•Energy service contract can be modelled as a two-stage optimization problem.•Renewable energy sources improve power efficiency under energy service contracting.•Levelized cost of electricity ...provides optimal capacities and contract duration.•Climatic conditions influence terms of the energy service contract.
Various mechanisms have been developed worldwide to support renewable energy sources. These mechanisms promote greater integration of renewable energy sources into power supply systems. Many support mechanisms can operate only in centralized power systems with well-structured market relations. As far as autonomous power systems are concerned, high expectations are placed on energy service contracting which offers a number of advantages such as instant investment, absence of risks for local authorities, fuel savings and efficient technical solutions.
This paper presents a methodology for installed capacity optimization of autonomous photovoltaic systems under energy service contracting. The proposed methodology is based on the chronological method for calculating power supply systems using multi-year meteorological data sets. The study uses classical mathematical models of components of power supply systems: solar panels, solar inverters and direct current combiner boxes with allowance for operational restrictions. The internal optimization algorithm is described for the installed capacity and standard size of solar inverters and direct current combiner boxes. A hierarchical two-stage model for interaction between energy service company and regional authorities is proposed. The installed capacity of the Tyoply Klyuch photovoltaic system (Far East, Russia) has been optimized. The optimization process took into consideration nine types of solar panels: monocrystalline, polycrystalline and heterojunction panels. The reported value of the installed capacity is 1600 kW under the nine-year long contract. The annual fuel economy constitutes 300 tons, and a profit for the energy service company is US$ 0.428 million at the expiration of the contract. The methodology described in the present paper is universal and can be applied throughout the world.
Changes in the properties of lithium-sulfur cells during cycling were studied by impedance spectroscopy. The electric conductivity of the electrolyte changed during the charging and discharging of ...the lithium-sulfur cells as a result of the dissolution of lithium polysulfides formed in electrochemical reactions. The maximum resistance of the electrolyte and the surface layers on the sulfur and lithium electrodes was achieved in the region of the transition between the low- and high-voltage areas on the charge and discharge curves of the cells. This region corresponded to the highest concentration of lithium polysulfides in the electrolyte. For nearly charged or discharged lithium-sulfur cells, the impedance spectra contained linear segments which could be attributed to diffusion limitations at low frequencies. An analysis of the results of impedance studies suggested that the electrochemical processes in lithium-sulfur cells were controlled by diffusion in the surface layer on the sulfur electrode at high degrees of charge or discharge and by the transport properties of the electrolytic system at moderate degrees of charging.
Electrochemical heat flow calorimeter Mochalov, S. E.; Nurgaliev, A. R.; Antipin, A. V. ...
Russian journal of electrochemistry,
05/2016, Letnik:
52, Številka:
5
Journal Article
Recenzirano
A device designed for research of heat phenomena occurring in chemical power sources (CPS) is described. The device includes two functional blocks: electrochemical and calorimetrical, operating under ...single control, which allows simultaneously performing electrochemical and calorimetric measurements. The calorimetric block is a heat flow calorimeter. The calorimetric chamber design provides the possibility of studying thermal processes in laboratory electrochemical cells and CPS of planar, disk, and prismatic design. The absolute measurement error of the heat flow is ±50 μW at the resolution of 1 μW. The operating temperature range of the calorimetric chamber is 0–90°C. The basis of the electrochemical block is a module of a four–range potentiostat–galvanostat. The maximum polarizing current of the potentiostat is ±200 mA at the maximum voltage on the auxiliary electrode of ±10 V. Multiuser remote access from the user computers over Ethernet to the device is provided for control and treatment of experimental data. Digital deconvolution filters allowing to compensate the response rate of the heat flow meter are used for processing primary data of calorimetric measurements.
The effect of sulfur content in positive electrodes (the surface capacity of sulfur electrodes) on the characteristics (such as the depth of sulfur electrochemical reduction, changes in capacitance ...and Coulomb efficiency during cycle life) of lithium-sulfur cells with electrolytes based on sulfolane was studied. It was shown that the reason for the capacitance decrease of the lithium-sulfur cells at the early stage of its cycle life is the displacement of sulfur of the porous positive electrode from the rear regions into the front ones. It was established that in order to achieve the maximum possible specific energy of the lithium-sulfur batteries with the electrolytes based on sulfolane, the surface capacitance of the positive electrodes should be in the range of 2-3 mA·h/cm2.
To assess the possibility of using solutions of perchlorates of alkali and alkaline earth metals in sulfolane as electrolytes for electrochemical energy storage devices with metal negative ...electrodes, the physicochemical properties of 0.5 M solutions of Me(ClO4) n (Me = Li, Na, K, Mg, and Ca) in sulfolane were simulated by the method of molecular dynamics. The density, viscosity, conductivity, self-diffusion coefficients, and transport numbers are calculated. Satisfactory agreement between the calculated and experimentally measured properties of 0.5 M solutions of LiClO4 and NaClO4 in sulfolane suggests that the calculated values of the physicochemical properties of solutions of K, Mg, and Ca perchlorates are also close to real values. The study of the structure of solvate complexes of salts of alkali and alkaline earth metals with sulfolane by quantum chemical and molecular dynamics modeling showed that the first solvate shell of metal cations consists of sulfolane molecules. Regardless of the nature of the cation, sulfolane is coordinated to the metal cation by only one oxygen atom. Based on the analysis of the calculated values of the physicochemical properties of solutions of metal perchlorates in sulfolane, it can be concluded that they can be used as electrolyte systems of electrochemical energy storage devices with negative electrodes made of alkali and alkaline earth metals.
The effect of lithium polysulfides on the cycling of a lithium electrode and the corrosion rate of lithium cathodic deposits in sulfolane electrolytes is studied. Lithium polysulfides are found to ...affect the shape of polarization curves, the overpotential of electrode processes, and the cycling time. The presence of lithium polysulfides in electrolyte systems increases the cycling time of a lithium electrode and positively affects the quality of lithium cathodic deposits. A suggested reason for the positive effect of lithium polysulfides is the appearance of a surface film on metallic lithium: this film has quite high protective properties but does not inhibit electrochemical processes.
The possibility of determining the charge state of lithium-sulfur batteries using the ANFIS model was estimated. Easily measurable in practice physical quantities were used as input parameters of the ...model. They are the battery voltage, the rate of its change and the number of previous cycles. The analysis of ANFIS models with various parameters (the number and type of membership functions) was carried out. It was shown that ANFIS is a model that makes it possible to estimate the charge state of a lithium-sulfur battery with the accuracy of more than 95%. The proposed type of models can be used in control and monitoring systems, together with digital aggregated twins, for additional training of models based on real data and increasing the accuracy of estimating the charge state of lithium-sulfur batteries.
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