Stable Electricity Production Research Articles

Future role of ocean thermal energy converters in a 100% renewable energy system on the case of the Maldives

Energy transition on small islands is limited by the scarce availability of land, restricting large-scale implementation of onshore renewable energy technologies such as solar photovoltaics and wind power. Ocean energy technologies provide novel opportunities for land-constrained islands to achieve 100% renewable energy systems. While wave power is increasingly implemented in energy system modelling research, ocean thermal energy converters are not yet a standard technology in renewable energy technology portfolios. This research aims to study the impacts of ocean thermal energy converters on the energy system of the Maldives through a structured sensitivity analysis for the two scenario clusters covering e-fuel import and domestic production. The ocean thermal energy conversion plants are modelled using spatially and temporally resolved resource data and cost assumptions from a global upscaling scenario, considering the technology’s current development stage. Results show that ocean thermal energy converters play a limited role in 'purely' cost-optimised sub-scenarios due to the availability of very low-cost offshore floating photovoltaics, making it difficult for them to compete. Nevertheless, reduced requirement of energy storage technologies due to the stable electricity production of ocean thermal energy converters offers an option to diversify the renewable energy technology portfolio with only a minor increase in cost.

Electricity production performance enhancement of microbial fuel cells with double-layer sodium alginate hydrogel bioanodes driven by high-salinity waste leachate

The poor bacterial loading capacity and biocompatibility of the anode lead to weak electricity production performance of microbial fuel cells (MFCs). Inspired by kelp, we developed a double-layer hydrogel bioanode based on sodium alginate (SA). The inner hydrogel layer of encapsulated Fe3O4 and electroactive microorganisms (EAMs) was used as the bioelectrochemical catalytic layer. The outer hydrogel layer formed by cross-linking SA with polyvinyl alcohol (PVA) was used as the protective layer. The 3D porous structure of the inner hydrogel formed based on Fe3O4 facilitated the electroactive bacteria colonization and electron transfer, while the high structural toughness, salt-resistance and antibacterial properties of the outer highly cross-linked hydrogel served to protect the catalytic layer for stable electricity production. When high-salt waste leachate was used as the nutrient, the amazing open-circuit voltage (OCV) of 1.17 V and the operating voltage of 781 mV were brought by the double-layer hydrogel bioanode PVA@SA&Fe3O4/EAMs@SA.

A geospatial comparative analysis of solar thermal concentrating power systems in Greece

Solar concentrating power is an important weapon for facing the energy crisis and environmental issues. Greece is a country with great solar potential and thus it is an ideal candidate for the development of important solar concentrating power plants. These plants present the advantage of easy energy storage with thermal storage tanks, something beneficial for the production of a relatively stable electricity production profile, something critical for the further development of renewable energy systems. The objective of the present work is the detailed investigation of the solar concentrating technologies in different Greek locations in order to define in which locations solar concentrating power is a promising solution. Moreover, three typical solar concentrating technologies are studied and more specifically the parabolic trough collector (PTC), the linear Fresnel reflector (LFR) and the solar DISH. Thirteen different Greek regions are investigated by using hourly weather data from the typical meteorological year (TMY). The solar potential, the available irradiation, the useful heat production, the electricity production and the exergy production, as well as the respective efficiency indexes and the levelized cost of electricity (LCOE), are calculated. It is important to highlight that this study is focused on the systems of small capacity which are ideal for distributed renewable power production. It was concluded that the most efficient and economically feasible technology is the solar DISH, with the PTC to follow and LFR to be the last choice. Moreover, southern Greece is found to be a better choice for the installation of solar-concentrating power plants compared to northern Greece. More specifically, in the Southern Aegean Sea, it was calculated that the specific electricity production is 253.0 kWh/m2 with PTC, 160.7 kWh/m2 with LFR and 296.8 kWh/m2 with DISH, while the LCOE at 0.0882 €/kWh with PTC, 0.1046 €/kWh with LFR and 0.0843 €/kWh with DISH.

