Fraunhofer USA Center for Sustainable Energy Systems

Consumer systems for home energy management can provide significant energy saving. Such systems may be based on nonintrusive appliance load monitoring (NIALM), in which individual appliance power consumption information is disaggregated from single-point measurements. The disaggregation methods constitute the most important part of NIALM systems. This paper reviews the methodology of consumer systems for NIALM in residential buildings.

Home energy displays are emerging home energy management devices. Their energy saving potential is limited, because most display whole-home electricity consumption data. We propose a new approach to disaggregation electricity consumption by individual appliances and/or end uses that would enhance the effectiveness of home energy displays. The proposed method decomposes a system of appliance models into tuplets of appliances overlapping in power draw. Each tuplet is disaggregated using a modified Viterbi algorithm. In this way, the complexity of the disaggregation algorithm is linearly proportional to the number of appliances. The superior accuracy of the method is illustrated by a simulation example and by actual household data.

Home energy displays are emerging home energy management devices. However, their energy savings potential is limited, because most display whole-home electricity consumption data. We propose a new approach to disaggregation electricity consumption by individual appliances and/or end uses that would enhance the effectiveness of home energy displays.

Traditional thermal designs of building envelope assemblies are based on static energy flows, yet building envelopes are subject to varying environmental conditions. This mismatch between the steady-state principles and their dynamic operation can decrease thermal efficiency. Design work supporting the development of low-energy houses showed that conventional insulations may not always be themost cost effective solution to improvement envelope thermal performance. PCM-enhanced building envelopes that simultaneously reduce the total cooling loads and shift the peak-hour loads are the focus of this report.

Consumer systems for home energy management can provide significant energy saving. Such systems may be based on nonintrusive appliance load monitoring (NIALM). This paper reviews algorithmic principles of consumer systems for NIALM in residential buildings.

Traditional thermal designs of building envelope assemblies are based on static energy flows, yet building envelopes are subject to varying environmental conditions. This mismatch between the steady-state principles and their dynamic operation can decrease thermal efficiency. Design work supporting the development of low-energy houses showed that conventional insulations may not always be the most cost effective solution to improvement envelope thermal performance. PCM-enhanced building envelopes that simultaneously reduce the total cooling loads and shift the peak-hour loads are the focus of this report.

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Human operators play a key role in the reliable operation of critical infrastructures. However, human operators may take actions that are far from optimum. This can be due to various factors affecting the operators' performance in time-sensitive and critical situations such as reacting to contingencies with significant monetary and social impacts. In this paper, an analytic framework is proposed based on Markov chains for modeling the dynamics of cascading failures in power grids. The model captures the effects of operators' behavior quantified by the probability of human error under various circumstances. In particular, the observations from historical data and information obtained from interviews with power-system operators are utilized to develop the model as well as identify its parameters. In light of the proposed model, the noncritical regions of power-system's operating characteristics with human-factor considerations are characterized under which the probability of large cascading failures is minimized.

Implementation of smart grid provides an opportunity for concurrent implementation of nonintrusive appliance load monitoring (NIALM), which disaggregates the total household electricity data into data on individual appliances. This paper introduces a new disaggregation algorithm for NIALM based on a modified Viterbi algorithm. This modification takes advantage of the sparsity of transitions between appliances' states to decompose the main algorithm, thus making the algorithm complexity linearly proportional to the number of appliances. By consideration of a series of data and integrating a priori information, such as the frequency of use and time on/time off statistics, the algorithm dramatically improves NIALM accuracy as compared to the accuracy of established NIALM algorithms.

Abstract Reduced optical transmittance of encapsulants resulting from ultraviolet (UV) degradation is frequently identified as a cause of decreased performance through the service life of photovoltaic modules. However, the present module safety and qualification standards apply short UV doses, only capable of examining design robustness and “infant mortality” failures. Furthermore, essential information remains unknown that might be used to screen encapsulants through product lifetime. We conducted an interlaboratory study to provide the understanding that will be used toward developing a higher‐fidelity, more‐rigorous UV weathering test. Five representative known formulations of poly (ethylene‐co‐vinyl acetate) were studied, in addition to one thermoplastic polyurethane material. Replicate laminated silica/polymer/silica specimens were examined at seven institutions using a variety of indoor chambers (including xenon, UVA‐340, and metal‐halide light sources). Specimens were artificially weathered for 180 cumulative days at steady‐state accelerated test conditions, predesignated relative to the default irradiance of 1.0 W·m −2 ·nm −1 at 340 nm, chamber temperature of 60°C, and chamber relative humidity of 30%. The solar‐weighted transmittance, yellowness index, and the UV cut‐off wavelength—each determined from the measured hemispherical transmittance—are examined to provide understanding and guidance for the UV light source (type lamp and filters), temperature, and humidity used in accelerated UV aging tests. The relative efficacy of xenon‐arc and UVA‐340 fluorescent sources and the typical range of activation energy for degradation is quantified from the experiments.

