Articles

Evaluation of Time Series Techniques to Characterise Domestic Electricity Demand

Fintan McLoughlin et al. — Tue, 05 Feb 2013 04:05:41 PST

This paper discusses time series approaches, often used by Transmission System Operators (TSOs) to forecast system demand, and applies them at an individual dwelling level. In particular, two techniques, Fourier transforms and Gaussian processes were evaluated and used to characterise individual household electricity demand. The performance of the characterisation approaches were evaluated based on Pearson correlation coefficient, descriptive statistics and paired sample t-tests for electrical parameters: Total Electricity Consumption, Maximum Demand, Load Factor and Time of Use of maximum electricity demand. Finally, a number of time series tests were carried out to ensure certain properties remained between the original and characterised series.

Both Fourier transforms and Gaussian processes were shown to be suitable techniques for characterising domestic electricity demand. Depending on customer demand load profiles, each approach has its own strengths and weaknesses. Fourier transforms are better at characterising the profiles of customers who consume electricity more evenly across the day (>1h). In contrast, Gaussian processes are better at characterising customers whose demand is high for only short periods of time (<1h).

The Generation of Domestic Electricity Load Profiles through Markov Chain Modelling

Fintan McLoughlin et al. — Mon, 04 Feb 2013 06:20:37 PST

Micro-generation technologies such as photovoltaics and micro-wind power are becoming increasing popular among homeowners, mainly a result of policy support mechanisms helping to improve cost competiveness as compared to traditional fossil fuel generation. National government strategies to reduce electricity demand generated from fossil fuels and to meet European Union 20/20/20 targets is driving this change. However, the real performance of these technologies in a domestic setting is not often known as high time resolution models for domestic electricity load profiles are not readily available. As a result, projections in terms of reducing electricity demand and financial paybacks for these micro-generation technologies are not always realistic.

Domestic electricity load profi les are often highly stochastic, influenced by many different independent variables such as environmental, dwelling and occupant characteristics that shape individual customer’s load across a single day. This paper presents a stochastic method for generating electricity load profiles based on the application of a Markov chain process. Electricity consumption was recorded at half hourly intervals over a six month period for fi ve individual Irish dwelling types and used to generate synthetic electricity load profi les. The purpose of this paper is to determine whether Markov chain modelling is an effective way of re-generating electricity load profiles for domestic dwellings and identify shortcomings with this particular technique. The results show that the magnitude component of the load profile can be reproduced effectively whilst the temporal distribution needs to be addressed further.

The Effects of Physical Activity on Greenhouse Gas Emissions for Common Transport Modes in European Countries

Aidan Duffy et al. — Mon, 07 Jan 2013 06:40:34 PST

This paper applies a life cycle methodology to estimate activity-related contributions of transport modes to GHG emissions. The methodology uses national input-output tables, environmental accounts, household budget data and nutritional data to derive food-sector GHG coefficients of consumption for ten European countries. The food energy requirements for each mode of transport are estimated taking account of the modal activity level and energy requirements. Walking, cycling, driving and bus travel are considered. Typical national food energy-related emissions for walking, cycling, and driving ranged from 25.6 - 77.3 gCO2-eq/pass.km, 10.4 - 31.4 gCO2-eq/pass.km and 1.7 - 5.2 gCO2-eq/pass.km; passenger transport was found to result in no food-related emissions above those for a resting individual. Emissions vary between countries and depend on the emissions intensities of their energy sectors as well as food prices and average body weights. A life cycle assessment of modal emissions in the UK was undertaken using the food-energy emissions intensities estimated. UK car travel was found to have the highest emissions intensity, followed by bus travel, cycling and walking.

Developing Archetypes for Domestic Dwellings:an Irish Case Study

A. A. Famuyibo et al. — Thu, 07 Jun 2012 04:03:02 PDT

Stock modelling, based on representative archetypes, is a promising tool for exploring areas for resource and emission reductions in the residential sector. The use of archetypes developed using detailed statistical analysis (multi-linear regression analysis, clustering and descriptive statistics) rather than traditional qualitative techniques allows a more accurate representation of the overall building stock variability in terms of geometric form, constructional materials and operation. This paper presents a methodology for the development of archetypes based on information from literature and a sample of detailed energy-related housing data. The methodology involves a literature review of studies to identify the most important variables which explain energy use and regression analysis of a housing database to identify the most relevant variables associated with energy consumption. A statistical analysis of the distributions for each key variable was used to identify representative parameters. Corresponding construction details were chosen based on knowledge of housing construction details. Clustering analysis was used to identify coincident groups of parameters and construction details; this led to the identification of 13 representative archetypes.