Dual functions of activated carbon air‐cathode: Nitrobenzene removal and electricity production in microbial fuel cells

AbstractThe removal of nitrobenzene (NB) in microbial electrochemical systems generally requires electrical power to operate systems in the mode of microbial electrolysis cells (MECs). The present study demonstrates that single‐chamber microbial fuel cells (S‐MFCs) assembled with a bioanode and an activated carbon (AC) air cathode could simultaneously remove NB and generate electricity. S‐MFCs with 1 mM NB exhibit long term NB tolerance and stable electricity production, with NB removal up to 98% in an operation cycle and a maximum power of 16.2 ± 1.3 W m−3. High NB loadings significantly inhibited the activity of anodic biofilms, but the inhibition was reversible. Investigating the removal of NB and its reduction product aniline (AN) in different operations supported the fact that the adsorption at the AC air cathode is the main pathway for the removal of NB and AN from solution, except for the partial conversion of NB to AN by anaerobic reduction in solution. In S‐MFCs, the activated carbon in the cathode plays both functions: catalyzing the oxygen reduction reaction and adsorbing NB and AN, so that the S‐MFC assembled with the AC air cathode, unlike most NB removing MECs, functions as a system with both NB removal and electricity production.

Low Frequency Oscillations in a Hydroelectric Generating System to the Variability of Wind and Solar Power

The penetration of multiple integrated renewable energies to the power grid are relevant for decision making in energy policy, environment and business. Such an electricity penetration is affected by the intermittent and volatile characteristics of integrated energies, mostly significantly related to the safe and stable electricity production and supply in real world. Here, this paper focuses on the low frequency oscillation analysis of the hydropower generation response to the wind and solar variability. To enable this analysis, a hybrid model of hydropower system integrating with the wind and solar power system is presented. The Nyquist and root-locus stability methods are used to investigate the sensitivity performance of the hydropower governor to the fluctuation of the integrated renewable energies. Additionally, to quantify the risk of the hybrid system, the low frequency oscillation response of hydropower system to wind/solar/hydropower quota and transmission line distance ratio is extensively investigated in this study. The results show that under the case of the wind, solar and hydropower ratio is 40:1:150, the optimal values for maximally reducing hydropower low frequency oscillation are finally determined as kp = 0.8, ki = 0.25 and kd = 0.5. Regarding a certain wind/solar/hydropower quota, it is a promising strategy to increase the solar-load transmission line in order to achieve the safe and stable operation of the hybrid system and a relatively excellent dynamic regulation capacity of the hydropower governor. The model, methods and results implemented in this study are exploited to markedly improve new knowledge applications, policy management, low carbon emissions and investment competitiveness of future energy systems.

Proton-Conducting Ceramics for Electrochemical Ammonia Synthesis

We report our progress in developing proton-conducting ceramics for flexible storage of intermittent renewable electricity in the form of ammonia. Various electrochemical and thermochemical synthesis strategies have been investigated in pursuit of “green ammonia”. Electrochemical ammonia synthesis can harness water-splitting to source hydrogen, displacing steam-methane reforming widely used in conventional ammonia production through the well-established Haber-Bosch process (HB).This electrochemical approach potentially provides an efficient solution to the energy-storage challenges presented by the expanding market penetration of solar and wind power. The intermittent nature of these renewables presents strain on the conventional power plants tasked with stable electricity production. Through creative application of novel proton-conducting electroceramics, intermittent renewable electricity can be used to drive the synthesis of green ammonia, effectively storing electricity in the form of an easily transported, carbon-neutral, energy-dense commodity chemical. Further, the process is reversible; NH3 can be electrochemically re-converted back into electricity as needed in meeting peak load demands.Displacing Haber-Bosch proves challenging, as it requires process solutions that can simultaneously achieve high NH3 conversion and high NH3-synthesis rate while minimizing energy costs. The Haber-Bosch process achieves both through high-pressure operation (up to 300 bar), where thermodynamics are more favorable. Electrochemical systems have yet to reach this stage of technological development. All previous work has been limited to atmospheric-pressure operation, where NH3-synthesis rates are orders-of-magnitude lower. Further, most reports on electrochemical ammonia synthesis have utilized molecular H2 as the source of protons for NH3 synthesis, rather than water electrolysis as described here.In this work, we present our efforts to apply proton-conducting ceramics to enable electrochemical ammonia synthesis from H2O and N2 feedstocks. Protonic ceramics are emerging materials finding applications in efficient electricity generation, energy storage, and fuels synthesis. As shown in the figure, renewable electricity is used to drive hydrogen production through high-temperature water splitting in the protonic-ceramic electrolyzer. The hydrogen mixes with nitrogen and is then converted to NH3 over a ruthenium catalyst. The process is executed at pressures up to 12 bar, bringing significant challenges in packaging of the protonic ceramic and the catalyst. In this presentation, we review our progress in establishing pressurized operation, and the benefits it brings to electrochemical synthesis of ammonia. Figure 1

