Spectral irradiance effects on the outdoor performance of photovoltaic modules

The outdoor performance of photovoltaic modules is influenced by spectrum. Even if the irradiance level and the operating temperature is the same, performance difference of photovoltaic modules between the seasons can be increase up to 15% depending on the photovoltaic module type. In this paper, seasonal spectral irradiance effects on the outdoor photovoltaic module performance and previous studies has been summarised thoroughly. The spectrum indicators which are used for spectra characteristics, Useful Fraction and Average Photon Energy are described in detail. This study also indicates spectrum effects on PV performance and outlines the present studies investigating this effect

Estimating rooftop capacity for PV: Are we asking the right question?

Precise estimation of solar energy potential on pitched roofs is crucial for modelling photovoltaic (PV) installation scenarios. However, there is no national database of building characteristics in the UK. This paper begins by reviewing and testing a range of existing techniques for identifying roof characteristics. These all attempt to estimate roof area with varying degrees of accuracy. Rather than attempting to achieve this, a method is developed which assesses each roof to discover whether it is suitable for PV installation. That is, its properties should allow the installation of at least a minimum size photovoltaic system. This contribution provides a tool to assess PV potential on city-wide scales. It develops a pixel-based approach to estimation of solar energy potential over pitched roofs. This is achieved by a combination of publicly available building outline maps and LiDAR (Light Detection and Ranging) data. These are analysed by using a simple statistical technique within a Geographical Information Systems (GIS) environment. The accuracy of the new method is known, following validation against a large housing database. The method is mathematically simple. It is suitable for estimating rooftop capacity of mixed housing type developments

A fast and effective approach to modelling solar energy potential in complex environments

A fast and effective approach to modelling solar energy potential in complex environment

A GIS-based method for identification of wide area rooftop suitability for minimum size PV systems using LiDAR data and photogrammetry

Knowledge of roof geometry and physical features is essential for evaluation of the impact of multiple rooftop solar photovoltaic (PV) system installations on local electricity networks. The paper starts by listing current methods used and stating their strengths and weaknesses. No current method is capable of delivering accurate results with publicly available input data. Hence a different approach is developed, based on slope and aspect using aircraft-based Light Detection and Ranging (LiDAR) data, building footprint data, GIS (Geographical Information Systems) tools, and aerial photographs. It assesses each roof’s suitability for PV deployment. That is, the characteristics of each roof are examined for fitting of at least a minimum size solar power system. In this way the minimum potential solar yield for region or city may be obtained. Accuracy is determined by ground-truthing against a database of 886 household systems. This is the largest validation of a rooftop assessment method to date. The method is flexible with few prior assumptions. It can generate data for various PV scenarios and future analyses

Compensation of temporal averaging bias in solar irradiance data

Solar irradiance data is used for the prediction of solar energy system performance but is presently a significant source of uncertainty in energy yield estimation. This also directly affects the expected revenue, so the irradiance uncertainty contributes to project risk and therefore the cost of finance. In this paper, the combined impact of temporal averaging, component deconstruction and plane translation mechanisms on uncertainty is analysed. A new method to redistribute (industry standard) hourly averaged data is proposed. This clearness index redistribution method is based on the statistical redistribution of clearness index values and largely corrects the bias error introduced by temporal averaging. Parameters for the redistribution model were derived using irradiance data measured at high temporal resolution by CREST, Loughborough University, over a 5 year period. The root mean square error (RMSE) of example net annual (2014) diffuse, beam and global yield of hourly averaged data were reduced from approximately 15% to 1%, 14% to 3% and 4% to 1%, respectively

Detection of roof shading for PV based on LiDAR data using a multi-modal approach

There is a current drive to increase rooftop deployment of PV. Suitable roofs need to be located, especially as regards shading. A shadow cast on one small section of a solar panel can disproportionately undermine output of the entire system. Nevertheless, few shading figures are available to researchers and developers. This paper reviews and categorizes a number of methods of determining shade losses on photovoltaic systems. Two existing methods are tested on case study areas: shadow simulation from buildings and ambient occlusion. The first is conceptually simple and was found to be useful where data is limited. The second is slightly more demanding in terms of data input and mathematical models. It produces attractive shadow maps but is intended for speed and represents an approximation to ray-tracing. Accordingly, a new model was developed which is fast, flexible and accurately models solar radiation

Satellite or ground-based measurements for production of site specific hourly irradiance data: Which is most accurate and where?

