A solar simulator was used to test whether a carbon black additive could increase the solar absorption of a low temperature organic PCM (consisting of a eutectic mixture of palmitic acid and stearic acid). Various PCM and carbon black composites (0.01 % to 6 %) were tested, with the 0.06 % carbon black composites showing the fastest temperature increase, reaching 75 °C much quicker (350 % faster) than the pure PCM. All of the tested PCM composites reached 75 °C in less than half the time it took the pure PCM. It can therefore be seen that carbon black is very effective at increasing the solar absorption of the PCM. The carbon black did not have a negative impact on the melting/solidifying onset temperature or the latent heat of the PCM. This proves that at these low concentrations carbon black can help reduce the shortcomings of the PCM without adversely affecting its energy storage properties. The optimal carbon black concentration changes with the size of the PCM: a shallow PCM layer (2 cm) showed the fastest temperature increase at higher concentrations (between 0.06 % and 0.5 % carbon black), while the deep PCM layer (9 cm) showed the fastest temperature increase at lower concentrations (between 0.01 % and 0.08 % carbon black). The poor optical properties of the PCM were vastly improved by the carbon black, making the composite an effective direct solar absorber. The carbon black, however, does not provide meaningful thermal conductivity enhancements. Therefore additional heat transfer enhancements (like graphite) are needed if this novel PCM composite is to be used in a combined system (direct solar absorber, heat transfer fluid and energy storage system). / Dissertation (MEng)--University of Pretoria, 2016. / Chemical Engineering / MEng / Unrestricted

A novel type of parabolic trough collector was characterised using a very basic theoretical model. This model looked at an ideal case and provided a basic expectation that was compared to actual measurements. The model showed that greater improvements can be achieved if heat losses to the environment are limited or omitted. This can be achieved by using a glass shield to insulate the receiver in a vacuum to limit the effect wind has and therefore limit convective losses. The experimental characterisation of the PTC consisted of taking six different temperature measurements to better understand the energy balances taking place. Four different configurations were tested, using two different types of concentrator and in each case a receiver that was either unpainted or painted with a semi matte black paint. The different types of concentrator were either stainless steel sheet metal or discretised glass mirror strips, similar to a linear Fresnel collector. Experimental runs were conducted on cloudless days for an hour and 15 minutes. This allowed for three runs to be performed on a single day. Using the theoretical model and comparing it to the experimental data, an efficiency was calculated. This efficiency averaged 14 % when the receiver was unpainted and 13 % when the receiver was painted for the metal sheets. The glass mirror strips had average efficiencies of 54 % and 45 % for an unpainted and painted receiver respectively. The model is very basic and can be improved upon if more variables are taken into consideration, such as convective heat losses. It was also recommended that wind measurements are taken in future tests. A property looked at to evaluate the effectiveness of each type of configuration was the average energy supplied to the thermal heating fluid over the course of an experimental run. For this the averaged values over all the experimental runs conducted for stainless steel sheet metal were 258 W and 332 W for an unpainted and painted pipe respectively. When using the glass mirrors an average energy value of 1049 W was supplied when the pipe was unpainted and an average of 1181 W was gained in the runs conducted after the pipe had been painted. Painting the receiver had little to no effect. The surface temperature of the receiver after painting the pipe was not higher and a slight increase in the energy gained by water was observed. This was explained by inaccuracies during testing as scattered light may have caused an interference on some of the measurements. There were also human inaccuracies in testing which should be omitted in future tests by implementing, for one, a functional tracking system. Future tests should be designed in such a way to completely omit irradiance affecting the thermocouple taking the measurement. Glass mirrors fared far better than the stainless steel sheet metal counterpart. It was recommended that they are used as the concentrator of choice. Higher efficiencies were achieved and in some cases almost four times the energy was supplied to the water in the pipe. This was attributed to a much lower concentrator temperature, on average 11 °C lower than the temperature of the metal sheets, as well as a much better ability to concentrate sunlight onto a single focal point. However, the glass mirror strips were proven to be very fragile and as such, require protection from the elements. While the strips were lighter and caused less of a load during windy conditions, they were susceptible to oscillations from gusty wind. This led to a number of strips breaking and needed to be replaced. By discretising the strips into individual pieces, they had the benefit of only needing to replace the strips that were damaged. This is also true for all future runs. It is still recommended that a tarp be used to protect the glass mirrors. Using glass mirror strips as a concentrator combined LFC technology with PTC technology and a novel PTC design was achieved. The design still required the installation area of a PTC. The novel design was compared to Industrial Solar’s industrial LFC module, LF-11, as it shares many similarities to LFC technology. The peak thermal output of the rig was significantly lower at 346 W/m2 compared to the industrial value of 562 W/m2. However, the noteworthy differences in design and optimisation between the two modules meant the results achieved were comparable. It is expected that better and more comparable results can be realised once the inherent flaws in the design, such as tracking the sun, aperture size and adding a vacuum absorber, are addressed. It is recommended that more research and emphasis is put into this field as an alternative energy power plant for South Africa. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

