A combined heat and power, CHP, system for converting heat to electricity using a multicomponent working fluid containing ammonia and water, the CHP system comprising: a feedpump to increase the pressure of the working fluid in its liquid form; a recuperator operably connected to said feedpump for heating and partially vaporizing said high-pressure working fluid leaving the feedpump using heat from cooling and partially condensing low-pressure working fluid leaving a turbine, such recuperator arranged such that said low-pressure working fluid is in counter-flow to the working fluid coming from the feedpump; a pre-heater operably connected to said recuperator and a heater such that the working fluid exists only in the vapour state within the heater, the pre-heater comprising a heat exchanger for heating and completely vaporizing said high-pressure working fluid leaving the recuperator using heat contained in working fluid vapour extracted from the heater at a point part way through the heater with such working fluid vapour being returned at a lower temperature to the heater at essentially that same point to continue through the heater, such pre-heater arranged such that said working fluid coming from the heater is in counter-flow to the working fluid coming from the recuperator; the heater for superheating the working fluid to a superheated vapour state, said heater comprising a first heat exchanger using a fluid to supply heat to the working fluid, said first heat exchanger arranged in counter-flow to the working fluid coming from the pre-heater, the turbine extracting usable energy from the superheated working fluid by reducing its pressure and enthalpy, a cooler for cooling and condensing the working fluid leaving the recuperator to a liquid state, said cooler comprising a second heat exchanger using a second fluid that absorbs heat from the working fluid, said second heat exchanger arranged such that said second fluid is in counter-flow to the working fluid leaving the recuperator and said second fluid entering and leaving said second heat exchanger at temperatures (18,21) suitable for use in a district heating system, means for returning the liquid working fluid leaving said cooler to said feedpump to form a closed loop system, and means to sealably interconnect the equipment with flow passages, and valves, sensors and control systems to manage the operation of the system. a feedpump to increase the pressure of the working fluid in its liquid form; a recuperator operably connected to said feedpump for heating and partially vaporizing said high-pressure working fluid leaving the feedpump using heat from cooling and partially condensing low-pressure working fluid leaving a turbine, such recuperator arranged such that said low-pressure working fluid is in counter-flow to the working fluid coming from the feedpump; a pre-heater operably connected to said recuperator and a heater such that the working fluid exists only in the vapour state within the heater, the pre-heater comprising a heat exchanger for heating and completely vaporizing said high-pressure working fluid leaving the recuperator using heat contained in working fluid vapour extracted from the heater at a point part way through the heater with such working fluid vapour being returned at a lower temperature to the heater at essentially that same point to continue through the heater, such pre-heater arranged such that said working fluid coming from the heater is in counter-flow to the working fluid coming from the recuperator; the heater for superheating the working fluid to a superheated vapour state, said heater comprising a first heat exchanger using a fluid to supply heat to the working fluid, said first heat exchanger arranged in counter-flow to the working fluid coming from the pre-heater, the turbine extracting usable energy from the superheated working fluid by reducing its pressure and enthalpy, a cooler for cooling and condensing the working fluid leaving the recuperator to a liquid state, said cooler comprising a second heat exchanger using a second fluid that absorbs heat from the working fluid, said second heat exchanger arranged such that said second fluid is in counter-flow to the working fluid leaving the recuperator and said second fluid entering and leaving said second heat exchanger at temperatures (18,21) suitable for use in a district heating system, means for returning the liquid working fluid leaving said cooler to said feedpump to form a closed loop system, and means to sealably interconnect the equipment with flow passages, and valves, sensors and control systems to manage the operation of the system.