Dissertations / Theses on the topic 'Solar heating'

This report describes the process of a thesis implemented in Colombia concerning solar energy. The project was to install a self-circulating solar heating system, as well as creating exchange of knowledge regarding renewable energy. One of the two major goals of the project was to achieve a functioning solar heating system in Timbio, a village outside the city of Popayán in south west Colombia. The purpose was to use the free power from the sun and show people how to use it in a way that is not complicated or too expensive. The second major goal was to hold workshops about renewable energy in general, and solar energy in particular. The preparatory work started in October 2010 by concretizing the project, applying for scholarships and establishing necessary contacts; both in Colombia and Sweden. Research and correspondence continued throughout 2011, along with the search for finance from companies and funds to cover the project costs. The implementation took approximately three months and was finished in April 2012. However, the project was limited due to time scale and financial resources. The project was successful; a functioning solar heater and workshops. The aim to arise interest for renewable energy is fulfilled plus the aim to show how to use solar energy in a practical and useful way.
Denna rapport beskriver processen av ett examensarbete som behandlar solenergi, implementerat i Colombia. Projektet innebar en installation av en självcirkulerande solvärmeanläggning, och även kunskapsutbyte om förnybar energi. Ett av de två huvudmålen var att installera en fungerande solvärmeanläggning i byn Timbio utanför staden Popayán i sydvästra Colombia. Syftet var att använda gratis energi från solen och visa människor hur man kan använda energin på ett inte alltför komplicerat eller dyrt sätt. Det andra huvudmålet var att hålla workshops om förnybar energi i allmänhet och solenergi i synnerhet. Förberedelserna började i oktober 2010 genom konkretisering av projektet, stipendieansökningar och skapandet av nödvändiga kontakter; i Colombia och Sverige. Efterforskningar och korrespondens fortsatte under 2011 samtidigt som finansiering till projektet söktes från företag och fonder. Installationen tog ungefär tre månader och färdigställdes i april 2012. Projektet begränsades av tillgänglig tid och ekonomiska resurser. Projektet blev framgångsrikt; en fungerande solvärmeanläggning och lyckade workshops. Målet att väcka intresse för förnybar energi uppfylldes, även målet att visa hur solenergi kan användas på ett praktiskt och användbart sätt.

As a part of Fortum's vision of a future Solar Economy, a feasibility study of a Solar District Heating facility was conducted. The focus of this study was to determine the technical, economic and environmental potential of a Solar District Heating facility, combined with a seasonal thermal storage, in the district heating network in Stockholm. Three different cases have been studied. The cases differ on the size of the available land area, on what type of storage technology utilized and if excess heat from different production facilities in the network is included or not. The results indicate that it is technically possible to implement a Solar District Heating facility in Stockholm, no obvious limitations in the network has been identified. The thermal storage should preferably be charged throughout the year and be discharged during December to March. The economic results indicate that none of the studied cases are economically feasible without any subsidies, increased revenues or other reductions of initial investment costs. The most economically beneficial system configuration was to utilize a smaller land area for solar collector installations, include excess heat from local production facilities and to utilize existing rock caverns and infrastructure in the area. The Solar District Heating facility could decrease the climate impact and the net primary energy use compared to the production of a biofuel production facility, but a further study is needed.

This report includes development of an already designed solar water heater. The product shall be constructed in a way that it will suit a manufacturing line in Kampala, Uganda. To find the most suitable design for each area a research was carried out which included study visits, interviews and background reading. It provided the following results: Regarding the attachment of in- and outgoing pipes from the water tank many methods were taken into consideration and it was found that the best and most suitable way for this case is to weld the fittings using a weld robot. Regarding the fitting of the acrylic, a suitable solution is to make a flange when vacuum forming the plastic casing to further support the design. This could also be used to waterproof the case by using a sealing material. A suggestion of using pre-molded PU-foam is also presented. Regarding the ability to open the case for maintenance, two solutions were recommended. Either the use of spire clips or having the clips integrated into the casing. Regarding the calculation of material usage when deep drawing the tank and collector, it is possible to do a reasonably accurate assumption. The complicated design in this product makes the estimation less accurate. It is recommended that test draws are done and often the machine producer has more precise numbers. Regarding the coloring of the collector; chemical coloration is not possible on a galvanized surface. The method used is painting, either with powder coating or with wet paint.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 1990.
Thesis Advisor(s): Titus, Harold A. Second Reader: Michael, Sherif. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Descriptor(s): Heat Transfer, Theory, Theses, Costs, Heating Elements, Fluid Dynamics, Photovoltaic Effect, Solar Heating, Swimming, Optimization, Installation. DTIC Identifier(s): Swimming Pools, Solar Heating, Photovoltaic Supplies, Filter Pumps, Theses. Author(s) subject terms: Optimization, Solar Heating, Photovoltaics. Includes bibliographical references (p. 57). Also available in print.

Thesis (MTech(Chemical engineering))--Cape Technikon, Cape Town, 2000
The demand for pool heating has increased dramatically over the last few years. This is ascribed to the idea that a swimming pool is expensive and can only be used for four months of the year. Therefore, a need for a relatively inexpensive solar heating system, capable of heating pool water to comfortable temperatures for an extended period, does exist. The least expensive solar heating system for swimming pool heating on the market in South Africa is in the order of R 11000. This is a fixed system, usually mounted on the roof of a house. In order to ensure the safety of minors, a safety net or sail must be installed. This is an additional cost, which approximates R1500, yielding a total cost for safety and heating in the order of R 12500. Copper pipes packed in black material are utilised in these conventional heating systems, and it is the cost of this good heat conductor that makes these units expensive. In this study an alternative pool heating system constructed of PVC was investigated. The system is designed to be flexible, mobile, act as a safety mechanism and absorbs the maximum amount of solar energy available. Dark blue material as opposed to black PVC was selected for aesthetic reasons at the expense of maximum efficiency. The material strength was tested as well as the strength of adhesion. The influence of factors such as exposure to the sun and the effect of water containing chlorine and acid on the material were evaluated. Also, various means of channelling the water through the system for increased efficiency was investigated. A pilot model was constructed and its performance evaluated. It has been concluded that the alternative approach provides effective heating at a lower cost than current systems. Also, the durability of the design was found to be acceptable.

Water has been heated with the sun has almost as long as there have been humans, but itis not until recently that more advanced and effective solar water heating systems havebecome common, and they are still gaining ground. Through the years new systems andnew solar collectors have been developed. In Kosovo, however, not much attention hasbeen paid to replace fossil fuels with renewable energy sources and solar water heatingsystems is a new concept.The United Nations Development Programme (UNDP) in Kosovo is working on a projecton sustainable development in Dragash Municipality in southern Kosovo. A solar waterheating system has recently been installed at the hospital in Dragash, as part of the UNDPproject. The system is a pilot project, to see how well solar energy can be used in thisarea.The existing solar water heating system at the hospital in Dragash was examined andevaluated. The possibilities of using the fundamental principle of the solar water heatingsystem at the hospital on residential houses in Dragash were looked into. Six prototypesof average residential houses in the village of Brod and Dragash Town were created. Thesolar collector size and storage needed to meet the demands for the six house prototypeswere calculated. Information on the incoming solar irradiation for each hour of a year wasobtained from the online service SoDa Solar Radiation Data. The total annual incomingsolar radiation for one square meter was calculated.The environmental, social and economic effects of solar water heating in Dragash wereconsidered and discussed. Rough economic calculations were made on the effects ofinstallation of solar water heating systems.The solar water heating system at the hospital in Dragash is a good pilot project, and islikely to work satisfyingly. The annual output effect of the system is approximately 7 400kWh. The fundamental principle needs to be altered to work on residential houses. Thesolar collector needs to be of a cheaper kind, and the collector and storage tank can be ofsmaller dimensions.Solar water heating can contribute to Kosovo’s work toward sustainable environmental,social and economic development focusing on hot water supply. Kosovo has sufficientsolar radiation for solar water heating systems to work in a satisfactory way. The outputeffect for a solar water heating system in Dragash is around 390 kWh/(m2∙year) with atotal efficiency for the system of 30%. If the solar water heating system replaces heatingby electricity the annual savings can be 31 €/m2 solar collector. The biggest obstacles forthe use of solar energy are the public’s lack of knowledge on solar water heating andenvironmental problems connected to energy, as well as economy.The work done in this thesis is a good foundation for future research on solar energy inKosovo. It can be extended and elaborated with more thorough economic calculations,since economy is an important factor in the future for solar energy. Only roughcalculations were made in this thesis, since it has a technical approach. More extensiveresearch could also be done to evaluate the possibilities of using solar water heating forspace heating.

