EPRI's comparison basis is called the "carbon intensity" ratio and reflects:
Many Environmentalists (and apparently Policymakers also) believe that in reducing greenhouse gas emissions that the key is just to develop more solar and wind energy generation resources -- and its just that simple.
The problem is that in the "Real World", there is more to the story -- based on something called the integrated resource dispatch grid.
Generally, wind and solar power generating resources are considered either peaking or intermediate units and on the "dispatch grid" will displace natural gas generation resources.
Generation options such as nuclear, geothermal, and biomass energy resources are typically classified as "base load units" and most often will displace coal units.