Most energy supply forecasts project rapid growth of floating offshore wind by the end of the decade. But many of the technologies proposed to drive the projects forward remain untested or still in the conceptual phase, with development consortia and their financial backers looking to classification societies and certification bodies for guidance.
Novel designs, components, sub-assemblies and interfaces often cannot be assessed using conventional processes or established codes and standards. International offshore wind standard committees and working groups are taking steps to develop new design requirements and certification schemes, and classification societies such as Lloyd’s Register (LR) are devising their own recommended practice for floating offshore wind.
LR also offers two alternative routes for assessing the risks or uncertainties associated with floating offshore wind innovations. Certification through Technology Qualification (CTQ), delivered since 2015, applies to any novel technology (excluding software) or operational method that cannot be certified via conventional schemes. The three-stage process involves verification, validation and a comprehensive performance review of the solution to ensure a reliable, safe and effective deployment in the intended environment. Typically, the process takes around 10-18 months to complete, assuming that the developer has secure finance in place to support the certification program.
CTQ has been awarded to various offshore technologies, including a life extension system for piping on oil production platforms and a subsea BOP system. According to LR’s Offshore Technology Manager Mark Tipping, some onshore equipment developers new to offshore wind have expressed interest in CTQ. “We have also seen growing requests from the offshore supply chain and service companies for qualification of new technologies.
“However, there has been a bigger increase in applications for further certification via LR’s Approval in Principle (AiP) process, which concerns the use of existing technologies and principles in a different way to achieve the desired result in an offshore wind setting. So, instead of qualifying a new technology, we are approving/qualifying the new concept and methodology being implemented.” AiP involves verification and validation of a design against its potential to conform to relevant or recognized codes and standards or normative rules.
“LR provides these services independently and indiscriminately to any company that might request them, whether the technology developer, the wind farm developer, a joint venture, or any other,” said George Kallenos, Clean Energy Commercial Manager at LR. “Over the past couple of years increasing numbers of offshore oil and gas majors have entered the offshore wind market, along with numerous supply chain companies. Overall, they do have a good understanding of what is required. They might not know or be aware of all the existing requirements and standards, but in those instances we have seen them engage with knowledgeable consultancies and independent bodies specializing in offshore wind to obtain advice and guidance. AiP can be sought for a complete system or to an individual a system component. With a floating offshore wind turbine, AIP could be applied specifically to the mooring lines, ballast system, and so on.”
“Typically with clean energy,” Tipping explains, “our clients are looking mainly for proof that a concept does not have any technical roadblocks. During the approval process, we will look at whether the solution under scrutiny has the strength to stand up to the metocean conditions it will likely be exposed to. Once the AiP has been confirmed, it’s normally a case of ensuring that the system’s nuts and bolts are secure enough. In general, AIP is used by the recipient to prove to various stakeholders that the concept is credible, from large operators, finance providers and insurers to regulators.”
Crown ballast control
One company that has recently secured AiP from LR is Seaplace for the ballast control system for its CROWN technology, covering two in-house developed floating offshore wind turbine concepts, one a buoy, the other a reduced-draft concrete spar. Seaplace, which employs a team of 45 naval architects and marine engineers, has 15 years of experience developing technological solutions and feasibility studies for structures for the offshore wind and renewable energy sectors, including jackets, semis, spars, and TLPs. Over the past few decades the company has also supported engineering of fixed and floating offshore oil and gas structures, from pre-FEED through commissioning, including fatigue and hydrodynamic analyses and riser/moorings design. Among its references are FPSOs built by Astano in northwest Spain in the 1990s, some of which still operate on fields in the North Sea; the Discoverer Enterprise drillship and the semisub Drillmar 1; and various well test and offshore construction vessels such as North Sea Giant.
The CROWN active ballast control system is used to ballast/de-ballast the wind turbine floating unit, switching it from its transport draft (while heading to the offshore location) to its operational draft, or vice versa. It can also be used to partly or fully compensate the mean tilt created by the wind loads, improving the floating platform’s stability. In addition, the system can stabilize the platform if a compartment suffers damage, with the in-built redundancy designed to keep the system in operation should a component such as a valve or pump malfunction. The software allows for remote manual or automatic operation, or semi-automatic control. The ballast control system is engineered to work not only with Seaplace’s reduced-draft spar and buoy for floating offshore wind, but also floating platforms developed by other companies.
LR reviewed the ballast control system against applicable Rules and Regulations for the Classification of Offshore Units, including acceptance of preliminary failure modes effects and critical analysis (FMECA). The system first underwent software-in-the loop tests followed by scale model tests at the IH Cantabria Offshore basin in Santander, northern Spain. The AiP award formed part of the final phase of the CROWN technology development, allowing Seaplace to push ahead with the full-size demonstration concept.
According to Naval Architect Jaime Moreu, “We started the AiP process with LR in summer 2019. For this project we have split the AiP works into three main packages. LR helps with the majority: they have been analyzing the ballast system, both for the technology and the CROWN buoy solution, which we think offers the best potential. Our reason for seeking AiP came from when we were showing the technology to developers and stakeholders: we realized how important it was for them to see that we had some third party validation. In this industry, some of the developers know a lot and have been working in the sector for years, but there are others that are relative newcomers with little or no knowledge. So it is key to have a third party confirm that what you are doing adds value to the industry. Tipping added: “LR has a reputation for doing the first and the hardest: the industry knows that we are comfortable working with novel technologies without a precedent. We can provide evidence so people can relate to what is out there.”
