Cost-competitiveness of distributed grid-connected solar photovoltaics in Ghana: case study of a 4 kWp polycrystalline system

Driven by improvements in solar photovoltaic (PV) technology, policy initiatives and module cost reduction, electricity from solar PV is becoming increasingly cost-competitive with conventional energy systems. In this paper, an economic assessment is conducted on a 4.05 kWp, polycrystalline silicon photovoltaic system installed at the College of Engineering of the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, located at latitude 6°40′N and longitude 1°37′W, and elevation of 250 m, with a hot and humid climatic condition. The concept of grid-parity, which compares the levelized cost of electricity (LCOE) from solar PV to the retail price of electricity is used in this assessment. The results show, that, at installed cost of €3567/kW and an LCOE of €0.28/kWh, the non-residential category of electricity consumers requires investment support/subsidy of up to 22.9% to achieve parity. Solar PV is already competitive for non-residential customers consuming above 600 kWh in a month, without any support. Residential electricity consumers require investment support of 40.6–92.5% to attain parity with grid electricity, while special load tariff customers (> 100 kVA maximum demand) require between 4 and 50.5% subsidy on capital investment to reach parity. This paper concludes by recommending a two-pronged approach (incentive- and legislation-based) for promoting distributed grid-connected solar PV energy system in Ghana.     

Analysis on the feasibility of a PV-diesel generator hybrid system without energy storage

A sustainable option in the mandatory use of diesel generator set (DG) is its integration into the solar photo-voltaic system (PV). A major issue, in this integration, is achieving an optimum mix of energy delivered by DG as well as that obtainable from PV. This paper determines the optimum mix of outputs from a PV and the DG on the basis of minimum cost of energy in Rs/kWh. A time step simulation-based methodology is adopted. Results indicate, if 70 % of the annual energy demand is met by DG while remaining 30 % is met by the PV, the cost of energy will be the least at 13.1 Rs/kWh. Sensitivity of the optimum mix is examined in the light of relevant parameters.     

Study on possible economic and environmental impacts of electric vehicle infrastructure in public road transport in Kolkata

Transport sector in India accounts for 20 % of total commercial energy demand of the country, of which a considerable amount is consumed in the form of liquid and gaseous fuel. A major part of these fuels are imported by the Government. Apart from the import expenditure, Government of India has subsidized these fuels to make it available at affordable prices. To check the financial burden and achieve environmental benefits, technical advancement in present system or alternative infrastructure is required. The present study examines the possible impacts on economy and environment by the implementation of battery electric vehicles (BEVs) along with the conventional road transport system in metropolitans with a case study of Kolkata. The major impact has been observed in controlling the vehicular emission with a decrease in CO₂ level by 26.27 t per day, on replacement of only 2 % of the present public transport by suitable BEVs. Maintaining similar service for the passengers the electrical energy required by the alternative vehicles has been estimated to be 41,766 kWh per day. This energy has been proposed to be supplied by remodeled fuel stations equipped with solar photovoltaic systems, if charging strategy is based on renewable sources. In case of fuel economy, the infrastructure has shown the potential in reducing the consumption of diesel and autogas (LPG) by 11,654 and 3,256 liter per day, respectively.     

Comparative analysis of storage modules under different dispatch strategies for an optimum decentralized hybrid energy solution: a case study of a remote Indian village

India has a large poor population in spite of having a steady economic growth. Supply of centralized grid power to remote villages of India is not feasible due to adverse topography and poor economic condition of the villagers. To supply the reliable power at a minimum cost including penalty due to carbon dioxide emission, a suitable decentralized energy combination using locally available resources may be a better sustainable solution. The economy of such a hybrid energy supply system significantly depends on storage devices and dispatch strategies. Therefore, selection of appropriate storage devices and dispatch strategy need to be optimized based on available local resources. In this study, the comparative analysis of techno-economic factors for five different storage devices (lead acid battery, lithium-ion battery, vanadium redox battery, zinc bromide battery and pumped hydro energy storage) are studied under two different dispatch strategies, i.e., Load Following and Cycle Charging. The estimated cost of energy and net present cost of the recommended optimum combined energy system are in the range of US$0.197/kWh–US$0.453/kWh and US$3,62,384–US$5,76,369, respectively. The cost of energy, net present cost and carbon dioxide emission for the selected energy generators combination with the zinc bromide battery is 48.964–56.512%, 24.149–32.147% and 43.419–55.865% lower than other storage-based energy systems, respectively. The abovementioned economic and environmental factors are lower by 34.113, 10.489 and 31.094%, respectively, under Load Following dispatch strategy with respect to the Cycle Charging dispatch strategy for the optimum energy combination with zinc bromide battery.

