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Energies, Volume 5, Issue 8 (August 2012), Pages 2626-3166

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Open AccessArticle World Energy Balance Outlook and OPEC Production Capacity: Implications for Global Oil Security
Energies 2012, 5(8), 2626-2651; doi:10.3390/en5082626
Received: 12 June 2012 / Revised: 13 July 2012 / Accepted: 17 July 2012 / Published: 25 July 2012
Cited by 19 | PDF Full-text (726 KB) | HTML Full-text | XML Full-text
Abstract
The imbalance between energy resource availability, demand, and production capacity, coupled with inherent economic and environmental uncertainties make strategic energy resources planning, management, and decision-making a challenging process. In this paper, a descriptive approach has been taken to synthesize the world’s energy portfolio
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The imbalance between energy resource availability, demand, and production capacity, coupled with inherent economic and environmental uncertainties make strategic energy resources planning, management, and decision-making a challenging process. In this paper, a descriptive approach has been taken to synthesize the world’s energy portfolio and the global energy balance outlook in order to provide insights into the role of Organization of Petroleum Exporting Countries (OPEC) in maintaining “stability” and “balance” of the world’s energy market. This synthesis illustrates that in the absence of stringent policies, i.e., if historical trends of the global energy production and consumption hold into the future, it is unlikely that non-conventional liquid fuels and renewable energy sources will play a dominant role in meeting global energy demand by 2030. This should be a source of major global concern as the world may be unprepared for an ultimate shift to other energy sources when the imminent peak oil production is reached. OPEC’s potential to impact the supply and price of oil could enable this organization to act as a facilitator or a barrier for energy transition policies, and to play a key role in the global energy security through cooperative or non-cooperative strategies. It is argued that, as the global energy portfolio becomes more balanced in the long run, OPEC may change its typical high oil price strategies to drive the market prices to lower equilibria, making alternative energy sources less competitive. Alternatively, OPEC can contribute to a cooperative portfolio management approach to help mitigate the gradually emerging energy crisis and global warming, facilitating a less turbulent energy transition path while there is time. Full article
Open AccessArticle MPPT for Photovoltaic Modules via Newton-Like Extremum Seeking Control
Energies 2012, 5(8), 2652-2666; doi:10.3390/en5082652
Received: 30 May 2012 / Revised: 12 July 2012 / Accepted: 18 July 2012 / Published: 25 July 2012
Cited by 11 | PDF Full-text (436 KB) | HTML Full-text | XML Full-text
Abstract
The paper adapts the Newton-like Extremum-Seeking Control technique to extract the maximum power from photovoltaic panels. This technique uses the gradient and Hessian of the panel characteristic in order to approximate the operating point to its optimum. The paper describes in detail the
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The paper adapts the Newton-like Extremum-Seeking Control technique to extract the maximum power from photovoltaic panels. This technique uses the gradient and Hessian of the panel characteristic in order to approximate the operating point to its optimum. The paper describes in detail the gradient and Hessian estimations carried out by means of sinusoidal dithering signals. Furthermore, we compare the proposed technique with the common Extremum Seeking Control that only uses the gradient. The comparison is done by means of PSIM simulations and it shows the different transient behaviors and the faster response of the Newton-like Extremum-Seeking Control solution. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
Open AccessArticle Esterification and Deacidification of a Waste Cooking Oil (TAN 68.81 mg KOH/g) for Biodiesel Production
Energies 2012, 5(8), 2683-2691; doi:10.3390/en5082683
Received: 6 June 2012 / Revised: 13 July 2012 / Accepted: 20 July 2012 / Published: 25 July 2012
Cited by 12 | PDF Full-text (205 KB) | HTML Full-text | XML Full-text
Abstract
Oils with high content of free fatty acid (FFA) can be treated by acid esterification where an alcohol reacts with the given oil in the presence of acid catalyst. The investigated parameters include methanol to oil ratio, temperature and amount of catalyst. The
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Oils with high content of free fatty acid (FFA) can be treated by acid esterification where an alcohol reacts with the given oil in the presence of acid catalyst. The investigated parameters include methanol to oil ratio, temperature and amount of catalyst. The optimum conditions for acid esterification which could reduce FFA content in the feedstock to less than 1.88% (acid value 3.76 mg KOH/g waste cooking oil) were 50 °C, 20% methanol to oil ratio (by volume) and 0.4 vol.% H2SO4 after 5 h. However, oil with an acid value of more than 1 mg KOH/g oil cannot meet the alkaline catalyzed transesterification conditions. Under the conditions of NaOH concentration 0.5 N, excess alkali 15%, 60 °C, 40 min, the FFA removal rate for deacidification reached 77.11% (acid value 0.86 mg KOH/g esterified oil). The acid value of deacidification product was reduced below 0.86 mg KOH/g esterified oil, thus meeting the base-catalyzed trans-esterification conditions. Full article
Open AccessArticle Collector Efficiency in Downward-Type Double-Pass Solar Air Heaters with Attached Fins and Operated by External Recycle
Energies 2012, 5(8), 2692-2707; doi:10.3390/en5082692
Received: 30 April 2012 / Revised: 4 June 2012 / Accepted: 19 July 2012 / Published: 26 July 2012
Cited by 1 | PDF Full-text (764 KB) | HTML Full-text | XML Full-text
Abstract
The collector efficiency in a downward-type double-pass external-recycle solar air heater with fins attached on the absorbing plate has been investigated theoretically. Considerable improvement in collector efficiency is obtainable if the collector is equipped with fins and the operation is carried out with
