The large-scale CO2 reductions envisioned to stabilize, and ultimately reverse, global atmospheric CO2 concentrations present major technical, economic, regulatory and policy challenges. Reconciling these challenges with continued growth in energy demand highlights the need for a diverse, economy-wide approach.
The Electric Power Research Institute (EPRI) conducted a three-part analysis to assess the technical feasibility of substantial CO2 emissions reductions from the U.S. electricity sector; to identify the technology development pathways and associated research, development, and demonstration (RD&D) funding needed to achieve this potential; and to evaluate the economic impact of realizing emissions reduction targets. Three major conclusions emerge in this study:
• The strategy for reducing electricity sector emissions will be technology-based. A technology-based strategy is sustainable, minimizes costs to the U.S. economy, and creates opportunities for decarbonization beyond the electricity sector and ultimately beyond the U.S. economy.
• A diverse portfolio of advanced technologies will be required. No single technological “silver bullet” will suffice. Rather, a full portfolio is needed that includes efficiency, renewable energy resources, nuclear, coal with carbon capture and sequestration, and other technologies enabled by expanded transmission and distribution system capabilities.
• Significant RD&D will be needed over a sustained period, and technology development lead times demand immediate action. Timely and sustained investment in public and private RD&D could lower the cost of emissions reductions on the order of $1 trillion, and significantly limit increases in wholesale electricity costs.
The EPRI analyses are documented in a public domain report entitled The Power to Reduce CO2: The Full Portfolio, available at www.epri.com. This article summarizes section 3 of that study, addressing the technology pathways that must be developed to enable substantial CO2 emissions reductions from the U.S. electricity sector. The RD&D pathways addressed in this analysis are providing the framework for a more detailed RD&D action plan that EPRI is developing.
EPRI’s analysis reveals four key strategic technology deployment challenges that must be met for the U.S. electricity sector to significantly reduce CO2 emissions over the coming decades:
• Deployment of smart distribution grids and communications infrastructures to enable widespread end-use efficiency technology deployment, distributed generation, and plug-in hybrid electric vehicles.
• Deployment of transmission grids and associated energy storage infrastructures with the capacity and reliability to operate with 20 to 30 percent intermittent renewables in specific regions of the United States.
• Deployment of advanced light water reactors enabled by continued safe and economic operation of the existing nuclear fleet.
• Deployment of commercial-scale coal-based generation units operating with 90 percent CO2 capture and with the associated infrastructures to transport and sequester the captured CO2.
The specific technologies associated with each of these challenges are at various stages of development.
While active RD&D and commercial development is advancing the capabilities of distribution-enabled technologies—such as energy efficient devices, distributed energy resources, and plug-in hybrid electric vehicles—their widespread deployment requires a smart, interactive infrastructure, including a range of solutions that can be integrated all along the distribution system. To reduce both energy consumption and CO2 emissions, greater synergy is needed between energy consuming and producing devices and the electrical distribution system.
Technology development pathways are described below for the grid-enabled technologies that will enable widespread commercialization of energy efficiency (EE), distributed energy resources (DER), and plug-in hybrid vehicles (PHEVs).
Energy-efficient technologies provide many of the most cost-effective, near-term options for CO2 emissions reduction, since many can be deployed faster and at lower cost than supply-side options such as new central power stations. Distributed energy resources deliver electricity closer to the point of use, better matching demand with supply, and mitigating the need for new generation and transmission facilities.
Key research milestones and deployment targets include:
• By 2010, ensure standards for interoperability are in place, and the advanced meter infrastructure (AMI) has the capability for real-time data acquisition and dynamic energy management.
• By 2012, complete pilot projects to assess the capability of dynamic energy management based upon first-generation AMI, providing real-time pricing signals and emergency demand condition signals to smart devices.
• By 2015, ensure that smart resources are built to standards. End-use devices and DER are routinely manufactured with interactive intelligence built into their operating systems based upon accepted communication standards.
• By 2020, ensure AMI can be integrated with smart resources (smart end-use devices and smart DER), allowing consumers to optimize energy use.
Plug-in hybrid vehicles (PHEVs), building upon the engineering and market acceptance of traditional hybrids, are expected to enter the U.S. market around 2010, and to gain market penetration through 2050 because of their superior fuel performance and environmental benefits. With parallel advances in smart vehicles and the smart grid, PHEVs will become an integral part of the distribution system itself within 20 years, providing storage, emergency supply, and grid stability.
Key research milestones and deployment targets include:
• By 2012, develop advanced on-board chargers capable of handling two-way power flow, opening the door for vehicles to become potential supply resources.
• By 2017, deploy PHEVs to represent 10 percent of new light vehicle sales in the United States.
