Abstract: The invention provides, in some aspects, a thermal energy storage and retrieval system with a cavity containing a working fluid and a heat transfer surface disposed in the cavity transverse to a gravity field and in thermal coupling with an ice that is formed from and floating in the working fluid. The heat transfer surface transfers to that ice heat from a heat transfer medium that is thermally coupled to the heat transfer surface. According to aspects of the invention in which the ice is less dense than the working fluid, the heat transfer surface is disposed above (with respect to the gravity field) a region of the cavity where that ice is formed or inlet. According to aspects of the invention in which the ice is more dense than the working fluid, the heat transfer surface is disposed below that region.

Abstract: According to some aspects of the invention a heat pump includes first and second heat extraction units to extract heat from first and second heat sources in first and second temperature ranges, respectively, where the second temperature range is, on average, higher than the first temperature range. A fluid via defines a pathway through which the working fluid flows serially from the first heat extraction unit to the second heat extraction unit to the thermal storage unit. A pressure reduction stage is coupled to the via and serially disposed on the fluid circuit between the thermal store and the first heat extraction unit. In addition, either a compressor or a recuperator (or both) are coupled to the via and disposed on the fluid circuit between the first heat extraction unit and the second heat extraction unit.