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The collector efficiency in a downward-type double-pass external-recycle solar air heater with fins attached on the absorbing plate has been investigated theoretically. Considerable improvement in collector efficiency is obtainable if the collector is equipped with fins and the operation is carried out with an external recycle. Due to the recycling, the desirable effect of increasing the heat transfer coefficient compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, while the attached fins provide an enlarged heat transfer area. The order of performances in the devices of same size is: double pass with recycle and fins > double pass with recycle but without fins > single pass without recycle and fins. Full article
Open AccessArticle A Hybrid Life-Cycle Assessment of Nonrenewable Energy and Greenhouse-Gas Emissions of a Village-Level Biomass Gasification Project in China
Energies 2012, 5(8), 2708-2723; doi:10.3390/en5082708
Received: 15 June 2012 / Revised: 16 July 2012 / Accepted: 18 July 2012 / Published: 26 July 2012
Cited by 13 | PDF Full-text (270 KB) | HTML Full-text | XML Full-text
Abstract
Small-scale bio-energy projects have been launched in rural areas of China and are considered as alternatives to fossil-fuel energy. However, energetic and environmental evaluation of these projects has rarely been carried out, though it is necessary for their long-term development. A village-level biomass
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Small-scale bio-energy projects have been launched in rural areas of China and are considered as alternatives to fossil-fuel energy. However, energetic and environmental evaluation of these projects has rarely been carried out, though it is necessary for their long-term development. A village-level biomass gasification project provides an example. A hybrid life-cycle assessment (LCA) of its total nonrenewable energy (NE) cost and associated greenhouse gas (GHG) emissions is presented in this paper. The results show that the total energy cost for one joule of biomass gas output from the project is 2.93 J, of which 0.89 J is from nonrenewable energy, and the related GHG emission cost is 1.17 × 10−4 g CO2-eq over its designed life cycle of 20 years. To provide equivalent effective calorific value for cooking work, the utilization of one joule of biomass gas will lead to more life cycle NE cost by 0.07 J and more GHG emissions by 8.92 × 10−5 g CO2-eq compared to natural gas taking into consideration of the difference in combustion efficiency and calorific value. The small-scale bio-energy project has fallen into dilemma, i.e., struggling for survival, and for a more successful future development of village-level gasification projects, much effort is needed to tide over the plight of its development, such as high cost and low efficiency caused by decentralized construction, technical shortcomings and low utilization rate of by-products. Full article
(This article belongs to the Special Issue Exergy Analysis of Energy Systems)
Open AccessArticle An Equivalent Electrical Circuit Model of Proton Exchange Membrane Fuel Cells Based on Mathematical Modelling
Energies 2012, 5(8), 2724-2744; doi:10.3390/en5082724
Received: 5 April 2012 / Revised: 16 July 2012 / Accepted: 18 July 2012 / Published: 27 July 2012
Cited by 11 | PDF Full-text (722 KB) | HTML Full-text | XML Full-text
Abstract
Many of the Proton Exchange Membrane Fuel Cell (PEMFC) models proposed in the literature consist of mathematical equations. However, they are not adequately practical for simulating power systems. The proposed model takes into account phenomena such as activation polarization, ohmic polarization, double layer
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Many of the Proton Exchange Membrane Fuel Cell (PEMFC) models proposed in the literature consist of mathematical equations. However, they are not adequately practical for simulating power systems. The proposed model takes into account phenomena such as activation polarization, ohmic polarization, double layer capacitance and mass transport effects present in a PEM fuel cell. Using electrical analogies and a mathematical modeling of PEMFC, the circuit model is established. To evaluate the effectiveness of the circuit model, its static and dynamic performances under load step changes are simulated and compared to the numerical results obtained by solving the mathematical model. Finally, the applicability of our model is demonstrated by simulating a practical system. Full article
(This article belongs to the Special Issue Hydrogen Energy and Fuel Cells)
Open AccessArticle Exergy Analysis of Overspray Process in Gas Turbine Systems
Energies 2012, 5(8), 2745-2758; doi:10.3390/en5082745
Received: 2 May 2012 / Revised: 11 July 2012 / Accepted: 11 July 2012 / Published: 30 July 2012
Cited by 5 | PDF Full-text (300 KB) | HTML Full-text | XML Full-text
Abstract
Gas turbine power can be augmented by overspray process which consists of inlet fogging and wet compression. In this study exergy analysis of the overspray process in gas turbine system is carried out with a non-equilibrium analytical modeling based on droplet evaporation and
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Gas turbine power can be augmented by overspray process which consists of inlet fogging and wet compression. In this study exergy analysis of the overspray process in gas turbine system is carried out with a non-equilibrium analytical modeling based on droplet evaporation and the second law of thermodynamics. This work focuses on the effects of system parameters such as pressure ratio, water injection ratio, and initial droplet diameter on exergetical performances including irreversibility and exergy efficiency of the process. The process performances are also estimated under the condition of saturated water injection ratio above which complete evaporation of injected water droplets within a compressor is not possible. The results show that the irreversibility increases but the saturated irreversibility decreases with increasing initial droplet diameter for a specified pressure ratio. Full article
(This article belongs to the Special Issue Exergy Analysis of Energy Systems)
Open AccessArticle Deacidification of Pistacia chinensis Oil as a Promising Non-Edible Feedstock for Biodiesel Production in China
Energies 2012, 5(8), 2759-2770; doi:10.3390/en5082759
Received: 1 March 2012 / Revised: 29 June 2012 / Accepted: 20 July 2012 / Published: 31 July 2012
Cited by 6 | PDF Full-text (224 KB) | HTML Full-text | XML Full-text
Abstract
Pistacia chinensis seed oil is proposed as a promising non-edible feedstock for biodiesel production. Different extraction methods were tested and compared to obtain crude oil from the seed of Pistacia chinensis, along with various deacidification measures of refined oil. The biodiesel was
[...] Read more.