Varmvatten har värmts med hjälp av solen nästan så länge det funnits människor, men detär inte förrän nyligen som mer avancerade och effektivare solvärmesystem har blivitvanliga, och de blir allt vanligare. Genom åren har nya system och nya solfångareutvecklats. I Kosovo däremot har inte mycket uppmärksamhet ägnats åt att ersätta fossilabränslen med förnyelsebara energikällor, och solvärme är ett nytt koncept.FN:s utvecklingsprogram (UNDP) i Kosovo arbetar med ett projekt med målet hållbarutveckling i Dragash kommun i södra Kosovo. Ett solvärmesystem har nyligeninstallerats på sjukhuset i Dragash, som en del av UNDP:s projekt. Systemet är ettpilotprojekt för att se hur bra solenergi fungerar i det här området.Det befintliga solvärmesystemet på sjukhuset i Dragash undersöktes och utvärderades.Möjligheterna att använda grundprincipen för solvärmesystemet på sjukhuset påbostadshus i Dragash undersöktes. Sex prototyper för genomsnittliga hus i byn Brod och iDragash centrum togs fram. Solfångararean och ackumulatortanksvolymen som krävs föratt klara behoven för de sex husprototyperna beräknades. Information om solinstrålningenför varje hus erhölls från SoDa Solar Radiation Data. Den totala solinstrålningen på enkvadratmeter beräknades.De miljömässiga, sociala och ekonomiska effekterna av solvärme i Dragash diskuterades.Ekonomiska överslagsberäkningar gjordes på effekterna av installation av solvärme.Solvärmesystemet på sjukhuset i Dragash är ett bra pilotprojekt, och är sannolikt attfungera tillfredsställande. Den årliga energi som systemet kan ge kommer att vara ungefär7 400 kWh. Grundprincipen behöver ändras för att fungera på bostadshus. Solfångarnabehöver vara av en billigare typ, och storleken på solfångare och ackumulatortankbehöver vara mindre.Solvärme kan bidra till Kosovos arbete mot hållbar miljömässig, social och ekonomiskutveckling med fokus på varmvattenbehov. Kosovo har tillräcklig solinstrålning för attsolvärmesystem ska fungera tillfredsställande. Med en totalverkningsgrad på 30 % för ettsolvärmesystem kan systemet ge ungefär 390 kWh/(m2∙year). Om systemet ersätteruppvärmning med el kan de årliga besparingarna bli ungefär 31 €/m2 solfångare. Destörsta hindren för användning av solenergi är allmänhetens brist på kunskap om solvärmeoch miljöproblem kopplade till energi, samt ekonomi.Arbetet i detta examensarbete är en bra grund för fortsatta studier om solenergi i Kosovo.Arbetet kan vidgas och utvecklas med mer ingående ekonomiska beräkningar, eftersomekonomi är en viktig faktor i framtiden för solenergi. Endast överslagsberäkningar gjordesi detta examensarbete, eftersom det har ett tekniskt förhållningssätt. Mer omfattandestudier kan också göras för att utvärdera möjligheterna ätt använda solvärme föruppvärmning av bostäder.

With the ever-growing energy demand that world is currently going through and the danger of climate change around the corner, wagering in renewable energy seems to be the right path to create a more smart and green future. Sweden has put great effort on decreasing its dependency on oil, in fact in 2012 more than 50 % of its electricity came from the renewable source and has a plan in making it 100 % in 2040. However, when it comes to heating systems Sweden depends greatly on district heating, and situations which buildings are located outside the district heating system’s reach is not uncommon, hence for those buildings, other options such as solar power or heat pumps are considered. Many buildings located in Skutskär suffer from the problem stated above. The particular building analyzed in this thesis uses electrical radiator and furnace as sources of heat, which implies high energy uses and financial expenses. For this reason technical and financial analysis of using each alternative system for a single family house located in Skutskär had been done. Using solar powered system is deemed to be quite ineffective, as Sweden has poor solar radiation. In order to compensate the poor sun hours during the winter, 51 photovoltaic (PV) panels or 19 solar thermal panels would be required. This high initial investment needs long period of time in order to be profitable, 15 years for solar thermal system and 21 years for solar PV system. On the other hand, the results from the heat pumps are quite satisfactory, the fastest payback period is around 4 years. This is achieved by using air source heat pump (ASHP), the annual saving in this case is three times higher than using solar photovoltaic panels, making the usage of ASHP more attractive than any solar energy system. However, when annual saving is concerned, the ground source heat pump (GSHP) system is capable of generating even higher saving, but the initial investment is significantly higher, extending the payback period to 6 years.

Passive solar gains to buildings in North European Climates can be significant and an investigation is made into the effect of orientation upon solar gains based upon known weather data. The conservatory is a particularly useful collector because of its inclusion to existing houses and its desirability to the householder for reasons other than solar collection. A conservatory was adapted and monitored. A computer model was written. The behaviour of the conservatory was examined for various criteria. The possibility of inclusion of a conservatory into houses in the existing housing stock was examined. The effect of occupancy on heating demand and solar delivery was reviewed and the likely overall energy saving was examined. A new house system was developed including the use of a first floor concrete slab and a gas warm air heating unit. A concrete floor slab was cast to examine its storage potential. A preliminary design for the heating system of the new houses was undertaken.

The performance of three types of passive solar feature has been studied; fifteen Roof-Space Collectors on an estate of low energy houses at the Milton Keynes Energy Park, 101m2 of Thermosyphoning Air Panels at a county primary school in Nazeing, Essex, and three Thermosyphon Solar Water Heaters installed on a group of three terraced cottages at Cranfield, Bedfordshire. Each of these passive solar features was monitored intensively for at least one heating season using dedicated data-acquisition systems. The maximum specific annual solar contributions to the auxiliary space/water heating systems were 128 kWh/M2 , 78 kWh/M2' and 104 kWh/M2 respectively. The corresponding payback periods were 25,37 & 21 years respectively, on replication.

The development of products which enable passive solar-energy air-heating to be integrated into the heating strategies of public, commercial and industrial buildings is described. These buildings are, in general, only occupied significantly during the day; consequently the bulk of heating demand coincides with the period of solar gain. In these circumstances collected solar heat should be delivered with the minimum of delay. The design and operation of units which are capable of supplying solar heated air in this manner is outlined. These are passive, naturalcirculation air-heating collectors, also known as natural-convection air-heaters, or thermosyphoning air panels. Four methods of retrofitting such solar collectors to non-domestic buildings have been identified, one of which, the overcladding collector, has not been proposed previously. Problems associated with the successful installation and operation of these units have also been considered. The relative merits of a number of methods of testing passive solarenergy air-heating collectors have been investigated. A method of determining instantaneous collector efficiency based on the measurement of glazing temperature, inlet and outlet air temperature, ambient temperature and insolation has been developed. Three novel design proposals have been presented: i) a collector constructed with the insulation fitted outside, rather than inside, so that the metal body of the collector may provide more symmetrical heating of the air flow than the conventional arrangement, ii) an absorber which consisted of parallel ducts to increase the rate of heat transfer to the air, heating it symmetrically, (iii) a hinged air-deflector for conversion from the heating to the ventilation mode.

