Energy Storage for Variable Renewable Energy

Variable renewable energy (VRE) sources, especially solar and wind, generate electricity according to sunlight and wind conditions rather than continuously on demand. Energy storage absorbs electricity when renewable generation is abundant and releases it later, converting variable output into a more predictable and dispatchable supply. Round-the-clock supply therefore results from coordinating storage with renewable capacity, demand forecasts and grid operations.

How storage shifts renewable electricity across time

Storage separates the time of electricity generation from the time of consumption, a process called energy shifting.

• During periods of surplus solar or wind generation, electricity charges a battery, pumps water uphill or is stored through another suitable medium.
• During low-generation or peak-demand periods, stored energy is converted back into electricity and supplied to the grid.
• The storage system's power rating determines how quickly it can charge or discharge, while its energy capacity determines how long it can sustain that output.

How it makes supply reliable

By scheduling charging and discharging with renewable forecasts, grid operators can create a firmed renewable profile that better follows demand.

• Storage can move daytime solar electricity to evening or night-time demand and compensate for short-term wind or solar forecast errors.
• Fast-responding storage can provide frequency regulation, operating reserves, ramp support and congestion relief, thereby improving grid stability.
• A dependable round-the-clock portfolio generally combines adequately sized storage with geographically diversified renewables, transmission, demand response and other flexible resources.

Technology choice and limitations

Different storage technologies serve different durations and grid requirements; no single technology is optimal for every application.

• Battery energy storage systems are modular and respond rapidly, making them useful for short-duration balancing and ancillary services.
• Pumped-storage hydropower can provide large-scale storage, subject to suitable sites, water availability and environmental safeguards.
• Storage incurs conversion losses, capital costs and, for batteries, degradation; prolonged renewable shortfalls may therefore require larger storage or complementary flexible resources.
• Storage does not generate primary energy, so round-the-clock supply depends on sufficient renewable generation as well as correctly sized charging and discharge capacity.