Characterising Domestic Electricity Consumption Patterns by Dwelling and Occupant Socio-economic Variables: An Irish Case Study

Fintan McLoughlin et al. — Fri, 24 Feb 2012 01:41:47 PST

This paper examines the influence of dwelling and occupant characteristics on domestic electricity consumption patterns by analysing data obtained from a smart metering survey of a representative cross section of approximately 4,200 domestic Irish dwellings. A multiple linear regression model was applied to four parameters: total electricity consumption, maximum demand, load factor and time of use (ToU) of maximum electricity demand for a number of different dwelling and occupant socio-economic variables. In particular, dwelling type, number of bedrooms, head of household (HoH) age, household composition, social class, water heating and cooking type all had a significant influence over total domestic electricity consumption. Maximum electricity demand was significantly influenced by household composition as well as water heating and cooking type. A strong relationship also existed between maximum demand and most household appliances but, in particular, tumble dryers, dishwashers and electric cookers had the greatest influence over this parameter. Time of use (ToU) for maximum electricity demand was found to be strongly influenced by occupant characteristics, HoH age and household composition. Younger head of households were more inclined to use electricity later in the evening than older occupants. The appliance that showed the greatest potential for shifting demand away from peak time use was the dishwasher.

Enhanced Quantum Dot Emission for Luminescent Solar Concentrators Using Plasmonic Interaction

Subhash Chandra et al. — Mon, 13 Feb 2012 01:36:51 PST

Plasmonic excitation enhanced fluorescence of CdSe/ZnS core-shell quantum dots (QDs) in the presence of Au nanoparticles (NPs) has been studied for application in quantum dot solar concentrator (QDSC) devices. We observe that there is an optimal concentration of Au NPs that gives a maximum 53% fluorescence emission enhancement for the particular QD/Au NP composite studied. The optimal concentration depends on the coupling and spacing between neighboring QDs and Au NPs. We show the continuous transition from fluorescence enhancement to quenching, depending on Au NP concentration. The locally enhanced electromagnetic field induced by the surface plasmon resonance in the Au NPs leads to an increased excitation rate for the QDs. This is evidenced by excitation wavelength dependent fluorescence enhancement, where the locally enhanced field around the Au NPs is more pronounced close to the surface plasmon resonance (SPR) wavelength. However, at higher concentrations of Au NPs non-radiative energy transfer from the QDs to the Au NPs particles leads to a decrease of the emission, which is confirmed by detection of both a double exponential lifetime decay in, and a decrease in the lifetime of the QDs. The overall fluorescence emission enhancement depends on these competing effects; increased excitation rate and non-radiative energy transfer.

Natural Convection in an Internally Finned Phase Change Material Heat Sink for the Thermal Management of Photovoltaics

M. J. Huang et al. — Wed, 06 Apr 2011 06:52:44 PDT

Elevated operating temperatures reduce the solar to electrical conversion efficiency of building integrated photovoltaic devices (BIPV). Phase change materials (PCM) can be used to passively limit this temperature rise although their effectiveness is limited by their low thermal conductivities and by crystallization segregation during solidification. This paper presents an experimental evaluation of the effects of convection and crystalline segregation in a PCM as a function of efficiency of heat transfer within the finned PV/PCM system. The thermal performances of bulk PCM with crystallization segregation for different internal fin arrangements are presented. It is noted that the addition of internal fins improves the temperature control of the PV in a PV/PCM system.

Identification of ‘Carbon Hot-Spots’ and Quantification 1 of GHG Intensities in the Biodiesel Supply Chain using Hybrid LCA and Structural Path Analysis

