Grey-box Modelling of a Household Refrigeration Unit Using Time Series Data in Application to Demand Side Management

This paper describes the application of stochastic grey-box modeling to identify electrical power consumption-to-temperature models of a domestic freezer using experimental measurements. The models are formulated using stochastic differential equations (SDEs), estimated by maximum likelihood estimation (MLE), validated through the model residuals analysis and cross-validated to detect model over-fitting. A nonlinear model based on the reversed Carnot cycle is also presented and included in the modeling performance analysis. As an application of the models, we apply model predictive control (MPC) to shift the electricity consumption of a freezer in demand response experiments, thereby addressing the model selection problem also from the application point of view and showing in an experimental context the ability of MPC to exploit the freezer as a demand side resource (DSR).Comment: Submitted to Sustainable Energy Grids and Networks (SEGAN). Accepted for publicatio

Enabling Micro-level Demand-Side Grid Flexiblity in Resource Constrained Environments

The increased penetration of uncertain and variable renewable energy presents various resource and operational electric grid challenges. Micro-level (household and small commercial) demand-side grid flexibility could be a cost-effective strategy to integrate high penetrations of wind and solar energy, but literature and field deployments exploring the necessary information and communication technologies (ICTs) are scant. This paper presents an exploratory framework for enabling information driven grid flexibility through the Internet of Things (IoT), and a proof-of-concept wireless sensor gateway (FlexBox) to collect the necessary parameters for adequately monitoring and actuating the micro-level demand-side. In the summer of 2015, thirty sensor gateways were deployed in the city of Managua (Nicaragua) to develop a baseline for a near future small-scale demand response pilot implementation. FlexBox field data has begun shedding light on relationships between ambient temperature and load energy consumption, load and building envelope energy efficiency challenges, latency communication network challenges, and opportunities to engage existing demand-side user behavioral patterns. Information driven grid flexibility strategies present great opportunity to develop new technologies, system architectures, and implementation approaches that can easily scale across regions, incomes, and levels of development

Latent Heat Energy Storage in a Household Refrigerator Powered by Photovoltaic Electricity – Heat Transfer Design and Technical Viability

In remote rural areas without access to the electrical grid, the use of a stand-alone photovoltaic (PV) installation to drive a domestic refrigerator can be a viable option for adequate food preservation. In this application, energy storage, probably in electric batteries, is required to guarantee refrigeration conditions during periods without solar energy availability. However, electric batteries are still costly, have limited lifespan and use materials with restricted availability. Latent heat thermal energy storage (LHTES) can be an alternative to electric batteries with reduced cost and lower environmental impact. The current study presents general design guidelines for a system with a household refrigerator driven by PV power and with LHTES units. The LHTES units consist of finned panels filled with phase change material (PCM) that are placed on the vertical walls of the compartments, and are passively discharged by free convection. A thermodynamic model is used to size the system components and assess the technical viability of the proposed configuration. Special attention is paid to the heat transfer considerations involved in the design of the LHTES units to guarantee the required charge and discharge powers. The analysis is applied to a 400 L sample commercial refrigerator operating in Medellín, Colombia. It is concluded that the refrigerator necessitates moderate modifications to achieve the technical viability of the proposed configuration

Energy Management of a Hybrid Photovoltaic-Wind System with Battery Storage: A Case Report

This work presents a case report related to the management and the monitoring of a hybrid photovoltaic-wind system with battery energy storage, installed at the administrative offices building of the municipality of Valderice (Italy) within the framework of the Italy-Tunisia ENPI cooperation project Le Développement Durable Dans la Production Energétique Dans le Territoire (DE.DU.ENER.T.). The paper describes the hybrid system and briefly reports the monitoring data for a whole year, comparing the real production with the expected one and evaluating some performance indexes of the system. The performance indexes are very simple and have been defined only with the purpose of showing the advantages of distributed generation. Then, two different control logics for the battery energy storage systems are compared in order to define the most suitable management of the local energy resources, in presence of different Time-of-Use electricity tariffs. In particular, the two logics are compared by varying the difference between the electricity prices in peak hours and in off-peak hours and the rate between the electricity consumption of the building and the battery energy storage’s capacity

