Magenta CdTe solar panels support broccoli cultivation in agrivoltaic trial

A research team from Sweden and Italy has investigated the performance of semitransparent, magenta-colored cadmium telluride (CdTe) thin-film PV panels designed to transmit wavelengths favorable for broccoli growth in an agrivoltaic system.

“Most existing agrivoltaic systems use conventional crystalline-silicon solar panels, which are opaque and therefore primarily manage how much sunlight reaches the crops. Our approach also considers the quality, or spectrum, of that light,” corresponding author Silvia Ma Lu told pv magazine. “The magenta-colored panels were specifically customized to transmit more blue and red light, corresponding to major absorption regions of plant chlorophyll pigments.”

Ma Lu said the research represents one of the largest published open-field experiments to date involving semitransparent, colored solar panels in agrivoltaics. “Our system explores the emerging concept of wavelength-selective agrivoltaics. The broader goal is to investigate whether sunlight can be used more efficiently by allocating different portions of the solar spectrum to crop growth and electricity generation,” she explained.

The researchers conducted a field experiment at Kärrbo Prästgård in central Sweden during the 2024 growing season, comparing broccoli grown in an open-field control plot with broccoli cultivated beneath two CdTe PV systems. The systems had nominal transparency levels of 50% and 70%, corresponding to average photosynthetically active radiation (PAR) transmittance values of 13.2% and 19.2%, respectively. Each PV system consisted of 21 panels supplied by Chinese manufacturer Advanced Solar Power, installed at a minimum height of 1.5 m and a tilt angle of 6 degrees.

Each plot contained 44 Marathon broccoli plants, transplanted on July 2 and protected by white insect nets. The researchers monitored light availability, air temperature, relative humidity, soil moisture, and soil temperature. They sampled six plants per treatment on Sept. 19, followed by six additional plants from each PV treatment on Oct. 14.

The team measured plant dimensions, fresh and dry biomass, broccoli head nutrient composition, and leaf photosynthetic responses. It also estimated electricity generation using the System Advisor Model (SAM).

At maturity, broccoli grown beneath the 50% and 70% transparency systems had average fresh head weights of 173.7 g and 168.5 g, respectively, compared with 187.6 g in the open-field control. The differences were not statistically significant. “One of the most interesting findings was how similarly the broccoli performed under the two systems despite their different transparency levels. We observed no meaningful differences in crop growth or nutrient composition between the two panel configurations at harvest,” Ma Lu said.

Broccoli grown beneath both PV systems reached maturity 104 days after transplanting, compared with 79 days for the open-field control, representing a 25-day delay.

“The delay in crop maturity compared with the full-sun reference was less surprising because both systems substantially reduced the amount of light reaching the plants,” explained the researcher. “Nevertheless, the similar performance between the two agrivoltaic treatments suggests that the broccoli responded to the conditions beneath both panel types in broadly similar ways despite differences in light availability.”

The comparable crop performance led the researchers to favor the 50% transparency configuration, which had a higher PV cell density and greater electricity generation potential. Radiation use efficiency, measured as aboveground dry biomass produced per unit of photosynthetically active radiation received, was 4.5 times higher under the 50% transparency system and 2.8 times higher under the 70% system than in the open-field control.

The researchers estimated that the approximately 1.1 kW prototype of the 50% transparency configuration could generate 447.6 kWh during the cultivation period. A theoretical hectare-scale calculation yielded a land equivalent ratio (LER) of 1.18.

“We have already started investigating how semi-transparent magenta panels, as well as panels that selectively transmit individual colors, such as red and blue, affect plant growth and physiological processes under more controlled experimental conditions,” concluded Ma Lu. “These experiments are designed to minimize light entering from outside the panels, allowing us to distinguish better the effects of different transmitted light spectra while keeping other environmental conditions as similar as possible.”

The findings are presented in Evaluating land productivity with semi-transparent colored CdTe thin-film PV and broccoli cultivation in agrivoltaic systems, published in Cell Reports Physical Science. Researchers from Sweden’s Mälardalen University, Italy’s National Research Council, and the Catholic University of the Sacred Heart contributed to the study.