7 minute read
Challenges and potential of ofshore solar
In the past few years, there has been an increasing interest in the development of ofshore foating solar power plants. The technology has a very large power generation potential, in particular in the areas used by ofshore wind farms.
Solar Duck offshore solar truss concept. The platform is located on a certain height above the waterline. Waves can move underneath the truss structure.
Photo courtesy of SolarDuck.
In some scenarios, 45GWp solar power in the Dutch part of the North Sea has been projected in 2050. The Dutch Roadmap Solar on Water concludes that in ten to twelve years, large scale application of ofshore solar on the North Sea could ofer possibilities, but it also expresses major concerns about the technical and economic challenges of ofshore foating solar systems.
Perspective
Signifcant innovation in this feld by commercial enterprises will only be undertaken if there is enough perspective for a proftable business case in a large market. This is only possible if technical problems are likely to be solved and costs can be decreased considerably. Nevertheless, several companies (especially in the Netherlands and in Norway) started investing in system developments that may lead to feasible and afordable solutions for ofshore solar. Based on this, some smaller scale pilots have been established or are planned.
CO2-free
There are substantial technological challenges to build and operate foating solar systems in a harsh maritime environment, with wave heights up to 15m. At the same time, there are major challenges on system design, O&M schemes, grid connection and cost. The Dutch top sectors strengthen the economy through innovations that target to help solving important societal challenges such as the energy transition. In this approach the societal and economic goals go hand in hand. Recently, this has substantiated in so called mission-driven innovation. For the energy transition thirteen multi-annual mission-oriented innovation programs (MMIP’s) have been formulated, and MMIP 1, titled ‘Renewable electricity at
sea’, has the goal to contribute to the mission ‘A CO2-free electricity system in 2050’.
1,000km2
For the development of the MMIP 1 program, a further analysis of the challenges related to ofshore foating solar was needed. For this, RVO (Netherlands Enterprise Agency) commissioned a report, requested by TKI Ofshore Wind, based on an analysis conducted by TNO. Recently, the results of this report, called ‘Challenges and Potential for Ofshore Solar’, was presented during a webinar. According to Wiep Folkerts, Program Manager Solar at TNO, the Dutch energy system would need an additional 1,000km2 of space to develop solar power plants. “On shore, the Netherlands lack sufcient space to realise the ambitious solar energy goals”, he says. “At sea however, there still is ample space available in the Dutch Economic Zone. Ofshore solar and ofshore wind ofer important synergies, for example because of the infrastructure that could be shared, such as cables and substations. Therefore, ofshore wind farms seem to be ideal location for solar power plants. Another beneft of developing solar power plants at sea is that, because of the higher radiation of the sun at sea, the output of ofshore of solar panels may be slightly higher compared to that of onshore panels.” “Ofshore solar and ofshore wind ofer important synergies, for example because of the infrastructure that could be shared, such as cables and substations.”
Various concepts
He continues, “Currently, in Europe, such as in the Netherlands and in Norway, there are already various concepts under development. The frst concept is the so-called elevated truss concept. A truss structure is equipped with foaters and some kind of mooring system. A platform with solar panels is placed on the truss structure, supported by foating elements. The platform is located on a certain height above the waterline. Waves can move underneath the truss structure. The concept avoids the direct contact between (slamming) waves and the solar panels. This way, the mechanical load on the solar panels caused by waves will be less, and the fouling of the solar panels due to sea water residues on the panel surfaces may be smaller. Companies like SolarDuck and Tractebel are working with this concept. The second concept is a pontoon where the solar system is much closer to the water level. The pontoons are substructures that are mechanically coupled into a massively modular structure. The complete foating structure is moored. Solar panels are mounted on the pontoons, relatively close to the water level. The advantage is that the wind load on the panels and the structure is relatively low. Oceans of Energy, and Heliorec are some of the pioneers in developing this concept. Then you have the mattress-like soft and fex approach that fully moves with the waves. The basic idea of this concept is to let the foating structure move with the waves as much as possible. The transfer of mechanical energy from the waves to the structure will therefore be smaller, compared to for instance the pontoon concept, which results in reduced mooring forces. Because of this the structure needs less strength and may achieve lower costs. Solar panels are mounted on the foating body. During high waves, part of the structure may be overfown. Being near the water surface, it is less sensitive to wind loads. Bluewater/Genap have embraced this concept. The fnal concept is based on the well-known technology of fsh farms. Especially in Norway, with companies such as OceanSun and Inseanergy, there is expertise on this approach. A membrane is stabilised with a moored ring and on top of the >>
Photo courtesy of TNO.
Wiep Folkerts, Program Manager Solar at TNO.
Photo courtesy of Oceans of Energy.
Oceans of Energy’s offshore solar energy pontoon installed at the North Sea. The pontoons are substructures that are mechanically coupled into a massively modular structure.
membrane a solar power installation is installed.”
Challenges
The TNO report registered four main challenges for the development of ofshore solar power plants. “When looking at constructing ofshore solar power plants,” Mr Folkerts states, “the frst challenge is how to design and construct a system that will survive the circumstances at sea, and also how to prove this survival. Relevant subjects in this are the connectors between the subsystems, the choice of materials used, the structural integrity and mooring, the dynamic power cable connection, and the calculation methodologies for prediction of hydrodynamic response. In fact, it is a matter of interaction between development of calculational methodologies and making the designs, do scale model testing for those designs, build pilots, see and measure how these models behave, give feedback to the methodologies, and thereby building up the knowledge on how to construct such foating structures in a costefective way.” Operations & maintenance has its challenges too, and therefore there is work to be done and more knowledge to be built up over the coming years for this as well. Think for example of ofshore resistant PV modules and electrical components. Not only is it important to fnd out for them how to survive at sea, but also how to make an efective maintenance schedule, for example for fouling prevention and fouling removal. For optimising O&M one could also look at digital twinning approaches.” The third challenge lies in the power production and LCOE, and according to Mr Folkerts this actually is the key challenge. “All ofshore solar projects are aimed at producing substantial volumes of power. It is important, for example for judging investment proposals, to make validated power yield models and reliable models for cost calculations and to show, how scale efects and other efects such as the combination of ofshore wind and solar will afect the LCOE.” Societal acceptance is the fourth challenge described in the report. Relevant aspects in this are recycling and other elements of circularity, the ecological efects of ofshore solar power plants, and the interaction with other uses of the sea. “All societal acceptance elements come together in permitting and permitting frames”, Mr Folkerts explains.
Photo courtesy of TNO.
Bluewater/Genap have embraced the soft and fex approach.
Photo courtesy of Ocean Sun.
Ocean Sun Floater. The fsh farm concept is based on the well-known technology of fsh farms. Especially in Norway, there is expertise on this approach. A membrane is stabilised with a moored ring and on top of the membrane a solar power installation is installed.
Solid solution
“Ofshore solar is promising, so much is true”, Mr Folkerts concludes. “It can be the solution for the large-scale solar power production that we need. Still, it is a challenging development that needs innovation investments from the sector, which should work together with governments and knowledge institutes. There are diferent concepts in development and all those concepts have their specifc advantages, values, and promises. Several pilots and demonstrators for accelerating the learning curve are underway, however more of them are needed towards scaling up and for winning the confdence of all stakeholders that ofshore solar indeed is a solid solution.”
