Performance analysis of a floating photovoltaic covering system in an Indian reservoir
Nagananthini Ravichandran and others. Performance analysis of a floating photovoltaic covering system in an Indian reservoir, Clean Energy, Volume 5, Issue 2, June 2021, Pages 208–228, https://doi.org/10.1093/ce/zkab006
Floating photovoltaic (FPV) systems are one of the globally emerging technologies of renewable energy production that tend to balance the water–energy demand by effectively saving the evaporated water from reservoirs while generating electrical power. This study presents the performance analysis of a model FPV plant in an Indian reservoir. The Mettur dam reservoir located in Tamil Nadu, India with a hydroelectric power plant of 150-MW capacity is considered as a test case. The preliminary design of the FPV plant is proposed based on a detailed study of the key design elements and their suitability for Indian reservoirs. The proposed plant is numerically analysed for various tilt angles, mounting systems and tracking mechanisms in order to assess its potential power generation. A flat-mount system in landscape orientation was found to exhibit a high performance ratio. Further, a fixed-tilt FPV system with a panel slope of 10° and an FPV system with single-axis tracking were found to be suitable for the Mettur reservoir. Further, cost analysis of the FPV system is also presented along with the carbon-footprint estimation to establish the economic and environmental benefits of the system. The results show that the total potential CO2 saving by a FPV system with tracking is 135 918.87 t CO2 and it is 12.5% higher than that of a fixed-mount FPV system.
Introduction
Gaseous emissions due to energy production from fossil fuels are polluting the atmosphere gradually, which not only diminishes the purity of the air, but also affects human health. The major pollutants from fossil-fuel combustion are the greenhouse gases, which include carbon dioxide, methane, benzene and nitrogen oxides. These are the major cause of global warming, air pollution and water pollution [ 1]. In order to combat climate change, moving towards clean energy while generating affordable electricity is necessary. Power generation through renewable energy sources (RES) plays a significant role in transforming the fossil-fuel-based power sector towards zero-carbon green energy by the production of solar, wind, hydro and geothermal power [ 2]. As per the statistics provided by the International Renewable Energy Agency, the global renewable-energy-generation capacity increased by 7.40%, which is equal to 176 GW, from 2018 to 2019 [ 2]. The growth of renewable energy production is spectacular particularly in India, where a 27% increase in renewable energy production has been achieved in recent years, of which 43% is accounted for by the solar photovoltaic (PV) sector [ 3]. The launch of the Jawaharlal Nehru National Solar Mission (JNNSM) has remarkably increased the deployment of PV systems and resulted in 32.53 GW solar energy production, making the nation the fourth-largest generator of renewable energy [ 4]. By 2022, JNNSM has a target of 175 GW renewable energy production, with 100 GW from the solar sector as per the report by the Solar Energy Corporation of India (SECI) [ 5].
With sunlight being the major source of energy production, power generation through PV panels is receiving worldwide attention. Also, the availability of technically advanced silicon panels and a cost-effective way of generating power even in low-light conditions motivate consumers for self-power generation. However, the unavailability of land for the installation of large-scale land-mounted PV systems is the major drawback. Thus, achieving the target solar energy production just through land-mounted and rooftop PV systems is quite challenging. One of the alternative solutions to compete with the target framed by the nation is FPV, also called floatovoltaics, a floating solar PV (FSPV) or a floating solar covering system (FSCS) [ 6–8]. This new emerging technology in which the solar panels are placed on the water surface of ponds, lakes, lagoons, reservoirs and oceans shows increased efficiency compared to land-mounted PV systems [ 9]. The other significant environmental impact of placing PV panels on the water is the reduction in evaporation, which helps in saving freshwater for domestic and agricultural purposes [ 10]. Studies revealed that covering the water surface has the potential to mitigate water loss through evaporation by ≤90% [ 11]. This highly efficient technology had faced real-time implementation since 2007; from then, it has shown dramatic growth with increased efficiency [ 12].
The cumulative capacity of FPV projects in India has reached 2.70 MW recently and the country aims at producing 1721 MW of renewable energy through the projects of the SECI, National Thermal Power Corporation, National Hydroelectric Power Corporation and state-level distribution companies and city-development authorities [ 6, 8]. The first FPV system in India was commissioned in the year 2014, with 10-kW capacity in West Bengal, following which the implementation of this technology had scaled up every year to a present cumulative capacity of 2.70 MW [ 2, 6]. According to the combined analysis from the Indian Energy Transition Commission (ETC) and the Energy and Resource Institute (TERI), water bodies with a surface area of ~18 000 km 2 across the states and union territories of India have the potential to implement 280 GW of FPV systems [ 6]. The cumulative tender announced by the Government of India during 2019 for the FPV installations with 1700-MW capacity is in the developmental stage in different states of the country. Considering the scope of massive development in this sector, it is mandatory to investigate the overall performance of the FPV systems as a reservoir cover to arrive at an environmentally friendly design solution.
