Onshore and Offshore Wind Farm Comparison

1.0 Introduction:

Wind is the movement of hot and cold air over the surface of the Earth (BWEA, 2010). Air is a combination of solid, liquid and gas particles (EWEA, 2011). Energy from the sun shines on our atmosphere all of the time, but the surface is heated unevenly. This results in some places being warm while others are cool. As the earth is heated unevenly and because hot air is lighter than cold air and therefore rises, differences in pressure are created (EWEA, 2011). Airflows try and equalise these pressure differences. Together with the rotation of the earth, the difference in air pressure causes an uneven flow of air. i.e. wind (EWEA, 2011). Due to the rise in greenhouse gas emissions into the atmosphere, from the burning of fossil fuels such as coal, gas, oil and peat. Wind energy acts as one of the greatest solution to our problems, as it is a clean, sustainable, renewable and inexhaustible solution (SEAI, 2011). This renewable form of energy can be used to generate electricity and with increasing environmental awareness, it acts as a major contributor to a clean and environmental friendly source of energy supply (EWEA, 2010). Wind energy is for the first time the leading technology in Europe (BWEA, 2010). In relation to installed wind energy capacity, there was over 10 GW installed in Europe in 2009, which produces an increase of 23% from 2008 (EWEA, 2010). By the end of 2009, a total of 192,000 workers were employed directly and indirectly in this sector (EWEA, 2010). By the end of 2009, the wind power capacity installed in Europe produced 4.8% of the electricity demand and the emission 106 million tonnes of carbon dioxide was avoided, this would be the equivalent of taking 25% of cars in the EU off the road (EWEA, 2010). This amount of electricity would be enough to power 82 million electric cars that would potentially be more environmentally friendly (EWEA, 2011). Since the introduction of wind turbines, it is saving Europe €6 billion per year in relation to fuel costs (EWEA, 2010). With such a huge environmental saving, and also the world oil supplies depleting, it is easy to see why renewable energy solutions is a big business.

1.1 Aims of the project: The aim of this project is to compare and contrast an onshore wind farm and an offshore wind farm in terms of feasibility, also to discover the advantages and disadvantages associated with both wind farms.

1.2 Technology of a wind farm:

The majority of wind turbines commercially operating in Ireland today consist of three rotor blades that rotate around a horizontal hub (SEAI, 2011). The wind passes through the blades which create a lift; this then causes the rotor to turn which causes the blades to turn (EWEA, 2011). The rotor is linked to the nacelle which houses the gearbox, the low-speed shaft, the high-speed shaft and the generator (EWEA, 2011). Per minute, the blades rotate the shaft between 30 and 60 times (EWEA, 2011). The gearbox connects the high and low speed shafts together which increases the rotation speed of the high-speed shaft to approximately 1,000 to 1,800 turns per minute (EWEA, 2011). The fast spinning shaft then forces the generator to create energy (EWEA, 2011). The generator converts mechanical power from the rotor into electrical power. Any electricity produced by the generator travels to a transformer which converts the electricity to the correct voltage for the distribution system (EWEA, 2011). The electricity is transported from the wind turbine to the grid along electrical cables (SEAI, 2011).

For wind turbines to work effectively and efficiently, it is necessary for the rotor to face directly into the prevailing wind. The stronger the winds, the more energy can be produced (EWEA, 2011). Wind turbines produce energy at wind speeds of 4-30 metres per second. The wind turbine control system ensures that if the wind speed exceeds a speed of 25m/s, the turbines control system will automatically shut down for safety reasons and to prevent any damage to the turbine (SEAI, 2011). Another variable which helps a turbine produce more electricity is the blade radius, where the larger the blade radius of the blades, more energy may be created (EWEA, 2011). Therefore, if the blade radius of a turbine was doubled, four times more power could be produced (EWEA, 2011). Finally, air density also impacts the amount of electricity produced. The heavier the air the better, this exerts a greater lift on the rotor. Whereas lighter air is a lot less productive (EWEA, 2011).

