Transmission 101: Exploring the Hidden Currents

By Joni Sliger, Energy Fellow

"Photoshop art created from two NREL-Image Gallery photos of
sunset view of electrical power towers combined with wind machines."
Credit: NREL and Raymond David (Photo Illustration)

Hailed as the world’s largest machine, our nation’s transmission and distribution infrastructure is a critical component of our electricity system. These power lines carry electricity from every electric power plant to every electricity consumer. Investing in this infrastructure is necessary for the transition to a clean energy future. This blog series explores the issues surrounding transmission, both nationally and in the Pacific Northwest, and considers various options for meeting our transmission needs in the 21^st century. This first post offers a basic introduction to transmission in the United States.

What is Transmission?

Transmission, in the electricity world, refers to the flow of electricity from its generation source, like a power plant or a wind farm, to a local substation, typically over long distances. The infrastructure that carries this electricity is the transmission system. At the substation, the transmission system connects to the distribution system, which carries electricity on to consumers. One may view a map of the nearly 200,000 circuit miles of transmission lines in the U.S. on the Energy Information Administration’s U.S. Energy Mapping System.

As electricity travels on a power line, some of it is lost due to inefficiencies in the system. For example, power lines may unintentionally produce heat, which uses up some of the electricity on the line. Heat losses are a common problem: consider the remarkably inefficient incandescent light bulb, which loses 90% of the electricity it draws to unintentionally producing heat. The energy lost in transmission or distribution is called a ‘line loss.’

In the U.S., 5 to 6% of the electricity generated is lost due to line losses nationally. Inside Energy provides an interactive graphic of the line losses in each state; Wyoming loses the least power at only 2.2%, while Idaho loses the most at 13.3%. Losses vary depending on whether a state has more transmission lines or more distribution lines. Transmission lines travel farther distances than distribution lines, but they have fewer line losses, because they operate at a higher voltage. High-voltage lines can carry more electricity to consumers, ensuring more sales. However, the voltage is too high for household use, so transformers reduce the voltage at the substation and along the distribution system.

To sum up, transmission and distribution lines carry power from a generating source to a user. Transmission lines carry power farther distances but are more efficient, because they operate at a higher voltage than distribution lines.

What are the Problems with Transmission?

With almost 200,000 miles of transmission lines in the U.S., one may be surprised to hear that a lack of transmission capacity is a major constraint to bringing renewable energy sources online. Unfortunately, our current transmission system suffers significant limitations.

Time plays two roles in affecting transmission systems. First, the passage of time decreases the efficiency of transmission systems. Over time, transmission lines suffer physical wear and tear and become less efficient. Additionally, new technologies are discovered, so the lines become outdated. Most transmission lines in the U.S. are based on 1950s technology. Replacing these lines and associated infrastructure with newer technologies is often referred to as ‘modernizing the grid.’

Second, time affects the demands on the transmission system. In the U.S., electricity must be kept operating at 60 Hertz, the frequency of choice for our systems. Grid operators constantly monitor the system to ensure its frequency is stable. If the frequency changes too much, the system crashes, causing brownouts or blackouts. As consumers draw power off the grid, electricity must be available to replace it, so that operators can balance the grid. If more electricity is available than consumers need, producers have to throw it away. Advances in energy storage technologies, like modern battery systems, may soon enable producers to save this excess energy and avoid the use of ‘peaking plants.’ Peaking plants operate only when demand is at a high, even if only for a few hours or days a year; with such limited use, the construction of peaking plants is very expensive relative to the energy they produce. Without energy storage, the transmission system cannot take advantage of changes in energy demands.

Transmission lines can only carry so much electricity at one time. Their capacity varies with the age and efficiency of the technology of the line; newer lines can operate at higher voltages, which allows them to carry more power, while suffering fewer line losses, as noted above. With only a limited amount of capacity available, generators have to compete to get their electricity to the market for sale. A congested transmission system, where too little transmission capacity is available, creates a bottleneck that constrains electricity from getting to where it is needed. Financing the deployment of new sources requires access to a market, so bottlenecks are a significant impediment to possible development.

