Feasibility and Optimization of Standalone PV-Biogas Hybrid Distributed Renewable System for Rural Electrification: A Case Study of a Cholistan Community

Now-a-days, electricity has become the most significant part of human life. For this purpose, renewable energy sources as the emergent sources are introduced in the system. In Pakistan, in spite of having abundant renewable sources and favorable climate conditions, there are some remote areas where the extension of national grid is still absent. In this research paper, one of the remote area of Pakistan, Chak 6-DRB, a village of Cholistan, is considered for the hybrid renewable sources. This research has been implemented on HOMER (Hybrid Optimization Model for Electric and Renewable) software, in which two renewable sources; solar and anaerobic biogas have been implemented in terms of COE (Cost of Energy), NPC (Net Present Cost), costs of different equipment used and then find an optimal size and costs of the system. This HDRP (Hybrid Distributed Renewable Power) system contains anaerobic biogas, and solar system which yield most accurate and inexpensive results and are quite feasible for this remote area. This standalone generation and distribution model is also analyzed through HOMER including sensitivity parameters. In future, this role model of proposed hybrid renewable system would be very effective and helpful for other remote areas of the country for implementation.


INTRODUCTION
reason of this state of energy sector is that, we had totally relied on non-renewable energy resources in past two decades in spite of world was and still moving towards renewable sources of energy. The panacea of this situation is only hidden in pursuing the renewable resources at national level.
These types of researches of standalone hybrid renewable system can be executed by implementing self-sustained systems under the current power sectors of the countries around the world. A small sized staff could be hired from these remote areas, after technical training they can be employed for operation and management of these systems. Same like in Pakistan, the implementation of this research for rural areas would not only be economical but also be beneficial as clean and safe energy for the residents. The AEDB (Alternative Energy Development Board) of Pakistan which is working under Ministry of Energy Division, can come forward for implementation, facilitation, and promotion of standalone hybrid renewable systems for rural development.

METHODOLOGY
This paper primarily focuses on optimization of hybrid system containing Solar and biogas energy for the proposed village. This research is simulated on HOMER Legacy v2.68 beta software for optimization of the system.

Load Profile Assessment of the Village
The village comprises more than of 80 houses with some shops and one school, each house consists of 5-7 members. The electric load survey was conducted by visiting the area and collecting the data from various types of consumers. Unlike urban areas, the houses are distant from one another and inhabitants of the area uses diesel generators for household loads and operation of tubewells for agriculture purposes. The primary household load is included with light bulbs, fans and other household appliances. While the deferrable load is included with timely requirement of the load like water pumps and small sized motor appliances etc. The average primary load of each house is considered 2.5 (kWh/d) including their domestic (fans, bulbs, and various household appliances) and agriculture (tube-well pumps) utilization. The primary load demand of the village is 240 kWh/d with peak of 20 kW and the deferrable load is 34 kWh/d with peak of 3.5kW. The primary and deferrable load profile of the village is given in Figs. 1-2 respectively.

Solar Energy Sources
The global horizontal irradiance has been calculated by

Biomass Sources
The cow manure is widely available in this village of Cholistan and has abundant supply to meet the major portion of energy requirements. At least each house has 1-2 cattle (Cow) for their dairy purposes. The average dung from a cow is 20 kg/day which produces one cubic meter of biogas that yields of 2 kW electricity per day [12]. Thus if we take at least 80 cow's manure, then yields 80 cubic meter of biogas it will be able to produce almost 160kW. So the availability of manure is little bit more than the manure required for biogas generation. Moreover, the available manure is ample and meets the requirements of where kW is the rated output power of the generator,mis the biogas consumption rate, and H is the lower heating value of biogas.
Efficiency Curve: The efficicency of the biogas generator is presented in Fig. 5, which is taken from HOMER simulation, shows the direct relation between efficiency vs. output (%).

Battery
The Surette 6CS25P battery has been selected from HOMER. The life time of these batteries is 9645 kWh (6.94 kWh), nominal capacity is 1150 Ah, and nominal voltage is 6V. The number of the batteries is selected according to desired amount energy which should be stored at a time. The per unit battery price is US$ 1179 [14]. In Fig. 6, the cost curve of the battery is clearly viewed.

Converter
Two

HYBRID SYSTEM MODELING
The system is designed to meet energy requirements; the area has plenty of solar radiations and biomass resources

HOMER INPUT SUMMARY
The costs comprising capital costs, replacement costs, O&M (Operation & Maintainance) costs of each equipmemt, which are contributed in HOMER as inputs are shown in Table 1.
The cost of Solar PV panels are included with installation price and other equipments like cables, junction boxes and stands [16].
The price of biogas generator has been included with prices of digester, biogas balloons, and other auxiliaries [17].

SIMULATION RESULTS AND DISCUSSION
The two most optimized systems were taken from the feasible combinations of HOMER simulation. These systems are considered as most effective and optimized in terms of COE and NPC.

Most Optimized Hybrid System
The most optimized system is the one which gives maximum feasible COE and has been selected with following component's rating as stated in Table 2.

Second Most Optimized Hybrid System
The second most optimized system has been selected with following component's ratings as stated in  kW/year which is 35% of total installed capacity of hybrid system as shown in Table 6.
The energy consumption of both primary and deferrable loads has been elaborated with their percentage share described in Table 7.

Comparison of Different COEs
The comparison of three systems' COEs among most optimized, second most optimized and fixed generation cost diesel generator has been specified in Table 8.
It can be seen that COEs of the most and second most optimized system are much less than that of fixed generation cost of diesel generator taken from HOMER.
Conclusively, it can be said that both optimized hybrid systems are utmost feasible for the proposed remote area as compared to electricity generated from fossil fuels.

CONCLUSION
In this paper, the optimization results of hybrid PV/Biogas system is briefly elaborated by using HOMER simulation.
In remote areas, where the electricity is out of reach, a standalone hybrid renewable system can be installed. The COE and NPC of optimized hybrid system is compared with grid electricity which is very economical and environment friendly for rural areas. Two most optimized systems are considered best for the selected community which can be installed. The proposed optimized hybrid system offers COE US$ 0.128/ kWh and NPC US$ 164,134.
The optimized COE is 30% less than that of energy produced from fixed generation cost of diesel generator.
Although the optimal conditions simulated by software sometimes cannot fulfill the entire requirements, so the second most optimized case can be considered as the best. This type of proposed standalone hybrid system can be a role model for other remote areas of Pakistan where the grid electricity is difficult to extend and it may also be implemented at large level to serve the huge demand of electricity for massive communities.

ACKNOWLEGDEMENT
Authors are thankful to the Department of Electrical