JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III ENERGY STORAGE SYSTEMS Previous Question Paper (January/February - 2021 - R16)

Electricity is a unique form of energy characterized by its instantaneous nature, high grade of utility, and the requirement for near-perfect balance between generation and consumption. Unlike other forms of energy, electricity cannot be stored directly in large quantities in its electrical form; it must be converted into chemical, mechanical, or potential energy for storage.

The fundamental characteristics of electricity include:

• Instantaneous Availability: Electricity is available on demand, but the generation must match the load at every millisecond to maintain grid stability and frequency.
• High Quality: It is a highly versatile energy carrier that can be converted into heat, light, motion, or chemical energy with high efficiency.
• Transmission Efficiency: It can be transported over long distances via grid infrastructure, though it is subject to transmission and distribution losses.
• Non-storability: Electricity itself is not a physical substance that can be contained in a reservoir; it requires conversion to other forms to be saved for later use.

The need for Electrical Energy Storage (EES) systems arises from several critical operational and economic requirements:

1. Load Leveling and Peak Shaving: EES systems allow utilities to store energy during off-peak hours when demand is low and discharge it during peak demand periods. This reduces the need for expensive, inefficient 'peaker' power plants and optimizes the utilization of base-load generation.
2. Integration of Renewable Energy Sources: Renewable sources like solar and wind are inherently intermittent and non-dispatchable. EES acts as a buffer, storing excess energy generated during periods of high resource availability and supplying it when generation is low, thereby ensuring grid reliability.
3. Grid Stability and Power Quality: EES provides ancillary services such as frequency regulation, voltage support, and synthetic inertia. By reacting rapidly to grid fluctuations, storage systems prevent blackouts and maintain the standard 50/60 Hz frequency.
4. Energy Security and Reliability: In the event of grid failure or natural disasters, EES provides backup power and islanding capabilities, ensuring that critical infrastructure and essential services remain operational.
5. Deferral of Infrastructure Upgrades: By managing local congestion and peak demand at the distribution level, EES can delay or eliminate the need for costly investments in upgrading transmission lines and transformers.

High generation cost during peak-demand periods is primarily driven by the need to operate inefficient, fossil-fuel-based peaking power plants (such as open-cycle gas turbines) and the requirement to maintain spinning reserves. Electrical energy storage (EES) addresses this by enabling peak shaving and load leveling. By charging storage systems during off-peak hours when electricity is inexpensive and abundant, and discharging them during peak periods, utilities can avoid the high marginal costs of dispatching expensive peaking units. Furthermore, EES reduces the need for costly infrastructure upgrades by deferring transmission and distribution capacity investments.

The need for a continuous and flexible supply is essential for grid stability and reliability for the following reasons:

• Grid Stability and Frequency Regulation: Power systems must maintain a strict balance between supply and demand to keep the frequency stable. As intermittent renewable energy sources like wind and solar increase, the grid requires flexible assets that can respond in milliseconds to seconds to compensate for sudden fluctuations in generation or load.
• Intermittency Management: Renewable energy is inherently variable. Continuous supply is ensured by storing excess energy generated during periods of high resource availability and releasing it when generation drops, effectively smoothing out the supply curve.
• Reliability and Power Quality: Flexible storage systems provide ancillary services such as voltage support and black-start capabilities, which are critical for restoring the grid after outages and ensuring high-quality power for sensitive industrial and commercial consumers.
• Economic Efficiency: A flexible supply allows grid operators to optimize the dispatch of generation assets, prioritizing low-cost, base-load plants while using storage to handle the dynamic variability of demand, thereby reducing the overall cost of electricity production.