Uncertainty - ORIGINAL CONTENT

Definition of uncertain (Merriam-Webster)

1a : not known beyond doubt : dubious an uncertain claim
b : not having certain knowledge : doubtful remains uncertain about her plans
c : not clearly identified or defined a fire of uncertain origin
2 : not constant : variable, fitful an uncertain breeze
3 : indefinite, indeterminate the time of departure is uncertain
4 : not certain to occur : problematical his success was uncertain
5 : not reliable : untrustworthy an uncertain ally

We live with uncertainty and make the best decisions we can based on the uncertain information available. Weather and climate are not constant, nor is our knowledge regarding what they are and what they will be in the future. Many factors regarding climate are not known beyond doubt, such as climate sensitivity and feedback. Many weather and climate events are problematical and their timing indefinite, including ENSO (El Niño-Southern Oscillation) events, PDO (Pacific decadal oscillation) and AMO (Atlantic Multidecadal Oscillation) shifts, tropical cyclone timing, frequency and intensity, tornadoes, droughts and floods. The origin of wildfires is frequently unidentified. Forecasts of future weather and climate events are not reliable. The existence of multiple but differing near-surface temperature records, sea level rise measurements and climate model projections are all examples of uncertainty regarding climate and climate change.

The uncertainty regarding weather and climate leads to uncertainty regarding the performance of systems dependent on weather, such as wind and solar electric generation. History provides some basis for estimating typical wind velocities and solar insolation levels in specific locations. However, sufficient uncertainty remains to require the inclusion of some redundant generating and storage capacity to deal with events beyond previous experience. The recent “wind drought” and extended period of below normal solar insolation which affected the UK and Western Europe are examples of such events. Daily variations in wind speed and solar insolation are reasonably predictable, but the accuracy of the predictions declines over longer periods.

The goals of electrifying all energy end uses and supplying all of them with a renewable electric generation and storage infrastructure add additional uncertainty regarding the pace of the transition and the relative efficiencies of the fossil and electric end uses. There are also end uses, such as the production of iron and steel and the calcining of cement, for which there are currently no non-fossil alternatives and for which the potential availability of alternatives is unknown.

The uncertainties regarding weather and its impact on the operation of weather-dependent electric generating systems greatly complicate the design and operation of a renewable plus storage electric grid. The frequency and duration of low/no wind and solar events affect the design capacity of the generation system, the relative design capacity of wind and solar generation in the system, and the capacity and discharge rates of the storage.

The mix of these system components would vary considerably from region to region within the US and around the globe as a function of wind and solar availability. The design of the storage systems will be heavily dependent upon the mix of wind and solar and upon the likely frequency and duration of low/no wind and solar events.