TODAY’S STUDY: THE FUTURE OF RENEWABLE ELECTRICITY, PT. 2 (GENERATION, STORAGE)

Volume 2: Renewable Electricity Generation and Storage Technologies

Augustine, Bain, et.al. June 2012 (National Renewable Energy Laboratory, et. al.)

Perspective

The Renewable Electricity Futures Study (RE Futures) provides an analysis of the grid integration opportunities, challenges, and implications of high levels of renewable electricity generation for the U.S. electric system. The study is not a market or policy assessment. Rather, RE Futures examines renewable energy resources and many technical issues related to the operability of the U.S. electricity grid, and provides initial answers to important questions about the integration of high penetrations of renewable electricity technologies from a national perspective. RE Futures results indicate that a future U.S. electricity system that is largely powered by renewable sources is possible and that further work is warranted to investigate this clean generation pathway. The central conclusion of the analysis is that renewable electricity generation from technologies that are commercially available today, in combination with a more flexible electric system, is more than adequate to supply 80% of total U.S. electricity generation in 2050 while meeting electricity demand on an hourly basis in every region of the United States.

The renewable technologies explored in this study are components of a diverse set of clean energy solutions that also includes nuclear, efficient natural gas, clean coal, and energy efficiency. Understanding all of these technology pathways and their potential contributions to the future U.S. electric power system can inform the development of integrated portfolio scenarios. RE Futures focuses on the extent to which U.S. electricity needs can be supplied by renewable energy sources, including biomass, geothermal, hydropower, solar, and wind.

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The study explores grid integration issues using models with unprecedented geographic and time resolution for the contiguous United States. The analysis (1) assesses a variety of scenarios with prescribed levels of renewable electricity generation in 2050, from 30% to 90%, with a focus on 80% (with nearly 50% from variable wind and solar photovoltaic generation); (2) identifies the characteristics of a U.S. electricity system that would be needed to accommodate such levels; and (3) describes some of the associated challenges and implications of realizing such a future. In addition to the central conclusion noted above, RE Futures finds that increased electric system flexibility, needed to enable electricity supply-demand balance with high levels of renewable generation, can come from a portfolio of supply- and demand-side options, including flexible conventional generation, grid storage, new transmission, more responsive loads, and changes in power system operations. The analysis also finds that the abundance and diversity of U.S. renewable energy resources can support multiple combinations of renewable technologies that result in deep reductions in electric sector greenhouse gas emissions and water use. The study finds that the direct incremental cost associated with high renewable generation is comparable to published cost estimates of other clean energy scenarios. Of the sensitivities examined, improvement in the cost and performance of renewable technologies is the most impactful lever for reducing this incremental cost. Assumptions reflecting the extent of this improvement are based on incremental or evolutionary improvements to currently commercial technologies and do not reflect U.S. Department of Energy activities to further lower renewable technology costs so that they achieve parity with conventional technologies.

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RE Futures is an initial analysis of scenarios for high levels of renewable electricity in the United States; additional research is needed to comprehensively investigate other facets of high renewable or other clean energy futures in the U.S. power system. First, this study focuses on renewable-specific technology pathways and does not explore the full portfolio of clean technologies that could contribute to future electricity supply. Second, the analysis does not attempt a full reliability analysis of the power system that includes addressing sub-hourly, transient, and distribution system requirements. Third, although RE Futures describes the system characteristics needed to accommodate high levels of renewable generation, it does not address the institutional, market, and regulatory changes that may be needed to facilitate such a transformation. Fourth, a full cost-benefit analysis was not conducted to comprehensively evaluate the relative impacts of renewable and non-renewable electricity generation options.

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Lastly, as a long-term analysis, uncertainties associated with assumptions and data, along with limitations of the modeling capabilities, contribute to significant uncertainty in the implications reported. Most of the scenario assessment was conducted in 2010 with assumptions concerning technology cost and performance and fossil energy prices generally based on data available in 2009 and early 2010. Significant changes in electricity and related markets have already occurred since the analysis was conducted, and the implications of these changes may not have been fully reflected in the study assumptions and results. For example, both the rapid development of domestic unconventional natural gas resources that has contributed to historically low natural gas prices, and the significant price declines for some renewable technologies (e.g., photovoltaics) since 2010, were not reflected in the study assumptions.

