Multiple Advantages of Floating Solar PV

Installing Solar PV panels on floats over existing water bodies – precious land required on ground mounted Solar PV is avoided in a thickly populated country. The floating solar panels reduce evaporation in two ways – firstly by reducing the temperature of water and secondly by reducing the speed of wind over it by providing a path resistance to wind flow. Water scarcity is a harsh reality in India, especially during the dry season. The cooling effect due to water underneath also leads to PV efficiency improvement. The reduction of sunlight exposure to water in reservoirs reduces the growth of algae and facilitates the growth of fisheries by providing a shelter.

The size FSPV projects are going up and NTPC has emerged as a leader in FSPV installations.

The Omkareshwar (600 MW) Floating Solar Project will be the world’s largest floating solar power plant upon completion. NTPC has also decided to augment the 100 MW at Ramagundam by 50 MW in the balancing reservoir and an additional 122 MW in the banks of it.

What is Floating Solar PV?

Floating Solar PV (FSPV) Project essentially is Solar panels installed on water bodies like reservoirs, lakes, industrial ponds, etc., the FSPV components of are listed below.

• Solar PV Modules
• Inverters
• Floats
• Anchors & Mooring Lines
• Combiner Boxes
• DC Cables
• MC4 Connectors

For larger Floating Solar PV systems or Systems with considerable distance to shore, it is recommended to locate the inverters, as well as the transformers, on a floating structure in proximity to the rest of the Floating PV Array with cable(s) to the onshore switching facilities and grid interconnection point. For smaller Floating Solar PV systems with short distance to shore, it can be considered to locate inverters and transformers on land.

Anchoring and Mooring Design

• Site-Specific Design: Base anchoring and mooring designs on thorough site analysis, including water depth, currents, wind, and substrate type.
• Redundancy: Use multiple anchors and mooring lines to distribute load and ensure system stability in case of line failure.
• Corrosion Resistance: Select materials with high corrosion resistance, especially for saline or harsh environments (e.g., galvanized steel, synthetic ropes).
• Flexibility: Incorporate elasticity in mooring lines to absorb dynamic loads from wind and waves, ensuring smooth system movement.
• Proper Scope Ratio: Ensure mooring line length is 3:1 to 5:1 relative to water depth to maintain stability with water level fluctuations.
• Environmental Impact: Minimize seabed disturbance and use eco-friendly materials that do not harm aquatic ecosystems.
• Regular Monitoring: Install sensors and schedule periodic inspections for early detection of wear, corrosion, or tension issues.
• Deadweight Anchors: Typically, large concrete or steel blocks used in calm waters with a stable substrate. Suitable for reservoirs with low current and minimal wave action.
• Screw Anchors: Ideal for soft sediment bottoms. These are drilled into the substrate and offer strong holding capacity in soft mud or clay.
• Pile Anchors: Long poles driven into the lakebed, effective for deep waters and resistant to vertical movements. They are ideal for sites with significant water level fluctuations.
• Drag Anchors: These are designed to dig into the substrate when tension is applied. Suitable for areas with soft sediment but less effective in hard or rocky bottoms.

Buoyancy and Load Distribution

• Buoyancy Requirements: The floating structure must have sufficient buoyancy to support the weight of the solar panels, inverters, cables, and other equipment, as well as withstand external forces from wind and water.
• Load Distribution: The weight of the equipment should be evenly distributed across the floating structure to avoid stress points that could cause sinking or instability.
• Safety Factor: Typically, the design incorporates a safety factor (e.g., 1.2 to 1.5) to ensure that the structure can handle excess weight from factors
  like additional equipment, rainwater accumulation, or debris.

Hydrodynamic Stability

• Water Current, Wind, and Wave Effects: The floating structure must be able to withstand forces from water currents, wind loads, and waves without excessive movement or tilting. Hydrodynamic simulations are often used to test stability.
• Pitch, Roll, and Yaw Resistance: The platform should minimize excessive motion (pitch, roll, and yaw) to ensure the solar panels remain optimally aligned and structurally safe.

Material Selection

• Corrosion Resistance: Materials used for the floating structure (e.g., HDPE, aluminium, or composites) should resist corrosion from constant exposure to water, UV radiation, and chemicals in the environment.
• Environmental Durability: The material must be durable enough to withstand environmental stressors such as varying temperatures, humidity, and exposure to pollutants.
• Weight and Strength: The material should be lightweight yet strong enough to support the system’s overall load and resist mechanical stress.

