Washington: A report prepared by The Brattle Group for the Advanced Energy Economy Institute (AEE Institute) finds that high penetration levels of renewable generation, on occasion up to 40% and beyond, are not only technically feasible but are already being managed without compromising reliability of electric power service. This suggests that an increasing share of renewable energy can be integrated into the nationwide electricity system going forward.
The new report, released June 10, follows a report prepared by The Brattle Group earlier this year in response to the North American Electric Reliability Corp.'s "initial reliability review" of the Environmental Protection Agency's proposed Clean Power Plan, showing the reliability concerns raised by NERC to be likely overstated. AEE Institute also published a critique of NERC's "Phase I" modeling assessment of the Plan, identifying similar flaws. Today's report examines in more detail one of the issues raised by NERC: the potential impact on reliability from the expanded use of renewable energy that would likely occur as a result of implementing the Clean Power Plan.
The new Brattle Group report, “Integrating Renewable Energy into the Electricity Grid,” consists of two in-depth case studies – one of a grid operator (Electric Reliability Council of Texas, or ERCOT) and the other a vertically integrated utility (Xcel Energy Colorado) – in both of which high levels of variable renewable energy, comparable to the extent that NERC has indicated it is concerned about under-CPP compliance, are being managed successfully today by means of established operational and technological tools.
In 2014, 10% of total electricity demand in ERCOT was met by wind power, with wind's contribution reaching nearly 40% at certain times. Xcel Energy Colorado gets nearly 20% of its electricity from wind. "The success to date of ERCOT and Xcel Energy Colorado shows that integrating variable renewable energy at penetration levels of 10 – 20% on average and at times above 50% – i.e., high relative to the current levels in most of the United States – is feasible," states the report.
"Ongoing technological progress and ongoing learning about how to manage the operations of the electric system will likely allow the integration not only of the levels of variable renewable energy capacity now in places like Texas and Colorado but even significantly larger amounts in the future," The Brattle Group authors conclude. "Specifically, integration of variable renewable energy at levels of penetration as high as those reliably managed by ERCOT and Xcel Energy Colorado, if not higher, should not be seen as a significant obstacle to compliance with EPA's proposed Clean Power Plan. Rather, carefully examining the lessons learned in states and regions such as the ones examined here should help [Independent Systems Operators] and utilities ensure that significantly larger amounts of variable renewable energy can be integrated while maintaining high levels of reliability in a cost-effective manner."
The full report is available for download at http://info.aee.net/integrating-renewable-energy-into-the-electricity-grid.
The report notes that use of variable renewable energy resources, primarily wind and solar, is on the rise around the country, independent of the Clean Power Plan, due to falling prices and increasing demand, including state requirements for renewable power. Given the complexities and time lags involved, grid operators and regulators must plan carefully for needed long-term investments in the transmission and distribution as a result. But in terms of handling issues around variability and reliability, the success to date of ERCOT and Xcel in accommodating ever higher shares of variable resources shows that integrating renewables at relatively high levels "is feasible and generally involves relatively modest additional cost," according to The Brattle Group.
The tools identified by The Brattle Group include:
• Changes in ancillary services, which manage short-term mismatches between electric supply and demand, with fast-ramping gas-fired generation, demand response, storage, and other technologies;
• Improved forecasting of production from wind;
• Increased flexibility of fossil power plants on the system; and
• Evolving capabilities of renewable generation that contribute to reliability.
Newer approaches under development include utilizing large-scale storage, dynamically managing the capacity of transmission lines, and allowing demand response to play a bigger role in managing system variability (and emergency situations).
Utility-scale PV is best
A subsequent Brattle Group report, released July 13, deals with a related aspect of photovoltaic power: utility-scale PV systems in the U.S. are significantly more cost effective than residential-scale (rooftop) PV systems as a vehicle for achieving the economic and policy benefits of PV solar.
The study, "Comparative Generation Costs of Utility-Scale and Residential-Scale PV in Xcel Energy Colorado's Service Area," is the first to focus on a "solar to solar" comparison of equal amounts of residential- and utility-scale PV solar deployed on an actual utility system.
The key findings of the study include:
The generation cost of energy from 300 MW of utility-scale PV solar is roughly one-half the cost per kWh of the output from an equivalent 300 MW of 5kW residential-scale systems when deployed on the Xcel Energy Colorado system, and utility-scale solar remains more cost effective in all scenarios considered in the study.
In that same setting, 300 MW of PV solar deployed in a utility-scale configuration also avoids approximately 50% more carbon emissions than an equivalent amount of residential-scale PV solar.
Using real-world scenarios based on data from Xcel Energy Colorado, the study compares the per-MWh customer supply costs of adding 300 MW-DC of PV panels in the form of either 60,000 distributed 5kW rooftop systems owned or leased by retail customers, or 300 MW of utility-scale solar power plants that sell their entire output to Xcel Energy Colorado under long-term power purchase agreements.
The study attributes the large difference in per-MWh costs between utility- and residential-scale systems primarily to economies of scale and greater solar electric output resulting from optimized panel orientation and tracking assumed for utility-scale systems. The improved orientation and tracking of utility-scale solar also result in a higher capacity factor that causes it to avoid approximately 50% more carbon dioxide emissions than the same capacity of residential-scale solar PV on the Xcel Energy Colorado system. In other words, the reason utility-scale solar saves so much more carbon than rooftop PV is because the energy delivered per MW of installed capacity is much higher on utility-scale due to better placement and tracking capability.