@inproceedings{Bertram2010,

title = {Condensation Heat Gains on Unglazed Solar Collectors in Heat Pump Systems},

author = {E Bertram and J Glembin and G Rockendorf and J Scheuren},

editor = {ISES},

doi = {10.18086/eurosun.2010.07.02},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {The performance of ground coupled heat pump systems with borehole heat exchangers can be significantly improved by unglazed solar collectors. In this combination, collector operation temperatures below the ambient air level and hence additional condensation heat gains occur. For an investigated and monitored system in Limburg, Germany, the condensation yield was determined to 3.7% or 19 kWh/(a m²). Thereby, condensation shows a significant dependency on the season. During the summer months, only 0.8% of the total collector yield is induced by condensation, while in winter it increases to 13%. The implementation of an established condensation model to the collector model according to EN 12975 is demonstrated. As main result the investigated the heat pump system performance is only marginally improved due to the condensation heat gains.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Steinweg2010,

title = {Development of a Cost Efficient Buried Hot Water Storage – Conception and First Results},

author = {J Steinweg and I Bellin and M Lienhard and G Rockendorf and E Schomburg and L Schäfer and M Stegmann},

editor = {ISES},

doi = {10.18086/eurosun.2010.16.29},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {Ground buried hot water storage tanks overcome the spatial limitations of an indoor installation. Larger storage volumes can be chosen in order to increase the solar fractions of the heating demand. The paper presents the tasks and aims of a research project1 in which a buried storage is developed, consisting of a concrete cistern, a XPS insulation and an inliner foil combining EPDM and aluminium. The storage operates under atmospheric pressure. During the prototypes construction and implementation, first experiences regarding methods of manufacturing and installation efforts have been gained. A large number of sensors has been installed for surveying long-term properties and the thermal performance of the storage. For the 5.5 m³ prototype a heat loss rate of about 5 W/K has been measured, corresponding to a temperature decrease of approximately 1 K/d when cooling down from 85 to 65°C. An important task beside the tank and heat exchanger design is the development of a new insulation material based on enhanced polystyrene foam, which shall have a long term reliability at temperatures up to 95°C.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Föste2010,

title = {Heat Losses of Highly Efficient Flat Plate Collectors with a Selectively Coated Double Glazing},

author = {S Föste and F Limprecht and N Tiedemann and G Rockendorf},

editor = {ISES},

doi = {10.18086/eurosun.2010.09.10},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {The heat losses of a flat plate collector with a selectively coated double glazing depend among other parameters on the height of the two gas-filled gaps. Within the hermetically sealed glazing cavity inert gases instead of air can be used to decrease the convective heat transfer. To identify the impact of the mentioned parameters, heat loss measurements at a prototype collector were carried out. Therefore the gap sizes were varied and as filling gases of the glazing cavities air, argon and krypton were applied. For each filling gas optimum gap sizes are experimentally identified. These results are in accordance to the Nusselt-equation developed by Hollands . Further the impact of different inclination angles on the heat losses of the collector was determined experimentally.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Glembin2010,

title = {Internal Thermal Coupling in Vacuum Tube Collectors with Coaxial Absorber Pipes},

author = {J Glembin and J Tang and G Rockendorf},

editor = {ISES},

doi = {10.18086/eurosun.2010.09.11},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {ISFH investigated the impact of the internal coupling in vacuum tube collectors with coaxial absorber pipes. Measurements show an efficiency reduction of 10% if reducing the flow rate from 78 kg/m2h to 31 kg/m2h for a collector group with 60 parallel coaxial vacuum tubes at one-sided connection. For a more detailed investigation a simulation model of a vacuum tube collector was developed. The simulations show non-linear temperature profiles along the inner and outer tubes with the maximum temperature not at the fluid outlet but inside the outer pipe. This non-linearity increases with decreasing flow rates. Significantly higher temperatures if compared to the standard flow direction are observed if the fluid is directed from the outer to the inner pipe. The model was extended to simulate a complete collector group with 60 vacuum tubes connected in parallel, whereat the tubes are operated with an experimentally determined flow distribution. The simulation results confirm the measured efficiency decrease at low flow rates. It was found, that the main reason for this is the coupling effect in the vacuum tubes, which is more pronounced at unequal flow distribution. Internal coupling in the header increases the efficiency reduction just slightly if not connected one-sided. As a consequence, low flow rates should be avoided for coaxial tube collectors, thus restricting the possible operation conditions.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Buchholz2010,

title = {Investigation of the Reduced Performance of a Collector Array with Direct Flow Vacuum Tubes},

author = {R Buchholz and J Glembin and D Eggert},

editor = {ISES},

doi = {10.18086/eurosun.2010.10.10},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {TU Berlin and ISFH investigated the reduced performance of a collector array with direct flow vacuum tubes and an aperture area of 258 m². A transient simulation of the collector loop has been performed using the TRNSYS software package. The simulation showed that the measured daily energy gain is only 60% of the gain indicated by the simulation. Measurements showed partial stagnation in several collectors of the array where the outlet temperature of single vacuum tubes fluctuates between the collector loop temperature and the boiling temperature of the fluid. The process of partial stagnation was investigated in detail at the ISFH. The results indicate no significant reduction in collector efficiency under partial stagnation. The main cause of partial stagnation is the reduced volume flow, thus indicating hydraulic problems in the investigated collector array. A reduction in the volume flow can reduce the collector efficiency due to an internal thermal coupling in the coaxial absorber pipes. Infrared photography indicated problems with the vacuum of several tubes as well as damage in the pipe insulation. By integrating the detected reduction factors in the simulation model, the measured collector gain shows good accordance to the simulated collector gain. The results point out the importance of a purge system in vacuum tubes as well as the need to improve the hydraulic layout of the whole collector system.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Glembin2010b,

