Performance characterisation of photovoltaic modules

A review of the performance characterization of photovoltaic modules is given, that charts the progress made in the European research project ‘PV-Performance’ as well as other work carried out in Europe. The aim is to illustrate the measurement and prediction accuracy of energy delivery. It is shown that direct inter-comparisons of PV modules may have as much as 6.5% uncertainty in the comparability between modules and that any difference much lower than this is not a meaningful conclusion. A significant contribution to this is the determination of the rated power of the modules chosen for the inter-comparison and the lack of statistical numbers. The rated power is also important in the context of modeling the performance and thus must be as accurately as somewhat possible. It is shown that the uncertainties of the calibration laboratories are not borne out by round robin inter-comparisons and further work is needed in this field. Uncertainties for wafer-based devices are shown to be in a range of ±3%, while different thin film technologies may have higher uncertainties. It is shown that even simple modeling approaches are good enough to predict PV performance to within the measurement accuracy of most datasets

Performance characterisation of photovoltaic modules

A review of the performance characterization of photovoltaic modules is given, that charts the progress made in the European research project ‘PV-Performance’ as well as other work carried out in Europe. The aim is to illustrate the measurement and prediction accuracy of energy delivery. It is shown that direct inter-comparisons of PV modules may have as much as 6.5% uncertainty in the comparability between modules and that any difference much lower than this is not a meaningful conclusion. A significant contribution to this is the determination of the rated power of the modules chosen for the inter-comparison and the lack of statistical numbers. The rated power is also important in the context of modeling the performance and thus must be as accurately as somewhat possible. It is shown that the uncertainties of the calibration laboratories are not borne out by round robin inter-comparisons and further work is needed in this field. Uncertainties for wafer-based devices are shown to be in a range of ±3%, while different thin film technologies may have higher uncertainties. It is shown that even simple modeling approaches are good enough to predict PV performance to within the measurement accuracy of most datasets

Optical modelling for concentrating photovoltaic systems: insolation transfer variations with solar source descriptions

Point source, pillbox and circumsolar ratio-dependent extended light source Sun models are used as solar source inputs into an analytical optical ray trace model for the calculation of plane restricted illumination profiles generated by three example lenses. The example lenses are: a low iron soda-lime glass plano-convex lens, a poly (methyl) methacrylate (PMMA) 3-facet Fresnel lens and a PMMA 20-facet Fresnel lens. Significant differences in illumination profiles are found with solar source description variation. Most notably, it is found that chromatic aberrations and spectrally variant effects specific to the multi-junction solar cell architecture are only identified using the extended light source Sun model. The spectral dependency of material optical properties are analysed in the context of the multi-junction cell architecture by means of spectrally weighted averages corresponding to the active range of the sub-cells

Energy yields of small grid connected photovoltaic system: effects of component reliability and maintenance

The likelihood of system failure of small systems is investigated in order to establish the risk associated for the investment into a photovoltaic (PV) system for small domestic applications. This is achieved by reviewing existing literature on PV system failure rates and using these as an input for a statistical PV system yield simulation tool that considers failure and repair. It is typically assumed that these systems do not require any maintenance, but it is shown that this will have near catastrophic impact on the energy production of PV systems. The no maintenance is not a likely scenario, as small systems have to register their generation to achieve a feed-in-tariff. In a later stage, when PV is used for self-consumption only, this may change but in the present market most users are forced to carry out a quarterly check and thus this catastrophic failure is avoided by the need of having to apply for the feed-in-tariff. Minimum maintenance strategies for ensuring profitable system operation are investigated and their cost-effectiveness is discussed. It is shown that the present situation where many systems are neither monitored nor is any maintenance carried out results in a high probability of unsuccessful system operation as failure detection may take a very long time. Successful system operation here is defined as not recovering the financial investment. It would be advisable to carry out at least monthly performance checks as otherwise it is likely to have more than 10% energy lost because of system downtime. This requires, however, availability of irradiance data as otherwise it is not possible to identify whether low yields are due to resource issues or really system yield issues

Wireless supervisory control and data acquisition system for photovoltaic installations

