Securing the Grid

Increasing share of renewables calls for smart solutions

The share of renewable energy in India’s total installed capacity has increased from about 8 per cent in 2007-08 to over 13.5 per cent in 2014-15. This is set to go up further, with the government setting an overall renewable energy target of 175 GW by 2022. Since these are infirm energy sources, it will be interesting to see how the grid absorbs this energy. The Central Electricity Regulatory Commission (CERC) is currently working on regulations to manage the variability of renewable generation, with the active involvement of Power System Operation Corporation Limited. In this, the issue of technical competency of the load despatch centres is being addressed through the setting up of renewable energy management centres (REMCs).

Transco perspective

The variable, intermittent and uncertain nature of renewable energy brings with it issues related to reactive power management, grid operations, the distant location of resources from the load centre, forecasting difficulties, the overruling of the merit order, balancing mechanisms, etc. Renewable energy also has a massive impact on conventional power plants, and leads to network inadequacy. New transmission capacity is often required to connect renewable energy-rich locations to the grid, giving rise to transmission costs. The large-scale integration of wind and solar may introduce new patterns in the flow of power, causing congestion in transmission and distribution networks.

During times of less renewable energy injection, there is an under-utilisation of the extra high voltage network. In addition, there is low voltage at the tail end, affecting grid stability. There is also a critical loading of the system elements. Very high or low renewable energy generation results in over-/under-loading in the associated transmission elements. Further, absorbing renewable power comes at a cost as a significant quantum of cheaper conventional power has to be backed down. Moreover, there are certain CERC-specified bands that require the grid to operate within a variation of +/-150 MW. There are penalties for violation and additional cap charges.

Wind and solar farms are known to provide less grid support during system disturbances in comparison with conventional power. Also, thermal power cannot ramp at the rate of renewable power variations. Reactive power management is another big challenge as the start-up reactive consumption requirements of wind turbine generators (WTGs) are high, sometimes equivalent to the power rating of the turbine.

For managing the variability and unpredictability of renewable energy generation, accurate forecasting is crucial for grid management and security. There is a need for day-ahead as well as intraday renewable energy forecasting, and the ramp requirement must also be predicted. Gujarat for instance, is making forecasts using BBC’s weather data, having recently appointed REConnect as its professional forecasting service provider. Besides this, even the smallest wind or solar farms in the state are being tele-metered; the data is available at the state load despatch centre (SLDC) and the sub-SLDC level and also transferred to the regional load despatch centre, SLDC, and Gujarat Energy Transmission Corporation’s website. Gujarat has also implemented a pilot forecasting project wherein it has appointed five forecasting service providers. The sites have been given to all providers, implying that forecasting at each site has been done by different providers for almost six months.

Technical and regulatory measures to enhance the flexibility of conventional and storage generation to increase the grid’s balancing capacity should be explored under ancillary services. In Madhya Pradesh, the state commission has come out with a draft ancillary services regulation. It has also come up with draft regulations for forecasting, scheduling and imbalance handling for wind and solar generators, which are based on the model regulations framed by the Forum of Regulators.

There is a requirement for a balancing mechanism. At present, costly gas-based generation is being used to handle renewable energy variations. The intermittent nature of renewable energy can be controlled by identifying flexible generation capacities and building energy storage capacities. While enough has been discussed about storage equipment, there has been no emphasis on the pumped mode operation of hydro plants. There is also a need for a good market mechanism. The renewable energy certificate market is there but certificates are not being traded.

In terms of transmission infrastructure, the Green Energy Corridors (GEC) project is coming up. At the state level, the GEC project in Madhya Pradesh is to be completed in 2018. The state transco has conducted system studies and identified the transmission system strengthening requirements and interconnection work for renewable energy projects during the next five years.

To handle the variability and intermittency of wind and solar power, the Ministry of Power is also establishing REMCs.