Solar energy constitutes one of the main alternatives for facing the energy problems of the future, taking into account the foreseeable depletion of the fossil fuels. Transpired solar air collectors are relatively simple alternatives, which do not need a continuous supervision and are mostly maintenance free. Their life cycle is relatively high, around 25 years, and the total investment can be fully recovered in the short-term. The aim of this master’s thesis is to analyze the feasibility of installing transpired solar air collectors as secondary systems in big industrial buildings, for heating purposes. The collectors would be designed for compensating the heat losses of a building which is mainly heated up by a heat pump system. Precisely, this work tries to evaluate the profitability of installing these collectors in Gävle, taking into account the particularities of this location in the considered study. This project work is focused on testing if these systems can provide enough thermal energy for heating up big-sized industrial buildings. For this purpose, firstly, the heat demand of the building for each month was calculated; secondly, the maximum output from the collector was estimated, using WINSUN simulator; and, finally, the energy difference that had to be covered by the main system was calculated. Once this was done, the yearly running cost for the main system and the total investment for the transpired air solar collector were estimated. Due to the lack of experimental data, the obtained results can only be taken as approximations. All the calculations and estimations have been made using WINSUN, a simulator that has been configured according to the particularities of the project. The results show that the solar collector provides a total thermal output of 29.700 kWh/year (system which has a total investment of 77.000 SEK). The total heat demand of the building is estimated to be of 87.100 kWh/year, being 51.800 kWh/year fulfilled by the heat pump system (which has a yearly running cost of 24.000 SEK/year). The collector has an average efficiency of 51,04%.

The model of Heyvaerts and Priest (1992) for steady-state heating of the turbulent medium within a sheared solar coronal arcade structure is here developed. The energy input into the corona is calculated at the large scales of the model. At the smaller scales the effects of coronal turbulence are modelled in the form of an enhanced turbulent viscosity and magnetic diffusivity, which are related to the injected power density in the steady state. Matching the expressions for the injected and dissipated power enables the calculation of a heating power consistent with both boundary motions and turbulent effects with a minimum of arbitrary parameters - the price to be paid is that the inertial range spectrum must be prescribed and imposed at all scales. While it is capable of reproducing the observed levels of coronal heating (300 Wm−2 3x105 erg cm−2 s−i for the quiet Sun, 800 Wm−2 (8 x 105 erg cm−2 s−i) for a coronal hole and 104 Wm −2 (107 erg cm−2 s−i) for an active region (Withbroe and Noyes, 1977)), there are some mathematical and physical difficulties present. These are eliminated as far as is possible and it is found that the final results for heating levels differ little from the original model although there is a much greater consistency between the imposed and predicted energy power spectra. The modified approach is applied to the problems of photospheric motions twisting a coronal flux tube and of rapid motions injecting Alfven waves into an arcade. In the former case comparable levels of heating are obtained. For a driven and damped standing wave, however, desired levels of heating are only obtained when a global resonance occurs. Attempts are also made to find similar steady-state equilibria possessing flow for fusion experiments in order to apply the above procedure to investigate turbulence in laboratory plasmas. This has been hampered by the difficulty in finding simple appropriate equilibria with many scales present.

The problem of how the Sun's corona is heated is of central importance in Solar Physics research. In this thesis, a model is constructed of a typical coronal magnetic loop in order to investigate the response of coronal plasma to a time-dependent heating source. It is not the aim of the research to study in detail a particular heating mechanism but rather to understand the important features arising from time-dependent heating in general. A time-varying energy input into the coronal loop is required because it is likely that none of the suggested theoretical heating methods can provide a constant supply of heat to the corona. The magnetic field is taken to be strong enough that the loop dynamics reduce to a one-dimensional problem along the field. In addition, it is assumed that the radiative timescale in the corona is much longer than the sound travel time and thus, the plasma evolves isobarically. The thermal equilibria profiles along the coronal loop are then investigated for a simplified form of the optically thin radiation. Initially, a heating function that displays a regular, sinusoidal variation in time is introduced and it is found that there is a critical heating frequency above which a hot coronal loop solution can be maintained and below which the plasma temperature cools to chromospheric values. Pulse heating and the deposition of random-sized energy quanta in a loop are also investigated. An evaluation of the isobaric assumption to the corona is presented by allowing sound waves to propagate back and forth along the loop. It is found that the system can exhibit isobaric-like behaviour provided the acoustic timescale is short enough. Possible extensions of the developed loop model are discussed as well as the implications of time-dependent heating upon observations from the SOHO satellite.

The aim of this thesis is to study the energy performance of a building integrated heating and cooling system. The research objectives are to investigate the system operating characters, to develop mathematical models for the heating and cooling systems, to demonstrate the technologies experimentally, to identify the best designs for a combined system and to investigate the cost effectiveness of the system. The main components of the systems are the aluminium plate façade and the building wall behind it, these form a plenum between them and the air is then heated or cooled as it flows through this plenum. Mathematical models were developed based on the energy balance equations and solved by matrix inversion method. These models were then validated with experimental results. The experiments were carried out in the laboratory with a facade area of 2m2. Two designs of facade were tested, i.e. flat and transpired plates. Results showed that the transpired design gave better thermal performance; the system efficiency for the flat plate was only about 30%, whereas it was about 85% for the transpired plate. On the other hand, a cooling system with double plenums was found to be better than a single plenum. Thus, a transpired plate with two plenums was identified as the best design for space heating and cooling. The cooling efficiency was nearly 2.0 even at low solar radiation intensity. A simulation study was carried out by assuming a 40m2 of façade was installed on an office building in London. The yearly energy saving was estimated as 10,877kWh, which is equivalent to 5,874kgCO2/year of emission avoidance. The system is calculated to cost about £70/m2, and for a discount rate of 5% and 30 years of lifetime, the payback period for this system would be less than a years.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Esta dissertação analisa aspectos da utilização da energia solar para aquecimento de água. Dois são os aspectos abordados: O primeiro é quanto à utilização de valores médios mensais ou diários de temperatura e insolação utilizados por diversos métodos de dimensionamento ou simulação de sistemas de aquecimento solar, e o segundo é a utilização de múltiplos tanques de armazenamento de água quente ao invés de um único reservatório de maior volume. Assim, este estudo tem como objetivo formular, simular e analisar diferentes cenários de configurações de sistemas de aquecimento solar de água, variando-se o número de reservatórios térmicos para um mesmo volume total do sistema. Tem-se por finalidade atender um mesmo padrão de consumo de água quente, condicionado a um mesmo perfil climático, visando otimizar a contribuição da energia solar ao sistema e consequentemente minimizar o consumo de energia auxiliar elétrica.
This dissertation examines aspects of the use of solar energy for water heating. Two aspects are handled: The first is regarding the use of average monthly or daily values of temperature and insolation used by different scaling methods or simulation of solar water heating systems, and the second is the use of multiple hot water storage tanks instead of a single larger volume reservoir of water. Thus, this study aims to formulate, simulate and analyze different configurations of solar water heating systems scenarios, varying the number of thermal reservoirs for the same total volume of the system. It intends to satisfy the same standard of hot water consumption, under same climatic conditions to optimize the contribution of solar energy to the system and consequently minimize the consumption of electric auxiliary energy.

This thesis consists of two parts, one dominating part concerning spectrally selective solar absorbers and one dealing with thermal solar systems. The appended papers I to VIII concern the solar absorber part, papers dealing with the systems part have not been included in the thesis.

A new spectrally selective absorber derived from a novel solution-chemistry method has been developed and optimized. The main objective was to investigate the potential of the spectrally selective surface. Some of the questions at issue were; would it be possible to create a suitable absorber composite using this method, how high selectivity could be obtained, could the performance be enhanced by using anti-reflection coatings, which was the optimal layer composition, would the thin films be durable and what was the structure and morphology like on a nano scale? The absorber consists of absorbing thin films of nickel nano-particles embedded in a dielectric matrix of alumina and an overlying anti-reflection film consisting of one of the following materials silica, hybrid-silica, alumina or silica-titania. Solution and sol-gel chemistry were used in the process. The thin films were spin-coated onto an aluminum substrate followed by a heat-treatment that generated the multi layer selective solar absorber.