title = {Partial Stagnation in Direct Flow Vacuum Tube Collectors: Conditions for Occurrence, Risks and Consequences},

author = {J Glembin and D Eggert and J Scheuren and G Rockendorf},

editor = {ISES},

doi = {10.18086/eurosun.2010.09.12},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {Partial stagnation means that the heat transfer fluid evaporates inside a solar thermal collector field although the pump is operating and the collector field outlet temperature is significantly below the evaporation temperature. This happens at a pronounced non-uniform temperature distribution in combination with a low mass flow rate and/or a high temperature level. ISFH investigated the conditions for the appearance of partial stagnation at a direct-flow vacuum tube collector group. Experiments were conducted to identify further criteria that promote partial stagnation: a low system pressure, an unequal flow distribution and a high gas content of the fluid. Measurements show no efficiency reduction during partial stagnation at a horizontal collector slope. With several collector groups connected in parallel, partial stagnation of high intensity could pass into full stagnation in some of the collector groups. This would lead to a significant efficiency reduction of the collector field. However, partial stagnation leads to an unstable operation and a high load of the collector fluid and should therefore be avoided in any case. Possible measures are a more equal flow distribution obtained by the collector and collector field design as well as the removal of air and/or solid particles. In addition the system pressure level may be increased or the gas content solved in the fluid may be reduced.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Bertram2010b,

title = {Unglazed Photovoltaic Thermal Collectors in Heat Pump Systems},

author = {E Bertram and M Stegmann and J Scheuren and C Rosinski and K Kundmüller},

editor = {ISES},

doi = {10.18086/eurosun.2010.07.03},

year  = {2010},

date = {2010-10-01},

booktitle = {Conference Proceedings EuroSun 2010},

address = {Graz, Austria},

abstract = {Unglazed Photovoltaic Thermal (PVT) collectors provide very high efficiency for heat and electricity generation at low temperatures. Therefore they are particularly suitable to support the heat source of heat pump systems, where low temperature heat is required. In this combination the PVT collector improves efficiency in two ways- of the heat pump by additional low temperature heat and of the photovoltaic module by lower cell temperatures. An increase of 4% of the annual and up to 9% for the daily photovoltaic electricity production and a high collector yield of 450 kWh/(m² a) was measured at a pilot system between April 2009 and April 2010. As the improvement of the PV and heat pump efficiency depends strongly on the thermal PVT collector performance, efficiency measurements of five different unglazed PVT collectors have been carried out. They showed significant differences, e.g. the conversion factor 0 without electricity production varies from 0.33 to 0.73. Further, a simulation model for unglazed PVT -collectors is presented. It is based on thermal performance parameters of EN 12975 and PV performance data at standard test conditions and it further includes thermal collector capacity and condensation effects.},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Eidelloth2010,

title = {Open Source Graphical User Interface in MATLAB for Two-Dimensional Simulations Solving the Fully Coupled Semiconductor Equations Using COMSOL},

author = {S Eidelloth and U Eitner and S Steingrube and R Brendel},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2DV.1.19},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {2477-2485},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Bock2010d,

title = {N-Type Cz-Silicon Solar Cells with Screen-Printed Alluminum-Alloyed Rear Emitter},

author = {R Bock and R Hesse and J Schmidt and R Brendel and J Maier and B Geyer and J Koopmann and H Kerp},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2DO.2.3},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {1449-1452},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Steingrube2010c,

title = {Reduced Passivation of Silicon Surfaces at Low Injection Densities Caused by H-Induced Defects},

author = {S Steingrube and P P Altermatt and D Zielke and F Werner and J Schmidt and R Brendel},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2CV.2.9},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {1748-1754},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Hinken2010b,

title = {Impact of Lateral Variations on the Solar Cell Efficiency},

author = {D Hinken and K Bothe and R Brendel},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2CO.4.3},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {1367-1372},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Holst2010,

title = {DAIDALOS – A Plugin Based Framework for Extendable Ray Tracing},

author = {H Holst and P P Altermatt and R Brendel},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2CV.3.24},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {2150-2153},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}

@inproceedings{Bothe2010b,

title = {Determining the Bulk Lifetime of Unpassivated Multicrystalline Silicon Wafers},

author = {K Bothe and R Krain and R Brendel and R Falster and R Sinton},

editor = {WIP},

doi = {10.4229/25thEUPVSEC2010-2CV.2.36},

isbn = {3-936338-26-4},

year  = {2010},

date = {2010-09-01},

booktitle = {25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion},

pages = {1828-1833},

address = {Valencia, Spain},

keywords = {},

pubstate = {published},

tppubtype = {inproceedings}

}