Countries across the world are increasingly turning to wind turbines for energy generation, both as part of an international drive to reduce atmospheric pollution, a major cause of climate change, and due to the increasing cost and stock depletion of carbon based fuels such as oil and gas.
By the end of 2011, global wind installed capacity stood at 237,669 MW. 41% of this is located in Europe, 22% in the USA, 35% in Asia and 2% in the rest of the world.
In 2008, China overtook the USA as the largest producer of wind energy, standing at 62,000 MW. China is also the home of the world’s largest wind farm, Gansu Win Park, producing over 5000MW (the park is actually a combination of small farms in the region).
The UK has become a leader in the development of larger offshore wind farms, due to higher wind speeds and large area of relatively shallow water. The London Array is believed to be the largest offshore wind farm in the world. Phase 1, commissioned in 2012, will bring a capacity of 630MW, with phase 2 due to increase this capacity to 1000MW.
2011 saw global investment in wind energy reach $260 billion, with a predicted annual growth rate of around 15%.
Renewable Energy in the UK (end of 2010)
UK national policy on climate change states that we are to “put ourselves on a path to cutting CO2 emissions by some 80% by about 2050, with real progress by 2020.” (Energy White Paper).
Achieving this will require renewable energy to play a key role in the transition to a low carbon energy supply. In 2010, renewable sources of energy amounted to a total of 8% of the UK’s power generation, of which wind contributes 3%.
Current EU policy requires member states to achieve 20% of all EU energy to come frome renewable sources by 2020. The UK’s contribution to this has been agreed at 15%. Much of the UK’s contribution is expected to come from electricity generation, and will require the UK to generate 35 – 40% of its electricity from renewable sources. This could require some 35,000 MW of wind capacity to be installed.
At present, there is approximately 6,633 MW of operational wind capacity in the UK, generated from 340 projects. In addition, there is around 3,800 MW in construction, 5,900 MW granted planning permission with 11,000 MW submitted for planning permission.
Wind Turbine Technology
Turbines used across UK onshore wind farms typically have a generating capacity of around 3 MW and are made up of:
- A three bladed rotor;
- 70 - 90m in diameter;
- A tower of 70 - 80m in height
Wind turbine power output involves a cube law whereby a 10% increase in wind speed yields about a 30% increase in available energy. High wind speed locations, large rotors and high towers therefore yield more energy, but are subject to other constraints.
Turbine sizes for offshore wind farms have been in the 90 to 126m rotor diameter range with a generating capacity of at least 3 MW but designs are being driven towards much larger units, due to the increase unit cost of foundations and installation incurred by offshore turbines. The largest current prototype has a 164m diameter rotor, with each blade weighing in at 35 tons, and a generating capacity of around 7 MW.
Wind turbines are designed to reach maximum rated power at a hub height wind speed of 12 - 18 m/s (33 - 40mph). Power is then regulated up to a designed cut-out sped of about 25 m/s (56 mph).
The capacity factor for wind projects is typically about 25 - 35% i.e. the average percentage of continuous output at maximum capacity actually achieved. These figures can increase to 35 - 40% on some offshore sites and in more exposed locations in the north of the UK. It is possible to alter the capacity factor using different turbine configurations such as larger rotors and smaller generators.
Costs of wind power
The main support mechanism is the Renewables Oblication (RO), which requires electricity generators to source an increasing percentage of the UK’s total electricity supply from renewable sources or pay an equivalent value which is recycled to renewable providers/ The RO in 2010/11 equated to 11.1% of UK electricity.
The cost of wind energy mainly depends on:
- Wind speed,
- The required rate of return on investment,
- World turbine prices and,
- Infrastructure costs
Current costs are varied and highly subject to location, size and local circumstances.
Whilst exact current costs are difficult to quite due to variable costs and conditions, comparative costs were produced for the Government by Ernst and Young in 2007. This provided the following range of costs for 2010:
- Onshore wind 6.5 – 7.7 p/kWh (high to low wind sites, > 10MW capacity
- Offshore wind 9.2 p/kWh
The latest prices for new build projects from 2010 were reviewed by Mott MacDonald for the Department of Climate Change. This predicted (at a discount rate of 10%) the baseline comparative price of Gas (CCGT) at 8p/kWh and gas (including carbon capture and storage (CCS)) at 11.3p/kWh. Onshore wind would amount to 9.4 p/kWh with offshore representing around 16 – 19 p/kWh.
