JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year ENERGY STORAGE SYSTEMS Previous Question Paper (February/March - 2022 - R16)

To minimize fossil fuel reliance and CO₂ emissions in electrical power generation, a multi-faceted approach focusing on supply-side transition and demand-side efficiency is required. The primary methods include:

1. Integration of Renewable Energy Sources: Transitioning to solar photovoltaic, wind, hydro, and geothermal energy. These sources generate electricity with near-zero operational emissions.
2. Nuclear Power Deployment: Utilizing nuclear fission as a baseload power source provides high energy density and consistent output without direct carbon emissions during operation.
3. Carbon Capture, Utilization, and Storage (CCUS): Implementing technologies to capture CO₂ emissions at the source from existing thermal power plants, compressing it, and storing it in geological formations to prevent atmospheric release.
4. Energy Storage Systems (ESS): Deploying large-scale battery energy storage systems (BESS), pumped hydro, and thermal storage to manage the intermittency of renewables, ensuring grid stability and reducing the need for fossil-fuel-based peaking plants.
5. Energy Efficiency and Demand-Side Management: Improving grid transmission efficiency, upgrading to smart grids, and incentivizing industrial and residential energy conservation to reduce the total load on the generation sector.

The adoption of these methods faces several key constraints:

1. Intermittency and Reliability: Renewable sources like wind and solar are variable. Without advanced storage, they cannot guarantee continuous power, necessitating expensive backup systems.
2. High Capital Costs: Technologies such as CCUS and advanced battery systems require significant initial investment, often making them less competitive than established fossil fuel infrastructure in the short term.
3. Geographical and Resource Limitations: Renewable energy potential is site-specific; for instance, high-wind areas or geothermal hotspots may be far from load centers, requiring extensive and costly transmission infrastructure.
4. Technological Maturity and Scalability: While some technologies are mature, others like large-scale hydrogen storage or advanced modular reactors are still in developmental or pilot stages, limiting immediate widespread deployment.
5. Policy and Economic Barriers: Lack of consistent carbon pricing, existing subsidies for fossil fuels, and complex regulatory frameworks often hinder the transition to cleaner energy alternatives.

On-grid energy storage systems (ESS) play a critical role in maintaining voltage quality by providing rapid active and reactive power support to stabilize the grid against fluctuations. As the integration of intermittent renewable energy sources like solar and wind increases, the grid faces challenges such as voltage sags, swells, and flickers. ESS acts as a buffer to mitigate these disturbances.

The primary mechanisms through which on-grid ESS maintains voltage quality include:

• Reactive Power Compensation: ESS inverters can be controlled to inject or absorb reactive power (VARs) almost instantaneously. By adjusting the reactive power output, the system can regulate the local bus voltage, effectively counteracting voltage drops during peak loads or voltage rises during low-load periods.
• Voltage Sag and Swell Mitigation: When a fault occurs on the transmission or distribution network, voltage levels can deviate significantly from the nominal value. ESS provides high-speed power injection or absorption to restore voltage levels within milliseconds, protecting sensitive industrial equipment from tripping.
• Harmonic Filtering: Modern grid-tied inverters used with ESS can be programmed to act as active power filters. By sensing harmonic distortions in the grid current, the inverter can inject compensating currents that cancel out these harmonics, thereby improving the total harmonic distortion (THD) profile of the voltage waveform.
• Frequency-Voltage Coupling Support: While primarily focused on frequency, ESS also supports voltage stability by maintaining the power balance. By stabilizing frequency, the system prevents cascading failures that often lead to severe voltage instability.
• Peak Shaving and Load Leveling: By storing energy during off-peak hours and discharging during peak demand, ESS reduces the stress on distribution transformers and feeders, preventing the voltage drops typically associated with heavy loading conditions.

In summary, the integration of ESS into the grid provides a dynamic, electronically controlled solution that enhances power quality by responding to transient events faster than traditional mechanical devices like tap changers or capacitor banks. This capability is essential for modern smart grids to ensure reliable operation and compliance with stringent power quality standards.