Kinetics of light-induced degradation in compensated boron-doped silicon investigated using photoluminescence and numerical simulation

We use photoluminescence to observe light-induced degradation in silicon in real time. Numerical simulations are used to match our results and lifetime decay data from the literature with theoretical models for the generation of the light-induced boron–oxygen defects. It is found that the existing model of the slowly generated defect SRC, where its saturated concentration is a function of the majority carrier concentration, does not explain certain results in both p- and n-type samples. A new model is proposed in which the saturated SRC concentration is controlled by the total hole concentration under illumination.     

Upper bounds for solar thermophotovoltaic efficiency

The main components of thermophotovoltaic (TPV) devices are the primary lens (or mirror), the absorber, the PV cell, and a photon recuperator system. A theory integrating all these components is used in this paper to analyse a particular type of TPV device (plane disk absorber and PV cell). The TPV efficiency is maximized by using three optimization parameters, namely absorber, PV cell temperatures, and cell voltage. Almost ideal operation conditions are envisaged and upper bounds are obtained for the TPV efficiency. They are strongly dependent on PV cell bandgap and radiation concentration. Preliminary results suggest the existence of an optimum solar radiation concentration ratio. The improvement in thermal design quality allows the usage of PV cells based on wide bandgap semiconductors.     

Means of enhancing and promoting the use of solar energy

The development of renewable technologies in the last decade has been exceptional. In photovoltaic (PV) for example, efforts were not only limited to merely improving their efficiency but also to the reduction of the cost of cells and modules via volume production for commercial markets. There are many national schemes promoting the use of PV technology and regional targets for a share of renewable energy production. This paper attempts to relay to the reader a journey, based on experience, approaches for enhancing the prospect of utilising solar energy within the society we live in. The issue of expansion or enhancing the utilisation of solar energy can be undertaken by individuals, groups, institutions and governments. The aim of this paper is to provide some examples, which could serve as a framework in which action could be taken to promote solar technology.     

The interplay of electronic structure,molecular orientation and charge transport in organic semiconductors: Poly(thiophene) and poly(bithiophene)

Ultrathin films of poly(thiophene) (PT) and poly(bithiophene) (PBT) were prepared by electrochemical route using ionic liquid (BFEE) as medium and electrolyte. Distinct morphologies and electrical properties were observed in these materials. To evaluate its response in photovoltaics, these films were used as active layer in bilayer geometry solar cells with the electron acceptor molecule C₆₀. The best performance was observed for PT films. In order to probe the differences in molecular dynamics and structural order, ultrafast electron dynamics in the low-femtosecond regime was evaluated by resonant Auger spectroscopy using the core–hole clock method at the sulfur K absorption edge. Electron delocalization times for the different polymeric films were derived as a function of the excitation energy. Photoabsorption measurements were conducted and molecular orientation derived. These results corroborated with the morphology found for these films and thus the performance of PT and PBT in the devices, and with the proposed conduction mechanism.     

Preparation of dye sensitized titanium oxide nanoparticles for solar cell applications

A new method for synthesis of titanium dioxide (TiO₂)-dye nanoparticles is reported. TiO₂ nanocrystals were obtained at 150 and 200 °C by using chemically bonded TiO₂-sensitizer dye as a precursor. Titanium tetraisopropoxide was first modified with a dye molecule and then precipitated by dropping into acidic water. A strongly colored precipitate was obtained. Hydrothermal growth of a colloidal solution was carried out in a Teflon-lined stainless steel autoclave. Dye sensitized solar cell efficiencies obtained were comparable and fill factor values were close to the analogous cells prepared by the use of conventional TiO₂ paste techniques. This method allows the use of different substrates together with nanocrystalline TiO₂ for many technological applications.     

