Browsing by Author "King, Peter"
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Item Open Access Airborne sand and dust soiling of solar collecting mirrors(AIP, 2017-06-27) Sansom, Christopher L.; Almond, Heather; King, Peter; Endaya, Essam; Bouaichaoui, SofianeThe reflectance of solar collecting mirrors can be significantly reduced by sand and dust soiling, particularly in arid environments. Larger airborne sand and dust particles can also cause damage by erosion, again reducing reflectance. This work describes investigations of the airborne particle size, shape, and composition in three arid locations that are considered suitable for CSP plants, namely in Iran, Libya, and Algeria. Sand and dust has been collected at heights between 0.5 to 2.0m by a variety of techniques, but are shown not to be representative of the particle size found either in ground dust and sand, or on the solar collecting mirror facets themselves. The possible reasons for this are proposed, most notably that larger particles may rebound from the mirror surface. The implications for mirror cleaning and collector facet erosion are discussedItem Open Access Design of a novel CSP/MED desalination system(American Institute of Physics (AIP), 2022-05-12) Sansom, Christopher L.; Patchigolla, Kumar; Jonnalagadda, Kranthi; King, PeterWe describe the design of a large-scale thermal desalination demonstrator unit for use in arid locations with a medium-to-high DNI. Most of thermal energy is provided by a conventional parabolic trough field, in the case of the demonstrator this being 4MWt. The desalination sub-system comprises a 3-effect MED, the first stage of which is a large 20 m diameter glass and steel-structured geodesic and transparent dome. The thermal energy is supplemented by direct sunlight transmitted through the dome and by an arc of small heliostats which focus yet more sunlight onto the dome itself. The prototype is under construction at Neom in KSA.Item Open Access The design of dust barriers to reduce collector mirror soiling in CSP plants(American Institute of Physics, 2018-11-08) Sansom, Christopher L.; King, Peter; Fernandez-Garcia, Aranzazu; Almond, Heather; Kayani, Talib; Boujjat, HoussammeIn this work we investigate, design, and evaluate a number of dust barrier designs that would be appropriate to reduce soiling of glass mirror solar collectors in the solar field of an existing CSP plant. The principal objective was to reduce the amount of soiling (and hence the amount of cleaning water consumed) by 50% in comparison with current cleaning procedures (considering particles of size >25 µm). “Fluent” CFD software was used to model of a range of potential dust barrier shapes, sizes, and porosities. Airflows and wind loadings were analyzed in this way. A number of potential designs were then taken forward for experimental validation. Initial validation involved wind tunnel evaluation of a small number of potential designs, using a new wind tunnel specifically designed and built for this project. Larger-scale outdoor validation was carried out both at Cranfield University in the UK and at CIEMAT-PSA (Plataforma Solar de Almeria) in Spain. Initial results were independent of location and barrier shape and showed that the percentage of particles that were stopped completely or travelled less than 1m beyond the barrier was in the range 45.8 ± 5%.Item Open Access Form measurement and durability of mirror surfaces for concentrating solar power applications(Cranfield University, 2014-11) King, Peter; Sansom, Christopher L.; Comley, PaulConcentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than directly electrical, which is attractive as thermal energy is easier and currently cheaper to store in large amounts. It is also used directly as processing heat including desalination and water purification. For the technology to compete against other generating systems it is important to reduce the electrical energy cost to the $0.05 per kilowatt-hour level. One of the significant capital costs is the solar field, which contains the concentrators. To reduce the cost of this field, novel constructions and improvements to the durability and lifetime of the concentrators are required. Techniques for characterising the shape, durability and optical properties of such novel mirrors are the focus of this thesis. The thesis describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. Photogrammetry has demonstrated its versatility and portability by successful measurements across concentrating solar power sites globally. The accuracy of the technique has been validated to show a measurement capability of better than 100 µm using a large coordinate measuring machine. Measurements performed on novel thin glass mirrors and their comparison with conventional thick glass mirrors are presented, showing that the increased flexibility of thin mirrors is an important consideration during installation, but that it is possible for such novel mirrors to perform to the same level. ...