• By 2020, ensure PHEVs can be integrated into the smart distribution system and managed in aggregate to meet peak loads and emergencies, and to provide ancillary services.
• By 2030, deploy PHEVs to represent 30 percent of new light vehicle sales in the United States.
The technologies discussed above share a number of common attributes. First, they have or will have high levels of distributed intelligence (embedded computers) built into their basic operating structure, allowing them to become “smart resources” that are interactive with their digital environment. Second, they incorporate standardized communication protocols, affording high levels of interoperability with other devices through AMI. Third, they are designed to be integrated with a smart electricity infrastructure at multiple levels—the distribution level, the energy management systems (EMS) level, and grid operations and planning. Consequently, while established research and commercial activities continue to develop core technologies for efficiency, PHEVs, and DER, parallel RD&D efforts are required to transform the distribution system into a smart enabling infrastructure.
Key research milestones and deployment targets include:
• By 2010, develop and deploy communication standards for AMI to ensure grid interoperability.
• By 2015, integrate AMI with smart resources, and complete pilot projects of distribution system optimization.
• By 2020, develop models for integrating smart resources with EMS, maximizing the energy efficiency benefit at the system level. Ensure smart resources can be aggregated into virtual loads and sources.
• By 2025, fully integrate EMS with distribution management systems (DMS) and smart resources. Ensure the seamless integration of smart distributed resources with distribution system operations and with the market for energy services.
Because the principal non-hydro renewable resources (i.e., wind, solar) are intermittent, integrating large quantities into the generation mix will require significant transmission system enhancements. Specific challenges include insufficient transmission for wind farms in remote locations, voltage and power supply problems because of fluctuating energy output, high ramping burdens requiring added reserves, and limited reactive power control. This section describes the RD&D steps needed to equip the transmission system with the resiliency and flexibility necessary to operate under conditions where potentially 20 to 30 percent of electricity generation is produced by intermittent renewables.
Technology development pathways are described below for the transmission-enabled technologies that will enable greater penetration of renewable energy into the U.S. grid.
Because they are inherently less controllable, renewable-energy resources challenge grid operations. Wind power provides the most striking example, with potential remedies including better wind turbines, improved fault tolerances, more accurate wind forecasting, power electronics for stabilization and compensation, and electric energy storage. Of these, only electric energy storage offers a comprehensive solution to the grid challenges of intermittent generation. Decoupling intermittent generation from demand by allowing large-scale energy storage and discharge increases resource dispatchability and allows intermittent renewable resources to operate during periods of maximum efficiency.
Key research milestones and deployment targets include:
• By 2017, demonstrate an energy storage plant to support widespread integration of wind turbines.
• By the mid-2020s, develop energy storage technology based on nano-supercapacitors.
Under-investment in transmission infrastructure relative to growth in electricity demand presents critical near-term concerns. Analytical and visualization tools can enable more accurate forecasting of renewable energy output and its impact on grid operations, providing operators with greater confidence in scheduling adequate capacity to meet energy requirements.
Key research milestones and deployment targets include:
• By 2015, apply new analysis tools to optimize regulation, reserves, and load-following requirements in regions with high penetration of intermittent resources.
• By 2020, develop visualization tools that more accurately reflect load and demand response capabilities, enabling higher wind penetration.
Renewable energy sites that are optimal in terms of primary energy resources often are far from load centers, requiring additional transmission infrastructure. Through advanced transmission systems, novel materials, and advanced power electronics, the transmission infrastructure can be adapted for increased renewable energy generation.
Key research milestones and deployment targets include:
• By the mid-2020s, incorporate novel superconducting materials into a “supercable” that provides a low-loss transmission medium and an energy storage medium that can also be used for low-emission transportation applications.
• By the late 2020s, develop high-voltage direct current systems incorporating power electronics controllers that could be used to increase the use of off-shore wind farms.
Nuclear power’s contribution to CO2 emissions reductions hinges on the continued safe and economic performance of the existing fleet, which currently accounts for 73 percent of the emission-free generation in the United States. Nuclear power is the only technologically mature non-emitting generation source that is proven and already deployed on a large scale. Nuclear energy’s R&D needs, therefore, span both the current fleet and new plant construction.
Technology development pathways are described below for the nuclear technologies that will enable nuclear power to sustain and extend its contributions to emission-free power generation.
The near-term technology needs for nuclear energy in the United States relate to light water reactor (LWR) technology, which is the technology used in more than 80 percent of the world’s current reactors. Existing U.S. plants have operated for 12 to 38 years, and almost half of the current fleet received their operating licenses between 1980 and 1995. Sustaining electricity production from these plants is critical to national efforts aimed at significant CO2 reductions.
