Energy

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Synthesis and characterization of (Pani/n-si)solar cell
(Science Direct, 2011-01-01) Zaidan, K. M.; Hussein, H. F.; Talib, R. A.; Hassan, A. K.
Polyaniline(PAni) doped with formic acid was synthesis by chemical polymerization method using ammonium persulphate as oxidizing agent. Polyaniline /n-silicon hetrojunction have been fabricated by spin coating of polyaniline onto n-type silicon substrates. I-V characteristic of these junction diode show rectifying behavior with rectifying ratio of about 100. The I-V characteristics of PAni/n-Si junction were measured at room temperature (303K) and after annulling at 363K. They are found to exhibit quality factors of 1.83 and 1.32, saturation current of 5x10-6A and 5x10-4A, and barrier heights of 0.73eV and 0.61eV respectively. The photovoltaic properties of this hybrid solar cell were studied in the dark and under illumination investigated hybrid and was found to deliver short circuit current density Jsc =45μA/cm2, open circuit voltage Voc = 400mV, and solar cell efficiency η =0.3% under AM 1.5 simulated solar light with the intensity of 100mW/cm2.
Graphene-Based Materials for Energy Conversion
(Wiley, 2012-05-10) Sahoo, Nanda Gopal; Pan, Yongzheng; Li, Lin; Chan, Siew Hwa
With the depletion of conventional energy sources, the demand for renewable energy and energy-efficient devices continues to grow. As a novel 2D nanomaterial, graphene attracts considerable research interest due to its unique properties and is a promising material for applications in energy conversion and storage devices. Recently, the fabrication of fuel cells and solar cells using graphene for various functional parts has been studied extensively. This research news summarizes and compares the advancements that have been made and are in progress in the utilization of graphene-based materials for energy conversion.
2013 ISES Solar World Congress Promotion of PV Uptake and Sector Growth in Kenya through Value Added Training in PV Sizing, Installation and Maintenance
(Science Direct, 2014) Justus Simiyu; Sebastian M. Waita; Alex Ogacho; Robinson Musembi
Sub-Saharan Africa, and more specifically the East African region, has the lowest rates of access to electricity in the world. On average, at most 15% of the rural population has access to electricity. Rural households and remote institutions use traditional energy sources such as charcoal, firewood, kerosene and diesel for generator sets, batteries and dry cell batteries. On the other hand, the region is one of the most promising in the world in economic development with growth levels being high and market saturation is a far away future problem. This growth has however been hampered by several factors with lack of energy being one of them. Kenya being one of the countries in the region faces a similar problem with the traditional sources of hydro facing weather related challenges. The situation is more wanting in the rural setting having only achieved electrification rates of between 5 and 10%. The rural being where the majority of low-income earning groups reside is further compounded with large geographical imbalance in electricity demand and supply. The main challenge to adopting pv utilization however, is lack of local capacity to handle the uptake all the way from solar home systems to grid connected and hybrid systems. According to Kenya Renewable Energy Association (KEREA), it is estimated that between 800 and 1000 pv technicians have been in practice since this sector started in Kenya in the late eighties, majority of them having the basic skills but no formal training to provide the service. They however have been offering necessary service to end-users and are hence an important aspect in the pv sector as a whole. Currently the pv (mainly SHS) comprise an over the counter trade system which provides loopholes when it comes to quality of products and installation. To safeguard the quality and safety of installations, formal training has to be incorporated in the system.
INVESTIGATION OF SOLAR ENERGY POTENTIAL IN NAKURU – KENYA, AND ITS IMPLICATIONS ON KENYA’S ENERGY POLICY Omwando
(Semantic Scholar, 2014) L.-M; Kinyua; J.O.H, Ndeda; S.N, Marigi; KibwageJ, K.
