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    Organic solar cells: Materials and prospects of graphene for active and interfacial layers
    (Taylor & Francis group, 2019-06-26) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
    Photovoltaics is a portentous alternative to the nonrenewable energy resources. Organic solar cells (OSCs) offer several advantages over inorganic counterparts in terms of low-cost device production, simple solution-based processing, flexibility, light-weight and compatibility with roll-to-roll fabrication. This review comprehensively examines the latest research developments towards high-performance OSCs. Device processing conditions and engineering along with material developments for the active and interfacial layers are examined. Different device structures and their benefits and limitations are highlighted. The interfacial layer materials including the polymers and metal oxides together with their integration and performance in functional OSCs are examined. A salient aspect of this review is the design of donor and acceptor materials to address the optical and electronic properties requirement for optimized device efficacy of OSCs. In this regard, the prospects of tailoring the band gap of donor polymers alongside the adoption of non-fullerene acceptors with complementary optical absorption for improved solar energy harvesting is elucidated. Further, graphene’s feasibility as an active or interfacial layer material is reviewed. Hence, this article provides perspectives and strategies on further development of solution-processable donor, acceptor and interfacial materials for high efficiency devices, required in commercialization of OSCs.
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    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.
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    Improved short-circuit current density in bulk heterojunction solar cells with reduced graphene oxide-germanium dioxide nanocomposite in the photoactive layer
    (Elsevier, 2020-11) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
    In the quest to improve the optical absorption and electrical transport of poly-3-hexylthiophene (P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) blend film, reduced graphene oxide-germanium dioxide nanocomposite (rGO-GeO2) was employed in the photoactive layer of thin film organic solar cells. Bulk heterojunction solar cells (BHJ SCs) with rGO-GeO2 composite in the active layer exhibited an increase in power conversion efficiency (PCE) of up to 53%. Significant improvement in the measured photocurrent is achieved by the incorporation of rGO-GeO2 in the active layer. High short-circuit current density (Jsc) of up to 17 mA/cm2 is attained in the BHJ SCs. The high Jsc shows that the inlay of rGO-GeO2 in the active layer facilitates exciton separation and creates percolation pathways for charge transport to the electrodes. Charge separation is energetically favoured by a built-in potential difference between the donor and acceptor phases of the active layer. Hence, the incorporation of rGO-GeO2 composite in the active layer improves its charge photogeneration, separation and transport to yield high Jsc and enhanced PCE.
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    Remaining useful life prediction of electric vehicle lithium-ion battery based on particle filter method
    (IEEE, 2018-05-28) Omariba, Zachary Bosire; Zhang, Lijun; Sun, Dongbai
    Lithium-ion batteries are popular today as their applications spans from portable electronics, electric vehicles, military, and aerospace applications. These batteries form a core component of these systems making them critical to the systems functional capability. Remaining useful life prediction is essential therefore as failure to which can lead to reduced performance, and or even catastrophic failure. The remaining useful life estimates are obtained by evaluating successive probability distributions of degrading states. If battery capacity is less than the failure threshold it poses a major danger to electric vehicles. This is because the battery capacity is an important indicator to monitor state of health (SOH), and its value can be less than the failure threshold due to degradation. This paper makes use of NASA's battery dataset to form the observed data sequence for prediction of remaining useful life. Afterwards a particle filter (PF) algorithm is used to perform the prediction of remaining useful life.
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    Structural, Electronic and Mechanical Properties of Re Doped FeMnP0.67A0.33 (A=Ga and Ge): A DFT Study
    (Science and Education publishing (SciEP), 2022-11) Chirchir, Gabriel Kipkemei; Mulwa, Winfred Mueni; Adetunji, Bamidele Ibrahim
    The structural, electronic and mechanical properties of Re doped FeMnP0.67A0.33 (A= Ga and Ge) were examined by use of density functional theory (DFT) within the generalized gradient approximations as demonstrated in Quantum ESPRESSO code. The optimized structural parameters as well as derived lattice parameters are in consistent with other computational and achievable experimental results. The computed independent elastic constants confirm the mechanical stability of the investigated materials. The computed Poisson’s and Pugh’s ratios as well as Cauchy pressure, verify that FeMn0.67Re0.33P0.67Ga0.33 is the most ductile among the studied compounds. The calculated values of bulk modulus, shear modulus and Young’s modulus confirm high values of bond strength, hardness and stiffness of the investigated materials respectively. Therefore, the four compounds considered may be appropriate for industrial applications. The results report that FeMn0.67Re0.33P0.67Ga0.33 compound is more ductile and mechanically stable compared to other investigated compounds. This is the first qualitative computational prediction of the elastic properties of FeMnP0.67Ge0.33, FeMnP0.67Ga0.33, FeMn0.67Re0.33P0.67Ge0.33 and FeMn0.67Re0.33P0.67Ga0.33 compounds and this awaits experimental ratification. The calculated electronic density of states confirms that the Re_2p states are located in the conduction band (CB) in the unite cell while Re_3d dominate the CB in the supercell. Results from the doped compounds could not be compared with experimental or computational findings because to the best of our knowledge, this has not been done.
