Assessing the Status of Electricity Generation in the Non-Interconnected Islands of the Aegean Sea Region

Assessment of the electricity generation status for Non-Interconnected Islands (NIIs) of the Aegean Sea region, excluding the electricity systems of Crete and Rhodes, is undertaken in the current study. The authors focus on the long-term analysis of thermal power generation characteristics and also on the challenges so far limiting the contribution of Renewable Energy Sources (RES) in covering the electricity needs of the specific area. According to the present analysis, due to the existing technical limitations, the annual RES shares in the electricity balance of NIIs of the Aegean Sea have since 2010 stagnated in the range of 15% to 18%. Moreover, the performance of thermal power stations for all 30 NII systems is evaluated on the basis of their utilization factor, associated fuel consumption and electricity production costs. The vast majority of these stations is characterized by low capacity factors in combination with high specific fuel consumption and high operational expenses that in the case of smaller scale island regions could even exceed 600€/MWh. At the same time, the authors discuss on the alternatives and encourage further investigation of novel, intelligent energy solutions, such as the smart microgrid and battery-based hybrid power station that are currently developed on the island of Tilos under the implementation of the TILOS Horizon 2020 program

Sizing, Optimization, and Financial Analysis of a Green Hydrogen Refueling Station in Remote Regions

Hydrogen (H2) can be a promising energy carrier for decarbonizing the economy and especially the transport sector, which is considered as one of the sectors with high carbon emissions due to the extensive use of fossil fuels. H2 is a nontoxic energy carrier that could replace fossil fuels. Fuel Cell Electric Vehicles (FCEVs) can decrease air pollution and reduce greenhouse gases when H2 is produced from Renewable Energy Sources (RES) and at the same time being accessible through a widespread network of Hydrogen Refueling Stations (HRSs). In this study, both the sizing of the equipment and financial analysis were performed for an HRS supplied with H2 from the excess electrical energy of a 10 MW wind park. The aim was to determine the optimum configuration of an HRS under the investigation of six different scenarios with various numbers of FCEVs and monthly demands, as well as ascertaining the economic viability of each examined scenario. The effect of the number of vehicles that the installation can refuel to balance the initial cost of the investment and the fuel cost in remote regions was investigated. The results showed that a wind-powered HRS could be a viable solution when sized appropriately and H2 can be used as a storage mean for the rejected wind energy. It was concluded that scenarios with low FCEVs penetration have low economic performance since the payback period presented significantly high values

Contemporary solar energy map of Greece with application in hybrid renewable energy systems

