VIDEO: Oncor plans transmission line for compressed air energy storage facility

(Photo Credit: APEX CAES)


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Oncor Electric Delivery Co. on July 10 filed an application with the Public Utility Commission of Texas (PUCT) for authority to construct a new 345 kV transmission line to connect the Bethel Energy Center in east Texas to the ERCOT grid.

In its application, Oncor Electric requested a certificate of convenience and necessity to construct the double-circuit transmission line to connect the proposed New Bethel switching station in Anderson County, Texas, to a point along one of four existing 345 kV transmission line segments in the region.

Oncor proposed multiple points of connection for the transmission line along the 345 kV Trinidad to Stryker Creek line in Henderson County, Texas; the 345 kV Richland Chambers to Trinidad line in the Texas counties of Henderson, Navarro or Freestone; the 345 kV Big Brown to Richland Chambers line in Freestone County, Texas; and the 345 kV Big Brown to Jewett line in Freestone County.

Oncor said that, depending on which connection the PUCT selects, additional work could be required at the Richland Chambers switching station, Trinidad switching station, Big Brown switching station and Jewett switching station.

In addition, Oncor said that the project would be constructed with double-circuit steel lattice towers with a height of 125 feet.

According to the application, Oncor Electric and Houston-based Apex Compressed Air Energy Storage entered an interconnection agreement to connect the Bethel Energy Center in Anderson County to Oncor Electric’s system.

The Bethel Energy Center is a proposed compressed air energy storage facility that will include two expander trains, each driving a generator capable of producing up to 164 MW of dispatchable electric power, with 328 MW total plant output, and a single electric motor-driven compression train, capable of consuming as much as 151 MW of power at maximum compressor flow.

The energy storage facility will be located above the Bethel Salt Dome, where Apex will create a storage cavern in the underlying salt deposit. When full, the storage cavern will contain sufficient air to generate about 30,000 MWh before recharge, according to the application.

Oncor said that ERCOT conducted an independent economic analysis of the Bethel Energy Center interconnection. Based on a 2020 case, ERCOT determined that interconnection of the new generator would result in $4.7 million to $6.9 million per year in production cost savings.

In the application, Oncor Electric proposed 72 alternative routes, ranging in length from 12.2 miles to 26.6 miles, and ranging in cost from $33.7 million to $63.3 million. The estimated cost of the transmission line construction only is between $26.5 million and $55.7 million, and the estimated cost for the proposed New Bethel switching station is about $7.5 million.

Oncor Electric said that its preferred route is about 13.5 miles long and would cost an estimated $33.7 million for construction of both the transmission line and switching station.

According to the application, while the preferred route is longer than the shortest route alternatives by a little more than one mile, it is the least expensive of the 72 proposed route alternatives. In addition, the preferred route has only three habitable structures within 500 feet of the centerline, it crosses no recorded cultural resources, and there are no currently identifiable engineering constraints that would affect the route.

Oncor Electric estimated that, if the PUCT approves the application, the company would begin construction activities for the project in May 2017, and place the facilities in service in December 2017.

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