The increased percentage of renewable energy in the generation of electricity, such as by means of photovoltaics or wind, has caused challenges in balancing supply in demand in electric grids. Currently, it is not possible to store electric energy at utility scale economically. Since neither demand, nor supply are constant, or change in fixed relation to each other, operation of an electric grid requires significant standby capacities, and has to content with valuable assets unable to find users for their full production capability. Additionally, in many countries, the locations where electricity is generated using renewables, and the places where additional electricity may be needed are long distances apart, and thus the supply grid generates bottlenecks.
The engineering effort described in this paper is an attempt to provide means to balance grids on a scale that can be easily controlled. The European natural gas pipeline grid relies on gas turbine or electric motor driven centrifugal compressors to pump the gas through the system. If the compressors are driven by electric motors, they rely on the electric grid for power, while gas turbines generally use small portions of the natural gas in the pipeline as fuel.
If a centrifugal compressor is set up as a dual drive, such that the same compressor can either be driven by a gas turbine, or an electric motor, we have a device that can help balance the electric grid, without curtailing its function to pump gas through the natural gas grid. Since the power demand is rather large, in the 10 to 20 MW range, it is easy to impact the electricity use in a meaningful way. This task can be accomplished with available technology: Low emissions gas turbines, variable speed electric motors and centrifugal compressors as they are already in use in the European pipeline system, using overrunning clutches (SSS clutch, referred to as ’the clutch in the following text) that have been used in numerous applications. The paper describes the technology necessary, together with control and sizing considerations, based on actual project considerations.