By Satish Pandey, Head – Analytics and Advisory; Sourav Kumar, Head – BU; Rakshita Mhatre, Senior Engineer and Sanya Verma, Mahindra Teqo Pvt Ltd
The only difference between floating and regular solar installations is that floating solar projects are mounted on a water body, negating the requirement for land. These solar plants use specialized technologies to float on water.
Some of the major components of these projects include main floaters, secondary floaters, walkway floaters, DC cable floaters (for array to platforms), and accessories such as float joining high density polyethylene (HDPE), module clamp, and spreader bar (anchor truss). The mooring system (dead weight), the array (design, supply, and installation), the anchoring (rope/chain), and the fasteners are all part of the mooring system and accessories, stainless steel handrails, and anchor truss are required for inverter platforms and inverter duty transformer (IDT) platforms. Meanwhile, assemblies of floaters and modules, DC and AC cable floaters are all part of the floaters array. Finally, the anchoring and mooring system installation includes floaters, platforms, and DC cable floaters.
This paper discusses the design considerations for floating solar plant to get maximum yield with the best use of materials.
Electrical and mechanical reliability
This part focuses on the design requirements and considerations for the electrical and mechanical components of the floating solar plants. It includes anchoring and mooring system, floaters, inverters installation and cabling.
Anchoring and Mooring System: A mooring system is required in the floating PV power plant to cope with the varying water levels, to position the module at a particular place, to keep floating solar arrays within reasonable proximity of some target location (station keeping) and to minimize the movement of solar arrays caused by environmental forces (such as winds, waves, currents).
For the design of the mooring system, following steps should be followed:
- Site Specifications
- System Specification
- Initial Load Calculations
Mooring Designing: When defining the proper design specifications for the mooring system, the accuracy of the site’s raw environmental data is crucial. For instance, there is a chance that several components, such as the float attachments, interconnections, mooring lines, and anchors, could break over time if the design maximum wind speed is 30 m/s but the actual maximum wind speed may be 40 m/s.
Anchoring Designing: The anchoring system design usually consist of Spreader bars made of aluminum that allow the mooring lines to be attached to the island and distribute the weight through the floats’ two connecting tabs. Cables are also used to connect anchors and spreader bars and are sized accordingly, taking into account water level variations. Adjustable length chains are present at the end of the wires to accommodate any changes in length. The main and secondary float rows are utilized to maintain buoyancy in strong winds, without the PV panel. Lastly, anchors are used to moor the island to the seabed or to coastlines, which helps decrease its movement on the water’s surface and withstand wind loads. Together these components create a stale anchoring system.
Pontoon/Floating Structure: The total floating system for attaching solar panels encloses, the High Density Polyethylene (HDPE) floaters that have successfully passed many tests, including the Hunt salability test, ageing test, Ultra Violet test, the Technischer Überwachungsverein(TUV) wind tunnel test, and others. These tests confirm that the floaters are of high higher tensile strength (2000 daN) than most comparable items, making them more reliable and sturdier. The aluminum alloy clamps make it simple to attach solar modules to main floaters, saving time and money on labor. Furthermore, the floaters have a 25-year service life, making them a worthwhile investment for those looking for a long term solution.
Primary Floaters Design Elements: The material used for designing the primary floaters must meet several requirements. Firstly, it must be completely recyclable and non-toxic. Additionally, it should be resistant to UV radiation, alkalis, and salt water. The material should also be adaptable to variations in reservoir water levels, making it easy to adjust as needed. Furthermore, the floating material used should also be completely recyclable. The buildings constructed must be capable of withstanding extreme temperature variations, ranging from -60°C and 80°C. Finally, it is essential that the material has a long lifespan or a 25-year capacity for resistance underwater.
Installation of Inverters: Similar to a normal solar power plant, a series of combiner boxes transport DC power produced by solar PV modules to the inverter, where it is ultimately transformed into AC power. A developer has the option of using central inverters or many string inverters. Inverters can either be installed on a separate floating platform or on the ground, depending on the size and proximity to the coast. Floating solar PV inverters can typically be found on land near solar arrays for lesser capacities, but not for larger ones.
Cabling: Cable management and routing in floating PV plants require careful planning. In contrast to ground-based solar PV systems, floating solar PV plants have variable cable length due to the movement of the floating platform on the water’s surface. The wind load and changes in water level are what cause the floating platform to move. In order to accommodate the floating platform’s movement, extra length in the form of slack must be provided. If this is neglected, inadequate cable length could cause cables to break and snap under tension. The cable’s voltage, current, and losses are the other factors that determine cable size in addition to its length.
Category I. Energy yield Assessment
In this section we are going to talk about the factors that may affect the energy yield from the floating PV plant.
Effect of temperature difference: As with land-based systems, the mounting structure (which significantly influences the U-value), wind, and air temperature will mostly dictate the working temperature of the module for FPV mounted above the water’s surface but not in direct contact with the water. As a result, lower air temperatures and changes in the air flow (wind/convection) beneath the modules have the effect of lowering the operational temperature of such systems.
The ambient medium for floating PV technology will be the temperature of the water on one side (or both for submerged structures). Water has a thermal conductivity of 0.6 W/mK compared to air’s 0.026 W/mK, hence for such structures, water temperature and flow will be dominant. As a result, in addition to air temperature, wind speed, and mounting structure, the operating temperature of the module is likely to be affected by the water temperature and water flow.
Floating PV power plants use specialized technologies to float on water, and the major components include main floaters, secondary floaters, walkway floaters, DC cable floaters, array to platforms, accessories, inverter platforms, inverter duty transformer (IDT) platforms, mooring system (dead weight), stainless steel handrails, anchoring (rope/chain), anchor truss, aasteners, and launching of floaters array. This paper discusses the design considerations for the floating solar PV plant, such as electrical and mechanical reliability, energy yield, and anchoring and mooring system.
The most important details are that the anchoring system design is composed of spreader bars made of aluminum, cables to connect anchors and spreader bars, adjustable length chains at the ends of the wires, main and secondary float rows to maintain buoyancy in strong winds, anchors to moor the island to the seabed or coastlines, aluminum alloy clamps to attach solar modules to main floaters, and primary floaters design elements such as recyclable, non-toxic, and resistant to UV radiation, alkalis, and salt water. Inverters are similar to a normal solar power plant, with a series of combiner boxes transporting DC power. The wind load and changes in water level are what cause the floating platform to move, so extra length in the form of slack must be provided.
The cable’s voltage, current, and losses are other factors that determine cable size in addition to its length. The ambient medium for floating PV technology will be the temperature of the water on one side, and the operating temperature of the module is likely to be affected by the water temperature and water flow.
- Kjeldstad, Torunn, Dag Lindholm, Erik Marstein, and Josefine Selj. “Cooling of floating photovoltaics and the importance of water temperature.” Solar Energy 218 (2021): 544-551.
- Floating Solar Anchoring and Mooring (tyt.com.tr)
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