SIEMENS PSE offers a suite of applications under the name gUTILTIES to monitor, manage and optimize energy consumption. A digital twin of the utility system will be built in gUTILITIES, validated and connected online. This technology has been deployed for different types of plants such refineries or chemical plants. Plants consume fuels, electricity and steam in time-varying quantities, and via multiple routes. The process plants themselves can generate steam and fuels, electricity can be sold to the grid and the prices of the various components can change hourly. Added to this complexity are day-to-day changes in major equipment availability. Given the large number of degrees of freedom, optimization is a challenging task. gUTILITIES applies rigorous optimization technology to process models of the utility system, taking into account demands, prices and availability, to find the economically optimal operating profile for any situation.