Importance of Wind Resource Assessment in the Indian Context and Improvements Required in Wind Measurement

What makes wind resource assessment so important in the emerging Indian wind industry? Well, the importance of wind resource assessment cannot be exaggerated anywhere. It is indeed an essential pre-requisite for energy production estimate that in turn determines the economic feasibility before starting construction of a project. But there is a special significance for wind resource measurement in the Indian context thanks to the Government policy to do away with accelerated depreciation with effect from the current fiscal (2012-13 ) and to substitute it with generation based incentive. This is a new paradigm favouring Independent Power Producers (IPPs). Generation is the key factor that decides the viability and success of a wind farm project in the country now and rightly or wrongly so. You just cannot start constructing a wind farm based on Centre for Wind Energy Technology (CWET) wind data in the general area. It is pertinent to note that many such areas in the CWET listing had only 20m high met masts. Such information helps in identification of potential sites and no more than that. No sensible investor or lender would like to take a decision based on sketchy and inaccurate information about wind. Accurate measurement of wind at the site is essential to assess the yield of a proposed wind farm; energy production over the life span of a project needs to be estimated as accurately as possible before investing in its construction. The fact of the matter is that one of the key drivers for the growth and expansion of Indian wind sector in the new paradigm is accurate wind resource assessment. Wind farm sites with reliable energy production estimates can and will lure large scale investments. We have to facilitate it by launching a powerful campaign for large scale and wide spread wind measurement and analyses of wind data collected from prospective wind farm sites.   

That said how can one get an accurate assessment of the wind potential at a site? The method is to collect the wind data over a period of time (1-2 years) by installing meteorological masts (met masts) at the proposed wind farm site. We have not yet started using other tools such as remote sensing (sodar and lidar) in India but there is scope to improve the coverage and quality of wind measurement by integrating them in the wind measurement program. Depending on the terrain and information already available about the general area the number, the location, the type of met mast, the instrument configuration and the monitoring duration can decided.

I wish to focus on the improvements that are required in the measurement of wind at a proposed wind farm site. I have had the opportunity to visit several prospective sites across the country in the recent past and see for myself how the met masts have been sited, installed and operated. The sites belong to different developers and the standards vary from acceptable to appalling. There is a dire need to be more professional in selection of mast location, installation and monitoring. In fact the wind measurement effort should enlarge into a campaign making full use of modern technology. Unless the basic data is correct and adequate no sophisticated analyses and interpretation can give reliable and accurate assessment of the wind potential and likely energy yield. Based on my observations I will cover the important areas as follows:-

• Location of Met Mast. It is important to locate the met mast at a proper place within the area of the proposed wind farm. It should be a representative location in relation with the WEG locations planned (as per micro-siting). Needless to say it may not be the location for highest wind speed. Another important factor is obstructions around. These obstructions may be buildings, rock formations, trees, power lines or structures. If in close vicinity, the impact of an obstruction becomes a serious concern. It is desirable to select a location clear of obstructions. However if the WEG locations have similar obstructions then it is acceptable for the met mast as well to conform to a representative character. In fact in forest land and complex terrain it may be hard to find locations that are clear of obstructions.
•   Number of Met Masts. The number of met masts should be dictated by the terrain complexity. For simple plain country a met mast can cover about 5-8 km. In hilly terrain with undulations posing higher complexity a mast can cover only 3-5 km. As the complexity increases you will require more met masts. Spatial coverage is essential to get a clear picture of the wind at different points and elevations. This is a factor that adds to the effort and cost but must not be overlooked if we want an accurate assessment of wind potential and optimal deployment of turbines.
  