Onshore Wind Projects
Onshore wind projects represent around 90% of wind farms globally. Their location is influenced by an abundance of large, sparsely populated areas, with the USA, China and India being home to some of the largest farms.
By 2012, there were 4,760 MW of onshore wind in operation across the UK. 62% of this can be found in Scotland, which has a high national target for wind energy. In addition:
- 1,470 MW are currently under construction
- 4,629 MW have been given planning consent
- 7,100 MW are awaiting consent, with around 50% expected to receive consent
Factors common to onshore wind farms include:
- the average size (MW rating) of a turbine is around 2 – 3 MW
- Foundations and civil costs are relatively low (around 13%). Turbine manufacture costs account for around 65% of total capital outlay
- Turbine size anf farm layouts are often dictated by environmental or planning constraints, road access and the availability of heavy lift craneage
- Regions with high electricity demand but lower wind speeds e.g. south-east England, are often of lower commercial viability than the windier north and Scotland
Offshore wind farms
Offshore wind is a relatively new approach in difficult terrain with sea depths of up to and over 45m. The overall project and its individual components will generally be on a much larger scale than onshore due to the need to minimize infrastructure costs. Globally, 4,200 MW of offshore projects are operational with around 90% of this located in Europe.
- 15 UK offshore projects are operation totalling 1,800 MW
- The Crown Estates owns the seabed and his issued three rounds of leases for development
- The first round allocated 18 licences for projects around the UK of up to 100 MW each. Construction of these is now complete including North Hoyle and Kentish Flats
- In 2003, the second round saw 15 sites chosen, totalling 7,169 MW, with most under construction
- A third round of lease offerings was announced in 2008 amounting to 25,000 MW
- Other main offshore wind players include Denmark, Netherlands and Ireland
Key Issues in the UK
By 2010, the wind energy sector, including marine renewables research, employed over 10,000 people. The skill base is multidisciplinary, from project management, civil, electrical and mechanical professionals and environmental specialists to supply change managers and financial modellers.
Many wind farms on land in the UK have difficulty in getting planning permission, particularly in England and Wales where there is also a shortage of grid capacity.
Whilst Scotland has been more receptive to the development of onshore wind, this has been somewhat constrained by national grid export capacity and infrastructure requirements.
The best sites for wind speed are often in exposed locations, which suffer from higher costs such as grid connection and road access for turbine delivery.
Environmental considerations, in particular the visual impact, but also the effects on aviation radar and designated landscapes have severely impacted the number of sites which are considered suitable for onshore wind farms.
Offshore siting offers a much larger opportunity for wind power to make a significant contribution to meeting the UK’s renewables target, but at greater cost. The current constrains of offshore wind include:
- Grid capacity
- Air defence radar
- The engineering of deeper foundations
- And the limited world-wide availability of turbines and components
Intermittency of wind energy is often cited as a drawback for wind and other variable renewable energy sources. The Select Committee on Science and Technology (2004) accepted evidence from National Grid and Intermittency of wind energy is often cited as a drawback for wind and other variable renewable energy sources. The Select Committee on Science and Technology (2004) accepted evidence from National Grid and other experts that any reserve ‘firm’ capacity for 10% penetration of the UK’s total generating capacity by wind is ‘not large’.
Increasing penetration by wind has no technical limitation but will require proportionately greater reserve costs. SDC (2007) and the Cabinet Office (2002) gave costs of back-up for 20% penetration at 0.17 – 0.2 p/kWh respectively.
Microgeneration has an increasing profile, as there has been recent publicity for domestic or small commercial generation including small, roof-mounted wind turbines and also solar panels. Whilst these may form part of a useful contribution, along with improved energy efficiency, it would require approximately 5,000 medium sized (1.75m in diameter) home turbines to equal the electricity output of a single medium-sized commercial wind turbine (80m diameter).
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