Zeifman M.,Fraunhofer Center for Sustainable Energy Systems
IEEE Transactions on Consumer Electronics | Year: 2012
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. © 2006 IEEE.
Zeifman M.,Fraunhofer Center for Sustainable Energy Systems
2015 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2015 | Year: 2015
Proper evaluation of energy saving effect due to implementation of smart building technologies in residences requires statistical samples of treatment and control households. We show how to create a non-experimental control sample and use it for saving evaluation on the basis of a novel algorithm for prediction of participation propensity. © 2015 IEEE.
Zeifman M.,Fraunhofer Center for Sustainable Energy Systems |
Roth K.,Fraunhofer Center for Sustainable Energy Systems
Digest of Technical Papers - IEEE International Conference on Consumer Electronics | Year: 2011
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. ©2011 IEEE.
Zeifman M.,Fraunhofer Center for Sustainable Energy Systems
Conference Proceedings - IEEE International Conference on Systems, Man and Cybernetics | Year: 2014
Massive rollout of residential smart meters has spurred interest in processing the highly granular data available from these devices. Whereas the majority of smart meter data analytics is devoted to characterization of household electric appliances and their operational schedules, little work has been done to leverage these data to predict household propensity to enroll in energy efficiency and demand response programs. The state-of-the-art methodology for household enrollment prediction involves measurable household characteristics (e.g., age, household income, education, presence of children, average energy bill) and a multivariate logistic regression that connects these predictor variables with the probability to enroll. Unfortunately, the prediction accuracy of this method is just slightly better than 50%, and the required household data are not freely available to utilities/ program contractors. We developed a new method for prediction of household propensity to enroll using only hourly electricity consumption data from households' smart meters, collected over twelve months. The method implements advanced machine learning algorithms to reach an unprecedented prediction accuracy of about 90%. This level of accuracy was obtained in our study of a US West Coast behavior-based residential program. © 2014 IEEE.
Tiefenbeck V.,Fraunhofer Center for Sustainable Energy Systems |
Tiefenbeck V.,ETH Zurich |
Staake T.,ETH Zurich |
Roth K.,Fraunhofer Center for Sustainable Energy Systems |
Sachs O.,Fraunhofer Center for Sustainable Energy Systems
Energy Policy | Year: 2013
Isolated environmental campaigns focusing on defined target behaviors are rolled out to millions of households every year. Yet it is still unclear whether these programs trigger cross-domain adoption of additional environment-friendly behaviors (positive spillover) or reduced engagement elsewhere. A thorough evaluation of the real net performance of these programs is lacking. This paper investigates whether positive or perverse side effects dominate by exemplifying the impact of a water conservation campaign on electricity consumption. The study draws on daily water (10,780 data points) and weekly electricity (1386 data points) consumption data of 154 apartments in a controlled field experiment at a multifamily residence. The results show that residents who received weekly feedback on their water consumption lowered their water use (6.0% on average), but at the same time increased their electricity consumption by 5.6% compared with control subjects. Income effects can be excluded. While follow-up research is needed on the precise mechanism of the psychological process at work, the findings are consistent with the concept of moral licensing, which can more than offset the benefits of focused energy efficiency campaigns, at least in the short-term. We advocate the adoption of a more comprehensive view in environmental program design/evaluation in order to quantify and mitigate these unintended effects. © 2013 Elsevier Ltd.