Pistacia chinensis seed oil is proposed as a promising non-edible feedstock for biodiesel production. Different extraction methods were tested and compared to obtain crude oil from the seed of Pistacia chinensis, along with various deacidification measures of refined oil. The biodiesel was produced through catalysis of sodium hydroxide (NaOH) and potassium hydroxide (KOH). The results showed that the acid value of Pistacia chinensis oil was successfully reduced to 0.23 mg KOH/g when it was extracted using ethanol. Consequently, the biodiesel product gave a high yield beyond 96.0%. The transesterification catalysed by KOH was also more complete. Fourier transform infrared (FTIR) spectroscopy was used to monitor the transesterification reaction. Analyses by gas chromatography-mass spectrometry (GC-MS) and gas chromatography with a flame ionisation detector (GC-FID) certified that the Pistacia chinensis biodiesel mainly consisted of C18 fatty acid methyl esters (81.07%) with a high percentage of methyl oleate. Furthermore, the measured fuel properties of the biodiesel met the required standards for fuel use. In conclusion, the Pistacia chinensis biodiesel is a qualified and feasible substitute for fossil diesel. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Determination of Steady-State and Faulty Regimes of Overhead Lines by Means of Multiconductor Cell Analysis (MCA)
Energies 2012, 5(8), 2771-2793; doi:10.3390/en5082771
Received: 15 June 2012 / Revised: 24 July 2012 / Accepted: 26 July 2012 / Published: 31 July 2012
Cited by 9 | PDF Full-text (1126 KB) | HTML Full-text | XML Full-text
Abstract
Single-phase positive sequence modelling is often used in power systems when power flows and short circuit analysis are assessed. Of course, the use of single-phase positive sequence modelling assumes purely three-phase configurations and perfectly symmetrical ones so that single-phase modelling considers that all
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Single-phase positive sequence modelling is often used in power systems when power flows and short circuit analysis are assessed. Of course, the use of single-phase positive sequence modelling assumes purely three-phase configurations and perfectly symmetrical ones so that single-phase modelling considers that all the phase conductors behave in the same way. When considering the physical reality of power networks, this assumption can be questionable and the behaviors of all the system conductors including the passive ones (earth wires for overhead lines, metallic screens and armours for cables and enclosures for gas insulated lines) is completely unknown. Therefore, the present multiconductor cell analysis (MCA) becomes necessary, since it allows one to achieve great precision results on the regimes of both phase conductors and passive conductors. MCA offers a powerful tool in order to validate (or less) approximated and simplified computation methods. In particular, for single and double circuit overhead lines (OHLs), the current phasors induced in the earth wires and the ground return current alongside the line can be directly computed by MCA in steady state and faulty regimes. It is worth noting that, for faulty regimes, MCA allows also evaluating the approximation degree and validity field of screening factors k. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
Open AccessArticle On the Efficiency of a Two-Power-Level Flywheel-Based All-Electric Driveline
Energies 2012, 5(8), 2794-2817; doi:10.3390/en5082794
Received: 13 June 2012 / Revised: 20 July 2012 / Accepted: 26 July 2012 / Published: 2 August 2012
Cited by 5 | PDF Full-text (988 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents experimental results on an innovative electric driveline employing a kinetic energy storage device as energy buffer. A conceptual division of losses in the system was created, separating the complete system into three parts according to their function. This conceptualization of
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This paper presents experimental results on an innovative electric driveline employing a kinetic energy storage device as energy buffer. A conceptual division of losses in the system was created, separating the complete system into three parts according to their function. This conceptualization of the system yielded a meaningful definition of the concept of efficiency. Additionally, a thorough theoretical framework for the prediction of losses associated with energy storage and transfer in the system was developed. A large number of spin-down tests at varying pressure levels were performed. A separation of the measured data into the different physical processes responsible for power loss was achieved from the corresponding dependence on rotational velocity. This comparison yielded an estimate of the perpendicular resistivity of the stranded copper conductor of 2.5 × 10−8 ± 3.5 × 10−9. Further, power and energy were measured system-wide during operation, and an analysis of the losses was performed. The analytical solution was able to reproduce the measured distribution of losses in the system to an accuracy of 4.7% (95% CI). It was found that the losses attributed to the function of kinetic energy storage in the system amounted to between 45% and 65%, depending on usage. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
Open AccessArticle A Fuzzy Utility-Based Multi-Criteria Model for Evaluating Households’ Energy Conservation Performance: A Taiwanese Case Study
Energies 2012, 5(8), 2818-2834; doi:10.3390/en5082818
Received: 25 April 2012 / Revised: 23 July 2012 / Accepted: 24 July 2012 / Published: 2 August 2012
Cited by 15 | PDF Full-text (3369 KB) | HTML Full-text | XML Full-text
Abstract
Industry and economy are developed to satisfy the needs and material desires of people. In addition to making high greenhouse gas emissions the responsibility of industry, individuals and families should also be held responsible for the production of greenhouse gas emissions. In this
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Industry and economy are developed to satisfy the needs and material desires of people. In addition to making high greenhouse gas emissions the responsibility of industry, individuals and families should also be held responsible for the production of greenhouse gas emissions. In this study, we applied the Delphi method, the analytical hierarchy process, utility theory, and fuzzy logic theory to establish an energy conservation assessment model for households. We also emphasize that subsidy policy makers should consider the social responsibility of households and individuals, as well as sustainability of energy conservation. Full article
Open AccessArticle Continuous Fermentation of Clostridium tyrobutyricum with Partial Cell Recycle as a Long-Term Strategy for Butyric Acid Production
Energies 2012, 5(8), 2835-2848; doi:10.3390/en5082835
Received: 6 June 2012 / Revised: 16 July 2012 / Accepted: 26 July 2012 / Published: 2 August 2012
Cited by 12 | PDF Full-text (321 KB) | HTML Full-text | XML Full-text
Abstract
In making alternative fuels from biomass feedstocks, the production of butyric acid is a key intermediate in the two-step production of butanol. The fermentation of glucose via Clostridium tyrobutyricum to butyric acid produces undesirable byproducts, including lactic acid and acetic acid, which significantly
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In making alternative fuels from biomass feedstocks, the production of butyric acid is a key intermediate in the two-step production of butanol. The fermentation of glucose via Clostridium tyrobutyricum to butyric acid produces undesirable byproducts, including lactic acid and acetic acid, which significantly affect the butyric acid yield and productivity. This paper focuses on the production of butyric acid using Clostridium tyrobutyricum in a partial cell recycle mode to improve fermenter yield and productivity. Experiments with fermentation in batch, continuous culture and continuous culture with partial cell recycle by ultrafiltration were conducted. The results show that a continuous fermentation can be sustained for more than 120 days, which is the first reported long-term production of butyric acid in a continuous operation. Further, the results also show that partial cell recycle via membrane ultrafiltration has a great influence on the selectivity and productivity of butyric acid, with an increase in selectivity from ≈9% to 95% butyric acid with productivities as high as 1.13 g/Lh. Continuous fermentation with low dilution rate and high cell recycle ratio has been found to be desirable for optimum productivity and selectivity toward butyric acid and a comprehensive model explaining this phenomenon is given. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Submarine Slope Failure Primed and Triggered by Bottom Water Warming in Oceanic Hydrate-Bearing Deposits
