Exploring uses of two-phase mixtures as a way to store peak solar energy for off-peak usage is a novel approach that has been gaining attention in recent years to address the issues tied to solid fuel dependence. This research explores a “solar salt” mixture (40%wt KNO3 and 60%wt NaNO3) in an aluminum enclosure under two test conditions: conduction enhancement and no conduction enhancement. The central aim is to develop an understanding of thermal distributions and melt developments as the system moves from room temperature to 300 oC. Thermal pattern development is explored by experimentally observing a 2-D temperature field at 8 co-planar points, comprised of 3 radial positions with complementary circumferential measurements, using thermocouples. The instrument array is traversed to three different axial positions where collected data is compared with results from a numerical solver. Results find three important details. First, the melt pattern of the fin experiments show quicker rates of melting after the onset of melt at the bottom of the enclosure. Second, the spatial effects of the instrumentation influence the presence of thermal phenomena. Lastly, approximations of the salts behavior using numerical simulations are supported in identifying phases of melt development.

The aim of this Master Thesis is to find the most suitable amount of photovoltaic (PV) panels to sustain an off-grid thermal energy storage (TES) system and to compare a maximum power point tracker (MPPT) with a pulse width modulator (PWM) in order to analyze which one of them that best suits the system. The purpose is to provide feedback on the design of the electrical part of the system in order to make it suitable for testing in a school in an Uganda refugee camp. This is done by developing a simulation model and by performing an economical analysis of the system. Additionally, visits to the considered refugee camps are done. The results are based on data from the camps and interviews at the Physics department at Makerere University and consider the number of meals cooked by the TES as well as economical profitability and payback time. The recommended amount of PV panels is nine and the recommended controller is an MPPT. The simulation shows that the system reaches a point where an increasing number of panels doesn't increase the number of cooked meals by much. The economic analysis shows that this small increase is not enough to make up for the extra costs of adding more PV panels. Having a lower cost, PWM is preferred in the early years by the economic analysis. However, having a low efficiency, it is less superior to the MPPT. The payback time and revenue are better for the MPPT in the investigated cases. It is important to consider that the model doesn't show reality to a full extent. Experiments are made where it is found that the model is inaccurate on an hourly level but can be considered valid over longer periods of time. When choosing the results, a trade-off is made between maximizing the revenue or shortening the payback time of the TES system. Considering rough circumstances and the uncertain future of the camps existence, short payback time is chosen. This results in nine panels being the optimum amount. However, if the aim is to maximize revenue, twelve panels are better than nine. The price of firewood is a factor of uncertainty which this study relays a lot on and it's thereby important to consider when reading the results. Suggestions for future studies are to investigate the price development of firewood further or to test the use of stones in the thermal storage tank to decrease costs. Additionally, possible utilization of surplus produced energy from the system could be investigated in order to find extra benefits from the installation.

Cooking is an integral part of each and every human being as food is one of the basic necessities for living. Commonly used sources of energy for cooking are firewood, crop residue, cow dung, kerosene, electricity, liquefied petroleum gas(LPG), biogas etc. Half of the world’s population is exposed to indoor air pollution, mainly the result of burning solid fuels for cooking and heating. Wood cut for cooking purpose contributes tothe16 million hectares(above4% of total area of India) of forest destroyed annually. The World Health Organization(WHO) reports that in 23 countries 10% of deaths are due to just two environmental risk factors: unsafe water, including poor sanitation and hygiene; and indoor air pollution due to solid fuel usage for cooking. In under-developed countries, women have to walk 2kms on average and spend significant amount of time for collecting the firewood for cooking. The cooking energy demand in rural areas of developing countries is largely met with bio-fuels such as fuel wood, charcoal, agricultural residues and dung cakes, whereas LPG or electricity is predominantly used in urban areas. India has abandon amount of solar energy