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    Safety of Rechargeable Energy Storage Systems with a focus on Li-ion Technology
    (Elsevier Ltd, 2017-02-10) Pfrang, A.; Kriston, A.; Ruiz, V.; Lebedeva, N.; di Persio, F.
    In this chapter the safety of rechargeable energy storage systems is discussed with a focus on Li-ion batteries. The main hazards, such as fire, explosion, direct electrical hazards (electrical shock and arcing), indirect electrical hazards, and chemical hazards are reviewed. Relevant failure scenarios—overheating, mechanical deformation, external short circuit, and overcharge—are presented together with the main approaches for risk mitigation. Potential safety implications of the application of nanomaterials in rechargeable energy storage systems are discussed. Finally, a comprehensive summary of the most common tests for assessing safety under thermal, electrical, and mechanical abusive conditions as described in relevant standards and regulations is given.
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    Germanium quantum dot/nitrogen-doped graphene nanocomposite for high-performance bulk heterojunction solar cells
    (Royal Society of Chemistry, 2018-06-30) Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.
    This study presents the successful synthesis of a novel nanocomposite, namely a germanium quantum dot/nitrogen-doped graphene nanocomposite (GeQD/NGr), and its use in the modification of the photoactive medium of bulk heterojunction solar cells (BHJ-SCs). The nanocomposite was prepared in two sequential steps. Firstly, a reduced graphene oxide-germanium oxide nanocomposite (rGO-GeO2) was synthesized by microwave-assisted solvothermal reaction. The second step involved simultaneous N-doping of graphene and reduction of GeO2 to obtain the GeQD/NGr nanocomposite by thermal treatment. The nanocomposite consists of highly crystalline, spherical shaped GeQDs with a mean diameter of 4.4 nm affixed on the basal planes of NGr sheets. Poly-3-hexylthiophene (P3HT), (6-6)phenyl-C60-butyric acid methyl ester (PCBM) and GeQD/NGr were used as the photoactive layer blend in the fabrication of BHJ-SCs. Enhanced short-circuit current density (Jsc) and fill factor (FF) is derived from the incorporation of the GeQD/NGr nanocomposite in the active layer. The nanocomposite in the active layer blend serves to ensure effective charge separation and transportation to the respective electrodes. Consequently, an improvement of up to 183% in the power conversion efficiency is achieved in the BHJ-SCs by the GeQD/NGr modification.
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    Ab Initio Study of Structural and Vibrational Properties of Fe2P-Type Materials for Near - Room - Temperature Refrigeration
    (Science and Education publishing (SciEP), 2022-01-23) Thirika, Anne Mwende; Mulwa, Winfred Mueni; Makau, Nicholus Wambua; Ibrahim, Adentuji Bamidele
    This work has applied density functional theory (DFT) based calculations to investigate the structural and vibrational properties of FeMnP1−xAx (A= Si, Se, Sn and In, x = 0.33) within the first-principles pseudopotential technique. The exchange correlation potentials were treated within generalized gradient approximation (GGA), in the Quantum ESPRESSO code. The Perdew, Burke, Ernzerhof (PBE) functional as implemented in Vanderbilt's ultra-soft pseudo potential (USPP) was used for all the calculations. Vibrational properties were calculated using phonopy code with 1 × 1 × 2 supercell of the conventional unit cell. Thermodynamic properties were predicted using the phonon density of states. The dependence of lattice thermal conductivity on temperature was determined using Debye theory. The optimized structural parameters and corresponding graphical values fit within available experimental data and other theoretical reports. There were no imaginary phonon modes in the phonon dispersion curves revealing that these materials are dynamically stable for magnetic refrigeration.