Graphical abstract

     

Cu-doping effect on the structural, optical and photoluminescence properties of Sn0.98Cr0.02O2 nanoparticles by co-precipitation method

Sn_0.98-xCr_0.02Cu_xO₂ nanoparticles were prepared by co-precipitation method with different Cu concentrations from x = 0 to 0.05 and annealed at 600°C for 2 h in air atmosphere. The prepared particle were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectra, UV–visible spectrophotometer, and Fourier transform infrared spectroscopy. The XRD measurement reveals that the prepared nanoparticles have different microstructure without changing a tetragonal structure. The calculated average crystalline size decreased from 12.2 to 10.5 nm for x = 0–0.02 then gradually increased up to 16.8 nm for x = 0.05 which were confirmed by Scanning electron microscope. The optical studies were done by UV–visible spectrometer and the energy band gap values were calculated from absorption spectra. A small red shift from 3.52 eV (Cu = 0) to 3.49 eV (Cu = 0.02, ΔE_g = 0.03 eV) at lower Cu concentrations and a remarkable blue shift from 3.49 eV (Cu = 0.02) to 3.71 eV (Cu = 0.05, ΔE_g = 0.22 eV) at higher Cu concentrations is due to Cu-doping in Cr–SnO₂ matrix. The presence of functional groups and the chemical bonding is confirmed by Fourier transforms infrared spectra. PL spectra of Sn_0.98-xCr_0.02Cu_xO₂ nanoparticle described the shift in UV emission from 366 to 381 nm (red shift) and a shift in blue band emission from 458 to 482 nm (red shift) which confirms the Cu-doping in Cr–SnO₂ matrix. The doping of Cu in the present system is useful to tune the emission wavelength and hence is appreciable for the fabrication of nano-optoelectronic devices and photo-catalytic applications.     

Evaluation of the energy saving opportunities for palm oil refining process: Sahabat Oil Products (SOP) in Lahad Datu,Malaysia

Palm Oil industry is one of the major contributors to Malaysia’s economic activity. Accounting for 39 % of the world palm oil production and 44 % of world exports, Malaysia holds an important niche in fulfiling the growing global needs for oils and fats sustainably. This industry has high potential for further improvements especially in terms of energy saving as a major contributor to cost and emission reduction. An analysis of the refining process of palm oil in Sahabat Oil Products, Lahad Datu has been performed and presented in this paper for scoping potential energy and cost savings using heat integration. A first stage optimisation of the minimum temperature difference, ?T _min, of a heat exchanger network (HEN) has been performed. The goal has been to evaluate the maximal possible heat recovery as well as the appropriate placement of utilities. The HEN design is presented in both grid diagram and shifted retrofit thermodynamic grid diagram (SRTGD). SRTGD representation has been illustrated in this paper as a useful tool for guiding eventual future retrofit. The capital-energy trade-off of the heat recovery targets indicates optimum ?T _min of 12.3 °C. The hot and cold utility targets at ?T _min = 12.3 °C are 1419 and 1649 kW, indicating potential saving of 3.5 and 3.1 % as compared to the existing utility consumption and emissions. Future work could proceed further to seek potentially viable retrofit of the existing heat recovery network.     

