifications for World Meteorological Organisation (WMO) moderate and good quality classifications and specifications for International Organisation of Standardisation (ISO) second class and first class classifications, but because of limited spectral sensitivity, they do not meet the spectral specification necessary for WMO or ISO certification.
Apogee Instruments SP series pyranometers consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodised aluminium housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space and are designed for continuous total shortwave radiation measurement on a planar surface in outdoor environments. SP series sensors output an analogue voltage that is directly proportional to total shortwave radiation from the sun. The voltage signal from the sensor is directly proportional to radiation incident on a planar surface (does not have to be horizontal), where the radiation emanates from all angles of a hemisphere. Oxygen below 1% requires special calibration.