The Kenyan Government is committed to promoting electricity generation from Renewable Energy Sources (RES) with priorities in solar, wind, hydros, biomass and geothermal. In this study, the potential of solar energy as a local source of clean and renewable resource for Nakuru was investigated. Global daily radiation intensity covering period 1986 to 2010 and air temperature records from 1960 to 2008 for Nakuru obtained from archives of the Kenya Metiorological Department (KMD) were subjected to a number of statistical analyses that included: Quality control and Homogeneity tests, temporal, time series as well as empirical statistics. The characteristics examined for the resource include diurnal; seasonal and annual power expectations. Results revealed that Nakuru is a moderate to high solar energy potential region, with an average daily insolation of 6.9kWh/m2. It was also revealed that the energy reaching the surface in this area is season dependant with December-February season receiving the highest amount of 678 kWh/m2 and September-November season receiving the least amount of 602.6kWh/m2. The study concludes that Nakuru is endowed with abundant solar energy resources, favorable for tapping at both small and medium scale levels. These levels are quite convenient, particularly for isolated households in the rural and pre-urban settings of the town. The solar energy potential revealed by the study is bound to go a long way in fulfilling the vision of Kenya energy policy as elaborated in sessional paper No4 of 2004.
POTENTIAL USE OF ALGAE FOR NUTRIENT REMEDIATION OF WASTEWATER AND PRODUCTION OF CLEAN ENERGY
(University of Eldoret, 2014) Rono, Mary
The reliance on fossil fuels as a source of energy has led to environmental degradation and a myriad of health problems leading to a need for renewable source of energy that is economical and sustainable. Likewise, eutrophication of water bodies is a matter of concern because it disturbs normal functioning of such an ecosystem. The release of improperly treated wastewater is one major cause of this problem. The objective of this study was to utilize nutrients present in wastewater for algal growth and later produce biofuel from the harvested biomass of the algae. Individual algae cultures of locally dominant genera Spirogyra, Oedogonium and Zygnema, collected in Kesses area of Uasin Gishu County were grown in laboratory conditions at Moi University. A 10g portion of the algae were grown in 250 ml Erlenmeyer flasks containing 100ml of sewage in an incubator set at 260C with continuous light provided by a 5 W fluorescent tube. The flasks were stirred once daily to prevent settling of algal cells. 0.05 mg of CO2 was bubbled to the flasks once. The control consisted of algae grown in Bold Basal media. Algal growth was monitored for seven days using daily measurements of chlorophyll a. Daily uptake of nitrate from the wastewater by the algae was also determined through automated hydrazine reduction method. After the seven days, the algae were harvested and dried. Lipids were obtained from the dried biomass by Soxhlet extraction using a mixture of hexane and ethanol, and weighed in grams. The quantities of starch were estimated using enzymatic-colorimetric method and given as a percentage of the sample. The lipids obtained were utilized to determine the calorific value of the fuel using a bomb calorimeter. All the data obtained were statistically analyzed using the SPSS program. Friedman test was utilized to check whether there was a statistical difference exhibited by the various taxa in amounts of nitrates reduced, as well as in the accumulation of chlorophyll a. Wilcoxon test was employed to check whether there was a statistical difference in the amounts of lipids, starch and calorific values between those algae that grew in sewage and those that had been grown in the growth medium. Results showed that all the algae genera grew better in Bold Basal Medium than on sewage. For all the genera that were grown on sewage, growth declined after the fourth day and Zygnema showed the highest growth in sewage. On nitrate removal from the wastewater, the length of contact time between the algae and wastewater was of paramount importance. After four days the studied Spirogyra decreased the quantities of nitrate in 100 mL sewage by 90.7%, Oedogonium by 89.48% and Zygnema by 83.84%. On lipid productivity, results obtained showed that growth of algae on sewage led to accumulation of higher quantities of lipid. Spirogyra increased lipid quantities when it was cultured on sewage by 73.99%, Oedogonium by 91.38 and Zygnema by 89.04%. However, those results acquired from estimation of starch illustrated that growth of the algae on sewage led to accumulation of less amounts of starch. Growth of Zygnema on the sewage reduced the quantities of starch by 82.11%, 79.63% in Spirogyra, and 58.13% in Oedogonium. In Spirogyra and Zygnema, lipids obtained from algae that grew in sewage had higher calorific values than those that had grown in the growth medium. From the results of this study, it can be concluded that sewage may be used as an alternative growth media for algae. The problem of eutrophication can also be counteracted using local genera of algae. The results also illustrate that sewage grown algae can produce biomass suitable for production of biofuel.v
