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Researchers from four Brazilian universities developed a hybrid floating system that combines submerged tidal energy turbines with solar panels installed on catamaran-type platforms for modular electricity generation in estuarine channels. Simulated in the Canal do Boqueirão, in Maranhão, the project showed that a farm with 17 columns and 138 units per column would produce almost 24 GWh per year.
Brazil may be facing an unprecedented solution to generate renewable energy in coastal regions without building dams or occupying large areas of land. Researchers from the Federal University of Maranhão, the Federal University of Itajubá, the Federal Institute of Maranhão and the State University of Campinas developed a floating system that simultaneously harnesses tidal force and solar radiation in estuarine channels, where rivers meet the sea and currents reach speeds capable of moving turbines with commercial efficiency. The concept was published in the scientific journal Energy Conversion and Management and presents simulation results that indicate technical and economic viability.
The location chosen for the case study was the Canal do Boqueirão, in Maranhão, a region with exceptional conditions for this type of generation. The channel presents tides with amplitudes exceeding 6 meters and currents that frequently surpass 2.5 meters per second, resulting in a maximum power density of 7.63 kW per square meter and an annual energy density of 17.96 MWh per square meter. In addition, the region receives strong solar irradiation of approximately 5 to 5.5 kWh per square meter per day, which makes it an ideal location for a floating system that combines the two energy sources.
How the hybrid floating system works
Each unit of the floating system is composed of two integrated elements: a submerged hydrokinetic turbine and a solar platform on the surface. The turbine used is the Yarama, a horizontal-axis model with six blades and an integrated diffuser, designed specifically for low to medium speed conditions in estuaries and rivers. It has a nominal hydraulic power of 5 kW, an effective electrical power of 4 kW, a starting speed of 0.5 meters per second, and a stopping speed of 2.4 meters per second. The throat diameter is 1.21 meters and the outer diameter reaches 1.64 meters.
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On the surface, each unit of the floating system features a catamaran-type platform measuring 4.5 meters in length by 2 meters in width. The pontoons have a diameter of 0.45 meters and a 1.5-meter vertical support connects the structure to the submerged turbine. On the platform, four solar panels with 23% efficiency add up to a capacity of 2.48 kW. The result is a compact unit that generates electricity both from the force of the water passing through the turbine and from the solar radiation hitting the panels, operating complementarily throughout the day and the tidal cycle.
The wake problem and why spacing matters
When a turbine extracts energy from the water current, it creates a downstream turbulence zone called a wake, where the flow velocity is reduced. If another turbine is positioned too close to this zone, its performance drops significantly because it receives water with less kinetic energy. The researchers investigated this phenomenon in the floating system and found that a lateral spacing of three times the turbine diameter practically eliminates interference losses between side-by-side units.
Longitudinal spacing, however, showed a much more critical effect. With turbines positioned 40 diameters apart in the direction of flow, the power coefficient of the downstream turbine dropped from 0.88 to 0.64. Increasing to 50 diameters, the coefficient rose to 0.76. With 60 diameters of spacing, it reached 0.80. This data creates a dilemma: the greater the spacing, the better the individual performance, but fewer turbines fit in the available area. It was precisely to solve this dilemma that the researchers decided to integrate solar panels into the floating system, compensating for the hydrokinetic losses caused by the wake with solar energy.
Production numbers that the Boqueirão Channel can deliver
Researchers simulated the floating system as a farm installed in a pilot area of 0.5 km by 3 km in the Boqueirão Channel. Each farm contained between one and 17 columns, with each column composed of 138 hybrid units arranged side-by-side along the channel. For each configuration, the team tested longitudinal spacings of 40, 50, and 60 diameters between the columns, generating a matrix of results that allows choosing the best cost-to-production ratio.
The most productive simulated configuration featured 17 columns and 60-diameter spacing, generating 23.956 GWh per year with a levelized cost of energy of US$ 0.32 per kWh. In smaller configurations, such as 9 columns with 60 diameters, production was 15.002 GWh annually at US$ 0.30 per kWh, the lowest cost among all simulations. The configuration with 50 diameters and 8 columns would produce 12.466 GWh per year at US$ 0.33 per kWh. The data shows that the hybrid floating system allows for modular production scaling, adding columns as demand grows and financial resources become available.
The sun that compensates for what the tide loses
One of the most relevant findings of the study is that photovoltaic integration partially compensates for efficiency losses caused by the wake in downstream turbines. When a turbine in the second or third column produces less energy because the current reaching it has already been partially decelerated by the previous column, the solar panels installed in the same unit continue to generate electricity normally. Solar radiation is not affected by the hydrokinetic wake, which means the photovoltaic component acts as a stabilizer of total production.
This complementarity between tides and sun also manifests throughout the day and year. The tidal regime in the Boqueirão Channel is semi-diurnal, with a period of approximately 12.4 hours, meaning that the strongest currents occur at variable times. Solar panels, in turn, produce more during the central hours of the day. When the tide is weak, the sun compensates. When the sun sets, the tide may be at full strength. This alternation reduces periods of low generation and makes the hybrid floating system more reliable than either of the two sources operating in isolation.
A methodology that serves other channels in Brazil and the world
The researchers made a point of highlighting that the study in the Boqueirão Channel is an illustrative case, but that the developed methodology can be applied to any estuarine channel with similar characteristics. Geometric restrictions, large tidal ranges, strong currents, and good availability of solar resources are the criteria that make a location viable for the floating system, and these conditions exist in various points along the Brazilian coast and in other tropical and equatorial countries.
Brazil’s northern coast, which includes Maranhão, Pará, and Amapá, has some of the largest tidal regimes on the planet, with amplitudes that in certain points exceed 8 meters. These same estuaries receive intense solar irradiation for most of the year, creating ideal conditions to replicate the concept tested in the Boqueirão Channel. For the researchers, the hybrid floating system offers an alternative to large hydroelectric plants and wind farms in regions where transmission infrastructure is limited and distributed generation makes more economic and logistical sense.
Brazilian science at the frontier of renewable energy
The floating system developed by researchers from four Brazilian universities combines submerged turbines and solar panels on catamaran platforms to generate tidal and solar energy simultaneously in estuarine channels. The study confirmed that the concept is technically viable and economically promising, with a 17-column farm in the Boqueirão Channel capable of producing almost 24 GWh per year, enough energy to supply thousands of homes in a region of Maranhão where access to electricity is not always guaranteed.
Did you know that Maranhão has tides over 6 meters and that Brazilian researchers are developing ways to transform this force into electricity? Tell us in the comments what you think of the hybrid floating system, if you believe this technology has a future in Brazil, and if the combination of tidal and solar energy makes sense to you. We want to hear your opinion on Brazilian science in the field of renewable energy.
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