This is not quite correct. ERCOT does import/export power to other grids across DC tie lines (see this doc for details, there's a DC tie at Oklaunion):The Annoyed Man wrote:I was watching a TV show either on Discovery or NatGeo a while back about power generation in the US. What I found interesting was that they showed a picture taken from space which depicted North America's power generation and distribution grid. Virtually the entire country shares power back and forth with Canada. The lone exception was Texas - which is apparently energy self-supporting, and neither imports nor exports electricity between itself and the rest of the nation. With the exception of part of the panhandle, you can see in the image below that Texas is energy independent. (The website I got this image from thinks this is wrong and advocates forcing Texas to come into the national grid.)
http://www.ercot.com/content/mktrules/g ... s_v3r2.doc" onclick="window.open(this.href);return false;
Though a 220MW tie is really just a drop in the bucket for ERCOT power (which most recently peaked at over 65000 MW in February during the cold spell). DC is used because the Texas grid runs on its own 60 Hz cycle, and that cannot be connected to other grid's 60 Hz cycles (they are out of phase with each other).
To me, the grid division is more about system stability. Control areas exist in order to maintain a stable system frequency (60.000 Hz ideally, but it's not quite that easy), while matching generation to load. Texas has a fairly good match between generation and load, but until some of these new plants come on line, it seems to be getting thinner and thinner. ERCOT seems to be cutting the 'required reserve margin' every few years, and we seem to dip in to it fairly often these days.