Researchers in Brazil have developed and simulated a hybrid tidal–PV floating farm concept for estuarine channels, analyzing wake effects, turbine spacing and hybrid energy trade-offs. Results show that integrating PV with hydrokinetic turbines improves overall energy yield by offsetting wake-related losses and optimizing modular farm configurations.
Model of the system
Image: Federal University of Maranhão
Researchers from Brazil have developed a hybrid tidal–PV generation concept for modular renewable energy deployment in estuarine channels.
In their simulation study, the team investigated longitudinal wake recovery, its effect on array efficiency, and the trade-offs between turbine spacing, installed capacity and energy yield. Wake refers to the turbulent water flow downstream of a turbine after energy extraction, which can reduce the performance of downstream turbines.
“Although the present work is illustrated through a case study in the Boqueirão Channel, the proposed methodology is not site-specific and can be extended to other estuarine channels with similar characteristics, such as geometric constraints, large tidal ranges, strong currents and favorable solar resource availability,” the team said. “Therefore, the framework provides a useful basis for the pre-feasibility assessment of modular hydrokinetic and hybrid energy farms in estuarine environments.”
According to the researchers, the tidal regime in the Boqueirão Channel is semidiurnal, with a period of approximately 12.4 hours. The region experiences tidal ranges above 6 m and current velocities often exceeding 2.5 m/s, resulting in a maximum power density of 7.63 kW/m² and an annual energy density of 17.96 MWh/m². Around 82.5% of annual current velocities fall within the turbine’s 0.5–2.0 m/s operating range. For the PV component, the area receives strong solar irradiation of around 5–5.5 kWh/m² per day, or about 1,900 kWh/m² annually.
The tidal current generation component was based on the Yarama hydrokinetic turbine, a six-blade horizontal-axis diffuser-augmented turbine designed for low-speed estuarine and river conditions. It has a rated hydraulic power of 5 kW, an effective electrical output of 4 kW, a cut-in speed of 0.5 m/s, and a cut-out speed of 2.4 m/s. The turbine features a 1.21 m throat diameter, a 1.64 m external diameter, and a 1 m diffuser length.
Before incorporating PV into the system, the researchers first estimated the turbines’ wake using numerical simulations. Based on this, they found that a lateral spacing of 3D (where D denotes the turbine diameter) resulted in almost no performance loss. In contrast, longitudinal spacing had a strong effect: when turbines were placed 40D apart along the flow direction, the downstream turbine’s power coefficient dropped from 0.88 to 0.64 due to wake losses. Increasing the spacing to 50D and 60D improved the downstream power coefficient to 0.76 and 0.80, respectively, showing that greater spacing allows better wake recovery and higher energy yield.
However, spacing the turbines lowers the number of units that can be installed within the available area, creating a trade-off between energy yield and installed capacity. Therefore, the scientists decided to install solar panels on top of each turbine on a catamaran-type floating platform. Each hybrid unit is 4.5 m long and 2.0 m wide, with 0.45 m diameter pontoons and a 1.5 m vertical strut connecting the floating structure to the submerged turbine. The PV system consists of four panels mounted above the platform, with a combined capacity of 2.48 kW and an efficiency of 23%.
The researchers simulated the hybrid system as a floating farm installed in a 0.5 km × 3 km pilot area in the Boqueirão Channel. Each farm contained between one and 17 columns, with each column consisting of 138 hybrid tidal-PV units arranged side by side across the channel. For each farm configuration, the team also tested longitudinal spacing of 40D, 50D, and 60D between columns.
The simulation series showed that a farm with a longitudinal spacing of 40D and three columns would generate 5.186 GWh of energy per year, with a levelized cost of energy (LCOE) of $0.36/kWh. Expanding the layout to four columns would increase annual generation to 6.401 GWh, with an LCOE of $0.37/kWh, while a five-column configuration would reach 7.468 GWh/year with an LCOE of $0.38/kWh.
For the 50D configuration, six columns would generate 10.043 GWh/year at an LCOE of $0.33/kWh, eight columns would generate 12.466 GWh/year at $0.33/kWh, and the 11-column layout would generate 15.605 GWh/year at $0.35/kWh. For the 60D configuration, nine columns would generate 15.002 GWh/year at $0.30/kWh, 12 columns would generate 18.680 GWh/year at $0.31/kWh, and the maximum 17-column layout would generate 23.956 GWh/year at $0.32/kWh.
The results also indicated that, while wake effects lead to reduced energy output from downstream hydrokinetic turbines, the integration of photovoltaic generation helps to partially compensate for these losses. As a result, the hybrid configuration improves the overall productivity of the site, enhancing total energy yield and making more effective use of the available environmental resources.
“Overall, the study confirms that hybrid hydrokinetic-photovoltaic systems represent a technically feasible and economically promising solution for modular renewable energy deployment in estuarine channels,” the academics concluded. “The proposed methodology provides a robust decision-support framework for early-stage project assessment, enabling realistic comparisons between array layouts, spacing strategies, and hybridization levels.”
The system was presented in “Design and techno-economic assessment of a hybrid diffuser-augmented hydrokinetic–PV array in an estuarine channel,” published in Energy Conversion and Management. Scientists from Brazil’s Federal University of Maranhão, Federal University of Itajubá, Federal Institute of Maranhão, and the University of Campinas have contributed to the research.
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