Energies 2012, 5(8), 2849-2873; doi:10.3390/en5082849
Received: 14 May 2012 / Revised: 13 July 2012 / Accepted: 25 July 2012 / Published: 6 August 2012
Cited by 8 | PDF Full-text (406 KB) | HTML Full-text | XML Full-text
Abstract
Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09
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Many submarine slope failures in hydrate-bearing sedimentary deposits might be directly triggered, or at least primed, by gas hydrate dissociation. It has been reported that during the past 55 years (1955–2010) the 0–2000 m layer of oceans worldwide has been warmed by 0.09 °C because of global warming. This raises the following scientific concern: if warming of the bottom water of deep oceans continues, it would dissociate natural gas hydrates and could eventually trigger massive slope failures. The present study explored the submarine slope instability of oceanic gas hydrate-bearing deposits subjected to bottom water warming. One-dimensional coupled thermal-hydraulic-mechanical (T-H-M) finite difference analyses were performed to capture the underlying physical processes initiated by bottom water warming, which includes thermal conduction through sediments, thermal dissociation of gas hydrates, excess pore pressure generation, pressure diffusion, and hydrate dissociation against depressurization. The temperature rise at the seafloor due to bottom water warming is found to create an excess pore pressure that is sufficiently large to reduce the stability of a slope in some cases. Parametric study results suggest that a slope becomes more susceptible to failure with increases in thermal diffusivity and hydrate saturation and decreases in pressure diffusivity, gas saturation, and water depth. Bottom water warming can be further explored to gain a better understanding of the past methane hydrate destabilization events on Earth, assuming that more reliable geological data is available. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2011)
Open AccessArticle Are the Greenhouse Gas Implications of New Residential Developments Understood Wrongly?
Energies 2012, 5(8), 2874-2893; doi:10.3390/en5082874
Received: 1 June 2012 / Revised: 26 July 2012 / Accepted: 27 July 2012 / Published: 6 August 2012
Cited by 8 | PDF Full-text (406 KB) | HTML Full-text | XML Full-text
Abstract
Built environment carbon reduction strategies materialize predominantly in city-level greenhouse gas (GHG) management, where new residential development appears as one of the key instruments. However, city-level assessments are often incapable of producing data at a community or neighborhood level and thus they may
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Built environment carbon reduction strategies materialize predominantly in city-level greenhouse gas (GHG) management, where new residential development appears as one of the key instruments. However, city-level assessments are often incapable of producing data at a community or neighborhood level and thus they may heavily underestimate the emissions from new construction. This paper explores the implications of low-energy residential construction as an instrument of climate change mitigation in the built environment and demonstrates why city-level approaches easily fail to identify the significance of the emissions from construction. We employ a hybrid life cycle assessment (LCA) approach to demonstrate that, when the temporal allocation of emissions from the construction and use phases is taken into account, construction phase emissions come to have a central role in finding effective GHG mitigation strategies—even when the emissions from all consumption activities during the use phase are included in the assessment. In fact, their role would seem to be so central that new residential construction cannot be utilized as an instrument of city carbon management, even over a relatively long period. While we analyze a case study from Finland, the analysis intends to highlight the situation throughout the globe. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle Dynamic Feasible Region Genetic Algorithm for Optimal Operation of a Multi-Reservoir System
Energies 2012, 5(8), 2894-2910; doi:10.3390/en5082894
Received: 19 April 2012 / Revised: 16 July 2012 / Accepted: 24 July 2012 / Published: 8 August 2012
Cited by 8 | PDF Full-text (909 KB) | HTML Full-text | XML Full-text
Abstract
Seeking the optimal strategy of a multi-reservoir system is an important approach to develop hydropower energy, in which the Genetic Algorithm (GA) is commonly used as an effective tool. However, when the traditional GA is applied in solving the problem, the constraints of
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Seeking the optimal strategy of a multi-reservoir system is an important approach to develop hydropower energy, in which the Genetic Algorithm (GA) is commonly used as an effective tool. However, when the traditional GA is applied in solving the problem, the constraints of water balance equation, hydraulic continuity relationship and power system load demand might be violated by the crossover and mutation operator, which decreases the efficiency of the algorithm in searching for a feasible region or even leads to a convergence on an infeasible chromosome within the expected generations. A modified GA taking stochastic operators within the feasible region of variables is proposed. When determining the feasible region of constraints, the progressive optimal approach is applied to transform constraints imposed on reservoirs into a singular-reservoir constraint, and a joint solution with consideration of adjacent periods at crossover or mutation points is used to turn the singular-reservoir constraints into singular variable constraints. Some statistic indexes are suggested to evaluate the performances of the algorithms. The experimental results show that compared to GA adopting a penalty function or pair-wise comparison in constraint handling, the proposed modified GA improves the refinement of the quality of a solution in a more efficient and robust way. Full article
Open AccessArticle Preparation and Electrical Properties of Insulation Paper Composed of SiO2 Hollow Spheres
Energies 2012, 5(8), 2943-2951; doi:10.3390/en5082943
Received: 17 February 2012 / Revised: 2 July 2012 / Accepted: 16 July 2012 / Published: 9 August 2012
Cited by 4 | PDF Full-text (1039 KB) | HTML Full-text | XML Full-text
Abstract
SiO2 hollow spheres and low relative permittivity insulation paper handsheets composed of these SiO2 hollow spheres with different weight percentages were successfully prepared. Low-content SiO2 hollow spheres were uniformly dispersed in the insulation paper handsheets. The relative permittivity of the
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SiO2 hollow spheres and low relative permittivity insulation paper handsheets composed of these SiO2 hollow spheres with different weight percentages were successfully prepared. Low-content SiO2 hollow spheres were uniformly dispersed in the insulation paper handsheets. The relative permittivity of the immersed oil Kraft-SiO2 hollow sphere handsheets (K-SiO2) initially decreased and then increased with increased amount of SiO2 hollow spheres. K-5% SiO2 possessed the lowest relative permittivity of approximately 1.68 at 50 Hz. The breakdown voltage of the paper-oil-paper composite insulation system increased from 26.4 kV to 30.5 kV with decreased relative permittivity of the paper from 2.55 to 1.68. The relationship between the relative permittivity and electric field strength of typical samples were also calculated. Full article
Open AccessArticle Rechargeable Energy Storage Systems for Plug-in Hybrid Electric Vehicles—Assessment of Electrical Characteristics
Energies 2012, 5(8), 2952-2988; doi:10.3390/en5082952
Received: 10 April 2012 / Revised: 30 July 2012 / Accepted: 31 July 2012 / Published: 10 August 2012
Cited by 61 | PDF Full-text (2052 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the performances of various lithium-ion chemistries for use in plug-in hybrid electric vehicles have been investigated and compared to several other rechargeable energy storage systems technologies such as lead-acid, nickel-metal hydride and electrical-double layer capacitors. The analysis has shown the
[...] Read more.
