Technical and economical evaluation of grid-connected renewable power generation system for a residential urban area
Abstract
In this present study, the feasibility, economic and technical evaluation of a hybrid grid system of solar and wind power for a residual urban area were done in KHAF town located in the eastern part of Iran. The temperature profiles of a 10-year period gathered based on the existed solar and wind condition data. Simulation, economic and technical evaluation of this hybrid system are studied with the aid of Homer software. To reach a proper independent structure from the total net present cost (NPC) and energy cost (COE) viewpoints, thousands cases were studied. Change of factor investing on PV panels together with the amount of sun radiance and change of the investing factor of wind turbine with the consideration of wind velocity and sun radiance on the system layout are studied and discussed. In addition, sensitivity analysis on the load demand of hybrid system and on the renewable energy resource are investigated. As a result, it is found that which variable has the most impact on the obtained results. Based on the economic and technical evaluation, establishing hybrid grid system for a residual urban area perfectly justified and investment return occurs in the fourth year of operation.
Keyword: Hybrid solar-wind grid system; Technical-Economical evaluation; Total net present cost; Finished cost of electricity
Long ago, before the invention of alternative current and manufacturing of large scale steam driven turbines, the required electrical power for various applications such as; heating, lighting, driving force and etc. was generated at the vicinity of the consumption area. As the industrial technology progress rapidly, the growing demand for electric energy caused construction of large-scale thermal power plants at the further distances with regard to energy consumption areas. These power generation units together with high-voltage transmission lines and distribution of low and high voltage lines were supplying the needed energy for consumers across the country. The main advantages of this type of power generation network were the economical features of large scale power generation and power transmission with high-voltage line and facile accessible fossil fuel usage[1].In this structure, the electric power was transmitted through High-voltage transmission network to the medium voltage distribution network and then to the Low voltage distribution network for distribution among the consumers. Currently, developing large-scale thermal power plants causes a rising demands for fossil fuel which result in the depletion in gas and oil reservoirs and the fact that these sources are limited and someday becoming extinct, expressing the need for alternative energy source[2].
As another standpoint, undesirable effects on the natural environment for the future generations including the effects of environmental pollution and the emission of greenhouse gasses which as a result, lead to creation of acid rain and increase of atmosphere temperature and vast changes in climate conditions of the earth[3]. Nevertheless, employing renewable energy sources seem to be a promising and rational solution that can help the mankind to face these side effect and preserved environment. Also the utilizing renewable energy resource such as wind, solar and geothermal due to the indigenous availability [4] helps country without fossil fuels resources to reduce their dependency of such fuels with implement vast renewable energy sources distributed in the environment to meet the electricity needs of different regions [5] and it is promising to the mention that renewable energy taking the leading role in the future of energy industries and by now in some regions of the world, a large percentage of the needed electricity supplied by the help of these energies[6].
The renewable energy sources mostly build to produce required power near consumers’ locations which is justifiable compared to large scale power production away from the energy consumption locations, from economical view point [7]. As a concern of modern society, the reasonable energy source must have the ability to continually provide supply of energy. Reaching a constant and favorable development requires stable energy supply. To provide sustainable energy, dependence on an energy carrier should be reduced and also energy production portfolio should be diversified.
The renewable energy resources in some period of times are not available or weak. Therefore in order to have a continuous supply of energy use of some sort of energy storage system becomes essential. According to the previous finding regarding the advantages and disadvantages between the usage of hydrogen electrolyzer and tank and the batteries for the purpose of energy storage alternative it was reported that batteries are still the most suitable option as energy storage[8, 9].
So accordingly, batteries are still common type of storage apparatus used in renewable systems, the life time of the battery is short in competition with the other system components and have to replace many time during the system life time which consists of a big share in the total cost of the renewable system. Utilizing more than one renewable energy source increase the reliability and reducing the system storage size and consequently reduce the cost of system in long time. Regarding the discussion, electricity production from wind and solar energies as distributed energy resources (DER) are much more proper compared to the development of thermal power plants and the other renewable energy sources from economical point of view [10].
Distributed power generators because of the small-size and production of power with low voltage and low current can be connected to the low-voltage power distribution network and securing the safe, reliable and stable function of the electrical energy for consumers and for the whole power grid network [11]. In the recent years due to the remarkable advancement of manufacturing technology of wind turbines and photovoltaic panels, reduction in the designing and operating costs are justified [12]. An economical, clean and reliable productive power system can be reached, with the right combination of energy resources that the purpose of applying these systems to reduce the amount of costs [11]. In last decades numerous research regarding utilization of renewable energy sources were conducted. The technical and economic aspects of renewable energy and effect of various parameters including location, area and shape on systems were analyzed, some of these studies are presented in the following.
