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Karytsas C.,Center for Renewable Energy Sources, Greece
Advances in Building Energy Research | Year: 2012

This paper summarizes the current state of the art of geothermal heat pumps as applies to buildings. Geothermal or ground source heat pump (GSHP) systems provide heating, cooling as well as domestic hot water, by the use of the underground or bodies of surface water as heat source or sink. More specifically, a GSHP system comprises a heat pump (usually waterto- water) and a ground source system (ground heat exchanger or groundwater well) in order to provide heating and cooling to the building through a low-temperature heating system and domestic hot water as well. The main concept of a GSHP system is the maximization of the heat pump efficiency i.e. minimization of electricity consumption mostly due to underground temperature which is almost invariant throughout the year. So, it is clear that GSHP systems have contribution to the environmental protection and reduction of greenhouse gas emissions. GSHPs are a mature industry, with a continuous trend of development and due to their increasing energy efficiency due to recent advances of the technology (described in the following chapters) are attractive and are more and more considered as an excellent substitute of conventional heating/cooling sources including air source heat pumps and variable refrigerant volume. Due to these advances in several cases the high efficiency of GSHP compared to the initial capital cost minimizes the need for subsidies. © 2012 Taylor & Francis. Source


Sakellaridis N.G.,Center for Renewable Energy Sources, Greece | Karystianos M.E.,Hellenic Transmission System Operator SA | Vournas C.D.,National Technical University of Athens
International Journal of Electrical Power and Energy Systems | Year: 2011

This paper presents a number of local and one global (homoclinic loop) bifurcation observed in a small power system involving a load tap changer transformer and an induction motor. Besides the well-known generic local bifurcations (saddle-node and generic Hopf), the paper presents examples of higher codimension bifurcations, such as fold with double zero eigenvalues, degenerate Hopf, and swallowtail bifurcation. © 2011 Elsevier Ltd. All rights reserved. Source


Kontogianni A.,University of Western Macedonia | Tourkolias C.,Center for Renewable Energy Sources, Greece | Skourtos M.,Agricultural University of Athens | Damigos D.,National Technical University of Athens
Renewable Energy | Year: 2014

The evidence is compelling that extended use and production of energy are globally responsible for the serious deterioration of physical environment and climate change. The further penetration of renewable energy sources (RES) emerges as a crucial factor contributing to the mitigation of global warming. Within this framework wind energy is expected to have a leading role for Greece's compliance with the EU environmental targets of 2020. However, the installation of wind parks in specific regions with high wind potential is seriously constrained by the reaction of local communities. Using a survey the present research dissects public acceptance for existing and proposed wind farms in the region of Southern Evia, Greece. Results indicate an overall support for wind energy and confirm the growing inconvenience with NIMBYism, especially in areas with existing wind parks in operation, as a theoretical framework explaining resistance to planned wind energy investments. By contrasting self-reported ex ante- and ex post-perceptions of impacts and benefits we highlight the role of experience in community acceptance of wind energy installations. Our statistical models prescribe the profile of those most probably in favour of existing installations, new installations in other parts of Evia or new installations elsewhere in Greece. Finally, we introduce the 'Not-In-My-Front-Yard' (NIMFY) syndrome suggesting that the impact of visibility on public acceptance is far from being a simple concept as it is linked to both a physical landscape context and socio-economic parameters. © 2013 Elsevier Ltd. Source


Parisio A.,Linnaeus Center | Rikos E.,Center for Renewable Energy Sources, Greece | Glielmo L.,Universitadegli Studi Del Sannio
IEEE Transactions on Control Systems Technology | Year: 2014

Microgrids are subsystems of the distribution grid, which comprises generation capacities, storage devices, and controllable loads, operating as a single controllable system either connected or isolated from the utility grid. In this paper, we present a study on applying a model predictive control approach to the problem of efficiently optimizing microgrid operations while satisfying a time-varying request and operation constraints. The overall problem is formulated using mixed-integer linear programming (MILP), which can be solved in an efficient way by using commercial solvers without resorting to complex heuristics or decompositions techniques. Then, the MILP formulation leads to significant improvements in solution quality and computational burden. A case study of a microgrid is employed to assess the performance of the online optimization-based control strategy and the simulation results are discussed. The method is applied to an experimental microgrid located in Athens, Greece. The experimental results show the feasibility and the effectiveness of the proposed approach. © 1993-2012 IEEE. Source


Bottger D.,University of Leipzig | Gotz M.,University of Leipzig | Theofilidi M.,Center for Renewable Energy Sources, Greece | Bruckner T.,University of Leipzig
Energy | Year: 2015

Control power for the reliability of electricity supply is currently mainly provided by conventional power plants. In the situation of low residual power demand, the provision of negative control power may lead to must-run generation through base load power plants. Due to low wholesale electricity prices during low residual power demand, the must-run power plants that provide control power are confronted with high opportunity costs. Alternatively to base load power plants, electric boilers in district heating grids could provide relatively cheap negative secondary control power. The effects of the availability of electric boilers in the German control power market on overall system-wide costs and CO2-emissions of the power supply are assessed using a model-based analysis for 2012 and 2025. Power-to-heat plants are able to dissolve the conflict of must-run generation of base load power plants for control power provision. Therefore, they can enhance the integration of fluctuating RES (renewable energy sources), which in turn can reduce overall CO2-emissions of the power supply. The growing share of RES in Germany as well as cost reductions of electric boilers that can be expected in the next years could lead to a situation where the overall cost savings exceed the necessary investment costs. © 2015 Elsevier Ltd. Source

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