The proposed system considers the reliability of the supply stream to be of utmost concern, i.e., the community has constant access to electricity. Li-ion batteries and Power-to-Hydrogen-to-Power (P2H2P) systems were regarded as energy storage systems that not only provided power in the absence of PV and but also assisted in overcoming the weather-oriented PV output variability and uncertainties.
The objective functions of the study are to minimize the levelized COE and ECE while maximizing the RE penetration by meeting the technical and financial constraints. Hence, several system configurations/designs were explored, analyzed, and compared using performance indicators – COE and ECE. The schematic diagram of the proposed system configuration has been outlined in Fig 1. A brief depiction of the site selection and associated technology measures have been discussed, as follows.
A. Location
The remote location considered for system design study is in Pirozali, Gazipur, near Dhaka, Bangladesh. It covers 31 square kilometres and has a population of 40 thousand people (approximately). Fig. 2 shows the site area. It includes ten villages & roughly 11,378 households. [16]. The types of electricity customers include general residential, a few institutional & commercial. The climate in this region is temperate, with an average annual temperature of 35°C. For electricity access, currently, the area is entirely reliant on the national grid, which often faces load shedding related reliability and power quality issues. With so many small to medium-sized industries in the area, the electricity demand is always present and predicted to increase in future.
B. Load Estimation
Extensive background studies on remote area livelihood lead to the load modelling for the community. Each general household has been considered to have five lights, four fans, and one of each of the following: TV, refrigerator, computer, oven and air conditioner. In addition, relevant commercial load profiles were considered. The seasonal variation of electricity demand considered the variations in summer, rainy season, and winter. It has been found that the annual peak occurs during August, which amounted to be 402.23 kW. The yearly average load is around 331.18 kW, with a load factor of 0.82. In the load model, an amount of 408 kW of peak load has been assigned based on a daily load fluctuation of 1%. Fig. 3 showcases the annual (a) and hourly (b) average daily load profile.
C. Load Estimation
Extensive background studies on remote area livelihood lead to the load modelling for the community. Each general household has been considered to have five lights, four fans, and one of each of the following: TV, refrigerator, computer, oven and air conditioner. In addition, relevant commercial load profiles were considered. The seasonal variation of electricity demand considered the variations in summer, rainy season, and winter. It has been found that the annual peak occurs during August, which amounted to be 402.23 kW. The yearly average load is around 331.18 kW, with a load factor of 0.82. In the load model, an amount of 408 kW of peak load has been assigned based on a daily load fluctuation of 1%. Fig. 3 showcases the annual (a) and hourly (b) average daily load profile.
D. Solar Irradiance Profile
The data for the global horizontal irradiance (GHI) and the sky clearness index (SCI) were obtained from NASA's Atmospheric Science Data Centre [17]. For the selected site, the yearly average solar irradiation is about 4.64 kWh/m2/day. Solar irradiance reaches as high as 5.86 kWh/m2/day (average) in April, the sunniest month of the year, while it is only approximately 3.82 kWh/m2/day (average) in September. The average clearness index is 0.522. The optimum title angle for PV arrays has been decided to be 25 degrees. Fig. 4 shows the yearly average monthly solar irradiance.
E. Diesel Generator(DG)
A generic diesel generator model has been employed in the design process. The generator's capacity was kept within the range of 790 kW to 1000 kW for conducting the system optimization study. It is expected that the generators would run at a 0.8 power factor on average. The generator's minimum runtime and minimum load ratio were chosen as 30 minutes and 20%, respectively.
F. Electrolyzer
The electrolyzer, hydrogen storage, and fuel cell are the three major components of the P2H2P systems. It has been considered in this study to generate Hydrogen from the excess electricity present in the system. For such, the PEM electrolyzer has been chosen. The PEM electrolyzer has maturity and appropriateness for acceptable efficiency at partial and complete load and quick response to input/output power fluctuations [12]. The electrolysis process can be expressed according to Eq. 1.
Anode reaction : 2H2O = 4H+ + 4e- + O2
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(1)
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Cathode reaction: 4H+ + 4e- = 2H2
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G. Hydrogen Tank
For long-term storage, Hydrogen storage systems have an economic and technical advantage over batteries. Of all chemical fuels, Hydrogen has the highest heating value per mass. The physical-based compressed gas technology in durable tanks has been employed in this study. According to the literature, this technique is the most mature and cost-effective hydrogen storage technology and is appropriate for the scale and purpose of the scenarios [18].
H. Fuel Cell (FC)
A fuel cell is an electrochemical engine that uses oxidation/reduction reactions to generate energy. An electrolyte membrane is placed between two catalyst-coated electrodes of a fuel cell (anode and cathode). Hydrogen and Oxygen are mixed to produce energy in fuel cells, essentially the reverse of electrolysis. Hydrogen gas oxidizes in the anode region, releasing electrons and producing H+ ions. Equation (2) explains the working principle of fuel cells:
Anode : 4H+ + 4e⁻ = 2H2
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(2)
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Cathode: 2H2O → O2 +4H+ + 4e-
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Overall : 2H2O + H⁻ + 4e⁻ → 2H2 + O2 + 4H⁺ + 4e⁻
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I. Batteries
The fast charging and discharging capabilities of battery energy storage systems significantly increase the flexibility of power grids. In this study, fast frequency-responsive (FFR) battery storage systems comprised of Li-ion technology has been employed - a string of 3 Li-ion batteries to create an 11.1 V DC bus. The FFR batteries help systems deal with transitory power quality challenges brought on by the changing PV power output characteristic. FFR Li-ion batteries are now widely used for their extended cycle life and fast-charging characteristics [14].
J. Converter
The converter consists of both the inverter and rectifier technologies. Solar PV arrays generate DC power, which must be transformed into AC power using inverters. In this study, a converter with a round-trip efficiency of 90% has been considered.