Smooth Integration

Solutions to ensure grid stability

With 175 GW of renewable energy capacity targeted to be installed by 2022, the power sector needs to gear up to integrate the electricity generated into the grid for transmission across the country. However, given the variable and uncertain nature of power from renewable sources, grid integration becomes particularly challenging.

As of March 2017, the installed renewable energy capacity stands at 57.2 GW, accounting for about 16 per cent of the country’s total generation capacity. However, as it is already proving difficult to integrate this power into the grid network, leading discoms to ask solar power producers to curtail their generation, especially in states rich in solar and wind potential, like Tamil Nadu. Curtailing not only results in financial losses for developers but also dampens investor interest in the sector, which could prevent achievement of the capacity growth targets. The government has drawn up grid expansion plans and launched programmes such as the Green Energy Corridors to address this issue, but the challenge of seamless power evacuation continues to exist.

The key challenges faced in integrating renewable energy into the grid are:

  •  Harmonising the evolving transmission network with the pace of renewable energy capacity addition.
  • Addressing technical concerns of reactive power management, harmonic current and low voltage ride through (LVRT).
  • Forecasting power generation, data acquisition, monitoring and visualisation of renewable energy in real time.
  • Justification of the low economic viability of the transmission system due to low capacity utilisation (20-30 per cent).
  • Load management and demand response requirements.

Key factors

To tackle these issues, multiple solutions have been introduced, including forecasting of renewable power generation and scheduling its input into the grid network, and using energy storage solutions to reduce the intermittency associated with renewable power. The Central Electricity Regulatory Commission (CERC), along with the Central Electricity Authority (CEA), has brought out a model scheduling and forecasting policy and has been working with states to formulate their respective forecasting and scheduling policies.

According to K.V.S. Baba, chief executive officer, Power System Operation Corporation, the four most important parameters for better renewable energy grid integration are a strong transmission grid, a vibrant electricity market, flexible power generating systems, and specialised forecasting and scheduling tools. India has made considerable progress in all these areas. With the inclusion and increase of renewable energy sources, the power market has become more vibrant and has options for discoms to purchase power at competitive rates. Grid strengthening is under way with the Green Energy Corridors project, especially for better renewable power evacuation at the interstate transmission level. However, there is still a long way to go for intra-state transmission strengthening. As most of the wind capacity that came online in the past few years has been installed on old grid networks and is not in synchronous mode, it will need to be renovated for efficient integration.

As far as flexible generating systems are concerned, regulations are in place to increase the use of flexible sources. Hydropower is a fairly flexible resource, which can be varied depending on the load requirement at the grid as well as climatic conditions that affect generation. For thermal power plants, there exists a flexibility buffer of 25-30 GW on an average. Studies conducted by the CERC have shown that effective integration of renewable energy into the grid is possible even with high plant load factors of thermal power plants, which has boosted the confidence of regulatory agencies.

The most important point, however, remains the use of specialised forecasting and scheduling tools. Almost all operators use their own forecasting tools, while the control centres are usually located with the discoms for security purposes where forecasting can be done. Besides forecasting of power generation, load forecasting is also essential. Barring a few states such as Maharashtra and Gujarat, most states do not have progressive forecasting methods that would allow them to forecast the load on the grid. Once load forecasting is taken care of, it is possible to reduce the error margins, which currently stand at 10 per cent, as opposed to 1.5 per cent in countries such as Denmark.

According to Ajit Pandit, director, Idam Infrastructure Advisory, there are three significant aspects of grid integration – planning, construction and operations. While India anticipated an increase in renewable energy and planned grid expansion and strengthening measures early on, it is yet to minimise the discrepancy in grid standards between the central and state transmission units. Also, there is a lack of uniformity in the planning mechanism at the state level, with wide variations across states. There is a need for specific plans for renewable energy, considering the variability and uncertainty associated with it. Another aspect that needs to be looked into is the construction of transmission systems. As interconnection to the central grid network is the state’s prerogative, it varies across states, creating a discrepancy in the system, especially for interstate power distribution. Also, it is unclear whether the onus of the construction of the transmission system for the wind farm is on the developer or the state agency. The operating standards for grids also need large-scale reforms. While regulations for forecasting and scheduling exist at the central and state levels, the implementation of these standards is patchy.

Grid stability

One of the most important factors to consider when integrating the targeted 160 GW of wind and solar energy into the grid by 2022 is the stability of the grid. Frequency, voltage and angular stability are the three factors that determine the stability of the grid. According to Pankaj Batra, member, CEA, there are no major issues with angular stability in India and standards have been specified for voltage stability so that renewable energy generators do not burn the grid with reactive power. Even so, in a situation where a large amount of power is being fed by renewable energy generators, it is imperative that the regulations specified are followed.

Batra also notes that an important difference between the grid stability in successful international renewable energy markets like Denmark and that in India lies in the business model adopted for power offtake. While power tariffs are market-determined in Denmark, India has fixed feed-in tariffs for wind energy and long-term power purchase agreements. The variability in prices is a concern for Indian consumers as they are price-sensitive and do not respond well to constant fluctuations. A more balanced approach is needed, wherein, along with long-term contracts, short-term power purchases through power exchanges are also improved. As opposed to the lead time of one hour in Denmark, India’s power exchanges have a lead time of four hours, during which time the load has to be anticipated and power bought and sold as required. Reducing the lead time would help stabilise the grid to a large extent, for better integration of renewable energy.

Outlook

The problem of variability of renewable power can be resolved by efficient use of balancing tools. Balancing refers to the generation mix from each state and the ability to procure renewable energy while backing down power from thermal plants. Regional balancing will have to be incentivised to cover the costs between the two sources of power generation. Balancing costs will have to be built into the tariff system of renewable energy procurement. Efficient balancing can also be achieved by improving load forecasting, enhancing flexibilisation of thermal power plants and increasing the area of balancing. In addition to balancing, the use of less-intermittent renewable energy sources can help in better grid integration. For this purpose, the development of the country’s hydropower potential and the use of pumped storage hydro plants should be encouraged as these have various advantages over other renewable energy sources. Hydropower with pumped storage has a large reactive capacity for regulation and has spinning reserves at nearly no cost to cater to sudden changes in the system.

While energy storage, in conjunction with renewable power, is a ready solution for grid integration of renewable energy, strengthening the grid by bringing in forecasting and scheduling as well as balancing tools provides a holistic, long-term solution. Instead of viewing these solutions as mutually exclusive, their combined usage must be encouraged to better integrate the growing renewable energy capacity into the country’s evolving grid network.

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