Microbial Structure and Energy Generation in Microbial Fuel Cells Powered with Waste Anaerobic Digestate

Development of economical and environment-friendly Microbial Fuel Cells (MFCs) technology should be associated with waste management. However, current knowledge regarding microbiological bases of electricity production from complex waste substrates is insufficient. In the following study, microbial composition and electricity generation were investigated in MFCs powered with waste volatile fatty acids (VFAs) from anaerobic digestion of primary sludge. Two anode sizes were tested, resulting in organic loading rates (OLRs) of 69.12 and 36.21 mg chemical oxygen demand (COD)/(g MLSS∙d) in MFC1 and MFC2, respectively. Time of MFC operation affected the microbial structure and the use of waste VFAs promoted microbial diversity. High abundance of Deftia sp. and Methanobacterium sp. characterized start-up period in MFCs. During stable operation, higher OLR in MFC1 favored growth of exoelectrogens from Rhodopseudomonas sp. (13.2%) resulting in a higher and more stable electricity production in comparison with MFC2. At a lower OLR in MFC2, the percentage of exoelectrogens in biomass decreased, while the abundance of genera Leucobacter, Frigoribacterium and Phenylobacterium increased. In turn, this efficiently decomposed complex organic substances, favoring high and stable COD removal (over 85%). Independent of the anode size, Clostridium sp. and exoelectrogens belonging to genera Desulfobulbus and Acinetobacter were abundant in MFCs powered with waste VFAs.

Sensitivity analysis of fusion power plant designs using the SYCOMORE system code

The next step after ITER is the demonstration of stable electricity production with a fusion reactor. Key design performance will have to be met by the corresponding power plant demonstrator (DEMO), fulfilling a large number of constraints. System codes such as SYCOMORE, by simulating all the fusion power plant sub-systems, address these questions. To be able to perform design optimizations, simplified models relying on physical and technological assumptions have to be used, resulting in a large number of input parameters. As these parameters are not always exactly known, the impact of their associated uncertainties on final design performance has to be evaluated. Sensitivity methods, by measuring the relative influence of inputs on the figures of merit of the design, allow the dominant parameters to be selected. This information helps the search for optimal working points, guides the priority for technical improvements and finally allows meaningful inputs for uncertainty propagation to be selected. A full set of sensitivity methods and their application to an ITER and DEMO design will be presented, discussing both the statistical method behaviours and the physical results. Plasma shape parameters (minor radius and plasma elongations) share half of the net electricity power sensitivity for the DEMO 2015 design, while the toroidal magnetic field and the 95% safety factor are responsible for 23% and 17% of the electric power sensitivity, respectively. The plasma minor radius is responsible for 45% of the pulse duration sensitivity for the DEMO 2015 design, while plasma physics parameters drive % of the pulse duration sensitivity.

