DLR has broad experience in the concentration and collection of direct solar radiation by a range of Concentrating Solar Power (CSP) technologies. Commercial Solar Thermal Power Plants (STPP) aimed at the production of electricity appear as a highly viable alternative to fulfil the world’s enormous expectation of clean electrical energy. However, human activity maintains high demand for electricity several hours after sunset; thus CSP plants need to provide such “after-sunset” base load power. High temperature heat storage is therefore, one of the key points for the development of solar power plants.
ThermoChemical Storage (TCS) of solar heat exploits the enthalpy effects of reversible chemical reactions for the storage of solar energy. The operation principle is as follows: the heat produced by the solar receiver during on-sun operation is used to excite an endothermic chemical reaction; if this reaction is completely reversible the thermal energy can be recovered completely by the reverse reaction (taking place during off-sun operation). Among the possible reversible gas-solid chemical reactions, utilization of a pair of reduction-oxidation (redox) reactions of solid oxides of multivalent metals like the exemplary reaction scheme for cobalt oxide below, can be directly coupled to Concentrated Solar Power (CSP) plants employing air as the heat transfer fluid avoiding thus the need for separate heat exchangers. Co3O4 is considered among the most attractive of these systems since its reduction in air under atmospheric pressure (forward reaction of scheme) takes place at about 900°C, a temperature that can be achieved within the new generation of volumetric-receivers-based solar tower power plants.
Co3O4 + ΔH 3CoO +1/2 O2 … ΔH=200 kJ/molreact
The particular thesis topic will be a part of an on-going research Project introducing the concept of employing as the heat storage medium, monolithic reactors/heat exchangers based on porous ceramic structures made entirely or partially from cobalt oxide-based redox oxide materials.
The study involves the design and manufacture of a pilot-scale (1 kW) structured, ceramic-based reactor/heat exchanger with enhanced transport, thermal and heat recovery properties, incorporating a high amount of cobalt oxide per volume. The complete system is going to be coupled to an existing test facility using simulated solar radiation obtained and concentrated by DLR’s solar high flux simulator in Köln. The reactor will be equipped with all peripherals necessary for adjustment and monitoring of the operational parameters as well as a LabView acquisition and control system for relevant data collection (e.g., gas flow, input/output gas stream temperature, etc.). The target of the operational campaigns will be on-site validation of the technology by demonstrating heat storage/release capability during on-sun and off-sun operation respectively within a typical solar tower plant operating temperature range of 900-150oC. Testing steps will include stepwise optimisation of operational behaviour and main process parameters such as long-term stability, total efficiency and temperature level of heat release phase by varying mass flows, temperatures, gas composition and hardware related parameters. The results of the test campaigns will be evaluated to establish the feasibility of the thermal storage process. This evaluation will include thermal balancing, determination of thermal losses and of the efficiency of the reactor/heat exchanger, as well as the structural and physico-chemical stability of the ceramic elements, after extended operation under real operating conditions, using suitable characterization techniques (post-operation characterization by SEM, XRD, mechanical strength tests etc.)
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Disabled applicants with equivalent qualifications will be given preferential treatment.
Duration of contract:
ca. 6 months
Institute of Solar Research
Tel: +49 2203 601-4132
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