The specific PhD thesis has two discrete objectives. The first objective concerns the creation of a reliable database of meteorological parameters. The developed database can be used to support the advanced simulation of the operation of Renewable Energy Sources (RES) hybrid systems which utilize solar energy and also for the long term assessment of solar energy systems' performance. The second objective concerns the evaluation of RES hybrid systems in Greece in terms of both energy performance and economic efficiency by implementing the database created in the context of the first objective of the thesis.More specifically, this thesis includes: a structured methodology that can be applied in order to create reliable time series of meteorological parameters and Typical Meteorological Years (TMY); the criteria and the method of geospatial interpolation, which can reliably describe the spatial distribution of the solar energy potential in Greece; a defined methodology for the evaluation of efficiency and energy consumption of RES hybrid systems that utilize solar and wind energy; the energy and efficiency performance of hybrid RES systems in different regions of Greece through the identification of limits in size and costs that can be achieved under specific circumstances.For the above mentioned objectives, 3-hour time series of meteorological data have been collected along with daily sunshine values, for a period of 15 years, from 44 different meteorological stations of the Hellenic National Meteorological Service (HNMS). The meteorological stations were chosen on the basis of long-term availability of sunshine observations, since sunshine is the basic parameter in calculating the solar radiation from the broadband atmospheric model used in this thesis. These measurements, having undergone quality control, have been used as input data at the Meteorological Radiation Model (MRM), which has been developed by the Atmospheric Research Team of the National Observatory of Athens. With the use of the MRM, the diffuse and global radiation for each meteorological station and time period under study were estimated at the horizontal plane, allowing in this way to enrich the initial database.By implementing the long term data series of meteorological parameters, Typical Meteorological Years (TMY) were produced for each one of the corresponding stations. The TMY includes values of direct, diffuse and global solar radiation, air temperature, relative humidity and atmospheric pressure.Based on the TMY an updated solar map of Greece was created, containing monthly and annual values of solar energy at the locations of the chosen meteorological stations of the HNMS. This map provides an up to date description of the solar potential in Greece and is of particular interest since Greece’s geographical location renders it as one of the most interesting areas of Europe with a special interest in the utilization of solar energy. Additionally, the definition of solar energy zones provides a fundamental parameter for the initial assessment of solar energy systems as well as for their modeling.TMY were used for the evaluation of autonomous hybrid systems that utilize mainly solar, but also wind energy, through a combination of photovoltaic panels and wind turbines. The evaluation is conducted on the basis of a complete energy and efficiency model, through which examination of the hybrid systems' hourly performance is carried out, and which in turn can allow evaluation in terms of energy production costs. The hybrid systems considered cover different locations throughout Greece and are dedicated to the complete satisfaction of a typical, domestic consumer's energy needs, solely with use of RES.In conclusion, the specific thesis contributes to scientific knowledge and applied engineering by providing TMY which cover almost the whole Greek territory, by highlighting the reliability of the MRM code which is applied in numerous locations where solar radiation measurements do not exist, by producing solar maps which are based on a large amount of solar energy data and by reflecting the energy and economic sustainability of RES hybrid systems which consider solar and wind energy assessment based on reliable meteorological data.H παρούσα διατριβή έχει δύο διακριτούς στόχους. Ο πρώτος στόχος αφορά στη δημιουργία αξιόπιστων χρονοσειρών μετεωρολογικών παραμέτρων, οι οποίες απαιτούνται κατά την προσομοίωση της λειτουργίας υβριδικών συστημάτων ανανεώσιμων πηγών ενέργειας (ΑΠΕ) αλλά και γενικότερα στη μακροχρόνια αξιολόγηση ηλιακών συστημάτων. Ο δεύτερος στόχος αφορά στη διερεύνηση της ενεργειακής και οικονομικής απόδοσης των υβριδικών συστημάτων ΑΠΕ στον ελλαδικό χώρο αξιοποιώντας τη βάση δεδομένων που δημιουργήθηκε στα πλαίσια της διατριβής.