By Ed Reid
The stated goal of the US Administration’s renewable energy transition is to replace all dispatchable fossil-fueled electricity generation and all direct fossil fuel usage with renewable electricity to reduce CO2 emissions. Logically, the first fossil-fueled generation to be replaced would be coal-fired generation, since it emits the largest quantity of CO2 per unit of electricity output.
There has yet to be a successful demonstration of an electric grid powered predominantly by renewable generation. Potential approaches to such a demonstration have been proposed here, here, here and here. However, each of these demonstration proposals would have involved a very extensive and expensive program.
The demonstration challenge proposed here would be a far simpler and less expensive demonstration, not of an entire renewable grid, but only of the direct replacement of a coal-fired generator with renewable generation plus storage sufficient to render the renewable generation the dispatchable equivalent of the displaced coal-fired generator.
Coal-fired generators are historically available to generate electricity at their rating plate capacity approximately 85% of the hours of the year. Therefore, a 100 MW coal-fired generator would be available to generate approximately 745,000 MWhrs (8760 hrs * 0.85 * 100 MW) each year.
Wind generators are historically able to generate at variable capacities up to rating plate capacity as a function of available wind speeds. Total generation in any given month historically ranges from 23-43% of rating plate capacity, averages approximately 36% and may approach or be zero for periods of hours or days. Therefore, a wind generation system capable of providing 100 MW capacity generation 85% of the time would require rating plate capacity of approximately 300 – 400 MW and storage sufficient to store excess electricity generated when the wind is blowing for use when the wind is not blowing or is blowing at lower speeds.
Solar generators are historically able to generate at variable capacities up to rating plate capacity as a function of available solar insolation. Total generation in any given month historically ranges from 13–32% of rating plate capacity, averages approximately 25%, may approach zero during the day and will achieve zero at night. Therefore, a solar generation system capable of providing 100 MW capacity generation 85% of the time would require a rating plate capacity of approximately 300-700 MW and storage sufficient to store excess electricity generated during the day for use at night and during periods of low insolation.
In both cases, some of the excess generation capacity required during months when generation is low could be offset with long-duration storage, though that storage is not currently available.
The challenge presented here is to build a wind plus storage generation system and a solar plus storage generation system which demonstrate the ability to be dispatched in the same way as a coal-fired generator is dispatched for 85% of the hours of the year. Once this capability has been demonstrated, it should be straightforward to calculate the adjustments to generation and storage capacity required to replace a natural gas fired combined-cycle generator (~90% availability) or a nuclear generator (~95% availability).
The installed cost of the demonstration systems could then be compared with the installed costs of the coal, natural gas and nuclear generators. The cost per kWh delivered by each of the systems could also be compared.
TANSTAAFL – There ain’t no such thing as a free lunch.
https://www.therightinsight.org/Demonstration-Challenge
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