Prime Minister Narendra Modi has promised to light up nearly 400 million Indian households through renewable energy by 2019. But experts feel that the Government will find it difficult to meet this target as it is proving difficult to integrate renewable energy with the national grid.
Taking into consideration the significant increase in the country´s wind and solar power generation during the last few years and also the government´s growing focus on green energy, the need to facilitate large scale integration of variable renewable energy resources (RES) is imperative in the interest of grid security. However, with the country moving towards a tighter frequency band, balancing variable RES is going to be more challenging.
´There is a need to have strong interconnections together with stable grid frequency maintained close to the nominal operating frequency in a narrower band so that energy injection from renewable sources can be safely absorbed in the grid,´ says V Ramakrishna, former member, Central Electricity Authority.
During the year 2013-14, the total target for RES to integrate with the national grid was 4,325 MW. However, the Ministry of New and Renewable Energy managed to achieve integration of only 1387.1 MW with the grid.
Meanwhile, generation from RE sources depends on nature, i.e. wind velocity and sunshine. Experts believe that the variability of RES power can be addressed through improved forecasting techniques, which are still evolving. When the percentage of RES becomes significant, special attention needs to be paid to accurately forecast their output.
´Renewable energy plants do have difficulty in forecasting or predicting the generation schedule with accuracy,´ says Umesh Agrawal, Associate Director Energy, Utilities & Mining, PwC.
Due to this issue the scheduling and dispatch planned by State Load Despatch Centres (SLDCs) becomes very difficult resulting in large devi¡ations. The CERC (IEGC) Regula¡tions, 2010 stipulate forecasting of generation from ren¡e¡wable sources to an extent of 70 per cent accuracy.
The deviation to the extent of 30 per cent is taken care through the Renewable Regulatory Fund (RRF) mechanism in the above IEGC. Deviation beyond 30 per cent attracts a penal charge of Renewable Regulatory Charge specified by IEGC. The RE generators should adopt new technologies for forecasting the generation so as to enable to qualify under the allowable deviation limits. Additionally, network specifications, such as the ABT metering need to be implemented by many of the RE generators. There is a long way to go before the integration of renewable energy to the grid is made a success story.
Pre-post grid syndication
The integration of the southern grid into the National Grid by synchronising the 765 kV Sholapur-Raipur line has led to the States Karnataka, Kerala, Tamil Nadu, Andhra Pradesh & Puducherry getting connected with the rest of the grids. This would have led to power flow from other regions helping the southern States to meet the deficit. The sourthern States had constraints in buying power from surplus States. This has been resolved by the integration of the southern grid with the rest of the regions enabling transfer of power from other regions.
The measure of success also has to be seen from the frequency profile improvement in the southern grid after the integration. On analysis of the frequency profile of the southern grid pre and post integration as sourced from SRLD, it is seen that there is improvement in the frequency profile as provided for sample comparative months below. The maximum frequency has been dipping and approaching the required frequency level of 50.5 Hz. However, the evaluation of this parameter would be possible only after a completion of all the seasonal cycles.
The analysis of loading conditions in transmission corridors getting relief due to integration of southern grid, and the analysis of actual frequency and transfer of power over a period of time would provide results for evaluating the success.
The 12th Five-Year Plan envisages a capacity addition of 88,537 MW from conventional generation. An assessment made by the CEA reveals that an RES capacity addition of 32,000 MW is likely in the eight states of Tamil Nadu, Andhra Pradesh, Karnataka, Gujarat, Maharashtra, Himachal Pradesh, Jammu & Kashmir and Rajasthan during the 12th Plan period. Out of the planned 32,000 MW RES capacity addition, approximately 30,000 MW will come from wind and solar, the CEA estimates. This will be helpful in balancing the variable output of renewable energy sources located in a few states, by integrating them into the all-India grid. The inter-state and inter-regional transmission infrastructure is already being developed. It is expected that all the five electrical regions of India would be synchronously connected in 2014.
As on September, 2013, the total all India Installed Capacity (IC) stood at 2,27,357 MW which includes 28,184 MW from Renewable Energy Sources (RES), constituting 12.4 per cent of the total capacity.
Meanwhile, the CEA report points out that the country´s RES capacity is concentrated in five states Rajasthan, Gujarat, Maharashtra, Karnataka and Tamil Nadu. Out of the five states, in Gujarat, Tamil Nadu and Rajasthan, the percentage of RES capacity in the total installed capacity is substantial. While in Gujarat it is 18 per cent, the RES capacity in Tamil Nadu and Rajasthan stands at 40.2 per cent and 26 per cent respectively. In all five states, the RES are predominantly wind and solar.
Gujarat, Tamil Nadu and Rajasthan together have 70 per cent of the country´s total wind generation capacity (18,500 MW). In solar, the three states lead with 91 per cent of the total capacity (1,500 MW).
The CEA report lays stress on balancing the variable output of power generated from RES located in these states through integration into the all-India grid.
However, States deploy different methods to manage the variations in generation from RES. Tamil Nadu, for example, resorts to cutting down generation in the old coal-based power plants. Gujarat keeps a margin in its thermal and hydro generation to manage the variations of wind and solar generation. Rajasthan uses its coal and lignite based generating plants to balance the wind variability by reducing generation to the extent that users do not need oil support for a steady flame in the boiler. The two gas-based stations in the state, Ramgarh (113 MW) and Dholpur (330 MW) are also used for balancing.