In this paper, the performances of various lithium-ion chemistries for use in plug-in hybrid electric vehicles have been investigated and compared to several other rechargeable energy storage systems technologies such as lead-acid, nickel-metal hydride and electrical-double layer capacitors. The analysis has shown the beneficial properties of lithium-ion in the terms of energy density, power density and rate capabilities. Particularly, the nickel manganese cobalt oxide cathode stands out with the high energy density up to 160 Wh/kg, compared to 70–110, 90 and 71 Wh/kg for lithium iron phosphate cathode, lithium nickel cobalt aluminum cathode and, lithium titanate oxide anode battery cells, respectively. These values are considerably higher than the lead-acid (23–28 Wh/kg) and nickel-metal hydride (44–53 Wh/kg) battery technologies. The dynamic discharge performance test shows that the energy efficiency of the lithium-ion batteries is significantly higher than the lead-acid and nickel-metal hydride technologies. The efficiency varies between 86% and 98%, with the best values obtained by pouch battery cells, ahead of cylindrical and prismatic battery design concepts. Also the power capacity of lithium-ion technology is superior compared to other technologies. The power density is in the range of 300–2400 W/kg against 200–400 and 90–120 W/kg for lead-acid and nickel-metal hydride, respectively. However, considering the influence of energy efficiency, the power density is in the range of 100–1150 W/kg. Lithium-ion batteries optimized for high energy are at the lower end of this range and are challenged to meet the United States Advanced Battery Consortium, SuperLIB and Massachusetts Institute of Technology goals. Their association with electric-double layer capacitors, which have low energy density (4–6 Wh/kg) but outstanding power capabilities, could be very interesting. The study of the rate capability of the lithium-ion batteries has allowed for a new state of charge estimation, encompassing all essential performance parameters. The rate capabilities tests are reflected by Peukert constants, which are significantly lower for lithium-ion batteries than for nickel-metal hydride and lead-acid. Furthermore, rate capabilities during charging have been investigated. Lithium-ion batteries are able to store about 80% of the capacity at current rate 2It, with high power cells accepting over 90%. At higher charging rates of 5It or more, the internal resistance impedes charge acceptance by high energy cells. The lithium titanate anode, due to its high surface area (100 m2/g compared to 3 m2/g for the graphite based anode) performs much better in this respect. The behavior of lithium-ion batteries has been investigated at different conditions. The analysis has leaded us to a new lithium ion battery model. This model will be compared to existing battery models in future research contributions. Full article
(This article belongs to the Special Issue Vehicle to Grid)
Open AccessArticle Exploring Malaysia’s Transformation to Net Oil Importer and Oil Import Dependence
Energies 2012, 5(8), 2989-3018; doi:10.3390/en5082989
Received: 4 May 2012 / Revised: 26 July 2012 / Accepted: 31 July 2012 / Published: 10 August 2012
Cited by 5 | PDF Full-text (1456 KB) | HTML Full-text | XML Full-text
Abstract
Within ASEAN, Malaysia is a major oil-exporting country; however, it is expected to become a net oil-importing country in the near future. This issue brings concerns over Malaysia’s energy security, particularly on the aspect of oil import dependency. This is because its transportation
[...] Read more.
