Renewable Energy Alternatives

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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.
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
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.
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.
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.
The effect of mesoporous TiO2 pore size on the performance of solid-state dye sensitized solar cells based on photoelectrochemically polymerized Poly(3,4-ethylenedioxythiophene) hole conductor
(Science Direct, 2016-08-20) Zhang, Jinbao; Pazoki, Meysam; Simiyu, Justus; Johansson, Malin B.; Cheung, Ocean; Häggman, Leif; Johansson, Erik M. J.; Vlachopoulos, Nick; Hagfeldt, Anders; Boschloo, Gerrit
Photoelectrochemical polymerization of poly(3,4-ethylenedioxythiphene) (PEDOT) has recently been introduced and widely investigated for fabrication of the hole transporting material (HTM) in highly efficient solid state dye sensitized solar cells (sDSCs). In this work, the effects of the surface area and pore size of TiO2 film were for the first time investigated in the sDSCs employing the in-situ polymerizated PEDOT HTM. Three different varieties of mesoporous TiO2 particles with controllable surface area and pore size were synthesized through the basic route in order to study the corresponding sDSC photovoltaic performances. It was found that the pore size plays an important role in the kinetics of the photoelectrochemical polymerization (PEP) process and the formation of the PEDOT capping layer. Larger pore sizes provided a more favourable pathway for the precursor diffusion through the mesoporous pores during the PEP process, which contributed towards a more efficient PEP. However, the interfacial contact area between the formed polymer and the dyes on the surface of TiO2 particle would be lower in the case of larger pore sizes, which consequently caused a less efficient dye regeneration process. Electronic diffusion on the other hand was improved for larger particle sizes. Employing an organic dye LEG4 and the self-made TiO2 with an optimal pore size of 25nm and particle size of 24nm, the sDSCs showed a promising power conversion efficiency (PCE) of 5.2%, higher than 4.5% for the commercial TiO2 Dyesol DSL-30. By measuring the dye regeneration yield and the kinetics through photoinduced absorption, it was observed that the homemade TiO2 based device had more efficient dye regeneration compared to the Dyesol based device, which could result from the better interfacial contact between the PEDOT and the dye. This work provides important information on the effect of meso-pore size on sDSCs and points to the necessity of further photoanode optimization toward the enhancement of the PCE of polymeric hole conductor-based DSCs.
Influence of Pore Size on the Optical and Electrical Properties of Screen Printed
(Hindawi Publishing Corporation, 2016-09-27) Domtau, Dinfa Luka; Simiyu, Justus; Ayieta, Elijah Omollo; Asiimwe, Godwin Mwebeze; Mwabora, Julius Mwakondo
Influence of pore size on the optical and electrical properties of TiO2 thin films was studied. TiO2 thin films with different weight percentages (wt%) of carbon black were deposited by screen printing method on fluorine doped tin oxide (FTO) coated on glass substrate. Carbon black decomposed on annealing and artificial pores were created in the films. All the films were 3.2 µm thick as measured by a surface profiler. UV-VIS-NIR spectrophotometer was used to study transmittance and reflectance spectra of the films in the photon wavelength of 300–900 nm while absorbance was studied in the range of 350–900 nm. Band gaps and refractive index of the films were studied using the spectra. Reflectance, absorbance, and refractive index were found to increase with concentrations of carbon black. There was no significant variation in band gaps of films with change in carbon black concentrations. Transmittance reduced as the concentration of carbon black in TiO2 increased (i.e., increase in pore size). Currents and voltages () characteristics of the films were measured by a 4-point probe. Resistivity () and conductivity () of the films were computed from the values. It was observed that resistivity increased with carbon black concentrations while conductivity decreased as the pore size of the films increased.
Selection and Verification of a Drying Model for Maize (Zea mays L.) in Forced Convection Solar Grain Dryer
(science and education publishing, 2017) Osodo, Booker; Nyaanga, Daudi; Muguthu, Joseph
Various researchers have fitted experimental drying curves for various products to existing drying models. In this study, an experimental forced convection solar grain dryer was used to select the best fitting drying model for shelled maize. 0.04 m thick grain layer of shelled maize was dried an air velocity of 0.408 m/s and a 40°C drying air temperature. Using Root Mean Square Error (RMSE), Coefficient of Determination (R2) and Chi Square (𝜒𝜒2) the selected drying model was the one by Midilli et al. (2002), with R2, 𝜒𝜒2 and RMSE values of 0.9487, 0.4278 and 0.1723 respectively. The model coefficients were determined for drying air temperatures of 40, 45, 50 and 55°C. It was found that the predicted and experimental data agreed satisfactorily with R2 and RMSE values of 0.9225-0.9786 and 0.0325-0.0750 respectively. A computer simulation model was developed to predict moisture ratio at a given drying time.
