The Electric Reliability Council of Texas (ERCOT) is contending with transmission congestion issues as West Texas electricity peak demand has increased tenfold in the past decade. Rapid additions of solar and wind generation have further complicated matters as the state fast tracks construction of new transmission lines to expand available transmission capacity (ATC).
As the electricity intensive oil industry has expanded in Texas, so has power generation demand as each of its estimated 187,000 operating pump jack motors can require an average of 10,000kWhr a month. Additionally, the Houston metroplex area has seen a population increase of 18% since 2010 stressing electricity supplies along the North to Houston Import region.
Demand has largely been met as solar additions are estimated to double from 2018 to 2019 to meet the estimated 5% demand increase across the state according to ERCOT. Wind additions tripled from 2009 to 2017 and is estimated to generate 19% of Texas’ total fuel mix.
Those capacity additions have helped end thin demand/supply margins in the state where the U.S. Energy Administration’s summer capacity estimates revealed generating resource demand reaching a critical 98.3% of capacity in 2011. Most regions operate at about 80% of capacity during peak load period as having 20% generating capacity in the bank ensures power reliability. Since then, capacity margins have eased year over year with a summer capacity margin of 21% in 2018.
The challenge for ERCOT is not in filling demand by adding new power generating sources but rather in delivering that supply, especially to West Texas’ Permian oil region. The overwhelming load growth of the Yucca Drive-Gas Pad 138kV Line and the Panhandle Export transmission area is in critical need of additional carrying capacity through the introduction of substation upgrades, efficiencies, and new transmission line construction. That load growth, or demand for energy, is only going to get worse with estimates of an 11% increase from 2017 to 2023. As there is no room on the lines now, Texas is scrambling to build new ones.
What happens when demand outpaces supply? First, electricity gets pulled down other lines to make up the difference, and that costs customers. Transmission limitations driven by what are called “power import constraints” in 2018 led to amazing cost increases due “congestion rents”. Those “rents” in the Yucca Drive line amounted to $257 million dollars (for October 2017 through September 2018). The Panhandle region's congestion rents were nearly $164 million.
“Congestion rents” is a rather complex set of calculations based on a number of factors, but for purposes here, they are the excess costs of finding power outside of where it usually comes from to keep the lights on.
According to ERCOT's “2018 Constraints and Needs Report”, West Texas congestion was unique as south to north power flow was high during daytime hours when solar generators were active, then flipped at night to a north-south flow when solar units were largely offline. Though transmission upgrades placed in service in July 2018 served to correct some congestion issues, other unique challenges exist in the West Texas region.
With the significant increase in wind generation in that region, and due to the inverter based design of wind generation, system strength and stability has limited reliable power flow. As ERCOT is studying planned additions of 16,990 MW of wind and solar generation which would amount to an increase of some 300% over the 5,424 MW of such power currently online, transmission expansion and stability has been a central concern.
What this means is that wind turbines weren’t really designed for use on the U.S. grid. The frequency at which they produce electricity just doesn’t match the electrical currents on the grid.
As that tech was originally developed overseas, U.S. wind companies solved the problem by adding components to turn the AC current coming from the turbine into DC current, then back again to AC current to match those frequencies. It works, but it also creates lags in the system when wind generation is not producing at a constant rate which causes so called inertia and ramping problems. A typical power plant spins its generator and can rev it up or down as needed. Wind turbines can’t do that. It’s basically either go, or stop, and ramping up back to “go” takes time.
However, as the quandary of invertor based systems which struggle with inertia and ramping problems will only grow with wind generation additions, solutions are being implemented with success in West Texas.
Improvement projects have already been completed including synchronous condenser installations at both the Alibates and Tule Canyon substations. Without the technical explanation, when voltage decreases from a spinning generator, so does power. A synchronous condenser increases the current flow when voltage is decreasing. What that does is keep the power flowing at a constant rate regardless of whether power generating voltage is going up or down.
A second 345 kV circuit connecting the Tule Canyon, Ogallala, Windmill, AJ Swope and Alibates substations was also completed, though ERCOT admits “they are not expected to eliminate the congestion in the area.” Regardless, the synchronous condensers have provided for power factor efficiencies that have increased substation performance.
Additionally, ERCOT anticipates the planned integration of the Lubbock Power and Light system in 2021, (approved in March of 2018) which will include additional 345kV lines connecting to the Panhandle, will reduce energy transfers out of the area.
Nearer the Permian’s more active oil development region in Midland County, the Bearkat Area Transmission Improvements project approved in October 2018 seeks to alleviate congestion which occurs 51% of the time. The $53 million dollar project will add new 345kV bays at both the Longshore and Bearkat stations and construct a new 27 mile long 345kV single circuit line from the Bearkat to Longshore stations. The Bearkat project is just one of eight planned transmission improvement and construction projects for West Texas to be completed by 2023.
In total, ERCOT spent $2.256 billion on transmission improvements in 2018 and estimated an additional $4.735 in expenditures from 2019 to 2021, which combined will add 1,500 new circuit miles and upgrade and rebuild an additional 3,200 miles.