This report summary comes from the Civil Society Institute.
The figure shows resource dispatch for a typical, balanced summer week for the Northeast region in 2050. In this case, demand is Integrating Variable Resources in a BBAU Future ▪ 3 being met by a combination of resources, including wind, solar, and natural gas. The level of load is indicated by the dotted line.
A “business as usual” strategy for the U.S. electric power industry means the country continues to rely heavily on coal and other fossil fuels to meet its energy needs. This is not tenable if we are to achieve substantial reductions in greenhouse gas emissions over the next several decades. In 2011, the organization Synapse prepared a study for the Civil Society Institute, Toward a Sustainable Future for the U.S. Power Sector: Beyond Business as Usual 2011 (BBAU 2011), that introduced a “Transition Scenario” in which the United States retires all of its coal plants and a quarter of its nuclear plants by 2050, moving instead toward a power system based on energy efficiency and renewable energy. The Synapse’s study showed that this transition scenario, in addition to achieving significant reductions in emissions of CO2 and other pollutants, ultimately costs society less than a “business as usual” strategy—even without considering the cost of carbon. BBAU 2011 projected that, over 40 years, the Transition Scenario would result in savings of $83 billion (present value) compared to the business as usual strategy.
As part of this lower-cost and low-emissions strategy, the Transition Scenario included large amounts of renewable energy resources with “variable output,” such as wind and solar. Without the inclusion of these resources, it will be difficult or impossible to reduce electric-sector greenhouse gas emissions to the levels necessary to materially mitigate our contribution to dangerous climate change.
While the need for variable-output resources is well defined, questions have been raised about the impact of large-scale wind and solar integration on electric system reliability.(1) In light of this important concern, Synapse paid attention to the amount of wind and solar in each region when designing the Transition Scenario for BBAU 2011, taking steps to ensure that the projected regional resource mixes could respond to all load conditions. These steps included:
- Improving the capability of the transmission system to handle large interregional power transfers
- Ensuring that regions with high levels of variable generation also had high levels of flexible generation and capacity
- Adding storage capacity in regions with high levels of wind generation
- Strengthening the capability and flexibility of electric systems through transmission and distribution investments, and
- Developing reliable demand-side management resources.
The current study takes the analysis deeper, to explore the extent to which the Transition Scenario’s resource mixes for 2030 and 2050 are capable of meeting projected load for each of the ten studied regions—not just during peak demand conditions, but in every hour of every
Footnotes 1
Numerous technical studies have demonstrated that it is feasible to add large quantities of variable-output resources to the grid without compromising reliability. Moreover, the studies have shown that the mechanisms for accomplishing this task consist of sensible improvements to grid operation practices, and greater coordination between “control areas” and regions—and that costs to the system would be fairly modest. See, for example, MIT 2012.
What’s more, additional storage was not added in the Northwest region, where the existing dispatchable hydro already serves as season of the year as consumers require. Using a simplified hourly dispatch model along with empirical load and resource output profiles, the authors assess the ability of the projected mix in each region to meet load under the varying conditions throughout a day, season, and year. An important limitation of the dispatch model is that it does not include the interregional transfers that were a fundamental part of the resource mix under BBAU 2011, because these have not been defined on an hourly basis. These transfers are an important part of the Transition Scenario for both economic and reliability reasons, and indeed we find that under certain extreme conditions, it is impossible to balance each region in isolation. Nonetheless, our analysis shows that the regional
Transition Scenario resource mixes would be capable of meeting load for almost all hours of the year in each region, and that a combination of interregional transfers, local storage, and demand response would be more than adequate to provide a high level of reliability. This analysis, along with BBAU, is solely based on today’s existing technology. We do not expect that the optimal sustainable electricity future for the United States will look exactly like our Transition Scenario, as we anticipate that changes in the technology and economics of carbon-free generation and energy storage will produce options that today would seem unachievable.
What we demonstrate in this report is that strategies to address one of the most pressing challenges faced by our species and our planet are already not only achievable, but cost effective. Future developments will only improve this potential—it is up to policymakers to make this potential a reality.
Study approach
Synapse developed a spreadsheet-based hourly dispatch model to test the capability of the Transition Scenario resource mix in each study region to meet hourly demand in that region. Hourly load data for each region was based on 2010 actual demand, and was adjusted—considering changes in demographics, wealth, and energy efficiency—so that the peak load and annual energy requirements closely matched those in the BBAU 2011 Transition Scenario. Data for these tasks were obtained from FERC 2011, NERC 2012, and U.S. EPA 2011. The generators used in the model came from the BBAU 2011 Transition Scenario.
