Hydroelectric power developer Snowdonia Pumped Hydro has withdrawn its application for environmental permits for the 99.9-MW Glyn Rhonwy pumped-storage plant from Natural Resources Wales.
Snowdonia's decision essentially halts development of the project as the NRW permits are necessary for construction and operation as they would allow for discharge into the lower Glyn Rhonwy reservoir.
"We only issue an environmental permit if we are wholly satisfied that a company's plans prove it will operate safely, without harming the environment or local communities," said Dylan Williams, NRW operations manager. "However, the applicant has not provided us with enough information to be able to make that decision."
The Welsh permitting agency said Snowdonia Pumped Hydro also did not provide enough information about its day-to-day operations and management in addition to a lack of technical information.
"If the applications were to be decided on the basis of the information provided, they would have been refused," Williams said.
The US$243 million proposal would use the abandoned Glyn Rhonwy and Chwarel Fawr slate quarries, with a 20-meter-high dam to be constructed on the upper reservoir and a 15-meter-high dam on the lower reservoir.
The project was proposed in 2013 as a 49.9 MW scheme before Snowdonia Pumped Hydro received approval from the UK Planning Inspectorate to increase its output by 50 MW in December 2014.
The Crown Estate agreed to lease 13 hectares of land to Snowdonia Pumped Hydro last April, at which point the project was expected to be operational by 2019.
The developer must now determine whether it will resubmit its application for environmental permits in greater detail.
If constructed, The Glyn Rhonwy would be Britain's first new grid-scale power storage facility in more than 30 years.
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