Positron-Impact Excitation of the Lowest Autoionizing State in Rubidium Atom using Distorted Wave Method
(2014-05) Marucha, Alex Magembe
Many calculations on atomic collisions and scattering processes have been performed on electron impact excitation of the lowest autoionizing state of rubidium, but not much attempt has been made with positron impact which is of equally fundamental importance and is receiving attention nowadays with the availability of improved positron beam experiments. So, in this study, total cross-sections, differential cross-sections, lambda parameter, R parameter and the alignment parameter for positron impact excitation of the lowest autoionizing state of rubidium have been calculated using Distorted Wave method. The wave functions used are the Roothan Hatree Fock double zeta and multi zeta wave functions due to Clementi and Roetti. Variations in distortion potential have been made such that the static potential of the initial state of rubidium atom is used as the initial channel distortion potential and a linear combination of static potentials of the initial and final states as the final channel distortion potential to check its effect on cross- sections. Numerical calculations have been done using a modified DWBA1 FORTRAN computer program which was originally made for hydrogen atom. The results for positron impact excitation of the lowest autoionizing state of rubidium have been analyzed and compared with experimental and theoretical results for positron and electron impact excitation of the same state available in literature. From the comparison of the results, it is seen that in general the electron impact excitation cross section results are higher than the positron impact excitation cross section especially near excitation threshold energy. This can be attributed to the exchange process which takes place in the case of electron impact and not in the case of positron impact and also due to larger interaction between the projectile and the target in case of electron impact than in case of positron impact. It is also found from the alignment parameter results that the integral cross section results for m=0 level are larger compared to m=1 level for impact energies up to about 500 eV beyond which integral cross-sections for the magnetic sublevel m=1 become greater. The lambda parameter indicates that more particles are scattered towards m=0 for electron impact compared to positron impact excitation near threshold energy. R parameter results have been calculated to account for phases of scattered amplitudes in the collision process
Energy Characteristics of Five Indigenous Tree Species at Kitulangalo Forest Reserve in Morogoro, Tanzania
(INTERNATIONAL JOURNAL of RENEWABLE ENERGY RESEARCH, 2014-11-29) Warburg, Christopher T; King’ondu, Cecil K
This study presents the investigation of material composition and energy characteristics of B. spiciformis, B. boehmii, C. molle, P. maprouneifolia, and S. birrea indigenous tree species at kitulangalo forest reserve in Tanzania. Energy content of each species mostly depends on its chemical content (C, H and O) and it is reduced by inorganic elements and moisture. Biomass chemical composition was done by proximate and ultimate analyses. Regarding the elemental composition, P. maprouneifolia and C. molle had high energy content of 18.62 and 18.30 MJ/Kg, respectively because of their higher H:C ratio and relatively low O:C ratio. Carbon, oxygen, and hydrogen were found to be highest in P. maprouneifolia with 46.71, 41.96, and 5.7%, respectively. In contrast, P. maprouneifolia had the lowest N:C ratio of 0.014, implying good efficiency for nitrogen use to fix carbon. On the other hand, ash, moisture, and volatiles were highest at 4, 55, and 85% for S. birrea, B. spiciformis, and S. birrea, correspondingly. The ratio of macronutrients to carbon for each species was also calculated. Results show that all species have high demand for nitrogen followed by potassium and calcium, in that order. Finally, heating values have been shown to decrease with increasing moisture content. These experimental results were used for ranking these biomass materials for energy generation. They also furnish vital biomass information for equipments and process designers.