Για την επίτευξη των στόχων, πραγματοποιήθηκε έρευνα σε διάφορα πεδία συμβάλλοντας στη διάδοση της επιστημονικής γνώσης σε κάθε ένα από αυτά. Ειδικότερα, η παρούσα διατριβή περιλαμβάνει μία δομημένη μεθοδολογία για τη δημιουργία αξιόπιστων χρονοσειρών μετεωρολογικών παραμέτρων και τυπικών μετεωρολογικών ετών (ΤΜΕ), τα κριτήρια και τη μέθοδο χωρικής παρεμβολής που μπορούν με αξιοπιστία να περιγράψουν τη χωρική κατανομή του ηλιακού δυναμικού στην ελληνική επικράτεια, συγκεκριμένη μεθοδολογία για την ενεργειακή και οικονομική αξιολόγηση υβριδικών συστημάτων ΑΠΕ που αξιοποιούν την ηλιακή και την αιολική ενέργεια, την ενεργειακή και οικονομική απόδοση των υβριδικών συστημάτων ΑΠΕ σε διαφορετικές περιοχές της Ελλάδας με καθορισμό των όριων μεταβολής τού μεγέθους και του κόστους που επιτυγχάνεται υπό τις συγκεκριμένες συνθήκες λειτουργία τους.Για τους σκοπούς της παρούσας διατριβής, συλλέχθηκαν 3-ωριαίες χρονοσειρές μετεωρολογικών δεδομένων καθώς και ημερήσιων τιμών ηλιοφάνειας για 15 έτη, από 44 σταθμούς της Εθνικής Μετεωρολογικής Υπηρεσίας (ΕΜΥ) που διαθέτουν μακροχρόνιες παρατηρήσεις ηλιοφάνειας. Οι μετρήσεις αυτές, μετά από ποιοτικό έλεγχο, χρησιμοποιήθηκαν ως δεδομένα εισόδου στο Μετεωρολογικό Μοντέλο Ακτινοβολίας (Meteorological Radiation Model, MRM), το οποίο έχει αναπτυχθεί από την Ομάδα Ατμοσφαιρικής Έρευνας του Εθνικού Αστεροσκοπείου Αθηνών, εμπλουτίζοντας τη βάση δεδομένων με τιμές ολικής και διάχυτης ηλιακής ακτινοβολίας σε οριζόντιο επίπεδο στη θέση του κάθε μετεωρολογικού σταθμού. Αξιοποιώντας τις μακροχρόνιες χρονοσειρές μετεωρολογικών παραμέτρων, δημιουργήθηκαν Τυπικά Μετεωρολογικά Έτη (ΤΜΕ) για κάθε έναν από τους σταθμούς. Τα ΤΜΕ περιλαμβάνουν ωριαίες τιμές άμεσης, διάχυτης και ολικής ηλιακής ακτινοβολίας, θερμοκρασίας αέρα, σχετικής υγρασίας και ατμοσφαιρικής πίεσης. Από τα ΤΜΕ δημιουργήθηκε επικαιροποιημένος ηλιακός χάρτης της Ελλάδας, με μηνιαίες και ετήσιες τιμές ηλιακής ενέργειας στις θέσεις των επιλεγμένων μετεωρολογικών σταθμών της ΕΜΥ. Ο χάρτης αυτός αποτελεί μία σύγχρονη αποτύπωση του ηλιακού δυναμικού στην ελληνική επικράτεια και παρουσιάζει ιδιαίτερο ενδιαφέρον καθώς η γεωφυσική θέση της Ελλάδας την καθιστά μία από τις περιοχές της Ευρώπης με εξαιρετικό ενδιαφέρον στην αξιοποίηση της ηλιακής ενέργειας. Παράλληλα, ο επιμερισμός της Ελλάδας σε κλιματικές ζώνες ηλιακής ακτινοβολίας αποτελεί βασική παράμετρο για την προκαταρκτική αξιολόγηση και μοντελοποίηση των ηλιακών συστημάτων παραγωγής ενέργειας.Για την ανάδειξη της χρησιμότητας των ΤΜΕ σε εφαρμοσμένους τομείς της επιστήμης, η βάση δεδομένων ΤΜΕ χρησιμοποιείται σε μια εκτεταμένη έρευνα που αφορά στην αξιολόγηση αυτόνομων υβριδικών συστημάτων που αξιοποιούν κατά βάση την ηλιακή ενέργεια αλλά και τον άνεμο συνδυάζοντας φωτοβολταϊκά πλαίσια και ανεμογεννήτριες. Η αξιολόγηση πραγματοποιείται βάσει ενός ολοκληρωμένου ενεργειακού και οικονομικού μοντέλου, το οποίο εξετάζει σε ωριαίο βήμα την ενεργειακή συμπεριφορά του υβριδικού συστήματος και υπολογίζει το μακροχρόνιο κόστος παραγωγής της ηλεκτρικής ενέργειας. Τα υβριδικά συστήματα εξετάζονται σε διαφορετικές θέσεις στην Ελλάδα με βασικό κριτήριο την παροχή αδιάλειπτης ηλεκτρικής ενέργειας σε οικιακό καταναλωτή ο οποίος επιλέγει να καλύψει τις ηλεκτρικές του ενεργειακές ανάγκες αποκλειστικά από ΑΠΕ.Εν κατακλείδι, η καινοτομία της παρούσας διατριβής και η συνεισφορά της στην επιστημονική γνώση συνίστανται στα εξής:•Δημιουργήθηκαν για πρώτη φορά στην Ελλάδα ΤΜΕ που καλύπτουν σε μεγάλο ποσοστό την ελληνική επικράτεια.•Η διαθεσιμότητα ΤΜΕ σε μεγάλο εύρος περιοχών αποτελεί σημαντικό εργαλείο για τη μελέτη ενεργειακής κατανάλωσης των κτηρίων και της ενεργειακής παραγωγής συστημάτων ΑΠΕ καθώς έως και σήμερα οι αντίστοιχες μελέτες βασίζονται σε παλαιά δεδομένα και σε μικρό αριθμό περιοχών, που δεν καλύπτουν επαρκώς την ελληνική επικράτεια.•Χρησιμοποιείται για πρώτη φορά στην Ελλάδα ο κώδικας MRM για την παραγωγή τιμών ηλιακής ακτινοβολίας σε περιοχές που δεν υφίστανται αντίστοιχες μετρήσεις.•Δημιουργήθηκαν ηλιακοί χάρτες για την ελληνική επικράτεια, που για πρώτη φορά βασίζονται σε μεγάλο αριθμό δεδομένων ηλιακής ακτινοβολίας, με συνέπεια να καθίστανται πιο ακριβείς σε σχέση με τους υπάρχοντες στη βιβλιογραφία.Αξιολογείται η ενεργειακή και η οικονομική απόδοση υβριδικών συστημάτων ΑΠΕ που συνδυάζουν Φ/Β πλαίσια και Α/Γ με τη χρήση χρονοσειρών ΤΜΕ, αναδεικνύοντας τις δυνατότητες αξιοποίησής τους στις διαφορετικές κλιματικές ζώνες της Ελλάδας

