OFFSHORE WIND RESOURCE ASSESSMENT

Dileep V Raj

Mtech Renewable Energy Technologies

Amrita Vishwa Vidyapeetham,Coimbatore

Why Offshore ?• Higher wind speeds -> higher yield• Larger wind farms possible – fewer space/land availability

constraints• No complex terrain or visual impact issues• No displacement of people

But

• A lot more expensive than onshore windfarms….• Vessel costs + turbine foundation/installation + electrical cabling

to land

INTRODUCTION

• The wind power community has a long record on onshore design and construction of wind turbine foundations.

• But the offshore wind power is still in the embryonic stage but with aggressive and ambitious plans for developments.

• Metocean data-

• Meterological data( Wind, Atmospheric data, Air Temperature, etc ) and Oceanographic data ( Waves, Current, water level, Salinity, Water temperature , Ice etc ) are the important design basis parameters.

Traditional offshore structures vs. wind turbine foundations

• Any structure used in offshore oil and gas exploration and production constitutes a vital part of a successful energy production, vital both in terms of construction costs, of safety, of human lives and the environment, and in terms of revenues from the production.

• An offshore wind turbine foundation is typically simpler and much cheaper to build than an oil platform.

• Furthermore, the wind turbine will be un-manned except for maintenance and repair, the environmental impact from a damaged structure is limited, and the value of the energy production per foundation unit is far less than the value from oil production from a platform.

Offshore wind resource

Yield assessment road map

Required data level : Absolute min of 1 year on site – 2 years best practice

Significance of Offshore WRA

• Energy yield prediction• Extreme wind and turbulence analysis -> turbine selection• Minimizing financial risk and securing project financing: • The importance of uncertainty

Challenges to resource assessment offshore

• Rough weather and sea conditions -> higher risk• High met mast costs: 6-12 mi dollors offshore as opposed to

115-175k dollors onshore• Very few existing data points to provide reference data ->

account for temporal variability of wind?• Account for atmospheric stability and sea surface roughness?

Hub-Height Wind Speed

• Turbines in offshore wind plants must be designed to withstand extreme wind events in the case of mechanical yaw error.

Hub-Height Shear and Natural Turbulence

• For turbine selection and load estimation, it is also important to know the expected distribution of shear and natural (non-wake) turbulence.

• There is no accurate method for scaling surface measurements to make accurate hub-height turbulence measurements.

• The situation is not much more encouraging with numerical models.

• Such models generate estimates both of wind shear and turbulence, but there is little evidence that validates their performance for hub-height shear and turbulence.

Air Temperature and Atmospheric Surface Pressure

• Air temperature is needed in conjunction with atmospheric pressure primarily to calculate the distribution of air density at prospective wind plant sites.

• Unlike dynamic variables, this information is well known both from surface measurements and from numerical models.

Lightning

• Lightning is a common feature of offshore environments, and lightning protection systems should be routinely included in the design of renewable energy plants.

• Lightning detection networks extend well offshore; thus, frequencies of lightning events can be mapped for offshore waters.

• This information may have some utility in assessing lightning risk to a facility.

Ice Loading

• Sea ice loading on structures is a significant design consideration in cold regions.• Ice accretion affects blade aerodynamics for wind turbines and, in severe cases, could

affect structural integrity of turbine components. • Icing can result both from freezing precipitation and fog and from sea spray in subfreezing

temperatures.

Tidal Elevations

• Tidal elevations for wind turbine structures are important primarily for designing access and for identifying the parts of structures that will need to be specially protected from sea water corrosion.

• Coverage and accuracy of tidal data is sufficient for wind development purposes.

Salinity

• Salinity information is important to inform design consideration for corrosion.

Measurement Campaign: Offshore Met Mast

• Cup anemometers and wind vanes; along with meteorological sensors.

• Only IEC compliant option available for WRA• Limited access at sea : site visits minimum; safety requirements

higher• Allows monitoring of birds and marine mammals as well as acts as

platform for measuring wave height, scour movement etc.• Data monitoring required: sector filtering, cup degradation etc.• Issue : Flow distortion

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Courtesy:OFFSHORE WIND CLIMATEWim BierboomsWind Energy Research Group (Aerospace Eng.)

