Long-Duration Energy Storage (LDES): Technologies and Why It Matters

Why duration matters

Most grid batteries installed so far deliver power for about 2 to 4 hours, which is ideal for shifting midday solar into the evening peak. But grids with high shares of wind and solar also face long stretches of low output, such as windless winter weeks. Covering those requires storage that can run far longer at low cost per kilowatt-hour of capacity.

Main technologies

• Pumped hydro: the largest and oldest form of storage, pumping water uphill and releasing it through turbines.
• Flow batteries: liquid electrolytes in tanks; duration scales with tank size.
• Iron-air batteries: use the rusting and un-rusting of iron to store energy for around 100 hours.
• Compressed and liquid air: store energy as pressurized or liquefied air.
• Thermal storage: heat stored in materials such as molten salt, sand or bricks.
• Hydrogen: produced by electrolysis and stored for seasonal use, with high conversion losses.

The economics

For LDES the critical metric is the cost of storage capacity (per kWh), because the asset may discharge only a handful of times a year during long events. Round-trip efficiency matters less than for daily-cycling batteries. Current market rules often do not pay for that rare-but-critical service, which is one of the main barriers to deployment.

Policy support

The US DOE Long Duration Storage Shot set a goal of cutting the cost of grid-scale storage lasting 10+ hours by 90% within a decade, and several states and countries run dedicated procurements.