Fig. 1 shows the schematic diagram of the proposed PV/fuel cell hybrid system developed using the Homer program. The system consisted of PV modules, a fuel cell generator with an electrolyzer, a hydrogen tank, a compressor, power conditioning units (converters), a DC/AC busbar, a grid, and load models. The main objective was to determine the present aggregate net cost based on Langkawi Island’s data. The simulation has gone through the optimization process and sensitivity analysis to achieve the best hybrid design. The results have been analyzed based on the cost-benefit and environmental impact, which were then compared with the conventional system.
All the costs calculated by the Homer software is based on the United States (US) currency. Since the proposed system is simulated for the Malaysian system, the costs need to convert to Ringgit Malaysia (RM) where for the trade currency of July 2019, US $1 was equivalent to RM 4.12. To analyze the economic effects of the developed system, three main economical parameters were identified: Levelized cost of energy (LCOE), total net present cost (TNPC), and residual cost. These costs were measured to decide the optimum system.
The technical properties of solar panels used in this system are given in Table 1. The size of PV arrays chosen in this study is 500 kW, which can be varied from 100 kW to 500 kW, with an interval of 100 kW. The variation is purposely for economic study analysis to identify the optimum size for the proposed hybrid system. The peak load of the system was set to 414 kW. In the case of surplus PV generation, the energy can be supplied to the electrolyzer which is important for hydrogen production. Each PV module is rated at 200 W with a nominal voltage of 12 V. The total modules for this system are 2500 units that cover the area of 3675.36 m2. The lifetime warranty is about 25 years with the derating factor presumed to be 80%.
Parameters Values Type of cell Polycrystalline silicon No. of cell 72 Maximum power 300.0 W Minimum power 181.3 W Open circuit voltage 33.4 V Short circuit current 8.12 A Module efficiency 13.6% Normal operating cell temperature 47.5 °C
Table 1. Electrical characteristics of PV panel
The performance of PV modules is affected by the temperature as it is less effective when the temperature increases,. The temperature coefficient of these modules is 0.5%/°C, stating that every 1 °C of temperature increment will reduce 0.5% of its power. In this case, the PV modules have a nominal operating temperature of about 47.5 °C, while its efficiency under the standard test condition is 13.7%. The initial capital, replacement, and operational and maintenance (O&M) costs are assumed to be $7000, $6000, and 10 $/year, respectively.
The function of a fuel cell is to transform chemical energy into electrical energy. The main fuels for the conversion process are hydrogen and oxygen gases. The by-product of this reaction is water which is safe to the environment. To represent a complete set of a fuel cell system, several components are included in the Homer simulation, such as the electrolyzer, compressor, and hydrogen tank.
To assess the implementation of the hybrid system, three different capacities of fuel cells were considered: 0, 200 kW, and 400 kW. Their lifetime, efficiency, and minimum load ratio were considered as 15000 h, 64%, and 30%, respectively. Meanwhile, the initial capital, replacement, and O&M costs were $450, $450, and 0.15 $/year, respectively, for a 100-kW fuel cell. The detailed specification of the fuel cell can be referred to Table 2.
Parameters Values Rated power (kW) 2.4 to 10.5 Rated current (A) 135 Voltage (V dc) 17.5 to 77.6 Cell efficiency (%) 54 to 64 Fuel consumption Hydrogen
Table 2. Fuel cell specification
Based on Fig. 1, there are two types of energy conversion involved in the proposed system: Alternating to direct and direct to alternating power. In this case, a 400-kW inverter and a 400-kW rectifier are used. The lifetime of the converters is 15 years. Meanwhile, the efficiency of the inverter and rectifier is 90% and 85%, respectively. There is no O&M cost involved for the converters but their initial capital and replacement costs are considered as $800 and $750, correspondingly.
To validate the effectiveness of the proposed system, comparative studies were performed between the proposed hybrid PV/fuel cell and the current system of SkyCab. For further analysis, the proposed system was also compared with other configurations: PV/battery and PV/battery/fuel cell.
