Offshore Solar Power
An Ocean of Solar Energy
Putting solar panels on the ocean may seem like a challenging idea, but it’s increasingly being explored.
By Elaine Maslin
A artist’s impression of a larger scale deployment of SolarDuck systemsImage courtesy SolarDuck
Dutch research organization TNO recently wrote that, in 2050, 200 gigawatt peak (GWp) of solar power is expected to be generated in the Netherlands; 25 GWp of that will be on inland waters and 45 at sea.
Maybe that’s a surprise? But floating solar isn’t that new. According to Wood Mackenzie, there’s about 8GW installed to date, mostly in Asia Pacific, with China (thought to have 70% of total capacity*), India and Indonesia leading.
A lot of that 8GW has been built in-land, e.g. on lakes or reservoirs. Dutch firm BayWa recently installed two farms, totaling 71MW, on former sand extraction lakes in the Netherlands.
“Lack of availability of land that can be used for ground-mount solar has encouraged PV developers to look at alternate development technologies, giving rise to the demand for floating solar (FPV) installations,” says Sagar Chopra, PV Research Analyst at Wood Mackenzie. “Costs associated with land lease, vegetation management, etc. can sometimes make FPV more favorable than ground-mount solar. The quick installation time is also an added driver for FPV project economics.” With competition for agricultural land, there’s also growing interest elsewhere, especially in Europe.
But not all areas have access to inland water or there could be restrictions on using these, says Chapra. So companies are looking offshore, which also offers hybridization opportunities with other renewables and unlimited expansion capability, he says.
Many have started in more benign waters. Vienna-based Swimsol claimed a world first “at sea” project in 2014, with a 15kW solar plant in the Maldives. But there are plenty of others taking steps offshore too.
OceanSun’s 0.5MWp floater in Statkrafts Albania hydropower reservoir.
Norway’s Ocean Sun has been building a track record in floating solar and is also targeting coastal waters. CEO Børge Bjørneklett founded the company in 2016 and they started their first pilot in Norway in 2017. Proximity to the user, land cost, transmission cable costs are all drivers to floating solar, he says.
Ocean Sun’s technology is based on placing panels on engineered textile membrane that sits directly on the sea surface, provides a large surface and behaves like a dampener, he says. It is held in place by a buoyant ring at the perimeter, that’s moored to the seabed.
The membrane is the type that’s used on top of large stadia or as roofing materials and contains e.g. biocides to prevent marine growth and UV stoppers to prevent UV degradation.
Using this method means it’s easier to transport in 40ft containers and quick to install, compared with arrays of pontoons, which are more difficult to anchor and also suffer greater fatigue from the forces of the waves in the ocean, says Bjørneklett. Instead, being in direct contact with the sea helps cool the panels, giving higher voltage and improving yield. For every 1 deg C cooling there’s approximately 0.4% efficiency gain, he says.
Ruggedized solar panels are used, comprising a “double glass sandwich” with an encapsulant that protects the solar cells inside. Each panel is up to about 2.5sq m with max power output of 600-700Wp (p = peak) each. A larger system, up to 75m diameter/>4,000sq m, can have 1,500 of them, and up to 0.7 MW of installed power, depending on the panels. The maximum size of each ring is limited to what can fit in a 40ft container, for ease of logistics.
To handle waves, there’s a freeboard, i.e. a flexible wall on the perimeter to take most of the spray from wave slamming, but they can take some salt water coming in, and rainwater, and there are surface bilge pumps that automatically operate to remove it – or collect it for use, where required, says Bjørneklett.
Hydropower dam – Ocean Sun’s Luzon Island project in the Philippines. A 230 kWp ring, owned by SN-Aboitiz Power.
Since the 2019, it’s been running a 230kW pilot in the Philippines, a country has experiences typhoons. This summer, Ocean Sun is expanding a single ring 0.5MWp ring that was initially installed on a hydropower reservoir run by Statkraft in Albania in 2021 to 2MW, by adding three more rings.
There have been challenges. The 0.5MWp Albanian plant suffered an accident caused by a tornado – conditions that had not been expected in that region. The design was since updated to better weather data and, following re-installation in April, has run successfully since, says Bjørneklett. In contrast, the design for the Philippines had been CFD tested to meet building codes there that include the ability to withstand 275km wind speed – or a Category 4 typhoon, from the beginning.
A lot else has also evolved, he says, including how to make improvements to make it easier from a supply chain perspective, i.e. being able to get the fabric made in the sizes needed. Things like this are important when moving to scale
What’s worth noting is that solar panels tend to be tilted and that’s for a reason: they work best when perpendicular to the sun. That means floating (mostly horizontal) installations closer to the equator will get more yield compared with Oslo, Norway, for example, at 60 deg north, says Bjørneklett. However, wind drag is a powerful force offshore and tilted panels acts like sails, , he says. But there’s a pivot point for horizontal panels due to the gain from cooling. That’s at about 45 degrees north, where you have more gain from cooling in comparison with traditional air-cooled panels with ideal angle to the sun, he says.
