@article{RauAlexopoulosBreitbachetal.2014,
  author    = {Rau, Christoph and Alexopoulos, Spiros and Breitbach, Gerd and Hoffschmidt, Bernhard and Latzke, Markus and Sattler, Johannes, Christoph},
  title     = {Transient simulation of a solar-hybrid tower power plant with open volumetric receiver at the location Barstow},
  series = {Energy procedia : proceedings of the SolarPACES 2013 International Conference},
  volume    = {49},
  journal   = {Energy procedia : proceedings of the SolarPACES 2013 International Conference},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1876-6102},
  doi       = {10.1016/j.egypro.2014.03.157},
  pages     = {1481 -- 1490},
  year      = {2014},
  abstract  = {In this work the transient simulations of four hybrid solar tower power plant concepts with open-volumetric receiver technology for a location in Barstow-Daggett, USA, are presented. The open-volumetric receiver uses ambient air as heat transfer fluid and the hybridization is realized with a gas turbine. The Rankine cycle is heated by solar-heated air and/or by the gas turbine's flue gases. The plant can be operated in solar-only, hybrid parallel or combined cycle-only mode as well as in any intermediate load levels where the solar portion can vary between 0 to 100\%. The simulated plant is based on the configuration of a solar-hybrid power tower project, which is in planning for a site in Northern Algeria. The meteorological data for Barstow-Daggett was taken from the software meteonorm. The solar power tower simulation tool has been developed in the simulation environment MATLAB/Simulink and is validated.},
  language  = {en}
}
@article{PuppeGiulianoFrantzetal.2018,
  author    = {Puppe, Michael and Giuliano, Stefano and Frantz, Cathy and Uhlig, Ralf and Schumacher, Ralph and Ibraheem, Wagdi and Schmalz, Stefan and Waldmann, Barbara and Guder, Christoph and Peter, Dennis and Schwager, Christian and Teixeira Boura, Cristiano Jos{\´e} and Alexopoulos, Spiros and Spiegel, Michael and Wortmann, J{\"u}rgen and Hinrichs, Matthias and Engelhard, Manfred and Aust, Michael},
  title     = {Techno-economic optimization of molten salt solar tower plants},
  series = {AIP Conference Proceedings art.no. 040033},
  volume    = {2033},
  journal   = {AIP Conference Proceedings art.no. 040033},
  number    = {Issue 1},
  publisher = {AIP Publishing},
  address   = {Melville, NY},
  doi       = {10.1063/1.5067069},
  year      = {2018},
  abstract  = {In this paper the results of a techno-economic analysis of improved and optimized molten salt solar tower plants (MSSTP plants) are presented. The potential improvements that were analyzed include different receiver designs, different designs of the HTF-system and plant control, increased molten salt temperatures (up to 640°C) and multi-tower systems. Detailed technological and economic models of the solar field, solar receiver and high temperature fluid system (HTF-system) were developed and used to find potential improvements compared to a reference plant based on Solar Two technology and up-to-date cost estimations. The annual yield model calculates the annual outputs and the LCOE of all variants. An improved external tubular receiver and improved HTF-system achieves a significant decrease of LCOE compared to the reference. This is caused by lower receiver cost as well as improvements of the HTF-system and plant operation strategy, significantly reducing the plant own consumption. A novel star receiver shows potential for further cost decrease. The cavity receiver concepts result in higher LCOE due to their high investment cost, despite achieving higher efficiencies. Increased molten salt temperatures seem possible with an adapted, closed loop HTF-system and achieve comparable results to the original improved system (with 565°C) under the given boundary conditions. In this analysis all multi tower systems show lower economic viability compared to single tower systems, caused by high additional cost for piping connections and higher cost of the receivers. REFERENCES},
  language  = {en}
}
@article{Alexopoulos2015,
  author    = {Alexopoulos, Spiros},
  title     = {Simulation model for the transient process behaviour of solar aluminium recycling in a rotary kiln},
  series = {Applied Thermal Engineering},
  volume    = {78},
  journal   = {Applied Thermal Engineering},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1359-4311},
  doi       = {10.1016/j.applthermaleng.2015.01.007},
  pages     = {387 -- 396},
  year      = {2015},
  language  = {en}
}
@article{KluczkaEcksteinAlexopoulosetal.2014,
  author    = {Kluczka, Sven and Eckstein, Julian and Alexopoulos, Spiros and Vaeßen, Christiane and Roeb, Martin},
  title     = {Process simulation for solar steam and dry reforming},
  series = {Energy procedia : Proceedings of the SolarPACES 2013 International Conference},
  volume    = {49},
  journal   = {Energy procedia : Proceedings of the SolarPACES 2013 International Conference},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1876-6102 (E-Journal)},
  doi       = {10.1016/j.egypro.2014.03.092},
  pages     = {850 -- 859},
  year      = {2014},
  abstract  = {In co-operation with the German Aerospace Center, the Solar-Institut J{\"u}lich has been analyzing the different technologies that are available for methanol production from CO2 using solar energy. The aim of the project is to extract CO2 from industrial exhaust gases or directly from the atmosphere to recycle it by use of solar energy. Part of the study was the modeling and simulating of a methane reformer for the production of synthesis gas, which can be operated by solar or hybrid heat sources. The reformer has been simplified in such a way that the model is accurate and enables fast calculations. The developed pseudo-homogeneous one- dimensional model can be regarded as a kind of counter-current heat exchanger and is able to incorporate a steam reforming reaction as well as a dry reforming reaction.},
  language  = {en}
}
@article{GoettscheAlexopoulosDuemmleretal.2019,
  author    = {G{\"o}ttsche, Joachim and Alexopoulos, Spiros and D{\"u}mmler, Andreas and Maddineni, S. K.},
  title     = {Multi-Mirror Array Calculations With Optical Error},