Discom perspective

Renewable energy technologies need to be carefully disseminated to suit the needs of different end-users through innovative business models that result in the lowest tariff impact. There is a need to create innovative financial incentives for the uptake of renewable energy on a large scale to counter the financial disincentive of procuring high-cost renewable electricity. In addition, there is a need for separate open access regulations for conventional and non-conventional generators. Maharashtra State Electricity Distribution Company Limited is also promoting the need for a renewable energy charge (based on the cost of power purchase) to be paid by the industry/commercial consumers generating greenhouse gases/pollution.

In the case of rooftop solar, Tata Power Delhi Distribution Limited has been facing net metering challenges in its rooftop solar installations. Under this regime, the utility pays the consumer for solar at the generated retail tariff. However, this is comparatively higher than the cost of supply, effectively leading to a reverse subsidy.

When it comes to large-scale integration, the future lies in smart grids as they complement the integration of rooftop solar. Smart grids come with the advantages of reduced electrical losses, improved outage management, near real-time energy information access for customers, increased use of demand response, and better management of renewable distributed energy resources. They also create a platform for smart applications.

Under the National Tariff Policy, the cross-subsidy surcharge formula for open access has been revised to contain renewable purchase obligations in every aspect. However, this may not work for every state. In addition, certain critical definitions mentioned in the draft Electricity (Amendment) Bill, 2014 regarding smart grids and renewable energy need to be clarified. If these changes are not made, implementing the regulations will be a major challenge for discoms. The bill imposes penalties and also requires the establishment of IT implementation agencies.

Generator and developer perspective

Technically, there are no major issues with regard to grid integration. With the emergence of Type III and Type IV machines, all aspects of the regulations can be complied with. However, despite the advancements in technology, companies are facing various challenges.

The Indian Electricity Grid Code (IEGC)  has mandated low voltage ride-through (LVRT) for all machines after April 15, 2014, but some developers have older plants in which this is technically not possible. It has been suggested that these plants be allowed to run for their remaining lifetime as their share will diminish with the increase in overall wind capacity. For old machines that can technically incorporate LVRT, economic challenges need to be addressed. LVRT monitoring also needs infrastructure development to provide communication links between operators and SLDCs.

Risks are also being observed in terms of the retrospective implications of the upcoming regulations for forecasting and scheduling and LVRT in renewable energy projects. Since wind projects work on a cost-plus-tariff basis, this risk and cost are not captured when projects are established. Another challenge is the variation in practices across states. For example, according to the Central Electricity Authority transmission manual, higher capacities can be evacuated from the same evacuation line for wind generators, but this is not being followed by many states.

The cost of constructing lines from the pooling station to the transmission substation is a challenge. Most wind projects need 200/400 kV evacuation lines, which are often built by wind operators and transferred to the state transmission utility without any charge. This is an extra cost encountered by operators and not calculated in initial wind project costs.

As the gestation period of wind projects is around two years, they entail massive investment risks owing to the development of transmission infrastructure. Certain states observe network congestion, which results in the backing down of wind generation. However, there is very limited data available to prove if this is for commercial or economic reasons.

Conclusion

There needs to be extensive planning in terms of transmission at the regional, state and national levels while keeping in mind the potential areas and timelines of future solar and wind power additions. The regulatory structure should also be uniform for all generation sources. There is a need for system upgrades at the SLDC level for the optimum utilisation of forecasting and scheduling data. There is also a need to establish real-time data to ensure that transmission planning precedes generation. A dedicated grid code for incorporating windy sites that otherwise do not have access to the grid is another requirement.

Mandating a forecasting and scheduling mechanism will ensure grid stability while the REMCs promote integration with real-time measurement and information flow. For this purpose, the CERC has also come up with the deviation settlement mechanism.

There should be a unified policy for the technical integration of renewables so that they can assume the role of base power and become must-run stations. At the state level, there is a need to implement central-level policies and modify them through learnings based on the composition of resources in the state. Manufacturers should adopt the latest technologies and focus on grid discipline while developers should focus on large-scale, world class asset establishment and develop hybrid plants. Consumers should improvise in terms of energy usage habits and be open to the concept of microgrids.

Based on presentations and remarks by industry stakeholders at a recent Power Line conference

GET ACCESS TO OUR ARTICLES

Enter your email address