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[en] Highlights: • Control of BES for smoothing and hourly dispatch of a PV farm output is developed. • Optimal control strategy for SOC and size of BES are evaluated using GA. • Effectiveness of the control system has been investigated for the case of Malaysia. • The proposed optimal SOC feedback controller has been found effective. • Payback calculations of BES investment is given to highlight the economic benefits. - Abstract: The effects of intermittent cloud and changes in temperature cause a randomly fluctuated output of a photovoltaic (PV) system. To mitigate the PV system impacts particularly on a weak electricity network, battery energy storage (BES) system is an effective means to smooth out the power fluctuations. Consequently, the net power injected to the electricity grid by PV and BES (PV/BES) systems can be dispatched smoothly such as on an hourly basis. This paper presents an improved control strategy for a grid-connected hybrid PV/BES systems for mitigating PV farm output power fluctuations. A feedback controller for BES state of charge is proposed, where the control parameters are optimized using genetic algorithm (GA). GA-based multi objective optimization utilizes the daily average PV farm output power profile which was obtained from simulation using the historical PV system input data of Malaysia. In this way, the optimal size for the BES is also determined to hourly dispatch a 1.2 MW PV farm. A case study for Malaysia is carried out to evaluate the effectiveness of the proposed control scheme using PSCAD/EMTDC software package. Furthermore, the validation of results of the proposed controller and BES size on the actual PV system output data are also given. Finally, a simple payback calculation is presented to study the economical aspects of the BES investment on the proposed mitigation strategy under Malaysian Feed-in Tariff program
[en] Highlights: ► We carried out coupled thermodynamic, multiphase fluid flow and heat transport analysis. ► Coupled behavior associated with underground lined caverns for CAES was investigated. ► Air leakage could be reduced by controlling the permeability of concrete lining. ► Heat loss during compression would be gained back at subsequent decompression phase. -- Abstract: This paper presents a numerical modeling study of coupled thermodynamic, multiphase fluid flow and heat transport associated with underground compressed air energy storage (CAES) in lined rock caverns. Specifically, we explored the concept of using concrete lined caverns at a relatively shallow depth for which constructing and operation costs may be reduced if air tightness and stability can be assured. Our analysis showed that the key parameter to assure long-term air tightness in such a system was the permeability of both the concrete lining and the surrounding rock. The analysis also indicated that a concrete lining with a permeability of less than 1 × 10−18 m2 would result in an acceptable air leakage rate of less than 1%, with the operation pressure range between 5 and 8 MPa at a depth of 100 m. It was further noted that capillary retention properties and the initial liquid saturation of the lining were very important. Indeed, air leakage could be effectively prevented when the air-entry pressure of the concrete lining is higher than the operation air pressure and when the lining is kept at relatively high moisture content. Our subsequent energy-balance analysis demonstrated that the energy loss for a daily compression and decompression cycle is governed by the air-pressure loss, as well as heat loss by conduction to the concrete liner and surrounding rock. For a sufficiently tight system, i.e., for a concrete permeability of less than 1 × 10−18 m2, heat loss by heat conduction tends to become proportionally more important. However, the energy loss by heat conduction can be minimized by keeping the air-injection temperature of compressed air closer to the ambient temperature of the underground storage cavern. In such a case, almost all the heat loss during compression is gained back during subsequent decompression. Finally, our numerical simulation study showed that CAES in shallow rock caverns is feasible from a leakage and energy efficiency viewpoint. Our numerical approach and energy analysis will next be applied in designing and evaluating the performance of a planned full-scale pilot test of the proposed underground CAES concept.
[en] Here, the energy density and cost of battery systems could be improved by moving to alternative battery chemistries such as Ca-ion. However, in order to switch chemistries many problems need to be solved including the identification of cathode materials with high energy density, and electrolytes that can plate and strip calcium metal. Herein, the feasibility and cycling performance of Ca2+ intercalation into a desodiated layered Na2FePO4F host is described. This is the first demonstration of Ca2+ intercalation into a polyanionic framework, which implies that other polyanionic framework materials may be active for Ca2+ intercalation. Although substantial effort is still needed to identify a high energy density cathode material, this study and others demonstrate the feasibility of Ca2+ intercalation into multiple materials making it more probable that such a cathode material can be found.
