Partially driven by clean energy and other policy goals, the electric industry is transitioning from legacy power plants to wind, solar, and other renewable resources. These renewable resources are often built in different locations from traditional ones and at a much faster pace. Developments in the past two decades suggest these renewable resources can be replaced at a much faster rate, and also distributed, leading to uncertainty in future locational transmission needs. In addition to this broad resource transition, load growth in many jurisdictions is limited, if not negative. Distributed energy resources (DERs) contribute to lower load growth while making the load profile more dynamic. For instance, high solar photovoltaic (PV) penetrations can cause former load centers to suddenly become exporters.
These changes have resulted in very different transmission needs from the past. The model of building transmission paired with large central generators to serve growing load may no longer be justified. However, transmission is a core sector of the power industry and the need to transfer power will remain for the foreseeable future. Fortunately, there are alternatives to building new transmission assets to accommodate the paradigm shift.
Traditional thinking treated transmission as if it is fixed and cannot be operated dynamically. In certain ways this is true. Transmission has a fixed capacity, much like roads do (that is, the number of cars that can go through at any given time). However, advancements in maps and GPS technology have allowed for easier and more efficient driving on the same roads. There are similar technologies that allow for such innovation in transmission operation.
Developed in recent years, these operation enhancement technologies (technology options) have been supported by advancements in power electronics, communication devices, computational processing power, and optimization algorithms. Similar to the comparison between building a road to reduce congestion (long-term investment) and having a good map/GPS system to avoid congested roads (operational improvements), these technology options that focus on operational improvements have a much lower cost with faster implementation.
These new technology options are generally of two types.
The first technology option type focuses on more accurate measurements and projections of transmission operating conditions. This is much like setting the speed limit of a highway under anticipated snow conditions. Understanding the local road conditions and adjusting the speed limit accordingly is better than conservatively assuming that it can snow at any time and permanently setting the speed limit at 40 mph.
One example of the first technology option type is dynamic line ratings (DLR). DLR provides more accurate capacity ratings (that is, the amount of power that can flow on a line) for individual lines under a given set of system and environmental conditions. It uses real-time line temperature and/or sag measurements to determine the line rating. For example, windier conditions increase cooling effects and can accommodate a higher flow without overheating the line. Practical DLR implementations require rating forecasts in addition to real-time measurements to aid in making operations decisions.
The Belgian transmission system operator Elia has deployed a utilitywide DLR system with sensors on 30 transmission lines. This has increased exchange capacities with France, Netherlands, Luxembourg, and Germany. Elia discovered that DLR provided savings of about €0.25 million (US$0.28 million) during a single four-hour congestion event by allowing for the additional import of 33 MW.
The second technology option type focuses on the flexible and dynamic control of transmission systems to optimize existing assets’ operations. This is similar to driving with a good map or GPS and avoiding congested roads. Flexible Alternating Current Transmission Systems (FACTS) — a common name for power electronic-based devices that allow for flexible and dynamic control of transmission systems — are examples of hardware solutions to control flow on the transmission network.
Distribution network operator UK Power Networks is testing modular FACTS power flow control devices. The first pilot installation solved a critical bottleneck on a 132-kV power line in southeast England. It has enabled an additional 95 MW of renewable sources to be connected to the system without building new electrical cabling and substations. The pilot, which began in 2018, has saved customers over £8 million (US$10.4 million) to date.
Transmission topology optimization is an elegant software alternative to flow control hardware. It enables flow control by adjusting the system topology (that is, opening or closing existing circuit breakers). This changes the flow distribution, defined by Kirchhoff’s Law, to achieve operational objectives. Topology optimization software supports operator decision-making analogously to how a GPS supports drivers. It finds the best routing options for current or forecasted system conditions.
Great Britain system operator National Grid ESO studied the feasibility and impact of using topology optimization algorithms to support its operations processes. The study used historical data from 2016 and 2017, and demonstrated that optimizing the network configuration could increase transfer capacity across large, heavily binding transmission constraints by 3% to 12%. This saves end users £14 to £40 million (US$18.2 to US$52.2 million) annually.
The benefits do not end here. These technology options complement building new lines. This is similar to the way that better maps and GPS technology do not replace the need for building new roads but enable more efficient use of existing roads to ease congestion during the construction of new roads. The technology options can magnify the cost-effectiveness and capabilities provided by new investments. For example, existing low-capacity lines can limit the use of high-capacity transmission investments. Using the new technology options to relieve power flows on low-capacity lines can better use the new high-capacity lines, yielding a more favorable benefit/cost ratio. The technology options also provide short-term solutions to temporary challenges, such as during transmission outages or the construction of new lines. They can bridge the gap until permanent expansion solutions can be put in place.
As the above examples illustrate, these technology options reduce transmission congestion costs and renewable curtailments significantly — sometimes eliminating them entirely. Partially because of the aforementioned industry transition, transmission congestion and its associated costs have been increasing. This can hinder utilities from achieving their goals or result in unwanted rate increases for end users and potential stranded costs for developers and utilities.
A number of projects and studies suggest that wide deployment of these technology options can provide economic benefits ranging from €10 to €100 million (US$11.1 to US$111.2 million) annually for an average transmission or distribution system operator of 100-kV+ assets, even before considering the additional benefits of complementing new builds. Overall, the need for operational technologies will likely rise as the pace of the industry’s clean-energy transition accelerates. Utilities and system operators should consider taking advantage of these newly available and proven technology options that enhance transmission operation to continue their successful transition to a new paradigm, as they have demonstrated their capability of adopting their generation operations to integrate large amounts of renewables within the last decade.
