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| Fig. 1: Floating photovoltaic power plant, Lac de la Madone (Rhne, France). (Source: Wikimedia Commons) |
Solar photovoltaics (PV) are the fastest-growing renewable energy technology. [1] In 2022, solar PV generation grew by 26%, adding 270 TWh of annual energy generation to reach a total of 1,300 TWh globally. [1] In 2023, solar PV accounted for three-quarters of global renewable capacity additions. [1]
This rapid growth in PV highlights their promising potential for meeting global energy demands. Yet, as solar PV integration increases, land use has become a commonly cited topic of concern. A study by Van de Ven et al. modeled the land requirements for utility-scale solar PV at various levels of grid integration and found that 25 - 80% integration would require 0.5 - 2.8% of land in the EU and 1.2 - 5.2% in Japan and South Korea. [2] While models show that large-scale solar farms in places like the Sahara can meet the worlds energy demands, covering large landmasses can disrupt the transport of water vapor and redistribute precipitation. Although such installations can increase regional rainfall and vegetation cover in the Saharan region, these changes may lead to droughts in the Amazon, global surface temperatures to rise, and sea ice loss, particularly over the Arctic, according to Lu et al. [3]
Floating photovoltaic (FPV) systems have emerged as an alternative to land-based PV systems. These systems are PV panels that are installed on a body of water and anchored into the waterbed or side of the body of water. [4] As of 2020, the global installed capacity of FPVs was 3 GW, relative to the 700 GW of land-based solar. [5] These FPV installations have been primarily focused on lakes and reservoirs. [4]
The FPVs structure has to optimize generation, withstand extreme environmental conditions, and avoid disturbing the surrounding ecosystem. According to Ramanan et al., there are 5 classes of FPV. [6] Type 1 involves rafts constructed that use reinforced parallel high-density polyethylene (HDPE) cylinders as floats. Type 2 contains individual panels fixed onto separate floats. Type 3 utilizes a large floating platform to provide walking space between the panels for maintenance and access. Type 4 involves a partially submersible floating structure, allowing the PV modules to float back to the surface if submerged. Lastly, Type 5 employs a flexible thin film structure designed with neoprene sheets and floats as support. [6] The transmission cables are typically made water-resistant using thermoset rubber. [6]
FPVs have some advantages over conventional land-based solar PVs. In general, PVs operate most efficiently at the standard operating temperature of 25°C. [6] As the temperature rises above this standard, efficiency decreases. For example, a 1°C increase in panel temperature can reduce the efficiency of monocrystalline PV panels by 0.45% and polycrystalline PV panels by 0.25%. [4] However, installing PVs on water provides passive cooling, which mitigates this thermal effect, which can become more pronounced in larger solar farms. [6] According to Claus et al., the overall efficiency gains from this cooling effect can reach up to 15%. [7] In addition, these passive cooling systems can reduce degradation in the panels, extending their lifespan.
Floating solar PVs also offer other benefits. Covering the water's surface can minimize evaporation from the body of water where they are installed. While exact values depend on geographic location, climate, water coverage, and panel materials, Nisar et al. evaluated small-scale floating PV systems. [4] They found that partially covering a body of water with FPVs reduced evaporation by 17% and fully covering a body of water reduced evaporation by 28%. Additional benefits include reduced land use costs as well as the potential integration with floating breakwaters, which can help mitigate the impact of waves on shorelines. [7]
While these panels increase the area available for solar installations, they are more complex in their design and maintenance. [6] FPVs installed in marine environments have to withstand extreme environmental events, saltwater erosion, UV degradation, and biofouling. [7] Biofouling by birds and microbial biofilms has the potential to reduce the efficiency and performance of the panels by obstructing sunlight and increasing maintenance requirements. Panel alignment also impacts performance, which becomes more complex when panels are floating. To address this, designs have been proposed that use wave energy to power a tracker that adjusts the angle of the PV modules. [4] Moreover, transmission lines require additional maintenance to ensure both operational efficiency and minimal environmental disruption. [6] Given these extra requirements, costs are higher. A report by NREL estimated that the levelized cost of energy (LCOE) for FPV systems is around 20% higher than for ground-mounted PV systems (excluding the solar Investment Tax Credit). [8]
Location also has a significant impact on FPV potential. Approximately 70% of the Earth's surface is covered by water. [6] However, oceans are often unsuitable for floating solar installations due to challenges posed by extreme weather and wave conditions. Installation locations are further limited by proximity to population centers, and sensitive ecosystems, such as habitats for endangered species. Given these restraints, hydropower dams have emerged as a promising location for floating solar installations. [6]
With this in mind, FPV systems still have significant potential to contribute to global energy needs as highlighted by recent modeling studies. One study by Woolway et al. modeled the total annual power output of a 1 kW FPV system. [9] Assuming a 10% water surface coverage and no constraints on available bodies of water, the model estimated a total annual power output of 14,906 TWh for these systems. This analyzed about 1 million bodies of water. Constraining the available bodies of water to those within 10 km of population centers and with stable water-level, while excluding protected areas and water bodies with ice cover lasting less than six months, the number of eligible water bodies fell to 67,893. The annual modeled output was 1,302 TWh. [9]
Given the limitations of available bodies of water and variations in solar irradiance potential, FPV system potentials exhibit significant geographic disparities. In this same study, they found that China contributed approximately 19.35% (252 TWh), Brazil contributed approximately 13.06% (170 TWh), and the United States contributed approximately 11.75% (153 TWh) to the annual modeled output. In addition, other countries such as Ethiopia and Papua New Guinea were found to have the potential to meet a significant portion of their energy demand, highlighting the opportunity for FPVs to help support the renewable energy transition. [9]
© Genevieve DiBari. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Renewables 2023," International Energy Agency, January 2024.
[2] D.-J. van de Ven et al., "The Potential Land Requirements and Related Land Use Change Emissions of Solar Energy," Sci. Rep. 11, 2907 (2021)..
[3] Z. Lu et al., "Impacts of Large-Scale Sahara Solar Farms on Global Climate and Vegetation Cover," Geophys. Res. Lett. 48, e2020GL090789 (2021).
[4] H. Nisar et al., "Thermal and Electrical Performance of Solar Floating PV System Compared to On-Ground PV System - an Experimental Investigation," Sol. Energy 241, 231 (2022).
[5] R.M. Almeida et al., "Floating Solar Power: Evaluate Trade-Offs," Nature 606, 246 (2022).
[6] C. J. Ramanan et al., "Towards Sustainable Power Generation: Recent Advancements in Floating Photovoltaic Technologies," Renew. Sustain. Energy Rev. 194, 114322 (2024).
[7] R. Claus, and M. López, "Key Issues in the Design of Floating Photovoltaic Structures for the Marine Environment," Renew. Sustain. Energy Rev. 164, 112502 (2022).
[8] V. Ramasamy and R. Margolis, "Floating Photovoltaic System Cost Benchmark: Q1 2021 Installations on Artificial Water Bodies," U.S. National Renewable Energy Laboratory, NREL/TP-7A40-80695, October 2021
[9] R. I. Woolway et al., "Decarbonization Potential of Floating Solar Photovoltaics on Lakes Worldwide," Nat. Water 2, 566 (2024).
