Paul Christodoulides

Bio: Paul Christodoulides is an academic researcher from Cyprus University of Technology. The author has contributed to research in topics: Renewable energy & Zero-energy building. The author has an hindex of 20, co-authored 109 publications receiving 1787 citations. Previous affiliations of Paul Christodoulides include University of Cyprus & University of Southern California.

Energy storage for electricity generation and related processes: Technologies appraisal and grid scale applications

Abstract: Renewable Energy Sources have been growing rapidly over the last few years. The spreading of renewables has become stronger due to the increased air pollution, which is largely believed to be irreversible for the environment. On the other hand, the penetration of renewable energy technologies causes major problems to the stability of the grid. Along with the fluctuations of the renewable energy technologies production, storage is important for power and voltage smoothing. Energy storage is also important for energy management, frequency regulation, peak shaving, load leveling, seasonal storage and standby generation during a fault. Thus, storage technologies have gained an increased attention and have become more than a necessity nowadays. This paper presents an up to date comprehensive overview of energy storage technologies. It incorporates characteristics and functionalities of each storage technology, as well as their advantages and disadvantages compared with other storage technologies. Comparison tables with several characteristics of each storage method are included, while different applications of energy storage technologies are described as well. Finally, several hybrid energy storage applications are analyzed and different combinations of energy storage technologies are reviewed.

Internal Drivers and Performance Consequences of Small Firm Green Business Strategy: The Moderating Role of External Forces

Abstract: Growing detrimental effects on the bio-physical environment have been responsible for a large number of small firms to adopt a more strategic stance toward exploiting green-related opportunities. This article aims to shed light on how internal company factors help to formulate a green business strategy among small manufacturing firms, and how this, in turn, influences their competitive advantage and performance. Based on data received from 153 small Cypriot manufacturers, we propose and test a conceptual model anchored on the Resource-based View of the firm. The findings underscore the critical role of both organizational resources and capabilities in pursuing a green business strategy. The adoption of this strategy was more evident in the case of firms operating in more harmful, as opposed to less harmful, industries. The implementation of a green business strategy was found to generate a positional competitive advantage, with this association becoming stronger under conditions of high regulatory intensity, high market dynamism, high public concern, and high competitive intensity. It was also revealed that this competitive advantage is conducive to gaining heightened market and financial performance. Our study makes a fivefold contribution: it injects a theoretical perspective into a relatively atheoretic field, underlines the role of organizational resources/capabilities as drivers of eco-friendly initiatives, highlights the often neglected strategic aspects of small firms’ ecological business activities, stresses the contingent role of external forces in moderating the positive impact of small firm green business strategy on competitive advantage, and focuses on the performance implications of the small firm’s engagement in environmental operations.

A review of the design aspects of ground heat exchangers

Abstract: The advancement of technology and renewable energy systems (RES) have evolved considerably through the years. Geothermal energy was first introduced in Italy in 1904 and has ever since dramatically increased in efficiency. One of the main types of RES, Ground Source Heat Pumps (GSHPs), are used for heating and cooling a space when coupled with Ground Heat Exchangers (GHEs). GSHPs extract or reject heat to the Earth via a network of tubes. The closed loop system, either vertical or horizontal, is the most common of the configurations. Alternatively, pipes can run all the way down to utilize natural underground water sources, when present, in an open loop configuration. GHEs have significantly higher performance over conventional air-to-air heat exchanger systems and the reduction of their cost and the improvement of their overall efficiency through their design are crucial in research. In this paper are presented and reviewed the design aspects of GHE systems. In particular are discussed the types of GHEs such as open or closed loop systems, vertical or horizontal, U-tube or spiral, energy piles and hybrid systems. A comparative analysis through the literature of the various geometrical aspects of GHEs and the geothermal investigation of the ground environment and the materials used in the construction of GHEs are also presented. Then is analyzed the modeling – experimental and mathematical – of GHEs, with terms that have been extensively studied, like borehole thermal resistance, thermal characteristics, thermal response test, line-source and cylindrical-source models, discussed in detail. Next a demonstration of designing a numerical model of a GHE system through a software, taking into consideration the thermal characteristics, is given. Finally, a comparative detailed list in the form of a table of more than 30 mathematical and/or experimental GHE studies is provided, focusing on the important factors analyzed and findings of each. The overall aim of the current review study is to help improve the efficiency and the total manufacturing cost of GHEs.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

On making causal claims : A review and recommendations

Abstract: Social scientists often estimate models from correlational data, where the independent variable has not been exogenously manipulated; they also make implicit or explicit causal claims based on these models. When can these claims be made? We answer this question by first discussing design and estimation conditions under which model estimates can be interpreted, using the randomized experiment as the gold standard. We show how endogeneity – which includes omitted variables, omitted selection, simultaneity, common-method variance, and measurement error – renders estimates causally uninterpretable. Second, we present methods that allow researchers to test causal claims in situations where randomization is not possible or when causal interpretation could be confounded; these methods include fixed-effects panel, sample selection, instrumental variable, regression discontinuity, and difference-in-differences models. Third, we take stock of the methodological rigor with which causal claims are being made in a social sciences discipline by reviewing a representative sample of 110 articles on leadership published in the previous 10 years in top-tier journals. Our key finding is that researchers fail to address at least 66% and up to 90% of design and estimation conditions that make causal claims invalid. We conclude by offering 10 suggestions on how to improve non-experimental research.