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Smart grids are rolling out internationally, with the United States (U.S.) nearing completion of a significant USD4-plus-billion federal program funded under the American Recovery and Reinvestment Act (ARRA-2009). The emergence of smart grids is widespread across developed countries. Multiple approaches to analyzing the benefits of smart grids haveemerged. The goals of this white paper are to review these approaches and analyze examples of each to highlight their differences, advantages, and disadvantages.This work was conducted under the auspices of a joint U.S.-China research effort, the Climate Change Working Group (CCWG) Implementation Plan, Smart Grid. We present comparative benefits assessments (BAs) of smart grid demonstrations in the U.S. and China along with a BA of a pilot project in Europe. In the U.S., we assess projects at two sites: (1) the University of California, Irvine campus (UCI), which consists of two distinct demonstrations: Southern California Edison’s (SCE) Irvine Smart Grid Demonstration Project (ISGD) and the UCI campus itself; and (2) the Navy Yard (TNY) area in Philadelphia, which has been repurposed as a mixed commercial-industrial, and possibly residential, development. In China, we cover several smart-grid aspects of the Sino-Singapore Tianjin Eco-city (TEC) and the Shenzhen Bay Technology and Ecology City (B-TEC). In Europe, we look at a BA of a pilot smart grid project in the Malagrotta area west of Rome, Italy, contributed by the Joint Research Centre (JRC) of the European Commission.The Irvine sub-project BAs use the U.S. Department of Energy (U.S. DOE) Smart Grid Computational Tool (SGCT), which is built on methods developed by the Electric Power Research Institute (EPRI). The TEC sub-project BAs apply Smart Grid Multi-Criteria Analysis (SG-MCA) developed by the State Grid Corporation of China (SGCC) based on the analytic hierarchy process (AHP) with fuzzy logic. The B-TEC and TNY sub-project BAs are evaluated using new approaches developed by those project teams. JRC has adopted an approach similar to EPRI’s but tailored to the Malagrotta distribution grid.

The introduction of fuel cell electric vehicles (FCEV) operating on hydrogen is a key strategy to mitigate pollutant emissions from the light duty vehicle (LDV) transportation sector in pursuit of air quality (AQ) improvements. Further, concomitant increases in renewable power generation could assist in achieving benefits via electrolysis-provided hydrogen as a vehicle fuel. However, it is unclear (1) reductions in emissions translate to changes in primary and secondary pollutant concentrations and (2) how effects compare to those from emissions in other transport sectors including heavy duty vehicles (HDV). This work assesses how the adoption of FCEVs in counties expected to support alternative LDV technologies affect atmospheric concentrations of ozone and fine particulate matter (PM2.5) throughout California (CA) in the year 2055 relative to a gasoline vehicle baseline. Further, impacts of reducing HDV emissions are explored to facilitate comparison among technology classes. A base year emissions inventory is grown to 2055 representing a business-as-usual progression of economic sectors, including primarily petroleum fuel consumption by LDV and HDVs. Emissions are spatially and temporally resolved and used in simulations of atmospheric chemistry and transport to evaluate distributions of primary and secondary pollutants respective to baseline. Results indicate that light-duty FCEV Cases achieve significant reductions in ozone and PM2.5 when LDV market shares reach 50–100% in early adoption counties, including areas distant from deployment sites. Reflecting a cleaner LDV baseline fleet in 2055, emissions from HDVs impact ozone and PM2.5 at comparable or greater levels than light duty FCEVs. Additionally, the importance of emissions from petroleum fuel infrastructure (PFI) activity is demonstrated in impacts on ozone and PM2.5 burdens, with large refinery complexes representing a key source of air pollution in 2055. Results presented provide insight into light duty FCEV deployment strategies that can achieve maximum reductions in ozone and PM2.5 and will assist decision makers in developing effective transportation sector AQ mitigation strategies.

A dynamic internal reforming-solid oxide fuel cell system model is developed and used to simulate the coproduction of electricity and hydrogen while meeting the measured dynamic load of a typical southern California commercial building. The simulated direct internal reforming-solid oxide fuel cell (DIR-SOFC) system is controlled to become an electrical load following device that well follows the measured building load data (3-s resolution). The feasibility of the DIR-SOFC system to meet the dynamic building demand while co-producing hydrogen is demonstrated. The resulting thermal responses of the system to the electrical load dynamics as well as those dynamics associated with the filling of a hydrogen collection tank are investigated. The DIR-SOFC system model also allows for resolution of the fuel cell species and temperature distributions during these dynamics since thermal gradients are a concern for DIR-SOFC. © 2013 Elsevier B.V. All rights reserved.

