Floating solar islands offer sea of opportunity

Graphic showing solar islands that could provide 'abundant energy'. Image: Kasper Pindsle

Covering less than 10% of the world's hydropower reservoirs with floating solar panels would yield as much energy as all hydropower does today.

That is the view of Professor Trygve Kristiansen, who is researching floating solar photovoltaics at the Norwegian University of Science & Technology (NTNU), and believes they have an important role in the global shift to renewables. However, his aspirations do not stop there, with even bigger opportunities presented at sea.

“If you look at the world's anticipated overall energy needs in 2050, we could have been even more ambitious. We calculated that if you put solar islands on 0.17% of the world's oceans, the power needs for the entire world would be covered,” says Kristiansen. That 0.17% represents around twice the land area of Norway.

“Many of the largest cities are located by the sea, and floating solar will be able to thrive there," Kristiansen adds. "In addition to large surfaces, the sea offers an important cooling effect.

“By covering between five and ten per cent of the world's hydropower reservoirs with floating solar, we could produce as much electricity as all hydropower does now,” he says, adding that the infrastructure would also directly limit evaporation from these reservoirs, conserving water. “Less evaporation would be a good thing in areas where water is a scarce resource,” says Kristiansen, who is professor of marine technology and a supervisor at SFI Blues, a centre for research-driven innovation for floating constructions on the ocean.

Some 173 000 terawatts shine continuously from the Sun to the Earth, radiating much more energy than we are able to use. Image: NASA

Floating photovoltaics are now regarded as a major opportunity to provide clean electric power to major cities, especially in Asia, as solar roofs are not sufficient to meet the need.

“I can also envision these solar islands being charging stations for ships," speculates Kristiansen. "They could also be used to generate electricity for floating factories that produce renewable fuels like hydrogen or methanol.”

“The ocean is big!” says Kristiansen, explaining that not all expanses are suitable for floating solar, which works best where weather conditions are calmer. “Placing floating solar cells in areas with the calmest weather, wind and wave conditions possible is clearly an advantage.

"The Doldrums, a belt around the Earth near the equator, have little wind and the sun shines directly down, so these places are well situated for floating solar. So are places that have swells rather than rough seas,” says Kristiansen.

“If you covered one square kilometre with solar panels in southern Spain, where the annual average solar radiation is 200 watts per square metre, floating solar would be able to produce about 44 megawatts. Today's wind turbines produce on average about 6 megawatts for the same area," he says.

"By covering between five and ten per cent of the world's hydropower reservoirs with floating solar, we could produce as much electricity as all hydropower does now."

Professor Trygve Kristiansen, NTNU

The technology for floating solar islands is still under development, according to Kristiansen. It has to be cost effective and able to tolerate some rough seas and strong winds. The floating structures have to follow the waves for it to work.

So how are the solar panels supposed to stay afloat, and what is the best solution to link them together? Kristiansen highlights two main concepts:

  • Floating membranes attached to floating collars - Norwegian company OceanSun has already built several full-scale membrane-supported systems
  • Smaller, rigid modules that are interconnected in large matrices. Several companies offer different variants of this system, including Equinor and Moss Maritime, who are testing a floating prototype off the island of Frøya

“Other concepts are also possible, like air cushion-supported constructions and flexible tubing connected in different configurations,” says Kristiansen.

A number of floating solar pilot plants currently exist around the world. They are often found on island bodies of water, in cities and in communities that do not have other sources of power. Floating solar panels have been installed on several hydropower reservoirs in Japan and China.

“We need this power in Norway as well, for example for onsite power at aquaculture facilities or to provide power for Norway's new power-intensive industries, such as battery factories," says Kristiansen. "The idea of expanding solar panels in floating structures on dams and other land-based water sources and in the ocean is relatively new.

“Floating solar is a field of research in its very early stages. Only in the last two years has it has started to attract attention. The EU has announced calls for research projects in the past year."

Research partners are: Sintef Ocean, NTNU Department of Marine Engineering, NGI (Norwegian Geotechnical Institute) and the Norwegian Meteorological Institute. Kristiansen has co-authored an article on the topic in the journal Proceedings of the National Academy of Sciences.