The optical constants for the thin film materials in question were determined. An optimal three layer structure was modeled using the experimentally determined optical constants. The theoretical three layer stack was experimentally confirmed and achieved a solar absorptance of 0.97 and a thermal emittance of 0.05 which definitely are commercially competitive values. The configuration of the three layer stack is: an 80%nickel-20%alumina film at the base, a 40%nickel-60%alumina film in the middle and a silica or hybrid-silica film at the top. The three layer absorber was subjected to high temperature and condensation accelerated ageing tests designed by IEA Task 27. The condensation test did not degrade the absorber whatsoever but the high temperature test did reveal some oxidation of the nickel particles. The oxidation occurs initially and then stops. A formed nickel-oxide layer hinders further oxidation. The level of oxidation is small and the absorber is qualified according to the IEA Task 27 test procedure.

Sri Lanka is one of the greatest producers and exporters of quality tea in the world. The tea industry plays a key role in the economy and there is a great interest of continuously improving it in order to stay competitive. The process of drying tea requires thermal energy which currently is supplied through combustion of fuel woods on which the industry is highly dependent. With the rising prices on fuel woods over the past recent years it has become increasingly urgent to find substitutes, or complements to this source of energy. One potential solution would be to utilize solar thermal energy by implementing solar collectors in the tea manufacturing process. Sri Lanka is located close to the equator and has ideal conditions for harnessing solar energy, why solar applications would be highly suitable in this context. This report aims to study an existing simple system of flat plate solar collectors at the University of Peradeniya, Sri Lanka. The solar collectors are built using local inexpensive material. The objectives are to calculate the collector efficiency and perform a cost analysis in order to determine the potential economic benefits of utilizing solar thermal power as opposed to fuel woods. Finally the report will present suggestions on improvements for the existing collector design, taking the practical and economic feasibility into consideration. The collector efficiency of the existing design was calculated to be approximately 35 % and the energy produced by the flat plate solar collectors was found to be less expensive than combustion of fuel woods, despite the many imperfections of the collector design. Suggestions on refinements include improving the selectivity of the absorber surface with a black chrome coating, equipping the collector with a sun-tracking system, adding obstacles in the collector air duct, using a v-corrugated absorber plate, shifting to downward air blowing, changing heat transfer fluid and using multiple sheets of glass as glazing. Through these relatively simple and cost-effective improvements on the system the collector efficiency could increase substantially, thereby reducing energy costs. Moreover the implementation of solar collectors in the Sri Lankan tea manufacturing process would be beneficial from an environmental perspective.

Sustainable Built Environments Senior Capstone
In today’s society we are faced with many problems that result from the use of traditional energy sources. Due to the lack of efficient alternative energy sources we are consistently trying to produce technologically advanced methods and tools to offset our dependency on traditional energy systems that are harming the planet as a whole. Every great accomplishment needs a starting point. The University of Arizona is going to an influential success story that gets the ball rolling. Implementing two energy saving tools known as photovoltaic panels and thermal water heating units will allow advocates to see the benefits that can come from sustainable technology. Through state and federal incentives solar panels are able to pay themselves off over the years in a majority of the states. Without federal or state incentives, the solar panels would not save the consumer enough money to repay their initial investment. Thermal water heating units save the consumer enough money to pay themselves off over the years. Overall both thermal water heating units and photovoltaic panels provide a clean source of energy.

In this report we will model a heat system consisting of a heat storage tank and an application. The heat storage tank is supplied by a heating element and heated water from a solar collector. The main objective of the heat system is to mainatian a reference temperature in the application (a house). Weather forecasts will be used as weather data affecting the heat system. We will assume that the weather forecasts and the actual weather will be the same. The heat sytem will consist of simplified nonlinear differential equations and be controlled by a model predictive controller (mpc). The mpc controller will use a linearized model of the nonlinear process. The average predicted outside temperature from the weather forecasts will be used as nominal value for the same temperature in the linearized model in the mpc controller. The mpc controller will measure some disturbances to make more efficient control. The most imortant disturbance will be the temperature of the water coming out of the solar collector, that will flow into the heat storage. By measuring this temperature, the mpc controller can apply it to its predictor and make sure that the power of the heating element in the heat storage is reduced when solar collector heated water is available. This is to make sure that the heat storage has enough capacity to receive the heated water from the solar collector, while still maintaining a reasonable temperature in the heat storage. Simulation with different weighting of the inputs in the mpc controller will show that heating element power consumption is influenced by these weights.

Firstly, we present reviews of the background atomic, magnetohydrodynamic, and solar, physics involved in the analysis of the problem. We proceed to produce a time dependent code to calculate the Ionisation state distribution of Iron and of Argon, using some of the recent data for Ionisation coefficients by Arnaud & Raymond (1992), and Fournier et al. (1997, 1998). We also look at some data for the excited ionised states using the Chianti database amongst others. Taking the engine developed, we continue by applying it to a three stage nanoflare simulation for the heating, spanning a 2000km range. This model is drawn from various previous models developed in the literature. We look for the indications of the non Local Thermodynamic Equilibrium (LTE) processes via the concept of "signature ions". By this we mean the presence of highly charged ions which would not be expected if the temperature were simply constant and everywhere was in LTE. We make a calculation of the actual experimental line of sight results that we would obtain, if we were to take Emission Measure calculations to ascertain the Ionisation distribution within the Solar Atmosphere. We also take a look at the problem of Diagnostics based on Emission Measure Analysis, and investigate the fundamental nature of the Inversion Problem. Simply stated, it is difficult to obtain the differential emission measure (DEM) of the Transition Region because the only information that we have available to us is the intensity of spectral lines emitted from the Sun. This consists of the integral of the DEM convolved with a function representing the physics of the transition. The problems associated with the inversion of the integral, form much of the discussion together with the philosophical implications of using phenomenology as an alternative.

