A method of controlling an on-site power plant that has a plurality of prime movers (26, 28, 30) for generating power, comprising: operating a plurality of prime movers (26, 28, 30) to generate a first level of power for a load; detecting a down transient in the load; determining an amount of decrease in power required by the load corresponding to the detected down transient; adjusting how the prime movers (26, 28, 30) operate responsive to the down transient in the load so that the on-site power plant provides power that is equal to or less than the power required by the load while continuing operating at least one of the plurality of prime movers (26, 28, 30) to generate a second, relatively lower level of power for the load, wherein each of the prime movers (26, 28, 30) is associated with a cogeneration unit (32, 34, 36) that utilizes exhaust from at least one of the associated prime movers (26, 28, 30) to provide a temperature control function; characterized by determining which of the prime movers (26, 28, 30) to turn off responsive to a requirement for temperature control associated with a thermal load including the steps of determining how many of the prime movers (26, 28, 30) to turn off so that a difference between the first and second levels of power generated by the on-site power plant is at least the determined amount of decrease in power required by the load; determining which of the cogeneration units (32, 34, 36) will meet a current temperature control need associated with a thermal load; determining a priority of the prime movers (26, 28, 30) based on the temperature control need; and selecting the highest priority prime mover (26, 28, 30) first to provide the desired power and to enable operation of the cogeneration unit (32, 34, 36). operating a plurality of prime movers (26, 28, 30) to generate a first level of power for a load; detecting a down transient in the load; determining an amount of decrease in power required by the load corresponding to the detected down transient; adjusting how the prime movers (26, 28, 30) operate responsive to the down transient in the load so that the on-site power plant provides power that is equal to or less than the power required by the load while continuing operating at least one of the plurality of prime movers (26, 28, 30) to generate a second, relatively lower level of power for the load, wherein each of the prime movers (26, 28, 30) is associated with a cogeneration unit (32, 34, 36) that utilizes exhaust from at least one of the associated prime movers (26, 28, 30) to provide a temperature control function; characterized by determining which of the prime movers (26, 28, 30) to turn off responsive to a requirement for temperature control associated with a thermal load including the steps of determining how many of the prime movers (26, 28, 30) to turn off so that a difference between the first and second levels of power generated by the on-site power plant is at least the determined amount of decrease in power required by the load; determining which of the cogeneration units (32, 34, 36) will meet a current temperature control need associated with a thermal load; determining a priority of the prime movers (26, 28, 30) based on the temperature control need; and selecting the highest priority prime mover (26, 28, 30) first to provide the desired power and to enable operation of the cogeneration unit (32, 34, 36). determining how many of the prime movers (26, 28, 30) to turn off so that a difference between the first and second levels of power generated by the on-site power plant is at least the determined amount of decrease in power required by the load; determining which of the cogeneration units (32, 34, 36) will meet a current temperature control need associated with a thermal load; determining a priority of the prime movers (26, 28, 30) based on the temperature control need; and selecting the highest priority prime mover (26, 28, 30) first to provide the desired power and to enable operation of the cogeneration unit (32, 34, 36).