Solar might also enter that market strongly during daytime if the alternative is curtailing it completely.

This article from before the blackout suggest Spain is trailing other nations on BESS because they have more Hydro (and thermal? which might mean solar concentrating power) and haven't been as driven to set up the necessary regulatory environment.

https://www.rabobank.com/knowledge/d011476239-backup-power-f...

> Along with the lack of urgency around battery storage on the Spanish grids, key regulatory and market fundamentals have been lacking for the BESS business in Spain. The Spanish market has primarily relied on pumped hydro storage and thermal storage. As a result, the regulation required for BESS projects to participate in energy and ancillary services markets has been lacking, and progress in the necessary regulatory updates has been slower than in other European countries.

"Ancillary services" here mean grid inertia and similar.