This study examines a suggested system solution consisting of flat plate solar thermal collectors in combination with a ground-source heat pump for building heating and cooling, and production of domestic hot water. The solar collectors are intended to constitute a part of the roof construction. The system design is suggested as an energy solution for a 202 m2 single-family demo dwelling of Zero Emission Building standard. The demo project is a collaboration between Brødrene Dahl and the Research Centre on Zero Emission Buildings. The dwelling will be constructed in Larvik in South Norway.A parametric study of the main design and operation parameters were conducted in order to find the optimum values which would result in the lowest total electricity use in the system. The design and operating parameters which were optimized included collector area, orientation and tilt angle, fluid type for both collectors and ground-source heat exchanger, collector mass flow rate, storage tank design, heat exchanger effectiveness, collector heat loss, design of ground-source heat exchanger, control settings, supply air and zone set point temperature, supply air volume flow rate, night setback control and heat distribution temperature. The optimum values were determined by using the dynamic simulation software tool IDA Indoor Climate and Energy 4.6. Scenarios with different configurations of optimized design and/or operating parameters were developed in order to investigate the effect of optimizing few, several or all of the components in the system, thus finding the composition which resulted in the lowest electricity use. As the marginal cost of expanding the solar collector area is relatively small compared to the system cost, the share of utilized renewable energy for space heating and domestic hot water was investigated for the optimized scenario with both 8 m2 and 16 m2 of installed solar collector area. The results showed that by optimizing the design of the storage tanks, a 5 % reduction in electricity use was achieved. Optimizing the tilt angle, orientation and heat loss coefficients of the solar collectors resulted in a 4 % reduction in electricity use. The results revealed that changing the operating parameters had the greatest effect on the electricity use relative to parameter changes. A total reduction of 7 % was obtained by optimizing the main system operating parameters. With all main design and operating parameters optimized, a total reduction of 18 % in electricity use was obtained with 16 m2 of solar collector area installed. A total reduction of 14 % in electricity use was obtained with 8 m2 of solar collectors installed. Without optimizing the solar collectors, a total reduction of 14 % was obtained with a collector area of 16 m2. The highest amount of renewable energy covering the total heating load was obtained with 16 m2 of solar collector area installed and all main design and operating parameters optimized. It was found that 85 % of the total heating demand was covered by renewable energy. The results showed that by utilizing solar energy the optimized system could provide 85-92 % and 12-70 % of the domestic hot water demand in summer and winter respectively, and 2.5-100 % of the space heating demand. It can be concluded that by installing a larger solar collector area in combination with a ground-source heat pump, a higher share of utilized renewable energy as well as a higher reduction in delivered energy is obtained. By tilting and orientating the solar collectors towards optimum directions, half the solar collector area is needed in order to obtain the same result as if the solar collector tilt angle and orientation are not optimized.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 193-198).
In this thesis, we examine the effects of tidal dissipation on solid bodies in application and in theory. First, we study the effects of tidal heating and tidal evolution in the Saturnian satellite system. We constrain the equilibrium heating of Enceladus to be less than 1.1(18000/QS) GW, where QS is the tidal quality factor of Saturn. The constraint on the heat flow is calculated from simple conservation of energy and angular momentum arguments and does not depend on the internal parameters of the satellites. We then look for dynamical disequilibrium by constructing a resonance model, tested by n-body integrations, to establish a consistent resonance history for Mimas, Enceladus, and Dione. We find that Enceladus is at or near equilibrium in its current 2:1 mean motion resonance with Dione. We also look for thermal disequilibrium using the oscillation model of Ojakangas and Stevenson (1986) [Icarus 66, 341-358]. We find that Enceladus does not experience oscillations in heat flow for any choice of parameters. We conclude that the most likely explanation for Enceladus' anomalous heat flow is a QS lower than 18,000, which implies either time or frequency dependent dissipation for Saturn. Next, we create a coupled thermal-orbital model for the early evolution of the Moon. We compute the tidal heating in a dissipative lid overlying a magma ocean and the associated tidal evolution of the lunar orbit. We find that moderately high orbital eccentricities can be obtained, but show that the nonhydrostatic shape of the Moon cannot be explained by the shape solution of Garrick-Bethell et al. (2006) [Science 313, 652-655]. First, the orbit corresponding to the shape solution cannot be reached without stretching the tidal dissipation in the Earth to unphysically large values. Second, we show that the Moon will either crack or deform following the epoch of the shape solution and cannot maintain the shape until the present. We continue our study of the Moon by considering the evolution of the precession of the lunar core as the Moon tidally evolves in its orbit. Early on in the Moon's history, we show that inertial coupling will force the spin axis of the core to precess along with the spin axis of the mantle. The coupling precludes a lunar dynamo before the Moon reaches a semimajor axis of 26.0-29.0 Earth radii. We also note that the Cassini transition happens after inertial coupling has weakened enough to allow the core to precess independently. The time of the Cassini transition is therefore a promising epoch for the existence of a powerful lunar dynamo. Finally, we present a new formulation of tides on solid bodies. Tidal deformations are modeled as the excitation of elastic modes. We derive general expressions for tidal heating, despinning, semimajor axis change, and eccentricity change for zero-obliquity bodies with a perturber on a non-inclined, eccentric orbit. We then specialize these equations to the constant time lag model and confirm our theory using the classical expressions.
by Jennifer Ann Meyer.
Ph.D.

The million-degree temperature of the solar corona might be due to the combined effect of barely distinguishable energy releases, called nanoflares, that occur throughout the solar atmosphere. Unfortunately, the high density of nanoflares, implied by this hypothesis, means that conclusive verification is beyond present observational capabilities. Nevertheless, it might be possible to investigate the plausibility of nanoflare heating by constructing a magnetohydrodynamic (MHD) model; one that can derive the energy of nanoflares, based on the assumption that the ideal kink instability of a twisted coronal loop triggers a relaxation to a minimum energy state. The energy release depends on the current profile at the time when the ideal kink instability threshold is crossed. Subsequent to instability onset, fast magnetic reconnection ensues in the non-linear phase. As the flare erupts and declines, the field transitions to a lower energy level, which can be modelled as a helicity-conserving relaxation to a linear force-free state. The aim of this thesis is to determine the implications of such a scheme with respect to coronal heating. Initially, the results of a linear stability analysis for loops that have net current are presented. There exists substantial variation in the radial magnetic twist profiles for the loop states along the instability threshold. These results suggest that instability cannot be predicted by any simple twist-derived property reaching a critical value. The model is applied such that the loop undergoes repeated episodes of instability followed by energy-releasing relaxation. Photospheric driving is simulated as an entirely random process. Hence, an energy distribution of the nanoflares produced is collated. These results are discussed and unrealistic features of the model are highlighted.

We have constructed the thermal structure of Neptune's stratosphere and low thermosphere with pressures between 10⁻³ μbar and 100 mbar using a radiative-conductive model which includes solar UV and EUV heating, non-LTE cooling by hydrocarbon fundamental bands, cooling by H₂ collisional induced opacities, and heating by the CH₄ near and far infrared bands. We have thoroughly investigated the availabilities of different techniques in modeling the CH₄ near-IR bands (3.3, 2.3, and 1.7 μm) and calculating the heating rates of these bands for pressures between 10⁻³ μbar and 100 mbar and temperatures between 50 K to 300 K. We have established an accurate and efficient way which is a combined method of correlated-k model and the Baines et al. (1993) empirical model to calculate these heating rates. The same method can also be applied to any other atmosphere of a Jovian planet. Through comparing the calculated temperature profiles and the measured one of Neptune's upper atmosphere, we have set constraints on the magnitudes, locations and the regions those are extended by for the stratospheric aerosol heating, heating by the source located in the mesosphere and heating by the conducted flux from the thermosphere. We also found that by using a constant CH₄ mixing ratio in the stratosphere of Neptune, 1.3 x 10⁻³, obtained by Yelle et al. (1993) through analyzing Voyager solar occultation data, the measured stratospheric temperatures between 20 to 100 mbar can be best matched by the calculational results.

This thesis reports the results of research into the modelling and simulation of solar water and space heating for Cyprus, and the investigation of the factors concerning the optimisation of such systems. Further a number of design criteria, which can be used by consultants and designers of solar heating systems, have been established. Five solar heating system configurations have been modelled using the component models of the TRNSYS programme. They concern thermosyphon solar water heating systems, active solar water heating systems, solar space heating systems, combined solar water and space heating systems and solar assisted heat pump systems for space and water heating. These models are used to simulate the thermal performance of the systems and investigate their cost effectiveness under the weather and socioeconomic conditions of Cyprus. The results of the simulations have been used to identify the optimum design criteria for such systems in the Cyprus environment. The design criteria that have been established are concerned mainly with the solar collector and the storage tank and they are key design factors for a solar heating system. The design factors include the collector orientation and tilt angle, the collector to load factor which relates the collector surface area to the annual thermal load, the storage factor which relates the capacity of the storage tank to the collector size, the collector water flow flux, which relates the water flow rate through the collector with the collector area, and other criteria, which concern the auxiliary heat supply and the heat exchangers. For space heating systems, in addition to the above factors, a new design criterion is introduced, the collector to floor area factor, which relates the collector area to the building floor area, while for domestic hot water systems, the collector to consumer factor is used to specify the collector surface area needed for each hot water consumer in the building. This work has resulted in the publication of four papers in refereed International Journals and the presentation of three other papers at International Conferences. A list of publications is included in the Appendices.