“With offshore wind in general,” Moreu continued, “developers like EPC companies to come up with specific products – unlike offshore oil and gas, where the operators typically select the technical solution, then appoint the contractors to deliver it. Offshore wind developers tend to favor engagement with a specific company to develop a concept: fixed offshore wind developers generally know which technology they want to use, but that is not the case with the still emerging floating offshore wind sector. Seaplace started work on CROWN six years ago, at a time when we had been analyzing a gravity-based design for a fixed offshore wind farm. Although the industry has the advantage of the prices they can obtain on the production of gravity-based structures, we could see that these solutions also suffered in terms of the seabed preparations required - so the benefits are not being harnessed when it comes to the final installation.
“In the same way monopiles are key to large-scale series production of bottom-fixed wind turbines, we decided to develop a specific approach to floating offshore wind that allows for efficient, mass production of concrete floating offshore wind turbines using floating docks that can be transported anywhere in the world. Today, with assembly of other types of floaters for offshore wind we are seeing production rates of typically one unit per month, with some developers claiming they can do it in 15 days. But floating docks in other industries have been proven to deliver one unit per week. We also wanted to be able to modify the caissons on our platforms to be watertight for 25 years.”
AiP documentation
“With the ballast control system, being able to validate the software to interested parties was really important, and LR’s experience was our main reason for choosing to apply for their AiP process. We arranged a list of documents that had to be released by them in order that they could validate the anti-heeling ballast control system.” The set of 11 documents included the safety philosophy and design principles; line diagram and functional specification of the control system and the facilities it provides; piping and instrumentation; and a report on the results of the software-in-the-loop and a description of the model tests in IH Cantabria’s ocean lab-controlled environment, including the hydrodynamic behavior of the floating offshore wind turbine and its mooring system while subjected to irregular waves and currents and the dynamic effect on the tanks, hydraulic equipment, sensors and control system. “These model tests proved that the ballast system performed as it had been engineered.
“Ballast control systems are in common use in the offshore wind industry, they represent the most relevant active system from the platform side. Some developers prefer them to be active during the operational stage, others not. We have conceived our system to be like dynamic positioning, where there are three redundancy levels. With DP1, your system operates fine as long as there is no component failure. Under DP2 a component failing is permitted, but you must still be able to maintain positioning. This is our approach: the system performs even if a pump or valve fails. LR and Seaplace worked extensively to help ensure that any potential failure had no impact on the unit’s performance. Our solution of adding water from one tank to another also adds value to the design. If damaged, it will still be able to get water out of the tank without compromising g stability.” Tipping added: “Demonstrating that the unit provides stability additionally proves a better bottom line to interested developers.”
The ballast system is also configured to work with other floating offshore wind turbine designs, potentially with three or more tanks. “We can easily adjust the number of pumps in our system, or add more or less volumes of water as required for other concepts,” Moreu explained. “And having certification of the product with AiP can actually help other clients to reduce the risk of their concepts.
“The tests we performed at IHC are fully representative of the anticipated operational lifetime of the CROWN units. The software-in-the-loop tests simulated years of operation, with just a few days needed for validation. Tests on both the CROWN buoy and spar ran for two months, and employed the ballast system in many cases. LR attended trials on specific days, when the focus was on proving the correct performance of the system. The floaters were 1/30 scale models, engineered to withstand conditions in the Atlantic Ocean, i.e. significant wave heights of up to 15 m (49.2 ft) and wave periods of 17 seconds, strong seas similar to those encountered around the Ekofisk platform in the North Sea. But we have also created a portfolio of floaters to perform well in different conditions, from the Mediterranean to the Baltic, North Sea and Atlantic.”
Seaplace’s next priority is to construct a full-size demonstrator unit, and the company hopes to choose a potential test site by the end of the year. “But now we are talking about an investment of tens of millions of euros to take the development to Technology Readiness Level. So we are seeking to attract investors, including industrial companies and developers with venture company subsidiaries. In this market there are 60-70 concepts under development, of which 10-15 will likely go forward for screening for floating offshore wind projects in the next few years. After that screening process, contracts will go to the ones associated with the most efficient supply chains in terms of construction, and we have been working specifically along these lines.” Going forward, LR aims to also support Seaplace in the CROWN development’s next construction and operations phase, Tipping said, and then for all stages of the units’ lives.
“Some developers say certain floaters may be most suitable for shallow depths where monopiles and jackets are hard to install, with rocky seabeds,” Moreu said. “We see the market from 50 m (164 ft) upwards – as for the highest depths, there is no reason why we cannot get to 3,000 m (9,842 ft) at some point with our concept, although 500 m (1,640 ft) is seen as the limit for the industry at present. One thousand meters (3,281 ft) should easily be doable: going deeper will depends on how the industry performs, and whether we can achieve good prices and production rates. But the new designs of turbines are increasing the capacity factors, so why not aim to go deeper? Typical future floating wind farm power generating capacities start with 150-250 MW for the early 2020s, rising to 500-1,000 MW by the end of decade to promote scale effect. At that point we should see 20-MW turbines, with 30-40 units for really big floating wind farms. Our aim is to produce up to 40 units per year with just one manufacturing line – with two floating docks, we could build 80 per year.”
GUIDELINES FOR FLOATING OFFSHORE WIND
LR is developing a Recommended Practice (RP) to support the development of floating offshore wind facilities with the support of an industry working group drawn from the membership of LR’s Offshore Technical Committee: this includes technology developers, energy majors and utilities companies. The RP will address the need to support facilities across the range of regulatory requirements that are evolving across the world, drawing together not only the various engineering disciplines but also promoting collaboration across the design, construction and operational phases of the projects. The goal is to help the projects address the major engineering challenges and technology step outs that are required in this advancing field especially as with the rapid rise in turbine output (15MW per turbine currently being developed).