• Height of Met Mast. The met mast should preferably have a height corresponding to the hub height of the turbine. If it is of lower or higher height extrapolation of the readings can serve as long as the difference is not very high. Needless to say with hub heights of 80m and 100m you cannot extrapolate the readings at 20 m or even 50 m without accepting corresponding high margin of error. That said, for a large wind farm it is not necessary for all towers to have heights matching hub height. With a fair understanding of wind shear the purpose can be served with masts of lower height combined with one or two that match the hub height.
• Type of Met Mast. There are two met mast designs that are popular; tubular and lattice. Tubular masts are used normally for lower heights. For higher heights, lattice towers are preferred. Tubular towers are easy to assemble and erect. However lattice towers offer several advantages at heights 80 m and above. The foundation, anchors and guys are parts of both types and it should be ensured that all tower parts are strong, metallic parts rust-free and guy wires tight in the interest of safety and stability.
• Sensors. The selection of wind sensors, their calibration and proper installation and maintenance are important issues. There are different makes of anemometers, wind vanes and temperature sensors available. It is wise to go for reputed makes and ensure proper installation, care and maintenance. It is desirable to go for redundancy in anemometers to ensure no loss of data. Normally at the highest level of measurement on a met tower two anemometers are mounted at the same level. You will require more anemometers for one or two lower levels as well. A minimum of two wind vanes at two different levels may be installed. Temperature sensor may be limited to one.
•  Instrument Configuration. This is an important aspect but enough attention is often not paid in how to configure various instruments on the tower. It is essential to mount anemometers and wind vanes not too close to the tower to prevent the tower affecting wind pattern at the instrument. I found this a serious shortcoming in several installations. International Electromechanical Commission (IEC) has carried out studies on wind flow distortion around towers. It is advisable to mount the sensors on horizontal booms that are fixed at right angle to the to the tower at a distance about 7 times the diameter for a tubular tower and 3.75 times the face width in the case of a lattice tower. Furthermore, the top most sensor should be well below the tower top with its boom fixed at a point about 10 times the tower diameter / face width below the tower top. The sensors should have sufficient clearance from the boom as well; the gap may be about 12 times diameter of the boom arm. It is advisable to fix the boom in a manner to bring the sensor oriented at 60 degrees to the main wind direction thus minimising the effect of the tower. The data logger is normally mounted about 3m above the ground level. Configurations of a typical  tubular tower and a  lattice tower are shown in the diagrams.   
• Sonar and Lidar. These are ground based remote sensing devices that find increasing application in the measurement of wind characteristics. Sonar stands for sound detection and ranging and lidar stands for light detection and ranging. Both these techniques provide certain advantages over fixed mast anemometers. The main advantage is the ability to measure wind characteristics well above the normal mast heights as they can cover 150 to 200 m above ground level. They are also useful to study the wind pattern at different points on long turbine blades. This equipment can be moved around and redeployed at ease. It is preferred to use it in conjunction with fixed masts for a detailed and accurate measurement of wind characteristics. In the assessment of wind shear and turbulence sonar and lidar measurements are very useful. In the future wind measurement programs it is desirable to include remote sensing and integrate well with the fixed masts for speedy, accurate and detailed measurement of wind characteristics.
• Site Visit and Verification.  It is necessary to subject the wind measurement at site to scrutiny by an independent and reputed agency. In fact a report of such visit adds to the authenticity of the wind resource assessment. It also helps in taking corrective action at site on any shortcomings noticed. Moreover investors and lenders treat such reports as bankable. In fact many foreign financial institutions insist upon such reports from internationally reputed consultants. There are well laid out procedures for site visit and verification by such agencies and they do provide detailed reports based on site visit, background information with them and wind data made available

In sum I advocate a campaign for extensive wind resource assessment. All developers of wind farm projects must undertake comprehensive wind measurement programs for their sites. In the new paradigm that Indian wind sector has entered, wind resource assessment has become a key factor for new projects. Armed with accurate and reliable energy production estimates the developers and IPPs will be able to lure large scale investments including foreign funds for wind farm projects thus paving the way for accelerated growth and expansion of wind industry in India.

