Energy storage technologies and challenges

Energy storage technologies (latest)

1. Lithium-ion batteries: dominant for EVs, phones and grid storage; falling costs; newer chemistries are LiFePO₄ (LFP) and NMC.
2. Sodium-ion, solid-state and flow batteries (vanadium redox): emerging for long-duration grid storage and safer, cheaper storage.
3. Pumped storage hydropower: the largest share of grid storage worldwide.
4. Compressed air energy storage (CAES) and liquid air storage.
5. Flywheels (short-duration, high power) and supercapacitors.
6. Thermal storage: molten salt in CSP plants, hot water tanks, ice storage.
7. Hydrogen (power-to-gas) and ammonia: long-term, seasonal storage from surplus renewable power.
8. Gravity storage and superconducting magnetic storage (SMES) (early stage).

Why storage is a challenge in the 21st century (complications)

• Renewables are intermittent: with high shares of solar and wind, electricity must be stored when there is surplus and used when there is a shortage; in Nepal, a monsoon surplus and a dry-season deficit require seasonal storage.
• Electricity cannot be stored directly; it must be converted into another form (chemical, potential, kinetic, heat) and back, with energy losses (round-trip efficiency 60–90%).
• Cost: capital cost per kWh is still high, and replacement is required after limited life cycles.
• Energy density: low energy density compared with fossil fuels (for example lithium-ion ~250 Wh/kg against petrol ~12,000 Wh/kg), which limits aviation, shipping and trucks.
• Resources: lithium, cobalt, nickel supply, mining impacts and geopolitics.
• Safety: fire and thermal runaway.
• Environment: battery manufacture, recycling and disposal.
• Site constraints: pumped storage needs suitable geography, long construction and big investment.
• Grid integration rules and market design are incomplete.
• Demand grows with electric vehicles and data centres.