Development of a Camera-based Measurement System for Circumsolar Radiation

CAD drawing of novel CSR camera
© Fraunhofer ISE
CAD drawing of novel CSR camera.
Detail of a false colour High Dynamic Range (HDR) image
© Fraunhofer ISE
Detail of a false colour High Dynamic Range (HDR) image taken on 2020/02/21 at Fraunhofer ISE in Freiburg im Breisgau, Germany. The intensity is normalized to a maximum value of one on the logarithmic color scale. In this image, one can easily identify a measurable expansion, surrounding the solar disk and leading to a CSR value of 17 %.
CSR Measurement System
© Fraunhofer ISE
CSR Measurement System mounted on a solar tracker at Fraunhofer ISE – Freiburg, Germany.

A critical aspect for the site selection, design and operation of a Solar Tower plant is the exact knowledge of the sunshape distribution, which characterizes the amount of direct radiation that comes from outside of the solar disc – the circumsolar radiation (quantified by the cirsumsolar ratio CSR). This effect originates from Rayleigh and Mie scattering in the atmosphere and is therefore strongly site and weather dependent. The sunshape distribution has a strong impact on the shape and size of the heliostats’ focal spot and thus affects the solar field’s efficiency (“spillage”), but as well plays a role with regard to the avoidance of hot spots on the absorber surfaces.

As part of the POLYPHEM project, Fraunhofer ISE works on the development of a novel and highly accurate measurement system for the circumsolar radiation. While being highly accurate, the device consists of affordable components, mainly a CCD camera and several filters, all mounted on a solar tracker. Amongst others, the elimination of optical noise and the thermal management of the device are crucial aspects for a high performance.

Over the duration of the project,

  • the measurement system has been designed optically and thermally,
  • the required components have been purchased or manufactured at Fraunhofer ISE
  • and the entire device has been assembled.

Tests at the Fraunhofer ISE campus in Freiburg, Germany, show promising results, highlighting the strong variation of CSR with varying DNI (Direct Normal Irradiance, typically exhibiting a lower CSR with higher DNI and vice versa) and also successfully demonstrating the simultaneous quantitative measurement of CSR and sunshape distribution.



Further Information on Project »POLYPHEM« and its Tasks:

Research Project: Polyphem – Small-Scale Solar Thermal Combined Cycle (Gas Turbine/ORC)

Task: Simulation model for the POLYPHEM prototype – Digital Twin

Task: Development of a camera-based measurement system for circumsolar radiation