George Papadakis

George Papadakis
Agricultural University of Athens · Department of Natural Resources Management and Agricultural Engineering (NRM&AE)

Proffessor of Renewable Energy

About

133
Publications
48,138
Reads
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6,884
Citations
Introduction
Energy, renewable energy technologies, solar energy technologies, renewable energy driven desalination, energy efficiency, technologies for increasing energy efficiency in agriculture, energy production from agriculture, bio-energy
Additional affiliations
January 2013 - December 2014
Agricultural University of Athens
Position
  • Scientific coordinator of the project funded by the EC, (FP7 SMEs): Improving the Performance of Concentrating PV by Exploiting the Excess Heat through a Low Temperature Supercritical Organic Rankine Cycle. Partners from Greece, Belgium, Sweden, Spain
January 2013 - December 2015
Agricultural University of Athens
Position
  • Scientific coordinator of the project funded by the Greek General Secretariat of Research and Development (GSRT SYNERGASIA II): Development of a small-scale low-temperature Supercritical Organic Rankine Cycle engine
November 2012 - December 2015
Agricultural University of Athens
Position
  • Scientific partner in the project funded by the EC (TEMPUS): Solar energy system design using advanced learning aids. Partners from Spain (co-ordinator), UK, Germany, Italy, Greece, Egypt
Education
December 1985 - December 1989
Agricultural University of Athens
Field of study
  • Agricultural Engineering