Key research milestones and deployment targets include:
• By 2016, ensure that all existing plants have been granted a 20-year life extension.
• By 2030, expand the application of digital control technology in both safety and plant control applications.
• By 2030, develop a new generation of highly reliable, high burnup nuclear fuel, capable of longer outage cycles and significantly reduced volumes of spent fuel.
After more than two decades of investment in design development and pre-licensing, ALWR designs are approaching “essentially complete design” status. Some ALWRs are in commercial operation or under construction today in Japan, Korea, Taiwan, France, and Finland. In the United States, 15 utilities have stated their intent to file a combined license application based on ALWR designs. Although ALWR technology is available today, projections for earliest commercial operations of an ALWR in the United States are in the 2015 time frame because of time required for licensing and construction. The RD&D focus is to build upon existing designs and programs, such as the U.S. DOE’s NP-2010, to enable completion of the detailed engineering necessary for detailed ALWR cost estimates and plant construction. Additional RD&D will ensure that ALWRs perform at high levels of safety, capacity factor, and reliability, comparable with levels now achieved in the existing fleet.
Key research milestones and deployment targets include:
• By 2011, resolve remaining ALWR generic regulatory issues—including instrumentation and control design criteria, high-frequency seismic design criteria, quality assurance standards, and fitness for duty—in support of a commercial operation goal of 2015.
• By 2020 to 2025, develop enhancements to ALWR design, construction, and operations (e.g., modular construction, advanced automated plant controls, enhanced standardization) based on successful technology transfer of construction and operating experience from the existing fleet and early ALWR deployments.
Two nuclear-energy related technology areas not specifically analyzed in the EPRI report nevertheless will have a bearing on the commercial electricity sector: spent-fuel management and high-temperature gas reactors (HTGR).
Spent-Fuel Management
Spent fuel management, although important to the long-term sustainability of nuclear energy, does not contribute directly to CO2 emissions reductions. Today’s plants and those to be constructed between now and 2030 will be able to store spent fuel on site. For economic, energy security, and sustainability reasons, however, there is an imperative to establish an integrated spent-fuel-management system consisting of centralized interim storage, long-term geologic storage, and, when necessary, a closed nuclear-fuel cycle (recycling, reprocessing, and advanced reactor strategies). The current analysis assumes a consensus strategy is established by 2012 for integrated and cost-effective spent fuel management. Long-term projections in the 2050 time frame include a closed fuel cycle and deployment of “fast” reactors enabling the new fuel cycle. While not an imperative to achieving substantial emissions reductions by 2030, future RD&D will be necessary to enable a successful, cost-effective transition from a once-through to closed fuel cycle.
High-Temperature Gas-Cooled Reactors (HTGR)
Operating at much higher temperatures (700ºC to 950ºC) than conventional LWR technology (300ºC), high-temperature gas-cooled reactors (HTGR) can generate both electricity and process heat for industrial processes. Although originating from electricity-sector technology, HTGRs will provide a non-emitting technology option to reduce CO2 emissions from large industrial energy consumers (e.g., hydrogen production, petrochemical operations, and desalination). The Next Generation Nuclear Plant (NGNP) commercial demonstration project—the U.S. Department of Energy’s name for the U.S. application of HTGR technology—already is underway. Key research milestones and deployment targets include prototype HTGR plant operation by 2018 and commercial HTGR introduction by the mid-2020s.
Coal currently accounts for more than half of the electricity generated in the United States, and is projected by most analyses to remain the backbone of U.S. electricity supply through 2050 and beyond. Sustaining coal as a viable option in a carbon-constrained world entails increasing the efficiency and reducing the capital cost of pulverized coal (PC) and integrated gasification combined-cycle (IGCC) technologies, and bringing CO2 carbon capture and storage to the point of cost-effective commercialization by 2020. Large- scale demonstrations will be necessary to convince private industry that technology commercialization is feasible.
The technology development pathways outlined in this section are intended to achieve two key targets: first, increase the efficiency of PC and IGCC baseload plants (with CO2 capture) to the 43- to 45-percent range by 2030; and second, ensure that all coal plants built after 2020 have the capability to capture and store 90 percent of the CO2 produced.
Significant efficiency gains for PC technology can be realized only by increasing the peak temperatures and pressures of the steam cycle; a 10-percent efficiency gain, for example, translates into a CO2 emissions reduction of 25 percent. Advanced materials such as corrosion-resistant nickel alloys, and new boiler and steam turbine designs, will be necessary to accommodate these higher temperatures and pressures. The targets for PC plants with carbon capture are efficiencies of 43 to 45 percent (with CO2 capture) with capital cost reductions of 25 percent by 2030 relative to 2005 costs documented in the EPRI/CURC Roadmap. It is expected that an advanced ultra-supercritical plant operating at about 1, 290°F (700°C) will be built during the next 7 to 10 years, following the demonstration and commercial availability of advanced materials from current research programs.
