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olar systems are gaining traction worldwide as alternative energy options. This is because they are environmentally friendly and a renewable source of energy.

This project is tasked in designing a 25kw solar system using HOMER. We are also required to provide a comprehensive description of the system; labeling components, their characteristics (electrical) cost, reasons for choosing the components and the parameters used while factoring them on.

This paper aims to study the feasibility of an independent (standalone) solar system in providing electrical energy needs for a setup of a 25kw load. The study will apply HOMER software to design a complete photovoltaic system with the requisite components. It is aimed that the net cost of this system in comparison with cost benefits will be established. HOMER is an effective software design suite (tool) for a photovoltaic system as it offers a comprehensive library of solar and energy system components and their characteristics.

INTRODUCTION
Renewable energy system and advantages/limitation.

Electrical energy needs have exponentially increased over the recent two centuries, this has also raised the global awareness of the adverse effects of conventional energy generation methods like hydro-electric, thermal, geothermal and nuclear. It is therefore not surprising that the world is moving towards renewable energy sources as an alternative. There is also the fact that main grid electricity is often not extensive; covering only renewable urban areas and frequently inaccessible in the rural or far-flung areas. The unavailability of grid-energy in such areas is often due to the high cost of connections coupled with the profits to be accrued hence, limiting coverage. This lack of coverage in remote locations gives an excellent opportunity in applying renewable energy to mitigate accessibility challenges in meeting the energy needs of the resident communities. Although a major drawback of the renewable source is their intermittent unreliable nature, the pros far outweigh the cons environmentally. The above-mentioned sources of renewable energy is a standalone (purely solar) PV (photovoltaic system); which employs a solar array with photovoltaic solar panels, inverters, battery banks, and solar charge controllers. The PV solar panels essentially convert the sun’s ultraviolet rays into direct-current electrical current. The amount of current produced is dependent on the size/power rating of the solar panel in watts.

The current is fed to a solar charge controller which employs pulse width modulation to limit and control (at an optimum-tolerable level) electric current fed to a battery to charge it. The battery bank stores energy when charging and discharges to an inverter with a certain wattage (depending on a system needs).

Various factors need to be considered in designing a standalone PV system. It has been stated that renewable energy is intermittent at best and fluctuating most of the time. Solar is no exception and is available during the daytime and unavailable during rainy/cloudy/night periods. It is therefore essential that a designer factors the amount of sunshine available at different times.

Another factor in choosing system components and design orientation is the varying direction and orientation of the sun. This will determine the type, number, and orientation of the solar panels.

The load (electrical) requirement for the system will depend on whether the establishment to be powered is domestic or commercial with commercial setups employing a greater load. Considering the design is for a 25kw commercial property, we will choose the solar panels, battery, and the inverter accordingly.

HOMER

To aid us in this design challenge, we will use HOMER (hybrid optimization model for electric renewable) (4) developed by Dr. Lilienthal. It is a micro-power optimization tool that employs a comprehensive suite of tools and an extensive library of renewable energy system components to ease the task of designing accurate systems Homer will optimize the system and also perfume a sensitivity analysis (HOMER Energy, 2018). HOMER will also perform an energy balance computation based on sizes and numbers of components. A sorted list displaying the different available configurations and based on total net present cost will thus be afforded (Ian, 2004).

The cost calculation is based on pre-factored and software build in variations of costs parameters for instance capital, operation maintenance and replacement of the components. The sensitivity analysis will query and let the varying factors in the system and the level of affectedness of the components while varying them. The simulation results will be displayed in graphs and tables.

ADVANTAGES AND DISADVANTAGES OF A STAND-ALONE.
Advantages

Pre-fabricated and pre-designed components hence enable easier/faster installation
Provides energy in remote locations where High voltage grid connection is uneconomical
Environmentally friendly, it reduces emissions from conventional and environmentally unconscious sources.
Lower costs over the term (there are no recurrent costs
They are less complex, the user may operate it and perform easy installation and maintenance tasks. The tasks can be performed with minimal injury risk

CONS

Intermittent and fluctuating therefore unreliable
Lower power output compared the conventional source. This means the load that can be supported is minimal
Depend on weather conditions
Prone to failure of components especially battery which have a limited operation life-cycle, inverter also frequently fail.

THEORY

In a PV system, semiconductor material absorbs U-V light/solar radiation photons which are converted to a current (DC) through the movement of semiconductor electrons. A solar module is formed by adding up solar cells. Modules are combined to form an array: Solar resources refers to the total solar the density index supposes the amount of abstraction of the sun rays before it reaches the earth.

Stand-alone energy systems consist of one independent type of energy sources like purely HEP (hydroelectric grid power) thermal, wind while hybrid system employs a combination of two or more. A hybrid system is more effective but a standalone system is cheaper and easier to install and operate.

RELATED WORK

Most other works use a more effective hybrid solution combining solar/PV and diesel generator or wind system. This solution is optimized using HOMER.