To model the hourly generation of variable resources, a number of National Renewable Energy Laboratory (NREL) studies and data sets were used. To model hourly wind generation, data sets from NREL’s Eastern Wind Integration and Transmission Study (EnerNex Corporation 2011) and Western Wind and Solar Integration Study (GE Energy 2010) were applied to the power curve of a Vestas V 112, 3.0-MW turbine. NREL’s PVWatts calculator was used to model solar output with site specific data. Annual hydroelectric capacity factors from the BBAU report were used for the Northeast, Southeast, Eastern Midwest, and Texas regions; monthly hydroelectric capacity factors from the U.S. Bureau of Reclamation were used for the Northwest, California, Arizona/New Mexico, Rocky Mountains, Western Midwest, and South Central regions.
The dispatch model used in this analysis is based on hourly, regional matching of resources to load. At a high level, there are two potential imbalance modes for the model—the available resources could be insufficient to meet projected load, or the output of the resources could exceed projected load, resulting in an unusable surplus. In the vast majority of hours, the model is able to balance resource output exactly with the projected load. Figure 1 shows resource dispatch for a typical, balanced summer week for the Northeast region in 2050. In this case being met by a combination of resources, including wind, solar, and natural gas. The level of load is indicated by the dotted line.
The imbalance mode in which resources exceed the projected load (to the extent that it results in an unusable surplus) typically occurs in a handful of spring and autumn days with very high wind output and very low demand. In most cases, this would not occur were the model capable of calling on interregional transfers, as is a common practice in physical electric systems and as anticipated in the BBAU report. In addition to such transfers, the dispatching authority would have other tools at its disposal to maintain balance. These include: economic incentives, such as realtime or time-of-use pricing, for shifting the load curve to match resource availability; demand response to encourage consumption when surplus energy is available, such as thermal storage in electric water heaters, pre-chilling water for use later in the day, or chemical storage in electric vehicle batteries. As a last resort, dispatchers and operators could angle wind turbine blades to make them less efficient, thereby reducing output.
The tools available for dealing with an unusable surplus ensure that this imbalance mode would not result in reliability or infrastructure impacts; however, angling wind turbine blades to lower output would impact the economics of the wind power facility.
The transition Scenario.
In some cases, additional research and/or modifications to the resource mixes posited by BBAU 2011 may be warranted. Discussed in Section 3 of this report, these cases may include the energy shortfalls observed in the southeast and western regions in the summer and winter seasons, and the energy surpluses that occur in Texas and other regions in the shoulder seasons. As noted above, the BBAU resource mix generally should be seen as an illustrative example, and was never identified as an “optimal” scenario. Integration analysis far beyond that presented here will be an integral part of defining the best combination of resources to provide reliable electric service in a carbon-constrained world. The earlier this sort of in-depth analysis is undertaken, the more options will be available for meeting resource adequacy requirements in a cost-effective way.
This study suggests that it will be feasible to reliably integrate the high levels of zero-carbon energy called for by the Transition Scenario, whether or not this scenario will ultimately provide the most cost effective or elegant nationwide low-carbon energy solution. Achieving this level of integration will likely require incremental improvements in technology and operational practices, including continuation of the current trend toward better interregional coordination. In contrast, the alternative—continuing to rely on increasing combustion of fossil fuels and to bear the growing toll on natural resources and the Earth’s climate presents far more daunting technical, economic, and social challenges to human and environmental welfare
Summary of findings
With few exceptions, this study finds that BBAU 2011’s Transition Scenario resource mixes, based entirely on existing technology and operational practices, are capable of balancing projected load in 2030 and 2050 for each region—in nearly every hour of every season of the year. Of course, any viable scenario must be based on much higher levels of reliability, such as a one-outage-inten-years standard currently used throughout the United States today. Thus we focus here on any hours with an energy imbalance, either as “unusable surplus” or shortages, to investigate their implications for the feasibility and implementation requirements of the Transition Scenario. This analysis highlights the ways in which interregional cooperation, followed by improvements in technology such as energy storage systems, can provide very high levels of reliability under the
The full report is here:
http://www.civilsocietyinstitute.org/media/pdfs/20130417Meeting%20Load%20with%20a%20Resource%20Mix%20Beyond%20Business%20as%20Usual%20-%20FINAL.pdf
The Civil Society Institute
www.civilsocietyinstitute.org
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