Agri-PV: Apples ripen well under solar modules

One of the central topics at this year's Agri-PV Conference in Freiburg im Breisgau is the impact of photovoltaic systems on yields. Since apples are the conference's partner crop this year, it's only fitting that the apple harvest be the focus. Greta Ott from the Agricultural Technology Center (LTZ) in Augustenberg took a closer look at the quality of the apple harvest in her own experimental field.

The apple trees were partially covered with solar panels – one section under semi-transparent modules with a light transmittance of 50 percent. Another section of the trees is under tracking systems. Some of the trees remain without solar canopies. This section of the area serves as a comparison field.

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Maturity level assessed

To assess quality, the researchers examined the ripeness of the apples at harvest. "The results were somewhat surprising," says Greta Ott. The fruit was harvested in early September 2024. The so-called Streif Index, which indicates the ripeness of the fruit, was then determined. This consists of three parameters: the firmness of the apples, their sugar content, and the breakdown of starch during the ripening process.

Less sugar, more starch

Here, it was shown that the firmness of the apples under the static modules was perfectly developed, while this value was too high for the fruit from the comparison area. These fruits were too firm. However, the sugar content of the fruit from the comparison area was perfect, while the apples under the solar modules had a sugar content that was too low. The apples under the modules were also not yet as far along in terms of starch breakdown. Here, the value was too low, while the apples from the comparison area had sufficiently broken down starch. However, the sugar content of the apples under the solar modules was perfect when harvested a few days later. By this time, however, too much starch had already been broken down.

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Apples under the modules take a little longer

Overall, it was found that the apples under the modules were not yet fully ripe when they were harvested on September 9. At that time, the apples in the test plot were also not yet ripe, but they had already reached a better level of ripeness. However, by the time of harvest on September 23, the apples under the solar modules were already overripe.

Determine the correct harvest time

The results show that when covering apple orchards, farmers should determine harvest times more precisely to ensure the quality of the fruit remains high. If the fruit is not ripe enough, it will find fewer buyers. If it is too ripe, it is no longer suitable for storage.

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At the same time, solar systems offer protection against the severe effects of climate change, which has reached the southern Black Forest. To further advance agri-PV, suitable framework conditions are necessary. Learn what's currently happening at the EU level regarding photovoltaics for agriculture in the next installment of our series on the Agrivoltaics World Conference in Freiburg. (see below)