Simulation of 16O (n, p) 16N reaction rate and nitrogen-16 inventory in a high performance light water reactor with one pass core
(Elsevier, 2014-12) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
The rate of activation of the isotope 16O to 16N in a typical HPLWR one pass concept was calculated using MCNP code. A mathematical model was used to track the inventory of the radioisotope 16N in a unit mass of coolant traversing the system. The water leaving the moderator channels has the highest activity in the circuit, but due to interaction with fresh coolant at the lower plenum, the activity is downscaled. The calculated core exit activity is higher than values reported in literature for commercial boiling water reactors.
Evaluation of candidate materials for SCWR turbine and balance of plant shielding
(Elsevier, 2014-12-13) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
Since the coolant leaving the SCWR core contains an assortment of radioisotopes, it is necessary to identify appropriate materials for shielding ex-core components. Photon attenuation characteristics, photo-neutron production capacity and cost effectiveness of candidate materials were investigated in this study. WinXcom computer code was used for attenuation studies while other properties were surveyed in literature. High Z materials (lead and tungsten) show excellent gamma attenuation properties however they are expensive and could be vulnerable to photo-neutron production if used for shielding turbines or the pressure vessel exit steam-line. Barite concrete which is a moderate attenuator could also be susceptible to photo-neutron production if used for shielding components with high Nitrogen-16 activity. Heavy concretes with iron aggregates on the other hand show fair attenuation and are not susceptible to photo-neutron production in the energy range of photons released from reactor water. In terms of cost, concretes are cheaper and easy to fabricate compared to high Z materials especially when a shield of intricate shape is required. Depending on the available space for the shield, heavy concretes would be the most appropriate materials for shielding the SCWR turbine and balance of plant. However in case of space limitation, their attenuation capacity can be enhanced by introducing high Z materials in reasonable proportions.
Design and optimization of HPLWR high pressure Turbine gamma ray shield
(Elsevier, 2014-12-20) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
This work proposes the optimum gamma ray shield thickness around the HPLWR high pressure turbine for different occupancy periods in the turbine building. Monte Carlo method was employed in the design process and only radioactive nitrogen-16 was considered as the source of radiation. Five grades of concrete (ordinary, magnetite, heavy magnetite, steel magnetite and barite) were used as shielding materials. The isotope source term in the high pressure turbine was estimated by modeling the HPLWR three pass core in MCNP and tracking the inventory using a simple algorithm. The high pressure turbine was thereafter modeled in MCNP with a concrete shield arrayed in layers around it. The surface flux tally and ICRP74 dose conversion coefficients were employed to estimate the dose profile across the shield. For some shielding materials, exponential functions were fitted on the calculated data to extrapolate dose values beyond the model thickness. The optimum shield thickness was determined by comparing the calculated dose profiles with dose limit proposals in the IAEA standard (NS-G-1.13) on radiation protection considerations during nuclear power plant design. It was observed that with a 120cm thick heavy concrete shield, the turbine building would be safe for most occupancy periods. However for ordinary concrete the shield would require some extension to guarantee safety. For very long occupancy (more than 10 person hours per week), magnetite shield may also require slight extension. It can therefore be concluded that the shield thickness recommended for BWR turbines (which operate on a direct cycle like HPLWR) could be sufficient for HPLWR if high density concretes are used.
