Sand Battery: Resistive Thermal Energy Storage

Mode

Charge Power

Resistive heater 400 kW

Discharge Power

Heat-exchanger draw 300 kW

Insulation Quality

Jacket R-value 1.0×

Live Readouts

Core temp

20 °C

Surface temp

20 °C

Stored energy

0.00 MWh

Heat loss

0 kW

State of charge: 0%t = 0.0 h

How it works

A sand battery stores energy as sensible heat in a bulk solid — hundreds of tonnes of ordinary sand inside an insulated silo. Electricity (often curtailed/cheap renewable power) drives a resistive coil at the core; the sand simply gets hotter. There is no chemistry and no combustion, so the round-trip is limited only by heat loss, not by degradation.

Stored heat:   Q = m · c · (T − T_amb)
Charging:      dT_core/dt = P_charge / (m_shell · c)
Conduction:    dQ_i→i+1/dt = G · (T_i − T_{i+1})
Ambient loss:  dQ_loss/dt = (U/insulation) · (T_surface − T_amb)

This model splits the sand into 8 concentric shells (core → surface). The heater injects power into the core shell only; heat then conducts outward shell-by-shell over hours, which is why the surface stays cool long after the core is charged — exactly the lag real sand batteries (e.g. Polar Night Energy, Finland) rely on for multi-day storage. Discharging draws heat through an exchanger coil threaded near the surface, pulled preferentially from whichever shells are hottest.

Charge / Idle / Discharge — switches which physical process runs; conduction and ambient loss keep running in every mode.
Charge Power — electrical power fed to the core heating element (typical pilot plants: 100 kW – a few MW).
Discharge Power — target thermal power extracted by the heat-exchanger loop, capped by how much heat is actually available above ambient.
Insulation Quality — scales the jacket's thermal resistance; better insulation (higher ×) means slower ambient loss and better multi-day retention.

Sand's low, steady thermal conductivity is the whole point: it is a poor enough conductor that a well-insulated silo can hold ~500–600 °C for days, cheaply, at any scale, with zero risk of thermal runaway (unlike lithium-ion chemistries) or geographic constraint (unlike pumped hydro).

Cold (≈20 °C) Mid (≈300 °C) Hot (≈600 °C)

Mode: Charging

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