The goal of the Energy Strategy 2050 with regard to the expansion of renewable energies is ambitious. Since photovoltaics will have to make a significant contribution to this, the potential of using agricultural land for energy production should be investigated in addition to roof and facade surfaces. However, land is a scarce resource, which is why the dual use of agricultural land for energy production and for growing crops or keeping animals, also known as agri-photovoltaics or agro-photovoltaics, is of increasing socio-political interest. The combination of agriculture and electricity generation requires comprehensive know-how in both technical and agricultural matters in order to find an ideal design for the respective location and specific use with the different requirements.

Agri-photovoltaics (agri-PV) aims to combine solar development and agriculture for mutual benefit, considering food and energy security not as competing concerns. The aim is to even achieve added value for agriculture through clever plant design. Research studies in neighboring countries and the United States already show that, for example, under dry conditions, photovoltaic modules on arable land have a positive effect on the yield of the sub-crops and at the same time water consumption is reduced. In addition, the plants are protected by the modules from heavy rain and hail.

The research at ZHAW is intended to provide insights into the effects of agri-photovoltaics on agricultural yields, as well as to illustrate the potential added value compared to open-field photovoltaic systems or conventional agricultural land without photovoltaic coverage. This part is being investigated by the horticulture research group led by Mareike Jäger.

On the other hand, the investigations should show what influence agricultural production and the agricultural environment have on electricity production. Among other things, the aim is to investigate how negative influences on the agri-PV system can be minimized by designing the agri-PV systems appropriately. Due to the special technology used in the photovoltaic modules (see below), there are also optimization possibilities with regard to the timing of light transmission.

The Agri-PV test facility uses photovoltaic modules from the Swiss company Insolight. The special feature of these modules lies in their design, whereby a glass plate equipped with small lenses is located above the PV cells, which directs the sunlight onto the individual PV cells in a concentrated manner. This means that only a small part of the module surface needs to be coated with semiconductor material, thus saving material and allowing diffuse light to reach the agricultural area below the modules. The movable lens-equipped plate is tracked throughout the day using optical micro-tracking technology to follow the position of the sun so that the sunlight always hits the PV cells exactly.

The light transmission of the modules can also be dynamically adjusted. There are basically two different standard operating modes that can be set: the “E-mode” is used for optimized energy production and the movable lenses are adjusted so that as much light as possible hits the PV cells directly. In the second mode, the maximum light transmission (“MLT mode”), 70% of the sunlight reaches the agricultural area and can thus be used for photosynthesis. However, the light transmission can be individually adjusted at any time using an algorithm or online input and linked to specific times, temperatures or irradiation, for example. Figure 1 describes the structure of the PV modules and how the operating modes work in more detail.

The experimental agri-photovoltaic plant on the Grüental campus in Wädenswil was built in collaboration with the Renewable Energies and Horticulture research groups. In order to investigate the agricultural effects, agricultural products (e.g. lamb's lettuce) are grown both under the modules and in a control area next to them, and their growth is monitored and compared between the two cultivation methods.
 

On the technical side, the electricity production of the PV modules and the electricity consumption of the system (servomotors for micro-tracking) are measured and evaluated. 100% of the PV electricity generated is fed into the grid. Evaluations of the technical results will be added to this page as soon as they are available. The agronomic evaluations can be viewed on the website of the Horticulture Research Group.