The AVUSpro project focused on developing an autonomous reflectometer, the pFlex system, to measure soiling rates on mirrors of concentrating solar power plants. The core technical achievements involved extending the pFlex prototype’s software and hardware to capture high‑resolution reflectance data together with precise geolocation. GPS coordinates were integrated into the ReflectUI application, allowing real‑time recording of the device’s position during each measurement. The data were synchronised with the reflectance values and stored automatically in a measurement log, enabling later spatial analysis. Accuracy tests on the Fraunhofer ISE roof demonstrated that the GPS‑derived positions deviated only by a few metres from the true corner points, confirming that the system provides reliable location information for mapping soiling across a plant.
Hardware upgrades included a battery‑management module that displays charging status in the app’s status bar, improving field usability. The team also implemented a transfer function for acceptance‑angle dependence, allowing cleanliness values measured at the fixed acceptance angle of the pFlex device to be converted in real time to the acceptance angle relevant for a specific solar plant. This feature enhances the relevance of the data for operation and maintenance decisions. The pFlex 2.0 prototype was mounted on a mirror and shipped in a new transport case designed by PSE Instruments GmbH, ensuring robustness during field deployment.
Temperature dependence of the reflectometer’s optical path was identified as a significant challenge. While a redesign using 3D‑printed materials with lower thermal expansion was considered, time constraints led the team to pursue alternative solutions. Further tests and analysis are planned to minimise temperature‑induced intensity fluctuations and to guarantee consistent light output through the collimator’s optical fibre.
The project’s scientific output also contributed to the development of international guidelines for measuring reflectance on soiled mirrors, published in 2022 and currently being updated. Results from AVUSpro were incorporated into the EU SFERA‑III consortium’s work on soiling assessment and into several peer‑reviewed publications, including a dissertation on optical efficiency of concentrating collectors and conference papers presented at SolarPACES and other venues. Media coverage in German radio and physics journals highlighted the autonomous nature of the reflectometer and its potential to optimise cleaning intervals.
Collaboration was structured around four work packages. Fraunhofer ISE led project management, site characterisation, and field testing (AP 1, AP 3). PSE Instruments GmbH headed device development (AP 2), delivering the hardware and transport case. Flagsol, a solar plant operator, managed the application of the system to operation and maintenance in a real CSP plant (AP 4). The project was funded under the German research grant code FKZ 03EE0529 A, B, C, with a revision date of 01 February 2022. The consortium’s combined expertise enabled the successful transition of a laboratory prototype into a field‑ready, autonomous measurement system that delivers accurate reflectance and location data, thereby supporting more efficient maintenance strategies for concentrating solar power facilities.