@KevinMarks @nworbmot Dinorwig has a C/P ratio of ~5 (5 hours of continuous generation at full reservoir). For (ULDES) we're looking into C/P ratios of > 100, i.e. orders of magnitude larger storage capacities.
For comparison: 9.1 GWh (capacity of Dinorwig according to Wikipedia) corresponds to ca. 1600-2700 t methanol (higher value from considering M2E efficiency) or approximately an Olympic swimming pool full of methanol.
PHS is great, but not for ULDES, capacities just don't scale well.