Insight into the Greek electric sector and energy planning with mature technologies and fuel diversification

The numerous available options for the development of the Greek electric sector in combination with the various techno-economic and political constraints make energy planning rather complex. Furthermore, as full auctioning of CO 2 allowances shall be the rule from 2013 onwards for the electric sector following free allocation, even more uncertainties emerge. This work aims at investigating the main characteristics of the Greek electric system taking into consideration the various allowance allocation schemes, evaluates fundamental energy scenarios and ultimately performs energy planning. The reliability of the algorithm utilised is assessed by predicting successfully key figure energy results for years 2004-2008. Main parameter under investigation in the study is the cost of CO 2 emissions allowances, while expansion scenarios are evaluated according to a newly developed set of indices standing for feasibility, environmental performance, cost effectiveness and energy safety. Many expansion scenarios examined were proved unrealistic as led to extremely high utilization of imported fuels for electricity production, while others proved inefficient on environmental or economic basis. Finally, it was proved that if a "conservative" energy planning is adopted, emissions reduction in 2020 can reach 6.3% over 2005

Professional system for energy planning in the greek electricity production sector

The present thesis develops a professional system for the energy planning in Greek electric sector. The main objective is the investigation and evaluation of various energy scenarios as regards their environmental, economic efficiency and realism of implementation. The legal and procedural framework concerning Climate Change was initially surveyed and was followed by the development of a database with technical end economic data and projections for existing electricity production units, fuels and technological solutions, the formulation of a model for the simulation of the Greek connected electric sector based on ENPEP BALANCE software, the evaluation of energy scenarios using newly designed indices and the creation of a methodology for energy planning taking into consideration the developed indices and the country’s European energy and environmental obligations. The last one is based on a step-by-step decision-making approach based on rules and restrictions. Its core advantage is that the outcome and the reasons that led to it are completely comprehensible in all stages. Consequently the introduction of improvements in any stage of the process becomes for the designer, who is the final decision maker, easier. With the aid of the developed system, various scenarios that were announced in the daily Press were studied, while the effects of CO2 allowances allocation mechanisms were analysed. Finally the potential of conservative and radical energy planning, with regard to the energy safety of country, the maturity of utilized technologies and the penetration of renewable energy sources, was investigated. Results showed that the full auctioning mechanism is fairer than free allocation, avoiding distortions in the electricity market; nevertheless its initiation in 2013 is expected to increase electricity production cost by 34.7%. Conservative planning can lead in emissions reduction of 3.8% in 2020 over 2005 levels, which corresponds in 608 kgCO2/MWhel. The design of an electric system without coal is difficult to be realized satisfying the aspect of country’s energy safety. Conservative planning without sufficient energy saving is not easy to lead Greece in compliance with its environmental EU targets, unless radical alternative energy policies are applied. As a solution without coal, large-scale decentralised cogeneration and replacement of electricity by thermal energy is proposed, in combination with offshore floating wind turbines and biomass co-firing.Στόχος της παρούσας διδακτορικής διατριβής είναι η δημιουργία ενός ολοκληρωμένου συστήματος ανάπτυξης ενεργειακού σχεδιασμού για τον Ελληνικό ηλεκτρικό τομέα. Κύριος σκοπός είναι η χρήση του συστήματος αυτού για σχεδιασμό, διερεύνηση και αξιολόγηση ενεργειακών σεναρίων ως προς την περιβαλλοντική και οικονομική τους αποδοτικότητα καθώς και το ρεαλισμό τους. Σε πρώτη φάση έγινε μελέτη του νομικού και διαδικαστικού πλαισίου που αφορά την Κλιματική Αλλαγή. Ακολούθως αναπτύχτηκαν βάση δεδομένων με στοιχεία των μονάδων ηλεκτροπαραγωγής, τα καύσιμα και τις τεχνολογικές λύσεις ηλεκτροπαραγωγής, μοντέλο προσομοίωσης του διασυνδεδεμένου ηλεκτρικού τομέα, με τη βοήθεια του λογισμικού ENPEP BALANCE, σύστημα αξιολόγησης ενεργειακών σεναρίων με δείκτες και μεθοδολογία ενεργειακού σχεδιασμού. Ο σχεδιασμός στηρίζεται σε βηματική προσέγγιση λήψης απόφασης βάσει κανόνων και περιορισμών, ώστε τα αποτελέσματά του αλλά και τα αίτια που οδήγησαν σε αυτά να είναι ανά πάσα στιγμή πλήρως κατανοητά. Διευκολύνεται επομένως για το σχεδιαστή, ο οποίος παίρνει και την τελική απόφαση, η εφαρμογή βελτιώσεων σε οποιοδήποτε στάδιο της διαδικασίας. Με τη βοήθεια του συστήματος που αναπτύχθηκε μελετήθηκαν σενάρια εγκατάστασης νέων σταθμών όπως ανακοινώθηκαν στον ημερήσιο Τύπο, ενώ έγινε συγκριτική ανάλυση των διαφόρων μηχανισμών κατανομής δικαιωμάτων CO2. Τέλος ακολούθησε διερεύνηση των δυνατοτήτων χάραξης συντηρητικού και μη, ενεργειακού σχεδιασμού, όσον αφορά την ενεργειακή ασφάλεια της χώρας, τη χρήση ώριμων τεχνολογιών και τη διείσδυση ανανεώσιμων πηγών ενέργειας. Συμπερασματικά, ο μηχανισμός πλήρους δημοπράτησης φαίνεται να είναι πιο δίκαιος σε σχέση με τη δωρεάν κατανομή, παρόλα αυτά η έναρξη του το 2013 αναμένεται να επιφέρει αύξηση του κόστους ηλεκτροπαραγωγής κατά 34.7%. Ο συντηρητικός ενεργειακός σχεδιασμός μπορεί να οδηγήσει σε μείωση των εκπομπών 3.8% το 2020 ως προς το 2005 που αντιστοιχεί σε 608 kgCO2/MWhel. Σύστημα ηλεκτροπαραγωγής χωρίς λιθανθρακικούς σταθμούς είναι δύσκολο να σχεδιαστεί πληρώντας ταυτόχρονα τις αρχές ενεργειακής ασφάλειας της χώρας. Συντηρητικός σχεδιασμός χωρίς ουσιαστική εξοικονόμηση ενέργειας είναι δύσκολο να οδηγήσει την Ελλάδα σε συμμόρφωση με τους περιβαλλοντικούς στόχους της Ε.Ε., εκτός αν εφαρμοσθούν ριζικές εναλλακτικές ενεργειακές πολιτικές. Ως λύση χωρίς λιθάνθρακα προτείνεται σύστημα με αποκεντρωμένη συμπαραγωγή και αντικατάσταση ηλεκτρισμού από θερμική ενέργεια, εγκατάσταση υπεράκτιων πλωτών Α/Γ και μικτή καύση βιομάζας

