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 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

A review of overcurrent protection methods for solar photovoltaic DC circuits

This paper investigates the current methodology for overcurrent protection in grid-connected solar photovoltaic (PV) systems. Overcurrent testing procedures for PV modules are examined. The report highlights several shortcomings in the current methodology for overcurrent protection, which may be causing premature module degradation and permanent reduction of generating capacity in PV arrays. A series of recommendations are made for improvements to the relevant guidelines and standards

Large scale PV systems under non-uniform and fault conditions

Current codes of practice for PV systems lack detailed guidance regarding circuit mismatch, over or reverse current protection and unbalanced operational conditions in large PV systems. Experimental work in this field is expensive and limited by hardware and environmental resources. The available commercial simulation tools do not rigorously model the complex behaviour of PV systems operating under non-uniform conditions. In this paper a detailed cell-by-cell model of large scale PV systems is developed. The parameter set used for simulations is based on real PV modules power tolerance data and the variance in its principal parameters, thus representing a realistic power frequency distribution. The model is used to estimate and analyse losses due to circuit mismatch, analyse the causes of reverse current in the system's strings and its consequences in the system performance and to estimate energy losses due to string's fuses failures

Potential for LED solar simulators

LED solar simulators have been discussed recently as a potential next generation solar simulator. This contribution evaluates the possibilities of generating a light field of appropriate spectrum with good uniformity. LEDs have very different optical characteristics compared to standard lights and this needs to be considered in the optical design. The aim in this paper is to achieve a close spectral match to the AM1.5 solar spectrum from 350nm to 1300nm. A total irradiance of 1000 W/m2 needs to be acquired. Additionally, the non-uniformity of light needs to be equal to or less than 1%. The key to mix spectra and achieve the desired intensity and uniformity is the optics. This paper evaluates different optical layouts to assess the potential for fully LED based solar simulators. The TIRs perform better collecting more light than other optics tested

Assessment of potential for photovoltaic roof installations by extraction of roof slope from lidar data and aggregation to census geography

Leading topics in PV research include field performance and grid impact. A national understanding of roof features (slope, orientation, area) is essential for modelling the timing of PV installation scenarios with their associated irradiance data. However, such information is not currently available. This paper demonstrates the extraction of building characteristics from LIDAR (Light Detection and Ranging) data. These characteristics are then aggregated and scaled-up to produce a UK-wide map of PV potential, based on suitable roof tilts and azimuths

Towards a fully LED-based solar simulator - spectral mismatch considerations

LED solar simulators have a high potential for high quality characterisation of solar cells. One of the main challenges is to achieve a close spectral match to the AM1.5 solar spectrum from 350nm to 1300nm. The main sources of measurement uncertainty are the spectral mismatch, the non-uniformity of light and the reference cell. The spectral mismatch can increase the measurement uncertainty significantly. In order to minimize a major uncertainty factor a close spectral match needs to be acquired. It will be shown that the usage of LEDs, which are narrow wavelength emitting light sources, can improve the measurement accuracy of the solar simulator by accurately matching the solar spectrum. The process of choosing the best combination of wavelengths and the LED population per wavelength is a complex, dual optimization problem. This paper evaluates the optimisation algorithms chosen and examines the influence of different fitness functions in acquiring a Class A+ spectral match