Where transmission lines are located affects whether generators face a bottleneck or not. Unfortunately, most transmission lines are currently located far away from the best sites for renewable energy development. As my colleague, Amy Schlusser blogged previously, we primarily built our transmission system to carry power from large, fossil fuel-fired power plants to power-hungry urban centers. In rural areas, where the potential to develop renewable energy is often greatest, there is often a lack of available transmission or capacity. In short, our transmission lines are built in the wrong places for a future powered by renewable sources.

To bring more renewable energy sources online, the most obvious solution is to build more transmission lines. This is extremely expensive and faces challenges in siting. Concerns include conflicts with local private property owners (and NIMBYism) as well as conflicts with other needs, such as environmental regulations to preserve wilderness and protect wildlife, such as sage-grouse. Other options exist though, such as more distributed generation and offshore energy development, as I’ll discuss later on in this series. Before discussing possible solutions, however, this series will next look deeper in how the transmission system operates, particularly in the Pacific Northwest, and explore open-access transmission policies, pancaked rates, balancing areas, and more. 

Renewables Too Variable? Here’s One Solution

Credit: Pacific Northwest National Lab and NREL

 By Joni Sliger, Policy Extern

Energy and Environmental Economics (E3) just released a study on the benefits of integrating the grids of California Independent System Operator (CAISO) and PacifiCorp. Together, CAISO’s and PacifiCorp’s grids cover parts of California, Idaho, Nevada, Oregon, Utah, Washington, and Wyoming. The study explores how connecting the grids could enable both entities to avoid inherent inefficiencies in our current energy system.

Many inefficiencies in our energy system arise from one critical flaw: a lack of energy storage. This lack necessitates generating power at the same time as power is consumed. Placing too much or too little on the grid can cause power outages. Unfortunately, renewable energy generation does not provide a consistent output like traditional fossil fuel sources do. A coal or natural gas plant can theoretically operate at a given capacity so long as there is fuel and demand. Wind or solar facilities vary based on the whims of nature, thus earning these sources the name “variable renewable energy.”

According to a report by the National Renewable Energy Laboratory, grid operators can respond to variable renewable energy by increasing flexibility elsewhere in the system. The report suggests operators find ways to reduce or increase supply from other generators as needed. According to the E3 report, some ways CAISO and PacifiCorp have managed variability thus far include building additional facilities to compensate for low renewable energy production and reducing production at other facilities to compensate for renewable energy overproduction. Both strategies translate into higher costs through increased construction and maintenance.

The E3 study reports that integrating the California and PacifiCorp grids could help avoid these sort of inefficiencies, to the tune of saving between $3.4 and $9.1 billion over the first 20 years. Instead of fighting variability by forcing flexibility, grid operators could embrace it. Accepting more variability and developing regional planning schemes seems to be the essence of CAISO’s and PacifiCorp’s proposed integration.

Intuitively, this proposal makes sense. With one wind farm, there is no guarantee of power production during a given period of time. But the wind is always blowing somewhere. With a few dozen dispersed wind farms, at least one is likely producing power. Managing variability in one state is far more problematic than managing variability across seven.

With an expanded “footprint” (the term for an area where the grid operators can reach), grid operators can reliably anticipate at least some minimal renewable energy production at any given time. Additionally, when renewable energy production is much higher than anticipated (“renewable overgeneration”), the expanded footprint enables operators to disperse (and sell and profit from) excess energy over the wider area with less risk of grid overload.

In addition to pure cost savings, integrating the two grids might even reduce greenhouse gas emissions. A brief explanation on the E3 study notes that doing so enables more renewable energy facilities to have access to a market and come online. Additionally, integrating would enable renewable energy to more easily displace even distant fossil fuel facilities. The E3 study did not investigate overall reductions in greenhouse gas emissions, but the explanation notes one assessment predicts integration could help lower emissions by almost 2.6 million metric tons every year. It is unclear how much of that reduction is separate from the overall push for various state Renewable Portfolio Standards.

Overall, though, it is clear that integrating the grids could improve the overall energy system while saving consumers money at the same time.

The Clean Power Plan and Grid Reliability: Fostering the Transition to a Modernized Transmission System

By Amelia Schlusser, Staff Attorney

The debate over the potential impacts of EPA’s proposed Clean Power Plan on grid reliability is gaining steam. Critics contend that the proposed rule calls for hasty and drastic changes to the nation’s electricity resource mix, which will result in widespread retirements of coal-fired power plants and increased deployment of renewable resources. The reliability debate centers around the fact that baseload resources, such as coal plants, provide stable and predictable electricity, while renewable resources, such as wind and solar power, provide variable and intermittent power. Therefore, the argument goes, replacing coal plants with variable renewable resources may jeopardize the reliability of the electrical grid.

