A method for generating electricity with a heat engine system, comprising: circulating a working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state; transferring thermal energy from a heat source stream to the working fluid by a first heat exchanger fluidly coupled to and in thermal communication with the heat source stream and high pressure side of the working fluid circuit; transferring the working fluid from the first heat exchanger to a recuperator fluidly coupled to the high pressure side and the low pressure side of the working fluid circuit; transferring thermal energy from the working fluid in the low pressure side to the working fluid in the high pressure side by the recuperator; transferring the working fluid from the recuperator to a second heat exchanger fluidly coupled to and in thermal communication with the heat source stream and the high pressure side of the working fluid circuit; transferring thermal energy from the heat source stream to the working fluid by the second heat exchanger; transferring the working fluid from the second heat exchanger to a power turbine; transferring thermal energy from the working fluid to the power turbine while converting a pressure drop in the working fluid to mechanical energy, wherein the power turbine is disposed between the high pressure side and the low pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the working fluid; converting the mechanical energy into electrical energy by a power generator coupled to the power turbine; transferring the electrical energy from the power generator to a power outlet, wherein the power outlet is electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid; controlling the power turbine by operating a power turbine throttle valve to adjust a flow of the working fluid, wherein the power turbine throttle valve is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit upstream from the power turbine; and monitoring and controlling process operation parameters of the heat engine system via a control system operatively connected to the working fluid circuit, wherein the control system is configured to control the power turbine by operating the power turbine throttle valve to adjust the flow of the working fluid. circulating a working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein at least a portion of the working fluid is in a supercritical state; transferring thermal energy from a heat source stream to the working fluid by a first heat exchanger fluidly coupled to and in thermal communication with the heat source stream and high pressure side of the working fluid circuit; transferring the working fluid from the first heat exchanger to a recuperator fluidly coupled to the high pressure side and the low pressure side of the working fluid circuit; transferring thermal energy from the working fluid in the low pressure side to the working fluid in the high pressure side by the recuperator; transferring the working fluid from the recuperator to a second heat exchanger fluidly coupled to and in thermal communication with the heat source stream and the high pressure side of the working fluid circuit; transferring thermal energy from the heat source stream to the working fluid by the second heat exchanger; transferring the working fluid from the second heat exchanger to a power turbine; transferring thermal energy from the working fluid to the power turbine while converting a pressure drop in the working fluid to mechanical energy, wherein the power turbine is disposed between the high pressure side and the low pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the working fluid; converting the mechanical energy into electrical energy by a power generator coupled to the power turbine; transferring the electrical energy from the power generator to a power outlet, wherein the power outlet is electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid; controlling the power turbine by operating a power turbine throttle valve to adjust a flow of the working fluid, wherein the power turbine throttle valve is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit upstream from the power turbine; and monitoring and controlling process operation parameters of the heat engine system via a control system operatively connected to the working fluid circuit, wherein the control system is configured to control the power turbine by operating the power turbine throttle valve to adjust the flow of the working fluid.