Οι Ανανεώσιμες Πηγές Ενέργειας έχουν διεισδύσει στη ζωή μας, αποτέλεσμα της κλιματικής αλλαγής αλλά και των αυξανόμενων απαιτήσεων του ανθρώπου για ηλεκτρική ενέργεια. Όσο η τεχνολογία αναπτύσσεται, η απαίτηση για φθηνότερο κόστος ενέργειας αλλά και φιλικής με το περιβάλλον έκανε επιτακτική τη δημιουργία της κατανεμημένης παραγωγής. Η ανάπτυξη των μικροδικτύων βοήθησε να φτάσει το ηλεκτρικό ρεύμα ακόμα και στην πιο απομακρυσμένη περιοχή, όπου το κεντρικό δίκτυο δε γινόταν να φτάσει λόγω των οικονομικών αλλά και τεχνικών μειονεκτημάτων. Μέσω των αναπτυγμένων μορφών αυτομάτου ελέγχου, δόθηκε η δυνατότητα ελέγχου των συστημάτων υβριδικών μικροδικτύων, δικτύων τα οποία αποτελούνται απο ΑΠΕ και μπορούν να δρουν αυτόνομα σε μια περιοχή, χωρίς την ανάγκη του κεντρικού δικτύου. Έτσι μπορούμε να ελέγξουμε την ενεργό και άεργο ισχύ που παράγει ή καταναλώνει ένα μικροδίκτυο με τη βοήθεια του droop ελέγχου, ο οποίος μας δίνει τη δυνατότητα να ελέγχουμε την ενέργεια μέσω της τάσης και της συχνότητας. Στο κεφάλαιο 1 παρουσιάζονται τα χαρακτηριστικά του υβριδικού μικροδικτύου, περιγράφοντας τις Ανανεώσιμες Πηγές Ενέργειας. Περιγράφεται επίσης η μέθοδος ελέγχου της ενέργειας μέσω συχνότητας και τάσης, droop. Στο κεφάλαιο 2 αναλύεται το μοντέλο μιας 3Φ πηγής τάσης προερχόμενης από αντιστροφέα του οποίου η έξοδος “βλέπει” ένα LC φίλτρο που χρησιμοποιεί μετασχηματισμό Park. Έτσι επιτρέπεται ο σχεδιασμός του ελεγκτή τάσης με σκοπό την εξομάλυνση της τάσης εξόδου σε συνθήκες γραμμικού φορτίου. Για να λάβουμε μηδενικό σφάλμα μόνιμης κατάστασης χρησιμοποιούμε ελεγκτές PID και τους εφαρμόζουμε στο block PWM , οι οποίοι βοηθούν στην επιτάχυνση της μεταβατικής απόκρισης του αντιστροφέα. Ο 7 αντιστροφέας συνδέεται με 3Φ ωμικό φορτίο του οποίου οι τιμές αλλάζουν για να εξετάσουμε τις διαταραχές οι οποίες δημιουργούνται. Η προσομοιίωση γίνεται στο περιβάλλον Matlab/Simulink και παρουσιάζονται οι γραφικές αποκρίσεις συνοδεία σχολίων. Στο κεφάλαιο 3 ο αντιστροφέας αντί να συνδεθεί με το 3Φ ωμικό φορτίο, συνδέεται με το δίκτυο και εξετάζουμε τη συμπεριφορά του συστήματος μας. Προσομοιώνεται στο περιβάλλον Matlab/Simulink και παρουσιάζονται οι γραφικές αποκρίσεις συνοδεία σχολίων. / Renewable Energy Sources (RES) have slowly filter in our lives as a result of climate change and growing human demands for electricity. As technology develops , the demand for less expensive energy, but also environmentally friendly , made imperative the creation of distributed generation. The development of microgrids helped to have electricity even in the most remote areas , where the central network could not reach due to economic and technical disadvantages. Via developed forms of automatic control ,we were granted control of hybrid microgrid systems. These networks are consisted of RES and may act autonomously in an area without the need of the central network. So we were able to control the active and reactive power that a microgrid produces or consumes, using the droop control, that enables us to control energy through frequency and voltage. Chapter 1 presents the characteristics of the hybrid microgrid , describing the Renewable Energy Sources . What is also described is the power control method through frequency and voltage (droop control). Chapter 2 analyzes the model of a three phase voltage source derived from the inverter which is connected to an LC filter that uses Park's transformation. This allows the design of the voltage controller in order to normalize the output voltage in linear load conditions. To obtain zero steady-state error we use PID controllers and we also apply PWM. The PID controllers accelerate the inverter transient response. The inverter is connected to a three phase resistive load whose values vary in order to observe the disturbances that are created. The simulation takes part in the Matlab/Simulnik environment and graphic comments are presented and followed by responses.

Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη μίας διάταξης ανεμογεννήτριας 1kW με σύγχρονη μηχανή μόνιμων μαγνητών και με ανορθωτική γέφυρα διόδων στην έξοδό της, καθώς και τη διασύνδεση αυτής με το εναλλασσόμενο δίκτυο χαμηλής τάσης. Επιπρόσθετα, πραγματεύεται την κατασκευή του μονοφασικού αντιστροφέα που ενσωματώνεται στην εν λόγω τοπολογία. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Απώτερος σκοπός είναι η συνολική κατασκευή μίας διάταξης δύο βαθμίδων για τη διασύνδεση της ανεμογεννήτριας με το δίκτυο χαμηλής τάσης. Οι διατάξεις αυτές περιλαμβάνουν μια πρώτη βαθμίδα ανύψωσης της τάσης της ανεμογεννήτριας μέσω της οποίας εκτελείται ένας αλγόριθμος εύρεσης του σημείου μέγιστης ισχύος της ανεμογεννήτριας (MPPT) και μια δεύτερη βαθμίδα που μετατρέπει τη συνεχή τάση σε εναλλασσόμενη (αντιστροφέας) και διατηρεί σταθερή την τάση στον πυκνωτή διασύνδεσης που παρεμβάλλεται μεταξύ των δύο βαθμίδων με έλεγχο της ενεργού ισχύος που εγχέει στο δίκτυο, ενώ παράλληλα παράγει ρεύμα συμφασικό με την τάση του δικτύου (μοναδιαίος συντελεστής ισχύος). Αυτός ο αντιστροφέας αποτελεί και ένα το κύριο αντικείμενο μελέτης και κατασκευής της παρούσας διπλωματικής εργασίας. Αρχικά παρουσιάζονται τα πλεονεκτήματα και οι δυσκολίες στην εκμετάλλευση ανανεώσιμων πηγών ενέργειας και ιδιαίτερα της αιολικής, αναλύονται οι προοπτικές σήμερα, ενώ παρατίθενται και συγκρίνονται οι τεχνολογίες διασύνδεσης ανεμογεννητριών στο δίκτυο χαμηλής, μέσης και υψηλής τάσης στοχεύοντας στο να δοθεί στον αναγνώστη μια σφαιρική άποψη του υπό μελέτη θέματος. Στη συνέχεια παραθέτουμε μια θεωρητική ανάλυση όλων των εμπλεκομένων μονάδων της τοπολογίας. Ιδιαίτερη βαρύτητα δίνεται στην ανάλυση της λειτουργίας του μονοφασικού αντιστροφέα και κυρίως στη μέθοδο παλμοδότησης, που είναι γνωστή υπό τον όρο “Ημιτονοειδής Διαμόρφωση του Εύρους Παλμών” (SPWM). Επόμενο βήμα αποτέλεσε η διαστασιολόγηση ολόκληρου του υπό μελέτη συστήματος, η μελέτη διαφόρων μεθόδων ελέγχου της ροής ισχύος του αντιστροφέα και η μετέπειτα προσομοίωση του μονοφασικού αντιστροφέα και των μεθόδων ελέγχου που μελετήθηκαν. Τέλος αναλύουμε τα τεχνικά χαρακτηριστικά του αντιστροφέα που κατασκευάστηκε, καθώς και των κυκλωμάτων από τα οποία αποτελείται και περιγράφουμε τη διαδικασία παραγωγής του κώδικα προγραμματισμού του μικροελεγκτή καθώς και των τεχνικών που χρησιμοποιήσαμε για τη ρύθμιση των παλμών. Παράλληλα παραθέτουμε παλμογραφήματα και μετρήσεις που προέκυψαν από τα πειράματα που διενεργήσαμε μετά την ολοκλήρωση της κατασκευής σε εργαστηριακό περιβάλλον. / This diploma thesis has to do with the study and the construction of a single phase inverter for the interconnection of a 1kW wind power generator with the low voltage grid. This research was conducted in the Laboratory of Electromechanical Energy Conversion, in the Department of Electrical and Computer Engineering, of the University of Patras. The ultimate aim of this work is the construction of an inverter in order to interconnect the wind turbine with the low voltage power grid with control of active power injected into the grid and generating current, in phase to the grid voltage (unity power factor). Initially, the advantages and challenges in exploiting the renewable energy sources, especially wind power, are analyzed; and today’s perspectives are seen as well. We also present technologies of interconnecting wind turbine technologies to the high, medium and low voltage grid, aiming to provide a complete presentation of the studied subject. We then present a theoretical analysis of all the topology units involved. Particular emphasis is given on the analysis of the inverter operation and especially on the single-phase pulse width modulation method, also known as SPWM. The next step was the sizing of the entire system, the study of different methods to control the flow of the inverter’s power and the subsequent simulation of the single-phase inverter and the control methods that were studied. We conclude by analyzing the technical characteristics of the inverter constructed, and the circuits that consist it and describe the logic of the flowchart of the microcontroller programming code and the techniques used to set the pulses. The final stage is the conduction of experiments with the construction in the lab and the writing of the results.