´The last mile connectivity is more in the local distribution grids than the national grid. Connectivity is quite difficult, especially in states like Tamil Nadu where concentration is high and networks are not commensurate.´ says Anish De, Chief Executive Officer, Mercados Energy Markets India Private Limited.
There is a growing need for a new transmission corridor in the country. Since most of the renewable energy addition is confined to certain States such as Tamil Nadu, Gujarat, Rajasthan and J&K, it will be a prime point on the agenda for the new government to evacuate green energy from these states.
´Such transmission corridors required in the next five years have already been firmed up through the established process of coordinated transmission planning and their implementation is being taken up progressively,´ says IS Jha, Director (Projects), Power Grid Corporation of India.
He adds: ´It has now been recognised by the transmission planners that in view of the short gestation period of RE plants, the transmission has to lead generation and would require upfront investment.´
Additions to the transmission system costing about Rs 32,000 crore have been planned to cater to the needs of the (approximately) 32 GW RE capacity addition program for the 12th Plan (2012-17). These systems include both intra-state and inter state transmission systems of 132 kV, 220 kV, 400 kV and 765 kV voltage levels.
Given that the penetration of electricity in India is of the order of 70 per cent, there is tremendous scope for supplementing the resources with RE generation including distributed micro grids and roof top solar plants. However, due to limited paying capacity of the people at large and poor financial health of the discoms, the demand for electricity is sensitive to price. The price of solar energy has come down by 50 per cent in the last five years due to introduction of competitive bidding for tariff. However, wind energy continues to be paid preferential or feed-in tariff and as such the price of wind energy has not come down in the last ten years. History of regulation worldwide bears out that cost plus tariff in generation does not normally result in reduction in tariff. Further technological breakthroughs and pressure of competition is required to make RE affordable in India.
In the last five years, power generation capacity has grown by 50 per cent, whereas transmission capacity has increased by 30 per cent. As per the 12th Five Year Plan, the future (planned) expansion in power generation capacity in India will be around 88,000 MW. In order to meet this capacity, investment in the transmission sector needs to be increased. Overall, an addition of 90,000 ckm of 765-220 kV lines, 154,000 MVA of substation capacity and 27,350 MW of national grid capacity is required in order to meet the 12th Five Year Plan requirements.
However, as many as 120 transmission projects have faced delays because of the developer's inability to acquire land and get timely clearances from all stakeholders. There have been instances of transmission lines being forced to take a different route than planned, resulting in the entire project budget going out of control. Power transmission constraints have also made it difficult to evacuate excess power and channel it to regions that face shortages. Projects have had to purchase power from costlier sources while others remained under-utilised. Hence, there is an urgent need to timely address underlying issues in the transmission sector to ensure power demand is effectively met in the future.
Analysis in the Indian context
According to CEA, the basic technical challenge comes from the variability of wind and solar power which affects the load generation balance, varying demand for reactive power and impact on voltage stability. Recently it has been decided that 16 SVCs (+300/-200, +400/-300, +600/- 400 MVAR) / STATCOMs ( + 200 MVAR û 7 nos., + 300 MVAR- 6 nos.) will be installed at various points in the Indian grid to provide dynamic voltage compensation. However, further action is required in this direction and more simulation studies and better modelling of RE sources needs to be done with the help of international cooperation.
Most of the wind generators are of the induction type. They absorb substantial reactive power during startup and some reactive power during normal operating conditions. Due to intermittent characteristic of wind, generator start up takes place multiple times during a day, resulting in huge quantum of reactive power absorption from the grid and causing voltage excursions/voltage stability.
Further, for type-1 and type-2 machines (as per CEA guidelines), since these are induction generators, they cannot participate in voltage regulation and require switched capacitor banks for reactive compensation. However, type-3 and type-4 wind turbine generators and solar inverters depend on AC-DC-AC converters which have inherent control of reactive power.
Measures must be available to mitigate the effects of the variable reactive generation of power. As a result of this, the dynamic reactive power compensation i.e. SVC/ STATCOM shall have to be provided at renewable energy pooling station for dynamic voltage support and avoid any undesirable reactive power flow to or from the grid. Experts feels that the RE development has placed a huge burden on the transmission network to fulfill the last mile connectivity to these RE generation plants. A majority of RE generation developers have preferred to invest in their own transmission evacuation system to connect to the nearest grid network. However, there are a large number of RE generation developers who have neither been granted connectivity to the grid by the respective transmission companies nor have they invested in their own transmission evacuation systems.
These upcoming generation plants are in limbo. Further, there are some States which have come up with policy incentives for providing reimbursements on the transmission evacuation from RE generation plants. In this scheme, the investments made by the RE generation developer is reimbursed by the State Government or State Transmission Company or State Renewable Development Agencies. However, there have been instances of delay or no reimbursement of these investments to the RE generation developers. These kind of instances would only hinder the large scale development of renewable generation projects.
Experts believe that there is a need for grid friendly RE generation. At the beginning of its development, RE generation technology focused more on tapping the maximum power from RE resources. It neglected to make any contribution to power system reliability and stability and in the absence of standards and incentives was not designed to operate in a coordinated fashion with the rest of the system. Therefore it is becoming increasingly important that RE generation should play a greater role in helping to maintain system reliability and stability, and this may be increasingly required by interconnection standards. Technologies have been developed and are continuously improving at the generating unit, plant and plant cluster level to make RE generation more predictable, controllable and dispatchable, or in other words more grid-friendly.