--- title: "Energy storage technologies and challenges" subject: "Energy Environment and Society" chapter: 5 key: "semester_7/energy_environment_and_society:energy-storage-technologies-challenge" source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/energy-storage-technologies-challenge site: BCT Engineering --- # Energy storage technologies and challenges Energy Environment and Society · Chapter 5: Energy Storage - Asked in: 2072 Kartik, 2+2 marks; 2073 Shrawan; 2074 Asoj, 2+3 marks (asked 3 times) - Video: [How to fix clean energy’s storage problem](https://www.youtube.com/watch?v=z-k5uS7ALXk) — Vox - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/energy-storage-technologies-challenge - Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-5 ## Question What are the (latest) energy storage technologies? Why does energy storage become a challenge in the 21st century (describe briefly the complications of storage)? ## Short answer Latest storage includes lithium-ion, sodium-ion, flow batteries, pumped hydro, compressed air, thermal, hydrogen, and supercapacitors. Storage is challenging because renewables are intermittent requiring conversion with losses (60-90% round-trip), high capital costs, low energy density compared to fossil fuels, resource constraints, safety issues, and site limitations for pumped hydro. ## Answer #### 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which technology has the largest share of grid storage worldwide? A. Flywheels B. Lithium-ion batteries C. Supercapacitors D. Pumped storage hydropower Answer: D. Pumped storage is the largest share, though it needs suitable geography. (Key point: Largest storage) 2. Which technology suits long-term seasonal storage? A. Hydrogen (power-to-gas) and ammonia B. Flywheels C. Supercapacitors D. Button cells Answer: A. Surplus renewable power can be converted to hydrogen. (Key point: Seasonal storage) 3. Why is storing electricity a challenge? A. It can be stored directly with no losses B. It must be converted to another form and back, with losses (round-trip efficiency 60-90%) C. Round-trip efficiency is 100% D. Demand is falling Answer: B. Electricity cannot be stored directly. (Key point: Why storage is hard) 4. Why does low energy density limit batteries? A. Li-ion has higher density than petrol B. Density is irrelevant to transport C. Li-ion has ~250 Wh/kg versus ~12,000 Wh/kg for petrol, limiting aviation, shipping and trucks D. Petrol has ~250 Wh/kg Answer: C. This is a key complication for heavy transport. (Key point: Energy density) ## Related in Energy Environment and Society - [Forms of energy storage](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aenergy-storage-forms-four) — Energy Environment and Society, chapter 5 - [Short note: Flywheel energy storage](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Aflywheel-storage) — Energy Environment and Society, chapter 5 - [Potentials and challenges of hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydropower-potential-challenges) — Energy Environment and Society, chapter 3 - [Advantages and challenges of solar PV](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apv-advantages-disadvantages) — Energy Environment and Society, chapter 3 - [Hydrogen production and storage](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Ahydrogen-production-storage) — Energy Environment and Society, chapter 3 - [Short note: Pumped storage hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apumped-storage-hydropower) — Energy Environment and Society, chapter 5 ## Related in other subjects - [Mechanical and thermal energy storage](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-storage-technologies) — Power Plant Design, chapter 1 - [Big data trends, challenges, characteristics](https://www.bctengineer.com/question.md?key=semester_8%2Fbig_data_technologies%3Abig-data-trends-challenges) — Big Data Technologies, chapter 1 - [RoR at 40% exceedence; storage regulation](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-40-percent-exceedence-storage-regulation) — Hydropower Engineering, chapter 3 - [Hydrogen storage and infrastructure requirements](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Ahydrogen-storage-infrastructure) — Energy Resources, chapter 6