[cont.]Item Open Access Investigating performance of hybrid photovoltaic–thermal collector for electricity and hot water production in Nigeria(MDPI, 2024-06-05) Awai, Kar R.; King, Peter; Patchigolla, Kumar; Jain, Sagar M.The research work explores the impact of temperature on Silicon photovoltaic (PV) panels, considering Nigeria as a case study. It is found that high solar radiation in Nigeria increases the surface temperature of PV panels above 25 °C of the optimal operating temperature. The redundant energy gain from solar irradiance creates heat at the rear of solar panels and reduces their efficiency. Cooling mechanisms are therefore needed to increase efficiency. In this study, we demonstrated a unique hybrid system design employing a heat exchanger at the back of the panel, with water circulated through the back of the PV panel to cool the system. The system was simulated using TRNSYS at three locations in Nigeria—Maiduguri, Makurdi, and Port Harcourt. The results of the peak annual electrical power output in Maiduguri give a power yield of 1907 kWh/kWp, which is the highest, due to a high solar radiation average of 727 W/m2 across the year. For Makurdi, the peak annual electrical power output is 1542 kWh/kWp, while for Port Harcourt the peak power output is 1355 kWh/kWp. It was observed that the surface temperature of Polycrystalline Si-PV was decreased from 49.25 °C to 38.38 °C. The electrical power was increased from 1526.83 W to 1566.82 W in a day, and efficiency increased from 13.99% to 15.01%.Item Open Access Numerical design and simulation of CSP multi-tower solar heliostat field.(Cranfield University, 2020-05) Hussaini, Zaharaddeen Ali; King, Peter; Sansom, Christopher L.In power tower systems, the heliostat field is one of the essential subsystems in the plant due to its significant contribution to the plant’s overall power losses and total plant investment cost. The design and optimisation of the heliostat field is hence an active area of research, with new field improvement processes and configurations being actively investigated. In this thesis, a different configuration of a multi-tower field is explored. This involves adding an auxiliary tower to the field of a conventional power tower Concentrated Solar Power (CSP) system. The methodology for the auxiliary towers positioning were based on the region in the field which has the least effective reflecting heliostats. The multi-tower configuration was initially applied to a 50MWth conventional field in the case study region of Nigeria. The results from an optimised multi-tower field, achieved through MATLAB Genetic Optimisation, show a marked increase in the annual thermal energy output and mean annual efficiency of the field over a typical conventional field. The efficiency and thermal energy output become even more pronounced in optimised multi-tower fields with two auxiliary towers. For the given thermal field power, the gain recorded in the thermal energy output could not offset the additional costs from the presence of additional towers and receivers in the field. However, in much larger fields a higher number of weaker heliostats were witnessed in the field. The auxiliary towers in the field thus provides an alternate aim point for the weaker heliostat, thereby considerably cutting down on some optical losses, which in turn gives rise to higher energy output. At 400MWth, the one auxiliary tower multi-tower field configuration provides both a lower LCOH and a higher field efficiency over a single conventional power tower field with similar thermal field output power. The thesis goes further to explore and develop methods in which the field layout generation methodologies in multi-tower fields can be improved. The Auxiliary Tower with Subfield Configuration (ATS) and Heliostat Repositioning Configuration (HRC). The addition of auxiliary tower has already shown to hold much potential in large plants. ATS and HRC further show that the same intended field thermal power output can be reached with a lesser LCOH and a higher field efficiency when compared to both conventional fields and optimised multi-tower fields of similar thermal ratings. These field improvement strategies were then applied to an existing field, the Gemasolar plant in Sevilla Spain, as a case study in order to further highlight their applications. In this work, multi-towers have shown that in large solar fields, a clear advantage over the conventional fields exists by proving a higher field efficiency and thermal energy output. Multi- tower fields have thus shown to provide a viable alternative to conventional fields and equally provide the potential to change the way power tower fields are being built in the future.Item Open Access Numerical simulation and design of multi-tower concentrated solar power fields(MDPI, 2020-03-19) Hussaini, Zaharaddeen Ali; King, Peter; Sansom, Christopher L.In power tower systems, the heliostat field is one of the essential subsystems in the plant due to its significant contribution to the plant’s overall power losses and total plant investment cost. The design and optimization of the heliostat field is hence an active area of research, with new field improvement processes and configurations being actively investigated. In this paper, a different configuration of a multi-tower field is explored. This involves adding an auxiliary