The nice thing about oil is that it's very energy dense. We could store excess energy in the summer to be used in the winter. In contrast, batteries can maybe provide a few days of storage, but with synthetic oil, we could buffer for multiple months.

It’s probably more efficient to use a fuel like methane as opposed to oil as a medium-long term storage, e.g. for turbines used to address peak power grid usage, or winter storms (especially as more homes electrify HVAC).