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    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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    Structural, Electrical, and Electrochemical Properties of a Na2O-V2O5 Ceramic Nanocomposite as an Active Cathode Material for a Na-Ion Battery
    (Crystals, 2023-10-20) Ibrahim, Ahmed; Watanabe, Satoshi; Razum, Marta; Pavić, Luka; Homonnay, Zoltán; Kuzmann, Ernő; Hassaan, Mohamed Yousry; Kubuki, Shiro
    In this paper, a relationship between the structure and the electrical properties of a nanocrystalline composite ceramics xNa2O·(100 − x)V2O5 with ‘x’ of 5, 15, 25, 35, and 45 mol%, abbreviated as xNV, was investigated by X-ray diffractometry (XRD), X-ray absorption spectroscopy (XAS), Cyclic Voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and cathode active performance in Na-ion battery (SIB). For the expected sodium vanadium bronzes (NaxV2O5) precipitation, the preparation of xNV was performed by keeping the system in the molten state at 1200 °C for one hour, followed by a temperature decrease in the electric furnace to room temperature at a cooling rate of 10 °C min−1. XRD patterns of the 15NV ceramic exhibited the formation of Na0.33V2O5 and NaV3O8 crystalline phases. Moreover, the V K-edge XANES showed that the absorption edge energy of ceramics 15NV recorded at 5479 eV is smaller than that of V2O5 at 5481 eV, evidently indicating a partial reduction from V5+ to V4+ due to the precipitation of Na0.33V2O5. In the cyclic voltammetry, reduction peaks of 15NV were observed at 1.12, 1.78 V, and 2.69 V, while the oxidation peak showed up only at 2.36 V. The values of the reduction peaks were related to the NaV3O8 crystalline phase. Moreover, the diffusion coefficient of Na+ (DNa+) gradually decreased from 8.28 × 10−11 cm2 s−1 to 1.23 × 10−12 cm2 s−1 with increasing Na2O content (x) from 5 to 45 mol%. In the evaluation of the active cathode performance of xNV in SIB, ceramics 15NV showed the highest discharge capacity 203 mAh g−1 at a current rate of 50 mA g−1. In the wider voltage range from 0.8 to 3.6 V, the capacity retention was maintained at 50% after 30 cycles, while it was significantly improved to 90% in the narrower voltage range from 1.8 to 4.0 V, although the initial capacity decreased to 56 mAh g−1. It is concluded that the precipitation of the Na0.33V2O5 phase improved the structural and electrical properties of 15NV, which provides a high capacity for the Na-ion battery when incorporated as a cathode active material.
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    Synthesis and characterization of aluminium oxide nanoparticles from waste aluminium foil and potential application in aluminium-ion cell
    (Science Direct, 2021-07-01) Nduni, Mercy Njeri; Osano, Aloys Mosima; Chaka, Bakari
    Aluminium waste accumulated in landfills is a solid waste in abundance. Various methods have been employed to alleviate the waste only to yield secondary pollution effects. This study seeks to provide an alternative greener recycling procedure that is beneficial to society in terms of health and economics through energy storage materials. The study aimed to synthesize and characterize aluminium oxide nanoparticles from waste aluminium foil and its potential applications in fabricating aluminium-ion cell, FAIC.11Aluminium-ion cell. Aluminium oxide nanoparticles were obtained by co-precipitation of waste aluminium foils at constant annealing room temperature followed by mechanical milling to nanoparticulate range. The particles were then characterized for particle size and phases (X-ray diffraction), functional groups and optical activity (infra-red and ultra-violet-visible spectroscopy respectively). Cell assembling of FAIC was done using a graphite anode while the cathode had a standard and the synthesized aluminium oxide nanoparticles. Sulfuric acid and magnesium sulfate electrolytes were used with two binders; polyacrylate and silicone adhesives. The average synthesis yield was 40.64 ± 19.69%. Most of the particles had a α-Al2O3 and γ-Al2O3 phase with an average size of 63.763 nm and 66.5144 nm for the two polymorphs respectively. There were several OH-groups coupled to Al–O bonds. The optimal absorption peak was λmax = 237 nm corresponding to a band gap of 5.25eV. The synthesized nanoparticles exhibited great electrochemical potential, nearing the standard one in most of the parameters. The FAIC potential, current, power densities and polarization curves from sulfuric acid electrolyte and polyacrylate binder were significantly higher to those of magnesium sulfate and silicone binder (P > 0.05).
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    A review of thermal energy storage designs, heat storage materials and cooking performance of solar cookers with heat storage
    (Elsevier, 2017-08-01) Nkhonjera, Lameck; Bello-Ochende, Tunde; John, Geoffrey; King’ondu, Cecil K.