Oil Palm Fibre Waste to Biogas Electricity Production Framework for Mill Operation

One of issue regarding of renewable energy supply chain is source sustainability and reliability to ensure continuous production. The aim of this paper is to suggest the oil palm fibre waste to biogas electricity production framework: mill operation perspective that suit to be practices based on evaluation of current practise of oil palm solid waste and Malaysia’s palm oil industry. The framework is based on palm oil mill operation to utilise annually solid waste generate as biomass source for stable biogas electricity production. This conceptual paper is the principal efforts that introduce the usage of storage system for biomass feed input to ensure sustainable stable electricity production from palm oil mill by manipulate their solid waste production. Prospective researchers are put forward to conduct further research to enhance biogas production as alternative for waste treatment strategy.

Efficient removal of nitrobenzene and concomitant electricity production by single-chamber microbial fuel cells with activated carbon air-cathode

Single-chamber microbial fuel cells (S-MFCs) with bio-anodes and activated carbon (AC) air-cathodes showed high nitrobenzene (NB) tolerance and NB removal with concomitant electricity production. The maximum power over 25Wm−3 could be obtained when S-MFCs were operated in the NB loading range of 1.2–6.2molm−3d−1, and stable electricity production over 13.7Wm−3 could be produced in a NB loading range of 1.2–14.7molm−3d−1. The present S-MFCs exhibited high NB removal performance with NB removal efficiency over 97% even when the NB loading rate was increased to 17.2molm−3d−1. The potential NB reduced product (i.e. aniline) could also be effectively removed from influents. The findings in this study means that single-chamber MFCs assembled with pre-enriched bio-anodes and AC air-cathodes could be developed as effective bio-electrochemical systems to remove NB from wastewaters and to harvest energy instead of consuming energy.

FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin

A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1–1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1–100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT).

Long-term stability of bioelectricity generation coupled with tetrathionate disproportionation

To prevent uncontrolled acidification of the environment, reduced inorganic sulfur compounds (RISCs) can be bioelectrochemically removed from water streams. The long-term stability of bioelectricity production from tetrathionate (S4O62−) was studied in highly acidic conditions (pH<2.5) in two-chamber fed-batch microbial fuel cells (MFCs). The maximum current density was improved from previously reported 80mAm−2 to 225mAm−2 by optimizing the external resistance. The observed reaction products of tetrathionate disproportionation were sulfate and elemental sulfur. In long-term run, stable electricity production was obtained for over 700days with the average current density of 150mAm−2. The internal resistance of the MFC decreased over time and no biofouling was observed. This study shows that tetrathionate is an efficient substrate also for long-term bioelectricity production.

Graphene oxide-dependent growth and self-aggregation into a hydrogel complex of exoelectrogenic bacteria.

Graphene oxide (GO) is reduced by certain exoelectrogenic bacteria, but its effects on bacterial growth and metabolism are a controversial issue. This study aimed to determine whether GO functions as the terminal electron acceptor to allow specific growth of and electricity production by exoelectrogenic bacteria. Cultivation of environmental samples with GO and acetate as the sole substrate could specifically enrich exoelectrogenic bacteria with Geobacter species predominating (51–68% of the total populations). Interestingly, bacteria in these cultures self-aggregated into a conductive hydrogel complex together with biologically reduced GO (rGO). A novel GO-respiring bacterium designated Geobacter sp. strain R4 was isolated from this hydrogel complex. This organism exhibited stable electricity production at >1000 μA/cm3 (at 200 mV vs Ag/AgCl) for more than 60 d via rGO while temporary electricity production using graphite felt. The better electricity production depends upon the characteristics of rGO such as a large surface area for biofilm growth, greater capacitance, and smaller internal resistance. This is the first report to demonstrate GO-dependent growth of exoelectrogenic bacteria while forming a conductive hydrogel complex with rGO. The simple put-and-wait process leading to the formation of hydrogel complexes of rGO and exoelectrogens will enable wider applications of GO to bioelectrochemical systems.

Inhibition of microbial growth on air cathodes of single chamber microbial fuel cells by incorporating enrofloxacin into the catalyst layer.