In this context, the present study aims at assessing the electrical performance of the FPV model in an Indian reservoir. The Mettur dam reservoir with hydroelectric power plants in Tamil Nadu is selected as a test case. The selected reservoir is the major source of water for irrigation and drinking purposes for the district of Salem. Potential evapotranspiration is calculated using Hamon’s method to assess the water loss from the reservoir. The model FPV plant is designed for a lesser reservoir coverage area to avoid hindrance to the hydropower generation and to maintain water quality. The system is also designed with suitable spacing between every row of the FPV array to maintain positive ecosystem services [ 18]. The effects of variation in tilt angle, tracking mechanisms and mounting mechanisms of the model FPV plants are assessed in detail. In addition, the carbon footprint and cost of the FPV system are also calculated to understand the environmental and economic feasibility of this technology. Finally, the benefits of a hybrid HEPP–FPV is assessed by calculating the direct and indirect water savings in the reservoir and the FPV model plant is compared with the existing FPV plants in India. As Tamil Nadu Generation and Distribution Corporation (TANGEDCO) is planning to deploy a 100-MW FPV plant in the Mettur reservoir, the key design parameters suggested in this study can aid during the design and implementation stages of the project. The simplified methodology followed in the study will also support in assessing the overall performance of FPV plants to be deployed in any reservoir all over the world.
Effects of evapotranspiration on freshwater sources in India
In the last two decades, per-capita water availability (m 3 /capita/year) has been continuously deteriorating in India. Due to the exponential increase in the population and acquisition of water-flow and storage areas for building construction, freshwater sources are diminishing rapidly in India, which in turn results in high water scarcity in summer. In addition, the country experiences an annual global horizontal irradiation ranging from 5.0 to 6.0 kW/m 2 and rainfall only for 3–4 months in a year. This arid climatic condition leaves the country experiencing acute freshwater shortages [ 19].
Over the past 100 years, carbon emission from burning fossil fuels has adversely increasing the global temperature, which in turn increases the potential evapotranspiration [ 19]. Out of 4000 km 3 of water received through precipitation in India, 700 km 3 of water are lost through evaporation [ 20]. The evapotranspiration reaches almost 1000 mm/year in the southern states of India such as Tamil Nadu and Kerala [ 21]. These regions are undergoing acute water scarcity during the lean seasons due to evaporation loss of water and diminishing water resources. This can be clearly seen from the reduction in the per-capita availability of water in India from 1950 to 2050 listed in Table 1 [ 22]. This also highlights the necessity to conserve diminishing freshwater sources like river basins, canals, dams and reservoirs to prevent the larger part of India from ‘water-stressed’ conditions (
Per-capita availability of water resources in India [ 22]
Technological advantages of FPV technology
Other than the fact that FPV installations help reduce land usage and also save the water from evaporating, FPV has some attractive technical benefits which include the design of the system and most importantly high energy yield when compared to their land-based counterparts.
There is a natural cooling effect of the water body below the solar panels this reduces the module temperature and increases the energy yield. In some cases, it will be difficult to anchor the FPV system but in cases where such difficulty is not there, installing these structures is simple. They are assembled on land and are pushed onto the water body. They are less prone to dust pollution and it also reduces water evaporation but it depends on technology, water body coverage, and characteristics, applied calculation methodology, etc.
Current market status
The United States was the first to demonstrate floating PV panels—with the first installation occurring 10 years ago on pontoons on an irrigation pond in Napa Valley, California. While Asia dominates the current project pipeline, other countries like Brazil, France, Netherlands join as deployment on reservoirs and lakes gathers momentum. It is estimated that the global FPV market will reach 1.6 GW by the end of 2021 which will be more than double the total installed capacity in 2020. The graph below represents the annual global FPV installations.
Figure 2: Annual Global Floating Solar Installations.Source: Wood and Mackenzie global market services.
It has been predicted that China will dominate FPV installations over the next five years, with India and South Korea trailing close behind. Asian markets like Taiwan, Malaysia, Indonesia, Thailand, and Vietnam. Outside Asia, the Netherlands will continue to lead the European FPV market through 2026, with other countries, such as France and Spain, expected to maintain a significant share of the European market by the same year.
While Asia and Europe are expected to hold most of the global FPV capacity through 2026, other markets will emerge over the coming years. The figure below represents the top 10 markets for FPV demand in the world.
Figure 3: Top 10 FPV market from 2020.2026.Source: Wood and Mackenzie global market services.
