> four-hour storage is forecast to fall a further 33% to $80/MWh by 2035, displacing gas peaking on cost across every gas market in the region.

This seems to be specifically in reference to "gas peakers" which are on-demand gas turbines used to pick up slack in the main grid during peak usage. They typically only run for hours at a go and commonly on very hot days when ACs drain the grid. In those use cases, batteries could be a viable replacement. They're not necessary charged by solar but by the main grid overnight.

Because the comparison is to peakers.