Performance assessment of solar-powered high pressure proton exchange membrane electrolyzer: A case study for Erzincan

In this study, a performance assessment of a solar-powered high-pressure proton exchange membrane (PEM) electrolyzer for hydrogen production is conducted. The feasibility analysis of photovoltaic systems equipped with a high pressure PEM electrolyzer is presented for a university campus-scale community in Erzincan- Turkey. Variable solar irradiance data sets are utilized to assess the performance of the proposed system. A parametric study is conducted in order to evaluate the influence of some design parameters as well as operating conditions on the efficiency of the system. Efficiency of the overall system in the case of relevant inverter sizing is in the range of 11–12%. An ascent of the number of stacks leads to an increase in production rate which is almost linear by photovoltaic (PV) array size. The results shows that in order to have a higher efficiency, the inverter size should be higher than 0.75% of maximum excess power. The proposed system investigated in this study shows great promise of opening up opportunity to develop the high pressure PEM electrolyzer.     

Photovoltaic performance of Organic Photovoltaics for indoor energy harvester

Wireless sensor network becomes widespread into home and offices to keep them comfort and save the energy. The battery-less wireless sensor nodes need the high performance indoor solar cells for stable and sustainable operation. Organic Photovoltaics (OPV) has great indoor photovoltaic performance because ultra-thin organic layer has strong absorption against the UV–visible spectrum that is good spectral matching with indoor lightings. In this study, OPV module has 8 cells in series and same size as the conventional amorphous silicon solar cells (a-Si) for indoor light harvesting. OPV and a-Si are measured their photovoltaic performance under the fluorescent light and demonstrated for energy harvester of wireless sensor network. The output power of OPV and a-Si is 43.4 μW cm⁻² and 28.5 μW cm⁻² at fluorescent light 1000lux respectively. The data transmission rate of the wireless sensor node driven by OPV is 30–40% improved under the dim light condition compared to a-Si.     

A review of the potential benefits and risks of photovoltaic hybrid mini-grid systems

Photovoltaic hybrid mini-grid systems (PVHMS) are expected to play a major role in facilitating rural electrification in the developing world, however these systems still face significant barriers to adoption. The technology occupies a middle ground of electrification options – between traditional network extension and individual home systems, possessing elements of each yet also their own distinctive characteristics. Given this, and their relatively limited application to date, such systems are the focus of a growing body of literature. This work has highlighted a range of potential benefits and risks associated with the technology. However, there still hasn't been a comprehensive review of these documented benefits and risks; an understanding of which is crucial for informed project investment and implementation decision making. This paper presents a preliminary review of the existing literature to identify claimed and demonstrated benefits and risks. The most commonly identified benefits are those that are easy to measure: reduced cost and provision of improved electrical services. Other benefits such as the social or environmental benefits are less commonly demonstrated, but are frequently claimed. The major risks identified included incorrect system sizing due to load uncertainty, challenges related to community integration, equipment compatibility issues, inappropriate business models and risks associated with geographical isolation. For all of these types of risks, associated mitigation strategies were also identified in the literature. Further research including industry surveys and additional case studies will be required to validate what has been observed in the literature to date, and identify progress as the technology matures, costs fall and stakeholders learn from these previous experiences.     

Applying the kriging method to predicting irradiance variability at a potential PV power plant

One-second irradiance data from forty-five sensors spaced over a one-mile square section of land were analyzed to characterize the short-term (1-s to 1-min) variability of the solar resource in Northern Arizona. The geostatistical interpolation model known as kriging was applied to our data set to better understand the method's strengths and weaknesses in accurately predicting the variations in the irradiance over this relatively small section of land. Of particular interest was to investigate the ability of the kriging method to show the variation in solar irradiance over the section of land as compared to that measured by the sensors. When using data from all the sensors as input to the prediction method, kriging performed very well compared to the sensors. However, because it is unlikely to have a large number of sensors to characterize the variability at a prospective solar site, it was also of interest to investigate how many sensors are required as input to the kriging technique in order to generate a reliable prediction. Solar data from four characteristic periods (related to the four seasons) were analyzed, and different sensor configurations, consisting of subsets of the actual sensor array, were employed using the method to demonstrate the number of sensors required to correctly characterize the short-term irradiance variability at the site. Using four measurement stations as input to the kriging method was shown to reasonably represent the variability in the 1-s to 1-min timescales.