Coire Glas under construction. Pumped hydro returns to the UK after forty years.

SSE Renewables has begun construction on the 1.4 GW Coire Glas pumped hydro project in the Scottish Highlands — the first major UK pumped hydro development since Dinorwig completed in 1984. Coire Glas is the lead project under Ofgem's Long-Duration Electricity Storage (LDES) Cap-and-Floor regime, the Window 1 process having assessed a 28.7 GW pipeline to identify priority schemes. Earba (1.8 GW, Gilkes Energy) and other Scottish and Welsh pumped hydro proposals sit in the Window 1 pipeline.

Cap-and-Floor is the change that makes it viable. Long-duration storage was structurally uneconomic under wholesale + balancing-only revenue. Cap-and-Floor provides a regulated revenue floor + cap structure analogous to the Regulated Asset Base used for Sizewell C (Gap 32) and water sector regulation (Gap 35).

The floor de-risks pumped hydro construction; the cap protects consumers from windfalls. The model is the broader regulatory template for capital-intensive long-life UK infrastructure that markets alone do not finance.

For developers (SSE Renewables, Gilkes Energy, Drax, ILI, others) the variables are construction delivery, planning consent, grid connection, environmental impact assessment and community engagement across remote Highland and Welsh upland sites. For UK civil engineering Tier 1 contractors (Costain, Balfour Beatty, Morgan Sindall) the pumped hydro programme is a multi-billion-pound capex pipeline requiring dam, tunnel, powerhouse and underground civils capability. For HSEQA + safety + EIA + sustainability advisory firms, pumped hydro construction is a high-value service line across hazardous civils environments.

Cross-volume: pumped hydro provides the post-2030 long-duration storage anchor alongside BESS (Gap 06 short-duration), nuclear (Gap 32 baseload), offshore wind + onshore wind + solar variable renewables, interconnectors (Gap 11) and DSR (Gap 12). The Clean Power 2030 balanced system is unviable without long-duration storage to manage seasonal and week-long variability.

GridteamAI's Gap 29 report decodes the UK pumped hydro programme — the Cap-and-Floor regime, the Window 1 pipeline, the Coire Glas + Earba programme, the supply chain capacity, the cross-volume integration with the wider Clean Power 2030 system mix.