Multi-Objective Dynamic Economic Dispatch with Demand Side Management of Residential Loads and Electric Vehicles

In this paper, a multi-objective optimization method based on the normal boundary intersection is proposed to solve the dynamic economic dispatch with demand side management of individual residential loads and electric vehicles. The proposed approach specifically addresses consumer comfort through acceptable appliance deferral times and electric vehicle charging requirements. The multi-objectives of minimizing generation costs, emissions, and energy loss in the system are balanced in a Pareto front approach in which a fuzzy decision making method has been implemented to find the best compromise solution based on desired system operating conditions. The normal boundary intersection method is described and validated

On demand: can demand response live up to expectations in managing electricity systems?

Residential demand response (meaning changes to electricity use at specific times) has been proposed as an important part of the low carbon energy system transition. Modelling studies suggest benefits may include deferral of distribution network reinforcement, reduced curtailment of wind generation, and avoided investment in reserve generation. To accurately assess the contribution of demand response such studies must be supported by realistic assumptions on consumer participation. A systematic review of international evidence on trials, surveys and programmes of residential demand response suggests that it is important that these assumptions about demand response are not overly optimistic. Customer participation in trials and existing programmes is often 10% or less of the target population, while responses of consumers in existing schemes have varied considerably for a complex set of reasons. Relatively little evidence was identified for engagement with more dynamic forms of demand response, making its wider applicability uncertain. The evidence suggests that the high levels of demand response modelled in some future energy system scenarios may be more than a little optimistic. There is good evidence on the potential of some of the least ‘smart’ options, such as static peak pricing and load control, which are well established and proven. More research and greater empirical evidence is needed to establish the potential role of more innovative and dynami

Simultaneous Charging/Discharging of Phase Change Materials: Characterization of Natural Convection Process

In recent decades, latent heat storage in phase change materials (PCMs) received considerable attention. This is due to their high latent heat capacity, which is essentially required for managing and overcoming the temporal mismatch between energy supply and demand. Thus, at the time of energy availability at supply side, it is stored in PCMs so as to be extracted later on when it is needed. In order to provide continuous operation, there are some periods when a thermal storage has to be simultaneously charged and discharged. Most studies focused either on charging, discharging, or consecutive charging and discharging process, while limited work has been conducted for the case of simultaneous charging and discharging (SCD). The first objective of this dissertation is to develop a numerical model to analyze the heat transfer mechanism within a horizontal PCM storage under SCD. Since the possible heat transfer mechanisms within PCMs are conduction, convection or a combination of both, two models are used to identify the mechanism under SCD; i.e. the pure conduction (PC) model and combined conduction and natural convection (CCNC) model. The PC model is a hypothetical model, which neglects the natural convection during phase change process; however, the CCNC model is the real case one. Validation of the model results by comparison with experimental data shows an acceptable agreement both under melting and solidification. Therefore, the developed model can be used to numerically study the phase change process in PCMs. Natural convection is the result of density changes, which create buoyancy forces within melted PCM and plays a significant role during melting. Currently, the most widely used method to account for natural convection is the effective thermal conductivity method. The method considers an artificial increase in thermal conductivity values to take into consideration the effect of natural convection by comparing the results with experimental data. Two major shortcomings of this method are that first, it is tedious to obtain the proper value and second, the method does not provide information about the melting front location. In this dissertation, a novel simplified front tracking method is presented to replace the thermal conductivity method. The novel method is based on considering two separate melting fronts for the upper and lower halves of a horizontal thermal storage system. Therefore, two dimensionless correlations are developed to map the results of the simple PC model to that of the complicated CCNC model based on the presented logic. The method essentially creates a link between CCNC and PC models, which is also missing in the literature. Based on verification, the correlations can provide results within ±15% discrepancy