It is time for the renewable integration discussion to move beyond simply identifying the challenges of ensuring reliability in a nation increasingly served by intermittent renewable resources and toward developing real-world solutions to these challenges.
Significant increases in intermittent renewable generation are expected this decade to meet renewable portfolio standard (RPS) requirements and greenhouse gas emissions reduction measures. In its 2010 Long-Term Reliability Assessment, the North American Electric Reliability Corp. estimates that approximately 180,000 MW of variable wind and solar generation may be added in North America by 2019. Such a massive build-out will place significant stress on grid operators across the country, who have traditionally assessed system needs in terms of planning reserve margins, as opposed to resource flexibility. However, the availability of flexible resources, such as gas-fired generation, is precisely where grid operators and regulators need to focus their attention to ensure grid reliability going forward.
Increased Reliance on the Gas-Fired Fleet Expected
From a grid operator’s perspective, wind and solar generation present several operational challenges. Generation from these resources varies over operational time periods as short as seconds, and forecasting actual production, while improving, is still prone to error. The net effect is that gas-fired resources will need to be utilized in new ways by grid operators to balance load and generation.
In a 2010 study, the California Independent System Operator (CAISO) looked at the operational requirements necessary to reliably integrate a 20% RPS requirement. CAISO found that responding to the inherent variability in wind and solar generation will require flexible resources capable of providing load-following and regulation services “in wider operating ranges and at ramp rates that are faster and of longer sustained duration than are currently experienced.” CAISO concluded that integrating the expected increase in renewable generation will require gas-fired generators to cycle more frequently, with an expected 35% increase in “starts” for combined cycle units.
More recently, the California Public Utilities Commission has been looking at renewable integration needs under the state’s new 33% RPS requirement. Early indications from preliminary modeling suggest that a significant amount of flexible gas-fired generation above current planning reserve margins (much of it already existing or planned) will be needed to ensure grid reliability.
Improved forecasting, additional transmission to facilitate inter–balancing authority transactions, greater demand response, and increased energy storage are other tools warranting further development to help integrate renewable resources. However, grid operators can be expected to lean heavily on the nation’s gas-fired generation fleet to meet integration needs.
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