Mooring and Anchoring System Compatibility

• Mooring System Integration: The floating structure must be compatible with the anchoring and mooring system to ensure it remains securely in place despite environmental forces.
• Cable Flexibility: The design should include pathways for flexible cables that can adjust to the movement of the floating structure, preventing damage to electrical components.

Thermal Expansion and Contraction

• Thermal Movement: The structure should account for expansion and contraction of materials due to changes in temperature, especially in areas with high temperature variation. Failure to do so could cause warping or structural stress.
• Allowances for Movements: The structure should be designed with expansion joints or allowances to accommodate material movement without compromising integrity.

Modularity and Scalability

• Modular Design: A modular approach allows for ease of assembly, transportation, and future expansion. Modular components also simplify repair or replacement of damaged sections.
• Scalability: The design should allow for easy scaling of the system, whether expanding the capacity or adapting to different site conditions.

Key Design Criteria for Floating Structures

Maintenance Access and Safety

• Accessibility: The structure should allow for easy access to solar panels and electrical components for regular maintenance and repairs.
• Safety Provisions: The design should include safety measures, such as railings or platforms, for technicians working on the floating array.

Cost Efficiency and Installation Ease

• Cost-Effective Materials: The design should balance cost efficiency with durability and performance, especially for large-scale projects.
• Ease of Installation: The structure should be easy to assemble, transport, and deploy at the project site, minimizing installation time and labour costs.

Site-Specific Conditions

• Water Depth: Anchoring systems must be designed to accommodate the varying water depths at the installation site (shallow or deep water). Anchors in shallow water might require different designs compared to those in deep water.
• Substrate Type: The type of lakebed or reservoir bed (sand, clay, mud, rock, etc.) determines the appropriate anchor type. For example, screw anchors are better for soft soils, while rock anchors may be needed for harder substrates.
• Wind Forces: The anchor system should be able to resist horizontal forces caused by wind pushing against the floating platform, especially in high-wind areas.

Capital Cost and LCCE

Capital cost of floating solar PV plants is 20-25% more than ground mounted solar plants.

Typically, floating solar costs INR 5-6Cr/MW with tariff at INR 3-3.2/kWh as against Rs 2-2.50/Kwh for Ground Mounted PV.

Benefits

• Land: About 4.5 acres of land per MW required for ground mounted Solar PV would be released for other use if it is decided to set up FSPV. India has a FSPV potential of 200 GW estimated conservatively with following criteria GHI >3 kWh/m²/day, i.e., greater than 900 units per day, Exclusion of water bodies in protected zones, Distance from substation (132kV) < 25 km, Depth of water bodies not considered.
• Prevents Evaporation of Water: Water is indeed an economic good, but a very special one. Water scarcity is a harsh reality in India: especially during the dry season. India’s projected water availability per capita was 1486 m³ in 2021 and is slated to decline to 1367 m3 by 2031. In terms of the Falkenmark indicator, this reflects water stress and not water scarcity. This is lower than the global average of 5500 m³ per capita. If current trends continue, India is on the path to becoming a severely water-scarce country, especially since, while 16-17% of the world’s population resides in the country, the landmass possesses only 4% of global freshwater resources.

India’s rapidly growing population, demand drivers will emerge amid the increased need for food, drinking water, sanitation, and development facilities. However, the constraints on water supply will be even more binding due to worsening water pollution, frequent droughts resulting from climate change. Water has no boundary; most rivers are either interstate rivers or international rivers bound by agreements for sharing of water. Disputes over sharing of water are hard to resolve with increasing population and industrialization.

The loss of water due to evaporation can be as high as 8 to 12% of the total water available and increasing due to global warming. If we cover only 10% of perennial water bodies with FSPV we save about 1% of the total potable water available which is a huge quantity. Simhadri Floating Solar PV Project (25MW project is spread across 75 acres in an RW reservoir. estimated to generate 55.11 million units of electricity annually Save 1,364 million litres of water per annum. The Ramagundam floating solar power plant in Telangana over 450 acres is estimated to generate 223 million units of energy annually. potentially avoiding water evaporation to the tune of approximately 3250 million litres per year.

