The future of offshore wind power on the US west coast

Offshore wind power in the world

Currently the world’s off-shore wind power plants are principally located in Northern Europe (Denmark, United Kingdom), in China (Shanghai) and are still only a project in the US: The Federal government just recently gave its approval to build the Cape Wind project which will be the first offshore installation in the USA, with 130 turbines along the coast of Massachusetts. In spite of this progress, the project is still not out of the starting block, notably because of strong opposition due to the impact on the scenery of this region and the important costs associated with updating the grid [1]. But nothing guarantees us that this will be the first project to see the light of day in North America. In the great lakes area, a Memorandum of Understanding (MOU) has just been signed between GE Energy and the Lake Erie Energy Development Corporation (LEED) [2]. This MOU is also planning the installation of 5 GE turbines of 4MW each, on the riverbanks of Cleveland. If this first step planned at the end of 2012 goes smoothly LEED is planning to increase the installation to 1000 MW in 2020, meaning around 200 turbines, with a potential for Lake Erie varying between 10 and 20 GW. Nonetheless, currently there is no offshore wind power installation in North America.

What is the advantage of offshore wind power when the turbines placed out at sea are subjected to more constraints than those on land :

• the cost of offshore wind power turbine installation is more costly and is limited to deep water;
• it needs the deployment of transmission cables whose costs are also relatively more expensive than overhead power lines;
• the conditions can force equipment to stay on shore and therefore generate additional rental costs (boats for installation are usually rented from private companies whose rates can be excessive);
• equipment maintenance is more difficult at sea.

In spite of that, there are a number of reasons to want to install offshore turbines:

• they can be installed in coastal urban areas where there is a strong demand for electricity;
• this proximity allows the optimization of costs linked to transmission and the congestion of the grid;
• wind is stronger at sea and more consistent at a lower altitude, and generates electricity in a less variable way and in larger quantities;
• the systems are less restricted in their dimensions because they weren’t necessarily transported via roadways, and therefore more powerful turbines can be installed.

Therefore there are a certain number of conditions which allow offshore to have an advantage. It’s therefore necessary to find the ideal location for this installation.

The cartography of the United States’ West coast

Dvorak, and al. [3] have done an important work of cartography of the West Coast of the US in terms of offshore wind farm installations. The method consists of considering the overall coast and of successively applying different known constraints to this area in order to reduce it to an optimal zone for installation.

First of all they have classified the ocean bottom into 3 categories:

1. Less than 20m, on which “one legged” turbines can be installed
2. Between 20 and 50m, on which turbines can be placed on a group of tripods
3. More than 50m and less than 200m, where moored floating turbines can be used.

The method identifies all ocean bottoms susceptible of having this type of installation, with the exclusion of those in proximity to military zones, harbor installations, etc… Then, winds in this region are evaluated and measurements taken are extrapolated to different points on the coast, and only the sites where average wind around 7m/s are kept.

In the end, Dvorak, and al.’s conclusions are that by using proven technologies – by excluding then, floating turbines – the installation of one offshore wind power plant off of Cape Mendocino would be sufficient enough to immediately produce 800 MW and reduce 4% of the share of energy production emitting green house gases in California. They give the example of an installation in shallower water of approximately 50m, near Eureka that has a certain number of transmission lines that would allow the redistribution of power towards main power lines in the central valley of California. In addition, a power plant within close proximity would also allow the connection to a electrical distribution grid. Finally, contrary to most installations on land whose peak production is at night, the installation of Cape Mendocino would have consistent production during summer months when demand is at its highest, which bypasses the problem of storage associated with a large number of installations.

The benefits of floating wind power technology

Dvorak, and al.’s study also show the full potential of the US’s West Coast for generating electricity using installations in deep water between 50 and 200m only accessible with floating turbines. In theory, current techniques if they were used in all the locations in California where average wind is more than 7m/s would generate between 17% and 30% of California’s energy bill. By using floating turbines, this potential would reach an interval of 174% to224%! Of course this doesn’t take into account the associated cost for all the installations, but it puts into perspective the gain that could be had with these floating installations.

There are a large number of advantages in this technical solution:

• first of all the access to the largest surfaces where there is strong and constant wind;
• an installation facility comparable to fixed structures, because the turbine can be simply towed by a small boat from the harbor;
• greater flexibility regarding waves and weather conditions that allow the equipment to deteriorate less;
• active piloting of orientation and possible positioning;
• and finally, access to the open sea allows the distancing of turbines from the shore and therefore the clearing up of the horizon for the detractors of the aspect given by the coast by these turbines.

A large number of companies such as Principle Power/Marine Technologies [5] are testing their technologies. They are developing the “Wind Float” and have signed a MOU with Energias of Portugal to develop for the first offshore demonstration near Lisbon [6]. The team of engineers in charge at Marine Technologies is almost entirely made up of French people having come from the Department of Naval Engineering at UC Berkeley. We are impatiently awaiting the rest of their adventures.

References

[1] Regulators Approve First Offshore Wind Farm in U.S., NY Times, April 28 2010
[2] The Great Lakes Gear Up for Offshore Wind, Green Tech Media, May 26 2010
[3] California offshore wind energy potential, Dvorak et al., Renewable Energy, Volume 35, Issue 6, June 2010
[4] Future for Offshore Wind Energy in the United States, Musial and Butterfield, 2004 NREL CP-500-36313 Preprint.
[5] WindFloat technology by Principle Power Inc.
[6] Utility-Scale Floating Offshore Wind Farm Coming to Portugal