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Reference:  Wind Resource Assessment Handbook, October 2010, NYSERDA, written by AWS Truepower

The author is a consultant to AWS Truepower; +919842210270, bk.unnikrishnan@gmail.com  

Tamil Nadu Wind Industry at the Cross-roads

An advertisement put up by Energy Department, Government of Tamil Nadu on May 21, 2012 has a caption; “Towards Energy Security from Energy Crisis.........” The crisis is on as of now but we can hope it is a passing phase. While the performance of the power sector by and large has been dismal, one of its subsets, the wind sector in Tamil Nadu has been showing spectacular growth. With the addition of 1087 MW of installed capacity during the last fiscal, Tamil Nadu continues to be the leader among the Indian states in harnessing wind power.  Its cumulative installed capacity as on   March 31, 2012 is 7094 MW out of the All India installed capacity of 19241 MW. With such an impressive record, is there a cause for concern? The answer is, yes. It is indeed a piquant situation for the power sector as a whole and wind sector is no exception. There are several wind turbines in “switched off” condition due to power evacuation constraints at a time when there is load shedding across Tamil Nadu.  The plight of wind industry has been exacerbated by the withdrawal of accelerated depreciation (AD) by the Central Government with effect from the current fiscal (2012-13). That apart, there are several hurdles that confront the wind sector in the country as a whole and there are a few concerns that are specific to Tamil Nadu.

Among the hurdles, withdrawal of AD deserves the first mention.  It has dampened investments in the retail segment of wind power projects. If you look at the investments in wind sector during the past two decades, AD was one of the most effective drivers in luring investments into wind farms across the country. The generation based incentive (GBI) introduced 2 years ago favors Independent Power Producers (IPPs) but it is not adequate to entice investors  at the present GBI rate of Rupees 0.50 per kWh. In the 2 year period wherein both AD and GBI had been in vogue there were few takers for GBI who could qualify for AD since the policy allowed either one of these benefits. Now that AD has been done away with a large segment of investors will move away from wind power projects. Tamil Nadu will feel the impact perhaps most since a large percentage of investors in the State’s wind projects come under the retail segment.

 Lack of adequate power evacuation infrastructure for transporting the electric power from potential wind farm sites that are in remote areas is a problem dogging the wind sector throughout India. Transmission of power from generating stations to load centers has always been a major issue in India. We do not have a national grid in place although there have been some efforts in this direction over the past several years. Even at state level we are way behind in the creation of grid infrastructure that is necessary for absorbing, transportation and distribution of electric power.

 Land availability for wind farm projects is affected due to competing demands for the land. The issue is further compounded due to cumbersome procedures in conversion for wind farm (industrial) usage of private agricultural land or Government revenue land. For using the forest land there is a procedure that takes several years. We have no policy in place for off-shore wind farm projects.

 Creamy sites for wind power generation have been more or less exhausted. The exploitation of lower wind regimes is a technical challenge. With improved design of the wind turbine and supporting tower and associated equipment it is possible to address this issue. Side by side, there is a requirement of policies to make projects viable in such areas.

We have not so far launched a nationwide campaign for a comprehensive assessment of wind resource. There are two important parts as far as wind resource assessment (WRA) is concerned; the first part is for identification of potential windy sites and to get a picture about the overall wind potential. The second part is a detailed wind measurement and study of a candidate site for a wind farm that leads to an estimation of energy production. The nationwide wind potential as assessed by Center for Wind Energy Technology (C-WET) is 49130 MW at 2% land availability. C-WET considered sites having wind power density above 200 watts / square meter at a height 50 m above ground level in its assessment. (Reference: Indian Wind Atlas published by C-WET in April 2010). This assessment has been questioned by several experts within India and without for its inaccuracy and conservative nature. When it comes to detailed wind measurement at a proposed site, we are graduating slowly towards a professional approach thanks to the due diligence of investors and lenders. But we have a long way to go in achieving accurate and reliable WRA.

Having listed the major hurdles that confront the wind sector in the country as a whole, it is for us to dwell on a few key concerns of Tamil Nadu.  No doubt, the lack of power evacuation infrastructure is a concern throughout India but it is of a crippling nature for the wind industry in Tamil Nadu. A large number of wind electric generators that were commissioned remains switched off and waits indefinitely for the transmission lines and sub stations to be constructed and commissioned. At the same time the State reels under severe power shortage forcing it to impose load shedding. Many windy areas of the State in Tirunelvei, Theni, Tiupur and Coimbatore districts are worst affected due to the inadequacy of power evacuation infrastructure. An associated problem, that is seasonal, is the inability of the grid to accept the power from wind turbines during the high wind season due to capacity limitation of transmission system or due to imbalance caused by the infirmity in wind power. It leads to forced back down of wind electric generators. It is indeed a problem of plenty and a challenge in grid management.

