A method for in situ measurement of directional and spatial radiosity distributions from complex-shaped solar thermal receivers

A methodology for in-situ measurements of radiative reflection and emission losses from a solar thermal receiver under high-flux irradiation is demonstrated. It combines radiosity analysis with photogrammetry and image recognition techniques to obtain directional and spatial radiosity distributions over receiver surfaces with a simple setup, mainly consisting of a camera. A CCD camera can acquire the radiosity in the visible range, which predominantly captures reflected solar irradiation. A thermal infrared camera can acquire the radiosity in the infrared range, which predominantly captures emission losses from the hot receiver surfaces. A hyperspectral camera can be used to obtain spectrally resolved results across a range of wavelengths. Images are taken from different directions in front of the receiver, and processed in software to obtain a point cloud via three-dimensional reconstruction, allowing the image data to be mapped onto a receiver mesh model. The receiver can be any shape, including those with complex-shaped cavity-like geometries exhibiting surface occlusion and light-trapping effects. These camera-based non-contact measurements allow for the performance of a receiver to be evaluated without interrupting its normal operation. The feasibility of the method is tested by quantifying the reflection losses from a multi-cavity tubular receiver under ~850 kW/m² concentrated solar irradiation. The proof of concept is established by comparing the measured results with those from Monte-Carlo ray-tracing simulations.