Direct internal reformation of methane in solid oxide fuel cells (SOFCs) leads to two major performance and longevity challenges: thermal stresses in the cell due to large temperature gradients and coke formation on the anode. A simplified quasi-two-dimensional direct internal reformation SOFC (DIR-SOFC) dynamic model was developed for investigation of the effects of various parameters and assumptions on the temperature gradients across the cell. The model consists of 64 nodes, each containing four control volumes: the positive electrode, electrolyte, negative electrode (PEN), interconnect, anode gas, and cathode gas. Within each node the corresponding conservation and chemical and electrochemical reaction rate equations are solved. The model simulates the counter-flow configuration since previous research (Achenbach, 1994, "Three-Dimensional and Time-Dependent Simulation of a Planar Solid Oxide Fuel Cell Stack," J. Power Sources, 49(1), p. 333) has shown this configuration to yield the smallest temperature differentials for DIR-SOFCs. Steady state simulations revealed several results where the temperature difference across the cell was considerably affected by operating conditions and cell design parameters. Increasing the performance of the cell through modifications to the electrochemical model to simulate modern cell performance produced significant changes in the cell temperature differential. Improved cell performance led to a maximum increase in the temperature differential across the cell of 31 K. An increase in the interconnect thickness from 3.5 to 4.5 mm was shown to reduce the PEN temperature difference about 50 K. Variation of other physical parameters such as the thermal conductivity of the interconnect and the rib width also showed significant effects on the temperature distribution. The sensitivity of temperature distribution to heat losses was also studied, showing a considerable effect near the fuel and air inlets. Increased heat transfer from the cell edges resulted in severe temperature gradients approaching 160 K/cm. The dynamic capability of the spatially resolved dynamic model was also demonstrated for a 45% power increase perturbation while maintaining constant fuel and air utilizations. Copyright © 2012 by American Society of Mechanical Engineers.

Spatial temperature feedback control has been developed for a simulated integrated non-pressurized simple cycle solid oxide fuel cell (SOFC) system. The fuel cell spatial temperature feedback controller is based on (1) feed-forward set-points that minimize temperature variation in the fuel cell electrode-electrolyte solid temperature profile for the system operating power range, and (2) decentralized proportional-integral based feedback to maintain the fuel cell spatial temperature profile during transients and disturbances. Simulation results indicate the fuel cell spatial temperature variation can be maintained within 15 degrees of nominal to significant load perturbations. Temperature gradients through the fuel cell are needed to remove the heat generated within the cell and cannot be avoided. The goal of the developed spatial temperature control is to minimize temperature variations from a nominal temperature profile in time. Minimal temperature variations in the SOFC electrode-electrolyte solid assembly will result in decreased thermal stresses and thereby decreased degradation and probability-of-failure. Simulation results demonstrating the ability to maintain the SOFC spatial temperature during large load perturbations indicates SOFC could be designed and controlled for rapid load following capability. Such performance can greatly improve SOFC system operating flexibility and thereby open new markets for SOFC systems including load following or spinning reserve services for the utility grid. © 2010 by ASME.

Direct internal reformation of methane in solid oxide fuel cells (SOFCs) leads to two major performance and longevity challenges: thermal stresses in the cell due to large temperature gradients and coke formation on the anode. A simplified quasi-two-dimensional direct internal reformation SOFC (DIR-SOFC) dynamic model was developed for investigation of the effects of various parameters and assumptions on the temperature gradients across the cell. The model consists of 64 nodes each of which contains four control volumes: the positive electrode, electrolyte, negative electrode (PEN); interconnect; anode gas; and cathode gas. Within each node the corresponding conservation, chemical, and electrochemical reaction equations are solved. The model simulates the counterflow configuration since previous research [8] has shown this configuration to yield the smallest temperature differentials. Steady state simulations revealed several results where the temperature difference across the cell was considerably affected by operating and cell design parameters. Increasing the performance of the cell through modifications to the electrochemical model to simulate modern cell performance produced significant changes in the cell temperature differential. Improved cell performance led to a maximum increase in the temperature differential across the cell of 31 K. An increase in the interconnect thickness also exhibits a considerable reduction in the temperature difference across the PEN. In particular, increasing the interconnect thickness from 3.5 to 4.5 mm can achieve about a 50 K reduction in the cross cell temperature difference. Variation of other physical parameters such as the thermal conductivity of the interconnect and the rib width also showed an effect on the temperature distribution. The sensitivity of temperature distribution to the adiabatic assumption was also performed and results showed a considerable effect near the fuel and air inlets. This resulted in severe temperature gradients approaching 160 K/cm. Copyright © 2009 by ASME.

A simplified quasi-3-dimensional model of a solid oxide fuel cell (SOFC) is developed to investigate the dynamics of internal reformation in an SOFC. The dynamic model solves dynamic equations that govern relevant physical and chemical processes in a simplified geometric representation of a planar SOFC. This makes the model complex enough to resolve major performance characteristics and simple enough to be used in dynamic analyses and controls development at the system level. The model solves dynamic mass, momentum and energy conservation equations to provide local temperature, species concentrations, and current density distributions. These distributions are resolved in two dimensions across the cell, but each 2-D distribution resolves 5 separate control volumes through the nodal unit cell: the PEN; anode and cathode gas compartments; and interconnects. Internal reforming chemical kinetic expressions are included in the model formulation. Simulations show that extent of internal reformation impacts the dynamic temperature difference across the cell. Steady state maximum temperature differential across the cell can be reduced to about 100 K with 100% internal reformation and a cross-flow configuration. A full hydrogen co-production system was then modeled by integrating the SOFC model with heat exchangers, combustor, blower, and hydrogen collector. For conditions of a constant cathode exhaust temperature of 1273 K and lower fuel utilization (60%-70%), the dominant thermal influence on the cell temperature was cooling by the endothermic reformation reactions. But at higher fuel utilization conditions, the dominant thermal influence was the convective cooling of the cathode gases. System simulations showed no tradeoff between power and H 2 production if the cathode exhaust temperature is held constant at 1273 K. High power and high H2 production conditions were found to be synergistic: high hydrogen production leads to high electrochemical efficiency and lower air flow rate leading to fewer parasitic losses. Dynamic SOFC responses to manipulation of fuel flow rate within the range of fuel utilization between 60 and 85% indicate that the system can be adequately controlled to produce various amounts of hydrogen and electricity. Copyright © 2008 by ASME.