The required load to power a university campus in Turkey with solar energy and the fuel cell system has been calculated by using the HOMER software. The different hybrid systems investigated by consideration of cost of energy (COE), renewable fraction, total net present cost (NPC) and hydrogen production. The obtained results clarify that the grid connected systems appear cost-effective, Although the grid-connected photovoltaic (PV) hybrid system owes the lowest COE and NPC, the grid-connected PV/fuel cell hybrid system with COE, 0.294$/kWh has a bit higher cost than the optimum one [13].
Arnau González et al.[14] Optimized the size of a hybrid grid-connected photovoltaic-wind power systems based on real environmental data for a specific location. The developed method was capable of determine the size that led to the minimum cycle cost on a presumed demand. The proposed optimization model, validated via case study. In addition, an analysis carried out to find the more affecting and sensitive parameters. Based on obtained results, It was concluded that a combined a grid of photovoltaic (PV) – wind power was found to be economically profitable in a considered rural area in Spain in such a way that after 18 years out of 25 years of system estimated life time,the system would pay off.
The effect of key parameters including the location, area and shape, of a considered site for establishing renewable energy harvesting was investigated by Alan Emanuel Duailibe Ribeiro et al.[15]. An integrated analysis was generated and adopted for two case study in two locations in Brazilian. A significant dependency between the amount of harvested power and key parameters was found.
The potential of implemented of wind and solar systems for energy production from brownfield sites using Michigan as the case study investigated by Adelaja et al.[16].The amount of calculated energy obtained considering PV panels and horizontal axis wind turbines. As results, the estimated harvest potential was obtained to be 4320 (MW) of plate capacity for wind and 1535 for solar which is equal to 43 percent of Michigan’s residential electricity consumption and as economical perspective over $15 billion in investment, 17,500 in construction are need to provide.
Ramli et al.[17]performed an analysis on the energy harvesting via hybrid wind-solar energy system by considering unmet electric load and excess electricity in the west coast of Saudi Arabia. The technical and economic analysis carried out with respect to the energy harvesting and finished cost of wind turbine and photovoltaic (PV) in the energy system via MATLAB and HOMER software. The reported results indicated that for a same size PV array and wind turbine more energy produced from PV array than wind turbine generator a in the considered placed and the levelized cost reported as $0.0637/kWh and $0.149/kWh respectively.
Belabes et al.[18] accomplished a technical and economic analysis concerning energy generation from wind for different location in the Algeria. The annual wind speed of locations and the WAsP, AN Bonus 300 kW/33, AN Bonus 1.0 MW/54 and Vestas V80/2 MW programs were used to evaluate the technical analysis with consideration of capacity factors, annual power and energy outputs. Moreover, the present value cost method (PVC) was adopted for economic analysis.
Geographically, Iran is located in West Asia and borders the Caspian Sea, Persian Gulf, and Gulf of Oman.
Iran has very diverse climate (11 climates out of the world’s 13) including arid, semi-arid to subtropical along the Caspian coast and the northern forests but the main part of Iran has an arid climate with high irradiated solar energy and strong winds in some parts which make this country a good candidate for renewable energy harvesting[19].
Qolipour et at.[20]studied the feasibility of the construction of hybrid wind and solar systems for the purpose energy harvesting and hydrogen production in the in the South West of Iran. Technical and economic analysis accomplished with aids of HOMER commercial software and the reported results showed that the produced electricity is equal to 3,153,762 kW h and 31,680 kg of hydrogen per year.
The above Literature reviews leads to the fact the utilization of renewable energy is the cure of the energy problems, pollution, global warning and the future of clean energy industries. Therefore, Technical and Economical investigation for the harvesting of available renewable energy is essential to find out investing on which area is logical and what kind of grid system is suitable for the place. The main aim of the present study is to investigate the potential of establishing solar-wind hybrid power systems for electricity generation from the available solar and wind resources in a residual urban area in KHAF town located in the eastern part of Iran with using Hybrid Optimization Model for Electric Renewable (HOMER) software.
