Apogee Silicon-Cell Pyranometers
Accurate and stable global shortwave radiation measurement in W m-2. Durable, and cost-effective, the range of Apogee Silicon-cell Pyranometers all feature a silicon-cell detector:
- SP-110 Millivolt Pyranometer;
- SP-212 Volt Pyranometer;
- SP-214 4-20mA Pyranometer, SP-215;
- SP-230 Heated Pyranometer;
- SP-420 Smart Pyranometer;
- SP-421 (SDI-12) Pyranometer;
- SP-422 Modbus Digital Output Silicon-cell Pyranometer
Silicon-cell Pyranometer Introduction
Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength rage 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 (W m-2, equal to Joules per second per square meter).
Pyranometers are sensors that measure global shortwave radiation. Apogee 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 meet the International Organization of Standardization (ISO) 9060:2018 Class C requirements.
Apogee Instruments SP series pyranometers consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space and domed-shaped head making the sensor fully weatherproof and self-cleaning, designed for continuous total shortwave radiation measurement on a planar surface in outdoor environments. SP series sensors output an analog 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.
Typical Applications
Total shortwave radiation is an important component in determining evapo-transpiration rates, energy balance, net radiation. Sensors are also used to optimize photovoltaic systems and solar panel arrays. Applications include shortwave radiation measurement in agricultural, ecological, and hydrological weather networks.
SP-110 Millivolt Pyranometer
The SP-110 is a low cost yet highly accurate self-powered sensor with a millivolt output and exhibits excellent cosine response. The SP-110 is ideally supported by the LSM3 Light Sensor Meter for Pyranometers for data logging and long term monitoring.
SP-212 Volt Pyranometer
The SP-212 is an amplified sensor with a 0-2.5 volt output and exhibits excellent cosine response.
SP-214 4-20mA Pyranometer
The SP-214 is an amplified sensor with a 4-20 mA output and exhibits excellent cosine response. The sensor was designed for use in environments with significant background electrical noise that can be found in many industrial applications.
SP-230 Heated Pyranometer
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). Apogee combined a tiny internal heater (0.18 Watt), a dome-shaped head, and an elevated base to keep the SP-230 tracking an 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-420 Smart Pyranometer
The new SP-420 smart pyranometer can be connected directly to a computer for taking spot measurements or graphing and datalogging real-time shortwave radiation using the included software. The sensor can also act as a stand-alone shortwave radiation datalogger by simply connecting it to any standard 5 V DC USB power plug. Internal memory within the sensor head is capable of storing 10,000 user-specified periodic measurements that can be downloaded as a CSV file to a computer for analysis.
SP-421 (SDI-12) Pyranometer
The SP-421 is a digital pyranometer sensor with SDI-12 communication protocol.
SP-422 Modbus Digital Output Silicon-cell Pyranometer
The SP-422 sensor outputs a digital signal using Modbus RTU protocol over RS-232 or RS-485. The sensor incorporates a silicon-cell photodiode with a rugged, self-cleaning sensor housing design, and high-quality cable terminating in pre-tinned pigtail leads for easy connection to dataloggers and controllers. Typical applications include shortwave radiation measurement in agricultural, ecological, and hydrological weather networks. Sensors are also used to optimize photovoltaic systems. Sensor includes IP68 marine-grade stainless-steel cable connector to simplify sensor removal and replacement for maintenance and recalibration.
Calibration Traceability
Apogee Instruments SP series pyranometers are calibrated through side-by-side comparison to the mean of four Apogee SP-110 transfer standard pyranometers (shortwave radiation reference) under high intensity discharge metal halide lamps. The transfer standard pyranometers are calibrated through side-by-side comparison to the mean of at least two ISO-classified reference pyranometers under sunlight (clear sky conditions) in Logan, Utah. Each of four ISO-classified reference pyanometers are recalibrated on an alternating year schedule (two instruments each year) at the National Renewable Energy Laboratory (NREL) in Golden, Colorado. NREL reference standards are calibrated to the World Radiometric Reference (WRR) in Davos, Switzerland.