Performance Evaluation of Silicon-Based Photovoltaic Modules Found in the Kenyan Market
(Kenyatta University, 2015) Njeru, Elosy Gatakaa
Various kinds of photovoltaic (PV) modules have been developed and practically deployed as PV systems over time. The performance of PV modules found in the Kenyan market has not been documented and therefore their reliability and stability in providing an alternative source of energy has not been sufficiently established. In this study the I-V data of Silicon-based mono crystalline, poly crystalline and amorphous modules was collected. The choice of the modules was done randomly depending on their availability, the cost of the modules and their power rating. They were selected randomly from PV module vendors within Nairobi Central Business District (CBD). The manufacturers’ specifications were taken. The modules were then mounted at an optimum fixed tilt angle of 15 degrees. Initial measurements of short circuit current Isc, open circuit voltage Voc, ambient temperature and module temperature were taken immediately on mounting the modules. Measurements of current and voltage to obtain I-V data was done daily at solar noon for four months. The back of the module temperature and ambient temperature at the time of measurement was measured using thermocouple while the irradiance at the time of measurement was measured using a pyranometer. The pyranometer was mounted at the plane of array of 15 degrees as the modules. The collected I-V data was normalized and I-V curves were plotted. Performance parameters of the modules were then calculated from the I-V curve. There was a decrease in Voc of the modules with time with the amorphous modules clearly showing the Staebler-Wronski effect. The Isc of the modules showed little variation while Pmax of the modules had reduced significantly. The Pmax of most of the modules was found not to match with the manufacturers specifications provided in their data sheet. On inspection of the modules, the 10W polycrystalline module revealed a defect which was as a result of overheating of the cells that contributed greatly to its poor performance in comparison to the other polycrystalline modules. The efficiency of the amorphous modules ranged between 3%- 5% while that of mono crystalline and polycrystalline was above 10%.
FUELWOOD CONSUMPTION PATTERNS IN MBARALI DISTRICT, SOUTH-WESTERN TANZANIA
(University of Eldoret, 2015) Kegode, Sayo
Biomass fuels account for much of domestic energy consumption in many developing countries. Despite the significance of these fuels in domestic energy provision, their unsustainable consumption often occurs at the expense of environmental conservation. Agroforestry has often been cited as a possible intervention to reduce high dependence on natural resources, which is a characteristic of many developing countries. This study aimed to analyze the determinants of choice of sources of fuelwood and fuelwood consumption, with a view to contributing to policy discussions on reducing environmental degradation through agroforestry interventions. Cross-sectional data was obtained from two hundred and fifty four (254) randomly selected households from Mbarali district in south-western Tanzania. Household data was complemented with information from focus group discussions and key informant interviews. Multinomial logit regression model was used to identify the determinants of choice of fuelwood sources while the ordinary least squares regression model was used to identify determinants of household consumption of fuelwood. The results show that 88% of households consider fuelwood to be the most important fuel especially for cooking and that 74% of households that consume fuelwood depend on natural forests as the main source. The choice of fuelwood sources was influenced by species composition of the source and some household characteristics. Significant determinants of fuelwood consumption included age of the household head, income and price of kerosene. The results show that consumers, both households and other end users preferred Faidherbia albida for fuelwood which is the key agroforestry tree species in the area. Thus, fuelwood consumption maybe a threat to the success of agroforestry interventions that promote Faidherbia albida for soil fertility and environmental conservation. To exploit the potential of agroforestry, alternative sources of energy should be made available and affordable to the community; in addition to fostering strategies to promote adoption of efficient use of available energy. Cultivation of tree species with characteristics similar to the preferred fuelwood species, for instance, Acacia tortilis is also recommended to divert long term fuelwood demand away from natural forests and to reduce competition with Faidherbia albida. To the extent that consumer preferences are likely to change over time, further research using panel datasets is necessary to reveal inter temporal preferences for fuelwood sources.