Within ASEAN, Malaysia is a major oil-exporting country; however, it is expected to become a net oil-importing country in the near future. This issue brings concerns over Malaysia’s energy security, particularly on the aspect of oil import dependency. This is because its transportation and industrial sectors are still heavily dependent on oil products. By simulating dynamic interplays between developments in Malaysia’s oil sector and its economy sectors, this study explores the possible years of the transformation and the extent to which it will be dependent on oil import. Four scenarios related to enhanced oil recovery, exploration and production investment, subsidy elimination and technology advances are considered for the simulation. In isolation, the subsidy elimination scenario provides the best result. However, if all scenarios are considered simultaneously, an undesired effect emerges. The earliest that Malaysia is expected to become a net oil-importing country is 2012 and the latest is 2021. Malaysia’s dependence on oil imports is expected to continue increasing. In all scenarios, the shares of oil import in the total supply rise to above 90% in 2030, with the highest share at 97%. Full article
Open AccessArticle Improving Production of Bioethanol from Duckweed (Landoltia punctata) by Pectinase Pretreatment
Energies 2012, 5(8), 3019-3032; doi:10.3390/en5083019
Received: 21 June 2012 / Revised: 18 July 2012 / Accepted: 6 August 2012 / Published: 10 August 2012
Cited by 30 | PDF Full-text (734 KB) | HTML Full-text | XML Full-text
Abstract
Landoltia punctata, a widely distributed duckweed strain with the ability to accumulate starch, was used as a novel feedstock for bioethanol production by Saccharomyces cerevisiae. To improve ethanol production, pectinase pretreatment was used to release much more glucose from L. punctata
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Landoltia punctata, a widely distributed duckweed strain with the ability to accumulate starch, was used as a novel feedstock for bioethanol production by Saccharomyces cerevisiae. To improve ethanol production, pectinase pretreatment was used to release much more glucose from L. punctata mash and the pretreatment conditions (enzyme loading, temperature and pretreatment time) for the duckweed were optimized by using a surface response design. The results showed that maximum glucose yield was 218.64 ± 3.10 mg/g dry matter, which is a 142% increase compared to the untreated mash, with a pectinase dose of 26.54 pectin transeliminase unit/g mash at 45 °C for 300 min. Pectinase pretreatment apparently changed the ultrastructure of L. punctata, as evidenced by scanning electron microscopy analysis. Further fermentation experiments were performed and 30.8 ± 0.8 g/L of ethanol concentration, 90.04% of fermentation efficiency and 2.20 g/L/h of productivity rate were achieved. This is the highest ethanol concentration reported to date using duckweed as the feedstock. Full article
Open AccessArticle Power Control Design for Variable-Speed Wind Turbines
Energies 2012, 5(8), 3033-3050; doi:10.3390/en5083033
Received: 25 June 2012 / Revised: 3 August 2012 / Accepted: 3 August 2012 / Published: 13 August 2012
Cited by 14 | PDF Full-text (1935 KB) | HTML Full-text | XML Full-text
Abstract
This paper considers power generation control in variable-speed variable-pitch horizontal-axis wind turbines operating at high wind speeds. A dynamic chattering torque control and a proportional integral (PI) pitch control strategy are proposed and validated using the National Renewable Energy Laboratory wind turbine simulator
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This paper considers power generation control in variable-speed variable-pitch horizontal-axis wind turbines operating at high wind speeds. A dynamic chattering torque control and a proportional integral (PI) pitch control strategy are proposed and validated using the National Renewable Energy Laboratory wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. Validation results show that the proposed controllers are effective for power regulation and demonstrate high-performances for all other state variables (turbine and generator rotational speeds; and smooth and adequate evolution of the control variables) for turbulent wind conditions. To highlight the improvements of the provided method, the proposed controllers are compared to relevant previously published studies. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Gamma Irradiation Induced Degradation of Orange Peels
Energies 2012, 5(8), 3051-3063; doi:10.3390/en5083051
Received: 8 June 2012 / Revised: 21 July 2012 / Accepted: 1 August 2012 / Published: 14 August 2012
Cited by 9 | PDF Full-text (465 KB) | HTML Full-text | XML Full-text
Abstract
In this study, gamma irradiation induced degradation of orange peels (OP) was investigated. The lignocellulosic biomass degradation was carried out at doses of 0 (control), 600, 1800 and 3500 kGy using a Co-60 gamma radiation source. The samples were tested for total and
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In this study, gamma irradiation induced degradation of orange peels (OP) was investigated. The lignocellulosic biomass degradation was carried out at doses of 0 (control), 600, 1800 and 3500 kGy using a Co-60 gamma radiation source. The samples were tested for total and reducing sugars. The concentrations of total sugars ranged from 0.530 g∙g−1 in control sample to 0.382 g∙g−1 of dry weight in the sample which received the highest radiation dose. The reducing sugars content varying from 0.018 to 0.184 g∙g−1 of dry weight with the largest rise occurring in the sample irradiated at 3500 kGy. The concentrations of sucrose, glucose and fructose were determined. The changes generated in physico-chemical properties were determined by Fourier Transform Infrared Spectroscopy (FTIR) and termogravimetric analysis (TG-DTG). The results show that OP was affected, but not significantly, which suggests that lignocellulose and sugars profiles were partially degraded after gamma irradiation. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle An Analysis of the Use of Biosludge as an Energy Source and Its Environmental Benefits in Taiwan
Energies 2012, 5(8), 3064-3073; doi:10.3390/en5083064
Received: 2 July 2012 / Revised: 25 July 2012 / Accepted: 2 August 2012 / Published: 14 August 2012
Cited by 4 | PDF Full-text (192 KB) | HTML Full-text | XML Full-text
Abstract
The objective of this paper was to provide a preliminary analysis of energy utilization from biological wastewater treatment sludge (biosludge) in Taiwan, a densely populated country (estimate 640 persons/km2) with a high dependence (over 99%) on imported energy. The discussion focused