Accurate Measurements – ISO 9060:2018
Calibration in controlled laboratory conditions is traceable to the World Radiometric Reference in Davos, Switzerland. The upward-looking model is cosine corrected, with directional errors less than 20 W m-2 at 80° solar zenith angle. Long-term non-stability determined from multiple replicate pyranometers in accelerated aging tests and field conditions is less than 2 % per year.
Rugged, Self-cleaning Housing
Patented domed shaped sensor head (diffuser and body) facilitate runoff of dew and rain to keep the diffuser clean and minimize errors caused by dust blocking the radiation path. Sensors are housed in a rugged anodize aluminum body and electronics are fully potted.
Output Options
Multiple analog output options are available including: 4 to 20 mA, 0 to 2.5 V, 0 to 5.0 V, and 0 to 350 mV ranges. The silicon-cell pyranometer is also available attached to a hand-held meter with digital readout, and as a digital ‘smart’ sensor that uses USB communication and custom software to interface directly to a computer.
Heated Option
A heated pyranometer (SP-230 All-season) is available with a 0.2 W heater to keep water (liquid and frozen) off the sensor and minimize errors caused by dew, frost, rain, or snow blocking the optical path.
High Quality Cable
Pigtail-lead sensors feature an IP68, marine-grade stainless-steel cable connector approximately 30 cm from the head to simplify sensor removal for maintenance and recalibration. Cable is shielded-twisted pair wire with a TPR jacket for high water resistance, UV stability, and flexibility in cold conditions.
| SP-110 | SP-212 | SP-214 | SP-215 | SP-230 | SP-420 | SP-421 | |
|---|---|---|---|---|---|---|---|
| ISO 9060:2018 | Class C (previously known as second class) | ||||||
| Power Supply | Self-powered | 3.3 to 24 V DC; current draw 10 µA | 7 to 24 V DC, maximum current draw of 22 mA (2 mA quiescent current draw) | 5.5 to 24 V DC; current draw 10 µA | 12 V DC for heater with a current draw of 15 mA | – | – |
| Output (Sensitivity) | 0.2 mV per W m-2 | 2 mV per W m-2 | 0.008 mA per W m-2 | 4 mV per W m-2 | 0.2 mV per W m-2 | – | – |
| Output Type | 0 to 400 mV | 0 to 2.5 V | 4 to 20 mA | 0 to 5 V | 0 to 400 mV | USB | SDI-12 |
| Resolution | – | – | – | – | – | 0.1 W m-2 | – |
| Digital Input Voltage | – | – | – | – | – | – | 5.5 to 24 V |
| Calibration Factor (reciprocal of output) | 5 W m-2 per mV | 0.5 W m-2 per mV | 125 W m-2 per mA, 4 mA offset | 0.25 W m-2 per mV | 5 W m-2 per mV | Custom for each sensor and stored in the firmware | Custom for each sensor and stored in the firmware |
| Calibration Uncertainty | ± 5 % | ||||||
| Measurement Repeatability | Less than 1 % | ||||||
| Long-term Drift | Less than 2 % per year | ||||||
| Non-linearity | Less than 1 % up to 2000 W m-2 | ||||||
| Response Time | Less than 1 ms | Less than 1 ms | Less than 1 ms | Less than 1 ms | Less than 1 ms | Software updates every second | Less than 0.6 s |
| Field of View | 180° | ||||||
| Spectral Range | 360 to 1120 nm | ||||||
| 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; can be submerged in water up to depths of 30 m |
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| Dimensions | 24 mm diameter, 33 mm height | 24 mm diameter, 33 mm height | 24 mm diameter, 33 mm height | 24 mm diameter, 33 mm height | 24 mm diameter, 33 mm height | 24 mm diameter, 33 mm height | 24 mm diameter, 44 mm height |
| Mass (with 5 m of cable) | 90 g | 90 g | 140 g | 90 g | 90 g | 90 g | 177 g |