OceanSun has an agreement for a 1.2 MWp floating PV demonstrator near an island south of Singapore, comprising of two rings, with construction scheduled in Q3. It’s also got an agreement with Keppel for a three-ring, 1.5 MWp floater near Jurong Island, Singapore, which is expected to be ready in 4Q 2023.
It’s also signed a licensing deal with Chinese developer String Capital and Sunneng Technology for the construction of a 1 MWp FPV pilot nearshore Yantai, Shandong province, with construction due to start later this year. A second agreement with Sunneng and SPIC (State Power Investment Corporation), will see a 0.5MWp FPV pilot connected to a wind turbine built at Haiyang, also off Shandong. Following successful operation through typhoon season there, the rest of the wind turbines at Haiyang are also expected to be connected to 0.5MWp floaters, amounting to a total 20MWp project in 2023.
Over in Europe, Ocean Sun is working with Fred Olsen Renewables and other partners on an EU Horizon 2020 program. This is expected to see a 0.25MWp floating solar power plant built off Gran Canaria, to explore the outer limits of the technology in a rougher ocean environment.
OceanSun’s test system from 2018 at Lerøy Seafood on the west coast of Norway.
Formed more recently, SolarDuck has been making quick headway, including a collaboration agreement with utility RWE for a 0.5MWp pilot off Belgium.
The company is a spin-out from Dutch shipbuilder Damen, which had previously dabbled in tidal energy with the BlueTEC platform. It’s named after the solar duck curve, which describes how energy demand drops at peak solar output times and vice versa (in northern latitudes at least). Damen liked the idea of floating solar, but decided it was outside its core expertise, so let Koen Burgers, a business strategist at Damen, run with it, forming a company in 2019, which went independent in 2020, with Damen holding a stake.
Its concept is based on triangular aluminum structures with grated flooring on which tilted panels are mounted. These would sit above the water surface (to keep water off the panels and limit issues such as algae formation) on three-column, semisubmersible bases. These can then be tessellated (more easily than squares and with more inherent flexibility) into giant hexagons producing 10MWp and upwards of solar power. To join the triangles into hexagons, SolarDuck has developed patented couplings that allow a certain amount of flex. The outer ring of the hexagon would be used for mooring points.
A King Eider duck
SolarDuck’s first demo unit, “King Eider” (a type of duck), was built at a Damen shipyard in early 2021, towed to its site 55km away and has been operating on the River Waal in the Netherlands since then. The 65kwp unit is over 30m along each side, made up of four triangular platforms, built to withstand 3.5 significant wave height and 6.5m maximum wave height, and went through storm Eunice without a problem. SolarDuck says the platform received the world´s first certification for offshore floating solar by Bureau Veritas.
The next unit, “Merganser,” another type of duck, is currently being built as part of a partnership with German utility RWE for installation on the North Sea next year. This will be an optimized 0.5MW unit, designed for 7.5m significant wave height and 14m maximum wave height, and using much less aluminum, per kW, than the previous system, says Burgers.
SolarDuck’s technology is also part of RWE’s bid for the Hollandse Kust West wind farm, winning bids for which are due to be announced in Q4. That could see 700MW of offshore wind twinned with 5Mwp of floating solar, all using the same export infrastructure, and, thanks to the natural patterns of solar and wind (often occurring at different times), less than 8% curtailment, says Burgers.
Some 8-12 of these hexagons could fit between turbines, and while some spatial planning would be needed to allow vessel access, that’s still feasible, says Burgers. “This offers great potential. Wind and solar are complementary. In sunnier conditions, you could more than double the energy capacity at a wind farm by bringing in solar,” he says.
“We are in this for utility-scale – scale is everything. We’re looking at 5-10MW and multiples of that and we are currently participating in projects of 100MWp and more,” he says. “It’s a really exciting journey. At the end of the day, it’s a very cost-effective, scalable technology, which can be deployed really fast. The cost levels are pretty low very competitive, and can be deployed either in combination with wind or as stand-alone energy plants.” In the future, there’s also capacity on the structures to build in energy storage. Initially, that would be with compressed air, says Burgers. But further in the future, that could also be hydrogen.
Developers getting in on it
RWE isn’t alone in offering floating solar in an offshore wind bid. For its Hollandse Kust Noord bid, Crosswind (Shell and Eneco JV) also included floating solar. Others are also working on floating solar technologies. In 2019, Oceans of Energy, a spin-off of Delft University of Technology, installed an 8.5kW offshore PV system 1km off the Dutch coast, as part of a consortium. In 2020, it was expanded to 50 kW and then placed 15km offshore where it withstood up to 13m high waves and 62kt winds. Operating since 2020, it’s now being expanded to 1MW. Oceans of Energy is also planning a 3MW project co-located with offshore wind offshore Belgium, under the European SCalable Offshore Renewable Energy Sources (EU-SCORES) project.
A Belgian consortium including DEME, solar manufacturer Soltech, Ghent University and Tractebel is working on a marine PV project. The €2 million PV array will be built near an aquaculture farm and offshore wind project. Norway’s Moss Maritime (part of Saipem) has also been working on floating solar concepts, working with Equinor.
Meanwhile TNO is leading a consortium including petrochemical company SABIC, Equinor, and the municipality of Westvoorne that’s testing three designs over a year on a lake near Rotterdam Europort.