Energy Storage Technologies Compared

Grid Signal

Cycle length 8 h

Sim speed 1.0x

Fleet Status (state of charge)

How it works

All four stations answer the same shared grid signal — a rising/falling surplus that alternates between "charge" and "discharge" every cycle. Each technology reacts differently, because each has its own power rating relative to its capacity, its own round-trip efficiency, and its own self-discharge rate:

d(SoC)/dt = ± rate(tech) · |signal| · √η(tech) − leak(tech)·SoC
rate(tech) = 1 / hoursToFull(tech)

Technology	Density	Round-trip η	Hrs to full	Self-discharge
Li-ion battery	~250 Wh/kg	92%	1 h	very low
Pumped hydro	~0.3 Wh/kg	80%	8 h	~none
Flywheel	~50 Wh/kg	90%	0.1 h	high (bearing/air drag)
Compressed air (CAES)	~40 Wh/kg	55%	6 h	low-moderate (leakage)

Cycle length sets how many simulated hours one full charge→discharge swing takes — a short cycle rewards fast-responding tech (Li-ion, flywheel); a long cycle favours bulk long-duration storage (pumped hydro, CAES).
Sim speed only compresses wall-clock time so you don't wait hours to see a cycle finish — the underlying hour-based rates are unchanged.
Idle freezes the grid signal at zero so you can watch self-discharge alone: the flywheel visibly bleeds down in seconds while pumped hydro barely moves — the central trade-off in long-duration storage.
Round-trip efficiency is applied as √η on the way in and √η on the way out, so a full charge→discharge round trip loses (1−η) of the energy, matching how utilities quote it.

Real-world relevance: no single technology wins on every axis — batteries dominate short, fast cycles; pumped hydro and CAES dominate multi-hour bulk storage where efficiency loss matters less than sheer duration; flywheels excel at instant power response but cannot hold charge for long.

Li-ion battery Pumped hydro Flywheel Compressed air

Grid signal
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