Due to the environment degradation and threats of the climate change, how to develop the technologies to use renewable energy and improve current energy systems to meet the increasing demand of human activities instead of using fossil fuels are amongst hot issues that being discussed nowadays. Due to the specific weather condition, district heating, which contains space heating and domestic hot water, is needed in Sweden. Solar energy is the most potential and environmental friendly energy resource. It can be utilized in many different aspects. The profitability of building solar heating plant for producing heat to supply the district heating in Sweden was discussed in the thesis. In order to achieve the result, central solar heating plant and solar combisystem were discussed. Information was collected from “Sciencedirect”, some related companies and institutions websites, and etc. Very few solar radiations are available during winter in Sweden, while the demands of district heating are the highest. During summer time, a lot of cities in Sweden can use the industrial waste heat to cover the district heating load, and in some cities where there is no industrial waste heat can operate biomass combined heat and power (CHP) plant to cover the heating load. Combined solar-biomass heating plant could improve the efficiency of biomass heating plant and reduce the unnecessary heat losses. Solar combisystem has a relatively high cost and complex system. The system which is able to supply some hot water for washing machine may have a good future, due to the possibility that the price of electricity in Sweden increases. Large-scale solar heating plants are less attractive in Sweden due to the existence of industrial waste heat and CHP plant that supplied by biomass. Combined solar-biomass heating plant would be a good system to build if there is no available industrial waste heat and biomass heating plant is used to supply the district heating. Due to the current electrical price and the cost of combisystem, it is not that attractive to build this system. In the coming future, if the transportation cost and the price of biomass itself become too high to make the CHP plant no longer cost effective, and the price of the electricity become high, the solar energy will make more contribution to the district heating in the coming future.

Photocatalytic water splitting using solar energy could contribute to the solution of environmental and energy issues related to the hydrogen production. Key research area in this field is the development of photo-catalyst able to provide high energy conversion efficiency. TiO2 has been mostly preferred material as the photo-electrode due to many advantages, mainly related to the cost factor and stability. We have studied on hydrogen production by water splitting in photo-electrochemical cells prepared by using photoanodes made by two different kinds of TiO2: one deposited by RF sputtering and the other one by sol-gel method. Depositions were performed on electrical conducting ITO whose electrical properties plays vital role to reduce the photon energy loss. The photoanodes have been characterised by several techniques to infer on their optical and compositional properties. The observed differences in hydrogen production have been attributed to the peculiarities in absorption properties of the two TiO2 films that in the case of sputter-deposited films are more prone to absorb radiation also because of the produced defects during the deposition process. Metals like Cr and Fe were doped in TiO2 by RF magnetron sputtering and sol-gel methods to increase the efficiency of hydrogen production by water splitting by sensitizing the doped-TiO2 in visible light spectrum. The doping method, dopant concentration, charge transfer from metal dopants to TiO2, and type of dopants used for modification of TiO2 were investigated for their ability to enhance photocatalytic activity. UV-Visible spectra show that the sputter-metaldoped- TiO2 films are much more efficient than the chemically-prepared samples to induce red shift of the absorption edge for absorbing visible light. In addition, we proved that dopant atoms must be located, at low concentration, near the ITO-TiO2 interface to avoid the formation of recombination centers for photo-generated electron-hole pairs. H2 production rate is higher with Fe-doped TiO2 (15.5 μmole/h) than with Cr-doped TiO2 (5.3 μmole/h) because Fe ions trap both electrons and holes thus avoiding recombination. On the other hand, Cr can only trap one type of charge carrier. To increase the light conversion efficiency and reduce the recombination processes of Cr-doped TiO2, a multilayer structure of ITO/Cr-doped-TiO2 (9 at.%) was developed. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Crdoped-TiO2. The enhanced photocurrent is attributed to: 1) higher absorption of visible light by Cr-doped-TiO2, 2) number of space-charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the spacecharge layer by decreasing the Cr-doped-TiO2 layer thickness. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water splitting: we obtained indeed 24.4 μmole/h of H2 production rate, a value about two times higher than that of pure TiO2 (12.5 μmole/h). Similar experiment we performed by doing TiO2 with vanadium metal. With 6-ilayers vanadium doped TiO2 film Shows higher hydrogen production rate of about 31.2 μmole/h. This rate is higher than that of CR doped and pure TiO2. A constant H2 generation rate is obtained for long periods of time by all the investigated TiO2 films because of the separate evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Even Ar+ or N+ ion implantation of energy 30 keV was adopted to vary the energy band gap of TiO2 film in order to absorb visible light.The original anatase phase was not changed by implantation. Increase in full visible absorption range was observed for both kinds of ion implanted-TiO2 films which further increases with the ion fluencies, while N+ ion implantation also causes the shift of the absorption edge from UV to visible light range. N+ implanted TiO2 showed narrowing of band gap from 3.2 eV for untreated anatase TiO2 to 2.78 eV for maximum implantation dose. The Ar+ and N+ implantation creates oxygen vacancies related defect energy level in the band gap. In case of N+ implantation, nitrogen also substitutionally replaces the oxygen atoms thus forming an energy level just above the valence band which further interacts with O 2p states resulting in the narrowing of band gap. The black solar absorber material develop over the copper target to absorb concentrated solar radiation and supply heat to the surrounding water. A black copper oxide layer was synthesized over copper substrate by using chemical oxidation treatment. We varied several treatment parameters and optimized the best condition to obtain a black textured layer which has the properties to absorb total solar radiation. The untreated polished copper showed 50 to 60 % reflectance (R) (incidence angle of 15o) and this value decreases to almost zero for whole wavelength range after formation of black copper oxide. The percentage absorption decreases by negligible amount as the angle of incidence increases. The SEM images of the copper oxide layer at high magnification showed a nano-petal like structure which causes the surface texture effect for higher absorption where surface irregularities such as grooves and pores with dimensions similar to the wavelength of the incident radiation simply increase the solar absorptance by multiple reflections. Long time thermal stability and corrosion resistance in hot water was also studied for the copper oxide film. The results revealed that the copper oxide was very stable and showed no changes in optical properties after the test. For the same water heating system a quartz window is used through which the solar radiation is transmitted on the copper target. Thus to acquire high power conversion efficiency it is necessary for quartz window to transmit the entire solar radiation incident on it without much lost due to the reflection on the surface. In general quartz window is able to transmit 90-91 % of the solar radiation while 1-2 % is absorbed and 7-8 % is reflected from the surface. Thus to have nearly complete transmittance it is necessary to cover the surface of quartz window with anti-reflecting (AR) coating: this was the part of my work. We developed single-layer and multi-layer AR coating for single specific wavelength and broad-band wavelength range respectively. Low reflective index material like MgF2 is deposited by e-beam technique to obtain single-layer AR coating. While Al2O3 and ZrO2 layers deposited, by RF-magnetron sputtering, on top of MgF2 forms multi-layer AR coating. The combination of MgF2/ZrO2/Al2O3/MgF2 deposited on both side of quartz showed excellent results with reflectance value of around 0.8% in broad spectral range. The heat exchanger efficiency obtained after using these developed black copper oxide absorber material and AR coating is around 83 % which seems to be significantly higher than the other commercially available water heating system. Concentrating solar power (CSP) systems are utilized to convert sunlight to thermal electric power by using solar absorber. However, the solar absorber are operated at elevated temperature (700-800 oC) and should be spectrally selective to act as perfect absorbers over the solar spectrum (high solar absorptance (α)) and perfect reflectors in the thermal infrared (IR) (low thermal emittance (ε)). Cermet composite solar absorber shows such selective properties at high temperatures. In the present work, we developed Al-AlN based multilayer cermet films by RF magnetron sputtering. We choose combination of Ni/AlxN(1-x)/AlN layers as a solar absorber due to its stability at elevated temperature and high corrosion resistance. In this combination, Ni layer, deposited near to substrate, act as the IR light reflector to provide high thermal emittance. While AlxN(1-x) layer act as an absorber layer for UV-Vis spectrum of solar radiation and transparent AlN layer on top functions as AR coating. To improve absorptance, 3 or 4 layers of AlxN(1-x) film with grading of metal content was synthesized by varying N2 flow during deposition. The optical measurement for these multilayer selective absorber films showed high solar absorptance of 0.92-0.96 and low thermal emittance of around 0.1-0.07. To test the stability of our multilayer coating at high temperature, we annealed these samples at 700 oC with holding time of 2 hrs in air, low vacuum and high vacuum. We observed a slight decrease in solar absorptance value (0.90) for the annealed samples but the results showed that overall performance was not hindered by heat treatment thus proving the thermal stability of our multilayer cermet coating.