Adolf Acquaye et al. — Wed, 23 Mar 2011 02:45:59 PDT

It is expected that biodiesel production in the EU will remain the dominant contributor as part of a 10% minimum binding target for biofuel in transportation fuel by 2020 within the 20% renewable energy target in the overall EU energy mix. Life cycle assessments (LCA) of biodiesel to evaluate its environmental impacts have, however, remained questionable, mainly because of the adoption of a traditional process analysis approach resulting in system boundary truncation and because of issues regarding the impacts of land use change and N2O emissions from fertiliser application. In this study, a hybrid LCA methodology is used to evaluate the life cycle CO2 equivalent emissions of rape methyl ester (RME) biodiesel. The methodology uses input-output analysis to estimate upstream indirect emissions in order to complement traditional process LCA in a hybrid framework. It was estimated that traditional LCA accounted for 2.7 kg CO2-eq per kg of RME or 36.6% of total life cycle emissions of
28 the RME supply chin. Further to the inclusion of upstream indirect impacts in the LCA system (which accounted for 23% of the total life cycle emissions), emissions due to direct land use change (6%) and indirect land use change (16.5%) and N2O emissions from fertiliser applications (17.9%) were also calculated. Structural path analysis is used to decompose upstream indirect emissions paths of the biodiesel supply chain in order to identify, quantify and rank high carbon emissions paths or ‘hot-spots’ in the biodiesel supply chain. It was shown, for instance, that inputs from the ‘Other Chemical Products’ sector (identified as phosphoric acid, H3PO4) into the biodiesel production process represented the highest carbon emission path (or hot-spot) with 5.35% of total upstream indirect emissions of the RME biodiesel supply chain.

Stochastic Hybrid Embodied CO2-eq Analysis: An Application to the Irish Apartment Building Sector

Adolf Acquaye et al. — Wed, 23 Mar 2011 02:45:57 PDT

Although embodiedCO2-eq analysis has seen recent developments as evident in the establishment of the ISO14040 and 14044 LCA standards, it is recognized that due to weaknesses in gathering data on product-related emissions,embodiedCO2-eq values are probabilistic. This paper presents a stochastic analysis of hybrid embodied CO2-eq in buildings to account for this weakness in traditional methods and, by way of example, applies it to an Irish construction-sector case study. Using seven apartment buildings, 70,000 results are simulated with Monte Carlo analysis and used to derive probabilistic and cumulative embodied CO2-eq intensity distributions for apartment buildings in Ireland. A Wakeby distribution with known statistical parameters and uncertainty was derived for the average embodied CO2-eq intensity of apartment building in Ireland. The mean hybrid embodied CO2-eq (ECO2-eq) intensity was estimated to be 1,636gCO2-eq/€ with an uncertainty of 73gCO2-eq/€ . The stochastic analysis helps to account for variability in input variables into embodied CO2-eq analysis. The application of the stochastic embodied CO2-eq analysis as demonstrated in this study can be extended to other building sectors and countries and can form the basis for the development of evidence-based policy formulation since it provides greater information on embodied CO2-eq intensities of buildings than deterministic approaches.

Solar Radiation Modeling for the Simulation of Photovoltaic Systems

J. Mondol et al. — Thu, 27 Jan 2011 09:51:23 PST

Quarter-Wave Metal Plate Solar Antenna

S.V. Shynu et al. — Thu, 27 Jan 2011 09:51:20 PST

A novel design of a quarter-wave shorted trapezoidal metal plate solar antenna using high efficiency polycrystalline silicon solar cells is presented. Using the DC conductive parts of the cell as RF antenna elements as well as choosing the radiating element to be a small base trapezoid, better coupling between the feed and shorting plates is ensured and 40.3% size reduction compared to a conventional shorted quarter-wave patch is obtained. The trapezoidal radiating element covers merely 2.7% of the total available illumination area of the solar cell, leaving its efficiency essentially unaffected. The proposed design strategy has been verified by an instantiation operating at 1.957 GHz and has a wide impedance bandwidth of 15.2% with a gain of 4.5dBi.

Emitter-Wrap-Through Photovoltaic Dipole Antenna with Solar Concentrator

Maria Roo Ons et al. — Thu, 27 Jan 2011 09:51:14 PST

A novel photovoltaic dipole antenna employing a solar concentrator as a reflector is proposed. Four identical emitter-wrap-through rear contact solar cells connected in series as a folded dipole are simultaneously used for power generation and as the antenna radiating element, which is located in the focal line of a parabolic solar concentrator. The parabolic structure acts as a solar concentrator for the photovoltaic cells as well as a reflector for the folded dipole antenna. Full-wave electromagnetic simulation with supportive experimental work validates this design. The measured fractional impedance bandwidth and gain were 21% and 11.1 dBi, respectively. The antenna/solar arrangement provide a power output of 73.7 mW for an irradiance of 1000 Wm22.