Publications

Publications (133)
Article
Full-text available
Energy and water are two of the most important components required to ensure prosperity and sustainable development to societies. This paper aims to review the status of renewable energy desalination for Greek islandic communities, deployed in two axes. The first one reviews the desalination systems state of the art technological solutions, their e...
Article
Full-text available
This study conducts a review of energy use in the EU greenhouse agriculture sector. The studies presented illustrate that energy use in greenhouses is varied and generally dependent on fossil sources. High energy systems, which are more dominant in northern Europe, are generally heavily climate controlled and energy use is dominated by heating and...
Article
This review combines results from a large number of studies investigating energy use in EU open-field agriculture, providing an overview of energy use and its concentrations. Such a review and its findings are important as it informs stakeholders and policymakers with evidence for supporting a green energy transition in open-field agriculture. Our...
Article
Full-text available
This study conducts a review bringing together data from a large number of studies investigating energy use in EU livestock systems. Such a study has not been conducted previously, and improvements in our understanding of energy use concentrations in livestock systems will aid in developing interventions to achieve the EU’s 2030 and 2050 sustainabi...
Article
Access to fresh water is a major human right as mankind existence depends on it. The balance between fresh water supply and actual water demand for agricultural purposes (irrigation) relies on the availability of fresh water in the underground aquifers or surface water resources. Water resources are under great pressure due to the high demand for i...
Article
Our economic analysis shows that for Greece no advanced biofuels, renewable gases or electrofuels are currently or will be, until 2050, cost competitive with the production or import costs of fossil fuel equivalents at current fossil fuel prices. This situation holds despite strong learning curve effects for the technologies covered in this study....
Article
Full-text available
Water and energy are two of the most important inputs for a community to thrive. While water is dominant on earth, only 2.5% of the water is fresh water and over 98% of that water is either ground water or locked up in glaciers and ice caps. Therefore, only about 1.2% of all the freshwater is surface water which is able to meet human needs. About 2...
Article
Full-text available
Today, 992 million people still do not have access to electricity globally. Most live in rural areas of the developing world. In 2018, the electrification rate for sub-Saharan Africa was only 27%. Furthermore, off-grid systems are projected to provide 65% of the newly electrified population in sub-Saharan Africa. Current estimations show that the a...
Article
Renewable energy driven desalination has been proven to be a sustainable, economic and environmental friendly solution for the water deficiency problems in remote areas. However, one of the most important issues is the determination of the optimal configuration so that the system meets the water load at the minimum cost. In this paper, five differe...
Conference Paper
This paper presents the comparison of three different approaches for the energy management in polygeneration microgrids. These microgrids consist of energy producers, such as photovoltaics and wind turbines, electricity storage in the form of a battery bank, a hydrogen subsystem and a desalination subsystem. The hydrogen, which is used both as fuel...
Conference Paper
This paper presents the design and implementation of an experimental test bench aiming at optimizing autonomous SWRO desalination systems which are powered by photovoltaics and a wind turbine. The test bench includes two small scale SWRO units; One with a capacity of 150 L/h equipped with a hydraulic energy recovery device of the Clark pump type wh...
Conference Paper
This paper presents an innovative reverse osmosis desalination system for sea water capable of covering the needs in potable water for settlements presenting low cost and minimized environmental footprint. The system is powered by PVs and a wind turbine and will be able to produce between 2.5 -5 m3 per day, capable of covering the needs between 25...
Conference Paper
Polygeneration microgrids aim to holistically cover the needs in remote areas by producing electrical energy, potable water through desalination, hydrogen as fuel for transportation and space heating and cooling. The primary energy is produced by photovoltaics and wind turbines. This topology has been investigated economically and has proved to be...
Article
Full-text available
Currently, 1.06 billion people still do not have access to electricity, with the majority living in rural areas around the world[...]
Conference Paper
Sea water reverse osmosis (SWRO) desalination units coupled with renewable energy systems (RES) such as photovoltaics and/or wind turbines is a very attractive proposition, especially in remote areas for covering potable water supply shortage. The intermittent energy production of RES, makes the integration of energy storage subsystems necessary, s...
Conference Paper
Sea water reverse osmosis (SWRO) desalination coupled with renewable energy (RE) technologies such as photovoltaics and wind turbines is a very attractive proposition, especially in remote areas such as islands and coastal regions, which often face low quality of the available potable water as well as lack of electrical energy supplies. Small-scale...
Article
Energy management systems are essential and indispensable for the secure and optimal operation of autonomous polygeneration microgrids which include distributed energy technologies and multiple electrical loads. In this paper, a multi-agent decentralized energy management system was designed. In particular, the devices of the microgrid under study...
Article
Sea Water Reverse Osmosis (SWRO) desalination systems powered by Renewable Energy (RE) can reduce drastically costs, specific energy consumption and CO2 emissions. A direct connection of a SWRO desalination system with RE technologies such as photovoltaics, can result in lowering the specific energy consumption due to the part-load operation of the...
Article
Full-text available
A novel open-drive scroll expander has been designed and included in a small-scale organic Rankine cycle (ORC) engine. According to the design, the heat input is 100 kWth with hot water temperature up to 100 °C and organic fluid pressure 40 bar. These conditions correspond to supercritical state of the vapour organic fluid (R-404a) with designed th...
Article
Full-text available
Herein a techno-economic assessment was performed on an energy-crop based biogas plant coupled with a greenhouse for utilizing thermal energy produced by cogeneration. Seven energy crops were evaluated: triticale, maize, alfalfa, sunflower, clover, barley and wheat. According to the evaluation, triticale was the most competitive energy crop under s...
Article
A detailed experimental investigation of a small-scale low-temperature organic Rankine cycle (ORC) with R-404A is presented. The tests are first conducted at laboratory conditions for detailed evaluation of the main components at both design and off-design conditions, for variable heat input up to 48 kWth and hot water temperature in the range of 6...
Article
A reverse osmosis (RO) desalination unit, composed of three identical skids connected in parallel and using an energy recovery system, has been designed and manufactured for operation at variable conditions. The main goal of the current experimental investigation is the evaluation of such a system for operation at variable power input and the incre...
Article
The autonomous polygeneration microgrid topology has been developed in order to cover holistically needs in a remote area such as electrical energy, space heating and cooling, potable water through desalination and hydrogen as fuel for transportation. The existence of an advanced energy management system is essential for the operation of an autonom...
Article
The detailed experimental investigation of an organic Rankine cycle (ORC) is presented, which is designed to operate at supercritical conditions. The net capacity of this engine is almost 3 kW and the laboratory testing of the engine includes the variation of the heat input and of the hot water temperature. The maximum heat input is 48kWth, while t...
Book
Considerable research is taking place globally concerning the energy consumption in residential buildings. The effort is aimed toward the creation of zero energy buildings or even positive energy ones. In order to accomplish this, energy production is needed at the building level. Electrical energy, thermal energy for space heating and cooling, and...
