OFFSHORE WIND ENERGY DEVELOPMENT: Indian Perspective
A consistent and smooth-flowing wind over the sea leads to a lower turbulence level. This exerts a steady load on wind turbines, thus offering a favourable operating condition and a reduced impact on the environment. Besides, higher wind speeds at the sea result in increased production of energy.
Despite these favourable conditions, the offshore wind potential of the country remains unexplored and unexploited mostly because of several constraints. In India, prior knowledge and experiences of offshore development of wind farms are not consolidated. In addition, essential datasets such as measured wind data, correlated mesoscale models, detailed Environmental Impact Assessment (EIA) studies, and oceanographic studies are not readily available. At the initial phase of development, social response and clearance activities provide significant challenge. Prior to construction, developers expect a detailed roadmap from the government with authenticated studies and technologies for harnessing the offshore wind potential. They would find it helpful if the government amends India’s offshore wind policies before entering into a mass development phase.
Among the many challenges to harnessing the offshore wind potential are the varying cost drivers associated with different technologies required for setting up any new offshore market. The cost of an offshore project is massive and would escalate quickly as a function of seabed conditions and water depth, apart from operating wind climate conditions. Therefore, one has to map out in detail environmental constraints, seabed conditions and structure, wind resource, array layout and grid connection, turbine technology for the site as well as installation methods to understand the scale of the opportunity and the capital expenditure required to realize the development.
GLOBAL AND NATIONAL OVERVIEW
Approximately, 14 GW of offshore wind capacity has been installed around the world till 2016 (Figure 1) with an equal capacity under construction. The major installations are in the United Kingdom (5,078 MW), Denmark (1,271 MW), Germany (1,049 MW), Belgium (712 MW), China (670 MW), The Netherlands (247 MW), and Sweden (212 MW). Japan has an ambitious plan to install wind turbines on innovative buoyant steel frames stabilized with ballast and anchored to the seabed. The offshore wind power capacity is expected to increase manifold in the near future with significant contributions from China and the United States. Compared to onshore turbines, the rotor size and power capacity of individual wind turbines available for offshore installations are higher, which would contribute to the increase in capacity (Figure 2).
India has the right to install wind farms in the country’s territorial waters, which extend up to 12 nautical miles (nm) from the baseline, and in the Exclusive Economic Zone (EEZ), beyond the 12 nm limit and up to 200 nm, under international laws. India’s coastline is more than 7,500 km in length from the western coast of Gujarat, Maharashtra, Karnataka, and Kerala to the eastern coast of Tamil Nadu, Andhra Pradesh, Odisha, and West Bengal. Under the Ministry of New and Renewable Energy (MNRE), the National Institute of Wind Energy (NIWE) has measured nearshore wind data at 78 locations along the Indian coast (Figure 3) by installing meteorological masts.
A preliminary assessment suggests the potential to establish wind farms, each of around 1 GW capacity, along the coastline of Rameshwaram and Kanyakumari in Tamil Nadu and in the Gulf of Khambhat, Gulf of Kutch, and Saurashtra open coast in Gujarat, where promising wind potential has been shown. These are two main maritime areas in which offshore wind farm structures can be built in the near future.
The study over Gujarat region (Figure 4) found higher average wind speeds. The areas of assessment included the Gulf of Kutch and the south coast of the peninsula. Using the remote-sensing technique of LIDAR (light detection and ranging), the NIWE found great potential for wind energy development at Dhanushkodi, Rameshwaram, in offshore Tamil Nadu.
OFFSHORE WIND RESOURCES
Different agencies have assessed wind resource potential with the help of buoybased and ship-based floating LIDAR systems. These systems are equipped to measure weather parameters, such as air temperature, barometric pressure, as well as wind speed and direction. They report these data via satellite radio links using the purpose-built communication system or commercial satellite phone networks to meteorological centres for use in forecasting and climate study.
During the preparation of the Indian Wind Atlas, Risø DTU of Denmark, along with the NIWE, indicated some offshore wind potential around the coastline of southern India at 80 m above the ground level. Also in collaboration with Risø DTU, and facilitated through an MNREfunded project, the NIWE carried out satellite-based wind resource mapping in a small region between Rameshwaram and Kanyakumari in the southern part of Tamil Nadu. It based the measurement and analysis on the satellite synthetic-aperture radar (SAR) data from the European Space Agency (ESA), conducted under the ENVISAT/ASAR mission.
