By Ric Austria

(This Blog presents the salient points of a presentation made to the North Carolina Utilities Commission in 2022 on the subject. A redacted version of the presentation can be found at this link. The author is Executive Principal at Pterra Consulting, and has conducted courses on Transmission Planning and related topics for over 40 years. He pioneered the concept of planning for Robustness and Flexibility, which are discussed further in this Blog.)


Transmission planning is changing. That is to say, it has always been changing, evolving to adapt to the changing electric supply and delivery landscape. From the early days of PURPA to deregulation to the development of energy markets to the first wind farms and on to zero emissions target portfolios, inverter-based resources, storage, offshore wind, high-voltage direct current (HVDC) transmission, distributed generation, data centers, and more, the building blocks for transmission plans have been constantly changing. In parallel, the perceptions on the role of electric energy in global commerce and livelihood, the desire for a greener energy mix, the acceptable costs for maintaining reliability and the aim for sustainability and resilience have likewise been factors for change. Furthermore, the end-game calls for electric transmission and the “ugly” structures that enable the transfer of potent energy have grown louder: that the future is in microgrids or beamed transmission, or portable energy sources, and other non-wires alternatives, and hence, that we need those towers and poles less and less, and eventually not at all. Perhaps, but not just yet, not by far. For the moment, whether that be a brief one or a longer timeframe, we still need to plan for transmission. To do so, we need to have a proper process for transmission planning, one that is appropriate for the present time to address the needs and objectives that we value today.

Recently, the prime drivers for change in the USA are federal and state mandates for improved planning, use and management of transmission systems. FERC’s initiative for an improved planning process to state mandates for various targets on solar, storage, offshore, mini-nuclear, and the like, are now necessary and important considerations in planning. (The FERC NOPR and examples from New York, New Jersey and California are discussed in more detail in the linked slide deck.)  Significant elements of these mandates, to name a few, are: “right-sizing” replacement transmission lines, consideration of advanced technologies, coordinated planning across states and regions, impact of distributed generation, unified planning models, and public policy transmission needs. These considerations introduce significant, even game-changing and paradigm-shifting, factors in developing transmission plans. However, the desired attributes and features for such plans can still be generalized into the following three key characteristics:

  1. Long-term viewpoint. Transmission lines have 40-plus years of effective lifetimes and plans need to account for at least a significant portion of that period.
  2. Plans need to provide for a future transmission grid that maximizes the desired attributes, or, if stated from the orthogonal perspective, that poses the least regret.
  3. Because the future is uncertain, the plan needs to have a built-in roadmap that provides for alternate tracks for when less expected events take place.

And yet, there is more. While not yet widely accepted, there is a growing and insistent demand to design transmission systems, not based on a capacity model but on an energy model. The capacity model for the transmission system is embodied in the so-called Umbrella Principle, which states that “if an electric grid is able to reliably withstand extreme conditions such as high peak demand, and uncustomary climate and/or market conditions, then it can reliably weather any other operating condition.” The thin membrane represented by the fabric of the umbrella defines the capacity boundary within which the grid operates reliably. The capacity model leads to transmission plans that are defined by extreme conditions of use. Energy planning, in contrast, relies on the application of advanced technology and non-wires alternatives, such as dynamic line rating, programmable storage, power flow controllers and advanced distribution management systems, among others, to mitigate extreme grid operating conditions. The least-cost objective of energy planning is thus modern technologies and programs in combination with transmission infrastructure plans. Energy-based transmission planning is starting to appear in the industry such as in the energy headroom measurements posted by New York utilities and the Energy Storage NOPR released by FERC.

Needless to say, there is much in flux in transmission planning processes. Some of the best practices that we can note are:

  • Coordinated planning involving more stakeholders, including state and local agencies, generation developers, customer groups, banks, regulatory agencies, research and development institutes, taxation authorities, etc. While not all parties can participate in the detailed simulation and modeling aspect of transmission planning, their input and oversight enable a broader perspective than the traditional centralized planning process.
  • Involvement, if not actual integration, of distribution planning. A significant portion of new and planned energy resources are smaller scale, interconnecting at distribution voltages. The issues of net metering, backfeed and upramp/downramp capacities have a significant impact on transmission systems.
  • Broader study sets. As noted earlier in this Blog, system use is changing. Even when still applying the Umbrella Principle, the number of unique conditions for grid stress has increased, necessitating more models and more simulations of future conditions.
  • Directed renewable development. Two efforts to attract the development of renewables where existing and planned transmission capacity is or will be available are: (1) renewable energy zones, or REZ, where bulk transmission capacity is planned ahead of supply availability to attract developers, and (2) hosting capacity and energy headroom which identify where transmission headroom is limited and where utilities may garner regulatory support/approval to expand the transmission to attract future developers. Directed development reduces the uncertainty of planning for the future.
  • Formalized procedures to accept advanced technologies and programs as planning components. Several are ongoing, such as FERC’s efforts to standardize dynamic line rating and utility efforts to use advanced distribution management to interconnect energy-only resources.

The link includes a sample outline for a capacity-based transmission planning process. While this is perhaps still best practice for today, it is easy to envision drastic changes to the process as the broader considerations discussed in this Blog have noted.