Conference Paper
Full-text available
Comparing storability and the energy yield of biogas production from individual feedstock, energy crops perform better than most organic wastes such as manure and food waste and therefore in several European countries biogas is produced using energy crops. The most frequently used energy crop is maize silage. However, although maize has a high biom...
Article
The development of an effective maximum power point tracking (MPPT) algorithm is important in order to achieve maximum power operation in a photovoltaic system (PV). In this study, a direct neural control (DNC) scheme is developed. The intelligent MPPT controller consists of a hybrid learning mechanism; an on-line learning rule based on gradient de...
Article
Various Rankine cycle architectures for single fluids and other improved versions operating with ammonia/water mixture are presented in this paper. Untapped heat resources and their potential for driving organic Rankine cycles are outlined. The nature – state and temperature of the heat source significantly influences the choice of the type of orga...
Poster
Description of involved technologies Description of involved technologies Solar collectors' field Solar collectors' field: High-performance evacuated tube solar collectors are used to produce the heat of up to 140 o C. The total heat capacity of the solar field is 100 kW th , supplying the ORC engine. 216 m 2 of col-lectors' surface are installed i...
Article
Sea water reverse osmosis (SWRO) desalination constitutes a successful technology for covering local fresh water supply shortage in many areas of the world and especially in isolated areas such as islands and coastal regions. SWRO units can be combined with renewable energy (RE) technologies such as photovoltaic and wind generators. Small-scale SWR...
Article
Full-text available
Hybrid renewable energy systems is one of the most promising applications of renewable energy technologies in remote areas, where the cost of grid extension is prohibitive and the price of fossil fuels increase drastically with the remoteness of the location. Applications of hybrid systems range from small power supplies for remote households provi...
Article
A major drawback of Reverse Osmosis (RO) desalination units is their poor performance at off-design conditions. On the other hand, they can operate with low specific energy consumption and produce high-quality fresh water when they are supplied with almost constant power, according to their design and nominal operating conditions. This aspect bring...
Article
Sea water reverse osmosis (SWRO) desalination constitutes a successful technology for covering the potable water needs of islands and coastal regions. SWRO units can be combined with renewable energy technologies such as photovoltaic and wind generators. Conventional small scale SWRO units are not often combined with energy recovery devices; howeve...
Article
Full-text available
An experimental investigation on a diesel engine was conducted to evaluate the performance and exhaust emissions of sunflower oil and three blends with diesel fuel (20, 40, and 70% oil content volumetrically) in comparison to diesel fuel. Three injection timing and three injector protrusion settings were tested to study engine performance and exhau...
Article
In order to maximise the share of biomass in the energy supplying system, the designers should adopt the appropriate changes to the traditional systems and become more familiar with the design details of the biomass heating systems. The aim of this study is to present the development of methodology and its associated implementation in software that...
Article
A small-scale, low-temperature solar organic Rankine cycle (ORC) is investigated, focusing on some key aspects of its design and operation, in order for the system to track the optimised point under variable weather conditions. Two major configurations can be identified for small-scale ORCs using two expansion stages, for improving the performance...
Data
The working fluid is one of the most important components of a Rankine cycle power system. It influences the performance and thereby the economics of the system. Therefore, special care should be taken when selecting the working fluid. In this paper a list of criteria that should fulfill a fluid to be considered as good for a Rankine cycle is given...
Article
Autonomous polygeneration microgrids (APM) are a relatively new approach in covering specific needs like power, potable water and fuel for transportation, in remote areas. This approach has been proved to be technically feasible nowadays and even present itself as an economically viable investment. The initial management system built for this appro...
Conference Paper
Full-text available
This study presents the performance analysis of two twin grid connected PV Systems, installed in two hellenic areas: the Agricultural University of Athens (37 o 59' N, 23 o 42' E) and the Technical University of Crete, Chania (35 o 31' N, 24 o 04' E). Both installations consist of tandem amorphous and microcrystalline silicon thin film (a-Si/μ-Si)...
Article
The present work concerns the simulation of an autonomous, two-stage solar organic Rankine cycle (SORC) for RO desalination. Aiming at improving the efficiency of the single-stage low temperature (operation temperature range in the order of 70–80°C) SORC for RO desalination, a high temperature (operation temperature range in the order of 140°C) sta...
Article
This paper presents the design and testing through simulation of a Fuzzy Logic Energy Management System (FLEMS) for an autonomous polygeneration microgrid. In this microgrid the energy is produced by photovoltaics and a wind turbine and the rest of the components include a battery bank, a Proton Exhange Membrane (PEM) fuel cell, a PEM electrolyzer,...
Article
Full-text available
This study presents the performance analysis of two twin grid connected PV Systems, installed in two hellenic areas: the Agricultural University of Athens (37° 59' N, 23° 42' E) and the Technical University of Crete, Chania (35° 31' N, 24° 04' E). Both installations consist of tandem amorphous and microcrystalline silicon thin film (a- Si/μ-Si ) so...
Article
This paper presents the concept and the design of a hybrid renewable energy polygeneration microgrid along with its technical and economical evaluation. The energy of the sun and the wind is harvested by photovoltaics and a wind turbine. Besides that, the components of the microgrid include a battery bank, a Proton Exchange Membrane (PEM) fuel cell...
Article
An organic Rankine cycle (ORC) machine is similar to a conventional steam cycle energy conversion system, but uses an organic fluid such as refrigerants and hydrocarbons instead of water. In recent years, research was intensified on this device as it is being progressively adopted as premier technology to convert low-temperature heat resources into...
Conference Paper
Full-text available
The performance of PV modules is usually specified under standard test conditions (STC); however the performance of the modules under real field conditions differs from the expectations derived from the results under STC due to variety of continuously changing conditions. Therefore it is important to monitor the behavior of PV modules under real fi...
Article
In concentrating photovoltaic (CPV) systems the incident solar radiation is multiplied by a factor equal to the concentration ratio, with the use of lenses or reflectors. This is implemented, in order to increase the electric power production, since this value has a linear dependence from the incident radiation. Therefore, the specific energy produ...
Article
Full-text available
A comparative experimental investigation was conducted to evaluate the performance and exhaust emissions of an agricultural tractor engine when fueled with sunflower oil, rapeseed oil, and cottonseed oil and their blends with diesel fuel (20/80, 40/60 and 70/30 volumetrically). Tests were also carried out with diesel fuel to be used as a reference...
Article
Full-text available
This paper presents a targeted approach for the estimation of the operational machinery costs on an annual basis in controlled traffic farming (CTF) systems. The approach combines four sub-models based on existing algorithmic approaches, to evaluate the consequences in terms of machinery performance of different driving directions when establishing...
Conference Paper
Full-text available
The Organic Rankine Cycle (ORC) appears progressively as a promising solution to recover waste heat energy from thermal processes for electricity generation. A prototype of small-scale ORC has been built and successfully tested at the University of Liège. It uses R-245fa and R-123 as working fluid, and an oil-free scroll compressor adapted to run i...