ASSESSMENT OF WIND CHARACTERISTICS AND POWER POTENTIAL AT KESSES LOCATION - UASIN-GISHU COUNTY, KENYA
(University of Eldoret, 2015) Cheruiyot, Wilkins
Wind energy is increasingly becoming popular all over the world as a green energy source for electricity generation since it is renewable and environmentally friendly. Pioneer wind turbines for electricity generation in Kenya were recently installed at Ngong Hills and Lake Turkana, and more is expected to be initiated in different parts of the country. Wind turbines extract the kinetic energy carried by the flowing wind and this energy is directly proportional to the cube of wind speed. Thus, the wind speed is the most important parameter to consider in designing and selecting an efficient wind energy conversion system. Meteorological Department (MET) and some learning institutions in Kenya have been collecting and storing climatic data for several years, including wind speeds and most of them have not been analyzed. Precise knowledge of availability of wind at any given location is a pre-requisite for the effective planning and implementation and speed analysis is useful for the assessment of wind characteristicsand power potential at a location. In this work, analyses of five years (2009-2013) wind speed data collected at a meteorological unit at Moi University, Kesses area, Uasin Gishu County- Kenya, was done. The station measures wind speed at a height of 2 m and were extrapolated to the standard height of measurements of 10 m and typical hub heights of 40 m, 70 m and 100 m for purposes of characterization and determination of energy potential respectively. The extrapolated results revealed that the average annual wind speed at the height of 10 m is 3.86 ms-1, meaning that the location wind speed can be classified as class IV with a maximum wind power density of 100 Wm-2. The average annual wind speed at the hub heights of 40 m, 70 m and 100 m were 5.48ms-1, 6.33ms-1and 6.93ms-1, giving corresponding power densities of 115.563Wm-2, 175.395Wm-2and 228.917 Wm-2respectively. Weibull distribution model was used in the analysis of wind speed distribution. The Weibull scale parameter range from 2.543 ms-1to a maximum of 3.046 ms-1. The Weibull shape parameter was peaked at 5.902 in the year 2012. Both cumulative and probability density function were assessed and graphically presented.Results showed that the site has potential for harnessing wind energy for electricity generation and both small and medium scale wind power turbines are recommended for installation at the site.
Investigation of photoneutron and capture gamma-ray production in Pb and W under irradiation from 16N decay radiation
(Elsevier, 2015-09-01) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
Lead and tungsten are potential alternative materials for shielding reactor ex-core components with high 16N activity when available space limits application of concrete. Since the two materials are vulnerable to photonuclear reactions, the nature and intensity of the secondary radiation resulting from (γ,n) and (n,γ) reactions when 16N decay radiation interact with these materials need to be well known for effective shielding design. In this study the MCNP code was used to calculate the photoneutron and capture gamma-ray spectra in the two materials when irradiated by 16N decay radiation. It was observed that some of the photoneutrons generated in the two materials lie in the low-energy range which is considered optimum for (n,γ) reactions. Lead is more transparent to the photoneutrons when compared to tungsten. The calculations also revealed that the bremsstrahlung generated by the beta spectrum was not sufficient to trigger any additional photoneutrons. Both energetic and less energetic capture gamma-rays are observed when photoneutrons interact with nuclei of the two materials. Depending on the strength of the 16N source term, the secondary radiation could affect the effectiveness of the shield and need to be considered during design.
A Simple Low Cost Solar Panel/cell Characterization Experiment for Senior Undergraduate Students
(ISES, 2015-11-11) Sebastian Waita*, Justus Simiyu, Alexander N. Kiragu, Vivian Imali and Bernard Aduda
A simple low cost solar cell characterization experiment has been developed for senior undergraduate students in the Department of Physics, University of Nairobi. Experiments were conducted with solar panels (also called solar modules/photovoltaic modules) rated 20 W and 40 W peak power on different sunny days on the roof top of Physics Department, University of Nairobi. It was observed that the current- voltage (I-V) curves obtained for all the measurements for each panel were comparable. The fill factor (FF), short circuit current (Isc), open circuit voltage (Voc), current at maximum power point (Im) and voltage at maximum power point (Vm) were within acceptable margins when compared with the manufacturer’s rated values, an indication of the reliability and accuracy of the method. The method eliminates the need for expensive characterization equipment like solar simulators, unaffordable by many developing country institutions. The experiment is recommended for senior undergraduate students with an interest in renewable energy as one way of introducing them to renewable energy. The experiment may also help in arousing the learner’s interest in solar energy.
