A power balance simulator to examine business continuity in hospital facilities due to power outages in a disaster

In hospitals, the energy supply is the key to ensuring modern medical care even during power outages due to a disaster. This study qualitatively examined whether the supply-demand balance can be stabilized by the private generator prepared by the hospital building during stand-alone operations under disaster conditions. In the nanogrid of the hospital building, the power quality was examined based on the AC frequency, which characterizes the supply-demand balance. Gas engine generators, emergency diesel generators, photovoltaic panels, and storage batteries were presumed to be the private generators in the hospital building. The output reference values for the emergency diesel and gas engine generators were set using droop control, and the C/D controller enabled synchronized operation. In addition, to keep the AC frequency fluctuation minor, the photovoltaic panels were designed to suppress the output fluctuation using storage batteries. As a result of case studies, the simulator predicts that the frequency fluctuation varies greatly depending on the weather conditions and the fluctuation suppression parameters, even for the same configuration with the same power generation capacity. Therefore, it is preferable to increase the moving average time of the output and reduce the feedback gain of the storage battery to suppress the output fluctuation from the photovoltaics. However, there is a tradeoff between suppressing the output fluctuation and the minimum required storage capacity. Furthermore, since the photovoltaics' output varies with the weather, other private generators' capacity and control parameters significantly impact power quality. The simulator proposed in this study makes it possible to study each hospital's desirable private generator configuration.

Electric Drive for an Agricultural Vehicle

The authors showed the relevance of creating agricultural machines using an electric drive. (Research purpose) The research objective is to develop an experimental prototype vehicle using an electrical schematic diagram of charge and electric drive control. (Materials and methods) The VAZ 111 Oka car was chosen as an experimental vehicle model with an electric drive, since it has a light weight of 645 kilograms, a simple design and a low cost. Mechanical characteristics of the electric motor were calculated and a frequency converter was chosen to control the electric drive. Laboratory bench tests were conducted. (Results and discussion)The authors installed storage batteries to power the electric drive, developed an electrical circuit schematics getting charged from a 220 volt alternating voltage network, and received graphs for the discharge of a 40-storage-battery power supply. (Conclusions) An electrical schematic diagram of charge and electric drive control was developed and implemented on an experimental vehicle model. It was determined that at the electric motor continuous operation with the load current of 1 ampere, the batteries get discharged within 104 minutes; with the current load of 2 amperes, they get discharged within 83 minutes; with 3 amperes – within 65 minutes, and with 5 amperes – within 50 minutes, which is enough to drive around the farm. The authors graphically depicted the dependence of the available capacity level on the voltage, as well as the batteries’ discharge on the time at various load currents. The authors carried out two experimental studies on storage batteries’ charging from alternating voltage with the current of 2 and 3 amperes: in the first case, the charging time was 350 minutes, in the second – 310 minutes. It was found out that when using the developed scheme, the batteries are charged evenly.

Renewable energy sources and storage batteries for electrification of Russian decentralized power supply systems

The use of renewable energy sources (RES) and storage batteries (SB) in decentralized power systems is a cost-effective way to supply power to consumers. In this case, storage batteries are one of the most important system components. The significance of storage batteries is conditioned by a stabilizing effect obtained at generation from RES that are defined by stochastic oscillating functions. However, it is worth noting that storage batteries also improve the cost-effectiveness of such systems by reducing consumption of diesel fuel. This is particularly noticeable at night when load is the least and the use of diesel generators is inefficient. One of the most important points is the determination of potential internal processes of aging and breakdowns that occur in storage batteries during operation. The use of a tested model for categorization of storage batteries according to the operating conditions makes it possible to take account of these factors at the stage of a system design. The paper presents a detailed analysis of decentralized power supply system Verkhnyaya Amga. The focus is made on the cost-effectiveness of a combined use of RES with storage batteries, annual saving of diesel fuel, operating parameters. The research reveals hidden problems that represent various uncertainties that affect greatly the economic and operation parameters of the system.

Service life tests for storage batteries used in islanded power systems with renewable energy sources

We investigated the service life of storage batteries to provide recommendations on the design of energy storage systems used in islanded energy systems based on renewable power sources. The service life of maintenance-free, sealed lead-acid batteries produced by absorbed glass mat (AGM) technology was determined by endurance tests carried out by repeated charge/discharge cycles according to specified load profiles, implemented at a specialized Chroma Test System station. Three battery load profiles were simulated: one for the standard DC charge/discharge mode, and two for the charge/discharge modes from renewable energy sources. To this end, the actual data obtained from monitoring the operating modes of a wind power plant were used. It was found that the battery service life depends on the intensity of stress factors. Among them, the throughput factor has the most pronounced influence on the battery lifespan. To extend the service life of storage batteries, it is proposed to separate the charge/discharge modes in time. For batteries operated on renewable energy profiles, this approach decreases time intervals between full charges and at low battery levels, which increases the battery service life by 14%. A solution to designing an energy storage system for microgrids was proposed, which consists in the use of a combined double-circuit energy storage unit. An experimental prototype of such a unit with a power of 15 kW was developed. The use of a combined energy storage unit in the microgrid system: increases the battery service life by 20–30% compared to analogues; improves the static and dynamic stability of the local energy system with a response time of no more than 50 ms towards power change; allows a fuel replacement level of at least 25%; reduces the electricity cost by 25–30%.

Enhancement of energy transfer efficiency for photovoltaic (PV) systems by cooling the panel surfaces

The thermal coefficient of a solar photovoltaic (PV) panel is a value that is provided with its specification sheet and tells us precisely the drop in panel performance with rising temperature. In desert climates, the PV panel temperatures are known to reach above 70 degrees centigrade. Exploring effective methods of increasing energy transfer efficiency is the issue that attracts researchers nowadays, which also contributes to reducing the cost of using solar photovoltaic (PV) systems with storage batteries. Temperature handling of solar PV modules is one of the techniques that improve the performance of such systems by cooling the bottom surface of the PV panels. This study initially reviews the effective methods of cooling the solar modules to select a proper, cost-effective, and easy to implement one. An active fan-based cooling method is considered in this research to make ventilation underneath the solar module. A portion of the output power at a prespecified high level of battery state-of-charge (SOC) is used to feed the fans. The developed comparator circuit is used to control the power ON/OFF of the fans. A Matlab-based simulation is employed to demonstrate the power rate improvements and that consumed by the fans. The results of simulations show that the presented approach can achieve significant improvements in the efficiency of PV systems that have storage batteries. The proposed method is demonstrated and evaluated for a 1.62 kW PV system. It is found from a simultaneous practical experiment on two identical PV panels of 180 W over a full day that the energy with the cooling system was 823.4 Wh, while that without cooling was 676 Wh. The adopted approach can play a role in enhancing energy sustainability.