SRA20-D2 albedometer

Digital secondary standard albedometer

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SRA20-D2 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.

Introduction

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 design

SRA20-D2 consists of two identical pyranometers model SR20-D2, one facing up, one facing down. The two sensors are delivered with one fixture with rod (15 x 10-3 m diameter) for mounting purposes. A glare screen is part of the delivery too. The user assembles these modular components into SRA20-D2 albedometer. A mounting and fixation instruction is included. SRA20 can be ordered optionally with longer cables. SRA20-D2, including its sun screen fixation, connector and desiccant holder, is very robust. The albedometer has an incorporated temperature sensor.

The best albedometer for the PV industry

SRA20-D2 is the most accurate digital secondary standard albedometer available. Its benefits:

  • Digital outputs: easy implementation & servicing
  • Best-in-class temperature response
    < ± 0.4 % (-30 to +50 °C), best  “zero offset a” and best calibration uncertainty
  • 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

Suggested use

  • PV monitoring with Bifacial solar modules
  • high-accuracy meteorological observations
  • building physics, roof reflectance studies
  • extreme climates (tropical / polar)

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