  pages     = {1 -- 6},
  year      = {2019},
  abstract  = {The optical performance of a 2-axis solar concentrator was simulated with the COMSOL Multiphysics® software. The concentrator consists of a mirror array, which was created using the application builder. The mirror facets are preconfigured to form a focal point. During tracking all mirrors are moved simultaneously in a coupled mode by 2 motors in two axes, in order to keep the system in focus with the moving sun. Optical errors on each reflecting surface were implemented in combination with the solar angular cone of ± 4.65 mrad. As a result, the intercept factor of solar radiation that is available to the receiver was calculated as a function of the transversal and longitudinal angles of incidence. In addition, the intensity distribution on the receiver plane was calculated as a function of the incidence angles.},
  language  = {en}
}
@article{KronhardtAlexopoulosReisseletal.2014,
  author    = {Kronhardt, Valentina and Alexopoulos, Spiros and Reißel, Martin and Sattler, Johannes, Christoph and Hoffschmidt, Bernhard and H{\"a}nel, Matthias and Doerbeck, Till},
  title     = {High-temperature thermal storage system for solar tower power plants with open-volumetric air receiver simulation and energy balancing of a discretized model},
  series = {Energy procedia},
  volume    = {49},
  journal   = {Energy procedia},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1876-6102 (E-Journal) ; 1876-6102 (Print)},
  doi       = {10.1016/j.egypro.2014.03.094},
  pages     = {870 -- 877},
  year      = {2014},
  abstract  = {This paper describes the modeling of a high-temperature storage system for an existing solar tower power plant with open volumetric receiver technology, which uses air as heat transfer medium (HTF). The storage system model has been developed in the simulation environment Matlab/Simulink®. The storage type under investigation is a packed bed thermal energy storage system which has the characteristics of a regenerator. Thermal energy can be stored and discharged as required via the HTF air. The air mass flow distribution is controlled by valves, and the mass flow by two blowers. The thermal storage operation strategy has a direct and significant impact on the energetic and economic efficiency of the solar tower power plants.},
  language  = {en}
}
@article{GoettscheHoffschmidtAlexopoulosetal.2008,
  author    = {G{\"o}ttsche, Joachim and Hoffschmidt, Bernhard and Alexopoulos, Spiros and Funke, J. and Schwarzb{\"o}zl, P.},
  title     = {First Simulation Results for the Hybridization of Small Solar Power Tower Plants},
  series = {EuroSun 2008 : 1st International Conference on Solar Heating, Cooling and Buildings, 2008-10-07 - 2008-10-10, Lissabon (Portugal). Vol. 1},
  journal   = {EuroSun 2008 : 1st International Conference on Solar Heating, Cooling and Buildings, 2008-10-07 - 2008-10-10, Lissabon (Portugal). Vol. 1},
  publisher = {Sociedade Portuguesa De Energia Solar (SPES)},
  address   = {Lisbon},
  isbn      = {978-1-61782-228-5},
  pages     = {1299 -- 1306},
  year      = {2008},
  language  = {en}
}
@article{Alexopoulos2012,
  author    = {Alexopoulos, Spiros},
  title     = {Biogas systems: basics, biogas multifunction, principle of fermentation and hybrid application with a solar tower for the treatment of waste animal manure},
  series = {Journal of Engineering Science and Technology Review},
  volume    = {5},
  journal   = {Journal of Engineering Science and Technology Review},
  number    = {4},
  issn      = {1791-2377},
  pages     = {48 -- 55},
  year      = {2012},
  abstract  = {Two of the main environmental problems of today's society are the continuously increasing production of organic wastes as well as the increase of carbon dioxide in the atmosphere and the related green house effect. A way to solve these problems is the production of biogas. Biogas is a combustible gas consisting of methane, carbon dioxide and small amounts of other gases and trace elements. Production of biogas through anaerobic digestion of animal manure and slurries as well as of a wide range of digestible organic wastes and agricultural residues, converts these substrates into electricity and heat and offers a natural fertiliser for agriculture. The microbiological process of decomposition of organic matter, in the absence of oxygen takes place in reactors, called digesters. Biogas can be used as a fuel in a gas turbine or burner and can be used in a hybrid solar tower system offering a solution for waste treatment of agricultural and animal residues. A solar tower system consists of a heliostat field, which concentrates direct solar irradiation on an open volumetric central receiver. The receiver heats up ambient air to temperatures of around 700°C. The hot air's heat energy is transferred to a steam Rankine cycle in a heat recovery steam generator (HRSG). The steam drives a steam turbine, which in turn drives a generator for producing electricity. In order to increase the operational hours of a solar tower power plant, a heat storage system and/ or hybridization may be considered. The advantage of solar-fossil hybrid power plants, compared to solar-only systems, lies in low additional investment costs due to an adaptable solar share and reduced technical and economical risks. On sunny days the hybrid system operates in a solar-only mode with the central receiver and on cloudy days and at night with the gas turbine only. As an alternative to methane gas, environmentally neutral biogas can be used for operating the gas turbine. Hence, the hybrid system is operated to 100\% from renewable energy sources},
  language  = {en}
}
@article{AlexopoulosHoffschmidt2017,
  author    = {Alexopoulos, Spiros and Hoffschmidt, Bernhard},
  title     = {Advances in solar tower technology},
  series = {Wiley interdisciplinary reviews : Energy and Environment : WIREs},
  volume    = {6},
  journal   = {Wiley interdisciplinary reviews : Energy and Environment : WIREs},
  number    = {1},
  publisher = {Wiley},
  address   = {Weinheim},
  issn      = {2041-840X},
  doi       = {10.1002/wene.217},
  pages     = {1 -- 19},
  year      = {2017},
  language  = {en}
}