Tracking Wind

NIWE’s efforts to map India’s onshore and offshore potential

Accurate wind resource assessment (WRA) is crucial to achieving India’s 60 GW wind power target by 2022. The National Institute of Wind Energy (NIWE) has been leading the WRA programme by carrying out studies in both onshore and offshore wind power segments. The upcoming wind map at 150 metres is the most anticipated as it will identify new sites for project development. The industry is also looking forward to the results of the offshore wind study along the coasts of Gujarat and Tamil Nadu.

Efforts towards the assessment of the country’s wind power potential have accelerated in recent years. The National Wind Monitoring Programme was launched in 1986 by the Ministry of New and Renewable Energy (MNRE). The programme was carried out by the Field Research Unit of the Indian Institute of Tropical Meteorology (IITM-FRU), Pune. In 1998, IITM-FRU was merged with the NIWE, which is responsible for the majority of WRA work. So far, the NIWE has established 913 stations under the MNRE’s national monitoring scheme, and taken up 59 additional stations for private parties in consultancy mode. It also has a mandate to help developers and stakeholders verify the wind mast data collected by private stakeholders. The NIWE has undertaken WRA at a total of 2,038 wind mast locations across the country, at heights ranging from 20 metres to 120 metres. Using the data obtained from wind masts, the NIWE has published nine volumes of wind energy resource surveys. At present, 95 wind mast locations are in operation.

Mapping the potential

Since flat terrain is highly accessible, it is also the first choice for wind project development. As a result, the high wind regimes in flat terrains have been mostly exhausted, propelling the development of complex and semi-complex terrains in the country. Currently, WRA is undertaken on the basis of measurements procured from mast data over a period of one year. While this gives a fairly accurate assessment of the flat terrain, it is not the case in semi-complex and complex terrains. Semi-complex and complex terrains experience periodic variations and undulations, and the mast data for one year is insufficient to mitigate the risk of underperformance. The need of the hour is to blend medium-term wind power models with real-time or on-site meteorological mast data. To this end, numerical wind atlas methodologies need to be developed further.

At a height of 50 metres, India’s wind potential is estimated at 49 GW while the wind potential at 80 metres is 103 GW. With the increasing sizes and heights of wind turbines, the NIWE is now assessing wind potential at higher levels. It has recently advanced to developing maps at 100 metre and 120 metre heights with dynamic, online geographic information system (GIS) layers as opposed to the static, digital GIS layers used in 50 metre and 80 metre maps. The maps that have been prepared or are being prepared for 100 metres and 120 metres use the National Remote Sensing Centre’s land use and land cover data to gauge the actual land availability instead of assuming only 2 per cent land availability as in the case of 50 metre and 80 metre maps. Another major development has been the inclusion of the capacity utilisation factor (CUF) in the maps for higher levels.

The wind potential at 100 metres has been estimated at 302 GW. The mapping at 100 metres and above was done using a weather research and forecasting model. Data on the atmosphere, land use and topography was used as an input for mapping, which was carried out at a spatial resolution of 500 metres. This data was corroborated by almost 1,300 actual measurements across the country. The NIWE assessed environmental parameters such as wind speed, wind direction, temperature and air density at every grid point. This information was also used to work out the CUF for 120 metre and 150 metre maps, which are currently under preparation.

Advancements in resource assessment technologies

The NIWE is in the process of preparing higher hub height maps. The map at 120 metres has already been submitted to the ministry and is expected to be officially launched by the government in 2019. According to the draft submitted by the NIWE, the country wide potential at the 120 metre level is estimated at 695 GW.

Meteorological masts are planned to be replaced with remote sensing devices such as LiDAR and SoDAR. These devices work on the Doppler shift principle and are a better alternative to meteorological masts due to their portability and ease of handling. These devices allow for short-term measurements as well as measurements at multiple heights. In contrast, the installation of meteorological masts, onshore as well as offshore, is costly, time consuming and laden with land constraints. The NIWE is exploring the possibilities of standardisation of remote sensing devices (SoDAR and LiDAR) through validation studies in various terrains.

A promising potential lies in the integration of wind-solar measurements. The NIWE is trying to identify wind pockets that not only have CUF greater than 32 per cent, but also receive solar radiation of over 1,800 W per metre square. In order to understand the wind-solar hybrid potential of the various regions in the country, the NIWE is preparing a hybrid map, which is expected to be made public by March 2020. The map is being prepared by combining the 120 metre wind potential map and solar irradiance data. A common measurement campaign for wind and solar is also expected to aid cost optimisation.

Offshore potential in India

The NIWE has made significant headway in analysing the country’s offshore wind power potential. It developed an offshore wind potential map using the meso-mapping technique, which will be used for shallow water areas (up to 12 nautical miles) in the initial phase. This will be extendable up to 200 nautical miles, which will be the exclusive economic zone. Further, considerable offshore wind potential has been identified along the southern and western coasts to achieve the 5 GW offshore wind capacity target by 2022. Gujarat and Tamil Nadu are in the spotlight with an estimated offshore wind potential of 36 GW and 31 GW respectively. The proposed capacity for offshore is 14.4 GW in the case of Gujarat and 5.5 GW for Tamil Nadu.

An offshore wind farm project has been proposed at the Gulf of Khambhat. A LiDAR device has been collecting data in this area since November 2017. The NIWE is planning to install two more such devices off the coast of Gujarat, which along with the existing LiDAR and supplementary satellite data can provide information for an area of about 4,800 square km. This area has a wind power potential of around 14 GW, which accounts for nearly 50 per cent of the target announced by the MNRE. To realise the potential in this area, a project of 1 GW has been proposed at the Gulf of Khambhat, for which micrositing has already been done. Three more LiDAR devices are in the pipeline in Tamil Nadu, which has a high offshore wind power potential due to high wind speeds. These devices will be installed off the coasts of Ramanathapuram and Tuticorin which hold a potential of 10-12 GW.

On an average, India has a lower wind speed as compared to European countries. Hence, Class I offshore wind turbines, which are the global industry standard, may result in lower plant load factors and consequently underperform.

The way forward

According to a draft report prepared by the Central Electricity Authority, the total installed wind power capacity is expected to reach 140 GW by 2030. To this end, the NIWE is undertaking preliminary region identification to find suitable sites for developers. One of the key requirements for the selection of these sites is a CUF of over 32 per cent.

The government has set a 30 GW target for offshore wind, which is to be achieved by 2030. In order to further explore the potential and test turbines, an offshore national test centre is being planned at Dhanushkodi in Tamil Nadu. The NIWE is also planning to deploy five more LiDAR devices to gather long-term wind measurements at new sites. These tests and measurement results will lay the groundwork for expansion in the Indian offshore segment.

Based on a presentation by Dr Rajesh Katyal, Deputy Director General and Group Head, NIWE, at the Wind Power in India conference, 2019

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