Cost-efficient emission abatement of energy and transportation technologies: mitigation costs and policy impacts for Belgium

In the light of global warming, this paper develops a framework to compare energy and transportation technologies in terms of cost-efficient GHG emission reduction. We conduct a simultaneous assessment of economic and environmental performances through life cycle costing and life cycle assessment. To calculate the GHG mitigation cost, we create reference systems within the base scenario. Further, we extend the concept of the mitigation cost, allowing (i) comparision of technologies given a limited investment resource, and (ii) evaluation of the direct impact of policy measures by means of the subsidized mitigation cost. The framework is illustrated with a case of solar photovoltaics (PV), grid powered battery electric vehicles (BEVs), and solar powered BEVs for a Belgian small and medium sized enterprise. The study’s conclusions are that the mitigation cost of solar PV is high, even though this is a mature technology. The emerging mass produced BEVs on the other hand are found to have a large potential for cost-efficient GHG mitigation as indicated by their low cost of mitigation. Finally, based on the subsidized mitigation cost, we conclude that the current financial stimuli for all three investigated technologies are excessive when compared to the CO₂ market value under the EU Emission Trading Scheme.     

New proposal for production of bioactive compounds by supercritical technology integrated to a sugarcane biorefinery

The construction of a supercritical fluid extraction (SFE) plant inside or in close proximity to a sugarcane biorefinery producing first and second generation ethanol demonstrated to be very promising, increasing the economic potential of the SFE process in up to 57 %, since the SFE plant could use directly the ethanol, CO₂, heat, and electricity already available, with lower prices. In this study, Brazilian ginseng roots were used as model bioactive compounds source and first the statistical influence of the extraction conditions including pressure (10–20 MPa), temperature (323–363 K), and CO₂/ethanol proportion ratio (90:10, 50:50, and 0:100 %, w/w) on the β-ecdysone content in the extracts was experimentally evaluated and compared with literature results. SFE process evaluated experimentally at the present study showed higher selective extraction for β-ecdysone from Brazilian ginseng roots, providing an extract with up to 2.16 times higher β-ecdysone than the results obtained in previous studies. Thermal integration of the SFE process diminished energy requirements of the process, resulting in a reduction of cold utility requirement of 87 % and a final electricity demand of 7.5 kWh/g of β-ecdysone in the extract. In a situation in which the Brazilian ginseng roots price was increased to 4.71 USD/g, only the SFE integrated with the biorefinery solution would be economically feasible. Finally, the selling of the ginseng roots leftover could be an interesting answer to increase the economical attractiveness of the integrated SFE process to the biorefinery.     

Porous nanocrystalline TiO2 with high lithium-ion insertion performance

Porous nanocrystalline anatase TiO₂ was prepared by a modified hydrolytic route coupled with an intermediary amorphization/recrystallization process. The phase structure and morphology of the products were analyzed by X-ray diffraction, transmission electron microscopy, and field-emission scanning electron microscopy. The electrochemical properties were investigated by cyclic voltammetry, constant current discharge–charge tests, and electrochemical impedance techniques. Applied as an anode in a lithium-ion battery, the material exhibited excellent specific capacities of 130 mAh g^?1 (at the rate of 2000 mA g^?1) and 96 mAh g^?1 (at the rate of 4000 mA g^?1) after 100 cycles; the coulombic efficiency was ~99.5 %, indicating excellent rate capability and reversibility. Furthermore, the electrochemical impedance spectra showed improved electrode kinetics after cycling. These results indicate that the porous nanocrystalline TiO₂ synthesized by this improved synthesis route might be a promising anode material for high energy and high power density lithium-ion battery applications.     

Jaya Learning-Based Optimization for Optimal Sizing of Stand-Alone Photovoltaic,Wind Turbine,and Battery Systems

Renewable energy sources (RESs) are considered to be reliable and green electric power generation sources. Photovoltaics (PVs) and wind turbines (WTs) are used to provide electricity in remote areas. Optimal sizing of hybrid RESs is a vital challenge in a stand-alone environment. The meta-heuristic algorithms proposed in the past are dependent on algorithm-specific parameters for achieving an optimal solution. This paper proposes a hybrid algorithm of Jaya and a teaching–learning-based optimization (TLBO) named the JLBO algorithm for the optimal unit sizing of a PV–WT–battery hybrid system to satisfy the consumer’s load at minimal total annual cost (TAC). The reliability of the system is considered by a maximum allowable loss of power supply probability (LPSP_max) concept. The results obtained from the JLBO algorithm are compared with the original Jaya, TLBO, and genetic algorithms. The JLBO results show superior performance in terms of TAC, and the PV–WT–battery hybrid system is found to be the most economical scenario. This system provides a cost-effective solution for all proposed LPSP_max values as compared with PV–battery and WT–battery systems.     

