Algorithms to Model and Optimize a Stand-Alone Photovoltaic-Diesel-Battery System: An Application in Rural Libya

This paper introduces a new optimum calculation technique for a stand-alone hybrid photovoltaic-diesel-battery system (PDBS), which meets the energy requirements of a small village in southern Libya. The bat algorithm design strategy is applied to reduce the annual cost of the system, taking into consideration the controlled electricity restriction and the optimal numbers of PV panels, diesel generators, and batteries. Comparative tests are performed using MATLAB for the bat algorithm with the grey wolf search algorithm and particle swarm optimization, demonstrating that the bat algorithm determines the optimum size of the PDBS effectively at a lower expense. Results then indicate that, taking into account the reliability characteristics, this has a significant effect on optimum capacity, load supply, and cost

Erinevate energia salvestustehnoloogiate uudsed rakenduspõhimõtted liginullenergiahoonetes

A Thesis for applying for the degree of Doctor of Philosophy in Technical Sciences.In this thesis the renewable energy storage options in residential buildings are under investigation. This is to store cheap electricity due to the temporary overproduction of large wind farms and also on-site solar and wind farms. In an electric system, there should be a balance at all times between energy production and consumption: as much as is produced should also be consumed. Deviating significantly from this balance can damage electrical equipment or cause serious network failures and even blackouts. Unfortunately, both solar and wind energy generation possibilities are associated with (rapid) changes in production. The simplest examples are wind gusts for wind turbines and intermittent cloud cover for solar panels where the electric output power changes in seconds. In order to smooth out the rapid changes in electricity production, the work proposes the possibility to add ultracapacitors to the battery bank for temporary energy storage, which would act as a buffer and are able to temporarily store the produced electricity. So far, the sale of green energy to the electricity grid has been supported at the state level. However, this paper examines the next step in how to support the storage capacity of the produced energy in order to increase self-consumption. To this, a state subsidy measure for battery banks is proposed. Due to short-term overproduction of electricity, there are more and more situations where electricity is sold at zero or even negative prices on the power exchange. The reason is simple - it is more practical for producers to temporarily pay to consumers for electricity consumption than to stop production for a while. This work also proposes a method for storing energy in heat carriers under favorable conditions for the consumer in order to ensure a balance between the production and consumption of the electricity network.Antud doktoritöö käsitleb taastuvenergia salvestusvõimaluste kasutamist elumajades. Seda nii kohapealsete päikeseparkide ja tuulegeneraatorite kui ka suurte tuuleparkide aeg-ajalisest energia ületootmisest tingitud odava elektrienergia salvestamiseks. Energia tootmise ja tarbimise puhul peaks valitsema igas hetkes tasakaal: sama palju kui toodetakse tuleb ka tarbida. Kui sellest tasakaalust väga kõrvale kalduda, võib see elektrilisi seadmed kahjustada või esineb tõsiseid võrgurikkeid ja isegi katkestusi. Paraku on aga nii päikese- kui ka tuuleenergia tootmine seotud (kiirete) muutustega toodangus. Lihtsaimad näited selleks on tuulepuhangud tuulegeneraatorite puhul ning vahelduv pilvisus päikesepaneelide puhul mil elektriline väljundvõimsus muutub sekunditega. Tasandamaks kiireid muutusi elektritootmisel, pakutakse töös välja võimalus lisada akupangale energia ajutiseks salvestamiseks ülikondensaatorid, mis käituks puhvrina ning on võimelised toodetud elektrienergiat ajutiselt salvestama. Senini on riiklikul tasandil toetatud roheenergia müüki elektrivõrku. Antud töös uuritakse aga järgmist etappi, kuidas toetada toodetud energia salvestusvõimalusi eesmärgiga suurendada omatarbimist. Selleks pakutakse välja riiklik akupankade subsideerimise meede. Elektrienergia lühiajalisest ületootmisest tulenevalt esineb üha rohkem olukordi, mil elektribörsil müüakse elektrit null või isegi negatiivse hinnaga. Põhjus on lihtne – tootjatel on otstarbekam ajutiselt elektritarbimisele peale maksta, kui tootmine korraks seisma panna. Antud töös pakutakse samuti välja meetod, kuidas tarbijale soodsatel tingimustel energiat soojuskandjatesse salvestada, tagamaks elektrivõrgu tootmise ja tarbimise tasakaalu.Publication of this theisis is supported by the Estonian University of Life Sciences; and the Doctoral School of Energy and Geotechnology III, (Estonian University of Life Sciences ASTRA project “Valuechain based bio-economy”); and the Estonian Centre of Excellence in Zero Energy and Resource Efficient Smart Buildings and Districts, ZEBE, grant 2014-2020.4.01.15-0016 funded by the European Regional Development Fund

