Oman like other countries has some remote communities that are not connected to the main grid system but are supplied mainly using diesel generators through islanded modes. Hasik is a residential area located in the Wilayat of Saadha in Dhofar Governorate in the Sultanate of Oman, is an example of such remote communities. Providing reliable, cost-effective electrical power to such communities which located far from the main networks, with sparsely populated is very expensive, and requires building infrastructures, such as towers and connecting electric lines for long distances, as well as the difficult geographic areas, makes installation, and supply of electricity through the grid is financially unviable or practically infeasible. In this case, resorting to diesel generators only to avoid connecting rural areas to the main network is very common, yet it is still costly due to diesel fuel cost and its transportation and storage. One solution to supply such areas with electrical energy is islanded power generation system that uses available renewable energy resources (RERs) and different power generation units to form what is so-called a hybrid system (HS).
The hybrid system is a combination of two or more power sources, such as solar-diesel system or solar-wind-diesel-battery system [1–3]. Hybrid system has many benefits as reliance on a single system could result in system oversizing, thus increasing the total capital investment. On the other hand, dependence on renewable energy resources lacks reliability as RERs are affected by weather conditions of either wind speed fluctuation in case of the wind turbine or solar radiation fluctuations in case of the solar system [4]. Hybrid systems of RER and diesel generators are applicable for rural areas which are supplied mainly by diesel generators. Furthermore, the research on this field is also driven by the fact of fossil fuel reserves depletion and its environmental effects which can be mitigated by the usage of eco-friendly RER. With the presence of various generating units in the HS as well as energy storage units, it is necessary to evaluate the economic feasibility of such a system. The options of the HS can be limited as hybrid power resources are affected by many factors including site topography, RER availability, energy storage cost, and load demand [5].
Different hybrid systems are discussed in the literature including different combinations of PV system, wind turbines, storage, and diesel generators. For instance, reference [5] concluded that, among three different combinations of hybrid systems, the most economical HS is PV-biodiesel generator-battery system. The renewable energy fraction of the proposed system is 91% and the cost of energy (CoE) is US$0.23/kWh. In reference [6] various options of hybrid systems were discussed including biomass, PV, diesel generator, and a battery system for off-grid application. For 19 kW peak load, the biomass-battery hybrid system was found optimal, but it depends on the biomass cost as the optimality moves to PV-biomass-battery hybrid system while biomass cost increases. Different peak loads were analyzed in [6], it was found that the optimal hybrid system is affected by various factors such as load factor, peak load, and cost of RE resources. Moreover, this study illustrated that for a peak load of 19kW, the off-grid hybrid system is still the optimum choice for a village that is 6.53 km away from the grid. However, this breakeven distance depends on the village load. A techno-economic study carried out in [7] for a hybrid system to supply a peak load of 17.08 kW. It concluded that PV- biomass- battery hybrid system is optimal solution with CoE of US$0.031/kWh which is almost half the CoE from the grid without HS. Reference [8] presented the results obtained from the use of the hybrid system in Sohag, Egypt, using HOMER Pro software, in addition to the simulation program (NEPALN). Furthermore, it was managed using C + + based on an online optimizer, for a network consisting of 48 busbars with a peak consumption of 6154 kW and 3271 kVar. The proposed hybrid system consists of diesel generators, PV, wind turbines, and electric grid. Different scenarios were analyzed to reach the lowest CoE and minimum net present cost (NPC), considering reduced carbon emissions, and reduce energy losses. The optimal combination was 2000 kW PV, 35 wind turbines of 100 kW each, and 700 kW diesel generator, in the presence of the electric grid. The cost of energy (CoE) was 0.117 US$/kWh. Moreover, the HS led to a 57% power losses reduction in the network. In reference [9] two types of algorithms were used to reach the optimal design for a hybrid system consisting of wind turbines, PV, and a battery storage system for a system connected to the electrical grid. The first algorithm was used to determine the optimal sizing of renewable energy generators, while the second algorithm was used to determine the optimal capacity of the battery storage system in order to reach the lowest cost and highest reliability. In the second algorithm, 1000 different combination possibilities of the hybrid system were selected, and the capacity was determined for each option of the hybrid mix. The optimal solution, which takes into account the highest reliability at the lowest cost, was selected to be a combination of 57 MW PV, 187 MW wind turbines, and 63 MWh battery storage system. The CoE for this combination was estimated to be 0.1873 $/kWh.