The inevitable growth of aerobic bacteria on the surface of air cathodes is an important factor reducing the performance stability of air cathode single-chamber membrane-free microbial fuel cells (MFCs). Thus searching for effective methods to inhibit the cathodic microbial growth is critical for the practical application of MFCs. In this study, enrofloxacin (ENR), a broad spectrum fluoroquinolone antibiotic, was incorporated into the catalyst layer of activated carbon air cathodes (ACACs) to inhibit the cathodic microbial growth. The biomass content on ACACs was substantially reduced by 60.2% with ENR treatment after 91 days of MFCs operation. As a result of the inhibited microbial growth, the oxygen reduction catalytic performance of the ENR treated ACACs was much stable compared to the fast performance decline of the untreated control. Consequently, a quite stable electricity production was obtained for the MFCs with the ENR treated ACACs, in contrast with a 22.5% decrease in maximum power density of the MFCs with the untreated cathode. ENR treatment of ACACs showed minimal effects on the anode performance. These results indicate that incorporating antibiotics into ACACs should be a simple and effective strategy to inhibit the microbial growth and improve the long-term stability of the performance of air cathode and the electricity production of MFCs.

Design of a Protection Thermal Energy Storage Using Phase Change Material Coupled to a Solar Receiver

AbstractThermal Energy Storage (TES) is the key for a stable electricity production in future Concentrated Solar Power (CSP) plants. This work presents a study on the thermal protection of the central receiver of CSP plant using a tower which is subject to considerable thermal stresses in case of cloudy events. The very high temperatures, 800 °C at design point, impose the use of special materials which are able to resist at high temperature and high mechanical constraints and high level of concentrated solar flux. In this paper we investigate a TES coupling a metallic matrix drilled with tubes of Phase Change Material (PCM) in order to store a large amount of thermal energy and release it in a short time. A numerical model is developed to optimize the arrangement of tubes into the TES. Then a methodology is given, based from the need in terms of thermal capacity, in order to help the choice of the geometry.

Electricity Production in Microbial Fuel Cells Using Brush Bio-Anode and Bio-Cathode Made of PAN-Based Carbon Fibers

Microbial fuel cells with brush bio-anode and bio-cathode made of PAN-based carbon fibers were constructed, and the electricity production was investigated. Experimental results indicate that both the anode and the cathode could be catalyzed by mixed bacterial cultures. Oxygen-reduction at the cathode could be carried out effectively with the assistance of catalytic action by bacteria, enhancing the electrochemical properties of the cathode. Stable electricity production could be obtained with maximum power 5.6 mW (corresponding power density ~2.1 W/m3 MFC volume) when operating MFC in continuous flow mode. PAN-based carbon fibers were shown to be suitable electrode materials for MFCs, especially in systems for the future applications.

Current Production by Bacterial Communities in Microbial Fuel Cells Enriched from Wastewater Sludge with Different Electron Donors

Electricity production by bacterial communities enriched from wastewater sludge with lactate, succinate, N-acetyl-D-glucosamine (NAG), acetate, formate, and uridine were monitored in dual-chamber microbial fuel cells (MFCs). Stable electricity production was observed after 300 h for communities enriched from lactate, acetate, and formate, while communities enriched with succinate, NAG, and uridine stabilized only after 700 h. The average peak current densities and maximum power densities generated from bacterial consortia were significantly higher than those generated from pure cultures of Shewanella oneidensis MR-1. Microbial assemblages were analyzed by DGGE, and planktonic and anode-attached bacterial communities varied as a function of electron donors: Firmicutes, β-Proteobacteria, and Bacteroidetes dominated the planktonic bacterial communities while anode-attached communities consisted mainly of δ-Proteobacteria, β-Proteobacteria, and Firmicutes. Similar bacterial populations were enriched in MFCs fed with lactate, NAG, and uridine and with succinate, acetate, and formate. Cross-feeding experiments with different fuels indicated that enriched microbial consortia were able to utilize a variety of fuel sources and displayed considerable stability, efficiency, and robustness of power generation in comparison to pure cultures. In addition, characterizations of cultivated Shewanella strains suggested that DGGE analysis likely missed active members of exoelectrogenic populations.