A vanadium redox flow battery stores energy in two liquid electrolyte tanks; pumps push electrolyte through a stack of cells where a Nernst-driven redox reaction charges/discharges the ion current. Capacity scales with tank volume (concentration × volume × Faraday constant), unlike a solid-state battery where power and energy are coupled. Alongside it, a molten-salt thermal tank stores excess energy as heat (E = mcΔT), useful for grid-scale multi-hour balancing.
Capacity E = n·F·c·V (Faraday's law, redox flow)
Thermal E = m·c·ΔT (sensible heat storage)
η_RT = E_out / E_in (round-trip, includes pump & ohmic losses)
- Flow rate — electrolyte pump speed; more flow feeds more ions to the stack, raising achievable current and reducing concentration polarization.
- Stack current — sets charge/discharge power; too high relative to flow rate drops efficiency (starvation).
- Tank size — decouples energy capacity from stack power, the defining trait of flow batteries.
- Thermal charge toggle — routes surplus power into the molten-salt tank, visualized by its rising internal temperature gradient.
Utility-scale flow batteries and molten-salt thermal stores are both used to shift renewable generation to match evening demand peaks.