Precautionary Principle

The Precautionary Principle is frequently cited as the justification for actions to halt or retard climate change. This commentary will question the application of the principle to the design of a renewable plus storage electric grid.

The application of the principle to the current US electric grid has centered on the maintenance of a 20% (+/-) capacity reserve margin relative to peak demand. This reserve capacity plus scheduling of generator maintenance during off-peak periods have been very successful in avoiding grid failure. Utility customers with critical loads frequently install standby generators to compensate for distribution or transmission outages caused by adverse weather and accidents.

In recent years, the introduction of intermittent renewable generation and the retirement of conventional generation has tended to reduce capacity reserve margins, as electricity generated by the intermittent renewable generators has displaced electricity generated by conventional sources when the intermittent renewable generators operate. This issue has surfaced in California, which no longer maintains sufficient conventional generation capacity to completely replace the output of intermittent generators when they are unable to generate because of time-of-day or weather conditions. This has resulted in the application of demand-side management programs and in the use of rolling blackouts to avoid grid failure. California also routinely relies on imports of electricity from neighboring states to meet demand.

The critical differences in a renewable plus storage grid with no conventional, dispatchable generation are the very limited availability or complete unavailability of generation sources which are not weather dependent and the unavailability of fossil-fueled standby generators for use in the event of distribution or transmission outages, or worse a grid failure. The unavailability of fossil-fueled standby generators is a particular issue for users with critical loads, such as hospitals.

In a renewable plus storage grid, the dispatchable element is storage. Therefore the Precautionary Principle would appear to require that there be sufficient charged storage capacity with sufficient deliverability to replace the output of the renewable generators over whatever time period the renewable generation is unable to perform or perform at capacity; and, that there be sufficient additional renewable generating capacity to rapidly recharge storage depleted during a renewable generation hiatus in anticipation of the next renewable generation hiatus.

The Precautionary Principle would also appear to require that conventional generating capacity be maintained until sufficient storage capacity and deliverability are installed and operational to replace the conventional generation and sufficient additional renewable generating capacity is available to recharge storage. Renewable generating capacity alone is insufficient to replace dispatchable generation capacity, though it can displace the output of the conventional generation, as is the case today.

While a renewable plus storage grid would require additional capacity to recharge storage, it might not require the type of capacity reserve margin typically used in grids with conventional generation. The individual renewable generators would be much more numerous and of much lower capacity than conventional generators and therefore failure of an individual generator would have far less impact on grid generating capacity.

It would seem that the Precautionary Principle would require that the initial renewable plus storage grid buildout consist of significantly more generating and storage capacity relative to peak demand than the conventional grid it replaces. Experience gained during the early operation of the renewable plus storage grid would help determine the appropriate level of generating and storage capacity and deliverability to be added and maintained as the conversion to an all-electric energy economy proceeds.