in most of the regions making it most ideal place for harvesting solar energy. With almost 300 sunny days each year, one can confidently relay on this source of energy. India’s geographical location is in such a way that theoretically it receives 5x1015 kWh/ year of solar energy. Solar cooking is the simplest, safest, environmental friendly and most convenient way to cook. It is a blessing for those who cook using firewood or cow dung, who walk for miles to collect wood, who suffer from indoor air pollution. Hence solar cooking is going to play major role in solving future energy problem. Solar based cooking has never been a strong contender in the commercial market or even close to being a preferred method of cooking. They have been relegated to demonstration appliances to show case the solar based concepts. In this mode, cooking is no longer a time independent activity that can be performed at any time of day. One is forced to cook only at certain times when there is sufficient insolation. The geography of the cooking activity also shifts away from the kitchen. The kitchen is no longer the hearth of the home as the actual cooking activity shifts to the roof tops or high insolation platforms. This further adds to the inconvenience apart from being unable to cook at night or during cloudy conditions or during most of the winter days. Another issue of significant inconvenience is the general social structure in most families of the developing countries wherein the cooking activity is carried out by the senior ladies of the home. They are generally not athletic enough to be moving to and from the kitchen and the roof top to carry out the cooking exercise. As the solar cookers are enclosed spaces, interactive cooking is not possible let alone having any control on the rate of cooking. These are some of the more significant issues in the social psyche that has abundantly impeded the acceptance of solar thermal based cooking appliances. These issues and problems are in fact the motivating factors for this thesis. Based on these motivating factors, this thesis aims to propose solutions keeping the following points as the major constraints. cooking should be performed in the kitchen. one should be able to perform the cooking activity independent of the time of day or insolation. the cooking activity should be interactive the time taken for cooking should be comparable with the conventional methods in vogue. there should be a reduction in the use of conventional energy. Using the constraints and the motivating factors discussed above as the central theme, this thesis proposes a method to transfer solar thermal energy to the kitchen and act as a supplement to the conventional source of energy like the LPG or other sources that are traditionally being used in the households. The method proposed is in fact a hybrid scenario wherein the solar thermal is used to supplement the traditional source. Solar photovoltaic cells are also used to power the electronics and apparatus proposed in this thesis. This thesis addresses in detail the issues in analysis, modeling, designing and fabrication of the proposed hybrid solar cooking topology. The main goal of the proposed system is to transfer heat from sun to the cooking load that is located in the kitchen. The topology includes an additional feature for storing the energy in a buffer. The heat is first transferred from the solar thermal collector to a heat storage tank(that acts as the buffer) by circulating the heat transfer fluid at a specific flow rate that is controlled by a pump. The stored heat energy that is collected in the buffer is directed into the kitchen by circulating the heat transfer fluid into the heat exchanger, located in the kitchen. This is accomplished by controlling the flow rate using another pump. The solar thermal collector raises the temperature of the thermic fluid. The collector can be of a concentrating type in order to attain high temperatures for cooking. Concentrating collector like linear parabolic collector or parabolic dish collector is used to convert solar energy into heat energy. Absorption of energy from the incident solar insolation is optimized by varying the flow rate of circulating thermic fluid using a pump. This pump is energized from a set of photovoltaic panels(PV cell) which convert solar energy into electrical energy. The energy absorbed from the solar thermal collector is stored in a buffer tank which is thermally insulated. Whenever cooking has to be carried out, the high temperature fluid from the buffer tank is circulated through a heat exchanger that is located in the kitchen. The rate of cooking can be varied by controlling both the flow rate of fluid from the buffer tank to heat exchanger and also by controlling the amount of energy drawn from the auxiliary source. If the available stored energy is not sufficient, the auxiliary source of energy is used for cooking in order to ensure that