Redundant Capacity - ORIGINAL CONTENT

The capacity of the US electric grid has historically been designed to meet peak demand, with limited additional generating capacity equal to +/- 20% of peak demand or sufficient to replace the capacity of the largest generating unit on the grid in the event of an unscheduled shutdown. That additional generating capacity can be considered to be redundant in that it is necessary on peak only in the event of an unscheduled generator shutdown. The conventional generators on the grid have capacity factors of ~85% (coal), ~90% (gas CCT) and ~95% (nuclear). The maintenance and repair downtime of these generators is typically scheduled for the shoulder months of the year when grid demand is expected to be well below peak. However, unscheduled shutdowns do occur.

The grid generation transition currently underway is intended to replace existing coal and natural gas generation with intermittent wind and solar generation plus electricity storage. However, most of the wind and solar generating capacity which has been installed to date has not included the electricity storage capacity required to replace dispatchable coal and natural gas generation. Therefore, the wind and solar generator output is capable only of displacing output from coal and natural gas generators when the wind and solar generators are operating. Wind generators currently on the grid have capacity factors ranging from ~24 – 46.6% depending on location, mounting height and season. Solar generators currently on the grid have capacity factors ranging from ~12.5 – 33.2% depending on location and season.

Wind and solar generators which are not paired with sufficient electricity storage capacity to render them dispatchable are, by definition, redundant capacity since conventional dispatchable generating capacity must remain available to provide backup during periods when the wind and solar generators provide low/no output. Redundant capacity always increases costs because of increased investment in generation and transmission infrastructure. Redundant generation also increases costs by reducing the output of conventional generators, which causes their fixed costs to be allocated across lower generator output, thus increasing the prices necessary to maintain profitable operation. These higher prices, in turn, increase the wholesale power prices paid to the renewable generators.

Installing sufficient storage to render the currently installed wind and solar generation dispatchable would make a portion of the existing conventional generating capacity redundant, which would be essential if that capacity is to be decommissioned as envisioned by the Administration. Installing sufficient storage capacity to render all additional wind and solar generation capacity dispatchable would allow replacement of additional conventional generation as it became redundant. However, the pace of replacement of conventional generating capacity would have to be slower than the pace of commissioning of new dispatchable renewable generation to accommodate the demand growth expected as the result of the Administration’s push for “all-electric everything”.

It appears increasingly unlikely that the dispatchable generating capacity required to replace current conventional generation as well as to meet the consumption and demand growth expected to result from the transition to “all-electric everything” would be installed and operational by 2050. It appears even less likely that the result would be reduced energy costs.