1.3 Connection to the Electricity grid:

All wind turbines must be connected to a national grid, which supplies us with electricity. Electricity is distributed to consumers through physical infrastructure i.e. transmission and distribution networks (EWEA, 2011). The transmission network is made up of cables and pylons which transports high voltage electrical power across long distances i.e. into cities and large towns (EWEA, 2011). The transmission and distribution network are linked at a region called a substation. This is where the high voltage is stepped down to medium voltage (EWEA, 2011). The consumers are only connected to a medium voltage level which is the distribution system. Once the electricity reaches its final destination i.e. small towns or individual customers, the power is stepped down to a low level (EWEA, 2011). According to the SEAI, Irelands electricity grid system includes a localized distribution system (10, 20 and 38kV network) and a higher voltage transmission system (110, 220 and 400kV network) (SEAI, 2011).

Turbines that are going to supply electricity need to be situated on a viable site. It is important to determine the distance from the site to the nearest connection point (SEAI, 2011). The further away a wind farm is from the national grid, the more costs associated with the transporting the power to the grid, approximately 15 km is an ideal distance (SEAI, 2011). The electricity is transported from the site by underground cables and overhead power cables (SEAI, 2011). These carry the electricity to a substation where it can connect to a national grid to supply customers with electricity (SEAI, 2011). However, it is not always viable to build a wind farm close to a grid connection point due to many reasons such as wind speed etc. Costs of connecting to the grid can be substantial (SEAI, 2011).

1.4 Targets in Europe

Wind energy is for the first time the leading technology in Europe. €13 billion was invested in wind farms in 2009 which was had an increase of 23% compared to 2008 (EWEA, 2011). Statistics released by the EWEA show targets for Europe by 2020 to produce 14-17% of Europe’s electricity demand, to avoid the emission of 333 million tonnes of carbon dioxide per year and to save fuel costs by €28 billion and to save €8.3 billion in avoided carbon dioxide costs (EWEA, 2010). Europe hopes to have a total of 230 GW installed wind capacity by 2020. (EWEA, 2010). However, by 2030, Europe hopes for wind energy to have even a higher demand with targets of producing 26-35% of the electricity required by Europe, to avoid 600 million tonnes of carbon dioxide per year and to save a massive €56 billion per year in avoided fuel costs and to save a substantial €15 billion per year in avoided carbon dioxide costs. (EWEA, 2010). By 2030, it is expected that Europe will have 40 GW installed wind capacity (EWEA, 2010).

1.4.1 Targets in Ireland

Wind energy’s contribution in Ireland continues to increase with additional capacity (IEA, 2009). Since the first wind farm was set up in Ireland in 1992, 110 wind farms were metered in June 2010 with a total installed capacity for wing to 1,379 MW. This was enough electricity to power over 500,000 homes across Ireland (SEAI, 2011). For Ireland to achieve its national target of 40% by 2020, approximately 5,500-6,000 MW of wind generation is required (SEAI, 2011).

2.0 Wind Farm Development

2.1 Introduction:

Wind energy is a huge industry across Europe with nearly all European countries have or having prospectus wind turbine installation (SEAI, 2011). Wind turbine technology continues to grow and advance. Irelands first wind farm was in 1992 in Co. Mayo (SEAI, 2011). Wind turbines are large complex industrial equipment and their manufacture involves the use of raw materials and energy. The materials can be recycled at the end of their useful existence, where the capital from this can be used to reestablish a wind farm to its original state (SEAI, 2011).

2.2 Financing wind energy

Like all developments, wind energy projects require finance. For any project to be economically viable, sufficient capital is required (SEAI, 2011). The development of wind farms is not only beneficial in producing electricity, it also creates employment. There are many things a financer will look for before entering a wind farm development.

Planning permission of the selected site is required which would have a huge time constraint. An assessment of the sites wind resource should be carried out on the proposed site to identify if the site has a good wind supply (SEAI, 2011). The project should have a power purchase agreement and have sufficient proof of the proposed site title and land rights. There should be a development team with relevant experience in the sector and also a plan for any development costs (SEAI, 2011). There should be details of any other funding of the site and also have a cash flow on a 15 year basis (SEAI, 2011).

During installation of a wind turbine, there are many costs involved. These costs account for 16-32% of the total investment (EWEA, 2009).

Any foundations for construction works and any construction costs for road ways. Electricity will be carried by underground cables which will need to be buried (EWEA, 2009). Transformers must be present to convert low voltage to medium voltage. Sub-stations are also required to convert voltage from medium to low (EWEA, 2009). Any transport costs of turbine pieces and use of heavy machinery. The turbine must be assembled and tested. Also any administrative, financing or legal costs must also be paid for (EWEA, 2009).