cooking is in-dependent of time and solar insolation. In the proposed hybrid solar cooking system, the thesis addresses the issues involved in optimization of energy extracted from sun to storage tank and its subsequent transfer from the storage tank to the load. The flow rate at which maximum energy is extracted from sun depends on many parameters. Solar insolation is one of the predominant parameters that affect the optimum flow rate. Insolation at any location varies with time on a daily basis (diurnal variations) and also with day on a yearly basis(seasonal variation). This implies that the flow rate of the fluid has to be varied appropriately to maximize the energy absorbed from sun. In the proposed system, flow rate control plays a very significant role in maximizing the energy transfer from the collector to the load. The flow rate of the thermic fluid in the proposed system is very small on the order of 0.02kg/s. It is very difficult to sense such low flows without disrupting the operating point of the system. Though there are many techniques to measure very low flow rates, they invariably disrupt the system in which flow rate has to be measured. Further, the low flow sensors are far too expensive to be included in the system. A reliable, accurate and inexpensive flow measuring technique has been proposed in this thesis which is non-disruptive and uses a null-deflection technique. The proposed measuring method compensates the pressure drop across the flow meter using a compensating pump. The analysis, modeling, design and fabrication of this novel flow meter are addressed. The design and implementation of different subsystems that involves the selection and design of solar concentrating collector and tracking are explained. Finally, it is essential to know the economic viability of the proposed system that is designed and implemented. To understand the economics, the life cycle cost analysis of the proposed system is presented in this thesis. The major contributions of this thesis are: Energy transport: Major challenge in energy transport is to bring heat energy obtained from the sun to the kitchen for cooking. Energy transferred from solar insolation to the cooking load has to be optimized to maximize the overall efficiency. This can be split in to two parts,(a) optimizing efficiency of energy transferred from the collect or to the energy buffer tank,(b) optimizing efficiency of energy transferred from the buffer tank to the load. The optimization is performed by means of a maximum power point tracking(MPPT) algorithm for a specific performance index. Modeling of the cooking system: There are several domains that exist in the solar cooking system such as electrical domain, thermal domain, and hydraulic domain. The analysis of power/energy flow across all these domains presents a challenging task in developing a model of the hybrid cooking system. A bond graph modeling approach is used for developing the mathematical model of the proposed hybrid cooking system. The power/energy flow across different domains can be seamlessly integrated using the bond graph modeling approach. In this approach, the various physical variables in the multi-domain environment are uniformly de-fined as generalized power variables such as effort and flow. The fundamental principle of conservation of power/energy issued in describing the flow of power/energy across different domains and thus constructing the dynamic model of the cooking system. This model is validated through experimentation and simulation. Flow measurement: A novel method of low fluid mass flow measurement by compensating the pressure drop across the ends of measuring unit using a compensating pump has been proposed. The pressure drop due to flow is balanced by feedback control loop. This is a null-deflection type of measurement. As insertion of such a measuring unit does not affect the functioning of the systems, this is also a non-disruptive flow measurement method. This allows the measurement of very low flow rate at very low resolution. Implementation and design of such a unit are discussed. The system is modeled using bond graph technique and then simulated. The flow meter is fabricated and the model is experimentally validated. Design Toolbox: Design of hybrid cooking system involves design of multi domain systems. The design becomes much more complex if the energy source to operate the system is hybrid solar based. The energy budget has to be evaluated considering the worst case conditions for the availability of the solar energy. The design toolbox helps in assessing the user requirement and help designing the cooking system to fulfill the user requirement. A detailed toolbox is proposed to be developed that can be used in designing/selecting sub-systems like collector, concentrator, tracking system, buffer tank, heat exchanger, PV panel, batteries etc. The toolbox can also be used for performing life cycle costing.

