Floating Solar as the third pillar 

As scientists grapple with the challenge of combatting climate change, one of the most innovative ideas of recent years is the floating solar farm. Mixing electricity and water might seem an odd combination at first, but the technology and its application are growing fast around the world.

First patented in 2008, the concept is to place banks of solar panels on floats or membranes on bodies of water, such as reservoirs, lakes, ponds and even the sea. The idea is gaining rapid acceptance, especially in Asia, where they’ve been installed in China, India, Japan, South Korea and Singapore. Other early adopters include the United States, United Kingdom, France and the UAE, where there’s an 80kW installation by Enerwhere at Nurai Island in Abu Dhabi.

Asia can boast the world’s five largest floating solar installations, with the three largest in China. The largest is the 150 MW Three Gorges New Energy Floating Solar Farm in Huainan City, while third place goes to the 70 MW farm owned by the China Energy Conservation and Environmental Protection Group (CECEP). That project spans more than 60 hectares and includes more than 194,000 solar panels.

The growth of installed capacity has been dramatic, rising from just 70 MW in 2015 to 2.6 GW in 2020, with 20% year-on-year growth forecast to 2025. Long-term projections by some analysts suggest an eventual global installed base of 400 GW.

Advantages over traditional approaches

This uptake in recent years is fuelled by the many advantages floating solar offers over more traditional ground-based or roof-mounted solar farms. Chief among them is the fact that they do not require land, apart from the small amounts needed for electric cabinetry and grid connections. Since the space required has no great commercial value, unlike many land sites, there can be significant cost benefits in a floating solution. If, as happens in many cases, the panels are located on an existing hydro project, the solar installation can enjoy further advantages by using existing distribution infrastructure. 

Running cooler for greater efficiency

Secondly, floating solar panels can offer an increase in operating efficiency of up to 15% due to the cooling effect of the water close to the photovoltaic panels. This can help offset the additional construction cost associated with a floating installation, estimated at between 10% and 25% above the cost of a land-based solution. The extra costs are due in part to floating solar being a relatively new technology, needing specialised equipment and different installation expertise. Solid anchoring is a critical factor, and comprehensive wind and tide analyses are needed for near-shore and onshore installations to ensure the safety of the solar park.

Savings can be made in the pre-construction phase, as there are no ground features to be factored in, or even moved. Many on-land sites require extensive preparation, including the removal of existing trees and vegetation.

Reduced water evaporation

Another, perhaps surprising, benefit is water conservation.  Scientists from the University of Ponta Grossa in Brazil and the University of Louisiana investigated the impact of floating solar on the water evaporation rate on the Passaúna reservoir in the Brazilian state of Paraná. The reservoir spans 8.5 square kilometres, has an average depth of 6.5 metres and a total volume of 69.3 cubic hectometres. They found that 4.47 million cubic metres of water evaporated from the reservoir in the space of a year, equivalent to 10.4% of the water volume consumed annually by the local population. The team calculated that the floating solar system reduced water evaporation by 60%, which is an important consideration in water-scarce areas. The researchers shared their results in a paper that was recently published in Energies. Similar research conducted with floating solar panels on a reservoir in Jordan in 2021 found that evaporation was reduced by 42%.

An associated environmental benefit is that the presence of floating panels provides shade for the water surface, preventing the growth of toxic blooms of blue-green algae, which causes health hazards. That same shade may cause problems for aquatic life, however, so some experts prefer to see floating solar installed on bodies of water without an abundance of wildlife.

Easier rotation for sun-tracking

Furthermore, large floating platforms can be rotated easily horizontally and vertically to enable sun-tracking using mechanical, geospatial and light sensors to follow the sun's path without the need the complex mechanical apparatus required for land-based PV installations; this can deliver an energy gain of up to 25%.

Safety is a key consideration, given the incompatibility of water and electricity, so more attention must be paid to cable management and insulation testing than on land, especially where cables will be in contact with water. Other challenges include taking account of the hydrodynamic loads on the structure, and the need for significantly greater corrosion resistance, particularly when installed on salt water.

However, with solar power becoming the lowest-cost option for new electricity generation in most of the world, according to the International Energy Agency, floating solar has an increasing role to play. The IEA says there needs to be more than a threefold increase in annual solar capacity deployment until 2030, “requiring much greater policy ambition and more effort from both public and private stakeholders”. We can expect increased interest and investment in floating solar projects in the years to come as the ‘third pillar’ alongside ground-based and rooftop installations.