Photovoltaics in Alpine regions make an important contribution to the accelerated expansion of electricity production in Switzerland. Thanks to generally high solar radiation, little high fog, reflections from the snow surface and low temperatures, a lot of electricity can be generated in the mountains even in winter. About three to four times as much winter electricity is generated per unit of area in the Alps than in the lowlands, which makes such installations particularly attractive from an economic point of view. However, due to snow reflections, the use of bifacial modules, and the installation on slopes, current simulation software is not suitable for estimating yields and optimizing alpine solar installations. To validate the software, data from real installations in sufficient quality and with a wide range of parameters is needed. Since such data is either non-existent or available only to a very limited extent, the construction of experimental facilities in alpine locations is necessary.
The model photovoltaic system presented here should be highly flexible in its application: it can dynamically change the row spacing, the module inclinations and the slope inclination over a wide range. At the same time, various external influences such as the ground albedo can be monitored as closely as possible and all relevant meteorological data recorded. The rapid change of the system configuration allows different parameter variations to be compared under virtually identical conditions. At the same time, yield measurements can be taken over a longer period for a wide range of configurations. The corresponding data will subsequently be freely available for viewing.
 

The system is built on a scale of 1:12 and designed so that it can be easily rebuilt at other locations (explanation video). It has three rows, each with seven bifacial modules. In order to obtain separate measurement values for the front and back, these are designed as two monofacial modules, each measuring 96 mm x 160 mm (Figure 2). Of the 42 installed modules, 24 are active and can be measured using precise electronic measuring equipment. The remaining modules are identical dummies. The positions to be approached (row spacing, module inclination and slope inclination) are defined via a configuration file. As soon as the positions are reached, the measurement is triggered, whereby each specified module is measured one after the other (Uoc, Isc and Pmpp). All weather data, as well as diffuse and direct radiation, the albedo of the snow and, where available, yield data from a full-scale reference module are attached to the measurement data. This allows the various influencing factors to be broken down and generally valid results to be achieved.

The row spacing can be adjusted using two trapezoidal spindles under the construction. While the center row is fixed, the northern and southern rows are moved by stepper motors. The ratio of row spacing/module height can be adjusted between 1.2 and 7.3 at 0° inclination. The module inclination is adjusted directly by stepper motors at each row end with a relative (to the horizontal) angular range of -40° to 90°. The slope inclination (angle of the entire construction) is adjustable over two linear actuators in an angular range of 0° - 40°. To prevent snow from building up on the experimental facility, heating mats are installed that are activated when precipitation occurs. To ensure precise positioning, all stepper motors are equipped with an encoder and are periodically referenced. All actuators are controlled via a central control system using Modbus RTU.
The system was installed in spring 2023 on the container roof of the existing alpine PV test facility at Totalp in Davos and has been in operation ever since (Video 1).

A first report on the results from the operation during the winter season 2023/24 has already been published. The measured values were validated using the large test plant set up at the same location. The measured yields over parts of this measurement period were compared with yield simulations for about 80 different plant configurations using the commercial software PVSyst, which was fed with measured weather data from the same period. In particular, when following the SFOE recommendations regarding the albedo values to be used, it was found that the yields were underestimated by 7 to 16%, depending on the plant configuration. This is partly relativized by a countervailing, systematic source of error on steep slopes. While this report compared specific measurement values and shorter time periods, evaluations of absolute yields over the entire winter season are in progress and will be published as soon as possible.

We would like to thank the Hauser Foundation for funding this project.