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The present paper proves that the vast water supply infrastructure of Athens and the region of Attica could produce useful hydropower. The first aim of this paper is to present the unconventional small hydro philosophy of recovering the hydraulic energy wasted in the existing break pressure devices and energy dissipating structures of the Water Supply Network of Athens, the capital of Greece and of the whole Attica region. The paper discusses themes concerning the replacement, in this large drinking water infrastructure, of all the existing break pressure devices, by a series of small hydro plants and also the efficient ways by which such small unconventional hydro schemes could be realized. The second aim of the paper is to highlight some important CFD simulation features which however needs further investigations and to present preliminary some Flow-3D results concerning the hydrodynamic performances of this series of small hydro plants harnessing the important wasted hydraulic energy of the Attica Water Supply Network. [ABSTRACT FROM AUTHOR]

Hydropower plays an essential role in Europe's energy transition and can serve as an important factor in the stability of the electricity system. This is even more crucial in areas that rely strongly on renewable energy production, for instance, solar and wind power, as for example the Peloponnese and the Ionian islands in Greece. To safeguard hydropower's contribution to total energy production, an accurate prediction of the annual precipitation is required. Valuable tools to obtain accurate predictions of future observations are firstly a series of sophisticated data preprocessing techniques and secondly the use of advanced machine learning algorithms. In the present paper, a complete procedure is proposed to obtain accurate predictions of meteorological data, such as precipitation. This procedure is applied to the Greek automated weather stations network, operated by the National Observatory of Athens, in the Peloponnese and the Ionian islands in Greece. The proposed prediction algorithm successfully identified the climatic zones based on their different geographic and climatic characteristics for most meteorological stations, resulting in realistic precipitation predictions. For some stations, the algorithm underestimated the annual total precipitation, a weakness also reported by other research works. [ABSTRACT FROM AUTHOR]

This paper examines the relationship between primary energy consumption and economic growth in Greece for the period 1965-2019 by using annual data. The main objective of this study is to investigate whether there is a causal relationship between economic growth and energy consumption. In terms of econometric specificity, ordinary least squares regression (OLS) is used to determine the model in the first step, while the vector self-regulating model (VAR) and the Wald test are used to detect causality. The study differs from the literature in terms of examining the individual energy sources. Total primary energy consumption in Greece is examined in relation to economic growth and individual energy sources separately. According to the results, primary energy consumption in Greece has a big impact on economic growth. The energy derived from non-renewable energy sources has the highest consumption rates. Causality tests show that there is a causal relationship between wind energy consumption and the GDP per capita while causality is observed from the GDP per capita to oil, coal, solar and hydropower consumption. [ABSTRACT FROM AUTHOR]

The present paper describes the evaluation of the Greek Archimedean Small Hydro Resources, considering the basic data for the 14 water regions of the country, adopting a holistic assessment methodology of the total theoretical hydro potential of Greece, which could be exploited by using Archimedean Screw Turbines (ASTs). The total evaluation of the theoretical Archimedean hydropower potential of Greece, which may be produced with ASTs, is of the order of several TWh / year, with a theoretical installed capacity of screw turbines in the range of thousands MW, with important values of special capacity and special capacity density, demonstrating the major existing unexploited hydropower potential for a future true sustainable development with small hydro plants in Greece based on environmentally friendly screw turbines. [ABSTRACT FROM AUTHOR]

PHPS is a mature energy storage technology, leading to more efficient energy management and further integration of Renewable Energy Sources (RES). This paper investigates the implementation of such a system at Kastraki, Greece, combined with a second upstream reservoir with a total capacity of 10 hm3 and evaluates its efficiency. The position and the geometric characteristics of the second reservoir are determined with ArcGIS. When excess of energy exists, water is pumped from Kastraki reservoir and stored in the upper one. Otherwise, the stored water is used for energy production. The simulation is performed for 40 years with a monthly time step. Furthermore, another simulation for a typical day in July is conducted, when water and energy needs are increased. The system is evaluated in terms of covering the water supply and energy needs, as well as in terms of efficient energy management. Several results can be obtained, as follows: i) the reliability of the PHPS system for the coverage of monthly water supply and irrigation needs is 82.84 %. ii) The coverage of water supply needs for a typical day in July is 99.99 %. iii) The average monthly coverage of energy needs amounts to 83.86 %. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to prove, according to our inventory that, beyond the horizon of the era of transition and economic crisis of nowadays, Greece is a real "Archimedean Screw Hydropower Development Terra Incognita", a country generously blessed with water, having an important hydropower potential. This inventory shows that the unexploited small hydropower capacity of Greece, including Archimedean possibilities, is approximately 3.500MW. The significant untapped small hydrodynamic potential demonstrates the important role of Pindos Mountain Range, controlling the annual rainfall difference between the North-Western and the Eastern Greece. The climatic and topographic conditions in Greece favor the development of many small Archimedean screw hydropower stations, harnessing the potential of a large number of small and big watercourses crossing mainland of the country. Pleiades of very promising Archimedean small hydro screw plants, having inclined and horizontal axis hydrodynamic rotors, could be installed following two hydro development axis (spears). [ABSTRACT FROM AUTHOR]

