A review of solar photovoltaic systems cooling technologies

Published ArticleCooling the operating surface is a key operational factor to take into consideration to achieve higher efficiency when operating solar photovoltaic systems. Proper cooling can improve the electrical efficiency, and decrease the rate of cell degradation with time, resulting in maximisation of the life span of photovoltaic modules. The excessive heat removed by the cooling system can be used in domestic, commercial or industrial applications. This paper presents a review of various methods that can be used to minimize the negative impacts of the increased temperature while making an attempt to enhance the efficiency of photovoltaic solar panels operating beyond the recommended temperature of the Standard Test Conditions (STC). Different cooling technologies are reviewed, namely Floating tracking concentrating cooling system (FTCC); Hybrid solar Photovoltaic/ Thermal system cooled by water spraying; Hybrid solar Photovoltaic/ Thermoelectric PV/TE system cooled by heat sink; Hybrid solar Photovoltaic/Thermal (PV/T) cooled by forced water circulation; Improving the performance of solar panels through the use of phase-change materials; Solar panel with water immersion cooling technique; Solar PV panel cooled by transparent coating (photonic crystal cooling); Hybrid solar Photovoltaic/Thermal system cooled by forced air circulation, and Solar panel with Thermoelectric cooling. Several research papers are reviewed and classified based on their focus, contribution and the type of technology used to achieve the cooling of photovoltaic panels. The discussion of the results has been done based on the advantages, disadvantages, area of application as well as techno-economic character of each technology reviewed. The purpose of this review is to provide an understanding for each of the above-mentioned technologies to reduce the surface temperature of the PV module. The study will focus on the surface temperature reduction array bound by each of the cooling technologies. The performance of each cooling technology will also be highlighted. In addition to this study, this review will include a discussion comparing the performance of each cooling technology. The outcomes of this study are detailed in the conclusion section. This paper has revealed that any adequate technology selected to cool photovoltaic panels should be used to keep the operating surface temperature low and stable, be simple and reliable and, if possible, enable the use of extracted thermal heat to enhance the overall conversion efficiency. The presented detailed review can be used by engineers working on theory, design and/or application of photovoltaic systems

A Review of Water Heating Technologies: An Application To The South African Context

Published Articleup to 40% of their total energy be allotted to the heating of water. The implementation of energy efficient or renewable energy source technologies, for the main purpose of heating water, may assist in reducing the magnitude of the energy crisis that South Africans are facing daily. This will, in turn, reduce energy consumption and costs, so that the energy price hikes do not affect the consumers as severely as it would otherwise. The purpose of this paper is to provide a survey of the most frequently used domestic water heating technologies. The paper aims to critically analyse and summarize recent advancements made in renewable and non-renewable water heating technologies, particularly in the South African case. These technologies include the electric storage tank water heater, solar water heaters (passive and active circulation), heat pump water heater, geothermal water heating, photovoltaic-thermal water heater, gasfired tankless water heater, biomass water heater and oil-fired water heater. Substantial research works and other academic studies focusing on efficiency improvement, optimal design and control, were consulted and categorized in terms of contributions, focus and respective technologies. The key findings of the review conducted on the various water heating technologies are discussed and organized, based on the advantages, drawbacks, approximate initial investment, average life expectancy and payback period. The results of this survey identify gaps in existing research. The aim is to propose a new perspective on the importance of energy efficient hybrid water heating systems and the cost savings they might offer

Systems optimization model for energy management of a parallel HPGR crushing process

This work proposes a systems optimization control model for energy management of a parallel crushing process made up with high-pressure grinding rolls (HPGR) machines. The aim is to reduce both energy consumption and cost through optimal control of the process and load shifting, respectively. A case study of a copper crushing process is solved under three scenarios in order to evaluate the effectiveness of the developed model. Simulation results show that 41.93% energy cost saving is achieved through load shifting by coordinating the rotational speed of HPGRs. It is further shown that the energy saving can be achieved when the two HPGRs are not operated with equal overall efficiency, but also through a small decrement in rolls operating pressure. In the first case, 1.87% energy saving is obtained while in the last case, about 4.5% energy saving is achieved for every decrement of 0:2 N=mm2 in rolls operating pressure without significant change in product quality.http://www.elsevier.com/locate/apenergyhb201

Optimal Energy Management and Economic Analysis of a Grid-Connected Hybrid Solar Water Heating System: A Case of Bloemfontein, South Africa