Emotions influence our everyday life in several ways. With the present study, we wanted to examine the impact of emotional information on neural correlates of semantic priming, a well-established technique to investigate semantic processing. Stimuli were presented with a short SOA of 200 ms as subjects performed a lexical decision task during fMRI measurement. Seven experimental conditions were compared: positive/negative/neutral related, positive/negative/neutral unrelated, nonwords (all words were nouns). Behavioral data revealed a valence specific semantic priming effect (i.e., unrelated > related) only for neutral and positive related word pairs. On a neural level, the comparison of emotional over neutral relations showed activation in left anterior medial frontal cortex, superior frontal gyrus, and posterior cingulate. Interactions for the different relations were located in left anterior part of the medial frontal cortex, cingulate regions, and right hippocampus (positive > neutral + negative) and left posterior part of medial frontal cortex (negative > neutral + positive). The results showed that emotional information have an influence on semantic association processes. While positive and neutral information seem to share a semantic network, negative relations might induce compensatory mechanisms that inhibit the spread of activation between related concepts. The neural correlates highlighted a distributed neural network, primarily involving attention, memory and emotion related processing areas in medial fronto-parietal cortices. The differentiation between anterior (positive) and posterior part (negative) of the medial frontal cortex was linked to the type of affective manipulation with more cognitive demands being involved in the automatic processing of negative information.

Mechanical load tests are a commonly-performed stress test where pressure is applied to the front and back sides of solar panels. In this paper we review the motivation for load tests and the different ways of performing them. We then discuss emerging durability concerns and ways in which the load tests can be modified and/or enhanced by combining them with other characterization methods. In particular, we present data from a new tool where the loads are applied by using vacuum and air pressure from the rear side of the panels, thus leaving the front side available for EL and IV characterization with the panels in the bent state. Tightly closed cracks in the cells can be temporarily opened by such a test, thus enabling a prediction of panel degradation in the field were these cracks to open up over time. Based on this predictive crack opening test, we introduce the concept of using a quick load test on each panel in the factory as a quality control tool and potentially as a type of burn-in test to initiate cracks that would certainly form early on during a panel's field life. We examine the stresses seen by the cells under panel load through Finite Element Modeling and demonstrate the importance of constraining the panel motion during testing as it will be constrained when mounted in the field.

Phase-change materials (PCMs) have a high heat of fusion compared to that of traditional material, and for this reason, they are able to store and release larger amounts of energy at their transition temperature. The inclusion of PCMs in buildings has attracted much interest worldwide because of their ability to reduce building energy demand and increase indoor comfort. This paper presents the development and testing results of a concrete tile system with microencapsulated PCMs. The concrete tiles were cast for use in a high-performance house built for the Solar Decathlon China 2013 competition. The paper shows that the addition of PCMs reduced the overall compressive and flexural strength properties of the concrete. A more than 25% decrease in compressive strength was observed with the addition of 20% PCM per volume of concrete. However, a significant improvement in the thermal properties of the concrete tile PCMs was measured. The thermal energy storage capability of the PCM-enhanced concrete tiles was determined using the dynamic heat flowmeter apparatus method. It was demonstrated that a 3.8-cm-thick concrete tile with 13.5% PCM had a thermal storage capacity equivalent to a 5.9-cm-thick tile of regular concrete, a 155% increase in thermal storage capability. Finally, the results indicate that the use of PCM in concrete floor tiles can significantly improve their thermal behavior, especially in lightweight buildings, while also keeping the concrete’s strength loss within an acceptable range.

Secondary frequency regulation is an electric grid ancillary service that balances the electric power system supply and demand on short time intervals. A companion article (Su and Norford 2015) developed and experimentally demonstrated a practical controller to modify chiller power demand to provide secondary frequency regulation with sufficient performance to meet market qualification requirements. This article compares experimental results to model predictions and to other sources of secondary frequency regulation. Delay time, ramp-rate limits, minimum power, and variable coefficient of performance are identified as factors that contribute to chiller power transient behavior and should be considered when predicting performance. This article additionally introduces results from a second building to assess the applicability of similar chiller control strategies for other HVAC systems. The second building produced less positive results due to communication delays associated with a modified setup and due to less favorable chiller characteristics, such as ramp-rate limitations and compressor cycling. While these constraints may be lessened with changes to chiller settings, the significant variations between the two buildings suggest that for a given site, observations are necessary in addition to design information to ascertain a chiller's suitability for providing secondary frequency regulation.