Integration of Microstrip Patch Antennas with Polycrystalline Silicon Solar Cells

S.V. Shynu et al. — Thu, 27 Jan 2011 09:51:12 PST

The implementation of a polycrystalline silicon solar cell as a microwave groundplane in a low-profile, reduced-footprint microstrip patch antenna design for autonomous communication applications is reported. The effects on the antenna/solar performances due to the integration, different electrical conductivities in the silicon layer and variation in incident light intensity are investigated. The antenna sensitivity to the orientation of the anisotropic solar cell geometry is discussed.

Evaluation of Phase Change Materials for Thermal Regulation Enhancement of Building Integrated Photovoltaics

A. Hasan et al. — Thu, 27 Jan 2011 09:51:10 PST

Regulating the temperature of building integrated photovoltaics (BIPV) using phase change materials (PCMs) reduces the loss of temperature dependent photovoltaic (PV) efficiency. Five PCMs were selected for evaluation all with melting temperatures 25 ± 4 C and heat of fusion between 140 and 213 kJ/kg. Experiments were conducted at three insolation intensities to evaluate the performance of each PCM in four different PV/PCM systems. The effect on thermal regulation of PV was determined by changing the (i) mass of PCM and (ii) thermal conductivities of the PCM and PV/PCM system. A maximum temperature reduction of 18 C was achieved for 30 min while 10 C temperature reduction was maintained for 5 h at 1000 W/m2 insolation.

Simulation Algorithm and Validation of a Photovoltaic Water Pumping System

I. Odeh et al. — Thu, 27 Jan 2011 09:51:06 PST

A photovoltaic (PV) water pumping system has been modelled using TRNSYS considering
a power supply, a direct current (DC)/alternating current (AC) inverter, an AC induction
motor, a centrifugal pump, a well, a water storage tank, and an overflow protection device. The
model emulates actual pumping head curves, uses numerical methods to determine pumpsystem
working points, and includes a storage tank as a component in the system. It simulates
PV-powered water pumping systems, constant voltage tracking, voltage frequency modulation,
and maximum power point tracking algorithms; variable inverter frequency with variable motor
efficiency, variable inverter frequency with constant motor efficiency, and constant inverter frequency
with variable motor efficiency algorithms. It also has the facility to calculate the accumulated
unused part of thePVenergy owing to thepumpreaching itsmaximumcapacity limit.Model
validation was accomplished by comparing simulated results with both the laboratory measurements and long-termfield data from Jordan; good match and accuracy have been achieved.

Including Embodied Energy Considerations at the Conceptual Stage of Building Design

Y. G. Yohanis et al. — Thu, 27 Jan 2011 08:50:45 PST

Geographic Variation of Solar Water Heater Performance in Europe

Y. Yohanis et al. — Thu, 27 Jan 2011 08:50:42 PST

Solar water heater (SWH) performance has been analysed using the ‘number of days’ method for 147 different sites in all European countries. The total number of days that the temperature of delivered solar heated water reaches or exceeds specified demand temperatures is correlated with solar radiation on a horizontal surface for summer, warm half-year, and whole year periods. Maps are presented and discussed showing the contours for the number of days that an illustrative SWH met different hot water demand temperatures. Correlations between number of days water is provided at a specified temperature and solar fractions for the same periods are determined.

Non-Concentrating and Asymmetric Compound Parabolic Concentrating Building Facade Integrated Photovoltaic

T. Malik et al. — Thu, 27 Jan 2011 08:50:41 PST

Quantum Solar Concentrator: Electrical Conversion Efficiencies and Comparative Concentrating Factors of Fabricated Devices

S. Gallagher et al. — Thu, 27 Jan 2011 08:50:25 PST

Validated Real-time Energy Models for Small-Scale Grid-Connected PV-Systems

Lacour Ayompe et al. — Fri, 14 Jan 2011 05:34:14 PST

This paper presents validated real-time energy models for small-scale grid-connected PV-systems suitable for domestic application. The models were used to predict real-time AC power output from a PV system in Dublin, Ireland using 30-min intervals of measured performance data between April 2009 and March 2010. Statistical analysis of the predicted results and measured data highlight possible sources of errors and the limitations and/or adequacy of existing models, to describe the temperature and efficiency of PV-cells and consequently, the accuracy of power prediction models. PV-system AC output power predictions using empirical models for PV-cell temperature and efficiency prediction showed lower percentage mean absolute errors (PMAEs) of 7.9-11.7% while non-empirical models had errors of 10.0-12.4%. Cumulative errors for PV-system AC output power predictions were 1.3% for empirical models and 3.3% for non-empirical models. The proposed models are suitable for predicting PV-system AC output power at time intervals suitable for smart metering.