 Repowering- a process to replace old wind turbines with modern machines- offers a lucrative opportunity to enhance energy production from the same site. According to an estimate in Indian Energy Outlook 2011 (A report prepared by Global Wind Energy Council, World Institute of Sustainable Energy and Indian Wind Turbine Manufacturers Association) Tamil Nadu has more than 800 MW repowering potential. It is a potential that can be tapped anytime and there is no gainsaying about the urgency when faced with a severe shortage of power and the State looks for quick-fire solutions.

Tamil Nadu could make rapid growth in wind turbine installed capacity thanks to a liberal policy in the 80s, 90s and until 2009 allowing grid connectivity for a wind turbine to the nearest power line (feeder) at voltage levels 11, 22 or 33 KV. The power evacuation was entirely the responsibility of Tamil Nadu Electricity Board (TNEB) for which it charged a fee called Infrastructure Development Charges (IDC). This system has undergone many changes in the recent past giving way to exclusive feeders, transformers and sub stations for wind power. The old system exists in some form under the name “open quota” but with several caveats. While promoting creation of such huge power evacuation infrastructure at the cost of wind power developers, side by side, it is prudent to revive the old practice to take advantage of existing capacity of the grid ( network) comprising a system of distribution feeders, transformers and sub stations.  This will result in optimal utilization of the facilities already created and also earn more revenue to the State besides speeding up capacity addition.

     

There has been inordinate delay of several months in releasing payment to the wind mill owners for the power purchased from them. This situation if continued will act as a deterrent in attracting new investment in wind power projects. 

Suggestions

 There are efforts made by some  agencies to get AD restored and also to get GBI increased. With the increase in GBI, AD can be reduced in a phased manner. In fact GBI should become so attractive that no one opts for AD These are policy issues which will be addressed by the Government.

 Power evacuation infrastructure may be developed on war footing. There are several 400 KV and 220 KV transmission lines and sub stations that are under construction in Tamil Nadu. Some are at the planning stage. All such projects need be closely monitored and accelerated for early completion while initiating more new projects to cater for future.

A number of thermal power projects are under construction. Their completion and commissioning will help in combating the power crisis. It will also facilitate greater acceptance of wind electric power to the grid. 

The revival of “open quota” is a step forward for capacity addition. It will reduce the number of power lines in the country side, speed up small scale wind power projects and also facilitate optimal utilization of land and power evacuation infrastructure.

Another important aspect is demand side management. Restricting use of domestic appliances that consume too much power such as washing machines to the night  between 10 PM and 6 AM is one such step. Once tariff is based on time of day certain staggering of load will take place.     

Pumped storage is an effective means to temporarily store the excess energy from wind farms that can be used to generate hydroelectric power. Tamil Nadu should explore this option aggressively.

Tamil Nadu may undertake a comprehensive campaign to identify new areas having sufficient wind potential, complimenting the effort of C-WET. Today turbine hub heights of 80 to 100 m above ground level are common in Tamil Nadu and there is scope to go higher. Remote sensing is in use to measure wind characteristics at 150 to 200 m that cannot be easily measured by anemometers mounted on towers. Private developers will take care of detailed wind measurement at prospective wind farm sites. Assessment of off shore wind potential is very relevant for Tamil Nadu in view of its coastline and the State may take it up vigorously.  

                                                  

 Needless to say, payment of power purchased as per the power purchase agreement promptly will enhance the image of the State and restore the confidence of investors in wind farm projects.