tower to the field of a conventional power tower Concentrated Solar Power (CSP) system. The choice of the position of the auxiliary tower was based on the region in the field which has the least effective reflecting heliostats. The multi-tower configuration was initially applied to a 50MWth conventional field in the case study region of Nigeria. The results from an optimized field show a marked increase in the annual thermal energy output and mean annual efficiency of the field. The biggest improvement in the optical efficiency loss factors be seen from the cosine, which records an improvement of 6.63%. Due to the size of the field, a minimal increment of 3020 MWht in the Levelized Cost of Heat (LCOH) was, however, recorded. In much larger fields, though, a higher number of weaker heliostats were witnessed in the field. The auxiliary tower in the field provides an alternate aim point for the weaker heliostat, thereby considerably cutting down on some optical losses, which in turn gives rise to higher energy output. At 400MWth, the multi-tower field configuration provides a lower LCOH than the single conventional power tower field.Item Open Access Photogrammetry for concentrating solar collector form measurement, validated using a coordinate measuring machine(MDPI, 2019-12-25) King, Peter; Sansom, Christopher L.; Comley, PaulConcentrating solar power systems currently have a high capital cost when compared with other energy generating systems. The solar energy is captured in the form of thermal energy rather than direct electrical, which is attractive as thermal energy is more straightforward and currently more cost-effective to store in the amounts required for extended plant operation. It is also used directly as industrial process heat, including desalination and water purification. For the technology to compete against other generating systems, it is crucial to reduce the electrical energy cost to less than $0.10 per kilowatt-hour. One of the significant capital costs is the solar field, which contains the concentrators. Novel constructions and improvements to the durability and lifetime of the concentrators are required to reduce the cost of this field. This paper describes the development and validation of an inexpensive, highly portable photogrammetry technique, which has been used to measure the shape of large mirror facets for solar collectors. The accuracy of the technique has been validated to show a whole surface measurement capability of better than 100 mm using a large coordinate measuring machine. Qualification of facets of the MATS plant was performed during its installation phase, giving results of the shape, slope and intercept errors over each facet.Item Open Access Post subsidy conditions: evaluating the techno-economic performance of concentrating solar power in Spai(Elsevier, 2021-03-21) Parent, Pierre-Antoine; Mirzania, Pegah; Balta-Ozkan, Nazmiye; King, PeterSpain is one of the front runners of the development of Concentrated Solar Power (CSP) projects. In recent years, however, the CSP industry in Spain has faced significant financial challenges due to a dramatic withdrawal of the Feed-in-Tariff (FIT) in 2013. The primary aim of this paper is to assess when, and under what conditions, CSP projects, in particular, Parabolic Trough Collectors can potentially reach grid parity in the absence of any subsidies. This paper also goes further to investigate whether and how Parabolic Trough Collector (PTC) projects can be financially viable in the post-subsidy period, using the System Advisor Model as a simulation tool to conduct techno-economic analyses. The simulation results indicated that a 50MWe PTC project with TES of 4 hours and a PPA price of €0.20 per kWh is the most viable model for developing CSP projects in Spain under post-subsidy condition. This paper concludes that, under current retail electricity prices and post-subsidy conditions, PTC projects can reach grid parity and become viable without direct incentives. Even though direct policy support will not be required, the CSP industry in Spain is still far from becoming fully self-sustained.Item Open Access Predicting the effects of sand erosion on collector surfaces in CSP plants(Elsevier, 2015-06-05) Sansom, Christopher L.; Comley, Paul; King, Peter; Almond, Heather; Atkinson, C.; Endaya, E.This paper presents a methodology to predict the optical performance and physical topography of the glass collector surfaces of any given CSP plant in the presence of sand and dust storms, providing that local climate conditions are known and representative sand and dust particles samples are available. Using existing meteorological data for a defined CSP plant in Egypt, plus sand and dust samples from two desert locations in Libya, we describe how to derive air speed, duration, and sand concentrations to use within the Global CSP Laboratory sand erosion simulation rig at Cranfield University. This then allows us to predict the optical performance of parabolic trough collector glass after an extended period by the use of accelerated ageing. However the behavior of particles in sandstorms is complex and has prompted a theoretical analysis of sand