There are three stations for the cable car: The base station, middle station, and top station. In general, the electricity is required to power the machine for the cable car operation, lighting, computers, and control room. Fig. 2 illustrates the average and the deviation of the monthly load profile for Langkawi SkyCab. It can be noticed that the lower load demand occurs in April, June, September, and November because they are not a school holiday season as well as the weather condition. The operation requires the peak demand of 414 kW and it has the base demand of approximately 71.4 kW with a load factor of 0.172.
The solar radiation data are obtained from Malaysia Meteorology Centre. The solar radiation ranges from 4.541 kWh/m2/day to 5.694 kWh/m2/day. The annual average of solar irradiance is estimated to be 4.97 kWh/m2/day. It is noticed that the solar irradiance is higher from February to April, while it is at the lowest in November due to the northeast monsoon. Fig. 3 illustrates the annual solar radiation and clearness index for Langkawi SkyCab.
Figs. 4 and 5 show the electrical diagram for current SkyCab and the proposed hybrid PV/fuel cell system, respectively. In the current system, SkyCab is fully supplied by the grid system and there are two diesel generators for emergency conditions, especially when faults or interruptions occur in the power system. Based on the current market price, 0.55 $/L is considered for diesel. Based on the simulation results, TNPC and LCOE of the system are about $1102129 and 0.138 $/kWh, respectively. In this system, the annual average electricity demand of the AC load is 625463 kWh, where the electricity is fully supplied by the grid. The emissions dissipated by the diesel consist of carbon dioxide (CO2) and nitrogen oxides (NOx) are 96712 kg/year, and 2130 kg/year, respectively. The results indicate that the conventional system had released a lot of hazardous emissions into the atmosphere.
Meanwhile, the proposed system had two types of renewable energy which are PV and a fuel cell system. For the operation of the fuel cell system, hydrogen is required for the reaction thus the hydrogen tank is one part of the system. The optimum size of the components is chosen based on the highest given renewable fraction. This value represents the fraction of energy from the renewable power sources supplied to the load. Based on Table 3, the highest renewable fraction value is 0.746 and the two configurations give the same value. The best size considered is 500-kW PV, a 400-kW fuel cell, and a 400-kW power converter which gives the lowest costs of capital, operating, TNPC, and LCOE. The amounts of CO2 and NOx emitted by the system are 20402 kg/year and 43.3 kg/year, respectively. It shows that the proposed system has produced lower emissions compared with the conventional system.
Renewable fraction 500 500 400 400 400 189467 37359 667043 0.083 0.746 500 500 800 400 400 191267 37704 673255 0.084 0.744 500 500 1200 400 400 193067 37737 675469 0.084 0.744 500 500 400 800 400 197467 37565 677674 0.085 0.746 500 500 1600 400 400 194867 37804 678124 0.085 0.743
Table 3. Size of grid-connected PV/fuel cell system proposed by Homer
The results show that the total power generated by the PV, fuel cell, and grid systems is 728814 kWh/year, 12283 kWh/year, and 251926 kWh/year, respectively. Meanwhile, the total power consumption of the load and that of the electrolyzer are 625463 kWh/year and 294223 kWh/year, correspondingly. In this regard, the surplus power is about 73337 kWh/year and there is no capacity shortage occurred in this system. To get some profit, this surplus power can be traded back to electric utility companies but restricted to the terms and conditions.
The above findings demonstrate that the proposed hybrid system is more efficient for SkyCab as it reduces both the costs and the environmental impact as summarized in Table 4.
