Kompetenzzentrum Obstbau Bodensee (KOB), a foundation for the promotion of fruit growing in the Lake Constance region, is investigating the growth and yield behaviour of various apple varieties under semi-transparent PV modules. After harvest, the fruit is assessed in terms of its external characteristics, such as colour development and fruit size, and its internal quality. The PV modules can protect the fruit and plants against hail- and sun-related damage, while simultaneously producing energy.

The site is also investigating to what extent the altered microclimate under the PV modules may reduce the need for crop protection products. Crops that are protected against moisture have a lower risk of fungal diseases like apple scab and rain spot, since these require sufficient humidity to spread. The project will also monitor the development of pest populations, such as rosy apple aphid and woolly aphid .

The findings will be compared with a reference plot protected with conventional hail nets.

Technical details

Apple growing

The KOB experimental station in Bavendorf grows four scab-resistant apple varieties using organic farming methods: Freya, Natyra, Delcored and Topaz. After installing the PV system at the end of April 2022, 18 rows of trees were planted with 80 young trees in each. The apple varieties were planted in alternating rows, so that there are four rows of each variety. The two outer rows are not included in the research because of possible edge effects.

Photovoltaics

Two types of PV system are set up at KOB:

• A fixed system in which the PV modules form a roof over the tree rows in an east-west orientation.

• A tracking system in which the modules can be tilted east-west, depending on the sun’s position. This helps to optimise the electrical output in the first instance. However, if the apple trees are found to be suffering from a lack of sunlight during the experiment, the system could be adjusted to optimise the agricultural yield instead.

To ensure that the trees receive sunlight despite being covered by the PV modules, the modules are light-transmissive with 49% transparency. They are installed 3.5 metres above the trees.

The plant was also designed in such a way that the concrete-free foundations can be dismantled without leaving any trace because there were no major interventions in the soil.

The plant was connected to the power grid in May 2023. The power is collected by Technische Werke Schussental (TWS), a local utility company and associated project partner. Most of the investment costs for the plant are being financed by Zweckverband Oberschwäbische Elektrizitätswerke (OEW), a joint electricity authority in southern Baden-Württemberg.
The KOB also investigates the effects of the PV modules on the trees and fruit quality at the fruit orchard »Bernhard« in Kressbronn.