National Renewable Energy Laboratory

Energy Analysis Office

Cost of Wind Transmission Access Data

One of the primary goals of the Wind Deployment Systems (WinDS) model is to address, in a more detailed approach than typically attempted, the transmission issues related to implementing wind power in the United States. The existence of transmission capacity across the United States varies greatly. For example, transmission lines are more prevalent in the northeastern states than in large, sparsely populated western states such as Nevada. The availability of existing transmission lines also varies considerably from one line to the next and from one hour to the next. Furthermore, the cost of developing remote wind resources in such areas with few and/or fully occupied transmission lines can be significantly higher than the cost of developing wind resources close to existing transmission lines with excess capacity. This section includes the results of a Geographic Information System (GIS)-based analysis of the cost of connecting potential wind resources to existing transmission lines with excess capacity.

The results are presented in the form of supply curves for the incremental cost to build transmission capacity from the potential wind resources in a region to the nearest existing transmission lines that have adequate capacity available to carry the generation.

These results were prepared using NREL's GIS system to optimize the allocation of wind resources to the existing transmission grid.

The GIS analysis begins with more than 400,000 wind resource sites and more than 15,000 transmission lines of 69 kV or larger. The size and length of the existing transmission lines are used to estimate their full capacity in MW considering thermal and stability limits. The GIS optimization then minimizes the total cost (including both generation and the construction of transmission line segments connecting the wind site to the grid) of filling the remaining capacity (after conventional generation use of the lines is considered) of the existing lines with wind generation.

The results of the GIS-based optimization are used to construct the supply curves shown in our interactive database. In these curves, the cost is only the levelized cost of building the transmission segment from the wind site to the grid (i.e. the cost of generation has been subtracted from the total levelized cost used in the optimization). By using this approach, the user can add in his/her own costs of generation from wind.

Note also that the costs to build to the grid are specified by wind class. This captures the fact that higher quality Class 5 and Class 6 wind resources are often more remote than lower-quality Class 3 and Class 4 resources. Finally, note that the cumulative capacity is listed for each wind class, not the total wind resource in the region.

Several scenarios were developed which vary:

• The cost of building transmission segments from the wind sites to the grid ($/MW-Mile),
• The fraction of existing transmission line capacity available for wind power (assuming the rest of the line is reserved for existing conventional generation), and
• Either the current wind-power technological performance (costs and capacity factor by wind class) or the projected 2030 values (based on DOE program goals).

Six scenarios were generated including (bold indicates what is different from the base case):

• Base Case: 1,000 $/MW-Mile transmission cost, 20% of each transmission line's capacity available, year 2000 wind costs and performance
• Scenario 1: 1,000 $/MW-Mile transmission cost, 100% of each transmission line's capacity available for new wind power, year 2000 wind costs and performance
• Scenario 2: 700 $/MW-Mile transmission cost, 20% of line available, year 2000 costs and performance
• Scenario 3: 1,400 $/MW-Mile transmission cost, 20% of line available, year 2000 costs and performance
• Scenario 4: 1,000 $/MW-Mile, 100% of line available, year 2030 costs and performance projections
• Scenario 5: 1,000 $/MW-Mile, 20% of the line available, year 2030 costs and performance projections

The transmission line capacity as a function of kV rating and length is drawn from Weiss, Larry and S. Spiewak, 1998, The Wheeling and Transmission Manual, The Fairmont Press Inc., Lilburn GA.