The purpose of this thesis is to investigate the development of new technologies in the energy industry and to explore how it is possible for these technologies to compete with incumbent technologies in a mature market. The pursuit of renewable energy has been at the forefront of national government and international institutional policy in recent years due to the desire to improve the security of energy supply and to reduce CO2e emissions. This thesis aims to contribute to this policy debate, particularly by focussing on the issue of governmental support for infant energy technologies. In order to conduct this investigation, two main topics have been analysed. Firstly, learning curves have been studied to establish whether support for new technologies can be justified by the potential cost reductions which arise from learning-by-doing. This research evolved into the investigation of econometric issues which affect learning curves. Patent counts are used to demonstrate an alternative output-based measurement of industry wide knowledge stock, which is used as a proxy for innovation. This alternative specification of knowledge stock corroborates recent findings in the literature, that learning curves which model cost using only cumulative capacity leads to the over-estimation of cost reductions from learning-by-doing and the failure to capture cost reductions resulting from innovation. This suggests that government support for infant technologies should form a dual strategy of incentivising the deployment of generators as well as encouraging innovation, instead of using feed-in tariffs or renewable obligations which narrowly focus on increasing deployment. A great deal of progress has been made in identifying further econometric problems affecting learning curves in recent years. In the progress of this study, it was identified that cumulative capacity, the cost of wind power and knowledge stock are all non-stationary time series variables. The hypothesis that these variables are cointegrated was rejected by the Westerlund test, which implies that learning curves produce spurious results. This has major consequences for government policy as it suggests that learning curves should not be used to justify support for infant technologies. Secondly, a choice experiment was conducted to determine Scottish households’ willingness to pay for electricity generated from renewable sources compared to conventional sources such as coal, oil and gas. A labelled choice experiment was used to determine whether households have preferences between onshore wind power, offshore wind power and wave power. The results of a latent class model reveal that the majority of households (76.5%) are willing to pay an additional £89-£196 per year to obtain electricity from renewable resources instead of conventional sources. However, there is no statistically significant difference in the willingness to pay between the renewable technologies included in the choice experiment. The latent class model also illustrated that there is a sizeable minority (23.5%) who are opposed to renewable energy development. Older respondents and those less concerned about CO2 emissions are significantly more likely to form part of this group at the 5% level of significance. The study also included a unique addition by identifying households which purchased a house in the previous seven years. Interacting the actual transaction prices of these houses in a multinomial logit model suggested that households may be concerned about renewable energy developments devaluing their properties or the additional expense required to power larger houses. Due to the increasing difficulty of conducting choice experiments in the UK, a novel method of eliciting choice experiment responses from online advertising was tested and was found to be a cost-effective method of eliciting choice experiment responses. Overall, the research indicates that caution should be exercised when interpreting the results of a choice experiment which elicits responses using Internet advertising. It can be observed that the pseudo R2 of the Internet-based sample is lower than the mail-based sample and that the mean respondent to the Internet-based choice experiment is willing to pay significantly more for renewable electricity than the mean respondent to the mail-based choice experiment at the 5% level of significance. Furthermore, the mean willingness to pay estimate in the Internet-based choice experiment appears to be unrealistically high. Further research investigating the elasticity of survey responses to the prize fund on offer would be valuable in identifying the most cost-effective strategy to obtain responses and to generate a more representative sample.

