Design process optimisation of solar photovoltaic systems

The design processes for solar photovoltaic (PV) systems is improved to achieve higher reliability and reduced levelised cost of energy (LCOE) throughout this thesis. The design processes currently used in the development of PV systems are reviewed. This review process included embedding the author in a project to deliver four rooftop PV systems which totalled a megawatt of installed generating capacity, which at the time represented very significant system sizes. The processes used in this are analysed to identify improvement potential. Shortcomings are identified in three main areas: safety assurance, design process integration and financial optimisation. Better design process integration is required because data is not readily exchanged between the industry standard software tools. There is also a lack of clarity about how to optimise design decisions with respect to factors such as shading and cable size. Financial optimisation is identified as a challenge because current software tools facilitate optimising for maximum output or minimum cost, but do not readily optimise for minimum levelised cost of energy which is the primary objective in striving for grid parity. To achieve improved design process integration and financial optimisation, a new modelling framework with the working title SolaSIM is conceived to accurately model the performance of solar photovoltaic systems. This framework is developed for grid connected systems operating in the UK climate, but it could readily be adapted for other climates with appropriate weather data. This software development was conducted using an overarching systems engineering approach from design and architecture through to verification and validation. Within this SolaSIM framework, the impact of shading on array and inverter efficiency is identified as a significant area of uncertainty. A novel method for the calculation of shaded irradiance on each cell of an array with high computational efficiency is presented. The shading sub-model is validated against outdoor measurements with a modelling accuracy within one percent. Final verification of the over-arching SolaSIM framework found that it satisfied the requirements which were identified and actioned. The author installed the new CREST outdoor measurement system version 4 (COMS4). COMS4 is a calibrated system which measures 26 PV devices simultaneously. Validation of SolaSIM models against COMS4 found the modelling error to be within the 4% accuracy target except two sub-systems which had electronic faults. The model is validated against PV systems and found to be within the specified limits

Oral History with Dr. Sylvia Goss & Dr. Willie Goss

The Cultural Research & Engagement Fellows (CREF) Program at Mississippi State University explores the social and cultural dimensions of food systems, food access, land in majority-Black, historically agrarian rural communities by engaging youth at the nexus of food access, farming, and culture. The CREF program is made possible by a grant from the Office of Research & Economic Development (ORED) and the Office of Institutional Diversity and Inclusion (OIDI) at Mississippi State University

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

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

The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results

We present methods and results from "21-cm Spectral Line Observations of Neutral Gas with the EVLA" (21-SPONGE), a large survey for Galactic neutral hydrogen (HI) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median root-mean-square (RMS) noise in optical depth of $\sigma_{\tau}=9\times 10^{-4}$ per $0.42\rm\,km\,s^{-1}$ channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest HI absorption survey with this high sensitivity. We discuss the observations and data reduction strategies, as well as line fitting techniques. We prove that the VLA bandpass is stable enough to detect broad, shallow lines associated with warm HI, and show that bandpass observations can be combined in time to reduce spectral noise. In combination with matching HI emission profiles from the Arecibo Observatory ($\sim3.5'$ angular resolution), we estimate excitation (or spin) temperatures ($\rm T_s$) and column densities for Gaussian components fitted to sightlines along which we detect HI absorption (30/31). We measure temperatures up to $\rm T_s\sim1500\rm\,K$ for individual lines, showing that we can probe the thermally unstable interstellar medium (ISM) directly. However, we detect fewer of these thermally unstable components than expected from previous observational studies. We probe a wide range in column density between $\sim10^{16}$ and $>10^{21}\rm\,cm^{-2}$ for individual HI clouds. In addition, we reproduce the trend between cold gas fraction and average $\rm T_s$ found by synthetic observations of a hydrodynamic ISM simulation by Kim et al. (2014). Finally, we investigate methods for estimating HI $\rm T_s$ and discuss their biases.Comment: Accepted for publication in ApJ; 24 pages, 14 figure

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