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Grid Reliability

Written by Dr. Madeleine Roberts
Published on February 13, 2024
Research Highlights

Reliability is the ability of an entire power grid to meet demand.

Demand for electricity is variable, so power generators are ramped up and down to meet demand just-in-time.

A variety of technologies contribute to a reliable power grid, based on each of their strengths and weaknesses.

Reliability of the electric grid is the top priority of stakeholders.

The electric power grid is made of plants that produce electricity, transmission infrastructure that carries power over distances, and a distribution system that delivers power to customers. The “bulk power system” includes generation and transmission infrastructure.

“Reliability” describes an entire grid’s ability to provide adequate power at any time. A reliable grid (FERC 2023, CRS 2019):

  • Provides sufficient electricity generation to meet projected demand
  • Withstands sudden disturbances (e.g. severe weather, national security events) that could lead to blackouts

Peak demand is in the early evening, and in the summer and winter months (CRS 2019).

  • “Baseload” power operate constantly to meet the consistent needs of a power grid. The U.S. uses coal, natural gas, nuclear, hydropower, and geothermal power plants as baseload sources (NEMA 2023).
  • To meet periods of increased demand, sources of electricity generation rapidly increase their output, called “ramping”.

The Federal government oversees the reliability of power generation and transmission (CRS 2022). Distributed energy systems, publicly owned utilities, and distribution systems fall under state and local control.

The North American Electric Reliability Corporation (NERC), made up of 6 regional groups, monitors the reliability of the North American power system (NERC 2023). NERC produces reports on grid reliability for the U.S. Federal Energy Regulatory Commission (FERC). FERC maintains mandatory technical standards for reliability that are imposed on U.S. regional power grid operators.

  • MO is within the Midcontinent Independent System Operator (MISO) and the Southwest Power Pool (SPP) regions.

Based on mandatory reliability standards, the U.S. power grid is very reliable.

  • Most power interruptions come from distribution system failure rather than power supply shortage (NREL 2023, EIA 2022).
  • Widespread outage caused by failure of the bulk supply is typically due to extreme weather and accounts for less than 5% of total service outage time (Eto 2019).
  • FERC recently added reliability standards to improve grid resilience in extreme weather events (FERC 2023).

 

A variety of power generation technologies contribute to a reliable grid.

Sources of electricity include:

  • Dispatchable sources that are constantly available due to a consistent supply of fuel, including coal, natural gas, nuclear, and hydroelectric power.
  • Intermittent sources, including solar and wind, that are not constantly available without paired energy storage. These energy sources are variable based on time of year, time of day, and weather.

Planned retirement of aging power facilities and anticipation of increased demand from nationwide electrification efforts mean that the U.S. power grid will need to add power generation to meet peak demand (MISO 2021).

  • NERC is concerned about lacking capacity in the MISO region in the next 10 years, despite planned resource additions (NERC 2023).

The current grid requires electricity to be generated as it is needed. Wind and solar resources tend to be maximized due to their inexpensive operating costs ($0 fuel costs). When they cannot provide enough power to meet demand, fossil fuel sources, nuclear sources, other renewable sources, or energy storage systems can ramp up to meet demand.

  • Choosing which generators are used to meet demand is dependent on affordability and reliability (Table 1).

Nationally, growth in wind and solar power generation from 1% in 2008 to 13% in 2022 has not caused the grid to become less reliable (EIA 2023, CRS 2022).

The U.S. power system was built around dispatchable sources of electric power that can be called upon at any time to meet demand. Incorporation of intermittent sources into the power grid requires changes to the grid design and operation that include (NERC 2023):

  • Expanding interregional transmission to move power from generation sites to areas of high demand (CRS 2019).
  • “Smart Grid” technologies that monitor and optimize a future grid system (CRS 2018, DOE).

Table 1. Benefits and limitations of reliability and affordability of energy generation sources (CRS 2022).

 

References

Congressional Research Service (2018) The Smart Grid: Status and Outlook.  Library of Congress. https://crsreports.congress.gov/product/pdf/R/R45156

Congressional Research Service (2019) Variable Renewable Energy: An Introduction. Library of Congress. https://crsreports.congress.gov/product/pdf/IF/IF11257

Congressional Research Service (2022) Maintaining Electric Reliability with Wind and Solar Sources: Background and Issues for Congress. Library of Congress. https://crsreports.congress.gov/product/pdf/R/R45764/4

Department of Energy Office of Electricity. Grid Modernization and The Smart Grid. Department of Energy. https://www.energy.gov/oe/grid-modernization-and-smart-grid

Eto JH, LaCommare KH, Caswell HC, & Till D (2019) Distribution system versus bulk power system: Identifying the source of electric service interruptions in the US. IET Generation, Transmission and Distribution, 13(5), 717–723. https://ietresearch.onlinelibrary.wiley.com/doi/10.1049/iet-gtd.2018.6452

Federal Energy Regulatory Commission (2020) Reliability Primer. https://www.ferc.gov/media/reliability-primer

Federal Energy Regulatory Commission (2023) FERC Finalizes Plans to Boost Grid Reliability in Extreme Weather Conditions. https://www.ferc.gov/news-events/news/ferc-finalizes-plans-boost-grid-reliability-extreme-weather-conditions

Midcontinent Independent System Operator (2021) ISO Electrification Insights. https://cdn.misoenergy.org/Electrification%20Insights538860.pdf

National Electrical Manufacturers Association. Baseload Generation. https://energytransition.nema.org/baseload-generation/

National Renewable Energy Laboratory (2018) Renewable Energy Data, Analysis, and Decisions: A Guide for Practitioners. Department of Energy. https://www.nrel.gov/docs/fy18osti/68913.pdf

North American Electrical Reliability Corporation (2023) 2023 Long-Term Reliability Assessment. https://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/NERC_LTRA_2023.pdf

U.S. Energy Information Administration (2023) Annual Energy Outlook 2023: Narrative. Department of Energy. https://www.eia.gov/outlooks/aeo/

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