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The objective of this paper was to provide a preliminary analysis of energy utilization from biological wastewater treatment sludge (biosludge) in Taiwan, a densely populated country (estimate 640 persons/km2) with a high dependence (over 99%) on imported energy. The discussion focused on the status of biosludge generation and its management in the years 2004–2010. Findings showed that the main types of combustible waste (i.e., biosludge) produced by the industrial and agricultural sectors of Taiwan included food processing sludge, wine brewery sludge and agricultural sludge which may be reused as auxiliary fuel in the utilities (e.g., generator, boiler and incinerator). Furthermore, two conceptual biosludge-to-energy systems have been addressed with regard to the thermochemical conversion processes. One is to adopt direct combustion for power generation in the combined heat and power system. Another system uses pyrolysis and gasification for producing biochar (solid fuel), bio-oil (liquid fuel) and syngas (gas fuel). Based on their thermochemical properties and reported generation quantities, the energy potential and the environmental benefits of mitigating CO2 emissions were also analyzed in the study, showing around 1.1 × 103 TJ/year and 57 Gg CO2/year, respectively. Full article
(This article belongs to the Special Issue Waste to Energy Technologies)
Open AccessArticle Assessment of Thailand’s Energy Policies and CO2 Emissions: Analyses of Energy Efficiency Measures and Renewable Power Generation
Energies 2012, 5(8), 3074-3093; doi:10.3390/en5083074
Received: 19 May 2012 / Revised: 31 July 2012 / Accepted: 8 August 2012 / Published: 15 August 2012
Cited by 9 | PDF Full-text (349 KB) | HTML Full-text | XML Full-text
Abstract
This study assesses Thailand’s energy policies on renewable electricity generation and energy efficiency in industries and buildings. The CO2 emissions from power generation expansion plans (PGEPs) are also evaluated. The PGEPs of CO2 reduction targets of 20% and 40% emissions are
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This study assesses Thailand’s energy policies on renewable electricity generation and energy efficiency in industries and buildings. The CO2 emissions from power generation expansion plans (PGEPs) are also evaluated. The PGEPs of CO2 reduction targets of 20% and 40% emissions are also evaluated. Since 2008 Thai government has proposed the Alternative Energy Development Plan (AEDP) for renewable energy utilization. Results from energy efficiency measures indicate total cost saving of 1.34% and cumulative CO2 emission reduction of 59 Mt-CO2 in 2030 when compared to the business-as-usual (BAU) scenario. It was found that subsidies in the AEDP will promote renewable energy utilization and provide substantial CO2 mitigation. As a co-benefit, fuel import vulnerability can be improved by 27.31% and 14.27% for CO2 reduction targets of 20% and 40%, respectively. Full article
Open AccessArticle Dynamic Coordinated Shifting Control of Automated Mechanical Transmissions without a Clutch in a Plug-In Hybrid Electric Vehicle
Energies 2012, 5(8), 3094-3109; doi:10.3390/en5083094
Received: 26 June 2012 / Revised: 9 August 2012 / Accepted: 10 August 2012 / Published: 16 August 2012
Cited by 15 | PDF Full-text (1963 KB) | HTML Full-text | XML Full-text
Abstract
On the basis of the shifting process of automated mechanical transmissions (AMTs) for traditional hybrid electric vehicles (HEVs), and by combining the features of electric machines with fast response speed, the dynamic model of the hybrid electric AMT vehicle powertrain is built up,
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On the basis of the shifting process of automated mechanical transmissions (AMTs) for traditional hybrid electric vehicles (HEVs), and by combining the features of electric machines with fast response speed, the dynamic model of the hybrid electric AMT vehicle powertrain is built up, the dynamic characteristics of each phase of shifting process are analyzed, and a control strategy in which torque and speed of the engine and electric machine are coordinatively controlled to achieve AMT shifting control for a plug-in hybrid electric vehicle (PHEV) without clutch is proposed. In the shifting process, the engine and electric machine are well controlled, and the shift jerk and power interruption and restoration time are reduced. Simulation and real car test results show that the proposed control strategy can more efficiently improve the shift quality for PHEVs equipped with AMTs. Full article
(This article belongs to the Special Issue Vehicle to Grid)
Open AccessArticle The Long-Term Prospects of Biofuels in the EU-15 Countries
Energies 2012, 5(8), 3110-3125; doi:10.3390/en5083110
Received: 18 June 2012 / Revised: 9 August 2012 / Accepted: 13 August 2012 / Published: 17 August 2012
PDF Full-text (272 KB) | HTML Full-text | XML Full-text
Abstract
The core objective of this paper is to analyze the energy and CO2 reduction potentials as well as the market prospects of biofuels in EU-15 in a dynamic framework till 2050. The most important result of this analysis is that 2nd generation
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The core objective of this paper is to analyze the energy and CO2 reduction potentials as well as the market prospects of biofuels in EU-15 in a dynamic framework till 2050. The most important result of this analysis is that 2nd generation biofuels might become economically competitive between 2020 and 2030, yet this can only be achieved if the following preconditions are fulfilled: (1) achievement of significant learning effects leading to considerably lower plant costs; (2) significant improvement of conversion efficiency from feedstock to fuel leading to lower feedstock costs and better ecological performance; (3) increases in conventional diesel and gasoline prices, e.g., due to CO2 based taxes. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Experimental Study on the Combustion and Microexplosion of Freely Falling Gelled Unsymmetrical Dimethylhydrazine (UDMH) Fuel Droplets
Energies 2012, 5(8), 3126-3136; doi:10.3390/en5083126
Received: 13 July 2012 / Revised: 7 August 2012 / Accepted: 13 August 2012 / Published: 17 August 2012
Cited by 4 | PDF Full-text (666 KB) | HTML Full-text | XML Full-text
Abstract
The increasing demand for high energy density fuels and the concern for their safety have propelled research in the field of gelled propellants, where understanding the combustion of single gelled fuel droplets is the first stage to predict the spray combustion characteristics. The
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The increasing demand for high energy density fuels and the concern for their safety have propelled research in the field of gelled propellants, where understanding the combustion of single gelled fuel droplets is the first stage to predict the spray combustion characteristics. The experiments utilized single-isolated freely falling gelled unsymmetrical dimethylhydrazine (UDMH) droplets instead of the conventional suspended droplet approach, in order to eliminate the perturbation associated with the suspension mechanism. Morphological transformations of the gelled droplet involved in the combustion processes were monitored by employing a high-speed digital camera, while the effects of ambient pressure and oxygen concentration on burning rate constants were also studied. The experimental results show that four main phenomena (droplet deformation, bubble formation and growth, vapor jetting and luminous jetting flame with “horn” shape) and three distinct phases were identified in the droplet combustion process; the high yield stress and polymer chain structure of polymer gellant are responsible for the appearance of bubbles with almost the same order of magnitude as the droplets. Increasing the ambient pressure can increase the burning rate, postpone the appearance of microexplosions, and weaken microexplosion intensity; while increasing the ambient oxygen concentration can promote the appearance of microexplosions, strengthen microexplosion intensity and increase the burning rate. Full article
