No description available.

The magnetic carpet is defined to be the small-scale photospheric magnetic field of the quiet Sun. Observations of the magnetic carpet show it to be highly dynamic, where the time taken for all flux within the magnetic carpet to be replaced is on the order of just a few hours. The magnetic carpet is continually evolving due to the Sun's underlying convection and the interaction of small-scale magnetic features with one another. Due to this, the small-scale coronal field of the magnetic carpet is also expected to be highly dynamic and complex. Previous modelling has shown that much of the flux from the magnetic carpet is stored along low-lying closed connections between magnetic features. This indicates that significant coronal heating could occur low down in the small-scale corona. In this thesis, a new two-component magnetic field model is developed for the evolution of the magnetic carpet. A 2D model is constructed to realistically simulate the evolution of the photospheric field of the magnetic carpet, where many of the parameters for the model are taken from observational studies. The photospheric model contains a granular and supergranular flow profile to describe the motion of the small-scale magnetic features, and includes the processes of flux emergence, cancellation, coalescence and fragmentation. This 2D model then couples to a 3D model as the lower boundary condition, which drives the evolution of the coronal field through a series of non-linear force-free states, via a magnetofrictional relaxation technique. We first apply the magnetofrictional technique to consider the coronal evolution of three basic small-scale photospheric processes: emergence, cancellation and flyby. We consider the interaction of the magnetic features with an overlying coronal magnetic field, and quantify magnetic energy build-up, storage and dissipation. The magnetofrictional technique is then applied to synthetic magnetograms produced from the 2D model, to simulate the evolution of the coronal field in a situation involving many hundreds of magnetic features. We conduct a preliminary analysis of the resultant 3D simulations, considering the magnetic energy stored and dissipated, as well as regions of enhanced velocity and electric current density within the coronal volume. The simulations show that the so-called 'quiet Sun' is not quiet and a significant amount of complex interactions take place.

No description available.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Most rural African villages enjoy high levels of sunlight, but rolling out solar power generation technology to tap into this renewable energy resource at remote rural sites in Africa pose a number of design challenges. To meet these challenges, a project has been initiated to design, build and test/evaluate a knock down 3 kW peak electrical stand-alone self-tracking dual-axis concentrating solar power system. This study focusses on the mechatronic engineering aspects in the design and development of a dynamic mechatronic platform and digital electronic control system for the stand-alone concentrating solar power system. Design specifications require an accurate automatic positioner and control system for a motorized parabolic solar reflector with an optical solar harnessing capacity of 12 kWt at solar noon. It must be suitable for stand-alone rural power generation. This study presents a conceptual design and engineering prototype of a balanced cantilever tilt-and-swing dual-axis slew drive actuation means as mechatronic solar tracking mobility platform for a ∼12 m2 lightweight parabolic solar concentrator. Digital automation of the concentrated solar platform is implemented using an industrial Siemens S7-1200 programmable logic controller (PLC) with digital remote control interfacing, pulse width modulated direct current driving, and electronic open loop/closed loop solar tracking control. The design and prototype incorporates off-the-shelf components to support local manufacturing at reduced cost and generally meets the goal of delivering a dynamic mechatronic platform for a concentrating solar power system that is easy to transport, assemble and install at remote rural sites in Africa. Real-time experiments, conducted in the summer of South Africa, validated and established the accuracy of the engineering prototype positioning system. It shows that the as-designed and -built continuous solar tracking performs to an optical accuracy of better than 1.0◦ on both the azimuth and elevation tracking axes; and which is also in compliance with the pre-defined design specifications. Structural aspects of the prototype parabolic dish are evaluated and optimized by other researchers while the Stirling and power handling units are under development in parallel projects. Ultimately, these joint research projects aim to produce a locally manufactured knock down do-it-yourself concentrated solar power generation kit, suitable for deployment into Africa. / AFRIKAANSE OPSOMMING: Landelike gebiede in Afrika geniet hoë vlakke van sonskyn, maar die ontwerp van betroubare sonkrag tegnologie vir die benutting van hierdie hernubare energie hulpbron by afgeleë gebiede in Afrika bied verskeie uitdagings. Om hierdie uitdagings te oorkom, is ’n projek van stapel gestuur om ’n afbreekbare 3 kW piek elektriese alleenstaande selfaangedrewe dubbel-as son-konsentreeder te ontwerp, bou en te toets. Hierdie studies fokus op die megatroniese ingenieurs-aspekte in die ontwerp en ontwikkeling van ’n dinamiese megatroniese platform en ’n digitale elektroniese beheerstelsel vir die alleenstaande gekonsentreerde sonkrag stelsel. Ontwerp spesifikasies vereis ’n akkurate outomatiese posisionering en beheer stelsel vir ’n motor aangedrewe paraboliese son reflekteerder met ’n optiesekollekteer- kapasiteit van 12 kWt by maksimum sonhoogte, en veral geskik wees vir afgeleë sonkrag opwekking. Hierdie studie lewer ’n konsepsuele ontwerp en ingenieurs-prototipe van ’n gebalanseerde dubbelas swaai-en-kantel swenkrat aandrywingsmeganisme as megatroniese sonvolg platform vir ’n ∼12 m2 liggewig paraboliese son konsentreerder. Digitale outomatisering van die son konsentreerder platform is geimplementeer op ’n industriële Siemens S7-1200 programmeerbare logiese beheerder (PLB) met ’n digitale afstandbeheer koppelvlak, puls-wydte-gemoduleerde gelykstroom aandrywing en elektroniese ooplus en geslote-lus sonvolg beheer. Die ontwerp en prototipe maak gebruik van beskikbare komponente om lae-koste plaaslike vervaardiging te ondersteun en slaag in die algemeen in die doel om ’n dinamiese megatroniese platform vir ’n gekonsentreerde sonkrag stelsel te lewer wat maklik vervoer, gebou en opgerig kan word op afgeleë persele in Afrika. Intydse eksperimente is gedurende die somer uitgevoer om die akkuraatheid van die prototipe posisionering sisteem te evalueer. Dit toon dat die sisteem die son deurlopend volg met ’n akkuraatheid beter as 1.0◦ op beide die azimut en elevasie sonvolg asse, wat voldoen aan die ontwerp spesifikasies. Strukturele aspekte van die prototipe paraboliese skottel word deur ander navorsers geëvalueer en verbeter terwyl die Stirling-eenheid en elektriese sisteme in parallelle projekte ontwikkel word. Die uiteindelike doel met hierdie groepnavorsing is om ’n plaaslik vervaardigde doen-dit-self sonkrag eenheid te ontwikkel wat in Afrika ontplooi kan word.