particle dynamics which is also described in this paper.Item Open Access Reflectometer comparison for assessment of back-silvered glass solar mirrors(Elsevier, 2017-06-29) Sansom, Christopher L.; Fernández-García, Aránzazu; King, Peter; Sutter, Florian; Garcia Segura, AlejandroThis paper compares the two most common reflectometers used to assess the specular reflectance of back-silvered glass mirrors for Concentrating Solar Power (CSP) applications, namely the Device and Services (D&S) 15R-USB and the Abengoa Condor SR-6.1 instruments. Comparisons are first made between the two instruments themselves using a Gage Repeatability and Reproducibility (R&R) study. Results are given for the as-cleaned collector mirrors and then as the mirrors become naturally soiled over a one month period. The results of the Gage R&R study show that for the D&S the gage itself contributes 40.97% of the variability, whilst 59.03% is due to part-to-part (location on the mirror under investigation) variability. For the Condor we show that the % Contribution from the gage is 62.18% of the total variability with only 37.82% of the contribution attributable to the location dependent reflectance. The Condor has a wider acceptance angle, and over the reflectance range of 0.91–0.95 the condor was found to measure higher than the D&S by an average of 1.53%. The differences between the soiling results obtained from the two instruments are explained, and the results are used to derive a predictive model for the soiling of solar collectors. In conclusion, both instruments have advantages and shortcomings, and the factors that influence which instrument to select are discussed.Item Open Access Soiling and cleaning of polymer film solar reflectors(MDPI, 2016-11-29) Sansom, Christopher L.; Fernández-García, Aránzazu; Sutter, Florian; Almond, Heather; King, Peter; Martínez-Arcos, LucíaThis paper describes the accelerated ageing of commercially available silvered polymer film by contact cleaning using brushes and water in the presence of soiling created by dust and sand particles. These conditions represent cleaning regimes in real concentrating solar power (CSP) solar fields in arid environments, where contact cleaning using brushes and water is often required to clean the reflecting surfaces. Whilst suitable for glass reflectors, this paper discusses the effects of these established cleaning processes on the optical and visual characteristics of polymer film surfaces, and then describes the development of a more benign but effective contact cleaning process for cleaning polymer reflectors. The effects of a range of cleaning brushes are discussed, with and without the presence of water, in the presence of sand and dust particles from selected representative locations. The experiments were repeated using different experimental equipment at Plataforma Solar de Almería (PSA) in Spain and Cranfield University in the UK. The results highlight differences that are attributable to the experimental methods used. Reflectance measurements and visual inspection show that a soft cleaning brush with a small amount of water, used in a cleaning head with both linear and rotational motion, can clean polymer film reflecting surfaces without inflicting surface damage or reducing specular reflectance.Item Open Access Theoretical and experimental analysis of an innovative dual-axis tracking linear Fresnel lenses concentrated solar thermal collector(Elsevier, 2017-06-21) Perini, Simoni; Tonnellier, Xavier; King, Peter; Sansom, Christopher L.Linear concentrating solar thermal systems offer a promising method for harvesting solar energy. In this paper, a model for a novel linear Fresnel lens collector with dual-axis tracking capability is presented. The main objective is to determine the performance curve of this technology by means of both experiment and theoretical analysis. A mathematical model including the optical model of the concentrator and the heat transfer model of the receiver pipe was developed. This tool was validated with experimental data collected using a proof of concept prototype installed in Bourne, UK. The performance curve of the collector was derived for temperatures between 40 °C and 90 °C. The results show that the global efficiency of the collector is limited to less than 20%. The energy losses have been analysed. The optical losses in the lens system accounts for 47% of the total energy dissipated. These are due to absorption, reflection and diffraction in the Fresnel lenses. Furthermore manufacturing error in the lens fabrication has to be considered. One third of the solar radiation collected is lost due to the low solar absorptance of the receiver pipe. Thermal radiation and convection accounts for 6% of the total as relatively low temperatures (up to 90 °C) are involved. In order to increase the performance of the system, it is recommended to install an evacuated receiver and to insulate the recirculation system. Considering data from manufacturers, these improvements could increase the global efficiency up to 55%. Utilising the results from this work, there is the intention of building an improved version of this prototype and to conduct further tests.