Challenges of FPV systems:
FPV applications are typically more expensive than ground-mount technologies of a similar size and location. This is typical because of high soft costs and the structural balance of system costs. The most important factor is the bathymetry of the water body determines the design layout of the anchoring and mooring system. It should also be able to withstand stronger wind loads. According to the report by Wood Mackenzie. Japan continues to be the highest cost market with average system costs of 5000.68/W in 2021, while India currently has the lowest system costs of.78/W.
As costs continue to fall, Solar’s share of power supply will rise and begin to displace other forms of generation which will greatly benefit the FPV market. FPV has an important role to play in the energy transition as it presents an opportunity for solar markets facing challenges with traditional PV applications. As more countries commit to competitive solar and overall renewable energy targets, FPV will be key to meeting these goals. This is still a niche industry that has a lot of opportunities in the future.
How to build a floating solar farm
Installing solar systems on water offers several advantages. RWE uses floating solar at the Amer power plant in Geertruidenberg/Netherlands.
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Installing solar systems on water offers several advantages. RWE uses floating solar at the Amer power plant in Geertruidenberg/Netherlands.
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An increasing number of solar farms is learning how to swim – and for good reason. Modules floating on a lake save space on land. In fact, this innovative technology, known as ‘floating solar,’ offers even more advantages. There is less shade on open waters and their cooling effect increases solar cell efficiency, which promises to deliver higher yields.
How a floating solar-powered artificial leaf generates synthetic fuels. Only5mins!
This is why floating technology is booming especially in Asia, which has many densely populated regions. We showcased some of the biggest farms on en:former. How are such solar farms built and how does their design differ from that of their conventional variants? Our image gallery presents answers to these questions and shows how RWE installed its first floating PV system in the Netherlands.
The construction of the floating photovoltaic system at the Amer power plant.
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This is the lake on which a 6.1 megawatt floating solar farm is to be installed immediately neighbouring the Amer power station in Geertruidenberg in the Dutch province of Noord-Brabant. The company has already set up a ground-mounted PV array at this site. In addition, the power plant is gradually being converted to fire biomass.
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A crane placing building material on a lakeside construction platform before construction begins.
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These are the blocks of concrete to which the floaters, carrying the solar modules will be anchored to.
This is the lake on which a 6.1 megawatt floating solar farm is to be installed immediately neighbouring the Amer power station in Geertruidenberg in the Dutch province of Noord-Brabant. The company has already set up a ground-mounted PV array at this site. In addition, the power plant is gradually being converted to fire biomass.
A crane placing building material on a lakeside construction platform before construction begins.
These are the blocks of concrete to which the floaters, carrying the solar modules will be anchored to.
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A crane parked on the platform lowers the anchoring blocks onto the bottom of the lake one by one.
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Scuba divers also play their part, attaching anchor cables to the concrete blocks to keep the floaters in place later on.
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The next step involves the floaters. They are made of durable plastic capable of easily withstanding the wind and weather for many years, which can be recycled at the end of their service life.
A crane parked on the platform lowers the anchoring blocks onto the bottom of the lake one by one.
Scuba divers also play their part, attaching anchor cables to the concrete blocks to keep the floaters in place later on.
The next step involves the floaters. They are made of durable plastic capable of easily withstanding the wind and weather for many years, which can be recycled at the end of their service life.
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Now electricians mount the solar modules to the floaters that are arranged to form a square. The system is quite clever. Although the modules have firm connections, the lattice-like structure is flexible enough to adjust to water movements. The connecting elements double as standing areas for maintenance work.
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The PV modules are slanted to maximise sunlight incidence. Each set of modules, referred to as a ‘string,’ has a dedicated cable running over the floaters to the shore.
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Assembly can be performed from the shore as the pontoons rest on wooden pallets and are guided onto the water using beams. The structure moves farther out onto the lake with every added row of modules.
Now electricians mount the solar modules to the floaters that are arranged to form a square. The system is quite clever. Although the modules have firm connections, the lattice-like structure is flexible enough to adjust to water movements. The connecting elements double as standing areas for maintenance work.
Triple Bottom Line Design Studio
Yanagisawa is the head of Tokyo-based design studio Triple Bottom Line. His studio has a unique FOCUS on a hybridization of modalities from functional interior design products to sustainable machines and mass-producible infrastructures. As a designer, Yanagisawa is naturally drawn to aesthetically pleasing shapes and lines. But as an engineer, he believes that objects should always have a practical function and should be easy to commercialize. It’s an ongoing pursuit to find a balance between those two sensibilities.
Originally from Japan, Yanagisawa attended university in the UK, where he studied design engineering and material engineering with a FOCUS on product design and sustainable furniture. Generative design—which uses algorithms driven by artificial intelligence (AI) to generate a wide range of design options well beyond what a team of humans can do—appealed to him early on, and has created many opportunities to hone his craft and explore practical solutions.