This bachelor thesis is written as a Minor Field Studies (MFS) project and funded by SIDA, Sweden’s International Development Cooperation Agency. The project was made in cooperation with Engineers Without Borders Sweden and the local organization Asulma Centre in Nairobi. As a part of their Integrated Solar Research collaboration between the two organizations, the project strives to contribute to the United Nations sustainable development goals. Most households in Kenya rely on wood, charcoal and other sources of fossil fuel to use for cooking food. Unfortunately, these fuels produce smoke that causes great problems for the environment and for human health and can, in the worst cases, be lethal. It is estimated that 23 000 Kenyans die yearly from household air pollution produced from the fossil fueled stoves. Using the sun to cook food is a cheap alternative to conventional methods that are also more sustainable as it does not produce any smoke. The aim of this research was to study, analyze and optimize the model of a solar cooker called a conical cooker. In order to improve a previously developed concept of the conical cooker, this project focuses on what material and manufacturing methods should be used. A functional means tree was used to generate concepts, which were then analyzed using tools such as EduPack and an evaluation matrix based on a developed specification of requirements. After analyzing all the plausible options, it was suggested that the conical body should be made from a 1 mm (gauge 19) stainless steel sheet that has been mechanically polished and then joined together by crimping to shape the cone. The resulting product would cost 1430 KSH to manufacture, which is just below the cost of today’s cooker. It is also produced to withstand corrosion damage as well as maintain a reflective surface in order to work as a sufficient solar cooking method. This would be a cheap alternative that reduces health risks among the citizens of Kenya. However, as a solar cooker, it must be used together with other solutions as the sun is not always available which is why the project is called the Integradet Solar Cooking project. / Denna kandidatuppsats är skriven som ett Minor Field Studies (MFS)-projekt och finansierades av SIDA, Sveriges biståndsmyndighet. Projektet genomfördes i samarbete Ingenjörer Utan Gränser Sverige och den lokala organisationen Asulma Centre i Nairobi. Som en del av ett samarbete mellan de två organisationerna strävar detta projekt efter att bidra till Förenta Nationernas hållbara utvecklingsmål. De flesta hushåll i Kenya förlitar sig på ved, kol och andra fossila bränslekällor för att laga mat. Tyvärr producerar dessa bränslen rök som orsakar stora problem för miljön och människors hälsa och kan i värsta fall vara dödliga. Uppskattningsvis dör 23 000 kenyaner årligen till följd av luftföroreningar i hemmet som produceras av spisar med fossila bränslen. Att använda solen för att laga mat är ett billigt alternativ till konventionella metoder som dessutom är mer hållbart eftersom det inte producerar någon rök. Syftet med denna forskning var att studera, analysera och optimera modellen för en solkokare som kallas en konisk kokare. För att förbättra ett tidigare utvecklat koncept av den koniska kokaren fokuserade detta projekt på vilket material och vilka tillverkningsmetoder som bör användas. Ett funktionsmedelträd användes för att generera koncept som sedan analyserades med hjälp av bland annat EduPack och en utvärderingsmatris som baserats på en framtagen kravspecifikation. Efter att ha analyserat alla möjliga alternativ föreslogs att den koniska kroppen bör tillverkas genom att skära ut önskad form ur en 1 mm rostfri stålplåt (gauge 19). Plåten i rostfritt stål ska sedan mekaniskt poleras och sedan sammanfogas med falsning för att forma konen. Den resulterande produkten skulle kosta 1430 KSH (112 SEK) att tillverka, vilket är strax under priset för dagens kokare. Den är också konstruerad för att motstå korrosionsskador och behålla en reflekterande yta för att fungera som en effektiv solkokningsmetod. Detta skulle vara ett billigt alternativ som minskar hälsoriskerna bland lokalbefolkningen i Kenya. En solkokare måste dock användas tillsammans med andra lösningar eftersom solen inte alltid är tillgänglig varför projektet kallas för det Integrerade solmatlagningsprojektet.

Firewood has been used as fuel since the beginning of mankind resulted in health problems and deforestation. The solar cooking technology has been first developed in 1767 by Horace-Bénédict de Saussure but did not find development due to lack of reliability. Studies showed the necessity of having a backup facility. The primary goal of this study is to design a fully functional kitchen for National Park in Nairobi, Kenya. The kitchen will be serving up to 100 people daily. The study is done with five steps, the first step is literature and exploring of solar cooking products as well as backup facility products around the world. The second step is interviewing a local entrepreneur to get familiar with the parameters of a restaurant in Kenya. The third step is evaluating the solar cooking and backup facility to make an educated decision. The fourth step is integrating the systems into a functional kitchen. The fifth and last step is to analyse and discuss the results to draw conclusions. As a result, choosing Scheffler reflector as a solar cooker and backed up with a biogas plant would be the chosen solution. / Ved har använts som bränsle sedan mänsklighetens början som resulterade i hälsoproblem och avskogning. Solar-matlagningstekniken utvecklades först 1767 av Horace-Bénédict de Saussure men hittade ingen utveckling på grund av bristande tillförlitlighet. Studier visade nödvändigheten av att ha en reservfacilitetenhet. Det primära målet med denna studie är att designa ett fungerande kök för National Park i Nairobi, Kenya. Köket serverar upp till 100 personer dagligen.  Studien gjordes av fem steg, första är litteraturstudie och utforskning av produkter för sollagning samt reservfacilitet alternativ från hela världen. Andra steget är att intervjua en lokal entreprenör för att bekanta sig med parametrarna för att gestalta en restaurang i Kenya. Tredje steget är att utvärdera olika solkokare-enheter och reservfacilitetsenhet för att fatta ett välgrundat beslut. Fjärde steget är att integrera systemen i ett funktionellt kök. Femte och sista steget är att analysera och diskutera resultaten för att dra slutsatser. Som ett resultat skulle det vara den bästa lösningen att välja Scheffler reflector som solkokare och biogasanläggning som reservfacilitetsenhet.