The present study explores the process of Greece's current decarbonisation transition and its energy policy regarding the country's two coal-mining areas. Using the Region of Western Macedonia as a case study, we aimed at providing a holistic approach—as until now only few attempts have been made to systematise the 'Just Transition Plans' in European Union (EU)—for raising awareness on issues related to water resource management in post-lignite areas and analysing the use of hydropower in Greece. Our research draws on a flexible method approach, serving as a tool to identify gaps in current knowledge and practices, based on two stages—first the analysis of existing literature, reviews, and sources from government's core strategies, as well as policy and decision-making papers, and then formulating research questions by synthesising relevant data. In Greece, both 'Just Transition Development Plan of Lignite Areas' and hydropower production practices overlook water resources management. By summarising our findings and identifying gaps that remain in current approaches, this work indicates future directions by suggesting processes necessary for addressing the complex issue of adoption of sustainable water resources management measures in post-lignite eras in accordance with EU's water policy. [ABSTRACT FROM AUTHOR]

Abstract: This paper applies a bootstrapped Data Envelopment Analysis (DEA) formulation aiming to evaluate the financial performance of the firms operating in the Greek renewable energy sector. With the use of financial ratios in a DEA setting, efficiency ratios are constructed in order to analyse firms’ financial performance. The results reveal that firms’ performances are positively influenced by the high levels of return on assets and equity and by lower levels of debt to equity. In addition it appears that there are not significant differences of firms’ efficiency levels indicating high competitiveness between firms. Finally, firms producing wind energy appear to perform better than firms producing hydropower energy. It emerges that the majority of firms are operating in the wind and hydropower energy production making the Greek market of solar energy production being an emerging segment of the Greek renewable energy sector. [Copyright &y& Elsevier]

Abstract: In autonomous islands, the wind penetration is restricted due to technical reasons related with the safe operation of the electrical systems. The combined use of wind energy with pumped storage (WPS) is considered as a mean to exploit the abundant wind potential, increase the wind installed capacity and substitute conventional peak supply. In this paper, the experience gained from the analysis of WPS in three specific islands is used towards the estimation of the WPS market in autonomous Greek islands. Parameterized diagrams and a methodology towards the pre-dimensioning and initial design of the WPS are proposed and used towards the estimation of the market in autonomous Greek islands. The objective is to make an initial general prefeasibility study of WPS prospects in the autonomous Greek islands. Results show that there is a significant market for WPS in Greece and the development cost of WPS is competitive to the fuel cost of local power stations in autonomous islands. [Copyright &y& Elsevier]

Abstract: In this paper, the question of freshwater induced stratification at the mouth of two dam-controlled Greek rivers is addressed. Results from a monitoring program are presented along Strymon River estuary and Nestos River coastal zone, two of the most important freshwater suppliers in the North Aegean Sea. Strymon River flow is man-controlled through Kerkini Dam, while Nestos River discharge patterns depict significant alterations, due to the operation of two hydropower dams. Moreover, a stratification–mixing model was developed based on the water column potential energy ϕ TOTAL, which accounted separately for the local contributions to stratification (solar heating and freshwater buoyancy) and mixing (wind and bottom shear stresses). The model was run under two different scenarios: a) the influence and the absence of Kerkini Dam for the case of Strymon River, and b) the presence and absence of the hydropower dams for the case of Nestos River. Results show that Kerkini Dam affects the stratification conditions in Strymon River mouth during spring and early summer (April to June), by reducing ϕ TOTAL by approximately 13%. In Nestos River mouth, the water column dynamics are highly affected by river damming, as ϕ TOTAL appeared reduced during November to July, by approximately 50.2%. [Copyright &y& Elsevier]

