Digital secondary standard albedometer

SRA20-D2 albedometer is an instrument that measures global and reflected solar radiation and the solar albedo, or solar reflectance, with the highest accuracy. It is composed of two SR20-D2 secondary standard pyranometers, one sun screen, one glare screen and one fixture with rod. Mounting hardware and tools are included. Each pyranometer offers two types of commonly used irradiance outputs: digital via Modbus RTU over RS-485 and analogue 4-20 mA (current loop). Individually tested for temperature and directional response, SRA20-D2 is the most accurate digital secondary standard albedometer available. SRA20-D2 complies with the latest ISO and WMO standards. The modular design facilitates maintenance and calibration.

  • Digital outputs: easy implementation & servicing
  • Best-in-class temperature response
  • Test certificates for temperature- and directional response included as required by ISO 9060
  • Re-calibration registers fully accessible to users
  • Modular; can be calibrated as separate pyranometers


Albedo, also called solar reflectance, is defined as the ratio of the reflected to the global radiation. The solar albedo depends on the directional distribution of incoming radiation and on surface properties at ground level. Albedos of typical surfaces range from about 4 % for fresh asphalt, and 15 % for green grass to 90 % for fresh snow.

Using SRA20-D2 albedometer is easy. The instrument is composed of two SRA20-D2 digital secondary standard pyranometers; the upfacing one measuring global solar radiation, the downfacing one measuring reflected solar radiation. SRA20-D2 offers two types of outputs commonly used in the solar PV industry: digital via Modbus RTU over RS-485 and analogue 4-20 mA (current loop). These industry standards allow for easy data acquisition, easy read-out and error-free instrument exchange when using SRA20-D2. The working principle and specifications of the pyranometers can be found in the SR20-D2 user manual. We recommend to use SRA20-D2 in particular in applications where the highest measurement accuracy is required.

SRA20-D2 consists of two identical pyranometers model SR20-D2, one facing up, one facing down. The two sensors should be ordered with one AMF02 albedometer mounting kit. AMF02 includes a fixture with rod for mounting purposes and a glare screen. The user assembles these modular components into SRA20-D2 albedometer. Mounting hardware, tools and a mounting and fixation instruction are part of the AMF02 delivery too.

Suggested Use

  • PV monitoring with Bifacial solar modules
  • High-accuracy meteorological observations
  • Building physics, roof reflectance studies
  • Extreme climates (tropical / polar)

Areas of Application

Meteorology / surface energy flux measurement
Solar energy / PV system performance monitoring


Longer cables, in multiples of 5 m, cable lengths above 20 m in multiples of 10 m






global solar radiation and reflected solar radiation

Measurement range

0 to 2000 W/m²

Optional measurand

albedo or solar reflectance ,net solar radiation

Included sensors

2 x identical ISO 9060 secondary standard pyranometer


mounting rod with 15 x 10⁻³ m diameter

Calibration uncertainty

< 1.2 % (k = 2)

Calibration traceability

to WRR

Spectral range

285 to 3000 x 10⁻⁹ m

Rated operating temperature range

-40 to +80 °C

Temperature response

< ± 0.4 % (-30 to +50 °C)

Temperature response test and directional response test of individual instrument

Reports included

Standard cable length

2 x 5 m (see options)

Communication protocol

Modbus over 2-wire RS-485

Transmission mode


Rated operating voltage

5 to 30 VDC range

Power consumption

< 150 x 10⁻³ W at 12 VDC (in total)


irradiance in W/m²

Transmitted range of 4-20 mA output

0 to 1600 W/m²

Rated operating voltage of 4-20 mA output

5.5 to 40 VDC range

- main supply

< 150 x 10⁻³ W at 12 VDC (in total)

- 4-20 mA current loop

< 80 x 10⁻³ W at 12 VDC, with recommended 2 x 100 Ω shunt resistors


(2 x) SR20-D2 secondary standard pyranometer

Included with AMF02

(1 x) glare screen; (1 x) fixture with rod; (2 x) o-ring; (1 x) conical positioner); (2 x) plug (pre-mounted); (2 x) M5x12 socket head cap screw; (1 x) M6x10 socket head cap screw; (2 x) M6x12 set screw (pre-mounted); (1 x) instruction sheet


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