Published ArticleIn this paper, the optimal energy management of a hybrid solar electric water heater is presented. A typical medium density household is considered. Actual historic exogenous data, obtained from a weather station in the considered area is used as input for the established model. The aim is to evaluate the energy and cost saving potential of the system, that may be achieved under timebased pricing, while maintaining a comfortable thermal level of the hot water user. Comparisons between the operation of a thermostatically controlled traditional electric storage tank water heater and the hybrid solar electric water heater, offered an energy saving of 75.8% in the winter and 51.5% during the summer period. A life cycle cost (LCC) analysis is presented, where the project lifetime is taken over 20 years. The LCC analysis of the hybrid system demonstrates a 44% saving in overall cost, as compared to a traditional water heating system. Simulation results conclude that the break-even point for the evaluated system was at R10 870 in 3.3 years, under the evaluated time-based pricing structure

Optimal energy management of crushing processes in the mining industry

It has been shown that mining processes, especially the comminution processes (grinding and crushing) are some of the biggest consumers of electricity in the world where energy management application would have a significant impact on the sustainability of both the energy supply and demand sides. However, very little research has been done in this area. Energy efficiency management in the mining industry can be done at four levels, namely the technology level, equipment level, operational level and performance level. In this work, operation energy management is considered for crushing circuits with the aim of minimizing the total energy cost by accounting for the time-of-use (TOU) electricity tariff. The work is limited to three types of crushing machines, namely the jaw crusher, vertical shaft impact (VSI) crusher and high-pressure grinding rolls (HPGR) crusher. Firstly, the energy model of each crusher is developed and expressed in terms of its control variables. Secondly, an optimal energy control model is formulated, where both physical and technical/operational constraints of the crushing process are taken into account. Thirdly, a case study is done in order to evaluate the effectiveness of the developed models. Lastly, experimental results of the performance model of the jaw crusher are presented. Simulation results show that when TOU electricity tariff is applied there is potential for achieving energy cost saving in all types of crushing processes, depending on the size of storage systems and plant production requirement. However, achieving energy saving is not always evident. When the throughput rate and product size distribution of the crusher are both controlled by a unique variable, as in the case of the jaw crusher, it is shown that no significant energy saving can be achieved. This is due to the trade-off between the throughput rate, product size distribution and specific energy consumption of the jaw crushing machine. Increasing the closed-side setting (unique control variable) of the jaw crusher with the aim to decrease the specific energy consumption will result in coarse particles in the product. However, there is a great opportunity for energy saving through optimal switching control due to the high no-load power consumption of the jaw crusher. On the other hand, when the throughput rate and product size distribution are controlled by more than one variable, as in the case of the VSI and HPGR crushers, more energy saving can be achieved in presence of varying feed size. In the VSI crushing process, for instance, the product size distribution is controlled by the rotor speed while the throughput rate is controlled by the rotor feed throttle. Hence, energy consumption reduction is achieved through any small decrease of the crusher rotor speed whenever the feed size decreases. The same applies to the HPGR crushing processes where the rolls operating pressure is used to control the product size distribution and the throughput rate is controlled by the rotor speed. The analysis of the performance model of the jaw crusher reveals that although the Bond energy model presents larger prediction error compared to the throughput and product quality index, this can still be used as performance indicator in jaw crushing energy optimization, as it shows a strong linear correlation with experimental results. However, for actual energy consumption and energy saving calculation, a field test should be conducted.Daar is aangetoon dat mynbouprosesse, veral die vergruisingproses (maal en breek) een van die grootste verbruikers van energie in die wêreld is, waar die toepassing van energiebestuur’ n beduidende impak sal hê op die volhoubaarheid van sowel die engergievoorsiening- as aanvraagkant. Daar is egter nog min navorsing op hierdie gebied gedoen. Die bestuur van energie-effektiwiteit in die mynbou-industrie kan op vier vlakke plaasvind, naamlik die vlakke van tegniek, toerusting, werkverrigting en prestasie. In hierdie werk word werkverrigtingbestuur oorweeg vir vergruisingkringlope, met die doel om die totale energiekoste te minimeer deur die tyd-van-gebruik-elektrisiteitstarief in berekening te bring. Die werk word beperk tot drie tipes vergruisingsmasjiene, naamlik die bekvergruiser, vertikaleskagimpakvergruiser (VSI) en parallele hoëdruk- breekrollervergruiser (HDBR). Eerstens word die energiemodel van elke vergruiser ontwikkel en uitgedruk volgens die kontrole-veranderlikes daarvan. Tweedens word ’n optimale energiekontrolemodel geformuleer, waarin sowel die fisiese as tegniese/operasionele beperkings van die proses in ag geneem word. Derdens word ’n gevallestudie gedoen om die effektiwiteit van die modelle wat ontwikkel is, te evalueer. Laastens word die eksperimentele resultate van die werkverrigtingmodel van die bekvergruiser aangebied. Simulasies toon aan dat wannneer die tyd-van-gebruik-elektrisiteitstarief toegepas word, energiekostebesparings potensieel in alle tipes vergruisingsprosesse bereik kan word, afhangend van die grootte van die bergingstelsels en aanlegproduksievereiste. Die bereiking van energiebesparing is nogtans nie altyd duidelik nie. Wanneer die toevoertempo en produkgrootteverspreiding van die vergruiser albei deur een veranderlike beheer word, soos in die geval van die bekvergruiser, word aangetoon dat geen beduidende energiebesparing bereik kan word nie. Dit is die gevolg van die ruil tusen die toevoertempo, produkgrootteverspreiding en spesifieke energieverbruik van die bekvergruisermasjien. Om die sluitsystelling (kontrole-veranderlike) van die bekvergruiser te verhoog met die doel om die spesifieke engergieverbruik te verminder, sal lei tot growwe deeltjies in die produk. Daar is nogtans goeie geleentheid vir energiebesparing deur optimale skakelkontrole omrede die hoë geenlading-kragverbruik van die bekvergruiser. Aan die ander kant, as die toevoertempo en produkgrootteverspreiding deur meer as een veranderlike beheer word, soos by die VSI- en HDBR-vergruiser, kan groter energiebesparing bereik word saam met veranderlike toevoergrootte. In die VSI-vergruisingproses word die produkgrootteverspreiding byvoorbeeld deur die rotorspoed beheer, terwyl die toevoertempo deur die rotortoevoerversneller beheer word. ’n Afname in energieverbruik word gevolglik verkry deur enige klein afname in die vergruiserrotorspoed wanneer die toevoergrootte afneem. Dieselfde geld in die HDBR-vergruisingprosesse, waar die operasionele druk van die rollers gebruik word om die produkgrootteverspreiding te beheer en die toevoertempo deur die rotorspoed beheer word. Analise van die werkverrigtingmodel van die bekvergruiser toon dat alhoewel die Bondenergiemodel ’n groot voorspelfout lewer, dit steeds gebruik kan word as ’n aanduiding van werkverrigting in energie-optimering vir die bekvergruiser, aangesien dit sterk lineêre korrelasie toon met eksperimentele resultate. Nietemin sal veldwerktoetse uitgevoer moet word om die werklike energieverbruik en energiebesparing te bepaal.Thesis (PhD)--University of Pretoria, 2015.tm2015Electrical, Electronic and Computer EngineeringPhDUnrestricte