KoSny J.,Fraunhofer Center for Sustainable Energy Systems |
Biswas K.,Oak Ridge National Laboratory |
Miller W.,Oak Ridge National Laboratory |
Kriner S.,Metal Construction Association
Solar Energy | Year: 2012
For decades, residential and commercial roofs have been considered a prime location for installation of building integrated solar systems. In climatic conditions of East Tennessee, USA, an experimental solar roof was tested during 2009/2010, by a research team representing Metal Construction Association (MCA), and a consortium of building insulation companies, photovoltaic (PV) manufacturers, and energy research centers. The main objective was to thermally evaluate a new roofing technology utilizing amorphous silicon PV laminates integrated with the metal roof panels. In order to mitigate thermal bridging and reduce roof-generated thermal loads, this novel roof/attic assembly contained a phase change material (PCM) heat sink, a ventilated air cavity over the roof deck, and thermal insulation with an integrated reflective surface. During winter, the experimental roof was expected to work as a passive solar collector storing solar heat absorbed during the day, and increasing overall attic air temperature during the night. During summer, the PCM was expected to act as a heat sink, reducing the heat gained by the attic and consequently, lowering the building cooling-loads. In this paper, field thermal performance data of the experimental PV-PCM roof/attic system are presented and discussed. Performance of the PV-PCM roof/attic is evaluated by comparing it to a control asphalt shingle roof. The test results showed about 30% heating and 50% cooling load reductions are possible with the experimental roof configuration. © 2012 Elsevier Ltd.
Li B.,Fraunhofer Center for Sustainable Energy Systems |
Stokes A.,Fraunhofer Center for Sustainable Energy Systems |
Doble D.M.J.,Fraunhofer Center for Sustainable Energy Systems
Progress in Photovoltaics: Research and Applications | Year: 2012
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. © 2011 John Wiley & Sons, Ltd.
Kosny J.,Fraunhofer Center for Sustainable Energy Systems |
Kossecka E.,Polish Academy of Sciences |
Brzezinski A.,LaserComp |
Tleoubaev A.,LaserComp |
Yarbrough D.,RandD Services
Energy and Buildings | Year: 2012
Experimental and theoretical analyses have been performed to determine dynamic thermal characteristics of fiber insulations containing microencapsulated phase change material (PCM). It was followed by a series of transient computer simulations to investigate the performance of a wood-framed wall assembly with PCM-enhanced fiber insulation in different climatic conditions. A novel lab-scale testing procedure with use of the heat flow meter apparatus (HFMA) was introduced in 2009 for the analysis of dynamic thermal characteristics of PCM-enhanced materials. Today, test data on these characteristics is necessary for whole-building simulations, energy analysis, and energy code work. The transient characteristics of PCM-enhanced products depend on the PCM content and a quality of the PCM carrier. In the past, the only existing readily-available method of thermal evaluation of PCMs utilized the differential scanning calorimeter (DSC) methodology. Unfortunately, this method required small and relatively uniform test specimens. This requirement is unrealistic in the case of many PCM-enhanced building envelope products. Small specimens are not representative of PCM-based blends, since these materials are not homogeneous. In this paper, dynamic thermal properties of materials, in which phase change processes occur, are analyzed based on a recently-upgraded dynamic experimental procedure: using the conventional HFMA. In order to theoretically analyze performance of these materials, an integral formula for the total heat flow in finite time interval, across the surface of a wall containing the phase change material, was derived. In numerical analysis of the southern-oriented wall the Typical Meteorological Year (TMY) weather data was used for the summer hot period between June 30th and July 3rd. In these simulations the following three climatic locations were used: Warsaw, Poland, Marseille, France, and Cairo, Egypt. It was found that for internal temperature of 24 °C, peak-hour heat gains were reduced by 23-37% for Marseille and 21-25% for Cairo; similar effects were observed for Warsaw. © 2012 Elsevier B.V. All rights reserved.
Fraunhofer Center for Sustainable Energy Systems | Date: 2011-06-21
A photovoltaic module includes a plurality of solar cells, each solar cell having an active front side and a back side. A busbar is provided and has a first portion that is electrically connected to an active front side of a first solar cell, and a second portion that is electrically connected to a back side of a second solar cell. At least a front side of the first portion of the busbar includes a diffuse reflective coating.
