opment at present. In fact, it is the underutilization of transmission corridors—built to move wind-derived electricity to load centers—that represents an inefficient use of resources. But there is a stopgap approach that several interested parties are exploring to potentially address this underutilization issue. It is “co-siting,” in either of two forms: (1) conventional dispatchable generating resources (natural-gas-fired combustion turbines or combined-cycle plants) paired with renewables; or (2) two or more renewable resources that interact synergistically in terms of transmission needs (e.g., solar power production during the day, wind power at night). Such a development strategy can rationalize the use of transmission resources and serve as an interim mechanism for increasing the value of renewables-generated electricity until advanced storage technologies are technically feasible and economical viable.
Scenarios of how renewables might significantly increase their contribution to the electricity system provide a quantitative and conceptual framework to help describe and assess issues related to greatly increasing the scale of renewables deployment. Such scenarios are a primary way of quantifying the materials and manufacturing requirements, human and financial resources, and environmental impacts associated with greatly expanding renewables’ electricity generation. In its report, the Panel on Electricity from Renewable Resources (NAS-NAE-NRC, 2009) considered scenarios recently developed by multiple sources. The scenarios typically incorporate computational models and other quantitative elements in an attempt to integrate environmental, technologic, economic, and deployment-related elements into an internally consistent assessment framework. These scenarios were chosen to represent aggressive but achievable rates of renewables deployment if considerable policy and financial resources were devoted to the effort. Other selection criteria used by the panel in choosing scenarios were whether they were developed with input from multiple stakeholder groups and underwent a peer review process. Thus the scenarios do not represent a simple extrapolation of historical growth rates but rather a more integrated perspective on the conditions needed to greatly scale up renewables deployment.
The panel considered two types of scenarios. The first involved increased penetration of a single resource, such as solar or wind. One prominent example is the 20% wind energy study (DOE, 2008a), which is described in more detail