CdTe photovoltaics: Life cycle environmental profile and comparisons

We discuss the emissions of cadmium throughout all the life stages of CdTe PV modules, from extracting, refining, and purifying the raw materials to producing, using, and disposing or recycling of the modules. Then, we compare these emissions with those in the life cycle of three different types of crystalline Si PV modules. The energy requirement and energy pay back times (EPBT) of CdTe PV modules are considerably shorter than that of crystalline Si modules, although the latter exhibit higher efficiencies. This difference is primarily due to the energy used to process silicon, a fraction of which is derived from fossil fuels, inevitably producing Cd and many other heavy-metal emissions. The lower energy requirement of CdTe PV results in lower emissions of all pollutants, including cadmium.     

Nanostructure, optical and photoluminescence properties of Zn1−xNixO nanoclusters by co-precipitation method

Zn_1?xNi_xO (x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05) nanoclusters have been successfully synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–visible spectrophotometer and Fourier transform infrared spectroscopy. The XRD and SEM measurements reveal that the prepared undoped and Ni-doped nanoclusters have different microstructure without changing a hexagonal wurtzite structure. The calculated average crystalline size from XRD measurement decreases from 37.5 to 26.6 nm for x = 0 to 0.05 which was confirmed by SEM micrographs. The change in lattice parameters, micro-strain, shift of XRD peaks and the blue shift of energy gap from 3.18 to 3.33 eV (ΔE_g = 0.15 eV) for Ni = 0–0.02 and red shift of E_g from 3.33 to 3.14 eV (ΔE_g = 0.19 eV) for Ni = 0.02 to 0.05 reveal the substitution of Ni²⁺ ions into Zn–O lattice. The presence of functional groups and the chemical bonding are confirmed by FTIR spectra. The shift of NBE UV emission between 374 and 395 nm, the shift of green band emission between 517 and 531 nm, the change in intensity and the broadening effect in the photoluminescence spectra confirms the substitution of Ni²⁺ ions into the Zn–O lattice. Ni-doped ZnO system shows a great pledge for the fabrication of nano-optoelectronic devices like tunable light emitting diode in the near future.     

VOC emission reduction and energy efficiency in the flexible packaging printing processes: analysis and implementation

Volatile organic compound (VOC) emissions into the atmosphere are among the primary environmental problems caused by flexible packaging printing plants. Since 1999, VOC emissions from the use of solvents in various technological processes have been limited by the volatile organic compounds solvents emissions directive, and by directive 2010/75/EU on industrial emissions since 2010. Thus, flexible packaging plants require processing technologies or other solutions to ensure compliance with these requirements. In this paper, combined VOC pollution prevention and treatment alternatives were suggested and were evaluated for their technical, environmental, and economic feasibility. A flexible plastic packaging company that produces over 1920 t/year of plastic packaging for the food industry was selected for detailed analysis. The material and energy flow analysis shows that VOC emissions from the main technological processes reached 112.2 kg/t of production, and a considerable amount of energy (up to 771.6 kWh/t of production) was used. Three integrated pollution prevention and control (IPPC) alternatives of the five analysed in this study were selected and implemented within the company to reduce its VOC emissions and energy consumption. The results indicate that after the implementation of the three suggested economically reasonable IPPC alternatives (replacement of solvent-based with water-based inks; modernisation of the ventilation and lighting system), the VOC emissions decreased to 8.4 kg/t (92.5%) and the total energy consumption for the production of 1 t of flexible packaging decreased to 605.6 kWh/t (21.5%). This study shows that IPPC methods not only significantly reduces VOC emissions from flexible packaging printing processes, but also saves energy and raw materials, and reduces costs.     

