The development of floating solar systems has witnessed a surge globally and in India as well. The key drivers have been land constraints, the availability of large waterbodies, and increased power generation due to the cooling effect of the waterbodies. The use of similar components as those used in ground-mounted systems has aided the uptake of such systems. For instance, the tracking solutions used in ground-mounted solar projects are also being tested for floating solar systems in a bid to increase power generation. The use of such technologies is currently at the demonstration stage. Despite the potential of floating solar systems, many technical challenges remain. These challenges add to the operations and maintenance (O&M) costs of plants.
A look at the technologies used in the various components of a floating solar system, the key technical challenges and the future outlook…
The electrical configuration of a floating solar system is similar to that of a ground-mounted solar PV system. Floating solar systems can be installed on various water bodies such as industrial ponds, hydropower reservoirs, agricultural ponds and man-made waterbodies such as flood control reservoirs. While all these are mainly inland freshwater waterbodies, these systems can be built offshore or near the shore. Apart from their electrical configuration, the design of these systems is also similar to that of a conventional solar plant. The only key difference is that floating solar systems float on the water surface. A floating solar plant comprises PV arrays, inverters, combiner boxes, lighting arresters, etc. These components are attached on a floating bed, which is made of fibre-reinforced plastic (FRP), high density poly ethylene (HDPE) or metal structures. These floating beds, in turn, are attached to anchoring and mooring systems.
PV modules and inverters
Just like conventional solar plants, floating solar systems typically have polycrystalline, monocrystalline or thin-film solar panels. The type of PV module technology is decided based on the space, cost, relative humidity and type of waterbodies, according to TERI’s report, “Floating Solar Photovoltaic: A Third Pillar to Solar PV Sector?”.
The developer may select either string inverters or central inverters. Further, depending on the scale and distance from the shore, inverters can be placed either on a separate floating platform or on land. For smaller capacity floating solar systems, inverters may be located on land near PV arrays, whereas for large capacity plants, it is advisable to place the inverter on a floating platform to avoid excessive resistive losses, according to the report.
Materials for the floating platform are the most important component of the floating solar system. The most common material used is HDPE. Other materials like FRP, medium density polyethylene and ferro-cement are also used often. There are various designs of floating platforms.
Most large-scale floating solar plants have pontoon-type floats, on which PV panels are mounted at a fixed-tilt angle. A floating structure may consist of pure floats, or floats with metal trusses, or special membranes and mats. The platform is held in place by an anchoring and mooring system, the design of which depends on factors such as wind load, float type, water depth and variations in the water level.
Pure-float configurations use buoyant bodies to support PV panels. These include two types of floats. The main float supports PV modules and provides an optimum tilt to the module while the secondary float ensures a connection with the main floats and provides sufficient spacing to limit the shading of PV modules. The secondary float is also used as a maintenance walkway.
Another common design is metal structures (frames or trusses) that support PV panels. These frames affix the structures to pontoons that provide buoyancy. In this case, there is no need for specially designed floats. In these structures, capped pipes are used with technical specifications similar to those of pure floats in terms of strength, non-toxicity and durability. The pipes may be easier to obtain locally than pure floats.
Another type of platform is created by simply covering the entire water surface with rubber mats to create a base for the PV installation. This type is not as common as the previous two types of platforms. Covering the entire water surface is particularly suitable in desert areas to prevent evaporation losses and save water for irrigation or drinking. This technology may not be easily scalable. At the moment, it is more suitable for small-scale systems on reservoirs or irrigation ponds that have a size of 100,000-200,000 square metres.
Anchoring and mooring systems
Variations in water levels by monsoon, wind velocity and changes in water quantity are a challenge for floating solar plants. These plants are anchored through mooring systems. The placement of a mooring system must take into account the location, bathymetry, soil conditions and water level variations, according to TERI’s report. Broadly, mooring can be done in three ways – bank anchoring, bottom anchoring and piles.
Bank anchoring: This type of anchoring is particularly suitable for sites that are shallow and small, where the bottom of the water basin does not allow any kind of anchoring. It is also the most cost-effective option, but its suitability depends on the conditions of the shore. Its main disadvantage is its visibility from outside, impacting the landscape view.
Bottom anchoring: This can be done by inserting anchors directly into the waterbody and anchoring through a concrete block placed at the bottom of the waterbody. The anchors are then connected to a floating platform with the help of a mooring cable and chain. The cost of bottom anchoring is typically higher than that of other types of anchoring as it requires rigorous planning and involves divers as well.
Piles: In this type, piles are drilled into the bottom of the waterbody and the floating platform is moored to the piles. The main advantage of this type of configuration is its capability to handle water level variations though the need for heavy equipment and civil work makes it expensive.
The electrical and electronic components of a floating plant are exposed to harsh environmental conditions and are prone to degradation, corrosion and bio-fouling. Therefore, unlike ground-mounted solar systems, there are many technical challenges in the adoption of floating solar systems. These include an increase in O&M costs and safety concerns for the workforce. The O&M of such plants is particularly cumbersome as anchoring and mooring takes place inside the water body, which requires trained divers.
Despite these technical challenges, the future outlook for the floating solar segment looks positive. The global demand for floating solar panels was 750.5 MW in 2020. According to Grand View Research, it is expected to grow at a compound annual growth rate of 28.9 per cent from 2020 to 2027, to reach 4,690 MW in 2027. The market size of the global floating solar market stood at $25.8 million in 2020 and the revenue forecast for 2027 at $92.3 million.
Based on the product technology type, the report has segregated the floating solar market into tracking floating solar panels and stationary floating solar panels. The stationary floating solar panels accounted for the largest revenue share of 80.2 per cent in 2019 owing to their cost advantages in comparison to its counterparts. The tracking solar technology is expected to witness increased uptake in floating solar farms due to its superior operational productivity. However, the high maintenance of tracking solar panels as compared to stationary floating solar panels farms owing to their moving parts will be the key challenge going forward. Despite the cost and maintenance challenges associated with tracking-based floating solar systems, such systems have a huge potential.
According to TERI’s report, both single- and dual-axis trackers can be used for floating solar systems, although the latter are more difficult to implement. Single-axis trackers are relatively simple as low resistance is offered by the water layer as compared to the land. In some of the initial designs, the platform is moored around a central pile and motors are used to rotate it around a vertical axis of the central pile, enabling single-axis rotation. In some other designs, the central pile is replaced with a fixed outer ring, which surrounds the floating platform.
As compared to ground-mounted solar systems, the cost of setting up floating solar systems is much higher. Therefore, several technological innovations are under way to further increase the efficiency of floating solar systems while also reducing the cost of setting up such systems. Work on both fronts will give positive dividends for the promotion of the floating solar segment in India.
By Sarthak Takyar