One approach to enabling a larger penetration of renewable sources of energy is the implementation of hybrid power plants. This work presents a process to determine the preliminary optimal configuration of a concentrating solar power-coal hybrid power plant with low solar augmentation, and is demonstrated on a coal power plant in Castle Dale, UT. A representative model is developed and validated against published data for a coal power plant of a different configuration than Hunter Unit 3. The simplifications within the representative model include combining multiple feedwater heaters, combining turbines that operate across the same boundary states, and the mass-average calculation for extraction properties to the combined feedwater heaters. It is shown that the representative model can accurately and consistently simulate a coal power plant. Comparing net power generation and boiler heating estimates from the representative model to the benchmark power plant, the representative model is accurate to within +/- 1% the accepted value from the benchmark power plant. The methods for quantifying solar resource with data from the National Renewable Energy Laboratory are presented with the derivation of an algorithm to simulate a concentrating solar power field arrangement. The solar contribution to electrical power output is estimated using an exergy balance. A simplified financial model is also developed to estimate the solar marginal levelized cost of electricity and payback time using a cash-flow analysis. Estimates for solar resource, solar contribution, and financial performance are consistent with data published by the National Renewable Energy Laboratory or in archival literature. A multi-objective optimization routine is developed consisting of the representative model, the augmentation of solar energy into the solar integration model by means of feedwater heater bypass, solar contribution, levelized cost of electricity, and payback time. Because this study considered complete FWH bypass, higher solar augmentation (>3% of boiler heating) is required for a hybrid design to be considered feasible. However, for higher solar augmentation, the costs are also considerably higher and the financial benefit is insufficient to make any hybrid designs feasible unless a carbon tax is in place. A carbon tax will amplify the financial benefit of hybridization, so optimization results are provided assuming a carbon tax value equivalent to the value used in California's Emissions Trading System (16 USD sh.tn.^-1). The impact of a green energy premium price paid by consumers is also explored in the context of payback time. The resulting optimal design for the Hunter Unit 3 with a carbon tax and no premium is using parabolic trough collector technology at an augment fraction of k=9% to bypass feedwater heater 6. The resulting marginal solar levelized cost of electricity is 9.5 x 10^-4 USD kWh^-1 with an estimated payback time of 25.2 years. This process can be applied to any coal power plant for which operating data and meteorological data are available to evaluate preliminary hybridization feasibility.

Energy efficiency and renewable energy become more attractive in smart grid. In order to efficiently reduce global energy usage in building energy systems and to improve local environmental sustainability, it is essential to optimize the operation and the performance of combined heat and power (CHP) systems. In addition, intermittent renewable energy and imprecisely predicted customer loads have introduced great challenges in energy-efficient buildings' optimal operation. In the deterministic optimal operation, we study the modeling of components in energy-efficient building systems, including the power grid interface, CHP and boiler units, energy storage devices, and building appliances. The mixed energy resources are applied to collaboratively supply both electric and thermal loads. The results show that CHP can effectively improve overall energy efficiency by coordinating electric and thermal power supplies. Through the coordinated operation of all power sources, the daily operation cost of building energy system for generating energy can be significantly reduced. In order to address the risk from energy consumption forecast errors and renewable energy production volatility, we utilize the approach of stochastic programming and robust optimizations to operate energy-efficient building systems under uncertainty. The multi-stage stochastic programming model is introduced so that the reliable operation of building energy systems would be probabilistically guaranteed with stochastic decisions. The simulation results show that the stochastic operation of building energy systems is a promising strategy to account for the impact of the uncertainty on power dispatch decisions of energy-efficient building systems. In order to provide absolute guarantee for the reliable operation of building energy systems, a robust energy supply to electric and thermal loads is studied by exploring the effectiveness of energy storage on energy supply against the uncertainty. The robustness can be adjusted to control the conservativeness of the proposed robust operation model. For the purpose of achieving adaptability in the robust optimal operation and attaining robustness in the stochastic optimal operation of building energy systems, we also develop an innovative robust stochastic optimization (RSO) model. The proposed RSO model not only overcomes the conservativeness in the robust operation model, but also circumvents the curse of dimensionality in the stochastic operation model.

