Abstract: There is disclosed a thermal energy storage and supply method that includes providing subcooled water to a pressure vessel; heating liquid water within the pressure vessel using an electrically-powered heater so that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to raise the storage pressure to a peak storage pressure of at least 2 MPa; and selectively discharging steam from an outlet of the pressure vessel to a thermal load, in response to a thermal energy demand, such that during a depletion period the storage pressure reduces by at least 1 MPa from the peak storage pressure.