The reliability debate first made headlines following the release of the National Energy Reliability Corporation’s (NERC) Initial Reliability Review of the Clean Power Plan, which voiced concerns that the rule could compromise the reliability of the power grid. NERC’s report recently made headlines for a different reason. According to Greenwire, the Energy and Policy Institute recently criticized NERC for failing to disclose that Energy Ventures Analysis, a contractor that worked on the NERC report, had ties to a coal technology company. However, there is little evidence that this potential conflict of interest actually influenced NERC’s findings regarding reliability impacts.

Meanwhile, politicians, regulators, and industry representatives are becoming increasingly vocal on the potential reliability impacts of the Clean Power Plan. On March 11, regulators from Wisconsin, Wyoming, and Indiana told the U.S. Senate Environment and Public Works Committee that the proposed rule would threaten grid reliability in their states. According to Greenwire’s coverage of the committee meeting, the commissioner of the Indiana Department of Environmental Management, Thomas Easterly, noted that he was very concerned “that we will see some catastrophic results somewhere in the implementation of this plan.” Senator Jim Inhofe (R-Okla.) also argued that the rule would threaten the reliability of the grid. Jeff Burleson, Vice President of System Planning at Southern Company, recently issued a statement asserting that the Clean Power Plan will jeopardize grid reliability.  Burleson claimed that the rule would “potentially put serious reliability and operational pressures on the grid,” and that “it does so under the guise of ‘environmental compliance’.”

NRDC’s John Moore argues that the reliability argument is a bluff intended to reduce utility compliance obligations under the Clean Power Plan. Moore’s blog specifically focuses on Southern Company’s claim that the rule will jeopardize grid reliability, which is not the first time the utility has made this argument in response to new environmental regulations. Moore points out that in 2011 Southern Company argued that EPA’s mercury and air toxics standards would cause “numerous rolling blackouts” starting in 2015. In 2014, however, the company stated that it was 98% in compliance with the standards, and as of 2015, the rolling blackouts have failed to materialize. 

It’s unclear whether the Clean Power Plan’s critics are intentionally crying wolf by asserting that the rule is incompatible with the reliable delivery of electricity. However, it is clear that these reliability challengers are failing to fully consider available technologies and strategies that utilities and grid operators have successfully implemented to maintain reliability under high penetrations of renewable generation.

The reliability challengers are also overlooking the energy sector’s ability to develop innovative solutions to respond to grid reliability constraints. Utilities are investing in smart grid improvements and other technologies to facilitate integrating renewable energy onto their systems. For example, one of my previous posts discussed how Idaho Power Company developed and implemented a new forecasting tool that has improved the utility’s ability to integrate wind energy onto the grid at a cost savings of approximately $100,000 a month.

Grid operators throughout the nation are also developing strategies to integrate increasing amounts of renewable energy onto the grid without impacting reliability. For example, Columbia Grid and Northern Tier Transmission Group initiated a Wind Integration Study Team, which in turn created a Dynamic Transfer Capability Task Force to assess the potential impacts of increasing dynamic transfers of electricity between balancing areas to integrate variable renewables and maintain grid reliability. And a recent report by Navigant Research estimated that utilities would spend $107 billion through 2023 on “synchophasors and wider-area situational awareness systems” which enable grid operators to collect and transmit data and rapidly identify grid disturbances before outages occur. These innovative grid improvements help maintain reliability and functionality, and according to the North American Synchophasor Initiative, these technologies provide significant benefits for integrating intermittent renewable resources.

These examples describe only a few of the countless efforts to improve and modernize our national grid systems to accommodate the evolving U.S. energy mix. These efforts help to demonstrate the electricity sector’s ability to proactively address emerging system constraints and develop innovative strategies to maintain grid reliability. Once finalized, the Clean Power Plan will shift the composition of the electricity generating mix in the country. However, this shift will be supported by the deployment of advanced grid technologies and innovative operational strategies that will ultimately improve the functionality of the grid and help facilitate the transition to a clean, sustainable energy system.