Presidio NaS Battery Project

Electric Transmission Texas, LLC (ETT) has completed a contract with NGK-Locke, Inc. for a state-of-the-art, sodium-sulfur 4-megawatt NAS® battery system, which will be installed in Presidio, Texas. ETT is a joint venture between subsidiaries of American Electric Power (NYSE:AEP) and MidAmerican Energy Holdings Company (MidAmerican). ETT acquires, constructs, owns and operates transmission facilities within the Electric Reliability Council of Texas (ERCOT), primarily in and around the AEP texas Central Company (TCC) and AEP texas North Company (TNC) service territories.

The NaS battery will be the first in Texas and the largest in the United States and represents part of a $67 million overall commitment by ETT to improve transmission reliability in Presidio and surrounding areas.

The battery, along with construction of the Gonzales substation, is currently scheduled to be completed by the first quarter 2010 in time for summer peak usage. Cost of the battery and substation is estimated at approximately $23 million. A 60-mile, 69-kilovolt transmission line from Marfa to Presidio is targeted for completion by 2012 with an estimated cost of approximately $44 million.

The NAS® battery system uses sodium-sulfur battery technology. This technology proposed by ETT for Presidio will provide the following benefits:

• Due to its quick response, the battery will address voltage fluctuations and momentary outages.
• In the event of an outage on the radial transmission line providing power to Presidio, the battery can supply four megawatts of uninterrupted power from Comisión Federal de Electricidad (CFE) during emergency situations.
• The battery will allow for maintenance on the new transmission line being built from Marfa to Presidio without loss of electric service.

Documents

• September 1 Press Release (PDF)
• NaS Battery Overview (PDF)