Meeting the challenge of wind integration in India1 September 2009
A significant increase in wind based generation in India is creating new challenges for the transmission sector. Issues around network reinforcement, transmission planning, adjustments in existing operation and reliability practices, improvement in regulations and obtaining more reliable wind forecasts need to be addressed now to ensure the maximum exploitation of India’s wind potential if power system reliability is to be maintained without major curtailments of wind power output.
Global warming, rising fossil fuel prices and an ever increasing supply demand gap has catapulted the status of wind from a peripheral role to that of a significant source of electricity generation. Recognising its pivotal role in providing critical and clean carbon free energy and thereby addressing climate change, India is seeking to implement a large wind-based electricity generation programme.
Wind capacity in India has grown at an average of 33% over the last five years and contributes over 6% to the current capacity mix with total installed grid interactive capacity of 8739 MW. This growth is primarily due to engineering and technology developments, provisions under Electricity Act 2003, and financial incentives. In order to promote the needed investments, the Indian government is introducing policies such as renewable purchase obligations, financial motives such as income tax benefits, accelerated depreciation and generation based incentives. Table 1 shows a summary of wind potential in key states in India and the financial incentives and policy mandates that exist in those states. In addition to these stimuli, sale of accrued carbon credits in the Clean Development Mechanism market provides additional revenue source for wind generators.
Even as these incentives stimulate development of large wind based power plants, transmission limitations are increasingly becoming roadblocks to the continued growth of wind in the foreseeable future. These transmission limitations force curtailment of wind generation to ensure reliable system operation and also act as an inhibitor to wind installations in system planning. For example, in 2005-06, around 15 % of wind generation in Tamil Nadu was lost because of congestion and a shortage of evacuation facilities. The current obstacles to transmission that concern wind developers, system operators, policy makers and regulators may be summarised as:
• Who should pay for the evacuation facility (transmission capacity) up to the interconnection point: developer, power purchaser, transmission utility or distribution company?
• What are the various methods to fund and attract investments for developing the wind transmission infrastructure?
• How to address grid connectivity and transmission infrastructure development under transmission planning
• What is the role of State Transmission Utility (STU) in developing transmission infrastructure for renewable energy projects?
• Should the technical parameters of interconnections like voltage level, number of circuits, interconnection points etc be revisited?
• So far, no renewable related standards are available in Central Electricity Authority (CEA) Regulations. Should the connection standards and Grid Code be modified to accommodate wind energy sources?
• What are the ideal transmission and wheeling charges, transmission and distribution (T&D) losses and other charges for wind under current regulations?
• At present, State Electricity Regulatory Commissions (SERCs) have exempted wind from the intra-state Availability Based Tariff (ABT) regime. How should wind be linked with Unscheduled Interchange (UI) mechanism and Intra-state ABT?
• Is there a need to study the dynamic interaction between wind farms and power systems including effects on and, due to unit commitment, balancing and reserve capacities?
Rethinking the cost sharing for transmission evacuation and upgrades. In India as in other countries, temporal and spatial variations in wind speed are for the most part dependent on geography and spread across the states.
Integrating an uncertain generation resource requires a robust and flexible transmission infrastructure which is the primary responsibility of state transmission utilities (STU). But many STUs are not in a financially healthy enough position to invest the necessary capital for the required transmission upgrades. Therefore some are demanding prior payment for transmission augmentation carried out upstream of an interconnection point. Grid upgrades and enhancements are needed for integrating planned large scale wind capacity. Without significant increases in the transmission capacity all the wind energy generated cannot be accommodated in the power system.
This lack of sufficient transmission capacity acts as a disincentive that could result in less than expected additions in wind generation. Resolving this issue requires the involvement of state and central government entities, STUs, power plant developers and power purchasers. In such a forum, the need of introducing a better cost sharing formula that clearly outlines the process of cost recovery, determination of rate of return, the entities that are responsible for building the needed transmission (either utilities or private players) and the process for allocating the cost of new transmission to loads and wind power plant owners, should be discussed and proper methodologies, processes and plans to increase transmission capacity formulated.
Transmission planning needs to be in tandem with generation. With a low gestation period for wind based power plants, ranging usually from six months to a year, the corresponding transmission needed to evacuate that power, has to be planned ahead (since transmission takes a much longer time to build) so that evacuation does not become a problem when the wind plants are finished. Neither the Central Transmission Utility (CTU) nor the STUs have traditionally included evacuation plans for renewable-based power as a part of their overall transmission planning. Resource constrained STUs are slow to invest in dedicated transmission systems due to the perceived low and/or uncertain utilisation of these transmission lines caused by the inherent nature of relatively lower capacity factors for wind plants. This lack of planning and unwillingness to invest in renewable-power dedicated transmission lines could stall the growth in wind turbine installations. Further, a component of the evacuation problem can also be attributed to the rapid rise in the installed capacity as a result of both central and state governments tweaking policies to encourage capacity addition. At present, there are no planning criteria, processes and standards in transmission system operations and planning specifically related to renewable capacity additions such as wind. One possible method to stimulate and facilitate transmission projects is by creating an entity such as a Renewable Energy Transmission Agency, which could facilitate the development of renewable specific processes and standards for transmission, interconnection and operation. In co-ordination with CTUs and STUs, this agency can conduct studies to plan and identify transmission projects, build (or cause to be built), operate and otherwise facilitate transmission corridors for power that evacuate power primarily from renewable sources. This agency could also be created as a part of the existing Power Grid Corporation of India.