Simplified Model for Optimal Sizing of the Off-Grid PV System Regarding Value of Loss of Load Probability

In this paper, a simplified model for optimal sizing of the off-grid PV system regarding value of loss of load probability is described. The model gives optimal size of system in terms of required number of PV modules, peak power, number of batteries and cost of system regarding the defined value of loss of load probability, load curve and period for which optimal size will be determined. The model is applied for determination of optimal size of the off-grid PV system for the city of Osijek. Based on measured load curve, optimal size of the system is determined for values of loss of load probability from 0.00 to 0.10 in steps of 0.01, and additionally for 0.15

Minimizing residential distribution system operating costs through intelligently scheduled plug-in hybrid electric vehicle charging

Rising fuel prices and environmental concerns are threatening the stability of current electrical grid systems. These factors are pushing the automobile industry towards more effcient, hybrid vehicles. Current trends show petroleum is being edged out in favor of electricity as the main vehicular motive force. The proposed methods create an optimized charging control schedule for all participating Plug-in Hybrid Electric Vehicles in a distribution grid. The optimization will minimize daily operating costs, reduce system losses, and improve power quality. This requires participation from Vehicle-to-Grid capable vehicles, load forecasting, and Locational Marginal Pricing market predictions. Vehicles equipped with bidirectional chargers further improve the optimization results by lowering peak demand and improving power quality

Análisis y gestión óptima de la demanda en sistemas eléctricos conectados a la red y en sistemas aislados basados en fuentes renovables

En esta tesis doctoral se han analizado, de forma detallada, los principales aspectos relacionados con el funcionamiento de los sistemas eléctricos aislados y conectados a la red eléctrica basados en fuentes de energía renovable. En lo referente al análisis de los sistemas aislados de la red eléctrica, se ha analizado el efecto de la eficiencia culómbica y del regulador de carga en la fiabilidad de los sistemas eólicos con baterías. También se ha tratado la estimación de las horas de operación, consumo de combustible y coste neto actualizado de los sistemas que utilizan como respaldo un generador convencional. Por otra lado, se ha desarrollado un modelo probabilístico que permite considerar la incertidumbre existente en la estimación de la vida del banco de baterías, la incertidumbre asociada a los precios del combustible, la producción del generador fotovoltaico, el perfil típico de carga, así como la variabilidad de los recursos eólico y solar. Además, teniendo en cuenta la importancia que tiene el uso racional de la energía eléctrica, en esta tesis se ha desarrollado una novedosa técnica para la gestión de la demanda de sistemas aislados de la red eléctrica que sugiere al usuario del mismo el mejor momento para hacer uso de sus electrodomésticos, reduciendo el consumo de combustible y mejorando el uso de la energía almacenada en el banco de baterías. Finalmente, considerando sistemas conectados a la red eléctrica, se ha desarrollado una estrategia de Adaptación de la Demanda para consumidores residenciales que, haciendo uso de las capacidades de comunicación de la futura Red Eléctrica Inteligente, determina mediante la optimización de la negociación entre el usuario y la empresa de distribución de energía eléctrica, la forma en que el consumidor debe utilizar sus electrodomésticos considerando sus preferencias y su poder adquisitivo. Los resultados obtenidos sugieren importantes mejoras en los modelos que se utilizan habitualmente en la simulación y optimización de sistemas híbridos, específicamente en la consideración del regulador de carga como un importante elemento del sistema, y en la estimación de la vida útil del banco de baterías. Además, las estrategias para la gestión de la demanda, presentadas en este trabajo de investigación, pueden ayudar a que los usuarios de sistemas aislados o conectados a la red eléctrica realicen un uso eficiente de las fuentes de energía locales, y adapten sus patrones de consumo de electricidad a su condición económica actual

