EPRI, a renouned institute in the USA has created a tool to evaluate the business case for storage applications based on mixed revenue sources.
Storage can regulate voltage levels, delaying the need to install new transmission lines by evening out spikes in power or demand, and storing power generated by renewable energy in times of low demand for use when demand, and prices are higher.
It is claimed that even today some business cases are positive, which would be a bit of a novelty. Applicaiton in Europe will probably not be trivial due to the different cost and revenue structures, and maybe even grid related differences. But it may be worth having a look.
Here is the EPRI page for the tool.