CHARACTERIZATION OF WATER HYACINTH (EICHHORNIA CRASSIPES) COMPOSITE BRIQUETTE AS AN ALTERNATIVE DOMESTIC ENERGY SOURCE
(University of Eldoret, 2016) Okia, Daniel Otieno
Biomass is one of the most promising energy sources to mitigate greenhouse gas emission during production and utilization. However, majority of biomass are not suitable to be utilized as fuel without an appropriate process since they are bulky, uneven and have low energy density. These characteristics make them difficult in handling, storage, transport and utilization. One of the promising solutions to overcome these problems is the briquetting technology. The study was conducted to characterize water hyacinth composite briquette as an alternative domestic energy source. Water hyacinth was chopped using a shredder and left for two weeks in a heap to partially decompose. The material was thoroughly mixed manually with dried and crushed charcoal dust and cow dung in the ratios of water hyacinth: charcoal dust: cow dung of 100:0:0 (control), 80:10:10, 70:20:10, 70:10:20, 60:30:10, 60:20:20 and 60:10:30 (by weight). The resulting material was then mixed into soupy slurry in water. Simple prototype briquetting mold was fabricated to facilitate densification of these residues into hollow cylindrical briquette at a pressure of 1MPa. The experimental results revealed that the mixture that gave optimal combustion characteristics was 60:30:10 and the calorific values ranged from 16.215 to 21.585 MJ/kg. Water hyacinth alone (100:0:0) gave the best emission characteristics having 28.51 ppm carbon monoxide and 452.80 ppm carbon dioxide though ranking third with 13,623 μg/m3 in particulate matter. For quality control, water hyacinth composite briquette gave good indications on physical parameters that were measured. The results showed that resistance to water penetration range from 79.5% to 88%, durability index range from 57.9% to 99.6% with 60:30:10 and 60:20:20 ratios exhibiting poor index of 57.88% and 59.23 respectively probably due to high charcoal dust content which is known to have low bonding. The rest of mixtures gave 80% and above, with water hyacinth (100:0:0 ratio) showing the highest durability index of 99.63% probably because of partial decomposition which increases the binding effect of biomass. Equilibrium moisture content range from 8.5% to 15.2% at 29 oC and 58% relative humidity; water hyacinth alone was having the highest. This study therefore demonstrates that water hyacinth composite briquette have good physical and combustion characteristics and can therefore be utilized as alternative domestic energy source.
Optical and Electrical Properties Dependence on Thickness of Screen-Printed TiO2 Thin Films
(Springer, 2016) Domtau, D. L.; Simiyu, J.; Ayieta, E. O.; Muthoka, B.; Mwabora, J. M.
Abstract Effect of film thickness on the optical and electrical properties of TiO2 thin films were studied. Thin films of different thicknesses were deposited by screen printing method on fluorine doped tin oxide coated on glass substrate. The film thickness was determined by surface profile measurement. The thicknesses were 3.2, 8.2, 13.5 and 18.9 µm. Transmittance, reflectance and absorbance spectra were studied using UV-VIS-NIR spectrophotometer in the photon wavelength range of 300-1500 nm for transmittance and reflectance and 350-1200 nm for absorbance. Band gap and refractive index of the films were determined using these spectra. It was found that reflectance, absorbance, band gap and refractive index increased with film thickness while transmittance decreased with increase in thickness. I-V characteristics of the films were also measured by a 4- point probe. Electrical resistivity (𝜌𝜌) and conductivity (σ) where calculated from the I-V values. Resistivity was found to increase with thickness while conductivity decreased with increase in film thickness. Keywords: TiO2 thin films, thickness, optical and electrical properties, screen printing
Study of Surface Defects on Co-Doped TiO2 Thin Films Deposited by Spray Pyrolysis
(MDPI, 2016-07) Henry Wafula; Albert Juma; Thomas Sakwa
Surface photovoltage (SPV) spectroscopy is a powerful tool for studying electronic defects on semiconductor surfaces, at interfaces, and in bulk for a wide range of materials. Undoped and Cobalt-doped TiO2 (CTO) thin films were deposited on Crystalline Silicon (c-Si) and Flourine doped Tin oxide (SnO2:F) substrates by chemical spray pyrolysis at a substrate temperature of 400 ˝C. The concentration of the Co dopant in the films was determined by Rutherford backscattering spectrometry and ranged between 0 and 4.51 at %. The amplitude of the SPV signals increased proportionately with the amount of Co in the films, which was a result of the enhancement of the slow processes of charge separation and recombination. Photogenerated holes were trapped at the surface, slowing down the time response and relaxation of the samples. The surface states were effectively passivated by a thin In2S3 over-layer sprayed on top of the TiO2 and CTO films.