Life Cycle Cost Analysis of a Diesel/Photovoltaic Hybrid Power Generating System

This work is a Life Cycle Cost (LCC) analysis of a diesel/photovoltaic hybrid power generating system for an off-grid residential building in Enugu, Nigeria. It aims at optimizing different hybrid system configurations, and comparing the result obtained with the photovoltaic standalone (PVSA) system and conventional diesel standalone (DSA) system. The lifetime of the project is 25 years and a real interest rate of 9% per annum is assumed for the system analysis. The average hourly electrical load demand data for residential sector in Enugu were obtained from the power holding company of Nigeria (PHCN). The solar resource data for the location for the year 2010 were gotten from the NASA Langley Research Centre. The sizes of different components were determined to make sure their sizes suit the load demand. A PV standalone system is firstly sized, after which modules of the PV array are removed in sequence to get six different sizes, at the same time, introducing the diesel generator to make a hybrid system. The hours of operation of the diesel generator increases as modules are removed from the PV array. Optimization of the hybrid system is done to determine the system configuration that would satisfy the load demand at minimum cost. The result shows that the hybrid system with 20 modules and a 2.5 kVA diesel generator will serve the load at minimum cost. A life cycle cost analysis of the systems is done using the Net Present Value (NPV) and Internal Rate of Return (IRR). The result shows that the LCC of the hybrid system is N3,459,274.00 that of DSA system is N7,098,192.00 and N3,594,881.00 for the PV standalone system. The NPV of the hybrid system is N3,638,918.00 when compared with the DSA system and the internal rate of return is at 26.3%. The NPV of the PV standalone system when compared with the DSA system is N3,428,747.00 with its internal rate of return at 24.6%. The results obtained show that the diesel/photovoltaic hybrid system is economically the best option for power generatio

Comparison of lead-acid and li-ion batteries lifetime prediction models in stand-alone photovoltaic systems

Several models for estimating the lifetimes of lead-acid and Li-ion (LiFePO4 ) batteries are analyzed and applied to a photovoltaic (PV)-battery standalone system. This kind of system usually includes a battery bank sized for 2.5 autonomy days or more. The results obtained by each model in different locations with very different average temperatures are compared. Two different locations have been considered: the Pyrenees mountains in Spain and Tindouf in Argelia. Classical battery aging models (equivalent full cycles model and rainflow cycle count model) generally used by researchers and software tools are not adequate as they overestimate the battery life in all cases. For OPzS lead-acid batteries, an advanced weighted Ah-throughput model is necessary to correctly estimate its lifetime, obtaining a battery life of roughly 12 years for the Pyrenees and around 5 years for the case Tindouf. For Li-ion batteries, both the cycle and calendar aging must be considered, obtaining more than 20 years of battery life estimation for the Pyrenees and 13 years for Tindouf. In the cases studied, the lifetime of LiFePO4 batteries is around two times the OPzS lifetime. As nowadays the cost of LiFePO4 batteries is around two times the OPzS ones, Li-ion batteries can be competitive with OPzS batteries in PV-battery standalone systems

A review of optimal operation of microgrids

The term microgrid refers to small-scale power grid that can operate autonomously or in concurrence with the area’s main electrical grid. The intermittent characteristic of DGs which defies the power quality and voltage manifests the requirement for new planning and operation approaches for microgrids. Consequently, conventional optimization methods in new power systems have been critically biased all through the previous decade. One of the main technological and inexpensive tools in this regard is the optimal generation scheduling of microgrid. As a primary optimization tool in the planning and operation fields, optimal operation has an undeniable part in the power system. This paper reviews and evaluates the optimal operation approaches mostly related to microgrids. In this work, the foremost optimal generation scheduling approaches are compared in terms of their objective functions, techniques and constraints. To conclude, a few fundamental challenges occurring from the latest optimal generation scheduling techniques in microgrids are addressed

Energy management in microgrids with renewable energy sources: A literature review

Renewable energy sources have emerged as an alternative to meet the growing demand for energy, mitigate climate change, and contribute to sustainable development. The integration of these systems is carried out in a distributed manner via microgrid systems; this provides a set of technological solutions that allows information exchange between the consumers and the distributed generation centers, which implies that they need to be managed optimally. Energy management in microgrids is defined as an information and control system that provides the necessary functionality, which ensures that both the generation and distribution systems supply energy at minimal operational costs. This paper presents a literature review of energy management in microgrid systems using renewable energies, along with a comparative analysis of the different optimization objectives, constraints, solution approaches, and simulation tools applied to both the interconnected and isolated microgrids. To manage the intermittent nature of renewable energy, energy storage technology is considered to be an attractive option due to increased technological maturity, energy density, and capability of providing grid services such as frequency response. Finally, future directions on predictive modeling mainly for energy storage systems are also proposed