Luminescent properties of Eu3+-doped α-NaYF4 single crystal under NUV-excitation

This paper reports on successful synthesis of α-NaYF₄ single crystal doped with Eu³⁺ at various concentrations by a modified Bridgman method. The crystal structure is characterized by means of X-ray diffraction. The absorption spectra, excitation spectra and emission spectra were measured to investigate the optical properties of the single crystals. An intense red emission located at 611 nm with long lifetime of 9.03 ms was observed in single crystal under the excitation of 394 nm light. It benefits from the low maximum phonon energy of α-NaYF₄ single crystal matrix (390 cm^?1). The CIE chromaticity coordinate of the α-NaYF₄ single crystal doped Eu³⁺ in 4 mol% concentration was calculated (x = 0.6055, y = 0.388), which was close to the National Television Standard Committee standard values for red phosphor (x = 0.67, y = 0.33). All these spectral properties suggest that that this kind of fluoride crystal with high thermal stability and high efficiency of red emission may be used as potential red phosphors for optical devices.     

Intense 2.0 µm emission from Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Na<Subscript>5</Subscript>Lu<Subscript>9</Subscript>F<Subscript>32</Subscript> single crystal excited by 980 nm

This paper reported on optical spectra of Na₅Lu₉F₃₂ single crystals co-doped with ~?0.91 mol% Ho³⁺ and various Yb³⁺ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho³⁺/Yb³⁺ co-doped Na₅Lu₉F₃₂ and the energy transfer process from Yb³⁺ to Ho³⁺ ion. Compared with the Ho³⁺ singly doped Na₅Lu₉F₃₂ crystal, the Ho³⁺/Yb³⁺ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb³⁺ to Ho³⁺ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb³⁺ concentration when the concentration of Ho³⁺ ions is fixed at ~?0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23?×?10^?20 cm² according to the measured emission spectrum. The energy transfer efficiency from Yb³⁺:²F_5/2 to Ho³⁺:⁵I₆ for the crystal was estimated up to 90.8% indicating that Yb³⁺ ions can efficiently sensitize the Ho³⁺ ions.     

Towards understanding the morphological,magnetic, optical and electrical properties of MnO<Subscript>2</Subscript> nanowires for magneto-and optoelectronic applications

Mixed solutions of manganese sulfate and potassium permanganate were hydrothermally used to synthesis α-MnO₂ nanowires. Energy dispersive analysis of X-ray revealed the formation of stoichiometric MnO₂ and X-ray diffraction revealed the formation of single crystalline α-MnO₂. Examinations using both SEM and TEM yielded nanowires with diameters ranged from 40 to 50 nm and lengths ranged from 5 to 6 µm. The magnetic properties revealed that the α-MnO₂ NWs exhibit ferromagnetic/antiferromagnetic characteristics at liquid nitrogen and room temperatures. This kind of materials may be find usage in electromagnetic shielding applications. Direct optical band gap of 2.6 eV, that was blue shifted from the bulk value, was reported. Photoluminescence examinations displayed a strong emission peak around 395 nm and broad peak around 477 nm. The α-MnO₂ NWs showed a semiconducting behavior where the resistivity decreased with increasing temperature. Two activation energies were reported; the low temperature activation energy was 0.089 eV and the high temperature activation energy was 0.782 eV. Based on the observed high intensity UV emission peak, the obtained α-MnO₂ NWs may find applications in UV light emitting diodes.     

The effects of oxygen-catalysed and heat treatment on the precipitation synthesised ZnO nanoparticles

Nanocrystalline ZnO particles prepared by precipitation method from Zn and I₂ reaction with oxygen as catalyst were investigated. The addition of diethanolamine (DEA) as capping agent and fast pyrolysis treatment at 550, 700 and 850?°C were also characterised and elaborated. Compact and small spherical particles were observed for ZnO synthesised with O₂ catalysed whilst, uneven surface, fewer dense packing particles and macropore structures were observed for ZnO prepared without excess of O₂. It was shown that diffusion of O₂ has improved the structural and photoluminescence behaviour of the prepared ZnO nanoparticles. ZnO synthesised with O₂-catalysed exhibited better crystalline and leaned towards a pure state as shown by shifting of PL peak to higher energy of pure ZnO while, sample prepared without excess of O₂ exhibits poor crystalline and decreasing of the energy band gap with respect to increment of calcination temperatures. Single violet emission was observed in all samples synthesised with excess of O₂ whereby the highest intensity was obtained by calcining at 850?°C with photon energy at 2.95 eV. In contrast to sample with excess of O₂, ZnO calcined without excess of O₂ at 850?°C displays violet and green emission with energy at 2.93 eV and 2.35 eV, respectively.     