In this paper, we model three layers of transportation disruption – first electrification, then autonomy, and finally sharing and pooling – in order to project transportation electricity demand and greenhouse gas emissions in the United States to 2050. Using an expanded kaya identity framework, we model vehicle stock, energy intensity, and vehicle miles traveled, progressively considering the effects of each of these three disruptions. We find that electricity use from light duty vehicle transport will likely be in the 570–1140 TWh range, 13–26%, respectively, of total electricity demand in 2050. Depending on the pace at which the electric sector decarbonizes, this increase in electric demand could correspond to a decrease in LDV greenhouse gas emissions of up to 80%. In the near term, rapid and complete transport electrification with a carbon-free grid should remain the cornerstones of transport decarbonization policy. However, long-term policy should also aim to mitigate autonomous vehicles’ potential to increase driving mileage, urban and suburban sprawl, and traffic congestion while incentivizing potential energy efficiency improvements through both better system management and the lightweighting of an accident-free vehicle fleet.

Phase change material (PCM), placed in an exterior wall, alters the temperature profile within the wall and thus influences the heat transport through the wall. This may reduce the net energy transport through the wall via interactions with diurnal temperature swings in the external environment or reduce the electricity needed to meet the net load through the wall by shifting the time of the peak load to a time when the cooling system operates more efficiently. This study covers a broad range of parameters that can influence the effectiveness of such a merged thermal storage-thermal insulation system. These parameters included climate, PCM location within the wall, amount of PCM, midpoint of the PCM melting and freezing range relative to the indoor setpoint temperature, temperature range over which phase change occurs, and the wall orientation. Two climates are investigated using finite difference and optimization analyses: Phoenix and Baltimore, with two utility rate schedules. Although potential savings for a PCM with optimized properties were greater when the PCM was concentrated near the inside wall surface, other considerations described here lead to a recommendation for a full-thickness application. An examination of the temperature distribution within the walls also revealed the potential for this system to reduce the amount of energy transported through the wall framing. Finally, economic benefits can exceed energy savings when time-of-day utility rates are in effect, reflecting the value of peak load reductions for the utility grid.

Reduced optical transmittance of encapsulants resulting from ultraviolet (UV) degradation has frequently been identified as a cause of decreased PV module performance through the life of service in the field. The present module safety and qualification standards, however, apply short UV doses only capable of examining design robustness or “infant mortality” failures. Essential information that might be used to screen encapsulation through product lifetime remains unknown. For example, the relative efficacy of xenon-arc and UVA-340 fluorescent sources or the typical range of activation energy for degradation is not quantified. We have conducted an interlaboratory experiment to provide the understanding that will be used towards developing a climate- and configuration-specific (UV) weathering test. Five representative, known formulations of EVA were studied in addition to one TPU material. Replicate laminated silica/polymer/silica specimens are being examined at 14 institutions using a variety of indoor chambers (including Xenon, UVA-340, and metal-halide light sources) or field aging. The solar-weighted transmittance, yellowness index, and the UV cut-off wavelength, determined from the measured hemispherical transmittance, are examined to provide understanding and guidance for the UV light source (lamp type) and temperature used in accelerated UV aging tests.

In 2011, Amonix installed over 35 MW of concentration photovoltaic arrays across the U.S. Southwest. In order to meet the competitive price targets of these projects, improvements have been made across the power path, from optics to cell. Modules that were fielded in 2011 produced over 20% more power than those fielded in 2009. The recent deployments provide feedback that enables ongoing optimization for field conditions. The ratio of currents that are generated by each of the subcells in the III-V multijunction is monitored and compared to prediction. An understanding of the balance in subcell currents leads to retuning of the epitaxial structure for higher energy yield. Losses in the optical path, including the effect of gridline width, have been reduced substantially. High-production cell efficiencies, combined with significant improvements in the optical path, have led to peak dc module efficiencies that exceed 34% under operating conditions. A record module rating of 33.5% outdoor operating efficiency has been confirmed by the National Renewable Energy Laboratory.

ABSTRACT An approach to deriving two‐dimensional maps of cell and module electrical properties from electroluminescence imaging is presented. The technique involves quantitative comparison of the intensity differences in the electroluminescence images at different bias currents, enabling the derivation of junction voltages of individual pixels. These data were then fitted to a distributed electrical model that allows the derivation of a two‐dimensional dark I–V curve for each point across the module. Interpretation of the dark I–V curve enabled the evaluation of series resistance, shunt resistance, ideality factor, and reverse saturation current for each pixel. These parameters were then used to enable the prediction of module performance under illumination. Copyright © 2011 John Wiley & Sons, Ltd.