    This paper discusses the thermal energy storage units, heat storage materials and cooking performance of solar cookers with heat storage surveyed in literature. It is revealed that rectangular and cylindrical containers are widely used in the heat storage devices of the solar cookers. The geometry of the storage units, however, depended on the mode of heat transport into the storage medium and out to the cooking vessel from which, three categories of solar cookers (2-stage, 3-stage, and 4-stage solar cookers) are identified. Furthermore, oils and organic phase change materials dominated in the sensible and latent heat storage units respectively. Additionally, the inclusion of high thermal conductive material into the storage medium was the principal technique used in enhancing effective thermal conductivity. Besides, it is shown that there is no significant difference between the cooking power of cookers equipped with sensible and latent heat storage units. However, the design parameters of the cookers as well as thermal diffusivity of the storage medium greatly influenced the cooking power. The 3-stage cookers outperformed their 2-stage counterparts whereas cookers with cooking vessels integrated to the thermal storage unit outperformed the ones with non-integrated cooking vessels. On the other hand, lower thermal diffusivity of the storage medium increased cooking power in cookers with sensible heat storage but decreased the cooking power in cookers with latent heat storage. Finally, it is shown that the quest for the development of high temperature thermal storage units, and the optimization of the geometry as well as heat transfer characteristics of thermal energy storage units remain the potential areas of research in heat storage for cooking.
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    Soil fertility inputs and tillage influence on maize crop performance and soil water content in the Central Highlands of Kenya
    (Elsevier, 2019-03-05) Kiboi, Milka N.; Ngetich, F. K.; Fliessbach, A.; Muriuki, A.; Mugendi, Daniel N.
    Rigorous land ploughing and cropping fertiliser treatment and mineral fertiliser combined with animal manure treatment) consistently enhanced maize crop growth and development as observed through enhanced chlorophyll content, plant height and yields. Application of soil fertility inputs significantly improved grain and stover yields except in the crop residue combined with animal manure and legume intercrop treatment (perhaps due to nutrients’ competition since Lablab has an intensive rooting system). Sole organic inputs enhanced soil moisture content in both sites. Emerging from the study, however, is the lack of advantage of minimum tillage over the conventional tillage, within the period under consideration. Thus, this study highlights the possibility of improving soil water holding capacity through application of organic inputs such as crop residues, Tithonia diversifolia and manure, either singly or in combination. It further underpins the uniqueness of an integrated approach to soil fertility and low soil moisture content in the tropical sub-humid regions experiencing erratic rainfallivity in the Central Highlands of Kenya due to low and declining soil fertility, inappropriate tillage methods, soil water scarcity and prolonged dry-spells. In this study, we assessed the effects of two tillage systems and soil fertility inputs on maize crop performance and soil water content. The research was carried out in Chuka and Kandara sites in the Central Highlands of Kenya for four seasons; long rains 2016, short rains 2016, long rains 2017 and short rains 2017. The experimental design was a split plot with tillage method (minimum and conventional) as the main treatments and soil fertility inputs as the sub-treatments: Sole mineral fertiliser, mineral fertiliser combined with crop residue, mineral fertiliser combined with animal manure, Tithonia diversifolia combined with phosphate rock (Minjingu), animal manure intercropped with Dolichos Lablab L. and a Control (conventional tillage with no inputs). Except for the control, and sole mineral fertiliser, crop residue was applied as mulch in all treatments. Based on the results, the treatments with mineral fertiliser (sole mineral fertiliser combined with mineral fertiliser treatment and mineral fertiliser combined with animal manure treatment) consistently enhanced maize crop growth and development as observed through enhanced chlorophyll content, plant height and yields. Application of soil fertility inputs significantly improved grain and stover yields except in the crop residue combined with animal manure and legume intercrop treatment (perhaps due to nutrients’ competition since Lablab has an intensive rooting system). Sole organic inputs enhanced soil moisture content in both sites. Emerging from the study, however, is the lack of advantage of minimum tillage over the conventional tillage, within the period under consideration. Thus, this study highlights the possibility of improving soil water holding capacity through application of organic inputs such as crop residues, Tithonia diversifolia and manure, either singly or in combination. It further underpins the uniqueness of an integrated approach to soil fertility and low soil moisture content in the tropical sub-humid regions experiencing erratic rainfall.