Insight into the Greek electric sector and energy planning with mature technologies and fuel diversification

The numerous available options for the development of the Greek electric sector in combination with the various techno-economic and political constraints make energy planning rather complex. Furthermore, as full auctioning of CO2 allowances shall be the rule from 2013 onwards for the electric sector following free allocation, even more uncertainties emerge. This work aims at investigating the main characteristics of the Greek electric system taking into consideration the various allowance allocation schemes, evaluates fundamental energy scenarios and ultimately performs energy planning. The reliability of the algorithm utilised is assessed by predicting successfully key figure energy results for years 2004-2008. Main parameter under investigation in the study is the cost of CO2 emissions allowances, while expansion scenarios are evaluated according to a newly developed set of indices standing for feasibility, environmental performance, cost effectiveness and energy safety. Many expansion scenarios examined were proved unrealistic as led to extremely high utilization of imported fuels for electricity production, while others proved inefficient on environmental or economic basis. Finally, it was proved that if a "conservative" energy planning is adopted, emissions reduction in 2020 can reach 6.3% over 2005.Greek electric sector Energy planning CO2 allowances

Myocardial creep-induced misalignment artifacts in PET/MR myocardial perfusion imaging

PURPOSE Misalignment between positron emission tomography (PET) datasets and attenuation correction (AC) maps is a potential source of artifacts in myocardial perfusion imaging (MPI). We assessed the impact of adenosine on the alignment of AC maps derived from magnetic resonance (MR) and PET datasets during MPI on a hybrid PET/MR scanner. METHODS Twenty-eight volunteers underwent adenosine stress and rest 13N-ammonia MPI on a PET/MR. We acquired Dixon sequences for the creation of MRAC maps. After reconstruction of the original non-shifted PET images, we examined MRAC and PET datasets for cardiac spatial misalignment and, if necessary, reconstructed a second set of shifted PET images after manually adjusting co-registration. Summed rest, stress, and difference scores (SRS, SSS, and SDS) were compared between shifted and non-shifted PET images. Additionally, we measured the amount of cranial movement of the heart (i.e., myocardial creep) after termination of adenosine infusion. RESULTS Realignment was necessary for 25 (89.3%) stress and 12 (42.9%) rest PET datasets. Median SRS, SSS, and SDS of the non-shifted images were 6 (IQR = 4-7), 12 (IQR = 7-18), and 8 (IQR = 2-11), respectively, and of the shifted images 2 (IQR = 1-6), 4 (IQR = 7-18), and 1 (IQR = 0-2), respectively. All three scores were significantly higher in non-shifted versus shifted images (all p < 0.05). The difference in SDS correlated moderately but significantly with the amount of myocardial creep (r = 0.541, p = 0.005). CONCLUSION Misalignment of MRAC and PET datasets commonly occurs during adenosine stress MPI on a hybrid PET/MR device, potentially leading to an increase in false-positive findings. Our results suggest that myocardial creep may substantially account for this and prompt for a careful review and correction of PET/MRAC data

Coronary artery lumen volume index as a marker of flow-limiting atherosclerosis-validation against 13 N-ammonia positron emission tomography