 Repowering of wind farms is a relevant option for Tamil Nadu. The scope to replace old wind turbines with the state of art machines which are superior in technology is immense. The State should take a lead in facilitating repowering by removing certain PPA constraints and giving better tariff at current rates. A new policy may be framed with a view to encourage repowering and make it attractive economically.

 With the substantial thrust from the Central Government for solar power generation, the Stat  my encourage integration of solar and wind farms. In fact the land surrounding a wind turbine can be used for installing solar panels thus utilizing the inter-turbine land optimally for power generation. This can be done in the case of new projects and to an extent in the case of existing ones as well.

 There is scope to spread the wind farms to new areas in the State thanks to the technological advance in the design of wind machines. But at the same time the State can facilitate it taking an example from Rajasthan or Maharashtra as regards promoting the power generation in areas having lower wind regimes. It is essentially through better tariffs. Maharashtra pays Rupees 5.67 per kWh in the areas that fall in the category of lowest in wind power density ( 200 to 250 Watts / square meter)

 Tamil Nadu is the hub for wind industry in India. This is a definite advantage for its people to become professionals in the wind sector. The State should invest in education, training and research and development and also encourage private investment in these activities.

There is a market for small turbines and hybrids which are often used in standalone or autonomous mode.  Small capacity wind turbines in the range below 100 KW can be installed in the backyard or on a roof top. The State may encourage this segment.

It is for Tamil Nadu to focus on a key infrastructure such as power and it will be prudent to encourage all available sources of power generation.  Wind can play a key role in achieving energy security and making the growth more sustainable. A proactive Government can facilitate an atmosphere that is conducive for rapid growth and expansion of wind industry. By taking timely action on the issues mentioned in this paper let us hope to sustain the momentum in wind power development in Tamil Nadu enabling sustainable growth and development.

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Reference: Indian Wind Energy Outlook 2011 prepared by Global Wind Energy Council, World

 Institute of Sustainable Energy & Indian Wind Turbine Manufacturers Association

Remains of Historical Importance in Pratapgarh District, Rajasthan

I visited a wind farm site spread over two villages, Dalot and Raipur in Pratapgarh District in Southern Rajasthan. In fact, Pratapgarh is close to Ratlam in Madhya Pradesh and I stayed there for two days for my work. During the visit, on the first day itself, I noticed the remains of old buildings between two wind turbine locations and made up my mind to visit that area next day after completing my work. I spoke to Vinay, the Site Manager and he showed interest in joining me for this visit, as well.

In the afternoon on March 4, 2012, having got free from the official work, Vinay and I went to explore the area of the remains.  Notwithstanding the hot sun, we enjoyed this exercise. What we saw was broken parts of a number of structures. But it did not take much time to figure out the symmetry and magnificence of the layout. What is visible is indeed remarkably beautiful from any angle. The main building is an imposing structure although damaged. There are several structures that surround this building, all of them attractive despite the severe damage suffered over the years.

It is a pity no one has bothered to take care of this place. These villages are in the remote parts of the State untouched by development except for the ubiquitous cell phones. As I gathered from the locals, the main activity around is farming and that is of poppy! It has been a tradition that dates back to many centuries. The farmers have permission to grow these exotic plants that produce quality opium. Pratapgarh can boast about its supremacy in the field of opium cultivation in the country!

Coming back to the remains and its surroundings, it is no more a sleepy state that one observes. It is bustling with activity; construction of a wind farm is in full swing. Heavy cranes erecting 85 m tall massive wind turbines, trucks and trailers ferrying men and material and earth moving equipment making roads and digging deep for wind mill foundations are a common sight. We have a good road access to this area now.

Vinay and I could not do much research in the limited time at hand. We took a few photographs. The villagers whom we met could not throw much light on the history and significance of the remains. Vinay who visits the wind farm under construction daily is busy with his work but I believe he will find time to explore further. Once the wind farm is complete the place will have a facelift automatically. I do hope Green Infra, the owner of the wind farm and Re-Gen Power, the turbine manufacturer and project developer will  look after this area and not only preserve it but also enhance its appeal.

I hope the District administration and the Archaeological Survey of India take note of these remains and take steps for restoration and preservation.