Structural and optical properties of phosphorous and antimony doped ZnO thin films deposited by spray pyrolysis: a comparative study
(International Advanced Research Journal in Science, Engineering and Technology, 2017) Nyarige, Justine S.; Sebastian, Waita; Simiyu, Justus; Mureramanzi, Silas; Aduda, Benard
A study of structural and properties of pure (undoped) Zinc oxide (ZnO) and phosphorous (P) and Antimony(Sb) doped Zinc Oxide films has been carried out. The films were deposited by an automated spray pyrolysisequipment on both microscope glass at various elevated temperatures (270 oC - 420 oC) and on fluorine doped tinOxide (FTO) substrates at 420 oC. Structural characterization using Raman spectroscopy showed the presence of themain peak for ZnO at 437 cm-1for all the films. Antimony doped films showed other peaks associated with the dopingbut phosphorous doping did not show extra peaks. Optical characterization using a UV-VIS-NIR Shimadzu (ModelDUV 3700) double beam spectrophotometer provided both reflectance and transmittance data and Scout software wasused to compute the band gap. At a wavelength of 600 nm, the average transmittance of the pure ZnO films was ~62% while it was transmittance was ~85 % and ~80 % for Sb and P doped films respectively, an increase of ~23 % and~18 % respectively. For the undoped ZnO films, high deposition temperatures led to band gap narrowing from 3.25eVto 3.10eVwhile doping resulted in band gap widening from 3.10 eV to 3.30 eV (for P-doped) and 3.10 eV to 3.33 eV(for Sb-doped),an observation confirmed by the increased transmittance on doping. The band gap narrowing for ZnOfilms makes the film become a better materials for visible light absorption which is good for photovoltaic applications.The wide gap broadening on doping makes the film more transparent to solar radiation making it suitable fortransparent conducting oxide applications.
Compositional analysis and optical properties of Co doped TiO2 thin films fabricated by spray pyrolysis method for dielectric and p hotocatalytic applications
(Science Direct, 2017-01-01) Wafula, Henry Barasa; Musembi, Robinson Juma; Juma, Albert Owino; Tonui, Patrick; Simiyu, Justus; Sakwa, Thomas; Prakash, Deo; Verma, K. D.
Cobalt doped TiO2 thin films (CTF) deposited by spray pyrolysis has been studied. The compositional analysis has been done using RBS method, while optical spectroscopy has been done by measuring the transmittance and reflectance of the films. The CTF thin films were prepared by doping TiO2 at different concentration levels of Co which was varied between 0 and 4.51 at.%. The optical transmittance of the thin film has been found to be about 80% in the visible and near infra red regions. The calculated optical band gap has been observed to shift by about 0.22 eV, this shows a high potential for application as a dielectric and a Photocatalyst material.
Graphene for Thermoelectric Applications: Prospects and Challenges
(Critical Reviews in Solid State and Materials Sciences, 2017-04-10) A, Amollo; Mola, Genene Tessema; Nyamori, Vincent
Thermoelectric power generators require high-efficiency thermoelectric materials to transform waste heat into usable electrical energy. An efficient thermoelectric material should have high Seebeck coefficient and excellent electrical conductivity as well as low thermal conductivity. Graphene, the first truly 2D nanomaterial, exhibits unique properties which suit it for use in thermoelectric power generators, but its application in thermoelectrics is limited by the high thermal conductivity and low Seebeck coefficient resulting from its gapless spectrum. However, with the possibility of modification of graphene's band structure to enhance Seebeck coefficient and the reduction of its thermal conductivity, it is an exciting prospect for application in thermoelectric power generation. This article examines the electronic, optical, thermal, and thermoelectric properties of graphene systems. The factors that contribute to these material properties in graphene systems like charge carriers scattering mechanisms are discussed. A salient aspect of this article is a synergistic perspective on the reduction of thermal conductivity and improvement of Seebeck coefficient of graphene for a higher thermoelectric energy conversion efficiency. In this regard, the effect of graphene nanostructuring and doping, forming of structural defects, as well as graphene integration into a polymer matrix on its thermal conductivity and Seebeck coefficient is elucidated.