Photocatalytic water splitting using solar energy could contribute to the solution of environmental and energy issues related to the hydrogen production. Key research area in this field is the development of photo-catalyst able to provide high energy conversion efficiency. TiO2 has been mostly preferred material as the photo-electrode due to many advantages, mainly related to the cost factor and stability. We have studied on hydrogen production by water splitting in photo-electrochemical cells prepared by using photoanodes made by two different kinds of TiO2: one deposited by RF sputtering and the other one by sol-gel method. Depositions were performed on electrical conducting ITO whose electrical properties plays vital role to reduce the photon energy loss. The photoanodes have been characterised by several techniques to infer on their optical and compositional properties. The observed differences in hydrogen production have been attributed to the peculiarities in absorption properties of the two TiO2 films that in the case of sputter-deposited films are more prone to absorb radiation also because of the produced defects during the deposition process. Metals like Cr and Fe were doped in TiO2 by RF magnetron sputtering and sol-gel methods to increase the efficiency of hydrogen production by water splitting by sensitizing the doped-TiO2 in visible light spectrum. The doping method, dopant concentration, charge transfer from metal dopants to TiO2, and type of dopants used for modification of TiO2 were investigated for their ability to enhance photocatalytic activity. UV-Visible spectra show that the sputter-metaldoped- TiO2 films are much more efficient than the chemically-prepared samples to induce red shift of the absorption edge for absorbing visible light. In addition, we proved that dopant atoms must be located, at low concentration, near the ITO-TiO2 interface to avoid the formation of recombination centers for photo-generated electron-hole pairs. H2 production rate is higher with Fe-doped TiO2 (15.5 μmole/h) than with Cr-doped TiO2 (5.3 μmole/h) because Fe ions trap both electrons and holes thus avoiding recombination. On the other hand, Cr can only trap one type of charge carrier. To increase the light conversion efficiency and reduce the recombination processes of Cr-doped TiO2, a multilayer structure of ITO/Cr-doped-TiO2 (9 at.%) was developed. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Crdoped-TiO2. The enhanced photocurrent is attributed to: 1) higher absorption of visible light by Cr-doped-TiO2, 2) number of space-charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the spacecharge layer by decreasing the Cr-doped-TiO2 layer thickness. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water splitting: we obtained indeed 24.4 μmole/h of H2 production rate, a value about two times higher than that of pure TiO2 (12.5 μmole/h). Similar experiment we performed by doing TiO2 with vanadium metal. With 6-ilayers vanadium doped TiO2 film Shows higher hydrogen production rate of about 31.2 μmole/h. This rate is higher than that of CR doped and pure TiO2. A constant H2 generation rate is obtained for long periods of time by all the investigated TiO2 films because of the separate evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Even Ar+ or N+ ion implantation of energy 30 keV was adopted to vary the energy band gap of TiO2 film in order to absorb visible light.The original anatase phase was not changed by implantation. Increase in full visible absorption range was observed for both kinds of ion implanted-TiO2 films which further increases with the ion fluencies, while N+ ion implantation also causes the shift of the absorption edge from UV to visible light range. N+ implanted TiO2 showed narrowing of band gap from 3.2 eV for untreated anatase TiO2 to 2.78 eV for maximum implantation dose. The Ar+ and N+ implantation creates oxygen vacancies related defect energy level in the band gap. In case of N+ implantation, nitrogen also substitutionally replaces the oxygen atoms thus forming an energy level just above the valence band which further interacts with O 2p states resulting in the narrowing of band gap. The black solar absorber material develop over the copper target to absorb concentrated solar radiation and supply heat to the surrounding water. A black copper oxide layer was synthesized over copper substrate by using chemical oxidation treatment. We varied several treatment parameters and optimized the best condition to obtain a black textured layer which has the properties to absorb total solar radiation. The untreated polished copper showed 50 to 60 % reflectance (R) (incidence angle of 15o) and this value decreases to almost zero for whole wavelength range after formation of black copper oxide. The percentage absorption decreases by negligible amount as the angle of incidence increases. The SEM images of the copper oxide layer at high magnification showed a nano-petal like structure which causes the surface texture effect for higher absorption where surface irregularities such as grooves and pores with dimensions similar to the wavelength of the incident radiation simply increase the solar absorptance by multiple reflections. Long time thermal stability and corrosion resistance in hot water was also studied for the copper oxide film. The results revealed that the copper oxide was very stable and showed no changes in optical properties after the test. For the same water heating system a quartz window is used through which the solar radiation is transmitted on the copper target. Thus to acquire high power conversion efficiency it is necessary for quartz window to transmit the entire solar radiation incident on it without much lost due to the reflection on the surface. In general quartz window is able to transmit 90-91 % of the solar radiation while 1-2 % is absorbed and 7-8 % is reflected from the surface. Thus to have nearly complete transmittance it is necessary to cover the surface of quartz window with anti-reflecting (AR) coating: this was the part of my work. We developed single-layer and multi-layer AR coating for single specific wavelength and broad-band wavelength range respectively. Low reflective index material like MgF2 is deposited by e-beam technique to obtain single-layer AR coating. While Al2O3 and ZrO2 layers deposited, by RF-magnetron sputtering, on top of MgF2 forms multi-layer AR coating. The combination of MgF2/ZrO2/Al2O3/MgF2 deposited on both side of quartz showed excellent results with reflectance value of around 0.8% in broad spectral range. The heat exchanger efficiency obtained after using these developed black copper oxide absorber material and AR coating is around 83 % which seems to be significantly higher than the other commercially available water heating system. Concentrating solar power (CSP) systems are utilized to convert sunlight to thermal electric power by using solar absorber. However, the solar absorber are operated at elevated temperature (700-800 oC) and should be spectrally selective to act as perfect absorbers over the solar spectrum (high solar absorptance (α)) and perfect reflectors in the thermal infrared (IR) (low thermal emittance (ε)). Cermet composite solar absorber shows such selective properties at high temperatures. In the present work, we developed Al-AlN based multilayer cermet films by RF magnetron sputtering. We choose combination of Ni/AlxN(1-x)/AlN layers as a solar absorber due to its stability at elevated temperature and high corrosion resistance. In this combination, Ni layer, deposited near to substrate, act as the IR light reflector to provide high thermal emittance. While AlxN(1-x) layer act as an absorber layer for UV-Vis spectrum of solar radiation and transparent AlN layer on top functions as AR coating. To improve absorptance, 3 or 4 layers of AlxN(1-x) film with grading of metal content was synthesized by varying N2 flow during deposition. The optical measurement for these multilayer selective absorber films showed high solar absorptance of 0.92-0.96 and low thermal emittance of around 0.1-0.07. To test the stability of our multilayer coating at high temperature, we annealed these samples at 700 oC with holding time of 2 hrs in air, low vacuum and high vacuum. We observed a slight decrease in solar absorptance value (0.90) for the annealed samples but the results showed that overall performance was not hindered by heat treatment thus proving the thermal stability of our multilayer cermet coating.