Reference [10] used HOMER to study the feasibility of hybrid system including Wind, PV, and battery system for a residential and agricultural peak load of 30.5 kW. It was found that PV, Wind, and battery system are the most economical configuration with CoE of 0.288 $/kWh. Furthermore, MATLAB/Simulink was used for further technical analysis to maintain power balance. A techno-economic feasibility study was demonstrated in [11] for an off-grid hybrid power system that includes solar, wind, and biomass. The system consists of 78.62 kW peak primary load and 40 kW peak deferrable load. Using HOMER, a combination of wind, PV, biomass, and battery were found to be feasible configurations of the HS with a CoE of $0.201/kWh. A 50MW wind, PV, and biomass grid-tied hybrid system was proposed in [12] for an area of 73.6MW peak. As the system was proposed for an on-grid application, the surplus power was assumed to be sold with the same CoE of 0.0574 $/kWh. Furthermore, the proposed system has contributed to emission reduction as the renewable penetration reached 87.7%. Reference [13] studied the economic and technical use of PV, wind, fuel cells, electrolyzer, and hydrogen tanks for a load of 2MW. Since, the study was intended for an off-grid application, hydrogen storage and electrolysis are proposed to balance the energy. Using HOMER optimization, the system levelized CoE reached 0.80 $/kWh. Moreover, the emissions were very low comparing to the previous mentioned systems; for an instance, carbon dioxide emission did not exceed 13 kg/year. The potential use of wind, PV, and battery HS to supply a peak load of 125kW was studied in reference [14]. The best combination was optimized using both HOMER and MATLAB, taking into consideration the unmet load and excess electricity. Moreover, it observed that PV has higher efficiency at this location than other resources, however, the inclusion of wind and battery -as an optimal configuration- had an important addition to meet load demand at night hours. The CoE for this system was $0.329/kWh. Table 1 summarizes different hybrid systems with their cost of energy found in some literature.
Table 1
Hybrid Systems summary in the literature reviews
Reference | Peak Load | Software | Hybrid System | Location | Renewable Energy Factor | COE (US$/kWh) |
[5] | 2.2kw | HOMER | PV, biodiesel generator, battery | Perumal Kovilpathy, Coimbatore, India | 91% | 0.23 |
[6] | 19 kW 25kW 41kW | HOMER | PV, biomass-battery | Jhawani, Tezpur, India | 100% | 0.119 0.116 0.100 |
[7] | 17.08 kWh | HOMER | PV, biomass-battery | Karor Lal Eason, Layyah, Pakistan. | 100% | 0.031 |
[8] | 6154 kw | HOMER, NEPALN | diesel generators, PV, wind | Sohag, Egypt, | - | 0.117 |
[9] | 100 MW | MATLAB | wind turbines, PV, and a battery storage system, Grid | Dammam, Saudi Arabia | - | 0.1873 |
[10] | 30.5 kW | HOMER, MATLAB | PV, Wind, battery system | Yamunanagar, Haryana, India | 100% | 0.288 |
[11] | 118.62 kW | HOMER | Wind, PV, biomass, battery | Leopard Beach village, West China, China | 100% | 0.201 |
[12] | 73.6MW | HOMER | Wind, PV, biomass | Kallar Kahar, Punjab province, Pakistan | 87.7%. | 0.0574 |
[13] | 2MW | HOMER | PV, wind, fuel cells, electrolyzer, hydrogen tanks | Catania city, Sicily Island, Italy | 100% | 0.80 |
[14] | 125kW | HOMER, MATLAB | PV, Wind, battery | Yanbu Industrial City, Saudi Arabia | 100% | 0.149 |
The objective of this paper is to determine the optimum size of an isolated PV diesel system to provide the energy requirements in the Hasik area which is a remote site located in the southern part of Oman. National Renewable Energy Laboratory (NREL)’s, HOMER Pro version 3.14.5 was used to perform the feasibility study [15]. The software performs economic analysis and ranks the systems according to their net present cost. It needs information about wind and solar resources, control methods, energy storage medium and economic constraints. The paper is organized as follow: section 2 talks about the existing system, section 3 presents the modeling of the proposed system, and section 4 discusses how to build the system using Helioscope. Section 5 presents the discussion of results, and section 6 concludes the paper.