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AbstractThis paper presents a theoretical and experimental analysis of Maximum Power Point Tracking (MPPT) method for photovoltaic (PV) systems based on Genetic Algorithms (GAs). The proposed algorithm is based on Genetic Algorithms (GAs) and it can estimate the current (Imp) and voltage (Vmp) at maximum power point by measuring the open circuit voltage (Voc) and the short circuit current (Isc) without knowing the irradiance and the cell temperature. The principle of GAs is searching for the maximum of fitness function and not for the minimum of power derivation; this gives more stability and minimize oscillation of output power around the maximum power point (MPP).We expose the method with a few tests; then a comparison with the famous Perturb and Observe (P&O) and Incremental Conductance (Inc-Cond) is given. We tested stability (power oscillation) with real panels. To compare response time (rapidity) we used a PV emulator (realized by Kadri et al.), so we can inject the same irradiance profile and see output PV power evolution. The response time of P&O and Inc-Cond, and the PV power oscillation varies with the duty cycle increment step; with a small step, we get less power oscillation but this needs an important time response, we can improve system rapidity with a bigger duty increment step but important power oscillation will result. With GAs based MPPT we can get more stability with rapid response time. The results obtained show better stability and less oscillation around the MPP with the new method.

AbstractLow Voltage Ride-Through (LVRT) is one of the most dominant grid connection requirements to be met by Wind Energy Conversion Systems (WECS). In presence of grid voltage dips, a mismatch is produced between the generated active power and the active power delivered to the grid. Low voltage ride through requirement demands management of this mismatch, which is a challenge for the WECS. In this paper, LVRT requirements provided by Wind Grid Codes have been reviewed. This paper discusses the standards for interconnection of wind generators to local grid during healthy and fault conditions. As per LVRT requirement, during dip occurrence, the wind power generation plant must remain connected to the grid and in addition, it has to deliver reactive power into the grid to aid the utility to hold the grid voltage. Voltage sag proves to be the most prominent power quality issue and the effect of voltage sag on different wind generator topologies has been investigated. Several methods for LVRT fulfillment have been explored and the LVRT scheme has been validated based on MATLAB-SIMULINK simulation.

AbstractMinority carrier lifetime measurements are a major characterization technique regarding the material quality of semiconductors. In particular, a large variety of electrically active defects can be detected at room temperature even if present in low concentrations down to 1010cm-3 only. Transient and (quasi) steady-state methods as well as combinations of both have been established. However, in either case, the measurable lifetime is influenced not only by the bulk lifetime itself but by a number of additional sample properties such as surface recombination, sample thickness, and wavelength of the carrier-generating light.An analytical model is investigated that relates the measurable lifetime to the bulk lifetime for samples of arbitrary thickness and surface quality when measured under steady-state conditions. It thus provides a generalization for the frequently used limiting expressions for thin Si-wafers and thick Si-blocks. In particular it allows the interpretation of data obtained for samples of intermediate thickness. Furthermore, it is shown under which conditions the surface properties can influence the lifetime measurements even for thick blocks. Finally, an approach is proposed that allows the simultaneous extraction of both bulk lifetime and surface recombination velocity. It is argued that reliable measurements of bulk properties are possible only for samples being thicker than some critical thickness while surface properties are best determined on samples thinner than this critical thickness. A quantitative estimate for this critical thickness is given. Experimental results are shown that demonstrate the applicability of the model.

AbstractThe International Energy Agency Energy Technologies Perspectives (ETP) model is used for the assessment of the prospects for carbon abatement options, including carbon capture and storage, up to 2050. Three main scenarios are considered: a baseline scenario with current energy policies, an accelerated technology scenario (ACT) with an associated CO2 reduction incentive development, and a scenario in which global greenhouse gas emissions are reduced by 50% compared to current levels in 2050 (BLUE). The analysis suggests that CCS can account for up to 19% of all CO2 reduction in 2050, which would equal 10.4 Gt CO2 capture and storage. The power sector would account for 54% of all CCS, the remainder is in manufacturing industry and the fuel transformation sector.CCS is a critical option. Without CCS, the cost to meet the same target would rise by 71%. The potential rate at which CCS can be introduced exceeds the rate at which regular capital stock is typically replaced, if plants are retrofitted or closed down before the end of their technical life span. Retrofitting of coal plants with CCS plays a very significant role in the ACT Map scenario. But at the price of USD 200/t CO2 envisaged in the BLUE scenario, there is sufficient economic incentive to accelerate the replacement of inefficient power plants with new plants equipped with CCS before the existing plants reach the end of their life span. In the BLUE scenario, 350 GW of coal-fired power-plant capacity is closed down early. The remaining 700 GW consists of 80% new capacity that is equipped with CCS, and 20% retrofits with CCS.Following IEA recommendations, the G8 countries have announced that they will commit 20 demonstration plants for CCS by 2010. Also the G8, China India and Korea have asked the IEA to continue its work on roadmaps and transition paths for CCS in power generation and in industry, in cooperation with other bodies such as CSLF. This work has started and final results will be reported in 2010.

AbstractThis work presents a novel insight to the aspects of silicon surface passivation and the influence of thin intermediate layers generated by chemically grown silicon oxides. Strong light induced effects on passivation properties are investigated. After exposure to light (0.25 suns) for about 60 s, samples based on a PECVD layer system consisting of SiNx and SiO2 deposited on crystalline silicon with native silicon oxides show an improvement of more than 100% in minority carrier lifetime. These improvements are stable over months and lead to effective surface recombination velocities as low as 10cm/s on chemically polished p-type FZ wafers. With the use of different light sources, corona charging and annealing experiments the effect is investigated in detail. Finally, the effect is proposed to be a photo induced curing process of defects in the Si/SiO2 interface with the incorporation of hydrogen.

AbstractAn entirely solar based supply of heat for energy efficient buildings is the motivation for the activities within the research project SolSpaces. A solar heating system, including a sorption store for seasonal energy storage, has been developed to approach this objective. Sorption processes are well suited for long term energy storage, due to the quasi loss free storage of energy and the high energy storage density, compared to water stores. However, large sorption stores go along with some kind of challenges concerning the efficient supply of the stored heat. A new sorption store, subdivided into several segments, has been developed to meet the requirements for an efficient heat supply despite the relatively large size of the store. The segmentation leads to an improved operation behaviour. The segmented sorption store has been built up in full-scale in a research building for testing and demonstration. Experimental investigations are carried out to analyse the achievable temperature lift and charging and discharging power and to demonstrate the thermal performance of the store. Key parameters, such as energy storage density, will be determined. In this paper, the solar heating concept will be presented, focussing on the segmented sorption store. The design of the sorption store will be explained, experimental results and the operation behaviour will be shown and the performance will be discussed.

AbstractWe present a detailed study about the influence of post-deposition temperature treatment on PECVD Al2O3 passivation layers. Fourier transform infrared spectroscopy (FTIR) and quasi-steady-state photoconductance (QSSPC) were applied for characterization. We observed several indications of structural changes of the Al2O3 layer with annealing duration, temperature and layer thickness. A shift and an increase of the Si-O vibrational mode (1100- 980cm-1) in the FTIR measured with changing temperature and layer thickness is presented. Structural changes of the Al2O3 layer with annealing duration, temperature, and layer thickness, caused by changes in the oxygen concentration within the SiOx layer are observed for the different FTIR spectra. We also detected a water band at 1650-1630cm-1 and other OH components around 3200cm-1-400cm-1 depending on annealing temperature and time. For a temperature of 820°C, a dramatic change of the Al2O3 peak (650-700cm-1) is observed. This is probably due to the crystallization of the film.