Accurate solar radiation measurements

Reliable measurements

Conducting reliable and accurate solar radiation measurements requires some knowledge and attention: think of environmental influences (wind, rain/snow, soling), re-calibration (bi-annually), not to mention data processing, spectral effects, etc. Essentially, accurate broadband solar radiation measurements are obtained using two components: a suitable set of pyranometers, including an optional pyrheliometer (DNI sensor) with sun tracker, and an adequate data logger.

Simple rules

EKO’s broadband pyranometer product line includes instruments of all ISO classes, ranging from the Second Class MS-40, via the First Class MS-60, up to the top-class Secondary Standard MS-80. The highly accurate MS-57 pyrheliometer combines unprecedented fast response time with a minimal temperature dependency.

EKO’s pyranometers and pyrheliometer have a flat spectral response which measure the broadband solar radiation homogeneously. Technically speaking, only pyranometers and pyrheliometers measure the broadband solar radiative fluxes correctly. Broadband radiation sensors are physical instruments which provide accurate measurements. Every user of such radiation sensors needs a reasonable awareness of their measurement quality. By taking into account some simple rules the data product generated by these radiometers will fulfil the requirements for your applications.

HOW-TO Application Guide

1

Method of application

Verify if the radiation measurement method of your application is described in norms, regulations or standards; there is a reason why those instructions give guidelines for radiation measurements; take these considerations into account when choosing your radiometer system.

2

Data quantity

Determine the interval of data you will need: daily totals or one minute values or something in between. The shorter the timing, the higher the quality of the radiometer must be. There is an ISO classification for pyranometers which is widely used and which states useful information about instruments and accuracies (see ISO 9060, also look at “CIMO Guide”, publication WMO-No. 8). Note, that an ISO secondary standard pyranometer, such as the MS-80, is the highest class pyranometer commercially available.

3

Data redundancy

Will you have data redundancy, meaning that more than one instrument is available to measure the radiative quantity? This significantly increases the quality of the measurements as any irregularities can be discovered quickly. For example, use a DNI sensor, i.e. the MS-57, along with a suntracker, shading ball assembly and two MS-80 pyranometers to measure all three components, which are the direct-normal, the diffuse and the global solar irradiance.

4

Data quality

Take care of data quality and instrument maintenance, such as cleaning, re-calibration, etc. It is very important not to lose sight of your radiation sensors: no instrument works well when its soiled or polluted. Furthermore, re-calibration is a logical, recurring necessity. Some critical maintenance procedures are built into EKO’s turn-key evaluation systems. The MV-01 ventilation units and heater can be combined with the sensor to improve the data availability under all conditions.