Thesis (MDF (Graduate School of Business))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Deforestation, increasing pollution levels, diminishing non-renewable energy reserves, the resulting global warming, and climate change are areas of concern to environmentalists and the whole global village. It appears that the solution lies in the exploitation of renewable, clean and sustainable energy resources. Solar energy is one of the renewable, clean and environmentally friendly energy resources readily available in most tropical countries of the world, including Namibia. The research was conducted in the Rocky Crest suburb of Windhoek, Namibia. The research focused on the exploration barriers in the diffusion of solar water heaters (SWHs) for generating hot water for Rocky Crest residents. The investigation involved data collection from the stakeholders, including the residents of Rocky Crest suburb, SWH suppliers, financial institutions, non-governmental organisations (NGOs) and the Ministry of Mines and Energy (MME) in Namibia. The results of this study introduce information that can largely benefit the Rocky Crest residents, MME, NGOs, financial institutions and relevant stakeholders. It can also act as a departure point for further studies on the subject of renewable energy sources, their exploitation and the impact thereof. Furthermore, solutions to the current problems of diminishing non-renewable energy reserves and the impact of pollutant energy sources can be identified and implemented.

This thesis considers the long term energy problem and the role which active solar collector systems for building application might play in alleviating this problem. The major part of this thesis describes the derivation and solution of the mathematical model to simulate the principal components in a solar energy collector system. The model is based on an implicit numerical technique which allows the investigation of the simultaneous interaction between system components in liquid and photovoltaic collectors. A simulation progam called FLARE, based on the aforementioned model, has been developed for use as a research and design model. This program forms the central core of a suite of interrelating computer programs which provide sophisticated user participation by means of a high level interactive graphics facility.

No description available.

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

A salt gradient solar pond offers an economical means of both collecting summer solar heat, and storing it in water over periods of a few months for use in winter space heating. The vertical gradient of salt density prevents convection in the pond and makes it self-insulating against heat losses. The solar pond project at the university of Sussex aimed to study the design, construction, filling, and operation of a salt gradient solar pond, and to develop inexpensive instrumentation for the harsh environment of hot salt water solution, for monitoring behaviour and performance. A new method of heat extraction, from both the insulation and storage layers of the pond, was tested, and a computer program was developed to model pond behaviour under non-steady techniques. Construction, filling, and operation of indoor and state conditions, using finite difference outdoor pilot solar ponds is described and a simple means of maintaining salt density gradient, as well as work on achieving good pond transparency over the two-year period of operation of the pond. To improve the efficiency of the pond successful experiments were carried out to extract heat from both the convecting storage layer and the non-convecting insulation layer of the pond. This permits interception and extraction of heat flow in the non-convecting layer which would otherwise be lost to the surface. Laboratory and outdoor exper iments were car ried out to test whether this causes unwanted convective mixing and increased upward diffusion of salt in the non-convective zone of the pond. Heat transfer coefficients were measured with the heat exchanger placed in the non-convecting insulation layer. Both steady-state and finite difference model calculations are presented to indicate the improvements in operating efficiency and temperatures that are achievable with the new method of heat extraction. Theoretical results from the finite difference model are in good agreement with observed performance.