The techniques of computer modeling and simulations are used to develop a design procedure for greenhouse solar heating systems. In this study a flexible computer program was written based on mathematical models that describe the various subsystems of the solar heating system that uses the greenhouse as the solar collector. Extensive simulation runs were carried out for predicting system thermal performance, and subsequently correlations were established between dimensionless variables and long term system performance. The combined greenhouse thermal environment - thermal storage model along with the empirical relationships and the values of constants approximated in the simulation yielded reasonably accurate computed results compared to observed data. The computer model was then applied to predict the system behaviour using long-term average climatological data as forcing functions. A parametric study was made to investigate the effects of various factors pertinent to greenhouse construction and thermal energy storage characteristics on system performance. The key performance indices were defined in terms of the 'total solar contribution' and the 'solar heating fraction'. Correlations were developed between monthly solar load ratio and total solar contribution, and between total solar contribution and solar heating fraction. The result is a simplified design method that covers a number of alternative design options. It requires users to obtain monthly average climatological data and determine the solar heating fraction in a sequence of computational steps. A crop photosynthesis model was used to compute the net photosynthetic rate of a greenhouse tomato canopy; the result may be used to compare crop performance under different aerial environments in greenhouses equipped with a solar heating system. This research program had attempted to generate technical information for a number of design alternatives, and as design optimization of greenhouse solar heating is subject to three major criteria of evaluation: thermal performance, crop yield and cost, recommendations were put forward for future work on economic analysis as the final step required for selecting the most cost effective solution for a given design problem.
Graduate and Postdoctoral Studies
Graduate

In this thesis we investigate current sheets in the solar corona. The well known 1D model for the tearing mode instability is presented, before progressing to 2D where we introduce a non-uniform resistivity. The effect this has on growth rates is investigated and we find that the inclusion of the non-uniform term in η cause a decrease in the growth rate of the dominant mode. Analytical approximations and numerical simulations are then used to model current sheet formation by considering two distinct experiments. First, a magnetic field is sheared in two directions, perpendicular to each other. A twisted current layer is formed and we find that as we increase grid resolution, the maximum current increases, the width of the current layer decreases and the total current in the layer is approximately constant. This, together with the residual Lorentz force calculated, suggests that a current sheet is trying to form. The current layer then starts to fragment. By considering the parallel electric field and calculating the perpendicular vorticity, we find evidence of reconnection. The resulting temperatures easily reach the required coronal values. The second set of simulations carried out model an initially straight magnetic field which is stressed by elliptical boundary motions. A highly twisted current layer is formed and analysis of the energetics, current structures, magnetic field and the resulting temperatures is carried out. Results are similar in nature to that of the shearing experiment.

International Energy Agency Solar Heating & Cooling (IEA SHC) programme states the fact that space/water heating and cooling demand account for over 75% of the energy consumed in single and multi-family homes. Solar energy technology can meet up to 100% of this demand depending on the size of the system, storage capacity, the heat load and the region’s climate. Solar thermal collectors are particular type of heat extracting devices that convert solar radiation into thermal energy through a transport medium or flowing fluid. Although hybrid PV/T or thermal-alone systems offer some advantages to improve the solar heat utilisation, there are a few technical challenges found in these systems in practice that prevented wide-scale applications. These technical drawbacks include being expensive to make and install, inability of switching already-built photovoltaic (PV) systems into PV/T systems, architectural design etc. The aims of this project, therefore, were to investigate roof integrated solar thermal roof collectors that properly blend into surrounding thus avoiding ‘add on’ appearance and having a dual function (heat absorption and roofing). Another objective was to address the inherent technical pitfalls and practical limitations of conventional solar thermal collectors by bringing unique, inexpensive, maintenance free and easily adaptable solutions. Thus, in this innovative research, unique and simple building integrated solar thermal roof collectors have been developed for heating & cooling applications. The roof systems which mainly based on low cost and structurally unique polyethylene heat exchanger are relatively cost effective, competitive and developed by primarily exploiting components and techniques widely available on the market. The following objectives have been independently achieved via evaluating three aspects of investigations as following: • Investigation on the performance of poly heat exchanger underneath PV units • Investigation on the performance of a Building Integrated PV/T Roof ‘Invisible’ Collector combined with a liquid desiccant enhanced indirect evaporative cooling system • Investigation on the build-up and performance test of a novel ‘Sandwich’ solar thermal roof for heat pump operation These works have been assessed by means of computer simulation, laboratory and field experimental work and have been demonstrated adequately. The key findings from the study confirm the potential of the examined technology, and elucidate the specific conclusions for the practice of such systems. The analysis showed that water temperature within the poly heat exchanger loop underneath PV units could reach up to 36°C and the system would achieve up to 20.25% overall thermal efficiency. Techno-economic analysis was carried out by applying the Life Cycle Cost (LCC) method. Evaluations showed that the estimated annual energy savings of the overall system was 10.3 MWh/year and the cost of power generation was found to be £0.0622 per kWh. The heat exchanger loop was coupled with a liquid desiccant enhanced indirect evaporative cooling unit and experimental results indicated that the proposed system could supply about 3 kW of heating and 5.2 kW of cooling power. Lastly, the results from test of a novel solar thermal collector for heat pump operation presented that the difference in water temperature could reach up to 18°C while maximum thermal efficiency found to be 26%. Coefficient Performance of the heat pump (COPHP) and overall system (COPSYS) averages were attained as COPHP=3.01 and COPSYS=2.29, respectively. An economic analysis pointed a minimum payback period of about 3 years for the system.

The main aim of this project is to develop an ESES lab on a full scale system. The solar combisystem used is available most of the time and is only used twice a year to carry out some technical courses. At the moment, there are no other laboratories about combisystems. The experiments were designed in a way to use the system to the most in order to help the students apply the theoretical knowledge in the solar thermal course as well as make them more familiar with solar systems components. The method adopted to reach this aim is to carry out several test sequences on the system, in order to help formulating at the end some educating experiments. A few tests were carried out at the beginning of the project just for the sake of understanding the system and figuring out if any additional measuring equipment is required. The level of these tests sequences was varying from a simple energy draw off or collector loop controller respond tests to more complicated tests, such as the use of the ‘collector’ heater to simulate the solar collector effect on the system. The tests results were compared and verified with the theoretical data wherever relevant. The results of the experiment about the use of the ‘collector’ heater instead of the collector were positively acceptable. Finally, the Lab guide was developed based on the results of these experiments and also the experience gotten while conducting them. The lab work covers the theories related to solar systems in general and combisystems in particular.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016.
Solar energy is still not being used effectively in countries in the developing world, though it's a partial solution to the problem of shortage and expensive energy. Normally harvested through flat plate collectors, converting solar radiation into heat is the most direct application that can be effected in water heating systems. Many researchers have attempted to develop means of improving the efficiency of the flat plate solar energy collector; however there appears to be no evidence of any work regarding the effect of geometric configuration on the performance of flat plate solar collector. This study presents results obtained when comparing the performance of a solar water heating system equipped with three manufactured flat plate solar collector panels of numerically identical surface area but of different geometric configuration as they were individually attached to a typical geyser. Data was obtained inside a laboratory. The amount of heat acquired from flat plate collectors of solar energy depends primarily on their surface area that is exposed to the solar irradiance, however, the geometry of the collectors was thought that it might affect to some extent the amount of heat harvested. The circulation of the water from the panel to the geyser was due to the self-induced thermo-syphon effect. The results obtained during the test period (7 hours per day for two consecutive days) indicated that the system’s thermal efficiency was best when the square geometrical configuration collector was used. A dimensional analysis using the Π Buckingham method that was performed on the parameters affecting a flat plate solar collector yielded three dimensionless numbers that lead to a power law relationship which might be useful in enhancing solar water heating systems’ design.

The main purpose of this research project was to do a comparative study, by identifying a testing methodology for transient conditions, through which to allow the expression of the relative thermal performance of two DSWH collectors in comparison. The study started off by considering literature about Solar Domestic Water Heaters and National Standards-based test methods, most of which were for Steady State testing conditions. Thereafter establishing a testing methodology and setup, identifying factors to be considered. The results were analyzed and conclusions drawn. The hypothesis was to allow the reduction in the complexity of testing equipment and methods, and by doing transient condition testing and still utilizing the Hottel-Whillier-Bliss relationship as a way of expressing efficiency, the hypothesis was proven.