Tamil Nadu has the highest installed capacity of wind energy in India, with 9.3 GW as of March 2020. The state has witnessed major strides in wind energy generation, with large scale project development commencing from the mid-90s. These Wind Power Plants (WPPs), installed at the outset of wind tapping, were located at wind-rich sites. These have now reached the end of or close to the end of their stipulated lifecycles. Most of these early machines are of low capacities (<500kW) and smaller hub heights (25-30m), resulting in underutilization. These aging turbines often result in low Capacity Utilization Factors (CUFs) (10-14%) due to associated mechanical difficulties and inefficiencies.
Repowering wind farms is a practical solution to address these issues and prevent the decommissioning of aging wind farms. Repowering can improve the CUFs (25-30%) and significantly increase the renewable energy capacity of the state. These modern machines, with optimized blade designs, higher hub heights, generate more power.
In August 2016, MNRE published a policy framework to encourage repowering initiatives and facilitate optimum utilisation of India’s wind resources. In 2018, the Tamil Nadu Generation and Distribution Corporation Limited (TANGEDCO) drafted repowering guidelines for the State, with proposed amends to the existing micro-siting guidelines. In 2019, TANGEDCO sought approval for its framework on repowering and related tariffs guidelines. Recently, in February 2021, Tamil Nadu Electricity Regulatory Commission (TNERC) issued an order in response to petitions filed that further clarified the MNRE repowering guidelines. However, progress on implementation of repowering has been slow.
WRI India organised a webinar to understand the repowering wind potential in Tamil Nadu and discuss its associated challenges. A keynote presentation was made by Mr. MU Krishnajith, General Manager, IDAM Infrastructure Advisory Private Limited. As of 2017, IDAM estimated about 834 MW of immediate potential in Tamil Nadu and a further 3979 MW needing repowering in the future. The webinar discussed the significant challenges that limit the realization of this significant potential. A recording of the webinar can be found here.
Most of the old machines occupying the best wind sites in Tamil Nadu have reached the end of their lifecycles and exhibit inefficiencies due to wear and tear in the mechanical and electrical components. Many of the manufacturers of these turbines are now non-operational or have discontinued support for the old models, thereby affecting the availability of spares. For example, early wind turbine OEMs such as Denmark-based MICON have been defunct since 2004 after its global merger with Vestas. Many old machines do not support component refits using new parts and technology, making retrofits and rejigs difficult.
Modern WPPs selected for repowering are significantly larger in terms of hub heights and rotor diameters than the older units. They require matching support towers and infrastructure, also considering 5D and 7D spacing. Careful micro-siting studies are also essential. Captain Kishore Sundaresan from Greentech Megawatt suggested looking at re-ageing or re-assessing the capacity of old turbines until full-fledged repowering is carried out, like the oil and gas sector which faced similar age-related issues.
Panelist Ms. Lakshmi Vaidyanathan from DNV-GL and Mr. MU Krishnajith pointed out that the existing grid infrastructure would need upgradation to handle the increase in power generation. There are sites where the curtailment of operational assets is 25-30% due to limitations with the grid infrastructure.
Wind sector stakeholders are keen on repowering, but many factors stemming from policy and regulatory gaps are major hurdles. Mr. Krishnan Nair, from IWPA pointed out that the term “repowering” has not been defined clearly in any of the key government policy documents and legislation. This had led to undue delays in issuing permits and approvals for repowering, that too only on a case to case basis. However, the February 2021 TNERC order does offer certain clarifications on repowering. Stakeholders have raised concerns regarding the existing MNRE policy guidelines, that prescribe grid augmentation as the state’s responsibility. Tamil Nadu is yet to come out with its own policy on repowering despite public hearings and discussion.
Financing and Contractual Arrangements
The current power purchase arrangements with TANGEDCO were finalized many years ago and need re-negotiation. Existing wind tariffs are very low and tend to the unviable for the developer. However, TANGEDCO is not in favour of increasing these power procurement tariffs. Incentive mechanisms can be introduced that compensate the project developer for this shortfall.
While considering repowering, a thorough economic assessment comparing the pros and cons of decommissioning the wind turbines early, versus running the turbines through the entire PPA term is essential. If the wind farm repowering requires a new project design with the decommissioning of the existing turbines, it is prudent to negotiate and develop new PPAs.
Old wind farms and its assets are rarely owned by a single party. Multiple turbine and landowners may or may not be in favour of repowering their old WPPs. Mr. Daniel Liu from Wood Mackenzie indicated that similar issues were witnessed in the European repowering market. A solution is the evolution of a suitable business model and formation of a Special Purpose Vehicle (SPV) with equity participation, where WPP owners can hold equity. Also, complete access to the land for micro-siting studies and repowering which can be handled through the use of an SPV to lease the land or gain usage rights.
Sustainable Disposal of Waste
Repowering would generate large quantities of waste that would need to be managed sustainably. The strength, durability and mixed nature of the blades makes this a challenge. India will need detailed guidelines, infrastructure, technology and markets to be in place. Various technologies for the recycling of wind turbine blades at different stages of development exist across the world. However, they are yet to achieve the required maturity and scale for economic viability, particularly for developing countries like India.
Globally, Germany and Denmark are leaders in repowering initiatives. The main drivers for these initiatives are supporting policy frameworks and regulatory interventions. Germany came out with amendments to its Renewable Energy Sources Act as early as 2004 to encourage repowering with follow-on legislation that addressed issues related to incentives, feed-in-tariffs and micro-siting. They also maintain a Central Turbine Registry that captures data on wind turbines, repowering and dismantling. In the case of Denmark, successful repowering of more than two-thirds of its oldest turbines were carried out in stages since 2001. This success has been attributed to the issue of Repowering Certificates, the holder of which is awarded a higher price for electricity produced from the repowered machines.
Repowering offers a robust methodology to extend the life of wind farms with a whole host of accompanying benefits for the state. Supporting factors include the availability of capable modern machines, advances in hybrids and storage, renewed interest from industry and ambitious renewable energy targets set by the government. Considering above suggestions can prevent the mass decommissioning of aging wind farms at prime properties in Tamil Nadu, and allow older WPPs to be replaced by modern, high-efficient repowered WPPs.