2-Description of the model system and the considered region
Hybrid power production systems can effectively enhance the power consumption factor and the reliability of securing energy. Due to the complementary effect of renewable energy output and the power grid network together, it can reduce the need for energy storage sources which would make up the main costs. This system is about to be implemented in KHAF city located at the Eastern part of Iran with warm and dry weather. This city has the favorable solar and wind power potentials, therefore the values of these potentials with respective energy conversion components are considered as the input variables of the software.
2-1 Configuration of the model system
The system model includes wind turbines, photovoltaic panels, electricity grid, controller and the other auxiliary equipment and grid cables.
Wind turbines over 10kw mostly produce alternative current (AC) and directly connecting to Ac bus [21] which considers to be an advantage. On the other hand, PV unites needs converters to convert the DC to the AC. The AC power output from the wind turbine directly supply the base load and if the electric load to be in excess of a certain load, the excess energy is fed into the grid network. If the wind turbine outlet cannot be responsible for the needed electrical load, it would be compensated and fed from the electricity grid network. The main component of the power distribution system is transformer that connects the AC/DC bus. The system architecture and energy flow for the wind-solar-grid system model is illustrated in Fig.1.
Fig.1. The energy flow diagram of the hybrid solar-wind grid system.
System controller:
The system can be controlled easily as there is only one dispatchable source of electricity that is the power grid system. The net electric load is the difference between the actual electric load and the electric load of the output of renewable energy and when it is negative, it means that the power produced by the renewable energy sources is enough to secure the needed load and therefore the excess of the generated energy could be transferred to the power grid network. In addition, when the net electric load is positive, the only backup power source, grid network, would provide the required electricity. The procedure of the operation of this kind of system is depicted in Fig.2.
Fig.2. The procedure of the operation of the Wind and Solar‘s system models connected to the grid network.
In order to model Hybrid Renewable Energy Systems the HOMER software which is energy modeling software was used. This software is capable to design, simulate analyzed such systems. It’s a conventional worldwide software for investigating either grid-tied or off-grid environments. With help of this software the optimal condition for integrating solar and wind energy sources into hybrid grid systems, economical facilities to mitigate the financial risk and an understanding of the Hybrid Renewable systems operating condition can be found. The HOMER contains a mix of conventional generators, combined heat and power, wind turbines, solar photovoltaic, batteries, fuel cells, hydropower, biomass and other inputs.
In this study, the daily electric load for a residential complex is estimated to be 530 KW per day. Accordingly the electric load for different days and months is generated synthetically by adding a random value to create a reasonable load profile for a year by the HOMER. The load profile for a year at different months is illustrated in Fig.3.
Fig.3. The consumed electric load profile of residential complex.
The climate data related for this region for the period of ten years including the amount of solar radiation, wind speed and the ambient temperature is obtained from the Iran Meteorological Organization. Fig.4 show the average of solar energy resources monthly and Clearness Index for the present study. The clearness index is an input parameter in HOMER which defines as the ratio of the solar radiation hitting Earth’s surface to the solar radiation striking the top of the atmosphere. This parameter is less than unity due to various affecting parameter including the moisture, dust, clouds, or even temperature differences in the lower atmosphere[22].The Graham algorithm adopted in HOMER in order to calculate realistically the solar radiation values for each hour of year. The minimum and maximum values of the data are for December and January, respectively.
Fig.4. The monthly average area density of solar energy and clearness index for the case study.
Fig.5 displays the mean wind speed in different months of the year. The highest values of the mean wind speed is in summer where the energy usage is higher than other seasons in Iran. Also the average values of wind speed in a year approximated to be 4.95 m/s which illustrates favorable conditions for the placement and operation of wind turbines at this region.
Fig.5. The average wind speed of the region.
In addition, the complementary nature of the two energy resources create stable energy supply. These two figures (Fig.4and5) show that the wind and solar energies together can provide a larger amount of energy compared to one energy resource and enhance reliability. This advantage causes reduction in the need for the other energy storage sources such as; batteries which raise the total cost of the system.
3. The information of the system components
A solar cell defines as a semiconductor apparatus which designed for the purpose of turning solar irradiate to electricity. An array of Photovoltaic panels produced DC power inherently and with the help of inverters the produced DC electricity convert to AC. The appropriate solar panel in the present study considered to be photovoltaic panels of Suntech co.(Model STP210-18/Ud) based on evaluation of different photovoltaic panels via HOMER. The technical specification of the chosen photovoltaic panels summarized in Table 1.
