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Monday, July 16, 2018

From the lab: Harnessing the wind at sea

Two years ago, India said it would aim to produce 100 GW of electricity through solar energy and another 60 GW through wind energy by the year 2020.

Updated: June 19, 2016 1:57:46 am

There has been a lot of discussion in the last couple of years around harnessing solar energy to meet climate change objectives as well as to strengthen India’s energy security. In these conversations, wind energy is seen only as a supplementary source of renewable energy.

Two years ago, India said it would aim to produce 100 GW of electricity through solar energy and another 60 GW through wind energy by the year 2020. But keeping in mind the higher energy production capacity and efficiency of wind turbines in comparison to solar panels, our doctoral study aims to estimate the quantum of extractable wind energy from viable offshore locations along the Indian shoreline.

Further we also aim to assess the sustainability of the harnessable energy in the future, in the light of long term climate change. India’s entire installed capacity of wind is based on land, either on the coastline or in the interiors. We are yet to have any offshore wind farms that countries like Denmark have exploited with great advantage. There are several advantages of locating windmills in the sea, some distance away from the coastline.

Wind speeds are higher by about 25 per cent on the sea due to a higher temperature gradient and smoother interface with the sea surface (there are no buildings or constructions to obstruct wind flow). These higher speeds are obtained at lower heights, and wind directions are more stable. As such, use of smaller size turbines are possible offshore.

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A general perception regarding offshore wind energy is that the cost of constructing a wind farm is more compared to those on the land. Nonetheless a study based on cost to benefit assessment by Chennai-based National Institute of Ocean Technology showed that offshore wind farm can cost about 111 per cent of an onshore one, but this additional cost can be offset by a 184 per cent rise in annual power production.

We have tried to assess the potential of three sites selected by the government for the development of the first offshore farms. These are Jakhau in Gujarat and Kanyakumari and Rameshwaram in Tamil Nadu. Simultaneously, we have also tried to determine the potential of offshore farms along the entire Indian shoreline.

We have studied the changes in characteristics of wind at these places in two 30-year time slots: from 1976 to 2005, and from 2006 to the present time, which has then been extrapolated till the year 2035. We ran ten general circulation models, which are state of the art climate models that simulate past and future climate data, considering various carbon emission scenarios.

For enhanced accuracy in site specific assessment of wind energy, we interpolated the square grids of 150 to 300 km to 50×50 km grid size. There is a certain apprehension about the sustainability of offshore wind farms in the light of climate change induced by global warming. Certain aspects of wind associated with climate change are expected to favour the wind energy industry while some others are likely to have an adverse impact on it.

Our results show that annual mean wind potential at the three selected sites are likely to increase by about 25 to 30 per cent by the year 2035. Annual average wind power production at Rameshwaram is likely to be 326 watt/square metre (w/sq m), while it is likely to be 257 w/sq m at Kanyakumari and 289 w/sq m at Jakhau. An annual average of 200 w/sq m or above is considered very good.

Sumeet Kulkarni, M C Deo and Subimal Ghosh
Department of Civil Engineering, IIT Bombay

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