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Industrial PERC cell process flows typically apply the polishing of the rear side after texturing as well as the edge isolation after POCl3 diffusion. In this paper, we present a novel single step polishing process which we apply post double sided texturing and diffusion in order to remove the rear emitter and to reduce the rear surface roughness. One challenge is to minimize the etch back of the front side emitter during rear side polishing due to the reactive gas phase of the polishing process. By optimizing the polishing process, we are able to limit the increase of the emitter sheet resistance below 5 Ω/sq. However, the wet cleaning post polishing contributes an additional 20 Ω/sq emitter sheet resistance increase which is subject to further optimization. We compensate the emitter sheet resistance increase due to wet cleaning by applying a 45 Ω/sq POCl3 diffusion instead of a 60 Ω/sq diffusion. The resulting PERC solar cells with polished rear surface post texture and diffusion show conversion efficiencies up to 19.6% which is comparable to the reference PERC cells which apply a rear protection layer instead of a polishing process.

Abstract With a higher share of renewable energies also the control of the grid must be organized by renewable energy generators. Storages are attractive for grid control and especially for primary reserve power. Theoretically, positive and negative frequency deviations should average to zero and charging and discharging of the battery should compensate each other. However, in reality, an offset may appear. Then, the state of charge of the battery quickly exceeds any limits. To avoid this, degrees of freedom are allowed while providing primary reserve power. This publication investigates their effect on the state of charge. It is shown that the compensation of a systematic frequency measurement error by applying a running average correction signal is most effective.

AbstractThe recently started European FP7 Project InSun aims to demonstrate the reliability and efficiency of three different collector technologies suitable for industrial process heat supply in different climatic regions. The technologies demonstrated reach from improved flat-plate collectors for supply temperatures of up to 95°C in moderate northern Europe climate to tracked concentrating collectors (linear Fresnel collectors and parabolic trough collectors) for supply temperatures between 160 and 250°C in hot and dry Mediterranean climate in Italy and Spain. The main problem for a fast market development if this young and innovative technology is that a reliable performance of the production process has still a much higher priority for the industrial companies than energy savings reached. In consequence often only proven and standardized solutions are considered with payback times not longer than 3 to 5 years. Apart from the cost issue which changes with changing energy prices and the industrialization of the production process of the collectors, the reliability of the technology needs to be demonstrated. Here, intelligent control strategies for the integration in different industrial processes and methods for automated performance observations are required. These topics are given a high priority within the InSun project team with ZAFH-NET as coordinating research partner, EURAC as scientific research partner and Soltigua, Solid and Solera as industrial partners. This paper reports on the preliminary design of the three installations in terms of system layout, foreseen operating conditions and the industrial processes involved.

AbstractThe demand for highly efficient photovoltaic modules at low costs leads to new solar cell designs. For enhanced module efficiency the cell efficiency has to be optimized regarding later operation under module conditions. This implies that the interconnected solar cell structure has to be assessed. Commonly the solar cell itself is optimized separately.In this work an easy to implement cell design was investigated where the number of busbars was varied to decrease the total series resistance of the interconnected solar cell. For this study a simulation program based on the two-diode model was applied to determine the optimal efficiency of the device. Furthermore, the simulations revealed that a device with multiple busbars has a high potential in cost savings due to a reduction in metal consumption for the front side metallization. For an optimized cell structure the amount of Ag paste needed for a sufficient front side metallization could be reduced to 7mg Ag paste for a 6 inch solar cell. In the same time the efficiency can be increased. A detailed simulation of a screen printed and stringed rear side of a multi-busbar solar cell revealed the amount of rear side pads necessary for a sufficient interconnection leading to low series resistances.

AbstractWorldwide coal contributes to over 40% of the electricity generation today and its share is expected to increase steadily over the coming decades. The continued dominance of coal in global energy structure and the growing concern of climate change necessitate accelerated development and deployment of new technologies for clean and efficient coal utilization. Coal fired power plants with CO2 capture and sequestration (CCS) are widely expected to be an important part of a sensible future technology portfolio to achieve overall global CO2 reductions required for stabilizing atmospheric CO2 concentration and stopping global warming.Within the last decades the efficiency of coal fired power plants was significantly raised by different technical steps as running the steam generator on higher temperatures and pressures. So an efficiency (based on LHV) of higher than 45% for hard coal and 43% for lignite coal are more or less the technical standard for modern supercritical coal fired power plants. The amine scrubbing carbon capturing technology, which is planed to be added for fossil fuel fired power stations, will raise the self consumption of the plant and so lower the efficiency drastically. To minimize this effect it is necessary not only to find solvents with a small heat duty for the carbon dioxide scrubbing process, but also to optimize the heat re-integration to the water steam cycle and reduce the electrical self consumption of the scrubbing plant.This can be successfully designed with a detailed review of all key components as the turbine, LP–and HP–preheaters, the steam generator, the flue gas cleaning systems including CO2 scrubbing equipment and the cooling system of the plant. By improving the internal heat recovery in the power station the efficiency penalty of carbon capture (including the compression) can be reduced to values of 8 percentage points instead of 12 or more percentage points for systems without heat recovery and turbine modifications. This optimization is shown for different stages of heat reintegration from the CO2-compression unit, CO2 capture unit to the water-steam and flue gas side of the power station. Hardware modifications of components like the steam turbine are as well discussed as the additional components to be inserted in the boiler and water-steam cycle.As a global technology and equipment provider for complete thermal power plants, Hitachi has the knowledge and capability to address the above challenges of CCS.

AbstractFor decreasing thicknesses of wafer based silicon solar cells, photon management structures to maintain high quantum efficiencies will gain importance. Diffractive gratings on the wafer back side can be designed to achieve very high path length enhancements, especially for weakly absorbed infrared radiation. This technologically demanding concept has to be realised using processes with upscaling potential. Therefore, we present a fabrication process for producing photonic structures in silicon based on interference lithography and nanoimprint lithography (NIL).We realised linear as well as crossed gratings of different depths, which were etched into the wafer back side. Polarisation dependent reflection measurements were made to get information about potential absorption enhancement as well as the occurrence of parasitic absorption in the metal reflector. This is conducted for a PECVD silicon oxide buffer layer between grating and reflector as well as a spin coated silicon oxide layer. Besides these optical characterisations, we further investigated the electrical properties of the back surface, where we applied a concept in which electrical and optical properties are decoupled. This is realised by a layer stack on the wafer back side, consisting of a thin Al2O3 passivation and a doped amorphous silicon layer.

Abstract ORC is a mature technology that can be used for Waste Heat Recovery (WHR) of Internal Combustion (IC) Engines. Direct Evaporation of the organic fluid from the hot exhaust is an interesting option compared to the often preferred intermediary thermal oil loop choice due to its thermal efficiency potential and reduction of system footprint and weight. However, concerns due to dynamic variability of the hot source still hinder its consideration. In this paper, a comparison of the dynamic response of ORC evaporators with both indirect and direct evaporation is performed, under fluctuations of an IC engine exhaust according to relevant frequencies and amplitudes of a standard driving cycle. The results show the range of frequencies and amplitudes of hot source fluctuations for which direct evaporation is most feasible and the range for which special consideration must be taken.