With multiple wind farms already constructed in Wyoming, more are proposed to take advantage of the state's exceptional wind resources. Multiple interstate transmission export lines also have been proposed to export wind power to distant load centers. The missing piece is a high-voltage collector system connecting the transmission export lines with the wind farms. A Wyoming Collector and Transmission System (WCTS) study presents some options for structuring such a network.

Conceptual Designs

WCTS aims to ensure the more efficient use of available rights-of-way, adopt higher voltages with lower net losses and capital costs, and examine the potential for incorporating a redundant network form of architecture. The WCTS study produced conceptual designs for connecting up to 12 GW of wind generation in Wyoming to the Wyoming terminals of the proposed extra-high-voltage lines. An alternative to this centrally organized WCTS is for each wind farm to build its own generator tie line to one of the new export hubs.

The Wyoming Wind Collector and Transmission Task Force was formed to examine the design concepts. The Wyoming Infrastructure Authority (WIA), Western Area Power Administration (Western), PacifiCorp and interstate transmission line developers — TransCanada, TransWest Express LLC and LS Power — compose the task force. In 2009, WIA retained ICF International to develop the conceptual designs, cost estimates and potential business structures. RetCo, an independent transmission developer, supported the task force with conceptual business structures.

General Principles

Because of the nature of the wind resource, wind generators (e.g., wind turbines) are geographically dispersed. This dispersed feature of wind generation necessitates a design in which the system collects the power generated from individual wind farms, transmits it to export hubs of the interstate transmission lines and, from there, transmits it to distant load centers. The following terms describe the components of the collector system:

• Wind farm: A collection of individual wind turbines within a single development and a single interconnection point to the transmission network.

• Wind hub: A transmission substation where transmission lines from the interconnection points of multiple wind farms converge.

• Transmission export hub: A major substation where transmission lines from multiple wind hubs meet, and it is either the starting or intermediate “uptake” point for an interstate transmission line.

Thus, the fundamental framework for the collector system consists of multiple wind farms connected to wind hubs and multiple wind hubs connected to each transmission export hub. This framework is scaled and replicated as needed to design a collector system for accommodating up to 12 GW of renewable energy in Wyoming.

Resource Scenarios

To frame the analysis, two illustrative resource scenarios were created that are differentiated by location and the amount of wind power development in Wyoming. The first scenario assumes the development of wind generation in a relatively widely dispersed manner in qualified resource areas (QRAs) primarily west of the Laramie Mountain Range. The second scenario covers wind generation within QRAs primarily to the east of the Laramie Mountain Range in a narrow north-south band.

Although the study does not predict or recommend where wind energy will be developed in Wyoming, the two resource scenarios bracket much of the QRAs identified through processes of the U.S. Department of Energy and Western Governors' Association Western Renewable Energy Zones.

For each resource scenario, collector system designs for four different configurations were developed and refined using steady-state power flows and limited N-1 contingency analysis. There are four collector system configuration designs:

• Radial single circuit
• Radial double circuit
• Networked wind hubs
• Networked wind hubs and transmission export hubs.

The study also developed a three-stage process to demonstrate one way of implementing the collector system that considers existing rights-of-way and common elements between the collector system configuration alternatives. The number, order and location of the stages and the collector system design in each stage could change substantially based on the actual location, amount and timing of wind farm development.

Precedent Collector Systems

Two collector systems in the United States are in an advanced stage of development — one is associated with the Texas Competitive Renewable Energy Zones project, the other is tied to the Tehachapi project in California. Collector systems are also proposed in New Mexico, Montana and Alberta, Canada, including the Wind Spirit project by Grasslands Renewable Energy LLC and the Green Power Express by ITC Holdings Corp.

Although useful precedents, the Texas and California collector systems were less challenging to structure commercially since both generation and load were within the same regulatory jurisdiction. Development was greatly facilitated by the large customer base, significant energy consumption resulting in economies of scale and postage-stamp, rate-based cost recovery approved by Texas and California.

In Wyoming, abundant wind energy supply is contrasted with low in-state energy demand. Most wind developments focus on remote export markets. Therefore, the cost socialization model adopted by Texas and California is not a practical business structure for WCTS.

Financing Mechanisms

One alternative to the rate-based, socialized form of cost recovery is a participant-funded model where new wind generators directly pay for utility network upgrades. Because of the scale of development in Wyoming, this model is not generally considered workable. More promising is an independent transmission developer building new infrastructure with the costs recovered from generators through a negotiated rate or merchant tariff.

An alternative to private finance is public finance. Significant portions of the grid are owned and operated through various federal (Western and Bonneville Power Administration), state (New York Power Authority), municipal (Los Angeles Department of Water & Power) and forms of cooperative or unique structures (Salt River Project). Although the governance and financing of these structures are different, they are similar to a utility rate-base mechanism where costs are spread across a broad group of customers. However, in the case of WCTS, a broad regional socialization of costs onto users by a publicly owned structure would be challenging.

One possibility is funding through general federal or state taxation, with no repayment obligation, as in the interstate highway system. Because of the scale of investment and Wyoming's wind operation in a competitive marketplace, this approach, too, is inappropriate.

Several transmission facilities have been developed using some form of public-private partnership. For example, public and private utilities jointly own many existing power sector assets in the West by using a tenants-in-common structure. Another partnership structure is found in Western's borrowing authority and ability to arrange loans for transmission projects under the American Recovery and Reinvestment Act of 2009.