Once the turbine has been installed, there are land rental, operation and management costs remaining; Insurance should be included for any damage, health or safety issues (EWEA, 2009). Regular maintenance to make sure turbine is working efficiently. Repair of turbine or Spare parts that need to be replaced also must be taken into account (EWEA, 2009). Any administration fees must be paid and also the land rental from the developer to the land owner (EWEA, 2009).

These costs are low when compared to most other power generating costs (EWEA, 2009). For wind turbines, there are no fuel costs and the wind is free. The capital costs (i.e. building the power infrastructure and connecting to the grid) of a wind energy development is approximately 75% of the total cost (EWEA, 2011).

Typical project costs in Ireland released by the IEA show that the major cost is the turbine itself accounting for 65%. This is a capital cost that should be paid immediately. Grid connection accounts for 12%, onsite electrical (8%), civil engineering (8%), development (4%) and legal/financial (3%) (IEA, 2009).

The total investment for a wind turbine averages €1.6 to €2 million per installed megawatt. So therefore, a 5 MW farm would cost about €1.6 million (SEAI, 2007).

This figure will, of course, vary according to technical choices made and the particular features of the site. A modern wind turbine produces electricity 75-80% of the time, but it generates different outputs depending on wind speed (IWEA, 2011). With most large modern wind turbines having a life expectancy, with regular maintenance, of between 20-25 years, therefore wind farms have the potential to be very profitable in the long term (EWEA, 2011).

2.3 Site selection:

Site selection is crucial when choosing where a wind turbine can be located as some sites can be more suitable than others. The most important requirement is the wind speed. Generally, the most exposed sites will generate the most electricity (SEAI, 2011). Other considerations must also be taken into account when selecting a site include; the size and the condition of the site, access to the site, existing land uses and connection to the electricity grid (SEAI, 2011).

2.4 Health and Safety:

As with all industries, wind energy must perform responsibly in relation to any health or safety concerns. The main safety concern with any turbine is blade failure. It can arise from a number of possible sources and results in either whole pieces of blades or pieces of blades being thrown from the turbine (Stankovic et al). This is why it is so important for the turbine to be located at an adequate distance from any dwellings.

Other safety concerns include; fire, structural failure, transport of large and bulky turbine pieces, parachutes crashing into one and development and construction workers (Stankovic et al). To date, there has been no reporting of wind turbines having serious negative health effects.

3.0 Wind energy impacts on local Environment:

Wind energy, as do other renewable resources, have their own environmental impacts. Environmental Impact Assessment (EIA) is a process which identifies the environmental effects (both positive and negative) of wind turbine development proposals. It aims to prevent, reduce and offset any adverse impacts (EWEA, 2010.) Impacts that can affect the local environment include;

Visual intrusion – the colour of the turbines tend to be neutral colours for the tower and the rotor blades to blend into the natural skyline. The layout and configuration of the turbines is also important, and if they are correctly positioned on site, they are more aesthetically pleasing to the eye (SEAI, 2011). The visual impacts of wind turbines are influenced by: form and characteristic of landscape, design and colour of turbines, the layout of the turbine, the existing skyline and the number and size of turbines (SEAI, 2011).

Noise – Virtually everything with moving parts generate some degree of sound, and wind turbines are no exception (SEAI, 2011). There are two sources of noise produced from the turbine; mechanical noise from the gearbox and generator of the turbine and aerodynamic noise which is produced from the blades passing through the air (SEAI, 2011).When the wind blows the noise level of the turbine is masked by the sound of the wind itself and when the wind is not blowing, the turbine will not be moving and therefore sit silently in the landscape (SEAI, 2011). It is rare to hear a wind turbine moving at distances of 300 metres or more (EWEA, 2010).

Wind turbines also have an impact on bird life. Birds can be affected by two main ways. The first by injury or death due to birds colliding with the turbine, or secondly, by birds being disturbed in their breeding, nesting or feeding habits. Research carried out by the European Wind Energy Association (EWEA) shows that the risk of bird deaths through collision with turbines is low (EWEA, 2010). For example, it is estimated that 28,500 birds are killed each year by wind turbines. In comparison to this, over 550 million birds are killed each year from collisions with buildings or windows (EWEA, 2010). To help minimize the risk of these problems towards birds, turbines should not be situated on migration routes or where there are high densities of nesting or foraging or birds (EWEA, 2010).

