Offshore wind power

Aerial view of Lillgrund Wind Farm, Sweden

Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Better wind speeds are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher.

Siemens and Vestas are the leading turbine suppliers for offshore wind power. Dong Energy, Vattenfall and E.on are the leading offshore operators. As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to BTM Consult, more than 16 GW of additional capacity will be installed before the end of 2014 and the United Kingdom and Germany will become the two leading markets. Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the United States.

History

Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Unlike the term typical usage of the term "offshore" in the marine industry, offshore wind power includes inshore water areas such as lakes, fjords and sheltered coastal areas, utilizing traditional fixed-bottom wind turbine technologies, as well as deep-water areas utilizing floating wind turbines.

In 2008, offshore wind power contributed 0.8 GigaWatt (GW) of the total 28 GW of wind power capacity constructed that year. By October 2009, 26 offshore wind farms had been constructed in Europe with an average rated capacity of 76 MW, and as of 2010 the United Kingdom has by far the largest capacity of offshore wind farms with 1.3 GW, more than the rest of the world combined at 1.1 GW (see List of offshore wind farms in the United Kingdom). As of October 2010, Danish wind turbine manufacturers Siemens Wind Power and Vestas have installed 91.8% of the world's 3.160 MW offshore wind power capacity. Based on current orders, BTM expects 15GW more between 2010 and 2014.

Economics and benefits

Most entities and individuals active in offshore wind power believe that prices of electricity will grow significantly from 2009, as global efforts to reduce Carbon emissions come into effect. Based on this, offshore wind power is expected to have independent viability in the mid-to-long term. BTM expects cost per kWh to fall from 2014, and that the resource will always be more than adequate in the three areas Europe, United States and China.

In 2009, offshore wind power depends on public schemes for its viability. Many governments, especially in Europe, have put such schemes into place in order to ensure increase the construction of Offshore wind farms. Typical schemes include Feed-in Tariffs, Renewables Obligation such as the UK's Renewables Obligations and direct public subsidies.

The rationale for the support schemes has several aspects, of which some or all may be relevant in each country or region that set them up:

• Current electricity prices do not include the costs of the carbon footprint of traditional sources of electricity (externalities)
• Supporting the offshore wind sector in its infancy is an investment into technologies, skills and organizations that will give an economic return in the future
• Offshore wind developments drive the need for local sourcing and manufacturing due to high cost of transportation, which stimulates local economies and creates jobs
• In the EU specifically, each country is working toward its goal as part of the commitment to increase the share of renewables in energy use by 20% by 2020
• Offshore wind can be built close to big consumption centra, which are typically located in coastal areas
• Offshore wind, especially if developed >20–30 km from land, tends to meet with much less public resistance than alternative means of solving electricity shortages (such as onshore wind, new transmission power lines or power plants)
• Offshore wind does not compete for the scarce supply of land in densely populated regions, such as in much of Europe, and the East Coast of the United States

Phases

Planning and permitting

Important elements:

• Siting (finding a site with i.e. good wind, proximity to onshore transmission capacity, favorable regulatory regime and the right conditions in terms of water depth, soil conditions etc.)
• Preliminary technical plan
• Environmental impact assessment
• Wind measurement
• Applications for various permits required by local authorities
• Communication with the public and stakeholders to ensure support for the plans
• Predictions of the yield of the plant
• Financial modelling
• Financing

In Denmark, many of these phases were deliberately streamlined by authorities in order to minimize hurdles.

In many cases, planning and permitting is done by specialized project development companies that do not intend to own and operate the plant, and that do not have the financial resources to do so. In other cases it is undertaken by utilities or independent power providers ("IPPs").

The planning and permitting phase can cost >$10 million, take 5–7 years and have an uncertain outcome. The industry puts pressure on the governments to improve the processes, and some governments are responding by streamlining them (e.g., UK, Ontario).

Procurement and construction

The owner of the wind farm typically procures it under a few, major [[EPCI|EPCI contracts]]):

• Wind turbines
• Marine structural elements
• Foundations -- required for fixed-bottom turbines, but not for floating turbines.
• Electrical cables (within the farm and to onshore connection point)
• Offshore Transformer substation(s)

All these items have special requirements for and special challenges in the offshore environment. For instance, turbines are much less accessible when offshore (requiring the use of a service vessel for routine access, and a jackup rig for heavy service such as gearbox replacement), and thus reliability is more important than for an onshore turbine.

Foundations transfer the loads from the turbine into the seabed. Major issues for offshore foundations include the need for special installation vessels and the resultant risk and costs of waiting for weather windows. Technology exists to install without use of offshore crane.

Operations and maintenance

After commissioning of the offshore wind farm, the operations and maintenance phase commences.

A control center uses weather forecasts to predict electricity generation and interfaces with the Transmission system operator to integrate the electricity into the grid. The control center also monitors and controls the individual turbines and other components of the plant.

A maintenance organization performs maintenance and repairs of the components, spending almost all its resources on the turbines. Access to turbines is by helicopter or service access vessel. Some wind farms located far from possible onshore bases have service teams living on site in offshore accommodation units.

Aesthetics

Main article: Environmental effects of wind power § Aesthetics

One of the main concerns with wind power is aesthetics. Most offshore wind farms are barely visible from shore. Noise is not necessarily an issue when it comes to Offshore Wind Power due to the remoteness of each turbine. A 2006 Survey by the University of Delaware near the proposed Cape Wind development found that residents most frequently based their decisions to support or oppose the wind farm on perceived impacts to marine life, the environment, electricity rates, aesthetics, fishing and boating.

See also

• Floating wind turbine
• List of offshore wind farms
• Lists of offshore wind farms by country
• Lists of offshore wind farms by water area