Objectives: Coronary artery volume indexed to left myocardial mass (CAVi), derived from coronary computed tomography angiography (CCTA), has been proposed as an indicator of diffuse atherosclerosis. We investigated the association of CAVi with quantitative flow parameters and its ability to predict ischemia as derived from 13N-ammonia positron emission tomography myocardial perfusion imaging (PET-MPI). Methods: Sixty patients who underwent hybrid CCTA/PET-MPI due to suspected CAD were retrospectively included. CAVi was defined as total coronary artery lumen volume over myocardial mass, both derived from CCTA. From PET-MPI, quantitative stress and rest myocardial blood flow (MBF) and myocardial flow reserve (MFR) were obtained and correlated with CAVi, and semi-quantitative perfusion images were analyzed for the presence of ischemia. Harrell's c-statistic and net reclassification improvement (NRI) analysis were performed to evaluate the incremental value of CAVi over the CCTA model (i.e., stenosis > 50% and > 70%). Results: CAVi correlated moderately with stress MBF and MFR (R = 0.50, p 20.2 mm3/g, n = 36) CAVi (p < 0.001 for both comparisons). CAVi was independently associated with abnormal stress MBF (OR 0.90, 95% CI 0.82-0.998, p = 0.045). CAVi increased the predictive ability of the CCTA model for abnormal stress MBF and ischemia (c-statistic 0.763 versus 0.596, pdiff < 0.05 and 0.770 versus 0.645, pdiff < 0.05, NRI 0.84, p = 0.001 and 0.96, p < 0.001, respectively). Conclusions: CAVi exhibits incremental value to predict both abnormal stress MBF and ischemia over CCTA alone. Key points: • Coronary artery volume indexed to left myocardial mass (CAVi), derived from coronary computed tomography angiography (CCTA), is correlated with myocardial blood flow indices derived from 13N-ammonia positron emission tomography myocardial perfusion imaging. • CAVi is independently associated with abnormal stress myocardial blood flow. • CAVi provides incremental diagnostic value over CCTA for both abnormal stress MBF and ischemia. Keywords: Computed tomography angiography; Myocardial ischemia; Positron emission tomograph

Relationship between Coronary Arterial Geometry and the Presence and Extend of Atherosclerotic Plaque Burden: A Review Discussing Methodology and Findings in the Era of Cardiac Computed Tomography Angiography

Coronary artery disease (CAD) represents a modern pandemic associated with significant morbidity and mortality. The multi-faceted pathogenesis of this entity has long been investigated, highlighting the contribution of systemic factors such as hyperlipidemia and hypertension. Nevertheless, recent research has drawn attention to the importance of geometrical features of coronary vasculature on the complexity and vulnerability of coronary atherosclerosis. Various parameters have been investigated so far, including vessel-length, coronary artery volume index, cross-sectional area, curvature, and tortuosity, using primarily invasive coronary angiography (ICA) and recently non-invasive cardiac computed tomography angiography (CCTA). It is clear that there is correlation between geometrical parameters and both the haemodynamic alterations augmenting the atherosclerosis-prone environment and the extent of plaque burden. The purpose of this review is to discuss the currently available literature regarding this issue and propose a potential non-invasive imaging biomarker, the geometric risk score, which could be of importance to allow the early detection of individuals at increased risk of developing CAD

Prognostic value of regional myocardial flow reserve derived from 13 N-ammonia positron emission tomography in patients with suspected coronary artery disease

Purpose: To assess the prognostic value of regional quantitative myocardial flow measures as assessed by 13N-ammonia positron emission tomography (PET) myocardial perfusion imaging (MPI) in patients with suspected coronary artery disease (CAD). Methods: We retrospectively included 150 consecutive patients with suspected CAD who underwent clinically indicated 13 N-ammonia PET-MPI and who did not undergo revascularization within 90 days of PET-MPI. The presence or absence of a decreased global myocardial flow reserve (i.e., MFR < 2) as well as decreased regional MFR (i.e., ≥ 2 adjacent segments with MFR < 2) was recorded, and patients were classified as having preserved global and regional MFR (MFR group 1), preserved global but decreased regional MFR (MFR group 2), or decreased global and regional MFR (MFR group 3). We obtained follow-up regarding major adverse cardiac events (MACE, i.e., a combined endpoint including all-cause death, non-fatal myocardial infarction, and late revascularization) and all-cause death. Results: Over a median follow-up of 50 months (IQR 38-103), 30 events occurred in 29 patients. Kaplan-Meier analysis showed significantly reduced event-free and overall survival in MFR groups 2 and 3 compared to MFR group 1 (log-rank: p = 0.015 and p = 0.013). In a multivariable Cox regression analysis, decreased regional MFR was an independent predictor for MACE (adjusted HR 3.44, 95% CI 1.17-10.11, p = 0.024) and all-cause death (adjusted HR 4.72, 95% CI 1.07-20.7, p = 0.04). Conclusions: A decreased regional MFR as assessed by 13 N-ammonia PET-MPI confers prognostic value by identifying patients at increased risk for future adverse cardiac outcomes and all-cause death. Keywords: Coronary artery disease; Myocardial blood flow; Myocardial flow reserve; Positron emission tomography