No description available.

Darbas susideda iš dviejų dalių teorinės bei praktinės. Darbo tikslas – įvertinti vėjo parametrus ir prognozuojamą vėjo elektrinių galią pajūrio ir Tauragės regionams. Teorinėje dalyje aprašoma vėjo energetikos pasiekimai ir perspektyvos Lietuvoje, aptariami vėjo srautų kitimo atmosferos pasienio sluoksnyje dėsningumai, vėjo prognozavimo metodai, vėjo jėgainių konstrukcija ir veikimo principas. Praktinėje dalyje pateikiama vėjo matavimo duomenų statistinė analizė, bei įvertinamas prognozuojamas metinis vėjo jėgainių pagamintos energijos kiekis. / The work consists of two parts: theoretical and practical. The aim of the work is to evaluate the parameters of the wind and prognosticated the power of wind- power- stations for near- shore zones and regions of Tauragė. In the theoretical part the achievements and perspectives of wind energetics in Lithuania are described, the regularity of wind flow changes in atmosphere terminal are discussed, the methods of wind prognostication, the construction and working principle of wind- power- stations. In the practical part the statistical analysis of wind measures is shown and the prognosticated amount of energy produced by wind- power- stations per year is evaluated.

No description available.

Climate change, greenhouse gas emissions (GHG), and environmental pollution have all become buzzwords of our time. The awareness in recent years of the degradation of the planet by prioritising economic gain has allowed for open debate about the way the planet is being affected by development. However, there is wide consensus that development cannot be stopped or slowed down, but may be conducted in a sustainable way. The aim of this research is to investigate the role of Clean Development Mechanism (CDM) as a tool to promote the use of renewable energy in South Africa. The Kyoto Protocol was adopted in 1997, which stipulated that developed nations of the world would take on emission reduction targets to reduce their GHG emissions by five percent below 1990 levels. These emissions will be evaluated by the CDM Executive Board at the end of 2012 and penalties are payable should countries not meet their stipulated targets. South Africa is defined as a country (under CDM) which is eligible for hosting CDM projects, and does not have emission reduction targets. This research aims to explore the barriers to the successful implementation of CDM projects in South Africa, with a particular focus on renewable energy projects. In order to address the research problem, the theory of ecological modernisation (Mol, 1995; Hajer, 1995; Christoff, 1996) is applied to analyse the policy decisions around renewable energy, thus highlighting areas that need attention in order to make significant changes in the climate change policy decisions prevailing at the time of the study. Ecological modernisation is a policy orientated discourse which describes environmental issues in a particular manner. In the developing country context of South Africa, a case of weak ecological modernisation has been established (Christoff, 1996; Scott and Oelofse, 2005; Blowers and Pain, 1999). This is in part due to the weak participatory approach which has been adopted by government. This study had found that South Africa has robust and progressive policies in terms of environmental management and renewable energy. However, the area in which it seems to be failing is implementation. The results of this study show that CDM is not popular in South Africa due to a host of reasons. Funding and lack of implementation of projects seem to be the key factors. Eskom’s relatively low electricity price still hinders the wide spread implementation of renewable energy and energy efficiency projects. This study concludes that CDM projects have not succeeded in South Africa due to the bureaucratic process that CDM projects need to undergo coupled with the two issues mentioned above (funding and relatively cheap electricity). This is completely different compared to its other developing country counterparts like India, China and Brazil. This study was conducted at a time when the Kyoto Protocol was nearing its end. Should the agreement not be extended, it would be a lost opportunity for South Africa in terms of gaining technology transfer from the developed world as well as much needed funding for climate change projects. / Thesis (M.Soc.Sc.)-University of KwaZulu-Natal, Durban, 2013.