Summary: River flow forecasting consists one of the most important applications in modern hydrology, especially for the effective hydropower reservoir management. In this paper, an innovative non-linear time-series fitting and forecasting model is proposed, consisting of the following sub-modules: (a) the division of the time-series into generations, by identifying the structural change points, (b) the generation decomposition into linear trend, harmonic component and autoregressive component, consisting of several gene ARMA models, (c) the use of fuzzy methods to determine the relative weight of each gene model, and (d) the time-series expansion for the optimal forecasting. The method was applied to the mean monthly Nestos River discharge data for the 1966–2006 period, recorded at the Greek–Bulgarian border, serving as inflow to the Thissavros Hydropower Reservoir. The selected series was divided into five distinctive generations representing periods of gradual surface runoff reduction. It occurred that mean monthly discharge during the fifth generation was almost halved, compared to the corresponding value of the first generation. Harmonic decomposition produced periods in agreement with the large-scale atmospheric fluctuations, while ARIMA modeling performed on the residuals from a pre-defined gene model-base, produced satisfactory fitting to the measured flow series. Model expansion for the last 2 years (2005–2006) of the time-series illustrated reasonable good approximations. Model forecasts during 2005 followed closely the recorded variability, with MAPE and RMSE statistics indicating increased model accuracy. Overall, it is evident that the model slightly underpredicts Nestos River discharge, while slight overestimation occurs under high river flow conditions (winter 2006). Although current research proved model’s distinct capability and advantages in river flow fitting and medium-scale forecast, future improvement could facilitate the use of more elaborative models (ARCH, fuzzy, ANN), in the developed gene model-base. [Copyright &y& Elsevier]

Although storage-reliability-yield (SRY) relationships have been widely used in the design and planning of water supply reservoirs, their application in hydroelectricity is practically nil. Here, we revisit the SRY analysis and seek its generic configuration for hydroelectric reservoirs, following a stochastic simulation approach. After defining key concepts and tools of conventional SRY studies, we adapt them for hydropower systems, which are subject to several peculiarities. We illustrate that under some reasonable assumptions, the problem can be substantially simplified. Major innovations are the storage-head-energy conversion via the use of a sole parameter, representing the reservoir geometry, and the development of an empirical statistical metric expressing the reservoir performance on the basis of the simulated energy-probability curve. The proposed framework is applied to numerous hypothetical reservoirs at three river sites in Greece, using monthly synthetic inflow data, to provide empirical expressions of reliable energy as a function of reservoir storage and geometry. [ABSTRACT FROM AUTHOR]

Hydropower is the most widely used renewable power source worldwide. The current work presents a methodological tool to determine the hydropower potential of a reservoir based on available hydrological information. A Bayesian analysis of the river flow process and of the reservoir water volume is applied, and the estimated probability density function parameters are integrated for a stochastic analysis and long-term simulation of the river flow process, which is then used as input for the water balance in the reservoir, and thus, for the estimation of the hydropower energy potential. The stochastic approach is employed in terms of the Monte Carlo ensemble technique in order to additionally account for the effect of the intermediate storage retention due to the thresholds of the reservoir. A synthetic river flow timeseries is simulated by preserving the marginal probability distribution function properties of the observed timeseries and also by explicitly preserving the second-order dependence structure of the river flow in the scale domain. The synthetic ensemble is used for the simulation of the reservoir water balance, and the estimation of the hydropower potential is used for covering residential energy needs. For the second-order dependence structure of the river flow, the climacogram metric is used. The proposed methodology has been implemented to assess different reservoir volume scenarios offering the associated hydropower potential for a case study at the island of Crete in Greece. The tool also provides information on the probability of occurrence of the specific volumes based on available hydrological data. Therefore, it constitutes a useful and integrated framework for evaluating the hydropower potential of any given reservoir. The effects of the intermediate storage retention of the reservoir, the marginal and dependence structures of the parent distribution of inflow and the final energy output are also discussed. [ABSTRACT FROM AUTHOR]

The characteristics (natural, socioeconomic and administrative/institutional) of Alfeios River basin, in Greece, are identified and presented, incorporating and critically reviewing all possibly found literature. The Alfeios River is a water resources system of great natural, ecological, social and economic importance for Western Greece, since it has the longest and highest flow rate watercourse in the Peloponnisos region. Moreover, the river basin was exposed in the last decades to a plethora of environmental stresses (such as hydrogeological alterations, intensively irrigated agriculture, surface and groundwater overexploitation and infrastructure developments), resulting in the degradation of its quantitative and qualitative characteristics. It is therefore necessary for the development of an integrated river basin management plan for this basin, to study and analyse the interplay between the river components and the exerted environmental stresses, taking into account the puzzle of various and conflicting water uses, including water supply, irrigation, hydropower generation, lignite thermal power production and recreation. Mitigative, preventive and control measures for the analysed environmental stresses are epigrammatically depicted. Focusing on the problematic features, the present work provides a concrete foundation for the determination and conceptualisation of management objectives and possible sustainable alternatives. [ABSTRACT FROM AUTHOR]

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