CHALLENGES TO OFFSHORE DEPLOYMENT
Deployment of offshore wind power faces significant challenges related to resource characterization, subsea cabling, turbine foundation, installation of turbines (including logistics), grid interconnection and operation, development of transmission infrastructure, and coastal security during construction and operation. Adding large capacities of offshore wind power generation to the power system requires reliable integration to the national grid. Moreover, measurements of wind potential in offshore regions are costly due to the higher cost of installing meteorological masts. Furthermore, the wind velocity can reach up to 200 km/h (55.55 m/s) during cyclones, and sea water may corrode the steel structure of wind turbines.
Other challenges include higher capital investment in offshore installations and submarine cables; complications of the offshore foundation, support structure, installation, and decommissioning; less accessibility than onshore installations; higher operations and maintenance costs; and downtime of machines.
Some technologies suitable for power transmission for offshore generation are as follows: For distances up to about 50 km, conventional three-phase highvoltage AC transmission is the most economical solution. For distances beyond 50 km, an alternative technical solution becomes increasingly attractive—highvoltage DC current (HVDC) transmission. For distances greater than 100 km, that is, for bulk transmission, HVDC is often used.
While land-based turbines are affected by wind alone, components of offshore turbines such as rotor, nacelle, and tower are affected by wind and the support structure is affected by winds, waves, ice, and water currents. The offshore turbines are subjected to additional loads such as sea wave loads, impact loads due to ship movement and ice movement, depth variation due to tidal and storm surges, effects of marine vegetation growth, earthquake loads, and scour effects.
INITIATIVES IN INDIA
The essential components of a policy for the development of offshore wind farms include the following: preliminary resource assessment and preliminary oceanographic and bathymetric studies for the demarcation of blocks; EIA of proposed offshore wind farms regarding aquatic life; studies relating to navigation, undersea mining and related exploration/ exploitation activities, and other users of the sea. Detailed studies and surveys would determine the construction costs for special foundations and special ships for both operation and maintenance requirements. Other necessities include seabed lease arrangement; statutory clearances and no objection from regulatory authorities; grid connectivity and evacuation of power (both offshore and onshore); business model and technology development; incentives; security of offshore installations and confidentiality of the data collected during studies and surveys; and financing.
The MNRE is overseeing the following aspects of development: monitoring the overall offshore wind development in the country; coordinating with other ministries/departments; issuing guidelines/directives for the development of offshore wind energy; providing necessary support for smooth functioning; developing international cooperation and coordination towards tariff setting and regulatory issues; calling for proposals; entering into contract with project developers; carrying out and also coordinating resource assessment and surveys; coordinating and monitoring technical activities of projects; promoting indigenous research for technology development; evaluating technical and financial aspects and reviewing development; creating and maintaining an offshore wind energy database and archive system.
The environmental impact of offshore wind farms is considerably reduced compared with onshore wind farms; both noise and visual impact are unlikely to be issues, but still some considerations remain. For example, an environmental impact is possible from carrying out offshore work, such as localized disturbance of the seabed. Some studies have suggested that the noise from rotating turbines travels under water and disturbs sea life. Nonetheless, ships, boats, and engines have been a fact of life for more than 100 years.
In addition to environmental issues, financial issues are also considerable. Capital costs are higher than those of onshore farms due to larger machine size and costs of transporting and installing equipment at sea. But this is partially offset by higher energy yields, as much as 30%. Also similar to onshore, these prices are expected to drop as technology improves and more experience is gained.
According to studies in Denmark, wind resources up to 40 km from the shore are currently considered economically feasible, with the key factor being water depth. As interest grows and technology advances, offshore wind appears headed for a prominent position in the renewable energy mix. In June 2016, a project consortium led by the Global Wind Energy Council (GWEC), along with the Centre for Study of Science, Technology and Policy (CSTEP), DNV GL, Gujarat Power Corporation Ltd (GPCL), World Institute of Sustainable Energy (WISE), and NIWE, prepared a detailed report, Facilitating Offshore Wind in India, as a roadmap for offshore wind energy development in India. The report evaluated supply chain, port infrastructure, and logistics for offshore wind farm development in Gujarat and Tamil Nadu. A new era of offshore wind power has dawned for the wind industry in India.
Professor Siraj Ahmed, Department of Mechanical Engineering, Maulana Azad National Institute of Technology, Bhopal 462003, MP, India; Email: email@example.com