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Mature

Pumped Hydro Storage (PHS)

The proven giant of grid-scale energy storage

Overview

Pumped hydro uses two water reservoirs at different elevations. During periods of low demand, water is pumped uphill. When demand peaks, water flows downhill through turbines to generate electricity. It accounts for ~95% of global grid storage capacity.

How It Works

Pumped hydro storage (PHS) is the most mature large-scale energy storage technology. Two reservoirs at different elevations are connected by penstocks and a power house. When charging, reversible pump-turbines move water from the lower to the upper reservoir. When discharging, water flows from upper to lower, spinning the turbines to generate electricity. The round-trip efficiency is typically 70-85%. Closed-loop (off-river) systems have less environmental impact than traditional open-loop systems. Variable-speed turbines improve efficiency and grid services capability.

Advantages & Disadvantages

βœ“ Advantages

  • Mature, proven technology with 100+ year history
  • Very large scale (GWh capacity possible)
  • Extremely long lifespan (50-100+ years)
  • Lowest cost per kWh at scale
  • Provides grid inertia and frequency response
  • Can provide black start capability

βœ• Disadvantages

  • Severe geographic constraints (need mountains + water)
  • High upfront capital cost
  • Long construction timelines (5-10 years)
  • Significant environmental impact (open-loop)
  • Limited suitable sites globally
  • Fixed energy to power ratio

Applications

Bulk grid energy storage Peak shaving and load shifting Frequency regulation and grid inertia Renewable energy integration Energy arbitrage Backup power and black start

Cost Breakdown

Civil works (dams, tunnels): 40-60% | Electro-mechanical equipment (turbines/generators): 20-30% | Reservoirs: 10-20% | Power conversion: 5-10% | Balance of plant: 5-10%

Market Outlook

While new pumped hydro development is limited by geography and cost, the existing fleet remains critical for grid stability. New closed-loop and underground designs are expanding possibilities. China is leading new capacity additions.