Table.1. The technical information of photovoltaic panels[23]
The nominal power of panels is about 210 watt and their efficiencies is 14.3 percent under the standard experimental conditions. The initial amount of investment on panels considered 2 dollar per watt based on the decreasing tendency in the cost of panels. In the present study the cost of maintenance and preservation is not consider due to negligibility[24]. The output energy of photovoltaic panels (kWh) is estimated based on Eq. (1) as given below:
(1)
where is representative of the nominal capacitance of panels (kW), is the total radiation on the panels’ surface area incidence (kWh/m2), Is is equal to 1000 W/m2 and fPV is derating factor due to dust and temperature effect and etc. which is assumed 80% percent for the current study[25].
The most important part of wind energy apparatus design is the selection of appropriate wind turbine. In this study, a wind turbine of model (Furunder FL100) was installed. The details of the wind turbine are shown in table.2 which in that, all costs for the wind turbine were obtained from the 143 vendor.
Table.2. The technical information of wind turbine[26].
Fig.6. The wind turbine power curve.
In the present research the residential complex has a 500 kW branch network from the national power network with the frequency and voltage of 50 Hz, 220 Volts, respectively considered. The electricity company announced low, medium and peak load hours Tariffs for the residential complex at the year 2015 as shown in Table.3. The climate condition data is collected from the I.R. of Iran organization for electric power affairs[27].
Table.3. The price of the power consumption at different intervals and periods[27].
4. Results and discussions
The physical configuration of the system is based on the meteorological and power consumption data, numerous systems were analyzed to achieve an optimal structure which the configuration shown in Figure.1. The simulation results of the Homer software show that, the optimized system includes wind turbines (4 units of 100 kWatt) and electricity network. The optimal system performance is discussed in the following sections and a sensitivity analysis on key parameters to detect changes performed on the results is done.
A summary of the operational performance of wind turbine and some economic results of wind turbine and power grid network are given in table.4. As seen, the wind turbine capacitance factor is fairly low due to the large amount of energy loss. The levelized cost for the wind turbine in dollars per kilowatt-hour is estimated to be 0.0775.
The average monthly share of electricity production from wind turbine and as well as buying electricity from the power grid network is illustrated in Fig.7.It is seen that because of the favorable wind potential of the region, a great proportion of the generated energy is provided by the wind turbine. The wind turbine output during the summer months from July to September is very high and this is a good thing due to the high demand for electricity for cooling during the heating season. In addition, as the national power grid in Iran often reaches its highest peak in summer, it is considered as a kind of peak shaving of the grid.
Table.4. Wind turbine performance specifications of the system.
Fig.7. The share of the produced electrical energy from the wind turbine and grid network.
The reason of high wind speed in summer is that, Khaf is located in a desert and the temperature difference between the night and day causes this phenomenon. This can be seen in Figure.8 that shows the wind turbine power output color profile. The climate condition data is collected from the I.R. of Iran meteorological organization[28].
Fig.8. Color profiles of the annual energy output from wind turbine.
After investigating the technical feasibility for establishing the hybrid power it is necessarily to pursue the economic analysis.it was shown that technically the system is capable of producing electricity but the price of each kilowatt hour must determine to analysis of hybrid power plant outcome.
The US dollar is considered as the currency in this research. The initial investment cost of the system (Including purchasing and cabling) and total net present cost are 440 and -895.3 thousand dollars, respectively. The final cost of electricity is equal to -0.088 dollars per kilowatt hour. Fig.9 depicts the annual cash flow of the system components with the type of cost.
The negative sign values mean the profits from the sale of electricity to the power grid. The initial investment cost, replacement cost and salvage value are all related to wind turbine. The annual and cumulative cash flows are indicated by positive and negative signs for profit and cost respectively which are brought in Table.5 which shows that the project investment return occurs in the fourth year of operation that is economically attractive.
Fig.9. The annual cash flow of the system components with the type of cost.
Table.5. Annual and cumulative cash flows for system.
Fig.10 summarizes the whole system’s flow of energy. Wind turbine generates electricity as much as 741732 kilowatt-hour per year which constitutes 93% percent of the total electricity produced and only 7 % percent of the required electricity would be purchased form the grid network when the speed of wind is low. The amount of 603178 kWh produced electricity per year is sold to the power grid which is the excess of production over load consumption.
Fig.10. Energy flow of the system.