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This bachelor thesis consists of a field study conducted in the canton of Machacamarca close to La Paz in Bolivia. The global climate change has affected the weather in the area which has caused higher temperatures, irregularity in precipitation and unexpected frost. This has complicated the traditional cultivation methods and affected the harvest yield. One of the more important sources of income in the canton is the local diary that is processing milk from the local farmers. The main purpose of the thesis was to investigate the economic improvements that could be achieved in the canton with the implementation of an irrigation system driven by photovoltaic power, and to evaluate if it would be feasible. The simulation program Decision support system for agrotechnology transfer, DSSAT, has been used to simulate the cultivation and harvest of the two main crops for forage, alfalfa and barley. The required input data has been collected from the canton of Machacamarca and used to simulate the harvest yield for three scenarios, business as usual, ideal irrigation and limited irrigation calculated from the local conditions. A Matlab code based on numbers and parameters collected during the field study is used to create economical simulations from the different harvest results to receive economical results from several steps in the process. The final economical outcomes are compared to each other and to the cost for the chosen pump and irrigation system. Both scenarios considering irrigation show a stabilized and improved harvest yield, but only the third scenario is possible to implement in Machacamarca due to water restrictions in the area. This makes it possible to feed 0.47 more cows per hectare which will improve the farmers and the diary ́s income with 94.57 %. The water use for irrigation is 1.33 litres per square meter which makes the Shurflo 8000 water pump the most suitable option to provide water to the irrigation system powered by a 130 W solar panel and a battery. The investment cost for the system would go up to 6114 BOB equal to 883 USD and the system has a maintenance cost of 200 BOB every second year. This would make it economically feasible for the farmers to buy a system, but it would require investors or funding. With a payment plan the farmers would be able to pay off the investment without any problem. / Detta kandidatexamensarbete utgörs av en fältstudie i samhället Machacamarca utanför La Paz, Bolivia. De globala klimatförändringarna har påverkat vädret i området med högre temperaturer, oregelbunden nederbörd och oväntad frost. Detta har komplicerat det traditionella jordbruket och påverkat skörden. En av de viktigaste inkomstkällorna i samhället är det lokala mejeriet som producerar mejerivaror av mjölken från de lokala bönderna. Huvudsyftet med denna rapport är att undersöka den ekonomiska förbättringen samhället skulle få vid en implementering av ett bevattningssystem drivet av solenergi och ifall det skulle vara genomförbart. Simuleringsprogrammet, Decision support system for agrotechnology transfer, DSSAT, har använts för att simulera jordbruket och skörden för de två grödorna alfalfa och korn som i första hand används till foder. Nödvändiga data har hämtats ifrån Machacamarca och används för att simulera skörden för de tre scenariona, business as usual, ideal bevattning och begränsad bevattning bestämd från de lokala förhållandena. En Matlab kod baserad på nummer och parametrar funna under fältstudien används för att skapa ekonomiska simulationer för de olika skördarna för att få ekonomiska resultat från flera steg i processen. De slutgiltiga ekonomiska resultaten jämförs mot varandra samt mot kostnaderna för det valda pump- och bevattningssystemet. De båda bevattnade scenariona visar på en stabiliserad och förbättrad skörd, men endast det tredje scenariot är genomförbart i Machacamarca på grund av vattenbegränsningar. Detta gör det möjligt att föda upp 0.47 fler kor per hektar vilket förbättrar böndernas och mejeriets inkomst med 94,57 %. Vattenanvändningen när bevattning är nödvändigt är 1.33 liter per kvadratmeter vilket gör att Shurflo 8000 är det lämpligaste alternativet drivet av en 130 W solpanel och ett batteri. Investeringskostnaden för systemet skulle uppgå till 6114 BOB med en underhållskostnad på 200 BOB vartannat år. Detta skulle innebära att det är ekonomiskt möjligt för bönderna att köpa ett sådant system, men det skulle krävas investerare eller någon typ av finansiering. Med en avbetalningsplan så skulle bönderna kunna betala av hela kostnaden utan problem.

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No description available.

The IEEE 802.11 standard has been widely adopted as a Wireless LAN (WLAN) technology. This widespread proliferation of the technology has lead to an increase in the number of users taking advantage of so-called "hot-spots" which leads to an increased demand on bandwidth provided by Access Points (APs) in the hot-spot. The logical solution is to deploy more overlapping access points in the same coverage area, thus increasing the capacity of the system by providing load balancing services. However, when a hot-spot is located in an outdoor environment, it becomes difficult to provide the AP with power which is traditionally carried over wired links thus causing the service provider to incur additional costs, not to mention the impossibility in some cases of delivering power to the AP. This problem can be overcome by using solar-panel powered APs which we will refer to as solar nodes (SNs). In this thesis we examine the load-balancing problem that arises when two or more SNs are co-located in the same coverage area. We propose and evaluate two algorithms for efficiently distributing the load among them (transferring stations (STAs) from SN to neighboring SNs) and increasing their lifetime by using power saving schemes that co-ordinate the wake/sleep patterns of the SNs based on traffic load. Finally, a Connection Admission Control (CAC) function is proposed that the SN should use in order to provide controlled access to services. We demonstrate through simulations that our proposals can significantly reduce the hardware requirements and cost of SNs and improve the service perceived by STAs in terms of transmission delay. / Thesis / Master of Applied Science (MASc)

A computer program to estimate the weights and volumes of space borne power systems has been written. The program runs on a Zenith Z-100 microcomputer. The weight and volume of the system is calculated based on component data stored in the form of databases. An executive program which provides maximum flexibility to the user in terms of specifying the desired characteristics of the target system has been written. Constraints on the weight and volume of the system may also be specified. Some of the characteristics that may be specified are power requirement, orbit, duty cycles, etc. A complete User's Manual which describes the working methods to create new databases and enter new data, and includes error handling techniques has been generated. The result is an interactive, menu driven, user friendly software package to estimate the parameters of a space borne power system. / M.S.