19 Rules for Transmission
Lessons Learned in Wind Generation
In 2002 when the Midwest Independent Transmission System Operator (MISO) started to address wind integration issues, dominate attitudes prevailed that wind was too intermittent to be a major source of power and energy. Wind was forecast to never provide more than 10,000 MW of connected generation in the MISO and SPP areas. Today, MISO alone has 10,000 MW of wind connected to the transmission system. The major driver was that MISO and others adopted the attitude to determine what could be done with wind generation and not what could not be done with wind generation. The lessons learned to date are discussed in this article.
LESSON 1: Transmission planning must include more than reliability considerations. Wind generation is primarily an energy resource and not a capacity resource that can be relied upon to deliver energy on at the time of peak or on demand. Wind energy is mainly produced at night and in the off-peak seasons. The transmission required to deliver wind energy must be planned for state renewable policy compliance, economics, and off-peak delivery of energy as well as capacity.
A portfolio of 17 multivalue projects (MVP) worth US$5.2 billion were approved in 2011 by the MISO Board of Directors to deliver up to 21,000 MW of wind energy, provide congestion relief by improving energy market efficiency, and avoid the cost of generation by raising the capacity credit of wind generation, thus avoiding other generation construction and other values (see Figure 1). The benefit to cost ratio of the transmission over 20 years is 1.8 to 1. The set of 17 lines was approved as a group. The dependence of lines 7–11 can be seen as they are all in line linking the lower cost energy in western MISO to eastern MISO. Taken one at a time, it is very difficult to justify transmission expansion for other than reliability purposes.
MISO is guided by a set of principles established by the MISO Board of Directors. These were created to improve and guide transmission investment in the region and to furnish an element of strategic direction to the MISO planning process. Certain conditions precedent to the construction of transmission is also required. Without the conditions precedent, the MVP lines could not be approved for construction.
MISO’s Guiding Principles
The guiding principles of MISO are as follows:
- Make the benefits of a competitive energy market available to all customers by proving access to the lowest possible electric energy costs.
- Provide a transmission infrastructure that safeguards local and regional reliability and supports interconnection wide reliability.
- Support state and federal renewable energy objectives by planning for access to all such resources, including wind, biomass and demand side management.
- Provide an appropriate cost allocation mechanism.
- Develop a transmission system scenario model and make it available to state and federal energy policy markets to provide context and inform their choices.
The transmission must meet a number of conditions precedents to construction to be approved:
- a robust business case
- increased consensus on regional energy policies
- a regional tariff matching who benefits with who pays
- cost-recovery mechanisms to reduce financial risk.
LESSON 2: Wind generation is a social choice, not an economic choice, required primarily by state legislation in the MISO region. Transmission is designed to deliver energy (including wind energy) at the lowest cost to the customer, as well as generation capacity for reliability. Federal programs enhance the economic choices that support the state renewable portfolio standards decisions.
LESSON 3: Decision makers have to be invited to the question and not just be involved after an answer is proposed.
The Midwest Governors Association, the Organization of MISO States (state regulators), MISO stakeholders, and staff worked together to choose renewable energy zones on which to locate the 345 kV substations. Those substations collect wind generation and deliver it over a network of primarily 345 kV lines to the load.
The total cost of energy delivered and the economic benefits of wind generation development to the local economy were considered. More than one-third of the cost of a wind generator installation is estimated to be delivered to the state economies during its first year of operation. The social choice of choosing wind extends to the choice of obtaining the economic benefits from wind generation construction.
LESSON 4: A long-range transmission plan that serves as a road map to the future is required. The regional generation outlet study (RGOS) map in Figure 2 is the MISO long-range transmission plan with the 25,000 MW total renewable energy zones connected to deliver energy at low cost to the customers. The RGOS is designed to deliver the total 25,000 MW of wind regional portfolio standards and other generation by the year 2025. The generation may locate anywhere they wish if they wish to pay for the transmission to connect to the cost shared transmission. The MVPs are the first step in implementing the RGOS
Interconnection Queue Procedures
LESSON 5: Robust interconnection queue procedures are needed to add order and obtain processing efficiency for studying and interconnecting the proposed generation. These procedures should align with the overall development of the generation project and should facilitate transmission access for projects that are ready to be built. The free market system does not produce the lowest cost of energy to the customer without some rules and order.
MISO has 10,000 MW of wind registered in the energy market that has been designated for connection through the generation interconnection queue study processes. Most of the wind generation has been connected to existing transmission that required modest transmission upgrades. The lower cost options have been used, so the next level of interconnections requires higher costs, more cooperation through cost allocation of transmission, and improved queue processes.
Operation and Market Practices Integrate Wind Generation More Economically
LESSON 6: Large balancing areas ease the integration of wind.
MISO consolidated 25 balancing areas operating prior to formation of the energy market into one balancing area after the energy market was formed. Having one control area shifts the responsibility of smaller balancing areas with relative high levels of wind generation compared to load to the larger single balancing area with a relatively low level of wind generation compared to load.
LESSON 7: Shorter dispatch periods reduce problems in integrating wind.
Before the energy markets were established in MISO, the time between changing the dispatch on the power system was one hour. The energy markets operate on a 5-min period. Shorter dispatch times reduce the error of forecasting wind generation and load.
LESSON 8: Geographical diversity reduces wind and load variations to improve the wind product, but transmission is required.
LESSON 9: Transmission does not need to be constructed to deliver 100% of rated wind output.
- MISO has a 6% wind curtailment on energy.
- Full wind output does not exceed 85% of the connected wind output.
LESSON 10: Geographical diversity adds to the capacity credit for wind.
The capacity credit for wind has gone from 8% in 2009 to 13% in 2011. The increase comes from the installation of wind in a diverse pattern across the MISO footprint. Higher capacity credits for wind mean that less generation of other types need to be built to provide a reliable generation resource at peak load.
LESSON 11: Ensembles of wind forecasts are necessary.
Wind forecasts using different methods produce different times and magnitude that a ramping event may occur. The timing is the more significant error for the system to respond. The different forecasts may be better for certain conditions than others. The dispersion of forecasts may require that more reserves be on line to handle the uncertainty that may occur.
LESSON 12: Local economic development and job creation off shore and local wind will limit wind development in the high plains.
LESSON 13: There are existing storage capabilities on the existing Manitoba Hydro Electric Board system. Studies have identified the conditions necessary for compressed air energy storage and other energy storage to feasible on the MISO system. More wind may allow less storage.
LESSON 14: The primary benefit to high-voltage dc (HVdc) is the ability of HVdc to affect the energy markets as energy market price signals dictate. HVdc is more effective than ac solutions to change market prices and provide the suppliers and the receivers of energy benefits.
LESSON 15: HVdc interconnections are easier to plan and cost allocate than ac interconnections in a single market or multiple markets.
LESSON 16: Cost allocation, free ridership issues, and congestion between terminals is easier to manage with HVdc than ac.
LESSON 17: Voltage source converter type HVdc has the capability to transfer power variability from wind resources from relatively weak transmission areas to loads.
LESSON 18: Single HVdc lines may be rated at 1,500 MW or lower to be able to work within the present operating reserve levels of MISO.
LESSON 19: Crude estimates indicate that it may be economically feasible to underground multiple HVdc lines or poles to transmit about 10,000 MW or more.
Wind generation has been and appears to be able to continue to be integrated successfully into the power systems by adapting the planning, operations, marketing, regulatory, and state renewable portfolio standards processes for the benefit of the region as a whole.