Cost/pollutant Current SkyCab system Proposed hybrid PV/fuel cell Percent of reduction (%) TNPC ($) 1102129 667043 39.48 LCOE ($) 0.138 0.083 39.85 CO2 (kg/year) 96712 20402 78.90 NOx (kg/year) 2130 433 97.96
Table 4. Comparison of costs and emissions for current and proposed systems
Table 5 shows the comparative costs of the three configurations. The results state that the proposed configuration obtained the lowest costs compared with the others. In contrast, the grid-connected PV/fuel cell/battery system and grid-connected PV/battery system required high initial capitals due to the expensive price of the batteries. Meanwhile, Table 6 shows the pollutants emitted by these three systems. The PV/fuel cell produced the lowest CO2 emission while producing the least sulfur dioxide (SO2) and NOx. Thus, it can be highlighted that the proposed PV/fuel cell is the most environmentally friendly option of the three configurations. Although the PV/battery and PV/fuel cell/battery systems are capable of satisfying the load, they are not suggested for the SkyCab, because the costs of these systems are higher than the proposed system as stated in Table 7.
System Initial capital cost ($) Replacement cost ($) O&M cost ($) TNPC ($) Grid-connected PV/fuel cell 189467 60996 431161 667043 Grid-connected PV/battery 226017 133676 377685 697185 Grid-connected PV/fuel cell/battery 371817 183748 387911 893600
Table 5. Costs comparison
System model Emission (kg/year) CO2 SO2 NOx Grid-connected PV/fuel cell 20402 88.5 43.3 Grid-connected PV/battery 55163 239.0 117 Grid-connected PV/fuel cell/battery 25708 111 54.5
Table 6. Emission reading comparison
Hybrid system TNPC ($) LCOE ($/kWh) Renewable fraction PV/fuel cell 667043 0.083 0.746 PV/battery 697185 0.087 0.763 PV/fuel cell/battery 893600 0.112 0.763
Table 7. TNPC, LCOE, and renewable fraction for each system
Based on the site investigation, the PV modules are strategic to be installed at the roof of the north and south platforms. The total number of solar panels to be installed at the suggested place is 2500 modules with a total area of 3675.36 m2. From the simulation result, the simple payback of the implemented system is around 3.98 years while the discounted payback is 4.69 years. In this analysis, the discounted payback is taken into account as it reflects the currency fluctuation in the inflation rate which directly affects the real interest rate. The return of investment is about 23.2% per year for around 4 years of the payback excluding the first year, which is the year of initial investment, while the internal rate of return is 24.4% per year. After the 5th year of returning on the investment, the system starts to gain the profit from the power generated. The proposed hybrid system shows good economic performance which can be the attraction point to the investor. Table 8 summarizes the economic performance for changing the current generation system to the hybrid system.
Metric Value Present worth ($) 372373 Annual worth ($/year) 29130 Return on investment (%) 23.2 Internal rate of return (%) 24.4 Simple payback (year) 3.98 Discounted payback (year) 4.69
Table 8. Economic performance for changing current generation system to the hybrid system
Future Hybrid of Photovoltaic and Fuel Cell for Langkawi SkyCab
- Received Date: 2019-07-26
- Rev Recd Date: 2019-08-19
- Publish Date: 2019-12-01
Abstract: Langkawi SkyCab has the highest energy demand in Langkawi Island and the demand keeps increasing year by year. This study proposed alternatives energy of a hybrid photovoltaic (PV) and fuel cell system for the SkyCab’s operation. The best sizing and configurations were chosen based on Homer simulation software. A comparative study was done between a conventional system and other hybrid combinations. The results revealed that the proposed system had reduced the cost as well as CO2 emission almost by 39% and 79%, respectively. The hybrid PV and fuel cell system is aligned with the Malaysian government’s goals of reducing carbon emissions 40% by the year 2030.
|Citation:||Siti Maherah bt Hussin, Zainal Salam, Norzanah Rosmin, Md Pauzi Abdullah, Dalila Mat Said, Madihah binti Md Rasid. Future Hybrid of Photovoltaic and Fuel Cell for Langkawi SkyCab[J]. Journal of Electronic Science and Technology, 2019, 17(4): 348-356. doi: 10.1016/j.jnlest.2020.100016|