Land acquisition challenges have long hindered the implementation of large solar power projects in India. Many projects have been delayed, tenders postponed and bids cancelled. Thus, other solar segments such as rooftop and floating solar are beginning to gain traction to overcome such issues. Floating solar, especially, has significant potential for development in the country, considering not only the large number of lakes and ponds but also big reservoirs created for hydro and thermal power projects.
Such projects are free from land-related constraints and when installed over hydro or thermal power plant reservoirs, they offer synergies in terms of adequate transmission infrastructure utilisation. In addition, various studies suggest that such projects are slightly better performing, owing to the cooling impact of water on the back of modules. Further, a reduction of dust deposition on modules has been observed in many cases.
On the implementation side, due to the absence of extensive civil work, the project execution timeline of floating solar is shorter than that of ground-mounted solar plants. An additional advantage is that the increasing tendering and deployment activity in this space over the past few years has improved the cost economics of these projects. For all these reasons, the floating solar market has been expanding consistently with a growing ecosystem of developers, service providers and suppliers, even without a dedicated policy or incentive programme.
In this backdrop, Renewable Watch explores various technology trends, key considerations and outlook for the growing floating solar market…
A floating solar project is like any other solar project, with the same electrical configuration as that of a ground-mounted system, except the inclusion of a floating platform and its anchoring and mooring. This floating platform is mostly a pontoon-type structure upon which solar panels are mounted. Meanwhile, anchoring and mooring systems hold these floating platforms in place. Due to their critical role, the design of these anchoring and mooring systems depends on a combination of factors, including wind load, float type, water depth and variation in water level. Similar to any solar project, floating solar systems can use either string or central inverters.
With the floating solar segment growing steadily, a variety of floating platform types and configurations are available in the market. Pure floats are the most commonly used configuration worldwide. With specially designed buoyant bodies that can support solar panels directly, they have fewer metal parts and are easy to assemble and install. The other common configuration is pontoons with metal frames. They do not require any specially designed floats since metal frames are used to mount solar panels to pontoons. In a few cases, rubber mats or membranes fixed to floating rings are also used to create a base for solar panel installation.
Materials and designs
Ciel & Terre International, Sumitomo Mitsui Construction Co., Ltd, Sungrow, ISIGENERE S.L., 4C Solar, Koine Multimedia, NRG Energia, Scotra, Yellow Tropus, SolarisFloat and Sunengy are some companies that offer floating solar platform technologies worldwide. Besides these, other players have developed various types of platforms with different materials, applications and designs.
The high density polyethylene (HDPE)-based float is the most common floating solar technology used today. HDPE is polymer manufactured through a blow moulding process and is resistant to UV radiation and corrosion, and has a high tensile strength. While many designs have emerged in the market for this float type, most include the installation of solar panels directly on the HDPE floating platform, with a maintenance float provided alongside the main float.
For instance, Ciel & Terre International’s Hydrelio® technology is made from recyclable HDPE and has modular “lego-type” floaters assembling into rows. Similarly, SMCC has HDPE-based floating platform technology with floats that can be easily connected using binding bands. Another example is Zimmermann PV-Stahlbau GmbH, which has developed a floating substructure called Zim Float that is completely system integrated with inverter boats, gang and maintenance ways, cable ducts, wave barriers, plant boats and floating transformer stations. It has a steel mounting structure with a corrosion protection coating and is supported on a series of HDPE floats that are embedded in the table structure of the solar and inverter boats.
Similar to conventional solar projects, tracking of the sun can be carried out in floating solar as well. This can be simply achieved by rotating the entire floating platform tracking to follow the sun from east to west. Platforms can be anchored around a central pile or a fixed outer ring and motors can be used to rotate the entire platform. For instance, Portugal-based SolarisFloat provides single- and -dual axis tracking solutions for floating solar projects.
Another design is based on a liquid solar array. Developed by Australia-based Sunengy, this uses lightweight plastic solar concentrators that float on water and are mounted on anchored rafts. These concentrator lens track the sun both daily and seasonally and then focus the direct solar energy down to a sealed alloy well containing solar cells.
Various other floating solar platform designs have been developed rapidly and more innovations are being carried out in this space. For instance, solar islands have been developed that have an outer boundary and a membrane, to place solar receivers and align them in position with cables. Adequate pressure is applied below the membrane for the load and trackers enable the island to rotate and capture more radiation. Similarly, floating grids consist of light weight structures with individual floating solar modules. This allows self-regulation of solar panel angle and ensures that the system is not affected by changes in the water level.
In a unique set-up, smart floating farms with a combination of solar power and polyculture are being developed. While the top level will have solar panels to produce energy, the second and third levels will house the growing crops and fish respectively. Solar power will run the facility and help in crop growth and waste products will be helpful in feeding fish. In another advancement, French start-up Heliores’s floating technology, called Hydro-Lock, can hold water to give it additional mass and stability.
Key considerations and outlook
Engineering, quality and bankability aspects need to be considered in any solar power project and the same holds true for floating solar projects as well. Greater attention is required to ensure material quality and whether it can sustain the constant exposure to various environmental factors such as water, salt, mechanical stress and winds.
While the actual project design and anchoring technology will vary with location and site conditions, the use of durable materials and sturdy structures is a pre-requisite. Materials should be resistant to corrosion and be able to adapt to changes in water levels. Extensive studies of the plant location, geographical conditions and bathymetric data need to be carried out, before actually implementing the project. While the project execution time is remarkably lesser than that for ground-mounted projects and installation is relatively simpler, it is quite critical to design floating platforms and anchoring systems properly to ensure project longevity.
On the operations and maintenance (O&M) side, maintenance activities are slightly more difficult in water than on land. In many cases, boats may be required to access solar plants, while in water some divers may also be needed for inspection of anchoring and mooring systems. Various studies suggest that floating solar projects attract birds and bird droppings are a major cause of module soiling. Thus, additional protection measures to protect both birds and panels can be deployed, if possible. Another issue to be considered for proper O&M is the season-dependent changing water levels in reservoirs of certain hydropower plants. In the case of thermal projects, ash deposition on solar panels can aggravate the soiling issue. However, these considerations are trivial when compared to the immense benefits that this segment offers. Considering India’s massive solar ambitions and never-ending land issues, floating solar’s potential as a game-changing technology should not be ignored. While steps have been taken in this direction, more focus should be placed on identifying suitable waterbodies in each state, where these projects can be implemented. Moreover, along with solar cells and modules, impetus should be given to promoting domestic manufacturing of floating platforms to reduce costs and further scale up deployment.
By Khushboo Goyal