Performance of the photovoltaic systems suffers from inappropriate level of supervisory. Limited availability of the information about key system parameters and lack of expert knowledge of the users are the most commonly found problems. In large scale installations, due to high level of complexity, faults become more likely to happen and more difficult to be found. In extreme they may stay uncovered for long periods of time. It decreases financial performance of the PV system putting investment at risk. In presented paper novel, wireless ZigBee technology has been applied to develop robust, accurate, easy to install, low cost and autonomous sensing solution for photovoltaic supervisory systems

Modelling solar flux distributions for fresnel lens CPV systems

A computer model for the simulation of solar flux distribution in the direct and circumsolar regions of the beam irradiation has been created. The model incorporates previous research into circumsolar ratios (CSRs) [1,2]. It is used to demonstrate the importance of realistic solar flux distributions as source inputs in Concentrator Photovoltaic (CPV) simulations. It is shown that the distribution of flux for different circumsolar ratios varies significantly. Such variation will have a considerable effect on the optical image formed at the receiver of a solar concentration system and thus is a necessary consideration in CPV modelling. Flux distributions incident on lenses of various entry apertures are generated and used to investigate the losses in incident flux resulting from tracking errors and CSR variation. It is found that, for a concentrating system with an entry aperture of 0.25°, a 20% loss of net annual incident energy is found with a tracking error of ~0.1°. The same loss is found with tracking errors of ~0.3°, 0.6° and 0.85° with apertures of 0.5°, 0.75° and 1°, respectively

Modelling the efficiency of terrestrial photovoltaic systems

A computer simulation capable of investigating the interrelationship of module packing densities and module inclination angles and their effects on overall energy yield for a given PV system installation area is presented. It is demonstrated that the simulation is a useful tool in the optimization of proposed system designs, the analysis of electrical performance and, moreover, the prediction of the occurrence of degenerative system effects such as hot-spots. In one case, it is shown that increasing the system height to module spacing ratio from 0.18 to 0.24 results in potentially severe shading effects. Results for Seville (Spain) and Loughborough (UK) are compared. The potential pros and cons of tracking systems are demonstrated, in that elevation only tracking results in an annual irradiance harvest reduction of 0.4% in Loughborough and increase of 3.4% in Seville. Varying module inclination angles shows how significant irradiance losses can occur when static PV arrays are not optimally mounted, reducing the inclination from 40 degrees to zero results in an annual irradiance harvest reduction of ~20% in Seville and ~14% in Loughborough

Intercomparison of pyranometers for distributed measurement system

Irradiance is one of the most important parameter measured by PV monitoring systems. Its value is needed to estimate reference yield (YR) and after then performance ratio index (PR). Uncertainty convolved with irradiance measurements has a strong influence on final monitoring quality. This paper presents intercomparison test of ten CMP11 pyranometers which will then be used for the measurement of PV systems distributed across two continents and four countries. Measurements were taken under different installation conditions (horizontal, inplane). Ten CV2 ventilation units were used as a part of system improvements. Finally pyranometers data were combined with EKO MS700 spectral measurements to evaluate spectral variations

Electrical mismatch within single junction amorphous silicon and micromorph tandem thin film PV modules

Due to the electrical mismatch between the individual cells, the actual efficiency of a PV module is always lower than the sum of the cells under normal measurement conditions. The effect of this electrical mismatch is simulated for single junction amorphous silicon PV modules as well as micromorph thin film PV modules. This paper reports on the design of the realistic parameter distribution for the I-V simulation. It shows that due to the current mismatch in a double junction solar cell, these devices seem to be more significantly affected by similar variation in parameters, which would indicate that tighter production control is necessary but also that it will be more involved to measure these devices with sufficient accuracy. It is shown that device mismatch actually results in a lower fill factor, which is slightly different to what is seen for single cells

An LED-based photovoltaic measurement system with variable spectrum and flash speed

Outdoor environmental variability generates the need for indoor systems for PV module characterisation. To combine the advantages of the most commonly used simulators (steady-state and pulsed) and eliminate their disadvantages, an LED-based solar simulator prototype has been developed. The system can produce light at variable flash speeds and pulse shapes or can operate as a continuous light source for long-term measurements. The system achieves 1-Sun intensity at a closely matched, continuous spectrum. Full control of all light sources allows variable intensity and spectral distribution during measurements. A technical description and the results of initial qualification tests are given