News Article | January 13, 2016
GTM has been following the employee exodus at NRG, since NRG's newly formed GreenCo (which includes NRG Home Solar and NRG Renew, as well as EVgo, the company’s electric-vehicle infrastructure business) could be moving toward the chopping block. Last month, GTM covered the resignation of NRG Energy CEO David Crane from a post he’d held since 2003. Also resigning from NRG recently was Robyn Beavers, the "founder and leader of the newly formed Station A Group, a microgrid skunk works within the power company." GTM has now learned that Tom Doyle, the CEO of NRG Renew, has left the firm. NRG has confirmed. Recently, GTM reported that Steve McBee, CEO at NRG Home for a little more than a year, will be leaving NRG as well. McBee is the founder and CEO of McBee Strategic, a Washington, D.C.-based lobbying and advisory firm that has served a number of energy clients. He intends to remain in the energy field. There are more names to add to the list. According to Power Finance & Risk, Denise Wilson, the executive VP and president of Alternative Energy Services, has left the firm. In 2014, Wilson told GTM, "NRG has decided to be a leader in residential solar." John Ragan, EVP and president of the Gulf Coast region, has also left the firm, according to reports. There are some more departures in the works. We'll keep you posted. Stem hired Larsh Johnson as CTO of the fast-growing behind-the-meter energy storage startup. Johnson was previously CTO and co-founder of eMeter, a VC-funded smart meter data management firm acquired by Siemens in 2012. Johnson will lead the hardware and software teams at Stem. Siluria Technologies, looking to convert natural gas to ethylene and from there to fuel, promoted Erik Scher, currently executive VP and co-founder, to the role of interim CEO, replacing Ed Dineen. Solaria, a VC-funded solar module technology startup, added Scott Hoover as VP of sales for building-integrated PV products for North America. Hoover has worked at building firms AGC and Pilkington and was most recently director of sales at defunct BIPV firm Pythagoras Solar. Mathew Sachs, previously VP of originations at K Road DG, has joined National Grid as VP of distributed energy development. Johanna (Wendlandt) Wolfson is now director of technology-to-market at the U.S. Department of Energy. Wolfson was previously TechBridge program lead at the Fraunhofer Center for Sustainable Energy Systems. Jake Carney is now a managing partner at solar project developer 38 Degrees North. He was most recently director of project finance at SunEdison. Maya Biery, formerly an associate in government affairs at SunEdison, is now renewable energy strategy analyst at PG&E. Enertech Search Partners, an executive search firm with a dedicated cleantech practice, is the sponsor of the GTM jobs column. The firm has an active opening for a CFO: The client is an intelligent distributed energy storage system that captures solar power and delivers it when needed most. It combines batteries, power electronics, and multiple energy inputs in a UL-certified appliance controlled by software running in the cloud. The client is seeking a Chief Financial Officer that will report directly to the CEO and will be responsible for all financial aspects of the company. In this role, you will provide guidance and support on financial and business matters, as well as growth strategy, business systems, human resources and financial and treasury issues. This role will also serve as the leader of a three-person team that includes the Controller and the Director of Financial Planning and Administration. The next West Texas energy boom? As we just reported, the U.S. solar industry provides more jobs than the oil and gas extraction industry. The Solar Foundation's annual Solar Jobs Census Report showed approximately 20 percent growth in solar employment across the U.S. in 2015. Recurrent Energy (a sponsor of the report) provides a video showing the impact of a 157.5-megawatt Roserock solar project on a small West Texas town's employment landscape. Tesla Motors has grown from 900 employees in 2010 to 14,000 employees today. Larry Weis, former head of Austin Energy, will become the new CEO of Seattle City Light, one of the largest publicly-owned utilities in the U.S., on February 1. The role has a base salary of $340,000 a year, making Weis the highest-paid city employee, according to the Austin American-Statesman. SunPower named Eduardo Medina as executive VP of power plants. Medina, based in SunPower's Lyon, France office, most recently served as executive managing director and head of business development for Acciona Energia, a Spanish-based developer of infrastructure, energy, water and sustainable services.