Hybrid Renewable Energy Systems’ Optimisation. A Review and Extended Comparison of the Most-Used Software Tools

To help stakeholders plan, research, and develop Hybrid Renewable Energy Systems (HRES), the elaboration of numerous modelling techniques and software simulation tools has been reported. The thorough analysis of these undoubtedly complex systems is strongly correlated with the efficient utilisation of the potential of renewable energy and the meticulous development of pertinent designs. In this context, various optimisation constraints/targets have also been utilised. This specific work initially carries out a thorough review of the modelling techniques and simulation software developed in an attempt to define a commonly accepted categorisation methodology for the various existing HRES simulation methods. Moreover, the widely utilised optimisation targets are analysed in detail. Finally, it identifies the sensitivity of two commercial software tools (HOMER Pro and iHOGA) by examining nine case studies based on different wind and solar potential combinations. The results obtained by the two commercial tools are compared with the ESA Microgrid Simulator, a software developed by the Soft Energy Applications and Environmental Protection Laboratory of the Mechanical Engineering Department of the University of West Attica. The evaluation of the results, based on the diversification of the renewable energy potential used as input, has led to an in-depth assessment of the deviances detected in the software tools selected

Hybrid Renewable Energy Systems’ Optimisation. A Review and Extended Comparison of the Most-Used Software Tools

To help stakeholders plan, research, and develop Hybrid Renewable Energy Systems (HRES), the elaboration of numerous modelling techniques and software simulation tools has been reported. The thorough analysis of these undoubtedly complex systems is strongly correlated with the efficient utilisation of the potential of renewable energy and the meticulous development of pertinent designs. In this context, various optimisation constraints/targets have also been utilised. This specific work initially carries out a thorough review of the modelling techniques and simulation software developed in an attempt to define a commonly accepted categorisation methodology for the various existing HRES simulation methods. Moreover, the widely utilised optimisation targets are analysed in detail. Finally, it identifies the sensitivity of two commercial software tools (HOMER Pro and iHOGA) by examining nine case studies based on different wind and solar potential combinations. The results obtained by the two commercial tools are compared with the ESA Microgrid Simulator, a software developed by the Soft Energy Applications and Environmental Protection Laboratory of the Mechanical Engineering Department of the University of West Attica. The evaluation of the results, based on the diversification of the renewable energy potential used as input, has led to an in-depth assessment of the deviances detected in the software tools selected

Medium and short term prognosis of load demand for the Greek Island of Tilos using artificial neural networks and human thermal comfort-discomfort biometeorological data

The objective of the present work is the medium and short term forecasting of load demand (LD) in Tilos Island, Greece. For this purpose, Artificial Neural Network (ANN) models were developed to predict the LD in Tilos Island 24 hours ahead in hourly intervals (medium-term prognosis) and 24 hours ahead in 10 minutes intervals (short-term prognosis). For training the ANNs, meteorological data covering the 2015-2017 period, were used. These data have been recorded in 1 minute intervals by a meteorological mast which has been installed in a specific location in Tilos Island. Furthermore, a biometeorological human thermal comfortdiscomfort index was calculated and used also during the training procedure. For the validation of the developed ANN forecasting models well established statistical evaluation indices were applied. Results show that in all cases, for both medium and short-term LD prognoses, the developed ANN forecasting models present a remarkable ability to predict LD with high accuracy. The proposed load demand forecasting models enable the design of an energy demand information tool for end-users and transmission system operators

First Law Comparison of a Forced-Circulation Solar Water Heating System with an Identical Thermosyphon

The main categories of solar water heating systems (SWHSs) are the thermosyphon and the forced circulation (FC). This paper presents an experiment carried out with the aim to compare the energy performance of the FC with a thermosyphon SHWS. Identical SWHSs were installed side by side at the University of West Attica in Athens, Greece. Domestic hot water load was applied to both systems via a microcontroller-based dispensing unit which mimics the demand profile. The trial period comprised the last two months of spring (April and May). For the first law assessment, two energy indicators were utilized: the solar fraction (SF) and the thermal efficiency of the system (ηth). On days with distinctive weather conditions, both systems obtained approximately equal SF and ηth values, without a specific preference between the ambient conditions and the type of SWHS. Regarding a four-day nonstop operation, the FC overperformed the thermosyphon system at both energy indicators. Namely, for the FC and the thermosyphon SWHS, the SF was calculated to be 0.62 and 0.48, and the ηth was 68.2% and 53.3%, respectively

Utilisation of Mass and Night Ventilation in Decreasing Cooling Load Demand

The building sector consumes 36% of the world’s energy and produces around 40% of energy-related carbon emissions. While the building industry moves towards a zero net greenhouse-gas emission policy, ventilation is, and will be, a necessity for the preservation of air quality—especially in climates defined by unsavoury conditions. Therefore, a “mixing mode” cooling system was employed to lower the required energy consumption at an earthen building situated in the premises of Istanbul Technical University. A room of the high-mass earthen building was monitored under different ventilation and shading conditions. Night ventilation was conducted using two modes, 3.2 and 2.3 air changes per hour, and the air conditioning unit, operating from 08:00 to 17:00, had a set temperature of 23 ∘C. Night ventilation was somewhat impactful, reducing the average expected cooling energy demand up to 27%. Furthermore, the earthen building proved to be extremely effective on moderating extremes of temperature under non-ventilated conditions. During a rather hot day, with an outdoor maximum temperature of 35 ∘C, the indoor maximum temperature of the high-mass building was only 25 ∘C, namely within thermal comfort levels. The diurnal temperature proved to be key in the effective application of night ventilation