An electricity generation device comprising: a storage tank for storing a cryogenic fluid, a fluid pump for compressing cryogenic fluid taken from the storage tank to a high pressure, an evaporator for evaporating the high pressure cryogenic fluid, to provide a high pressure gas, a first expansion turbine (440, 442) for expanding the high pressure gas and extracting work from the high pressure gas; a first reheater (450, 452) for reheating the gas exhausted from the first expansion turbine using heat from the ambient environment or waste heat; a second expansion turbine (460, 462) for expanding the working fluid exhausted from the first reheater and extracting work from the working fluid exhausted from the first reheater; wherein the second expansion turbine has an exhaust outlet which is split into first and second paths such that the working fluid exhausted from the second expansion turbine is divided into first and second portions, wherein the first portion of working fluid is directed along the first path to ambient through a first exhaust, and the second portion of working fluid is directed along the second path to an inlet of the evaporator such that the second portion of working fluid exchanges thermal energy with the high pressure cryogenic fluid within the evaporator; and a first compressor for compressing the second portion of working fluid after it has passed through the evaporator, wherein an exhaust outlet of the compressor is connected with an exhaust outlet of the first expansion turbine such that the second portion of working fluid and the gas exhausted from the first expansion turbine are combined and directed into the first reheater to be reheated using the heat from the ambient environment or waste heat, a generator, wherein at least one of the first and second expansion turbines is configured to drive said generator to produce electricity. a storage tank for storing a cryogenic fluid, a fluid pump for compressing cryogenic fluid taken from the storage tank to a high pressure, an evaporator for evaporating the high pressure cryogenic fluid, to provide a high pressure gas, a first expansion turbine (440, 442) for expanding the high pressure gas and extracting work from the high pressure gas; a first reheater (450, 452) for reheating the gas exhausted from the first expansion turbine using heat from the ambient environment or waste heat; a second expansion turbine (460, 462) for expanding the working fluid exhausted from the first reheater and extracting work from the working fluid exhausted from the first reheater; wherein the second expansion turbine has an exhaust outlet which is split into first and second paths such that the working fluid exhausted from the second expansion turbine is divided into first and second portions, wherein the first portion of working fluid is directed along the first path to ambient through a first exhaust, and the second portion of working fluid is directed along the second path to an inlet of the evaporator such that the second portion of working fluid exchanges thermal energy with the high pressure cryogenic fluid within the evaporator; and a first compressor for compressing the second portion of working fluid after it has passed through the evaporator, wherein an exhaust outlet of the compressor is connected with an exhaust outlet of the first expansion turbine such that the second portion of working fluid and the gas exhausted from the first expansion turbine are combined and directed into the first reheater to be reheated using the heat from the ambient environment or waste heat, a generator, wherein at least one of the first and second expansion turbines is configured to drive said generator to produce electricity.