Yanagisawa’s portfolio includes everything from LED pendant lights to a 3D-printed road bike with Internet of Things (IoT) functionality, which won him a CES Innovation Award in 2016. He also worked on the 2019 iF Design Award-winning DENSO engine control unit (ECU), which uses generative design to reduce the weight of an automobile ECU by at least 12%. His most recent accomplishment is a floating device used to generate solar power on water—a project that Yanagisawa and a small team of five completed in just six months. He estimates this process would have taken more than two years without strategically applying generative design in Autodesk Fusion 360.
Generative Design and AI for Large-Scale Sustainability Projects
A general contractor in Japan was hired to develop a new kind of float for PV systems but didn’t have the mass-production knowledge or background needed to make the deadline, so Yanagisawa was called in for his expertise.
The contractor had already spent many hours and a good portion of the budget on employee training and sought a way to avoid starting from zero. A project stakeholder knew Yanagisawa’s work and thought his background aligned with the mission.
At the time, Yanagisawa was working with a small team and decided early on that traditional design and testing methods would not suffice, considering the client had only 15 months to complete the entire project. Many floating PV systems had already been developed, but the actual floats weren’t standardized and needed to be designed from scratch. Yanagisawa applied generative design, which quickly turned out 500 float shape options with minimum and optimum wall thickness, based on the assumed strength needed.
“Even with the 500 solutions, we realized we needed to modify a few things to meet certain standards,” Yanagisawa says. “We had to make modifications to the concept models based on feedback from the engineers on the factory side who would be responsible for production. The process is known as DFM [design for manufacturing] or MVT [mass-production verification test], which is generally mandatory for mass-produced products. We also needed to avoid conflicting patent issues as there were already two major companies in the world that did floating PV systems—a French company and a Chinese company.”
Laws, regulations, and standards related to floating solar systems are not fully developed yet, so Yanagisawa and his team established their own standards for the floats based on well-researched existing standards for land-based power generation equipment, floats, and anchors in other fields, as well as standards for water pollution. While incorporating necessary functional design elements, they narrowed 500 options down to just a few and ultimately settled on a final design.
BayWa r.e. Floating PV – Transforming unused bodies of water into high-yield green energy generators
Float Test in Kagawa, Japan
Once Yanagisawa and his team completed the design prototype, they needed to test the device in a suitable location. They chose Kagawa, a Japanese prefecture in the northeast of Shikoku Island that’s well known in the agricultural industry. The Kagawa soil is fertile and conducive to crop production, and to make up for minimal rain, the locals have developed their own self-sustaining water supply.
To verify the floats’ functionality, a testing facility in Kagawa was created in collaboration with locals in the agricultural industry. There, they began generating their own electricity to power the facility. Computer-aided engineering specialist Misao Mizuno, an expert in structural analysis and fluid dynamics, was enlisted to help throughout the testing phase. He used simulation to analyze whether the model met specific performance requirements.
“Computer simulation speeds up the development process and also helps reduce the waste from validation work, as it reduces the need for physical testing,” Yanagisawa says. “The original plan was to test the actual product for five to six months, but since Misao could replicate most of the tests in the simulation environment, the time was reduced to two months.”
After the two-month period, Yanagisawa’s floats passed and have been cleared for mass production. “Our system has been working,” Yanagisawa says. “Right now, it’s only in some Asian fields because there’s no globally standardized safety regulation yet, but a few European companies are interested.”
PV power generation is still an emerging market, and some new regulations must pass for companies to justify funding something of market scale, but there’s definitely momentum. Generative design opens up all types of opportunities for Rapid prototyping and testing floating solar; mainstream acceptance could be on the horizon.
Human-AI Collaboration
With a growing population using more space on the planet, outside-the-box solutions like Yanagisawa’s floats could potentially make a huge impact on sustainability. “Originally, I’m a designer, and I want to make beautiful, clean things,” he says. And he would love to see a better translation of style within AI and generative design.
“Currently, generative design focuses on proposing mass- and structure-optimized models based on mechanical properties, price, and so on,” Yanagisawa says. “It is not making aesthetic decisions, but merely processing to meet the mechanical and functional requirements established under specific conditions using metacognition given in advance. The AI’s answers may seem disjointed, but to truly collaborate successfully with AI, we need to correctly understand the design language they use and translate it into our own.”
Yanagisawa also hopes to solve creating floating solar for the sea. Of course, with sea-based PV systems, there are extreme elements to contend with, including rising sea levels, harsh conditions, and the impact floats could have on biodiversity. Perhaps generative design will be able to pinpoint environmentally friendly solutions in this arena. The collaboration between humans and AI is exciting territory, and when they can build on each other’s strengths, the possibilities are limitless.
About the Author
Elizabeth Rosselle is a freelance journalist, copywriter, and designer who splits her time between San Francisco and Bali, Indonesia.