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    Simulated performance of a novel solid-state dye-sensitized solar cell based on phenyl-C61-butyric acid methyl ester (PC61BM) electron transport layer
    (Springer, 2021) Korir, Benjamin K.; Kibet, Joshua K.; Ngari, Silas M.
    Climate change has approached a major crisis limit worldwide due to exhaust emissions arising from the use of traditional transport fuels. Solar energy, therefore, appears to be the most promising alternative energy that can mitigate air quality and environmental degradation. Herein, we report numerical simulation of a novel model solid-state dye-sensitized solar cell consisting of solid-state layers with the configuration FTO/PC61BM/N719/CuSCN/Au using 1-dimensional solar cell capacitance simulator software (SCAPS-1D). The motivation underpinning the numerical simulation of the solar cell architecture proposed in this study was to optimize phenyl-C61-butyric acid methyl ester (PC61BM) performance as the electron transport layer. In this model, the effects of varying several parameters—temperature, absorber thickness, defect density, and metallic back contact on the overall solar cell performance have been critically examined. After optimizing the input parameters, the optimal conversion efficiency was 5.38% while the optimized open-circuit voltage was 0.885 V. Besides, 70.94% was the optimum fill factor and the peak short-circuit current of 8.563 mA cm−2 was achieved. Built-in voltage of ~ 1.0 V was estimated from the Mott–Schottky curve and the cell band diagram. The power conversion efficiency obtained in this study is robust for this cell configuration, and is toxic-free compared to the lead-based perovskite solar cells. These findings are therefore useful in the advancement and fabrication of high-performance dye-based photovoltaic devices for large-scale industrial production.
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    Theoretical analysis of the electrical characteristics of lead‐free formamidinium tin iodide solar cell
    (The Institution of Engineering and Technology (IET), 2023) Katunge, Elizabeth K.; Njema, George G.; Kibet, Joshua K.
    Abstract Green energy transition and climate change have gathered significant momentum in the world because of the rising population and increased clean energy demands. For this reason, renewable energy alternatives such as inexhaustible photo energy from the sun appear to be the ultimate solution to the world's energy needs. Formamidinium tin tri‐iodide (HC(NH 2 ) 2 SnI 3 )‐based perovskites are found to be more efficient and stable than their methylammonium tin tri‐iodide (MASnI 3 ) counterparts because of its wider bandgap and better temperature stability. A device simulation of FASnI 3 ‐based solar cell is numerically performed using solar cell capacitance simulator (SCAPS‐1D). The focus is to investigate the effect of changing working temperature, metal back contact, absorber thickness, defect density, and doping concentration on the performance of the proposed solar cell device. The optimised solar cell parameters of the proposed solar cell were: short‐circuit current density (Jsc) of 28.45 mAcm −2 , open‐circuit voltage (Voc) of 1.0042 V, fill factor of 63.73%, and power conversion efficiency of 18.21% at 300 K, thus, paving the way for novel perovskite solar cells which are environmentally benign because they are lead‐free, have better absorption efficiency, and can be injected into the production work flow for commercial applications.
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    Effect of Process Techniques on Three Feedstocks Mix on Briquette Performance Properties
    (2022) Okwara, Wilberforce; Nyaanga, Daudi; Kabok, Peter; Nyaanga, Jane
    Energy availability at domestic level is a challenge across the world and especially in Africa. Firewood is the major source of energy for cooking for households in Kenya and there is need for a friendly sustainable environmental fuel. Carbonized biomass materials (briquettes) are considered a substitute. This study thus evaluated effect of selected briquetting techniques on briquettes’ performance properties. Milled charcoal dusts mixed in a ratio of 1:1:1 (Rice husk, maize cob, and sugarcane bagasse) with molasses binder in the ratio of 6:1 was hence ready for densification and agglomeration. The Water Boiling Test was used in determination of the briquette’s performance characteristics for various parameters. High (screw press); and low (drum agglomerator and hand making) pressure briquetting techniques were distinctly different in ignition time (minutes), time to boil (minutes) burning rate (g/min), specific fuel consumption (g/ml) and power output (kW) values as (4, 3, 3; 14, 12, 11: 0.8, 1.1, 1.3; 0.11, 0.13, 0.15; and 1.8, 1.4, 0.75). Diversified briquetting techniques, number and type of feedstocks are thus factors that influence performance characteristics of briquettes in converting the agricultural and or other wastes for useful energy application. This knowledge should enable users to make choices on techniques for optimum efficiency towards realization of Sustainable Development Goal Number #7 on affordable and clean energy.