Dust effect on PV modules

This paper investigates the effect of dust on photovoltaic (PV) modules with respect to dust concentration, wavelength and spectral transmittance. Dust samples were collected from Kuwait in the form of raw dust and accumulated dust on sample glass at different tilt angles. The spectral transmittance was measured in the Centre for Renewable Energy Systems Technology (CREST) laboratory with a spectrophotometer. Spectral transmittance variation was identified for samples at different tilted positions, where the worst case was presented at a tilt angle of 30o with a non uniformity of 4.4% in comparison to 0.2% for the 90o tilt between the top, middle and bottom. The effect of this on PV is investigated by calculating a modified spectral response for different technologies using spectral response data measured by the European Solar Test Installation (ESTI). The measured data showed a faster rate of decrease in transmittance at wavelengths <570 nm. This affects wide band-gap technologies more than crystalline silicon technologies and especially amorphous silicon which showed a 33% reduction in the spectral photocurrent when a dust concentration of 8.5 mg/cm2 was applied. In comparison, the crystalline silicon and copper indium gallium diselenide (CIGS) technologies showed 28.6% and 28.5% reductions at the same dust density

Effect of dust shading on photovoltaic modules

This paper investigates the effect of dust on photovoltaic (PV) modules with respect to dust concentration and spectral transmittance. Dust samples were collected from Kuwait in the form of raw dust and accumulated dust on sample glasses at different tilt angles. The spectral transmittance was measured at the Centre for Renewable Energy Systems Technology (CREST) laboratory with a spectrophotometer. Total transmittance variation was identified for samples at different tilted positions, where the worst case was presented at a tilt angle of 30o with a non uniformity of 4.4% in comparison to 0.2% for the 90o tilt between the top, middle and bottom. Finally the data was translated to an effective spectral response for different technologies using spectral response data measured by the European Solar Test Installation (ESTI). The measured data showed a decrease in transmittance at wavelengths <570 nm. This affects wide band-gap thin-film technologies more than crystalline silicon technologies and especially amorphous silicon which showed a 33% reduction in photocurrent when a dust concentration of 4.25 mg/cm2 was applied. In comparison, the crystalline silicon and CIGS technologies showed 28.6% and 28.5% reductions at the same dust density

Indoor measurement of photovoltaic device characteristics at varying irradiance, temperature and spectrum for energy rating

This was accepted for publication in the journal Measurement Science and Technology. The definitive published version can be found at: http://dx.doi.org/10.1088/0957-0233/21/11/115701The first three-dimensional performance matrix for use in photovoltaic (PV) energy rating is reported utilizing a novel energy rating solar simulator based on LEDs. Device characteristics are measured indoors at varying irradiance (G), temperature (T) and spectrum (E). This opens the possibility for a more accurate measurement system for energy yield prediction of PV devices, especially for devices with high spectral dependence such as wide bandgap solar cells as they take into account spectral changes in the light. The main aspects of the LED-based solar simulator used are briefly described. A measurement method is developed and detailed in the paper, which takes into account the current imperfections in the achievable spectrum. Measurement results for a crystalline silicon solar cell are used to demonstrate the measurement approach. An uncertainty analysis of the measurement system is given, resulting in an overall absolute uncertainty of 4.3% (coverage factor k = 2) in maximum power measurements at 765 W m−2 irradiance with scope for further improvements

Dust-induced shading on photovoltaic modules

The effect of dust on photovoltaic modules is investigated with respect to concentration and spectral transmittance. Samples were collected in the form of raw dust as well as accumulated dust on exposed sheets of glass at different tilt angles. Spectral transmittance of the samples was determined. Transmittance variation between top, middle and bottom was identified for samples collected at different inclinations, where the worst case was seen at a tilt angle of 30o with a non-uniformity of 4.4% in comparison with 0.2% for the 90° tilt. The measured data showed a decrease in transmittance at wavelengths <570 nm. Integrating this with measured spectral responses of different technologies demonstrates that wide band-gap thin-film technologies are affected more than, for example crystalline silicon technologies. The worst case is amorphous silicon, where a 33% reduction in photocurrent is predicted for a dust concentration of 4.25 mg/cm2. Similarly, crystalline silicon and CIGS technologies are predicted to be less affected, with 28.6% and 28.5% reductions in photocurrent, respectively. The same procedure was repeated with varying Air Mass (AM), tilt angle and dust concentration values to produce a soiling ratio table for different technologies under different AM, tilt angle and dust concentration values

Challenges to teaching posterior composites in the United Kingdom and Ireland

Recent surveys from general dental practice have found increased placement of direct composite resin restorations in occlusal (Class I) and occlusoproximal (Class II) cavities in permanent teeth by general dental practitioners. This has been matched, and possibly driven, at least in part, by the development of new composite resin materials and bonding technologies. Recent studies by the authors have found an increase in the teaching of Class I and Class II composite resin restorations in the UK, Ireland, the US, and Canada. The increased teaching in the UK and Ireland, however, was not as great as in North America, and several worrying trends were observed. The aim of this paper is to discuss these trends and related factors considered important to the necessary further development of the teaching of Class I and Class II direct composite resin restorations, let alone modern operative dentistry in general, in the UK and Ireland

Teaching of direct posterior resin composite restorations in UK dental therapy training programmes

Aim: With the number of dental therapists involved in the delivery of dental care in the UK on the increase, and the trend towards the use of direct resin composites (composites) for the restoration of posterior teeth, this study was undertaken to describe the teaching of posterior composites in dental therapy training programmes in the UK. A secondary aim was to identify differences in techniques for posterior composites taught within these dental therapy training programmes. Methods: In 2008/9, a questionnaire seeking information on the teaching of posterior composites was distributed by email to 13 centres with dental therapy training programmes in the UK. This questionnaire sought information relating to the teaching of direct posterior composites to dental therapy students, including the amounts of preclinical and clinical teaching in respect of deciduous and permanent teeth, numbers of restorations placed, contraindications to placement, and details in respect of operative techniques. Results: Ten completed responses were received (response rate = 77%). In ten programmes, student dental therapists received clinical training in the placement of composite restorations in the occlusal surfaces of premolar and permanent molar teeth, and nine programmes included such training for two and three surface occlusoproximal restorations. The mean proportions of posterior restorations placed clinically by student dental therapists in permanent teeth using dental amalgam and composite were 52% and 46% respectively (range: amalgam = 20-95%; composite = 5-70%). Conclusion: With the exception of one programme, the teaching of posterior composites is a well established element of dental therapy training. Some variations were noted in the teaching of clinical techniques between respondent training centres. It is suggested that to ensure harmony in approaches to treatments provided by graduated therapists that training centres look to relevant consensus documents, such as those of the British Association of Teachers of Conservative Dentistry. The findings of our study are important for the future provision of oral healthcare, given the growing evidence base in favour of minimally invasive dentistry