Key research milestones and deployment targets include:
• By 2020, achieve efficiencies of 33 to 35 percent for advanced pulverized coal plants with CO2 capture.
• By 2020, design, construct, and operate “Ultragen-I” facilities—ultra-supercritical pulverized coal plants operating at greater than 1,100°F (593°C) with 25 to 50 percent CO2 capture.
• By 2025, design, construct, and operate “Ultragen-II” facilities—ultra-supercritical pulverized coal near zero emissions plant operating at 1,200 to 1,300°F (649 to 704°C) with 50+ percent CO2 capture.
With aggressive RD&D, IGCC capital cost reductions are targeted at 30 percent by 2030 relative to 2005 costs documented in the EPRI/CURC roadmap, with efficiencies climbing from 30 percent today to the 45-percent range (with CO2 capture). Expected technology advances include development of larger gasifiers, integration of these gasifiers with larger, more efficient combustion turbines, and use of ion transfer membrane (ITM) or other low-energy-demand oxygen supply technologies. Over the longer term, warm-gas cleanup and membrane separation processes for CO2 capture will reduce energy losses in these areas.
Key research milestones and deployment targets include:
• By 2012, field test ion transfer membrane technology, leading to pre-commercial testing of IGCC with oxy-combustion.
• By 2012, develop and evaluate hydrogen-fired F-class gas turbines, extending to G/H class gas turbine testing in 2020 and beyond.
• By 2017, achieve efficiencies of 33 to 35 percent for advanced integrated gasification combined-cycle coal plants equipped with CO2 capture.
• By 2020, demonstrate the FutureGen project with CO2 capture and storage.
• By 2025, demonstrate G/H-class turbine IGCC plants with CO2 capture.
• By 2030, demonstrate integrated gasification fuel cell (IGFC) plants.
The greatest reductions in future U.S. electric sector CO2 emissions likely will come from applying carbon capture and storage (CCS) technologies to nearly all new coal-based power plants coming on line after 2020. CCS technologies can be feasibly integrated into virtually all types of new coal-fired power plants, including IGCC, PC, circulating fluidized bed (CFB), and variants such as oxy-fuel combustion.
Currently, adding CO2 capture, drying, compression, transportation, and storage capabilities to IGCC plant designs would increase the wholesale cost of electricity by 40 to 50 percent. One promising cost-reduction pathway involves membrane technology for separating the CO2 from syngas, which could enable a 50-percent reduction in both the capital cost and auxiliary power requirements.
Post-combustion CO2 capture for PC plants uses a solvent to interact with the flue gas and adsorb the CO2. A 2000 EPRI-DOE study concluded that the energy needed by the current monoethanolamine (MEA) process would reduce net power by 29 percent and raise the cost of electricity by 65 percent. Extensive research is being done to test and develop better solvents, such as chilled ammonia, which may reduce power consumption to as low as 10 percent, with an associated cost-of-electricity increase of about 25 percent. Alstom and EPRI are conducting a 5-MWt pilot scale test of a chilled ammonia process at We Energies’ Pleasant Prairie Power Station. If successful, a 30-MW pilot will follow around 2010.
Key research milestones and deployment targets include:
• By 2012, conduct multiple 10-MW scale oxy-combustion pilot projects, leading to pre-commercial demonstration around 2020 and beyond.
• By 2015, conduct pilot projects demonstrating chilled ammonia and improved amine capture technologies.
• By 2020, develop new/improved processes and membrane contactors for post-combustion capture in support of Ultragen-II demonstration.
Geologic CO2 storage has been proven effective by nature, as evidenced by the numerous natural underground CO2 reservoirs in Colorado, Utah, and other Western states. Large-scale injection and storage of CO2 produced from electricity generation, however, has not been proven. DOE has an active R&D program, the “Regional Carbon Sequestration Partnerships,” which is mapping geologic formations suitable for CO2 storage and conducting pilot-scale CO2 injection validation tests across the country.
Key research milestones and deployment targets include:
• By 2010, complete the validation phase of the U.S. Department of Energy regional partnerships.
• By 2018, complete the deployment phase of the U.S. Department of Energy regional partnerships deployment phase.
• By 2020, conduct 3 to 5 large-scale demonstrations of CO2 storage (for multiple geologies) receiving captured CO2 from coal plants.
• By 2020, demonstrate commercial availability of CO2 storage capable of supporting new coal plants capturing 90 percent of CO2.