Renewable power generation from the controlled mixing of sea and fresh water is relatively unexplored when compared to the development for solar, wind, and other sustainable power alternatives. When global river discharge was taken into account, an estimated 2.6 TW of obtainable energy exists in untapped salinity gradients. Reverse electrodialysis is one proposed power-generating mechanism for harnessing energy from brackish environments and relies on the transport of aqueous salt ions through an apparatus of ion-exchange membranes. In this thesis, operational parameters, including flow direction, salinity composition, and membrane selectivity, are investigated. For optimal performance, I have employed counter-current flow mode with monovalent ion selective membranes and pure 0.5 M NaCl saline solution. The results show that a maximum open circuit voltage (OCV) level of 2.01 V is obtained with an active membrane area of 0.0756 m². The presence of multivalent ions in the feed solutions hinders OCV levels, but the effects are reduced with monovalent-selective membranes. Preliminary results are insightful; in order to increase the commercially viability of this technology, future work is needed to enhance the performance properties of the ion exchange membranes.

Crystalline silicon solar cells translate energy from the sun into electrical energy via the photoelectric effect. This technology has the potential to simultaneously reduce carbon emissions and our dependence on fossil fuels. The cost of photovoltaic energy, however, is still higher than the cost of electricity off of the grid which hampers this technologies adoption. Raising solar cell efficiency without significantly raising the cost is crucial to lowering the cost of photovoltaic produced energy. One technology which holds promise to increase solar cell efficiency is a selective emitter solar cell. In this work the benefit of selective emitter solar cells is quantified through numerical modeling. Further, the use of ultraviolet laser to create a laser doped selective emitter solar cell is explored. Through optimization of the laser doping process to minimize laser induced defects it is shown that this process can increase solar cell efficiency to over 19.1%. Additionally, 2D and 3D numerical modeling are performed to determine the limitations screen printed interdigitated back contact solar cells and the practical efficiency limit for crystalline Si solar cells.

Access to modern energy is central to addressing important global development challenges including poverty, inequality, climate change, food security, health and education. The understanding of the concept of energy poverty is critical when making any attempts to alleviate it. Lack of access to sustainable energy is also a major factor preventing social and economic development, both of which are linked to sustainable poverty reduction. However, worldwide access to energy has shown very slow progress because of the costs associated with electric grid extensions and decentralized systems by which power is offered. This study investigates the viability of implementing solar energy in poor communities in Inanda, which is located in Durban, South Africa. Inanda is known to be an area with high unemployment and high poverty levels. Most important to this study are high energy poverty levels in the area. It was found that these communities prioritised energy for cooking, lighting and heating. The results of this study also indicate that in most households, multiple sources of unsustainable energy sources were being used. These included electricity, fuelwood, gas, paraffin and candles. Illegal electrical connections are a growing problem in this community, and other traditional sources were found to have numerous effects on human and environmental health. Upon investigation of the potential for renewable energy implementation in these communities, it found that there was a high willingness to use it, specifically solar energy; however, more education is needed regarding solar energy and related benefits. It was also indicated that the provision of sustainable energy will allow more time for income-generating activities in the community. The biggest challenge with regard to provision of solar energy was cost. These communities cannot afford to pay high start-up and maintenance costs for the technology. It is for this reason that efforts should be made to subsidize these costs and integrate this plan into policy-making. This will not only provide poor communities with sustainable energy, but also help advance the renewable energy industry in South Africa. / M.A. University of KwaZulu-Natal, Durban 2013.