Abstract: In some implementations, there is provided an apparatus. The apparatus may include a first steam engine, an intermediate storage, and a second steam engine. The first steam engine may include a first inlet and a first exhaust, wherein the first inlet receives steam from a source of thermal energy. The intermediate storage may be coupled to the first exhaust, wherein the intermediate storage stores thermal energy provided by steam from the first exhaust. The second steam engine may include a second inlet coupled to the intermediate storage. Moreover, at least one of the first steam engine and the second steam engine may produce work. Furthermore, the first steam engine may be driven by the steam received from the source of thermal energy, and the second steam engine may be driven by steam from at least one of the intermediate storage and the first exhaust. Related apparatus and methods are also described.

Abstract: A variety of energy storage and retrieval systems are described. Generally “hot” and “cold thermal reservoirs are provided. The “hot” reservoir holds both liquid and saturated vapor phase working fluid. The “cold” reservoir holds working fluid at a lower temperature than the hot reservoir. A heat engine/heat pump unit: (a) extracts energy from vapor passing from the hot reservoir to the cold reservoir via expansion of the vapor in a manner that generates mechanical energy to facilitate retrieval of energy; and (b) compresses vapor passing from the cold reservoir to the hot reservoir to facilitate the storage of energy. In some embodiments, the heat engine/heat pump takes the form of a reversible positive displacement heat engine that can act as both an expander and a compressor. To facilitate the storage and retrieval of electrical energy, an electric motor/generator unit may be mechanically coupled to the heat engine/heat pump unit.