There is a lack of grid codes that incorporate the behaviour of renewable generation. One of the major constraints in harnessing the full potential of wind is the inability of the grid to absorb the power generated by all the wind turbines simultaneously. This is a problem because wind farms are located in remote areas, with limited transmission capacity and limited local power demand. Moreover, most wind power plants are small in size and hence are connected into the distribution network with distribution licensees holding the primary responsibility to evacuate wind power. In some cases where significant load is present closer to the wind power plants, increased renewable power injection at distribution level will relieve stress on transmission network to a certain extent.
However, as wind power plants gets larger, they need to be connected to the transmission network to supply load in other areas. In remote areas where large wind farms are planned the existing transmission grid is limited and at a lower voltage level. Thus, transmission over long distances to load centres and at lower voltage levels could result in higher technical losses and potential system instability in the case of faults or other problems. These issues can be addressed by modifying the existing connection standards and grid codes in addition to upgrading the transmission network.
Currently, no standard renewable related provisions are available in CEA Regulations. The existing grid codes need to be modified to provide standards for system stability and reliability. These standards should include the impact of significant penetration of renewable based generation such as wind on the operation of the transmission network. One of the challenges in reforming grid codes to account for renewable generation is in the contribution of wind generation to faults on the network. For example, if all wind generation trips off the grid immediately during a fault, the system may lose its capability for a quick recovery. Therefore, one requirement from the wind turbines could be to stay on the grid during a low-voltage event for a period of time before eventually disconnecting from the grid. Other challenges include provision of sufficient reactive power by the wind turbines, and maintaining voltage profiles at the point of interconnection.
Thus, grid codes that include standards for wind integration are required to ensure that wind farms do not adversely affect the power system operation with respect to security of supply, reliability of the grid and power quality of the injected power.
Regulations are still at a cross roads. The grid connected renewable generation has been made the major focus area of the Ministry of New and Renewable Energy (MNRE). Further, the Electricity Act mandates SERCs to assist renewable generation in terms of obtaining grid connectivity and promotion of sale of electricity. But regulations across SERCs regarding renewable generation grid connections and transmission charges are not yet uniform, sometimes vague, and are still at the nascent stage.
MNRE guidelines stipulate 2% of energy as wheeling charges for captive and third party sale transactions. However, in reality, the costs involved in wheeling of energy are higher than this and fall in the range of 2% to 10% of energy. The lower end of the range of charges is primarily attributed to the promotional nature of policies. Lowering and standardisation of wheeling costs across the country will incentivise and hence increase renewable and other forms of captive and third party generation.
Wind generation is also facing additional hurdles to open access because of reluctance by the host discom (distribution company) to allow merchant generation located within its service territory to sell power outside the state to customers that are willing to pay higher rates. In some states it is being insisted that the host discom has the first right of refusal on sale of power by a renewable captive facility. This message is often conveyed indirectly through delayed responses, complex and time-consuming procedural formalities and high wheeling charges. CERC should set an example by enacting regulations that give preferential treatment to renewable sources for arranging inter-state open access. Clear policies and their enforcement, clarity on the role of regulator along with creating an independent management structure for the State Load Despatch Centre (SLDC) are some of the major drivers that are required to overcome the access hurdles faced by wind and other captive generation.
Evolving a towards a better framework will require some innovative measures. Due to their inherent variability and intermittence, wind power plants have generation characteristics different to conventional sources of energy. These characteristics could cause changes in the cost of unit commitment (to allow for wind speed uncertainty), frequency regulation (needed to compensate for sudden changes in wind speeds) and, provision of ancillary services (such as voltage support, regulation and load following).
Short term forecasting for the day ahead and hour ahead power system operation and dispatch is critical for any market for reliable power supply and to minimise the cost of power supply. Therefore it is important to ensure that the best available forecast of wind speeds in both day ahead and hour ahead time intervals is utilised. For enabling increased integration of wind based power generation into the grid, incorporation of wind energy forecasts by power system operators in their day ahead and hour ahead dispatch schedules should be made a requirement. It is possible to achieve a significant reduction in long-term power production cost by using accurate forecasts of wind speed. The cost of infrastructure and equipment needed to provide such forecasts will be justified by savings in the cost of electricity over the long term. In order to maximise benefits and minimise cost impacts, utilities incorporating wind energy in their resources must learn to accommodate the uncertainty and variability of wind energy in their operational and planning practices.
Thus, the CTU, STUs, RLDCs and SLDCs should have in place the infrastructure for wind based power plants that would enable them to (a) monitor and if possible, control the amount of wind power output from each wind farm and, (b) forecast with the maximum possible accuracy, the amount of wind power that would be available over the desired operating interval. Such an infrastructure would assist in developing long term generation and transmission resource plans with successful integration of renewable based generation into the system without compromising system operational efficiency, reliability and security.
The full utilisation of wind power generation potential depends on solving transmission evacuation issues, accommodating wind generation in the power system without negative bias (such as high wheeling charges and procedural bottlenecks) and developing renewable-friendly grid codes, without degrading system reliability, in addition to providing the necessary financial and policy incentives.
Several SERCs have already taken important and proactive steps towards formulating and implementing solutions that could stimulate the growth of wind generation. However, the pace and extent to which these policies and reforms could be implemented still remains uncertain. Wind energy can bring considerable benefits to utilities in terms of clean, cost effective energy, long-term price stability, and increase in system capacity. Wind based power generation is expected to grow in India as in other parts of the world. To ensure full exploitation of the existing wind potential in India, transmission limitation issues and other operational constraints identified in this article must be addressed with suitable policies, mandates and standards as soon as possible.