New irrigation tech helps reduce water use in agrivoltaics

From pv magazine Global

A research group from Spain has used regulated deficit irrigation (RDI) under agrivoltaic systems to grow tomatoes in both Madrid and Seville.

RDI is a technique used to reduce irrigation water use by intentionally giving plants less water during less sensitive growth stages, while monitoring leaf water potential to prevent excessive stress and maintain yield.

“This innovative combination aims to reduce the plants’ evaporative demand through the shade provided by photovoltaic panels, enabling a more efficient use of land and water,” the academics said in a statement.

“Our results indicate that, although the shade from the panels reduces available radiation, the design of the system permits adequate plant development to be maintained at most stages of the crop cycle.”

In both Madrid and Seville, the experiments took place during the 2024 spring growing season. Maximum temperatures were frequently higher in Seville than in Madrid throughout most of the season, and the specific tomato seed varieties were selected based on the climatic conditions.

The agrivoltaic systems at the two locations consisted of a 2-monopole structure per plot, supporting 5 monocrystalline silicon modules rated at 450 W each.

The structures were 2.5 m high in Madrid and 3 m high in Seville, with spacing of 5 m and 4.5 m, respectively. The tilt angle was 17° in Madrid and 20° in Seville, while orientation was 25° and 15° off the north-south axis, respectively. In addition, both sites included a plot using only RDI without an agrivoltaic system, as well as a control plot that received full irrigation to meet crop water requirements and avoid water stress.

The researchers evaluated three irrigation treatments with three replications under different shading and water-management conditions. Control plots received full irrigation based on crop evapotranspiration (ETc) to avoid water stress, while the RDI applied controlled water stress according to plant growth stages and midday leaf water potential thresholds.

Irrigation levels in RDI varied dynamically between 25% and 125% of ETc depending on plant stress measurements. The agrivoltaic plot combined the same irrigation strategy as RDI with crop cultivation under photovoltaic structures. Measurements were taken only from centrally located plants within each plot to minimise border effects.

The analysis showed that agrivoltaic design and latitude strongly influenced radiation distribution and crop microclimate in Madrid and Seville. In both locations, agrivoltaic plots received radiation levels similar to control plots, while agrivoltaic shaded plots showed major reductions in photosynthetically active radiation (PAR) radiation, especially around midday.

In Madrid, shading effects persisted throughout the season, with midday PAR reductions of about 90% and daily light integral (DLI) values remaining around 70% of open-field conditions. In Seville, shading impacts were limited mainly to the early growth stages, and DLI differences nearly disappeared later in the season.

Moreover, the scientists found that air temperatures increased progressively during the experiments, with maximum temperatures approaching 40 C in both sites, with agrivoltaic plots showing slightly higher average temperatures than control plots, particularly during hot days and nighttime conditions. During daytime, however, agrivoltaic shading reduced temperatures in Madrid but not in Seville, where agrivoltaic plots were often slightly warmer.

Soil temperature responses also differed by location: agrivoltaic shading lowered soil temperatures in Madrid early in the season, while RDI increased soil temperatures later due to reduced irrigation and canopy cover. In Seville, control plots remained coolest because of higher irrigation, whereas agrivoltaic plots became the warmest due to limited shading and heat released by photovoltaic panels.

“One of the most notable findings is that the deficit irrigation strategy reduced water consumption by approximately 50% compared to traditional irrigation,” the scientists said.

“However, this drastic reduction in water led to a yield decrease of around 20% in the RDI treatment, attributed mainly to severe water stress conditions during the ripening phase. Despite this drop in total tomato production, irrigation water productivity increased significantly in the Seville treatments, demonstrating that more fruit can be obtained for every drop of water invested.”

In addition, the overall performance of the agrovoltaic system was validated by the land equivalent ratio (LER), which combines the efficiency of agricultural and electricity production. In Madrid, the obtained LER value was 1.54, while in Seville it was 1.67, confirming that combined production is more efficient than growing tomatoes and generating energy on separate plots.

“This implies that, although tomato yield decreases under the panels, the system’s profitability and sustainability increase thanks to the generation of clean energy in the same space,” the researchers said.

Their findings were presented in “Regulated deficit irrigation based on plant water status and Agrivoltaic systems as possible improvements on water resources management in tomato,” published in Agricultural Water Management. Scientists from Spain’s Research Center for the Management of Agricultural and Environmental Risks (CEIGRAM), the Technical University of Madrid, the University of Seville, the Spanish National Research Council, and the University of Castilla–La Mancha have participated in the study.

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