FUSIO INCREASES FLOATING SOLAR PANELS PRODUCTIVITY : REPORT ON THE COOLING ANALYSIS

[Chloé Stringaro]

One of the properties of our new floating solar solution, Fusio, is to enhance the energy yield of the solar panel compared to other floating solar (FPV) systems. This is partly due to the honeycomb structure, which provides excellent thermal exchange with water and then improves the panel’s passive cooling.

But how can we ensure that?


At Ciel & Terre, we always seek to provide solid, measurable, and concrete evidence of the benefits we claim. To demonstrate this cooling phenomenon, we worked closely with the CEA, and ITE INES.2S, one of the major Research & Technology Organisation in France. They helped us conduct a comparative study of our Fusio technology versus conventional flexible FPV solutions. In this article, we present the results of this study, the methodology applied, and the model that emerged from it.

How to analyse the impact of the cooling effect on the floating solar power plant productivity?​

Understanding the temperature effect on PV panel​

First, a quick reminder: photovoltaic cells convert part of the solar energy into electricity, but a significant fraction, approximately 70-85%, is dissipated as heat. Besides, the efficiency of photovoltaic cells is greater at lower ambient temperatures due to the semiconductor properties of the materials used, typically silicon. A typical crystalline silicon panel may lose 0.3% to 0.5% of its efficiency for every 1°C increase in temperature above 25°C. Then, assessing and optimizing thermal phenomena of a solar plant is key to ensuring the highest electricity production possible.

the cooling impact study, what is the aim:​

The project aims to model the contribution of Fusio structure design to the thermal exchanges around panels compared to a conventional flexible floating structure, installed on 4 different sites (France, India and Japan). These 4 sites cover different climates and environmental conditions to get an overall and representative assessment. This approach is quite standard. However, the key factor is the model’s correlation with reality. In our case, working with researchers at CEA aims to have access to complex thermal models correlated with reality, based on previous measurements at the various sites.

Comparing floating solar technologies for enhanced cooling effect and productivity​

To evaluate how design impacts the energy yield of floating solar panels, this study compares two floating structures for photovoltaics (FPV), focusing on the analysis of the cooling effect.


The first system analyzed is Fusio, Ciel & Terre’s latest innovation in floating solar solution. This advanced structure is based on a unique geometry of interconnected triangular floats, forming a honeycomb platform (see Figure 1a). By removing maintenance walkways, Fusio allows more airflow across the photovoltaic modules. This design is expected to enhance the cooling effect of floating solar panels, which is a key driver in improving their efficiency and, ultimately, the overall energy yield of floating solar panels. This assumption is further analyzed and validated in the following sections of the article.

Figure 1.a : Unique geometry of interconnected triangular floats, forming a honeycomb platform of the Fusio system​

Figure 1.b : Commonly deployed floating solar configuration of the conventional flexible FPV solution (b)​

The second system serves as a reference: a conventional flexible FPV solution, representing the most commonly deployed floating solar configuration (see Figure 1b). Each panel is mounted on an individual float, arranged in paired rows (“2-in-a-row”) separated by maintenance aisles. While this design facilitates access for operation and maintenance, the presence of walkways may disrupt airflow circulation. This can potentially limit the cooling effect, thereby impacting the operating temperature of the modules and reducing the productivity of floating solar panels compared to more optimized designs.

Our initial assumptions regarding structural differences​

One thing that stands out even before examining the study in detail is that the Fusio’s structure reduces the coverage ratio of the floats to 20%, compared to 40% for a conventional flexible FPV structure (see Figure 2b and d). This suggests that there is greater air-water exchange (see Figure 2a and c).
Another factor that leads us to believe the Fusio provides better cooling is that the panel mounting is higher than in conventional structures, which greatly facilitates air circulation around the panel.

Figure 2 : Front view and rear view of elementary PVF fields including Fusio system (a and b) and of the conventional flexible PVF solution (c and d)​

What is the methodology carried to measure the Fusio’s cooling impact ?​

The thermal cooling depends on the intensities of wind velocity, of the ambient temperature, and of the water temperature, varying throughout the year. More precisely, according to their values, heat exchanges by convection or radiation become predominant on each side of the PV modules.


First, we have collected weather data from meteorological stations located near the 4 sites selected. Besides, our R&D department used CFD simulations to assess 3D wind pattern velocities through the two floating structures, Fusio structure on one hand, and the conventional flexible FPV structure on the other hand.


Then, along with CEA, we run the thermal model with these data as inputs to calculate the temperature gradient from the water to the top surface of PV panels. Finally, we calculated the Performance ratio (PR) and Final energy yield (kWh/kWp) over 1 year for each site and each floating structure type based on the same electrical assumptions (cabling and inverter’s properties) for a relevant comparison.

What do we learn from the study of the cooling effect on solar panels productivity?​

The key impact of the surrounding environment​

These extensive studies show the key influence of environmental parameters on the thermal effect of each floating structure at different levels. The most impactful parameter is the wind velocity. Indeed, the higher wind velocity leads to increase thermal convection.
Then, an open geometry allows the breeze both below and around the PV panel, and thus it will increase the convection and then the cooling effect around the PV.
Finally, comes the temperature of the air and the temperature of the water. The highest difference between these two temperatures will maximize the thermal phenomena (heat exchanges) around PVs.

The benefits of the honeycomb structure on the increase of the PV yield​

This analysis and its corresponding results validated our initial assumptions. Thanks to its unique and open honeycomb shape, Fusio structure is well optimized to maximize the heat exchange between the PV panels and its environment. It is mainly thanks to two features:


Higher distance from water is a key design choice enabled by Fusio’s open honeycomb structure, which keeps the PV modules higher above the water surface. With more free space underneath and fewer obstructions (no walkways), Fusio allows wind to circulate more easily below and around the panels. This improved airflow is clearly visible in the CFD simulation results shown in the figure below.

Figure 4 : Wind flow on the 2 floating structures types : top : conventional flexible structure, below : Fusio structure​

Greater radiative transfer from water to PV occurs when more water surface is exposed beneath the modules. In this study, Fusio’s triangular floats halve the coverage compared to conventional flexible structures, increasing active surface for heat exchange and enhancing water-driven cooling of PV by, at least nearly 1.4.

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The conclusion of the study​

Below is an example of the resulting PV temperatures output from the thermal model on one site studied (South India). Temperatures are averaged on a monthly basis through a whole year.

Figure 6 : Example of monthly averaged module temperatures calculated on the two floating structures for one site studied​

Based on the graph above, the benefits of the Fusio structure are clearly demonstrated in term of PV cooling. On average, photovoltaic modules installed on Fusio remain cooler by -0.9°C to -1.7°C over the course of a year with a maximum difference of -9,5°C during hottest days over the year.

This improved cooling effect translates into a measurable increase in energy output: across the 4sites analysed in the study, Fusio’s design alone delivers an electricity production gain as below:


Sites :

Site 1 – France


Site 2 – South India


Site 3 – South India


Site 4 – Japan​

Energy gain (%) :

+0.6%


+1.7%


+3.2%


+0.9%​

It represents nearly +1.8 to +11.5 kWh/m² of cumulated energy yield gain.

The impact of Fusio is particularly significant in locations with high annual average temperatures, where the cooling of solar panels is a key factor in maximizing efficiency. In these conditions, the enhanced thermal performance provided by Fusio clearly contributes to the overall productivity of floating solar panels, reinforcing the advantages of this innovative honeycomb design.

Discover Fusio® technology

By Olivier, Deputy head of Research & Development​

& Chloé, marketing​

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