Offshore – Met mast vs. RS instruments

• Met mast – accepted worldwide and bankable data provided, with international standards (MEASNET, IEC 61400-12) available

• LiDARs and SoDARs – few validation studies offshore

• RS (Remote Sensing) equipment such as LiDARs and SoDARs:

ease of transportation and installation on existing platforms cost effective compared to tall masts easier maintenance compared to tall masts multiple height measurements

• Commercially used offshore along with a met mast till now Exception: Beatrice project, UK – LiDAR only

Metadata location fields and categories include the following:

• Physical location (latitude, longitude, and elevation) • Site name and number • Political region (county and state) • Local environment description and photographs (topography, vegetation, and

buildings or obstructions)

Instrumentation and equipment metadata and categories include the following:

• Data logger model and serial number • Sensors (model, serial number, height, orientation or boom direction, and

calibration information) • Tower description (size, height, face width, and so on, lattice or tubular, guyed or

non-guyed, face orientation, and tower commissioning report) • Remote sensing data (type of instrument, model, and serial number) • Data collection history (data outages, sensor changes, and unusual conditions such

as severe weather)

Data set description metadata include the following:

• Starting and ending dates and times • Data sampling interval • Total number of records collected • Data collection rate (0%–100%) • Data format (ASCII text, database files, binary, and so on) • Channel number for each sensor • Name and contact of responsible person • Quality control and data screening procedures that have been applied

Remote Sensing instruments

How do they work?

Principle of Doppler effect : change in frequency of a signal related to the line-of-sight velocity

• LiDARs – Light Detection and Ranging; electromagnetic radiation reflected from aerosols

• SoDARs- Sound Detection and Ranging; acoustic pulse reflected from the varying temperature structure of the atmosphere

LiDAR types: Continuous WavePulsed Floating LiDAR

Floating LiDAR

• Innovate to give concurrent wind, wave, current data• Motion compensated• Must be used carefully to ensure uncertainty reduction• Can be used to provide project data at much reduced cost

LiDAR fixed Platform

• LiDAR now bankable with appropriate traceability• High reliability if looked after• Need a fixed platform in vicinity of project

Atlas & Satellite

• Satellite data: 10m wind speeds• Needs to be scaled to hub height• Dependent on satellite coverage/length of system deployment• Can provide spatial variation and long term

Uncertainty

• Concerned with Uncertainty in Wind:a. Measurementb. Long termc. Coverage

• Uncertainty in Yielda. Modelingb. Wakes

Uncertainity

Europe is the global leader in offshore wind energyinstallation.

Globally installations have reached over 5,000 MW (Europe :4995 MW followed by China: 390 MW and Japan: 25 MW).

India has significant off shore wind power potential - Offshore wind potential of Tamil Nadu estimated as 127 GW at 80 m height in a WISE study (needs further validation).Preliminary assessment conducted by Scottish Development International - Tamil Nadu has potential of about 1 GW in north of Rameswaram and 1 GW in south of Kanyakumari.

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CASE STUDY1.INDIA

Offshore Wind Energy – Technology

Technology for offshore turbines same as that of onshore turbines and their operational life also same (~ 20 years).

The rated capacity of turbines higher than that ofonshore - in range of 3 MW-5 MW.

Off shore wind farms in water depths from 0.8 to 220 mwith monopile, jacket, tripod and floating technologies.

At different depths, turbine installations requiredifferent type of bases for stability .

Monopile base is used for water upto 30 m depth,whereas turbines installed on tripod or steel jacket basefor 20-80 m depths.

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Offshore Wind Energy- India Status

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India is blessed with coastline of about 7600 Km.

United Nations Convention on Law of the Sea givesIndia exclusive rights over its Exclusive EconomicZone (200 nautical miles from baseline) to developoffshore wind energy.

• Efforts so far limited to preliminary resourceassessment.

• C-WET has measured near shore wind data at 54locations along the coast.

