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Paper from America's Power: Can't We Just Replace Coal With Renewables? (Hint: No)



December 16, 2019 - A new paper (PDF) from America's Power examines the all-too-common claim that generation from coal-fueled power plants can easily and inexpensively be replaced by generation from renewable sources.  The paper is a direct response to a study submitted to the Indiana legislature's 21st Century Energy Policy Development Task Force, but it also serves broadly as a rebuttal to all studies that make this simple claim.

The paper looks at the Midcontinent Independent System Operator (MISO) territory and explores what would have happened if historic coal generation was replaced with an equal amount of wind generation in 2018.  We found that the MISO system would have been severely strained, with substantial overgeneration during periods of low demand and undergeneration during periods of peak demand.  The undergeneration was so severe that the difference could not have been made up by the rest of MISO’s generators, and would likely have required load shedding and caused power outages.

This is a direct result of the timing of power generation.  Wind power typically peaks in overnight hours when electricity demand is lowest and drops off during the daytime peak in electricity demand, while dispatchable coal units generate when power demand needs them to.  This exercise illustrates how difficult it to plan and operate a reliable grid, and the importance of considering the day-by-day and hour-by-hour needs of the system when considering policy options.  The grid needs dispatchable generators like coal that can provide power when needed.