Vegetable oil
Technologies of hydrogen economy, batteries, compressed air energy storage, and flywheel energy storage address the energy storage problem but not the source of primary energy. Other technologies like fission power, fusion power, and solar power address the problem of a source of primary energy but not energy storage. Vegetable oil addresses both the source of primary energy and of energy storage. The cost and weight to store a given amount of energy as vegetable oil is low compared to many of the potential replacements for fossil fuels.