Overlapping transmission grids in West Texas will give power plants the power to choose

Michael Giberson

At the Gulf Coast Power Association meetings last week in Houston, Jay Caspary of the Southwest Power Pool (SPP) was discussing transmission expansion plans, and at slide 20 offered a map showing the overlapping transmission plans of SPP and ERCOT.  The purple lines are proposed 765 kV lines in SPP, the red lines are proposed 345 kV lines in ERCOT.

This slide was by far my favorite from among the numerous slides shown at the conference.

Caspary_GCPA_2009_p20

(Clicking on the image should bring up a larger view at Flickr. You can also download the full Caspary presentation from the GCPA website.)

Typically, neighboring transmission grids don’t overlap in this way. Usually at the transmission level grids have clear boundaries, meaning that generators (and transmission-scale load connections) don’t have much of a choice as to which transmission system to hook up with.  Or rather, more precisely, the choice of a site embeds the choice of the transmission system to link to.

The prospect of two separate, high-capacity transmission systems serving the same area means that generation units in the area will be able to choose which system – SPP or ERCOT – that it sells its power into. In fact, as in the case of the Tenaska Frontier generating plant, generators in the Texas panhandle might even connect to both systems and sell power in both directions at once.

Given the location – with its good wind resource and limited water supplies – it is likely much of the new generation resource development in the region will be wind power.  Having dual connections will not only add a strategic option to the wind power plant developer, but also aid the ability of the two power systems to accommodate the variable power supplies at lower cost.

And if you check out Caspary’s following slide, which shows a bigger area, it isn’t too hard to imagine a third possible delivery alternative for power plant developments in the area.

[ADDITIONAL NOTE: The ERCOT expansion plans are pretty established. Regulatory approval has been granted and contracts are being put in place to build the new lines. My understanding is the the SPP plans are at a more preliminary stage, and other options are also under consideration. But since SPP already has transmission infrastructure in place, the result will be overlapping transmission grids. The question is just how good the SPP transmission capacity will be.

For those of you wondering where Lubbock, Texas is, it is just south of the southwesternmost point of SPP’s planned expansion, shown in purple in the image.]