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Product Abstract

Program on Technology Innovation: Fossil Fleet Transition with Fuel Changes and Large Scale Variable Renewable Integration

Product ID:3002006517
Date Published:02-Oct-2015
Sector Name:Generation
Document Type:Technical Results
Price:No Charge

This Product is publicly available

   7.23 MB - Adobe PDF (.pdf)


Variability in demand as seen by grid-connected dispatchable generators can increase due to factors such as greater production from variable generation assets (for example, wind and solar), increased reliance on demand response or customer-driven automation, and aggregation of loads. This study is designed to inform power companies, researchers, and policymakers of the scope and trends in increasing levels of flexible operations as well as reliability challenges and impacts for dispatchable assets.


Because there is rarely a direct monetization of the value of operational flexibility, the decision to provide such flexibility is typically dependent on unit- and region-specific decisions made by asset owners. It is very likely that much greater and more widespread flexible operations capabilities will be needed due to increased variability in demand seen by grid-connected generators, uncertainty regarding investment in new units to provide adequate operational flexibility, and the retirement of older, uncontrolled sub-critical pulverized coal units.

To enhance understanding of the technical challenges and operational impacts associated with dispatchable assets needed to increase operational flexibility and support variable demand.

The study approach consists of three elements: a literature review of relevant prior studies, analysis of detailed scenarios for evolution of the future fleet over the next 35 years, and engineering assessment of the degree and scope of technical challenges associated with transformation to the future fleet. The study approach integrated two key elements rarely brought together in a single analysis—1) long-term capacity planning, which enables modeling of unit retirements and new asset investments, and 2) unit commitment analysis, which permits examination of hourly unit dispatch while considering operational limitations relevant to flexible operations capabilities.

The three key dimensions of systemic challenges in terms of variable generation include the following:

  • Increased unit operations and maintenance costs due to equipment damage resulting from flexible operations
  • Impacts on unit emissions and ability to maintain compliance with environmental regulations
  • Technical challenges associated with providing flexible operations capabilities across a large number and variety of dispatchable generation assets

Driven by existing regulatory policies (including renewable portfolio standards) and fuel prices, significant levels of renewable electricity generation (11%–41% of total generation) are likely to emerge by 2050. Despite variations in the generation technology mix in different regions, widespread high levels of flexible operations are predicted across most regions for much of the year by 2050. Also predicted are frequent, large changes in average hourly generation for combustion turbine combined-cycle and coal assets as well as significant periods of low-load operations and reserve standby.

Applications, Value, and Use
The feasibility of achieving the very high levels of operational flexibility across the generation fleet as shown in this study is highly uncertain without additional technical capabilities. Such capabilities are necessary to enable increased flexible operations, expand inter-regional transmission capacity, and advance economic drivers that incentivize asset owners to invest in creating greater unit flexibility.

2015 Program 65   Steam Turbines-Generators and Auxiliary Systems
  • Variable generation
  • Flexible operation
  • Renewable integration
  • Unit commitment
  • Energy analysis
  • Fossil fleet transition

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