The Urbanbox from iWorks AG is a retractable photovoltaic roof for the economical generation of solar power above car parks, sewage treatment plants or even roads. The first demonstration system was put into operation in autumn 2022 at the Bendern WWTP in the Principality of Liechtenstein (see image). The PV system has a DC output of 50 kW and covers an area of almost 300 m2. The relatively light substructure is made of steel and wood. The highlight of the flexible photovoltaic solution: in bad weather, the foldable PV roof retracts permanently. The maximum wind and snow load is therefore reduced and material for the substructure can be saved. When the weather improves, the PV modules extend automatically and are cleaned by rotating brushes. This eliminates the need for maintenance and the PV yield is said to be 1 to 5 percent higher than with uncleaned systems, depending on the level of soiling. 

ZHAW engineers implement automatic cleaning of PV modules 
As part of the validation, the seven-member ZHAW engineering team from the Institute of Energy Systems and Fluid Engineering (IEFE) and the Institute of Mechanical Systems (IMES) also implemented the automatic module cleaning system together with iWorks and carried out a failure mode and effects analysis. To do this, the roof was retracted and extended 400 times and the cleaning mechanism was tested on site. The results of the analysis were used to optimise the key components of the traction and thus prove that the various elements would achieve the expected service life. The team also developed a method that can be used to visually determine the degree of soiling on the PV modules. To this end, a bachelor's thesis was carried out at the ZHAW in spring 2023, which examined this issue in detail. The work shows that thanks to the optical measurement of soiling, the modules do not have to be cleaned every time they are retracted. As a result, the brushes are less worn and do not need to be replaced during the service life of the PV power plant.

Further plant in planning
The first phase of the endurance test of the demonstration plant in Bendern by the ZHAW institutes IEFE and IMES has now been successfully completed. The results were presented by Franz Baumgartner, Urbanbox project manager at the ZHAW School of Engineering, at the European Photovoltaic Conference in Lisbon in September. The company iWorks is now analysing the results and would like to create another Urbanbox in the canton of Zurich next year, which will again be supported by the two ZHAW institutes.

Urbanbox-Film
https://www.urbanbox.li/extra/01_UrbanBox_deutsch.mp4

Contact:
Prof. Dr. Franz Baumgartner, Institut für Energiesysteme und Fluid-Engineering (IEFE)
Roland Fehr, Prof. Dr. Robert Eberlein, Institut für Mechanische Systeme (IMES)
Arthur Büchel, iWorks AG; www.urbanbox.li

ZHAW-Research database
https://www.zhaw.ch/en/research/research-database/project-detailview/projektid/5569/