Site-specific satellite-derived hourly global horizontal irradiance is compared with that obtained from extrapolation and interpolation of values measured by ground-based weather stations. A national assessment of three satellite models and two ground-based techniques is described. A number of physiographic factors are examined to allow identification of the optimal resource. The chief influences are determined as: factors associated with latitude; terrain ruggedness; and weather station clustering/density. Whilst these factors act in combination, weather station density was found to be fundamental for a country like the UK, with its ever-changing weather. The decision between satellite and ground-based irradiance data based on accuracy is not straightforward. It depends on the exactitude of the selected satellite model and the concentration of pyranometric stations

Assessment and improvement of thermoelectric pyranometer measurements

This work evaluates the variability of thermoelectric pyranometer calibration values seen when using different calibration methods and practices. The pyranometer calibration ISO 9847:1992 standard leaves many procedural details to the user’s discretion. The variability resulting from different interpretations influences PV system performance monitoring and energy yield modelling. Improved methods and more robust standardisation are therefore needed to reduce uncertainty in field-deployed thermoelectric pyranometers and consequently reduce risk in PV system energy yield assessment. This paper investigates the variability induced by relaxed calibration procedures defined in the standard Furthermore, it proposes indoor procedures for the characterisation of pyranometer response to incidence angle and temperature which have not yet been defined in the standards. Uncertainty of calibration factors including under high angles of incidence and a few cloudy data series from outdoor methods were found to be up to 2.08%, compared with 1.4% stated by the manufacturer. Uncertainty increases up to 4.73% when reference and test sensors are of different types. Results of indoor calibration procedures agreed to within 1.21% even when calibrating multiple sensors at the same time. The instability of the irradiance source contributed more to the overall uncertainty than the selection of the procedure. The angular response of the devices tested was close to the prescribed limits [1]

Treatment of pathophysiologic propagation outside of the pulmonary veins in retreatment of atrial fibrillation patients:RECOVER AF study

Aims RECOVER AF evaluated the performance of whole-chamber non-contact charge-density mapping to guide the ablation of non-pulmonary vein (PV) targets in persistent atrial fibrillation (AF) patients following either a first or second failed procedure. Methods RECOVER AF was a prospective, non-randomized trial that enrolled patients scheduled for a first or second ablation re- and results treatment for recurrent AF. The PVs were assessed and re-isolated if necessary. The AF maps were used to guide the ablation of non-PV targets through elimination of pathologic conduction patterns (PCPs). Primary endpoint was freedom from AF on or off antiarrhythmic drugs (AADs) at 12 months. Patients undergoing retreatment with the AcQMap System (n = 103) were 76% AF-free at 12 months [67% after single procedure (SP)] on or off AADs (80% free from AF on AADs). Patients who had only received a pulmonary vein isolation (PVI) prior to study treatment of non-PV targets with the AcQMap System were 91% AF-free at 12 months (83% SP). No major adverse events were reported. Conclusion Non-contact mapping can be used to target and guide the ablation of PCPs beyond the PVs in persistent AF patients returning for a first or second retreatment with 76% freedom from AF at 12 months. The AF freedom was particularly high, 91% (43/47), for patients enrolled having only a prior de novo PVI, and freedom from all atrial arrhythmias for this cohort was 74% (35/47). These early results are encouraging and suggest that guiding individualized targeted ablation of PCPs may therefore be advantageous to target at the earliest opportunity in patients with persistent AF.</p