Solar Radiation Prediction Models Analysis for Varying Climatic Conditions
(International Journal of Engineering and Technology, 2017-07) Wainaina, Patrick M.; Owino, George O.; Musa, Njue R.
This study has investigated global solar predictive models, modiﬁed, validated and compared ﬁve models, for prediction of monthly daily mean solar radiation in four different locations of Kenya that represents the four major climatic conditions. The input variables to the models Were; latitude, day length, sunshine hours, relative sunshine hours, temperature, and precipitation. Solar radiation data from 2000 to 2013 was used to obtain the monthly daily mean global solar radiation, to analyze, validate and compare the performance of the models. The predicted and measured data was simulated using MATLAB. Statistical indicators, MBE, RMSE, t-test and R, were performed to determine the models performance. The results showed that sunshine hours based models predicted global solar radiation with higher accuracy in wet and cold, wet and warm climatic conditions, while the temperature and precipitation models were accurate in solar radiation prediction in hot and dry climatic conditions. Key words: Global solar radiationl, Sunshine hours2, Day length3
Isolation of Actinomycetes from Geothermal Vents of Menengai Crater in Kenya
(International Journal of Molecular Biology, 2017-07-20) Waithaka, Paul Njenga; Mwaura, Francis; Wagacha, John M.; Gathuru, Eliud Mugu
The current study was carried out to isolate actinomycetes from the geothermal vents of Menengai crater. Soil samples were collected from vents A and D in sterile polythene papers and transported to Egerton University, Department of biological sciences laboratories. The samples were air dried on the benches for one week. To kill vegetative bacteria, the soil samples were heat in a hot air oven for 1h before serial dilution to 10-6. The samples separately plated on Starch casein agar, Luria Bertani agar and starch nitrate agar in which nystatin and nalidixic acid had been added to reduce the growth of fungi and other types of bacteria. Incubation was carried out at 30 o C for up to a period of one Month. The isolated actinomycetes were characterized by cultural, morphological and biochemical means. There was no significant difference in the number of actinomycetes isolated between vents A and vents D(P=0.439). However, the number of actinomycetes isolated using the three isolation media varied significantly (F=37, P=0.03). Totally, 16 actinomycetes were isolated from the vents. It is recommended that the isolates be tested for antagonism against pathogenic microorganism.
Polymer solar cells with reduced graphene oxide–germanium quantum dots nanocomposite in the hole transport layer
(Journal of Materials Science: Materials in Electronics, 2018-02-19) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
Reduced graphene oxide–germanium quantum dots (rGO–Ge QDs) nanocomposite has been successfully employed in modifying poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL) in the preparation of a P3HT:PCBM-based polymer solar cell (PSC). The effect of the surface morphology and the optical transmittance of the PEDOT:PSS/rGO–Ge QDs HTL on the devices’ photovoltaic performance is examined. A significant improvement of up to 50% in the power conversion efficiency is achieved by the incorporation of the composite in the HTL. The modified HTL devices exhibited higher short-circuit current density values which resulted from better transportation and collection of photo-generated charge carriers. The synergistic effect of the high electrical conductivity of the composites and the formation of good ohmic contact at the interface between the anode and the active layer not only facilitates charge carrier transport but also impairs their recombination to yield better photovoltaic performance.
High-performance organic solar cells utilizing graphene oxide in the active and hole transport layers
(Elsevier Ltd, 2018-06-22) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
We have successfully synthesized and employed graphene oxide (GO) to boost photons harvesting and charge transport process in thin film organic solar cells (TFOSCs). The graphene oxide was inlayed in both the P3HT:PCBM-based photoactive medium of the device, as well as, a dopant in PEDOT:PSS hole transport buffer layer (HTL). The parameters of the solar cells produced with the inclusion of GO in the HTL and the active layer results in high short-circuit current densities (Jsc), which translated into high power conversion efficiencies (PCEs). GO in the HTL facilitates charge transport, selective electron blocking and hole injection at the interface for enhanced device performance. On the other hand, the use of GO in the active layer remarkably improves the optical absorption leading to high charge carriers photogeneration requisite to efficient OSCs. Similarly, effective exciton dissociation is energetically favoured in the GO modified active layer devices which corroborated with improved conductivity of the medium that assisted charge carriers transport processes. Enhanced photocurrent has been recorded, as high as 18 mA cm−2, from the TFOSCs by the inlay of GO in the active layer. Consequently, increased PCE of up to 40% and 120% is achieved by the inclusion of GO in the HTL and photoactive layers, respectively.

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