Equations and solutions are presented for determining the flash pressure that will optimize the turbine output for a single flash geothermal power plant. An Excel steam properties add-in is used to calculate the optimal flash pressure for a single flash geothermal power plant. This add-in includes the partial derivatives of steam properties, in addition to the steam properties themselves. This allows for a real time solution for optimizing power plant output without depending upon curvefits or rules-of-thumb. The DCS (distributed control system) for geothermal power plants typically have the capability to have real-time interactions with a Microsoft Excel program. This paper describes such a solution.