PV-FeldLab: On-site performance determinations and ageing analyses of photovoltaic generators
Photovoltaic generators are operated for several decades. The modules are covered by a linear performance guarantee from the manufacturers, who promise 90 percent of the original rated output power after ten years and 80 percent after 20 years. Depending on the system design and module technology, the system voltage of the photovoltaic generator can lead to potential-induced degradation (PID). This power reduction cannot be determined by simple measurements with multimeters during the operation of a PV power plant. For a meaningful and reproducible analysis of the module parameters, a current-voltage curve must be recorded in the laboratory under standard test conditions (1000 W/m², 25 °C, AM1.5). For this purpose, an LED sun simulator is used at the University of Applied Sciences Nordhausen (Fig. 3). Internal damages of modules such as cell cracks and inactive cell areas can only be made visible using special imaging techniques such as infrared thermography (Fig. 1) or electroluminescence (Fig. 2). Carrying out all these measurements in the laboratory requires the disassembly, transport and handling of all individual modules, which results in high costs and requires a lot of time.
The aim of the PV-FeldLab project is to create an overall concept according to which all these measurements can be carried out on large-scale plants directly in the field. The aim is to achieve the accuracy of laboratory measurements. By further developing the approaches for field measurements of individual modules given in IEC 61853, a method for measuring entire strings will be developed. The sebstreferencing algorithm (SRA) co-developed by Coburg University of Applied Sciences will be further developed from its use with individual modules to its use with module strings.
The aging process of various module technologies is very different. At the Nordhausen University of Applied Sciences, the ageing behaviour of different module technologies is analysed with the aid of accelerated ageing tests in the climatic chamber (Fig. 4). The ageing parameters determined under laboratory conditions are converted into an ageing model with the aid of free-field measurement data. The results of the measurement campaign serve on the one hand to predict the service life and on the other hand to train the measurement concept for the recognition of degraded modules. In the course of the project, a large number of module technologies will be used to teach the measurement procedure in order to ensure reliable use of the measurement procedure on as many plant types as possible.
(Workmanship University of Applied Sciences Nordhausen: Amélie Oberdorfer, Lukas Gerstenberg, Sebastian Voswinckel, Viktor Wesselak; Workmanship University of Applied Sciences Coburg: Bernd Hüttl, Samuel Schneider)
We would like to thank the German Federal Ministry of Education and Research (BMBF) for financing the "PV-FeldLab" project as part of the research funding programme for universities of applied sciences under the reference number FKZ 13FH600IB6 (2018-2022).
Zero-emission engine for stationary storage solutions (ZEEPA) - experimental investigations
In Germany, electrolytic production of hydrogen from water and its subsequent reconversion to power is one of the most promising options for the long-term storage of electricity, which will be needed in the medium term. If the occurring oxygen is also used in the reconversion process, there are new design possibilities for the use of hydrogen in combustion engines. In a process developed by the Nordhausen University of Applied Sciences, the classic combustion engine is combined with steam expansion in an expander and combustion takes place in an oxygen/water steam atmosphere. In this way, apart from water vapour, no pollutants are produced and efficiencies and power densities can be achieved that are significantly higher than those of current hydrogen/air engines. The designed concept is characterized by high efficiencies and low-cost plant technology and thus offers an innovative variant of the reconversion of hydrogen.
The core of the project is an engine process that promises higher efficiency than conventional diesel or gasoline-like hydrogen combustion without emitting pollutants. Starting with a modified stationary engine, the process combines the stoichiometric combustion of hydrogen with pure oxygen produced in hydrogen production with a steam power process. The engine operates with a zero-emission process that can be implemented at a lower cost and with comparable electrical efficiency to today's fuel cell systems.
The development status to date is based on thermodynamic comparison processes and zero or one-dimensional models of the cycle. The next necessary development steps are based on the design and prototype phase in engine development and include the complex 3D flow simulation (CFD) and the construction of a test facility to examine the charge stratification and the combustion process.
The objective of the experimental investigations is the verification of the developed method and the precalculated characteristic values as well as the identification of possible limits to the process control. In the project, a test stand is to be set up which allows measurements of the cylinder pressure curve on a simple engine geometry and thus provides conclusions on the quality of the combustion process. In addition to the experiment, complex 3D CFD simulations are also used to design the experiment and transfer the results to other engine geometries and modifications.
The project on which these results are based was supported by the Free State of Thuringia under the number 2017 FGI 0033 and co-financed by the European Union under the European Regional Development Fund (ERDF).
