Two new absorber coatings for mid-temperature operation (300–350 1C) in collectors for solar thermal electricity plants are presented in this study. The absorbers consist of two cermet layers of either W–SiO2 or Nb–TiO2, deposited on a molybdenum infrared reflector and coated with an antireflection layer of silicon oxide. The optimization of the optical performance was made in two steps. First, the layer structure was optimized in model calculations. The optical constants used in this modelling were derived directly from sputtered films of the cermet constituents using reflectance and transmittance measure- ments. The absorber coatings were then sputter-deposited using parameters from the modelling. The results show good agreement between modelled and sputtered optical performance evaluated as solar absorptance and thermal emittance at 350 1C. The optimal values reached for W–SiO2 was 0.91 in combination with 0.08 and 0.93 in combination with 0.09 for Nb–TiO2. The materials characterization from XRD, AES and TEM shows that the composite coatings contain nano-metal inclusions, meaning that they are cermet coatings. Scratch tests show that the coatings adhere well to the substrate of stainless steel. Temperature testing at 350 1C in vacuum for up to 1500 h shows that both coatings are stable under such conditions. Only a slight change occurs during the first 72 h that decreases the emittance but does not change the solar absorptance. ERDA confirms that there is no detectable level of ion migration between layers, only a small decrease in hydrogen content was observed, which indicates outgassing.Digespo projec

Four grades of sinter hardening materials have been compared, using industrial equipment. Three powder types were completely prealloyed; the last one was a hybrid, combining prealloying and diffusion bonding. Different amounts of Cu have been added by mixing. The lubricated mixes, containing 0.6% graphite, have been compacted at different pressures, to form gears at green densities ≥7.0 g cm⁻³ ; the compacts have been sintered at 1120°C, under endogas from methane and fast cooled (at least 7 K s⁻¹ within the range 850–400°C). The final step has been stress relieving, at 180°C, for 1 h. Material properties have been investigated, focusing on porosity, pore shape, hardness, microhardness, microstructure, local chemical composition and mechanical properties. For comparison, other gears, compacted in the same tool and at the same density level, but manufactured according to a more conventional cycle, i.e. starting from less alloyed powders and adding carbonitriding, quenching and stress relieving, have been used. The analysis of the different experimental results enabled the authors to find out and outline some criteria suitable for selecting sinter hardening materials and for choosing more reliable manufacturing conditions to fulfill specific application requirements.

The present work describes the realization of a modular 1-3 kWe, 3-9 kWth micro Combined Heat and Power (m-CHP) system based on innovative Concentrated Solar Power (CSP) and Stirling engine technology. The cogeneration of energy at distributed level is one of leading argument in large part of energy policies related to renewable energy resources and systems. This CSP m-CHP will provide electrical power, heating and cooling for single and multiple domestic dwellings and other small buildings.The developed system integrates small-scale concentrator optics with moving and tracking components, solar absorbers in the form of evacuated tube collectors, a heat transfer fluid, a Stirling engine with generator, and heating and/or cooling systems; it incorporates them into buildings in an architecturally acceptable manner, with low visual impact. Some good results have already been achieved, while developments on several technology subcomponents will be finalized through first part of 2013.Two Cer. Met. have been modelled, realized and tested. The up scaled receiver, in form of Cer. Met. coating based on TiO2 – Nb, has been confirmed an absorptance of 0.94 and emittance of 0.1 (@350̊C). A second Cer. Met. coating based on SiO2 – W has demonstrated an absorptance of 0.93 and emittance of 0.09 (@350̊C). A full-evacuated solar tube has been designed and realized, with absorber of 12mm in diameter and length in 2 meters.The system is provided of a concentration ratio 12:1, and a single module is 200cm long, 40cm wide and 20-25cm high. Two or more modules can be combined. The evacuated solar tube, located on the focus, has the selective absorber on a tube of 12mm in diameter. A very thin glass mirror has been developed (< 1mm). The overall mirror reflectivity has been measured, the verified value is 0,954.Research has proposed a high energy density, double acting Stirling engine, provided of innovative heat exchangers realized through Selective Laser Melting process. The engine is a low speed (250 RPM), high pressure (130 Bars) and compact solution able to be run at 300̊C and generate 3,5kW nominal power.The solar technology has actually entered the proof-of-concept stage. A solar plant has been installed in Malta, by Arrow Pharm company, supplying the industrial process of generated steam at 180̊C and 3.5 absolute pressure. The solar collector's efficiency is close to 47% in presence of 900W/m2 of direct solar radiation.During 2013, solar evacuated tubes with innovative Cer. Met. coating, together with new thin glass mirrors will upgrade the demonstration site, together with a new and innovative low temperature difference and high energy density Stirling. By end-2013, the system will be demonstrated, with the overall objective to achieve a minimum of 65% in solar collectors’ efficiency at 300̊C, and 12 – 15% of overall electrical efficiency by the Stirling cycle.The actual work is part of a FP7 European Funded project, DIGESPO [1]