Conventional coal power plants in India presently are facing challenges that are weird and unsettling. In usual circumstances, few years back, India was seen as a rising economy with huge potential for growth. With growth in economy, energy demand too was on the rise. The GDP value still as an indicator shows a rising trend but even the experts agree to the fact that scenario is not exactly what it was predicted to be years ago.

Per capita electricity consumption in India by far still is one among the lowest in the world. Though demand is certainly not as expected with slowdown in manufacturing sector being one of the main reasons, still it is surely on the rise. Lowering of overall power demand and a substantial growth in renewable power in recent time, has contributed to reduction of average plant load factor of coal plant. In simple words, coal plants are not running as they would like to, business wise, or would need to, for maintaining health of major equipment/machine.

In India, presently most of the conventional power plants are designed for base load operation. To exist in tandem with renewable power, these need to be operated in flexible mode of operation, which primarily involves quick ramp up or ramp down from low load to high load and intermittent loads.

In countries like Germany, where renewable has made a mark in big way, many conventional plants have undergone suitable modifications to prepare the mechanical equipment and other associated systems like control systems etc. for flexible operation. Now, these modifications involve huge expenditures and hence at the present scenario, nonviable for Indian generators, as it would increase cost of generation and will add extra burden, in an already complicated cost-tariff scenario.

But, truth is, that many conventional power plants are now running most of the time in part load due to increased presence of renewable in the grid. Part load operation, large number of start stops and deviation from running as per design, are causing fatigue to plant equipment, causing occasional failures and finally reducing life of these equipment and efficiency. Reduction of efficiency results into more heat rate and more emission.

According to India’s INDC pledge, 40% of electricity will be produced from non-fossil fuel source, by 2030. Emission would also reduce by 35% of 2005 value. If everything goes as per plan, fossil fuel would be contributing to 60% of electricity produced, with coal as major source, for some time in future (INDIA-INDC, 2015). Indian energy outlook also predicts a power demand growth of average 4.9% per year (IEA, 2015). Hence, it is necessary to run these conventional power plants in an optimized load condition, to reduce fatigue of equipment and increase equipment lifespan and efficiency.

Renewable electricity on the other hand, has its own issues especially the way India is going for it, in large scale utility projects. First of all, the renewable capacity installed is not exactly near to the capacity generated. The capacity utilization factor of renewable sources is a tat bit on the lower side, for solar PV, it is nearing 18-20% on an average sunny period and for onshore wind a little better with 30%. Secondly, the nature of generation is intermittent depending largely on weather condition and time of the day. The solar PV (photo-voltaic) generates electricity in the daytime when domestic consumption is low except for air conditioning in the summer days. There is a mismatch between demand and supply not only for solar PV but for other renewable sources as well.

If the intermittent renewable energy is 15 – 20% of the overall energy consumption, the grid operators are able to compensate for its effect on grid stability (European Energy Commission, 2013). But, particularly when the demand is high, there are significant issues when the contribution of intermittent energy exceeds 20 – 25% (U. S. Energy Information Administration, 2014).

To accommodate and facilitate renewable in the present grid system, gaps in generation has to be filled for continuous and smooth supply, by other sources, mainly, flexible conventional sources and electric energy storage. Fig 1 describes the problems and solutions of renewable in grid.

Fig 1. Problems in renewable energy installations and solution (TEPCO)

Electrical energy storage (EES) can be a solution to the instability caused by increased presence of renewable power in Indian grid system, once it becomes cost competitive. A grid attached storage where power comes from both renewable and conventional source would be a solution to provide grid stability in India.

Integration of EES to the grid will demand different capacity for power and energy for storage and also, the required response time, depending on the circumstances of grid application. For short time fluctuations in demand, there is a need to respond quickly to maintain frequency. But the demand for the peak period may be taken care of by relatively larger flow of energy from EES.

Fig.2 shows schematically a host of EES technologies covering different ranges of energy capacity and response time. Based on these data, it is apparent that some technologies will not be suitable for power quality applications due to higher response time while some others are not appropriate for its inability to store relatively larger power to provide for peak demand of power from a grid.

Fig.2: Different storage technologies and their ranges of capacity and response time (drawn by Badwal et al, 2014 from the data given by Chatzivasileiadi et al, 2013)

Different energy storage technologies have different levels of maturity (International Electro-technical Commission, 2011). Some technologies are ready to be employed in the grid while others need considerable development further to achieve low installation cost, high durability and reliability, long service lifetime and high round trip efficiency (U.S. Energy Information Administration, 2014). In addition operation and maintenance costs are also important factors determining their suitability for applications.

Actually, if estimated considering reliable power and safe running of conventional power plants, EES is being proved cost effective in countries like Germany and US, and share of non pumped hydro storage technology is increasing worldwide, due to more funding in technology research not only for electric power, but also in electric automobile needs.

Fig 3. Shares in annual storage technology addition (IEA-ETP, 2017)

Conventional power can operate with optimized load during peak hours or when renewable is off and EES can take care of flexible demand of the grid. Thus, EES can provide grid stability and reliability, minimize the requirement of flexible operation and take care of intermittent power supplies of renewable sources.

The required capacity of EES with increased renewable share in electricity, has been calculated by various agencies, depending on the percentage share and amount of variation of renewable. One study calculates the amount to be 2-8% of renewable capacity.

With increase in renewable capacity, market for EES is increasing globally. It is expected to mature to a cost competitiveness, as especially battery storage technology development research is being hugely funded in electric vehicle segment as well.Thus, with a huge target and growing pace of renewable, India too would need to grow its EES market, otherwise renewable installation would result in multiple problems and an unbalanced grid.

The policies on renewable need to be revisited for encouraging EES development through factors like learning and scale, i.e. technology development as well as market development.

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