Senior Energy System Modeler and Analyst, Vibrant Clean Energy

Joshua Rhodes


Director of Regulatory Affairs, First Solar

Colin Meehan

Interviewer:  David Spence, August 7, 2019

Keywords: ancillary services, frequency control, inverters, rotational inertia




Keeping the Lights on in a High-Renewables Electric Grid

by Joshua Rhodes and Colin Meehan

Rhodes: “Inertia is traditionally how we maintain grid frequency … If we have a [sudden] loss of supply, … that can be a problem. ‘Inertia’ refers to the spinning of the steel shafts inside power plants [which] keep spinning, and that gives the grid enough time to react, and to [re]match supply with demand. … What we found in this paper is that we could get up to about 30% of total energy in ERCOT from wind and solar and not run into the inertia constraint. … Beyond 30% we do run into times when the inertial constraint becomes binding, meaning that the model has to do other things to keep [the system in balance]. … What the model does is bring additional plants on line to keep the system in balance. … [However,] emissions can rise in those instances.”

Meehan: “Renewable energy can provide services that are equivalent to inertia, like ‘fast frequency response.’ … Today we have a market where the ancillary services rules don’t enable the [full] participation of renewables. … The technical capability is there, but the markets just aren’t there. … It’s one of the real difficulties for developing a market for a totally different set of [renewable] technologies.”

Rhodes: “The inertia level is set … based upon possibility of losing the largest project, the South Texas nuclear plant. If we remove that constraint , it allows us to get more renewable energy on the system because the inertia requirement is lower. … But our carbon emissions go up because a lot of those megawatt-hours are made up by coal and natural gas.”

Meehan: “As you increase the use of solar project capabilities … the ability to ramp up and down depending on system needs, you can dramatically increase the ability of the system to incorporate solar power and still reduce ratepayer costs … What this shows is that if we want to really take advantage of inverter-based resources [wind and solar], we need to design markets that incorporate these capabilities.”

Joshua Rhodes joins is a Senior Energy System Modeler & Analyst. His current work is in the area of smart grid and the bulk electricity system, including spatial system-level applications and impacts of energy efficiency, resource planning, distributed generation, and storage.

Colin Meehan is Director of Regulatory and Public Affairs at First Solar, with responsibility over Texas and the eastern U.S. Most recently, Mr. Meehan led Comverge, Inc.’s demand response regulatory and market strategy in Texas and California. Prior experience includes serving as Environmental Defense Fund’s Policy Manager for U.S. Climate and Energy.

To learn more about Josh Rhodes and Colin Meehan, please visit Josh Rhodes’ home page: HERE and Colin’s home page: HERE

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