Optimal operation of a hybrid multisource energy system considering grid load shedding

On-site grid-connected hybrid renewable energy systems are extensively used in the mitigation of scheduled grid load shedding in commercial buildings. This paper proposes an optimal operation of grid-connected hybrid PV-battery-Diesel generator (DG) energy system under scheduled grid load shedding for a commercial building. A mathematical model for an optimal operation of a grid-connected PV-Battery-DG energy system that has a potential of mitigating the scheduled load shedding is developed and implemented. The impact assessment of scheduled load shedding on commercial consumers is also assessed on the cost saving as compared to the baseline without load shedding. Results showcase the potential of the proposed grid-connected hybrid PV-Battery-DG to mitigate scheduled grid load shedding in commercial buildings. Scheduled grid load shedding impacts differently on commercial consumers depending on the scheduled time of a day

Optimal energy management for a jaw crushing process in deep mines

This paper develops two optimal control models for the energy management of a mining crushing process based on jaw crushers. The performance index for both models is defined as the energy cost to be minimized by accounting for the time-of-use electricity tariff. The first model is referred to as a variable load-based optimal control with the feeder speed and closed-side setting of the jaw crusher as control variables. The second model is the optimal switching control. From the simulation results, it is demonstrated that there is a potential of reducing the energy cost and energy consumption associated with the operation of jaw crushing stations in deep mines while meeting technical and operational constraints. Due to the inefficiency of the jaw crushing machine, whose no-load power consumption is between 40 and 50% of its rated power, the optimal switching control technique is shown to be a better candidate in reducing both energy cost and consumption of the jaw crushing station. The benefit of having an ore pass with a big storage capacity is shown to be of great importance in achieving more energy cost reduction of the primary jaw crushing station while improving the switching frequency profile associated with the switching controller