This report studies the importance of solar cooking when moving towards a more sustainable and egalitarian future. The problems regarding its implementation, in fact, technological, social and economic problems, are presented. A historic overview is offered as well as the theory behind the technology. After studying the current situation concerning cooking, different devices have been analysed and considered, from small ones suitable for households to bigger ones for institutions. Furthermore, several backup systems are also proposed aiming to obtain an ideal Integrated Solar Cooker (ISC). Possible hybrid systems have also been evaluated during the work. Furthermore, state-of-the-art technology in Thermal Energy Storage (TES) is also commented and taken into account for the most efficient combination of technologies. Several photovoltaic kitchens are mentioned in this report as well. Two main conclusions have been drawn: trying to solely rely on the sun is a mistake and the ideal and universal ISC does not exist. Other factors besides the income are determinant when choosing an energy source, therefore, a thorough investigation in every particular case is completely necessary for a successful implementation of an ISC. However, the countless devices available make the adoption of solar technology possible in every situation, helping to achieve some of the Sustainable Development Goals.

A promising and novel solar concentrator design has been thoroughly investigated and optimised. A prototype concentrator based on this novel geometry was validated using ray tracing techniques. This ray tracing demonstrated the comparative performance of this novel concentrator in regards to equivalent parabolic dishes. The effect of mirror surface normal errors on performance was established using Monte-Carlo based ray tracing code, which agreed well with the optical performance of this prototype which was determined experimentally. A need for low-cost solar cookers to replace bio-mass worldwide was identified, and the concentrator design was then developed as a low-cost solar oven. Despite existing in some number, no current design is able to achieve high performance at low-cost. An industrial partner, Dytecna, was initially involved in the process of this development of the system as a solar cooker. In support of a field trial for the solar cooker developed with Dytecna, a detailed thermal model of the oven was developed. A low-cost lightmeter was constructed and calibrated in order to measure the direct normal irradiance during the field trial in Italy. Laboratory work provided baseline results for the heating of various thermal masses in the oven. The Italian field trials provided a wealth of feedback into the design of the system and many valuable results. The solar cooker was able to bring 0.75L of water to the boil in 33 minutes with an average heat throughput of 203W. Important benchmark results and practical experience of several competing receiver materials was obtained; further lab testing provided more accurate measurements of the receivers' performances. The experiences of the Italian field trial were fed back into the design of a subsequent prototype, intended for a much larger field trial in Tanzania. Improvements in the hotplate, receiver material, and the oven were all incorporated into the design. Additionally, the structure of the solar cooker was redesigned to incorporate a low-cost wooden construction. Supporting work was conducted for the month long trial in which 8 solar cookers would be distributed to families in Tanzania. The field trial in Tanzania provided a wealth of user feedback into the design. At the same time the new solar cooker exceeded previously established performances in Italy. The new design was able to provide an average of 246W of heat to 1kg of water, which was brought to boiling point in 25 minutes. This represents a heating efficiency of 66% compared to the incident solar flux on the hotplate. In response to findings during the Tanzanian trials, further laboratory work was conducted into establishing the reflectivities of low-cost candidate mirror materials. Throughout all phases of the project the design of the solar cooker was refined and improved with the goal of a solar cooker design that could reach price-point, performance, and usability standards which would ensure market success.