Study Finds 0.5-Meter Row Spacing Improves Cooling in Floating Solar Farms

A computational fluid dynamics study on a floating solar plant project in the Occhito Dam reservoir, which marks the border between the Puglia and Molise regions, identified a spacing of approximately 50 centimeters between panel rows in a three-row configuration as the most effective alternative for reducing operating temperatures. The 50-centimeter solution is the intermediate option.

At a wind speed of 3.5 m/s, the preferred configuration achieved an average panel temperature of 27.16 °C, compared to 31.07 °C for the most compact layout. Under weaker wind conditions of 1.5 m/s, the same configuration reached an average temperature of 37.02 °C.

The research, conducted by Reza Hamidi Jahromi, Furio Cascetta, Pasquale Contestabile, and Alessandro Mauro, reports that the efficiency of crystalline silicon modules generally decreases by approximately 0.3%–0.5% for every 1 °C increase in cell temperature. However, the study’s results highlight the importance of airflow management in the design of floating photovoltaic systems, once again challenging the assumption that proximity to water alone ensures better cooling.

The paper suggests that the spacing between rows should be considered not only in terms of installed capacity, shading, and floating platform requirements, but also as a critical thermal design parameter.

The research, the result of a collaboration between the University of Naples Parthenope and the University of Campania “Luigi Vanvitelli,” then introduced a relatively new concept. Although the maximum spacing allowed the airflow to recover more completely, it did not consistently produce the lowest temperatures. The researchers attributed this phenomenon to a reduced acceleration of the airflow between the rows.

The work therefore demonstrated that it is necessary to find a balance between wake recovery and airflow acceleration, further clarifying that this balance depends on the specific conditions of the installation.

Cooling performance indeed depends on several interacting factors, including wind speed, the geometry of the installation, airflow pathways, and the formation of aerodynamic wakes behind individual rows of panels.

These wakes can restrict air movement around the modules, reducing convective heat transfer and increasing operating temperatures. While increasing the spacing between rows may allow the airflow to recover before reaching the next panel, wider spacing does not necessarily yield the best results. As anticipated, the researchers found that excessive spacing can weaken the acceleration of airflow between rows.

A spacing of 0.5 times the panel length produced the best result, with an average temperature of 37.02 °C. The wider configuration, equal to one panel length, recorded the worst performance, reaching 37.74 °C. The differences became more pronounced at 3.5 m/s: the configuration with a spacing of 0.5 times the panel length achieved an average temperature of 27.16 °C, compared to 29.26 °C for the configuration with a spacing of 0.75 times the panel length, 29.75 °C for the wider configuration, and 31.07 °C for the most compact arrangement.

The study published in Solar Energy further explains that these differences also vary depending on the specific panel row considered. The central row of panels proved to be particularly sensitive to changes in spacing. At a wind speed of 3.5 m/s, its temperature reached 23.30 °C when the spacing was set to 0.5 times the panel length, compared to 29.66 °C for the most compact configuration and 30.17 °C for the widest configuration. According to the researchers, this behavior reflects the central row’s exposure to the opposing effects of upstream wake formation and airflow recovery.

In addition to finding that intermediate spacing yields the lowest temperatures, the simulations revealed that the relationship between row spacing and module temperature is not linear. The study then analyzed the airflow velocity under various conditions.

The simulations showed that, at the lowest wind speed, the airflow between the first two rows remained below 0.5 m/s in the most compact configuration. Increasing the spacing to 0.5 panel lengths raised the local velocity to approximately 0.9–1.1 m/s. At higher wind speeds, the difference was even more pronounced. The intermediate configuration produced inter-row velocities of approximately 2.5–3.0 m/s, compared to 1.0–1.5 m/s for the most compact layout.

Methodology: Four configurations tested at the Occhito Dam

Researchers developed a two-dimensional conjugate heat transfer model to simulate the interaction between photovoltaic modules, the surrounding air, and the underlying water.

The proposed installation was modeled using three consecutive rows of panels, each tilted at 15 degrees and positioned 25 cm above the water surface. The panel length was approximately 0.99 meters. Four row spacing configurations were examined, corresponding to 0.25, 0.5, 0.75, and 1.0 times the panel length. The simulations considered two incoming wind speeds: 1.5 m/s and 3.5 m/s, representing relatively weak and more intense convective cooling conditions, respectively.

Meteorological conditions were derived from hourly ERA5 reanalysis data for 2024 for the Occhito reservoir. The model used an annual average air temperature of 15.37 °C, a water temperature of 14.67 °C, and a net shortwave radiation flux of 146.65 W/m².

Need for further research

The findings are particularly relevant for inland water bodies in Mediterranean climates, where high summer temperatures and variable wind conditions can affect module operating temperatures. However, the authors caution against treating the identified spacing as a universal design recommendation. The analysis was limited to a two-dimensional model consisting of three rows of panels and two wind speeds. It did not account for three-dimensional turbulence, wind direction variations, shading effects, the detailed structure of floating support systems, or the full range of weather conditions recorded over a year.

In addition, the study “Influence of row spacings on the thermal performance of floating photovoltaic arrays at the Occhito Dam reservoir, Italy: A numerical study” focused on thermal behavior rather than direct calculations of electricity generation or annual energy yield. The authors recommend extending the work through three-dimensional CFD simulations, additional wind conditions and directions, and integrated electrothermal modeling to determine how the observed temperature differences translate into actual generation gains.