10.4 Energy storage and grid stabilization capabilities

Energy storage is crucial for grid integration of renewable energy sources. It enables power generation even when the sun isn't shining or the wind isn't blowing, making solar and wind more reliable and dispatchable.

Various storage technologies, from thermal to electrochemical, offer different benefits. They provide essential grid services like frequency regulation and voltage support, enhancing overall grid stability and reliability as we transition to cleaner energy sources.

Energy Storage Technologies

Thermal Energy Storage Systems

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• Thermal energy storage (TES) captures excess heat for later use in power generation
• Molten salt storage utilizes high-temperature salts to retain thermal energy
  • Consists of two tanks: hot tank (typically 565°C) and cold tank (typically 290°C)
  • Allows for 24/7 power generation in concentrated solar power plants
• Phase change materials (PCMs) store and release energy during state transitions
  • Latent heat storage provides higher energy density compared to sensible heat storage
  • Common PCMs include paraffin wax, salt hydrates, and metallic alloys
• Sensible heat storage systems use temperature changes in materials (water, rocks, concrete)
  • Lower energy density but often more cost-effective than latent heat storage

Electrochemical and Mechanical Storage

• Battery integration enhances grid flexibility and renewable energy integration
  • Lithium-ion batteries offer high energy density and fast response times
  • Flow batteries (vanadium redox, zinc-bromine) provide long-duration storage capabilities
  • Sodium-sulfur batteries operate at high temperatures, suitable for large-scale applications
• Pumped hydro storage remains the most widely used large-scale energy storage technology
  • Uses excess electricity to pump water to an elevated reservoir
  • Generates power by releasing water through turbines during peak demand
  • Provides long-duration storage with typical round-trip efficiencies of 70-80%

Emerging Storage Technologies

• Compressed air energy storage (CAES) uses excess electricity to compress air in underground caverns
  • Air is released and heated to drive turbines during peak demand periods
• Flywheel energy storage systems store kinetic energy in rotating masses
  • Offer rapid response times and high cycle life, suitable for short-duration applications
• Hydrogen energy storage converts excess electricity to hydrogen through electrolysis
  • Stored hydrogen can be used in fuel cells or combustion turbines for power generation
• Cryogenic energy storage liquefies air or nitrogen for later expansion and power generation
  • Offers potential for long-duration, large-scale energy storage

Grid Stabilization Services

Frequency and Voltage Regulation

• Frequency regulation maintains grid frequency within acceptable limits (typically ±0.05 Hz)
  • Energy storage systems respond rapidly to supply-demand imbalances
  • Automatic Generation Control (AGC) signals adjust power output of participating units
• Voltage support maintains grid voltage within specified ranges
  • Reactive power injection or absorption helps stabilize voltage levels
  • Static VAR Compensators (SVCs) and STATCOMs provide fast-acting voltage support
• Energy storage systems offer faster response times compared to conventional generators
  • Can provide both up and down regulation, improving overall grid flexibility

Grid Resilience and Reliability

• Black start capability allows power plants to restart without external power supply
  • Energy storage systems can provide initial power to kickstart larger generators
  • Critical for rapid grid restoration following widespread outages (blackouts)
• Grid inertia resists sudden changes in system frequency
  • Traditionally provided by rotating masses in conventional generators
  • Synthetic inertia from energy storage systems mimics this stabilizing effect
  • Particularly important with increasing penetration of inverter-based renewables
• Ramp rate control smooths rapid changes in power output from intermittent renewables
  • Energy storage acts as a buffer, absorbing or releasing power as needed
  • Improves overall grid stability and reduces stress on conventional generators

Ancillary Services and Market Participation

• Spinning and non-spinning reserves provide backup power during unexpected events
  • Energy storage can respond faster than traditional generators, improving grid reliability
• Capacity firming ensures consistent power output from variable renewable sources
  • Energy storage systems smooth out fluctuations in wind and solar generation
• Transmission and distribution deferral reduces the need for grid infrastructure upgrades
  • Strategically placed energy storage can alleviate congestion and improve power quality
• Energy arbitrage allows storage operators to buy low and sell high
  • Charge during periods of low demand/prices, discharge during high demand/prices
  • Improves overall grid efficiency and can provide additional revenue streams