• Water consumption in electricity: As against about 3 litres per Kwh of electricity from coal-based generation and 0.05-0.10 litres/kWh ground mounted Solar PV systems use minimal water, primarily for panel cleaning, the Hydro Projects though considered renewable are not without huge evaporation loss. But FSPV generate electricity and prevent evaporation to the extent of 15 to 25 litres/Kwh. If we price water for electricity at rates for industrial use   at Rs 0.03- 0.06, FSPV comes at par with ground mounted solar PV or even cheaper.
• Efficiency improvement: The cooling effect of water underneath improves the efficiency of Solar PV by 2-3%.
• Algae growth:  Covering 40% of a waterbody restricts the sunlight to the waterbody and reduces algae growth improving the aquatic ecosystem.
• Sheltering fisheries: Fish find shelter under the panel boosting their growth.
• Erosion: Limits erosion of reservoirs by moderating waves.

Conclusion

The challenge of keeping a plant floating and keeping it connected to the grid through suitable anchoring and mooring and designing floats not only for the panels but also for the inverter panels is quite daunting.

The winds and waves and the dangers of electricity near water need to be kept under reckoning. High wind speeds and water currents can be challenging, necessitating robust anchoring and mooring systems.

The floats for inverter panels made from ferro cement require extensive testing before installation.

FSPV can be damaged by speeding boats and fishermen. The panels are fixed with a tilt of 5 degree unlike a ground mounted flexible system. Safety hazard of electricity near water require careful planning.

CRZ and other environmental restrictions may come up. Reduced sunlight may lead to reduction in invective current in the water body leading to drop in oxygen levels.

Yet, the minimal land requirement, the 15 to 25 litres of additional water saving per kwh and efficiency improvement cannot be overlooked at a time GHG mitigation, water conservation and circularity of waste assume primacy.

Floating Solar PV presents a unique opportunity for India to address its renewable energy goals while also addressing water conservation. By making efficient use of existing water bodies, increasing energy generation efficiency, conserving water, and reducing land-use pressures, floating solar can support India’s goals for energy security, water management, and environmental sustainability.

Postscript

Cost of FSPV systems is currently higher than ground-mounted systems at LCOE of approx. Rs 3.25/Kwh in contrast to Rs 2.50/Kwhr for ground mounted Solar PV due to requirements of anchoring, mooring, and underwater cabling. Efforts are being made to reduce costs through technological advancements and
scaling up.

Installed alongside a conventional power plant, the floating plant can use existing plant’s transmission infrastructure and avoid expenses on the same. Hybrid projects, floating solar PV systems combined with hydropower or thermal power plants maximize resource utilization and enhance power generation efficiency.

Make up water reservoirs in power plants can be utilized to set up FSPV generating RE and preventing water loss to evaporation.

Floating Solar Inverter panels currently designed from ferro cement can utilize a huge quantity of ash and can be designed as an innovative product.

The water availability currently thought off with sewage water treatment or desalination has   a better alternative in FSPV.

The ground mounted solar PV projects can be converted to floating Solar reservoirs, storing water for the lean season, creating potential for fisheries, improving efficiency of PV panels.

The coastal areas are replete with ponds these ponds can be utilized for FSPV in a big way.

Many reservoirs used for hydropower generation can support floating solar installations, a hybrid system with solar power in the day, and hydropower at night can complement it during cloudy days or peak demand periods.

Developing larger FSPV projects can help achieve economies of scale. As project sizes increase, the cost per megawatt (MW) tends to decrease, particularly in procurement, installation, and maintenance.

Adopting bulk procurement strategies for components such as solar panels, floats, cables, and anchors can reduce unit costs.

• Improved Floatation Devices: Innovation in floatation platforms can lead to reduced material use, lighter designs, and lower costs. More robust and cost-effective materials could reduce capital expenditure.
• Efficient Anchoring & Mooring Systems: Developing advanced anchoring and mooring techniques that minimize costs while maintaining safety and reliability can significantly lower installation expenses.
• Optimized Panel Design: Using bi-facial panels or lightweight, high-efficiency modules can improve energy generation, reducing the Levelized Cost of Energy (LCOE).

Dr. Bibhu Prasad Rath, an Additional General Manager at NTPC Limited, holds an M.Tech from IIT Delhi and a Ph.D. in Business Administration from Aligarh Muslim University. With nearly 35 years of experience in the power sector, he specializes in energy, environment, economics, and sustainability, with extensive expertise in operations, design, procurement, feasibility studies, policy formulation, investment decisions, and carbon credits. He recently completed a 13-month tenure at the Ministry of Power’s Fuel Supply Coordination, focusing on coal supply chain improvements. He currently oversees NTPC’s 20,000 MW coal-based capacity addition project and has published numerous papers on climate change, sustainability, decision-making, and leadership.