A single phase photovoltaic inverter control for grid connected system

This paper presents a control scheme for single phase grid connected photovoltaic (PV) system operating under both grid connected and isolated grid mode. The control techniques include voltage and current control of grid-tie PV inverter. During grid connected mode, grid controls the amplitude and frequency of the PV inverter output voltage, and the inverter operates in a current controlled mode. The current controller for grid connected mode fulfills two requirements – namely, (i) during light load condition the excess energy generated from the PV inverter is fed to the grid and (ii) during an overload condition or in case of unfavorable atmospheric conditions the load demand is met by both PV inverter and the grid. In order to synchronize the PV inverter with the grid a dual transport delay based phase locked loop (PLL) is used. On the other hand, during isolated grid operation the PV inverter operates in voltage-controlled mode to maintain a constant amplitude and frequency of the voltage across the load. For the optimum use of the PV module, a modified P&O based maximum power point tracking (MPPT) controller is used which enables the maximum power extraction under varying irradiation and temperature conditions. The validity of the proposed system is verified through simulation as well as hardware implementation.     

Synthesis of transparent Er-doped fluorotellurite glass–ceramics through controlled crystallization

This work presents a detailed study of the preparation and microstructure of transparent glass–ceramics obtained from a TeO₂?ZnO?ZnF₂ fluorotellurite glass doped with ErF₃. The determination of nucleation and crystal growth rate-like curves allows establishing a narrow temperature range (340–350 °C) for a controlled crystallization. Thereafter, a crystalline phase was grown through a two-step heat treatment: 10–20 h at a temperature slightly above the glass transition temperature, followed by a 2.5–3 h treatment at 340 °C. Structural analysis showed the nucleation of ErF₃ nanocrystals (NCs) with a typical size of ≈50 nm that were homogeneously distributed in the glass matrix. The resulting glass–ceramic material remains highly transparent, with a small crystalline to amorphous ratio; yet the presence of ErF₃ NCs has a large impact on the photoluminescence response of Er³⁺ ions. Upconverted visible emission is analyzed under 980 nm excitation: red emission from the ⁴F_9/2 level is dramatically enhanced with respect to green ²H_11/2, ⁴S_3/2 → ⁴I_15/2 hypersensitive transitions. The observed behaviour is attributed to the presence of Er³⁺ ions in the NCs, which are sites with lower phonon energy than the glass matrix. Moreover, the shorter inter-ionic distance between Er³⁺ ions in the NCs eases energy transfer between them.     

Optical and Magnetic Properties of Ten-Period InGaMnAs/GaAs Quantum Wells

Ten layers of InGaMnAs/GaAs multiquantum wells (MQWs) structure were grown on high resistivity (100) p-type GaAs substrates by molecular beam epitaxy (MBE). A presence of the ferromagnetic structure was confirmed in the InGaMnAs/GaAs MQWs structure, and have ferromagnetic ordering with a Curie temperature, T _C=50 K. It is likely that the ferromagnetic exchange coupling of the sample with T _C=50 K is hole-mediated resulting in Mn substituting In or Ga sites. PL emission spectra of the InGaMnAs MQWs sample grown at a temperature of 170 °C show that an activation energy of the Mn ion on the first quantum confinement level in InGaAs QW is 32 meV and impurity Mn is partly ionized. The fact that the activation energy of 32 meV of Mn ion in the QW is lower than an activation energy of 110 meV for a substitutional Mn impurity in GaAs, indicating an impurity band existing in the bandgap due to substitutional Mn ions.