Open AccessArticle A Complementary Biodiesel Blend from Soapnut Oil and Free Fatty Acids
Energies 2012, 5(8), 3137-3148; doi:10.3390/en5083137
Received: 29 June 2012 / Revised: 24 July 2012 / Accepted: 16 August 2012 / Published: 17 August 2012
Cited by 2 | PDF Full-text (286 KB) | HTML Full-text | XML Full-text
Abstract
Blends of biodiesels produced from soapnut oil and high-oleic free fatty acids (FFAs), which are potential non-edible oil feedstocks, were investigated with respect to their fuel properties. The soapnut oil methyl esters (SNME) had satisfactory fuel properties with the exception of its high
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Blends of biodiesels produced from soapnut oil and high-oleic free fatty acids (FFAs), which are potential non-edible oil feedstocks, were investigated with respect to their fuel properties. The soapnut oil methyl esters (SNME) had satisfactory fuel properties with the exception of its high cold filter plugging point. In contrast, the biodiesel from the FFAs had favorable fuel properties such as a low cold filter plugging point of −6 °C; however, it exhibits poor oxidation stability with an induction period (IP) of 0.2 h. The complementary blend of the SNME and the FFA-based biodiesel at various weight ratios was studied to improve the fuel properties. As a result, the biodiesel blend at a weight ratio of 70:30 can successfully meet all the biodiesel specifications, except the marginal oxidation stability. Furthermore, the effectiveness of N,N’-di-sec-butyl-p-phenylenediamine at the concentration between 100 and 500 ppm on the improvement in the oxidation stability of the biodiesel blend was examined. The relationship between the IP values associated with the consumption of antioxidants in the biodiesel blends was described by first-order reaction rate kinetics. In addition, the natural logarithm of IP (ln IP) at various concentrations of antioxidant presented a linear relation with the test temperature. The IP at ambient temperature can be predicted based on the extrapolation of the temperature dependence relation. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle An Innovative Use of Renewable Ground Heat for Insulation in Low Exergy Building Systems
Energies 2012, 5(8), 3149-3166; doi:10.3390/en5083149
Received: 12 June 2012 / Revised: 12 July 2012 / Accepted: 13 July 2012 / Published: 20 August 2012
PDF Full-text (683 KB) | HTML Full-text | XML Full-text
Abstract
Ground heat is a renewable resource that is readily available for buildings in cool climates, but its relatively low temperature requires the use of a heat pump to extract it for heating. We developed a system that uses low temperature ground heat directly
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Ground heat is a renewable resource that is readily available for buildings in cool climates, but its relatively low temperature requires the use of a heat pump to extract it for heating. We developed a system that uses low temperature ground heat directly in a building wall to reduce transmission heat losses. The Active Low Exergy Geothermal Insulation Systems (ALEGIS) minimizes exergy demand and maximizes the use of renewable geothermal heat from the ground. A fluid is pumped into a small pipe network in an external layer of a wall construction that is linked to a ground heat source. This decouples the building from the outside temperature, therefore eliminating large peak demands and reducing the primary energy demand. Our steady-state analysis shows that at a design temperature of −10 °C the 6 cm thick active insulation system has equivalent performance to 11 cm of passive insulation. Our comparison of heating performance of a building with our active insulation system versus a building with static insulation of the same thickness shows a 15% reduction in annual electricity demand, and thus exergy input. We present an overview of the operation and analysis of our low exergy concept and its modeled performance. Full article
(This article belongs to the Special Issue Exergy Analysis of Energy Systems)

Review

Jump to: Research

Open AccessReview Current Status and Prospects of Biodiesel Production from Microalgae
Energies 2012, 5(8), 2667-2682; doi:10.3390/en5082667
Received: 15 May 2012 / Revised: 13 July 2012 / Accepted: 20 July 2012 / Published: 25 July 2012
Cited by 15 | PDF Full-text (197 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae represent a sustainable energy source because of their high biomass productivity and ability to remove air and water born pollutants. This paper reviews the current status of production and conversion of microalgae, including the advantages of microalgae biodiesel, high density cultivation of
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Microalgae represent a sustainable energy source because of their high biomass productivity and ability to remove air and water born pollutants. This paper reviews the current status of production and conversion of microalgae, including the advantages of microalgae biodiesel, high density cultivation of microalgae, high-lipid content microalgae selection and metabolic control, and innovative harvesting and processing technologies. The key barriers to commercial production of microalgae biodiesel and future perspective of the technologies are also discussed. Full article
(This article belongs to the Special Issue Algae Fuel)
Open AccessReview Household Biogas Digesters—A Review
Energies 2012, 5(8), 2911-2942; doi:10.3390/en5082911
Received: 11 May 2012 / Revised: 27 July 2012 / Accepted: 30 July 2012 / Published: 8 August 2012
Cited by 49 | PDF Full-text (398 KB) | HTML Full-text | XML Full-text
Abstract
This review is a summary of different aspects of the design and operation of small-scale, household, biogas digesters. It covers different digester designs and materials used for construction, important operating parameters such as pH, temperature, substrate, and loading rate, applications of the biogas,
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This review is a summary of different aspects of the design and operation of small-scale, household, biogas digesters. It covers different digester designs and materials used for construction, important operating parameters such as pH, temperature, substrate, and loading rate, applications of the biogas, the government policies concerning the use of household digesters, and the social and environmental effects of the digesters. Biogas is a value-added product of anaerobic digestion of organic compounds. Biogas production depends on different factors including: pH, temperature, substrate, loading rate, hydraulic retention time (HRT), C/N ratio, and mixing. Household digesters are cheap, easy to handle, and reduce the amount of organic household waste. The size of these digesters varies between 1 and 150 m3. The common designs include fixed dome, floating drum, and plug flow type. Biogas and fertilizer obtained at the end of anaerobic digestion could be used for cooking, lighting, and electricity. Full article

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