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Preliminary studies by C-WET and Indian National Centre

•for Ocean Information Services (INCOIS), Hyderabadsuggest potential along Tamil Nadu, Gujarat andMaharashtra coasts.

Scottish Development

• International’s study done inatJanuary, 2012 has indicated potential of 1 GW each

Kanniyakumari and North of Rameshwaram.

• These results required validation by settingdata.

up ofoffshore masts to measure 2-3 years wind

• C-WET to carry out 100 m anemometry at Dhanuskodi,Rameshwaram (near the sea).

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Potential Locations at Rameshwaram andKanniyakumari suggested by Scottish Consultant

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Offshore Wind Energy Development in India-Relevant Issues

• High Cost-times than

The cost of offshore wind farms almost 1.5 –that of onshore wind farms.

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• Offshore resource characterization required for firming up potential.

• Development of a policy framework including theregulatory process.

• Capability creation for understanding the nuances ofturbine and array design consideration and grid integration.

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Nodal Ministry

MNRE to act as nodal ministry for development wind energy in the country.

of offshore

Functions:

• Overall monitoring of the offshore wind development in thecountry.

Co-ordination with other Ministries/Departments.Issuing guidelines/directives for development of offshore wind energy.Oversee working and to provide necessary support to National Offshore Wind Energy Authority (NOWA) for smooth functioning.Promoting indigenous research for technology development.

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National Offshore Wind Energy Authority(NOWA)

National Offshore Wind Energy Authority (NOWA) to beestablished under the aegis of MNRE - to be responsible forthe following:

Carry out Resource Assessment and Surveys in the EEZ ofthe country.

Enter into contract with the project developers forthedevelopment of offshore wind energy project in

territorial water (12 nm).

Single Window Agency to facilitate clearances.

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2.DENMARK

• In 1991, Denmark began operating the world’s first offshore wind farm.• Denmark has the industry’s simplest permitting framework. • The Danish Energy Agency acts a “one-stop-shop” for offshore wind farm

permitting, coordinating with other agencies to issue all three required licenses: a license to carry out preliminary investigations, a license to establish the offshore wind turbines, and a license to exploit wind power for a given number of years including, for projects greater than 25 MW, an approval for electricity production. All offshore wind projects are subject to an environmental impact assessment

3.United kingdom

• The UK has a mandate to reach 15 percent renewable energy sources for electricity by 2020.

• Since the UK’s first offshore wind farm was commissioned in December 2000, the UK has moved aggressively to continue developing this renewable resource.

• In 2008, the UK overtook Denmark as a leader in MW capacity of offshore wind power.

• In September 2010, the 300 MW Thanet wind farm came online,bringing the UK total to operational offshore wind farms with a cumulative capacity of 1,341 MW.

• Another four offshore wind farms are under construction, and seven more have been approved, which would add another 3,772 MW of capacity upon completion.

• Germany’s first offshore wind farm was installed in 2008. • The German wind industry expects 300 MW of new offshore wind capacity to be

installed in 2010. • A new Power Line Expansion Law makes it easier to use underground cables and • allows the costs of connecting the offshore wind farm to the grid to be spread

nationwide. • Offshore wind is projected to reach a capacity of 10,000 MW in Germany by 2020.

4.Germany

REFERENCES• Barthelmie, R.J., 1993, Prospects for Offshore Wind Energy, Wind Engineering, 17, 2, 86-89.

• Ladenburg, J., Dubgaard, A., Preferences of coastal zone users regarding the siting of offshore wind farms, Ocean & Coastal Management, 52 (2009) 233-242.

• Offshore Wind Resource Assessment of the Gulf of Thailand J. Waewsak1, M. Landry2 and Y. Gagnon2

• Nikolaos, N., 2004. Deep water offshore wind technologies. A thesis submitted for the degree of Master in Science In Energy Systems and the Environment. University of Strathclyde. Department of Mechanical Engineering September 2004. Available at: www.esru.strath.ac.uk/Documents/ MSc_2004/nikolaos.pdf [Accessed 26 March 2009].

• IEA, 2005. Offshore Wind Experiences. International Energy Agency, Brussels.