An example of simulation results on July summer hours during four consecutive days with maximum wind speed and minimum wind speed in late January was conducted. In Fig.11, when the output energy of wind turbine excesses the amount of energy demand, electricity will be sold to the power grid network and in Fig.12 the output of turbine for providing the required energy is not sufficient and therefore, electricity would be purchased form the grid network.
Fig.11. Selling electricity to the power grid in summer.
Fig.12. Purchase electricity from the grid in the winter.
Key parameters in this study are the cost of wind turbines and solar panels, along with wind speed and solar radiation. To find the most optimal system/model, the model is simulated by frequently change of the parameters that have control effect on the output.
In this case, it is considered that the cost of wind turbine to be constant and the speed of wind is 4.95 meter per second. The results in Fig.13 show that when the cost of photovoltaic panel is 0.6 times higher than the current cost, a system consisting four wind turbines connected to the gird network is still the optimal system.
Fig.13. The impact of the change of the amount of radiation and cost of photovoltaic panel on the optimal arrangement of system.
The results in Fig.14 show that the optimal system by reduction of wind speed to lower than 3 m/s, is the PV- grid systems that secure the lowest cost of electricity (COE) as the wind turbine (WT) cannot operate because of the low cut-in speed. With the increase of solar radiation, the optimal system is still the one without photovoltaic panels and this indicates that the current cost of photovoltaic panels is high and should be reduced.
Fig. 14. Effect of changes in the amount of solar radiation and wind speed on the optimal system layout.
In Figure.15 the optimal system with lower mean wind speed of 3 meters per second is preferred that involves 13 kilowatt photovoltaic panels, one wind turbine and a 10 kW converter with a power grid network. At this condition (the mean wind speed of 3 meters per second), the cost of wind turbine to be 0.3 times of the current cost, the optimal system includes two units of wind turbine with a power grid.
Fig. 15. The effect of the change of wind speed and the cost of wind turbine on the optimal system layout.
In Fig.16 when the cost of investment of photovoltaic panel is 0.45 times lower than the current cost, then using photovoltaic panels is economical and employing them in the system layout is justifiable. Since the wind potential of the region is favorable for the use of wind turbine even with the considerable reduction cost of the photovoltaic panels, employing wind turbine in the system configuration is recommended.
Fig. 16. Effect of changes in the cost of photovoltaic panel and wind turbine on the optimal system layout.
5. Conclusion
Despite of high potential for renewable energy generation in Iran, this kind of clean energy source has not been significantly studied and used. In the present study, the feasibility, economic and technical evaluation of a Hybrid grid system of solar and wind power for a residual urban area were carried out in KHAF town located in the eastern part of Iran via HOMER software. 640 hybrid systems were simulated with a variety of layouts that only 182 of these systems have the capability to supply electric charge. Among these systems, a system with four wind turbines and power grid system is chosen as an optimal system. Based on the wind potential of the area, it’s convenient to increase the number of wind turbines which result in more profit. The initial investment is 440 thousand dollars and the contribution portion of renewable energies is 84 percent for the case containing four wind turbines and power grid system. The finished cost of electricity is -0/.88 dollars per kilowatt-hour, and the current net cost is -895.3 thousand dollars. The maximum amount electricity sold to the power grid network occurs in July and August as in these months, wind turbines having high capacities of power production due to high average wind speed which would neutralize the effect of the cooling load in summer.
Nomenclature
NPC | Net present cost |
COE | Cost of electricity/energy |
DER | Distributed energy resources |
DC | Direct Current |
AC | Alternative current |
PV | Photovoltaic panel |
fPV | Derating factor due to dust and temperature effect and etc. |
IT | Total radiation on the panels’ surface area incidence (kWh/m2) |
Is | Solar Radiation Intensity (kWh/m2) |
YPV | The nominal capacitance of panels (kW) |
WT | Wind turbine |
6. References
F. E. R. Commission, The Potential Benefits of Distributed Generation and Rate-Related Issues That May Impede Their Expansion: A study pursuant to Section 1817 of the Energy Policy Act of 2005, Washington, DC: US Department of Energy, 2007.
bidabadi-amrolah
Suntech company- photovoltaic panels-< http://www.suntech-power.com>.
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Fuhrlander company- wind turbines-<http://www.fuhrlaender.de/en/>.
RAHBARI
The Iran organization for electric power affairs <http://www.tavanir.org.ir/hadaf/default.asp>.
ERFAN+RAHBARI
[13] I.R. of Iran meteorological organization-<http://www.irimo.ir/eng/index.php>.
mr afzalabadi
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