Offshore wind is expected to grow massively over the next several decades. Most existing wind farms at sea are in northern Europe, where 5 gigawatts have been installed. China has started pilot projects (with plans to build 30 gigawatts by 2020), and the United States has many offshore developments in the works (plans for 10 gigawatts by 2020). There are a number of reasons expectations are so high for offshore wind, but the industry also faces some significant challenges that must be addressed before offshore can grow to meet its potential.
Advantage: Better wind resource
A map of average wind speeds in North America reveals a stark contrast between land and sea. The wind is much stronger on the ocean (and in the Great Lakes) where there are no terrain features, buildings, or other obstructions to slow it down. That means that a turbine can generate more energy over the year compared to the same model in most locations on land.
Challenge: Difficult conditions
The ocean’s surface is a brutal place. Those higher winds bring storms, big waves, and corrosion from salty water and air. Installing and maintaining wind farms at sea is much more complex than on land, requiring special equipment and good weather. Projects in the North Sea have proven that it can be done, but at great cost — more than double the maintenance costs onshore.
Advantage: Closer to population and load centers
Nearly half of the population of the United States lives along the coast, and the same is true in many parts of the world — according to the UN the figure is 44% of global population. Lots of people means lots of electricity use, but not much space to generate it. Building turbines off the coast of major cities eliminates the need for thousands of miles of transmission lines to bring wind power from the midwest or solar power from the southwest.
Challenge: Stuck in shallow water
Every commercial wind turbine installed offshore uses a foundation on or in the seabed, which means that most projects exist in waters no deeper than 30 meters. Europe’s North Sea has an optimal combination of shallow water and strong winds, which explains the success of offshore wind in the region. The east coast of the US has similar conditions, but the continental shelf on the west coast falls off steeply, making fixed-bottom wind projects unlikely. Floating platform designs are in development, but add more cost and complexity. For now, conventional offshore wind can only access a small fraction of the available resource.
Advantage: Room to scale
All energy projects have fixed costs — permitting and regulatory reviews, transmission lines and other infrastructure. These costs exist whether you’re putting up one turbine or one thousand. So the bigger the project can be, the more fixed costs can be spread out, making the electricity cheaper. On land, most wind projects are constrained by surrounding areas and can only expand so far. But offshore, there is potential to build massive projects, like the 1 gigawatt farm Japan wants to build off the coast of Fukushima.
Challenge: Offshore wind is still expensive
Scaling to gigawatt size projects will require the floating turbines still in development, which drive costs up substantially. The physics of conventional turbines result in a very unstable machine that requires massive ballast below the water to prevent tipping over. We know from industry partners that installed costs for fixed bottom offshore projects are currently around $5/Watt, more than double the costs onshore. The most successful floating pilot project — Statoil’s Hywind — cost a staggering $31/Watt to build, though that cost will clearly come down in commercial production.
Advantage: Lower impacts
Many of the criticisms of conventional wind power derive from proximity to people and wildlife. Putting turbines out at sea, where they can’t be seen or heard from the coast, and are out of the way of bird migrations and other sensitive habitats, could solve those problems.
Challenge: New impacts at sea
Environmentalists have already raised concerns about the potential impact of wind turbines offshore. Construction could harm whales and other migrating sea life, and could destroy important habitat. Electromagnetic fields from undersea cables could have impacts as well. Some research has been done in this area, but developers will need more information and a plan to prevent the controversies we’ve seen on land in the last decade.
At Makani, we’re excited about the potential of offshore wind. Airborne Wind Turbines can access even stronger winds at higher altitudes offshore. And our cost advantage through drastically reduced system mass is even greater at sea. We have a lot of work to do in the coming years to get our turbines ready for deployment at sea, but our roadmap matches up nicely with the opportunity offshore.