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

Irradiance modelling for individual cells of shaded solar photovoltaic arrays

Developments in Photovoltaic (PV) design software have progressed to modelling the string or even the module as the smallest system unit but current methods lack computational efficiency to fully consider cell mismatch effects due to partial shading. This paper presents a more efficient shading loss algorithm which generates an irradiance map of the array for each time step for individual cells or cell portions. Irradiance losses are calculated from both near and far obstructions which might cause shading of both beam and diffuse irradiance in a three-dimensional reference field. The irradiance map output from this model could be used to calculate the performance of each solar cell individually as part of an overarching energy yield model. A validation demonstrates the calculation of shading losses due to a chimney with less than one percent error when compared with measured values

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

Large scale evaluation of photovoltaic technologies in different climates

Photovoltaic systems are typically optimised for performance or cost. In order to evaluate the wider parameter space and extensive measurement campaign has been designed that will provide guidance on future system designs. Four near-identical, grid-connected 200kW PV systems are being installed onto IKEA home furnishings stores in four countries with different climatic classification. The systems are integrated with comprehensive weather and power monitoring systems. This paper reports on the design, installation and scientific objectives of the project

Low cost current measurement of three phase cables

© 2018 IEEE. Recent growth in embedded generation alongside the anticipated consumer uptake of electric vehicles (EVs) and heat pumps present new challenges for distribution networks. This includes greater fluctuation in electricity demand. Data from existing maximum demand indicators in distribution substations is inadequate to understand the spread of demand over time. Retro-fit datalogging solutions are available for substation monitoring, but cost typically >£1200, which would be difficult to justify for all distribution substations. This paper looks at the development of a novel low cost alternative designed for measuring load on three phase cables