Nonetheless, as the most comprehensive analysis of U.S. high-penetration renewable electricity conducted to date, this study can inform broader discussion of the evolution of the electric system and electricity markets toward clean systems.

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The RE Futures team was made up of experts in the fields of renewable technologies, grid integration, and end-use demand. The team included leadership from a core team with members from the National Renewable Energy Laboratory (NREL) and the Massachusetts Institute of Technology (MIT), and subject matter experts from U.S. Department of Energy (DOE) national laboratories, including NREL, Idaho National Laboratory (INL), Lawrence Berkeley National Laboratory (LBNL), Oak Ridge National Laboratory (ORNL), Pacific Northwest National Laboratory (PNNL), and Sandia National Laboratories (SNL), as well as Black & Veatch and other utility, industry, university, public sector, and non-profit participants. Over the course of the project, an executive steering committee provided input from multiple perspectives to support study balance and objectivity.

RE Futures is documented in four volumes of a single report: Volume 1 describes the analysis approach and models, along with the key results and insights; This volume—Volume 2—describes the renewable generation and storage technologies included in the study; Volume 3 presents end-use demand and energy efficiency assumptions; and Volume 4 discusses operational and institutional challenges of integrating high levels of renewable energy into the electric grid.

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Introduction

The United States has diverse and abundant renewable resources, including biomass, geothermal, hydropower, ocean, solar, and wind resources. These renewable resources are geographically constrained but widespread—most are distributed across all or most of the contiguous states. Within these broad resource types, a variety of commercially-available renewable electricity generation technologies have been deployed in the United States and other countries, including stand-alone biopower, co-fired biopower (in coal plants), hydrothermal geothermal, hydropower, distributed PV, utility-scale PV, CSP, onshore wind, and fixed-bottom offshore wind. Today, these resources contribute about 10% of total U.S. electricity supply. Renewable generation sources have varying degrees of variability and uncertainty, and the output characteristics of the associated technologies vary substantially. These characteristics must be considered in grid planning and operations to ensure a real-time balance of electricity supply and demand over various timescales as renewable technologies provide greater levels of electricity to the grid.

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The Renewable Electricity Futures Study (RE Futures) is an initial investigation of the extent to which renewable energy supply can meet the electricity demands of the contiguous United States over the next several decades. This study includes geographic and electric system operation resolution that is unprecedented for long-term studies of the U.S. electric sector. The analysis examines the implications and challenges of renewable electricity generation levels—from 30% up to 90%, with a focus on 80%, of all U.S. electricity generation from renewable technologies—in 2050. The study focuses on some key technical implications of this environment, exploring whether the U.S. power system can supply electricity to meet customer demand with high levels of renewable electricity, including variable wind and solar generation. The study also begins to address the potential economic, environmental, and social implications of deploying and integrating high levels of renewable electricity in the United States.

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The RE Futures study is documented in four volumes: Volume 1 describes the analysis approach and models along with the key results and insights from the analysis; Volume 2—this volume—documents in detail the renewable generation and storage technologies included in the study; Volume 3 describes the end-use electricity demand and efficiency assumptions; Volume 4 documents the operational and institutional challenges of integrating high levels of renewable energy into the electric grid.

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This volume includes chapters discussing biopower, geothermal, hydropower, ocean, solar, wind, and storage technologies. Each chapter includes a resource availability estimate, technology cost and performance characterization, discussions of output characteristics and grid service possibilities, large-scale production and deployment issues, and barriers to high penetration along with possible responses to them. Only technologies that are currently commercially available—biomass, geothermal, hydropower, solar PV, CSP, and wind-powered systems—are included in the modeling analysis. Some of these renewable technologies—such as run-of-river hydropower, onshore wind, hydrothermal geothermal, dedicated and co-fired-with-coal biomass—are relatively mature and well-characterized. Other renewable technologies—such as fixed-bottom offshore wind, solar PV, and solar CSP—are at earlier stages of deployment with greater potential for future technology advancements over the next 40 years. Technologies such as enhanced geothermal systems, ocean energy technologies, floating platform offshore wind technology, and others that are currently under development and pilot testing were not included in the modeling analysis but are discussed in this volume…

Biopower Technologies…Geothermal Energy Technologies…Hydropower…Ocean Energy Technologies…Solar Energy Technologies…Wind Energy Technologies…Energy Storage Technologies…

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