Also, during development stages, impacts on the local environment may include; transporting of bulky compartments of the turbine with large vehicles which must use national roads as much as possible, manage the site i.e. remove any waste, increase in traffic flow or an increase in noise levels i.e. use of heavy machinery (SEAI, 2011).

4.0 Wind energy and the current Economic downturn:

Everybody is talking about the downturn in the economy of late, and it is not just a national problem, but a global problem. The construction industry has hit a major downturn, and there is a lot of unemployment of late. The key to survival I feel, is further training, and companies diversifying into other areas. For instance, the area of renewable energy is getting stronger each year, the amount of jobs been created in this industry is steadily increasing each year. The EU wind energy sector employed 192,000 people directly and indirectly in 2009 (EWEA, 2010). Whereas in 2007, 150,000 people were employed both directly and indirectly in the EU (EWEA, 2009). There was a huge increase in employment from 2007 to 2009 and it is predicted that the number of jobs will more than double to almost 446,000 by 2020 if current conditions continue (EWEA, 2010). There are vast employment opportunities in this sector.

5.0 Advantages and Disadvantages of wind energy from wind turbines

Based on this literature review, the following advantages and disadvantages associated with wind energy being produced from wind turbines have been noted:


  • Saves fuel costs, reduces dependence on fuel and importing fuel (EWEA, 2010).
  • Avoids emission of greenhouse gases (GHG) and air pollutants (EWEA, 2010).
  • Creates employment during the development and maintaining stages (EWEA, 2010).
  • Affordable electricity produced (EWEA, 2010).
  • Clean and environmental friendly energy source (SEAI, 2011).
  • Local area receives an income from renting out land (EWEA, 2010).
  • Reduce electricity cost as it has a lower marginal cost (EWEA, 2010).
  • Wind energy is free (BWEA, 2010).
  • Europe’s leading renewable energy resource (BWEA, 2010).
  • Land beneath the turbine can still be used i.e. in agriculture (EWEA, 2009).
  • Turbines are available in different sizes (EWEA, 2009).
  • Turbines can be a tourist attraction (EWEA, 2009).


  • Have negative effects on bird and bat life (EWEA, 2010).
  • Not all areas have a great wind resource (EWEA, 2009).
  • Wind dependant, therefore if there is no wind on a given day, production of electricity can be poor (EWEA, 2009).
  • Some people find wind turbines noisy and an unsightly structure blocking a countryside view (SEAI, 2011).

Feasibility of Study:

The aim of this study is to investigate and compare onshore and offshore wind farms. – Onshore farms were first developed in the UK in 1991 (BWEA, 2010). Since then onshore wind energy has become more cleaner and a more mature technology (BWEA, 2010). Onshore wind farms are located widely across Europe, with Ireland, Denmark, France, Norway and the UK having the best coastal locations with the UK having the windiest sites (BWEA, 2010). Medium wind speed sites include the inlands of southern and central Europe including; France, Germany, Spain, Italy and Holland (EWEA, 2009). The wind speed on site has a major influence over the profitability of the turbine (EWEA, 2009).

  • Offshore wind farms now have a cumulative capacity of 2,063 MW across Europe with a total of 39 wind farms. Offshore wind turbine farms are a new and leading technology in Europe that provides a cleaner and more affordable form of electricity (EWEA, 2010). In Europe from 2008 to 2009, there was a 56% increase in total installed capacity, with Europe having 374 MW in 2008 and a value of 582 MW year ending 2009 (EWEA, 2010).
  •  Offshore wind power is more expensive than onshore, with a dramatic price increase of 50% (EWEA, 2009). This huge price difference is due to the larger wind structures and complex logistics of the installation of the wind turbine (EWEA, 2009). However, with offshore turbines having greater wind speeds than onshore turbines, these have a higher electricity production (EWEA, 2009). Depending on locations, typically an onshore installation usually reaches 2,000-2,500 full load hours per week whereas; an offshore installation is almost doubled with 4,000 full load hours per week (EWEA, 2009).
  • Depending on site considerations, usually offshore wind turbines provides greater wind speeds and has a lower visual impact of the larger turbines (EWEA, 2009).
  • There are differences in cost between the onshore and offshore farm with the foundations being more expensive on the offshore turbine. However cost will vary depending on the type of foundation being built and also the depth of the sea (EWEA, 2009). Also connection to the electricity network will vary between sites. Connection costs from the turbine to the transformer station must also be taken into account (EWEA, 2009). The further away from the connection point, the more expensive the project will be.

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