Glyn Rhonwy Pumped Storage

Scheme components

The design of the scheme to generate 99.9 MW of power will be the same as that of the approved 49.9 MW scheme which has a T&CPA 1990 planning consent.

The scheme is composed of the following elements which can be viewed on a map here:

  • upper reservoir (Q1 - Chwarel Fawr Quarry);
  • its dam and spillway to the Nant Y Betws;
  • lower reservoir (Q6 – Glyn Rhonwy Quarry);
  • its dam and spillway to Llyn Padarn;
  • a penstock connecting Q1 to the power station located adjacent to Q6;
  • a tailrace connecting the power station to Q6; and
  • the power station itself consisting of the turbines and pumps at depth with electrical distribution equipment on the surface adjacent to the power station building.

The footprint of the 99.9 MW scheme has increased to allow flexibility in the construction process but the size of all the above ground elements of the scheme will not change:

Scheme element 49.9 MW 99.9 MW
 Upper dam and spillway
 upto 25 m high
 same as 49.9 MW
 Upper reservoir (Q1 - Chwarel Fawr)
 1.1 Million m3
 same as 49.9 MW
 4m diameter underground tunnel in 10m corridor 
 4m diameter underground tunnel in 100m corridor 
 Turbine house
 footprint as shown on the map
 same as 49.9 MW
 2 x 24.95 MW
 2 x 49.95 MW
 footprint as shown on the map
 same as 49.9 MW
 Lower dam
 up to 15 m high
 same as 49.9 MW
 Lower reservoir (Q6 - Glyn Rhonwy Quarry)
 1.1 Million m3 
 same as 49.9 MW
 Spillway to Llyn Padarn
 footprint as shown on the map
 same as 49.9 MW
 Pumphouse at Llyn Padarn
 footprint as shown on the map
 same as 49.9 MW
 Abstraction rate from Llyn Padarn
 2000 m3 per day
 same as 49.9 MW
 limits set by 49.9 MW planning conditions
 same as 49.9 MW
 limits set by 49.9 MW planning conditions
 same as 49.9 MW
 Air / water pollution
 limits set by 49.9 MW planning conditions
 same as 49.9 MW
 as described in 49.9 MW Environmental Statement
 slightly higher traffic to Q6
 Build time
 3 to 4 years
 same as 49.9 MW
 Development cost
 c. £130 million
 c. £160 million
 £ payback
 c. 20 years
 c. 15 years
 c. 9 months
 c. 6 months



As part of the DCO application SPH has undertaken an Environmental Impact Assessment (EIA) to safeguard the environment at Glyn Rhonwy. SPH will present the findings of the EIA within an Environmental Statement (ES) which will form part of the final DCO application. SPH have progressed the EIA through a series of consultations with Gwynedd Council, Natural Resources Wales (NRW), Snowdonia National Park Authority (SNPA) and Gwynedd Archaeology Planning Services (GAPS). SPH has presented the preliminary environmental information for the Development in a Draft ES which has been issued as part of the statutory consultation process.

An ES was completed in 2012 as part of the approved scheme and the current draft ES builds upon the regulatory agreements for the various technical assessments which supported the 2012 ES. The scope of the EIA for the Development is in the process of being agreed with the regulatory bodies and has been supplemented with early engagement with the statutory consultees and also with the Planning Inspectorate. This scope has taken account of the precautionary approach to the construction methods, resulting in changes to site boundary (or Order Limits), which are required by the DCO process. 

Electrical connection

The Development will be connected to the electricity distribution network via a new electrical connection. This will be exported from an onsite substation to an offsite substation near Pentir. The consenting of the electrical connection is the responsibility of the District Network Operator, SP Manweb. SPH has requested the connection to be provided underground. 

What will the scheme look like?


We've taken a range of viewpoints around the proposed site to indicate how the proposed development will look. Download a PDF of the viewpoints map showing where the viewpoints are located.

If you are unable to open these reports you will need to install a PDF reader such as Adobe Reader. 




Video tour of the Viewpoints

The video shows a virtual tour around the locations of the site viewpoints



Viewpoint Photomontage

Viewpoint 5: Llanberis /A4086

View Direction: North West. Distance From Site: 1.5km. Elevation: 110m


Viewpoint 8: Dinorwig

View Direction: South West. Distance From Site: 1.2km. Elevation: 297m


Viewpoint 9: Dolbadarn Castle

View Direction: North West. Distance From Site: 2km. Elevation: 120m


Viewpoint 12: Hebron Station

View Direction: North West. Distance From Site: 2.8km. Elevation: 210m