[en] Development of fuel cell (FC) and hydrogen metal-hydride storage (MH) technologies continuously demonstrate higher efficiency rates and higher safety, as hydrogen is stored at low pressures of about 2 bar in a bounded state. A combination of a FC/MH system with an electrolyser, powered with a renewable source, allows creation of an almost fully autonomous power system, which could potentially replace a diesel-generator as a back-up power supply. However, the system must be extended with an electro-chemical battery to start-up the FC and compensate the electric load when FC fails to deliver the necessary power. Present paper delivers the results of experimental and theoretical investigation of a hybrid energy system, including a proton exchange membrane (PEM) FC, MH- accumulator and an electro-chemical battery, development methodology for such systems and the modelling of different battery types, using hardware-in-the-loop approach. The economic efficiency of the proposed solution is discussed using an example of power supply of a real town of Batamai in Russia. (paper)
[en] Highlights: • We assessed integration of energy storage systems into hybrid system architectures. • We considered mechanical and electrical energy storage systems. • Potential of different combinations has been analyzed by standardized duty cycles. • Most promising are diesel-driven suburban, regional and shunting operations. • Double-layer capacitors and Lithium-ion batteries have the highest potential. - Abstract: The use of diesel-driven traction is an intrinsic part of the functioning of railway systems and it is expected to continue being so for the foreseeable future. The recent introduction of more restrictive greenhouse gas emission levels and other legislation aiming at the improvement of the environmental performance of railway systems has led to the need of exploring alternatives for cleaner diesel rolling stock. This paper focuses on assessing energy storage systems and the design of hybrid system architectures to determine their potential use in specific diesel-driven rail duty cycles. Hydrostatic accumulators, flywheels, Lithium-ion batteries and double-layer capacitors have been assessed and used to design hybrid system architectures. The potential of the different technology combinations has been analyzed using standardized duty cycles enhanced with gradient profiles related to suburban, regional and shunting operations. The results show that double-layer capacitors and Lithium-ion batteries have the highest potential to be successfully integrated into the system architecture of diesel-driven rail vehicles. Furthermore, the results also suggest that combining these two energy storage technologies into a single hybridisation package is a highly promising design that draws on their strengthens without any significant drawbacks.
[en] Highlights: • Energy storage value increases with tighter carbon dioxide (CO_2) emissions limits. • The marginal value of storage declines as storage penetration increases. • Large-scale deployment of available battery technologies requires cost reductions. • Energy storage increases utilization of the cheapest low-CO_2 resources. • Longer-duration storage increases the share of wind more than solar photovoltaics. - Abstract: Electrical energy storage could play an important role in decarbonizing the electricity sector by offering a new, carbon-free source of operational flexibility, improving the utilization of generation assets, and facilitating the integration of variable renewable energy sources. Yet, the future cost of energy storage technologies is uncertain, and the value that they can bring to the system depends on multiple factors. Moreover, the marginal value of storage diminishes as more energy storage capacity is deployed. To explore the potential value of energy storage in deep decarbonization of the electricity sector, we assess the impact of increasing levels of energy storage capacity on both power system operations and investments in generation capacity using a generation capacity expansion model with detailed unit commitment constraints. In a case study of a system with load and renewable resource characteristics from the U.S. state of Texas, we find that energy storage delivers value by increasing the cost-effective penetration of renewable energy, reducing total investments in nuclear power and gas-fired peaking units, and improving the utilization of all installed capacity. However, we find that the value delivered by energy storage with a 2-hour storage capacity only exceeds current technology costs under strict emissions limits, implying that substantial cost reductions in battery storage are needed to justify large-scale deployment. In contrast, storage resources with a 10-hour storage capacity deliver value consistent with the current cost of pumped hydroelectric storage. In general, while energy storage appears essential to enable decarbonization strategies dependent on very high shares of wind and solar energy, storage is not a requisite if a diverse mix of flexible, low-carbon power sources is employed, including flexible nuclear power.
[en] Renewable energies are asked for more and more worldwide. Even though they cannot generate electricity 8760 h/a year. This can be accomplished by flexible conventional power stations as well as storage systems. Especially the storage systems have to be developed technical wise and especially economic wise. An example of an integrated approach is the methanol production with a coal fired power plant. An overview showing the technical features as well as the strategic opportunities of such kind of approach is given.
[en] Used as low-cost anode in the majority of lithium ion batteries, layered graphite has got critical issues. Owing to its low voltage operation, they reduce electrolyte by stealing lithium from cathode to form an SET (Solid Electrolyte Interphase), and pose fire risk from dendrite based short-circuit likely at times of fast charging or erroneous over-lithiation towards end of discharge. In this talk we are addressing this problems
[en] What existed first, the energy problem or the energy transition? For the clarification of this question the author gives a survey about the actual situation of our energy demand and the means and ways to its satisfaction. The reader learns to know the function of numerous energy transformers, from the wind mill via the automobile motor until the solar cell. The advantages and disadvantages of the different transformers are explained, just so their efficiencies and cost as well as the physical natural laws, which they must obey. A perpetuum mobile doesn't exist, but indeed an almost inexhaustible energy source, the sun, which can meet many thousandfold our demand, if we use it intelligently. Who has read this book can go confidently in each discussion about the energy problem and the energy transition.