The Levelized Cost of Electricity from Existing Generation Resources
Continuing to operate existing coal, natural gas, hydroelectric, and nuclear plants provides a cheaper source of electricity than replacing them with new plants or renewable sources of power like wind or solar.
From the Executive Summary:
[O]n average, continuing to operate existing natural gas, coal, nuclear and hydroelectric resources is far less costly than building and operating new plants to replace them.
Non-dispatchable wind and solar generation resources impose [up to $24 Mwh in costs] on the dispatchable generation resources which are required to remain in service but are forced to generate less in combination with them. ... Wind and solar resources increase the [levelized cost of electricity] of dispatchable resources they cannot replace by reducing their utilization rates without reducing their fixed costs, resulting in a levelized fixed cost increase.