Modular electricity generation systems that use large numbers of low-cost Multiplexed Automotive Engines (MAE) to provide dispatchable electricity for decarbonized grid reliability or for non-grid backup power are disclosed. The engines may be disposed in power modules that are readily transportable containers that house several engine-generator units and typically produce 1 to 2 MW of maximum power. The MAE-based generation approach could provide greater flexibility in fuel use; power rating; transportability and location, along with faster startup time and very low air pollution. MAE electricity generation systems can be fueled with natural gas, low-carbon hydrogen and/or various liquids that may or may not be produced by grid electricity. The MAE generation systems can be employed in an energy storage process that uses surplus grid generated electricity from wind or solar energy to produce a fuel that is stored and later converted back into electricity when needed.