Electrical and Structural Properties of Aluminium Doped tin Oxide Codoped with Sulphur for Solar Energy
(Elsevier, 2016-08) Muramba, Valentine Wabwire; Mageto, Maxwell
Thin films of Tin Oxide co-doped with 28 atomic percentages of Aluminium (i.e. 28 at% Al) and varied concentration of Sulphur were prepared on 1mm thick, 1cm by 1cm glass substrates at 470 0C by Spray Pyrolysis technique. Films were produced from 2.0M solution of hydrous Tin Chloride dissolved in Ethanol with 38% Hydrochloric acid concentration, 1.5M aqueous Aluminium chloride and 2.0M aqueous solution of Ammonium Sulphide. The effects of Sulphur concentration on structural and electrical properties of transparent Tin Oxide thin films were investigated in the atomic percentage of Sulphur content ranging from zero to fifty (i.e. 0at%S -50at%S) with a fixed 28at%Al content. Polycrystalline structures without any second phases were observed with preferential orientations along the (110), (101), (200) and (211) planes. The average grain size as determined from the (110) peaks lay in the range 19.2 nm-47.7nm. The minimum resistivity was found to be 1.15x10-3Ωcm for the Tin Oxide films doped with 32 at% Al content and 9.59x10-3Ωcm for Tin Oxide films co-doped with 28 at% Al and 20 at% S content. It was observed that Aluminium doping lowered the grain size significantly but doping to optimum level of 32 at% Al content increases electrical conductivity of tin oxide. When Sulphur was intentionally introduced in the crystal structure of 28 at% Al doped Tin Oxide, the electrical conductivity decreased appreciably and the grain size increased.
Electrical and Structural Properties of Aluminium Doped tin Oxide Codoped with Sulphur for Solar Energy
(Elsevier, 2016-08) Muramba, Valentine Wabwire; Mageto, Maxwell
Thin films of Tin Oxide co-doped with 28 atomic percentages of Aluminium (i.e. 28 at% Al) and varied concentration of Sulphur were prepared on 1mm thick, 1cm by 1cm glass substrates at 470 0C by Spray Pyrolysis technique. Films were produced from 2.0M solution of hydrous Tin Chloride dissolved in Ethanol with 38% Hydrochloric acid concentration, 1.5M aqueous Aluminium chloride and 2.0M aqueous solution of Ammonium Sulphide. The effects of Sulphur concentration on structural and electrical properties of transparent Tin Oxide thin films were investigated in the atomic percentage of Sulphur content ranging from zero to fifty (i.e. 0at%S -50at%S) with a fixed 28at%Al content. Polycrystalline structures without any second phases were observed with preferential orientations along the (110), (101), (200) and (211) planes. The average grain size as determined from the (110) peaks lay in the range 19.2 nm-47.7nm. The minimum resistivity was found to be 1.15x10-3Ωcm for the Tin Oxide films doped with 32 at% Al content and 9.59x10-3Ωcm for Tin Oxide films co-doped with 28 at% Al and 20 at% S content. It was observed that Aluminium doping lowered the grain size significantly but doping to optimum level of 32 at% Al content increases electrical conductivity of tin oxide. When Sulphur was intentionally introduced in the crystal structure of 28 at% Al doped Tin Oxide, the electrical conductivity decreased appreciably and the grain size increased.

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