(Editing: Johannes Haller, Thomas Link)
Next Generation[BIOGAS] - a step forward
Comprehensive, region-specific analysis of follow-up concepts for assessing the financing requirements of existing plants worthy of preservation
With the years 2020/21, the first biogas plants will drop out of the 20-years funding period under the German Renewable Energy Sources Act (EEG). From a technical point of view nothing stands in the way of the continued operation of many existing plants. The service life of important components significantly exceeds the EEG runtime with correct operation. However, the end of the first EEG funding period also offers the opportunity to develop and rethink concepts for biogas plants. It is crucial to cover the financing requirements of the plants in the long term and to justify this logically from the effects of bioenergy, insofar as the financing is to come from public funds. Such reasons can lie in the role of these plants for renewable energy production, for systemic efficiency (e.g. flexible operation), for greenhouse gas (GHG) emission reduction, especially in relation to Germany's climate protection goals, for regional nutrient cycles or in their importance as an important pillar in the agricultural sector. In addition, there should be additional financing instruments beyond the EEG 2017, e.g. for the compensation of environmental services in the agricultural sector, and new, cause-related cost allocations.
The aim of the project is therefore to examine innovative concepts, operational adjustments and diversification strategies for the further operation of existing biogas plants in Germany in an integrated manner and to evaluate them (quantitatively). This takes into account e.g. regional technology variants, substrate alternatives or the fulfilment of quality requirements with regard to efficiency, environmental effects and costs. The difference costs for electricity generation from biogas plants is to be evaluated and put in relation to the current conditions of the electricity market and the EEG. The applicability and practical feasibility will be discussed at regional workshops with representatives from the biogas industry and relevant stakeholders such as energy supply companies.
With the help of a region-specific approach, in which three regions (Thuringia, Lower Saxony and Baden-Württemberg) in Germany are examined in detail, the heterogeneous, decentralised structure of the biogas plants is mapped and results are graphically presented using representative plant examples and the transferability to Germany is checked.
Quality criteria are developed for the guarantee and documentation of continued operation “worthy of preservation” as well as standardized comparability and thus as justification for public funding. Building on this, alternative financing instruments and organisational solutions are proposed and examined.
The results are presented and published in the form of recommendations for plant operators and supporting information for the discourse on the design options of the framework conditions.
(Adaptation: Lynn Vincent, Joachim Fischer)
Development of a flow water turbine with optimized blade profiles and performance
The flow water turbine developed as part of this project is designed for a head of water of 1 to 8 m and a volume flow of 0.3 m³/s to 2 m³/s. This puts the turbine in the classic working area of old mill wheels. On the one hand, the design has a high degree of efficiency and, on the other hand, it can still be produced cost-effectively using new production techniques. For this reason, it is possible to upgrade or redevelop orphaned sites of small hydropower plants.
In the project, the in.RET is responsible for the pre-development, simulation and design of the turbine. The design and layout of the machine also took into account the fish-friendly factor in order to simplify water authority approval and possibly omitting a fine screen. The hydraulic design was optimized with CFD simulation calculations, which gives the turbine a comparatively high degree of efficiency.
The overall design has a generator integrated directly into the turbine. The turbine can operate at variable speeds thanks to converter operation of the generator. The inverter has an MPP tracker so that the system automatically adjusts to an optimum operating point.
The project is completed with the construction and operation of a prototype of the plant. Three test sites are planned for this purpose. In Beiseförth (Hesse), a functional model of the turbine is to be installed in September 2017 based on existing water rights. The relevant official approval procedures have been initiated for the Radeburg (Saxony) and Mecklar (Hesse) locations. Project partners are the companies KD Stahl- und Maschinenbau from Breitenworbis and RSV GmbH from Rotenburg/Fulda.
(Editing: Matthias Haenecke, Claudia Langlotz, Holger Langlotz, Thomas Link, Rio M. Rathje)
R&D joint project between companies and research institutions:
Flat-plate glass-only collector - Development of a more cost-effective flat-plate solar collector system based on glass
Within the scope of the research project, a collector with low production costs is to be developed, which consists primarily of glass (see figure below). Due to the simplified design, cost-intensive production steps, such as absorber welding, are not necessary and enable an automated production process. The production costs can thus be reduced by approx. 20% compared to conventional standard flat-plate collectors. Another advantage is the desired overall height of less than 50 mm, which simplifies installation and connection so that further areas of application (especially in façade construction) can be opened up.
Through thermal modeling of the collector, flow simulations, accompanying metrological investigations and fundamental scientific investigations, the defined goals with regard to performance, production costs and stability are to be investigated in depth. In order to successfully establish the collector on the solar thermal market, practical requirements regarding handling, installation and reliability must be taken into account and fulfilled.
(Editing: Michael Dölz, Martin Rhein, Pascal Leibbrandt, Thomas Schabbach)