Sand Battery: Resistive Thermal Energy Storage

A sand battery stores surplus renewable electricity as heat rather than chemical energy: a resistive coil warms a silo of ordinary sand to hundreds of degrees, and a heat-exchanger loop draws that heat back out for district heating or industrial process heat on demand. This simulation splits an insulated silo into eight concentric shells and integrates real sensible-heat physics — Q = m·c·ΔT for storage, shell-to-shell conduction for how the heat spreads from the core heater outward, and an insulation-scaled ambient-loss term for how it slowly bleeds away. Switch between charging, idle and discharging, tune the heater and heat-exchanger power and the jacket's insulation quality, and watch the 3D sand bed's colour and the core/surface/stored-energy readouts respond exactly as the underlying heat-diffusion equations dictate.