The cost of onshore wind farm developments has dropped dramatically over the past decade, and onshore wind is often the cheapest technology to utilize for new electrical generation facilities. (See
OWOE: What is the cost of electricity produced from wind energy?) The latest summary of LCOE by
Lazard (Version 15) shows new onshore unsubsidized wind costs ranging from $26-$50 per MWh. However, offshore wind is still significantly more expensive with Lazard estimating it at $83 per MWh on average.
While there are several advantages of offshore wind power (see
OWOE: What are offshore wind farms?), there are several significant technical challenges to be overcome before offshore wind can become a major source of electricity in the United States, all of which drive up the lifetime cost of a development:
- costs associated with the turbine foundations. In shallow waters where a monopile foundation can be used, which is what most of the offshore wind farms around the world currently use, additional costs are not overly burdensome. However, in deeper water where a floating substructure is required, foundations are a significant portion of the cost. This is particularly important for offshore wind developments off the west coast of the US and Hawaii, where the seafloor slopes quickly from shore.
- advanced materials to resist corrosion due to the salt water environment
- installation that requires special marine vessels. There are a limited number of vessels in the world which are capable of installing offshore facilities, and most of these are located overseas.
- subsea cables to bring the power to shore. There are a number of challenges to be overcome including: supply chain constraints for the manufacturing of high voltage cables, protecting the cables by burying or other means, protecting the environment during installation, and routing the export cables to an onshore point of interconnection.
- grid transmission capacity. Once the power has reached shore, it must be transmitted to cities where it will ultimately be used. Existing transmission infrastructure in locations where offshore wind farms are being planned in the US is typically not sufficient for the additional power loads and must be upgraded.
- offshore maintenance costs. Workers and materials must be transported offshore, which is more expensive, requires more time, and makes it difficult to address issues that arise during the work and for which the crew is not prepared. Major repairs often require remobilization of one of the special marine vessels.
The earliest floating turbine platforms were based on offshore oil and gas platforms, modified as required to support the turbine and handle the complex aerodynamic and hydrodynamic response of a wind platform. These included the first semisubmersible platform developed by Principle Power for its WindFloat 1 prototype platform and WindFloat Atlantic development and the spar platform used by Equinor for its Hywind Scotland project (see
OWOE: What are offshore wind farms?). More recently, companies have focused on optimizing platform configurations to better address the unique requirements of supporting wind turbines and reduce the cost of the platform. These include:
- Equinor's concrete spars being built for the Hywind Tampen project offshore Norway that began providing power for the Snorre and Gullfaks offshore oil fields in November 2022. See Figure 1.
- Hexicon's TwinWind floating foundation, a 3-column semisubmersible which supports two full size turbines on a single foundation. See Figure 2.
- BW Ideol's Floatgen floating barge foundation. See Figure 3.
- Stiesdahl's TetraSpar, which is a spar-type structure with a tetrahedral steel support structure at the waterline. See Figure 4.
- VL Offshore's Mars-Wind (Modular Assembly and Reconfigurable System) floating offshore wind turbine solution applicable for semi-submersible and TLP configurations. See Figure 5 and watch the MARS-Wind video. (Disclaimer: VL Offshore is a sponsor of OWOE and collaborates with OWOE's parent company, Pacific Sky Productions.)
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