A schematic of a hybrid compressed air system is shown in the figure below. The benefit of a hybrid system is its flexibility to allow base-loading the unit whose fuel cost is the least expensive at the time of use. Normally, this means base-loading natural gas units during peak cost periods for electric rates and base-loading electric units during other electric rate periods.
Hybrid Compressed Air System Schematic
A sample operating schedule for a hybrid system is shown in the figure below. In this case, two compressors were installed at 66% of peak capacity. The compressors operate two shifts per day. The gas engine-driven machine (dark gray) is shown to be operating at 100% of its capacity during the on-peak hours of operation, while the electric machine (light gray) picks up the remainder of the load. During mid- and off-peak periods, this situation is reversed. By operating in this manner. Maximum energy expense reduction can be realized by always using the least expensive fuel to compress air.