Concept 1 / 3
Energy Storage — Key Metrics
Power-to-Power efficiency:
η_P2P = W_out / W_in = ∫P_out dt / ∫P_in dt
State of Charge: SOC = C / C_max [%]
Storage technologies:
| Technology | η_P2P | Timescale | Key feature |
|---|---|---|---|
| Li-ion battery | ~90% | Hours | EVs, short-term grid |
| Pumped hydro | ~80% | Hours–days | >90% of global storage |
| Compressed air | ~60% | Hours | Site-dependent |
| Hydrogen (P2G2P) | ~35–45% | Seasonal | Low round-trip, but high energy density |
| Thermal storage | ~95% | Hours | Simple, cheap |
Seasonal storage challenge:
Batteries/pumped hydro: efficient for daily/weekly.
For seasonal (summer → winter): only hydrogen/P2G has sufficient capacity.