METHODOLOGY

As proposed, HOMER will be used to design a 25kw/day standalone commercial PV system. As a snapshot of the methodology to be used, it is imperative to note that the methodology will mainly focus on describing system inputs and calculation that will be used in HOMER simulation. These are the technical specifications of the solar panels, inverters, batteries, and the weather data for the chosen study location, the solar radiation density and average temperature of the location of interest.

To clarify farther, the method to be used in the HOMER PV system will focus on three major areas;

HOMER Simulation
HOMER Optimization.
HOMER Sensitivity Analysis.

Input Specification.
Electrical Load

The project required a design for a constant load of 25kw/day as per the requirements.

Solar Radiation.

The global solar radiation average on the earth surface and the specification hourly per annum as a pre-factor for the design was required. Khartoum, Sudan was chosen as the study location (15Degrees 31’N latitude and 32Degrees 35’E) longitude. Data pertaining to an hourly radiation was obtained from the NASA website, surface meteorology and solar energy. Based on our source the average radiation from the sun daily was 6.31(Km/m2/d) for a horizontal surface in the said location.

Process

The below screenshots show actions took on HOMER online version

 

 

 

STRUCTURE OF THE PROPOSED DESIGN

For the case study, commercial polycrystalline silicon PV cell we selected at the optimal cost for required design. Besides PV cells, other additional components will be required for the Photovoltaic design, for instance, an inverter that is required for the conversion of the DC current at the PV modules to AC current, for our case synchronous with the grid. Additionally, due to the sunshine variability both on the twenty four hour basis and seasons as well, there is the need to balance the mismatch between the production and the consumption of electricity using a battery design.

The PV modules produce DC current, this current is converted to AC current with the aid of an inverter for the AC current electrical loads. The electric energy can be stored and used later by utilizing a battery. Batteries used in this cases have a huge storage capability. The PV design creates DC current that is converted to AC current by an inverter as mentioned earlier. From the design there are, PV modules, batteries, inverters, circuit breakers, and cables that are specific, this is to have an efficient power supply for a specified electrical load.

PV Array

The PV design, a semiconductor is used for the absorption of solar energy as photons, the photons are converted to a voltage through electrons movement; PV cells together form a module. The modules are wired to a large array referred to as a PV array.

The suggested modules to be used for our simulation are 24 V, 2.8 kW (at 1000 W/m2, and 25 degree Celsius). The modules are linked, forming an array with 24v.

The cost estimates including the replacement cost for the PV is $ 7/W. A lifetime of 25 years was estimated. An 80% de-rating factor was applied from each PV solar module to the electricity production. The modeling of the PV Solar panel modules was fixed, tilted south an angle equal to the site`s latitude. The capacities from different PV Solar panel modules (0, 0.28, 0.42, 0.56, 0.70, 0.84, 0.98, 1.12, 1.26, 1.40, 1.54 and 1.68 kW) were considered during analysis.

The image below shows a summary of the system.

 

 

Batteries

Since the design factors a working period of 24 hours, an essential part of the system has to include a battery bank and a solar charge controller mechanism. During the battery`s lifetime, HOMER software presumes that the properties are constant, external factors such as temperature are not considered. Our battery of choice had 24v, 360 capacities. The estimated battery cost is at $ 200. The battery`s lifetime is 1,075 kWh of throughput per battery. Several batteries were considered in the analysis (0, 1, 2, 3, and 4).

Discover AES 2.8kWhr 24VDC without Xanbus Communication Nominal Capacity is 110 Ah or 2816 Whr. The max discharge current of 600A is based on a 3 second rating. The lifetime is 16MWh within 10 years, with failure meaning <60% or the original capacity. Price estimate for hardware with Xanbus Communication is approximately $3560, and without is $3308. Capital cost and replacement cost represent hardware costs, but should be edited to include the cost of installation and logistics, etc. P/N 44-24-2800 (with Xanbus); P/N 14-24-2800 (without Xanbus)

The figure shows a general block diagram of the system

 

 

Inverter

An inverter is a device that is responsible for the conversion of DC current produced by the solar module array to AC current. Its efficiency is understood to be 95 percent for the PV design sizes of interest for the study. The probable price of an inverter is $ 300/kW, and the lifetime an approximate fifteen years. Inverters of an assortment of sizes in kW (0.25, 0.50, 0.75, 1.00, 1.25, and 1.5 kW) were used for analysis.

The electric loads proposed are energy conservative in comparison to electric load type used recently in Khartoum, Sudan. Here, a typical 24hr. electricity for commercial use is in place, we identified the energy generated in 24hrs. by the PV design.

An hourly load profile is shown below, the electric load is 25kWh daily.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RESULTS AND DISCUSSION

 

 

NetPresentCost($)

Cost Summary

Total net present cost Leveled cost of energy

48972$

0.345$/kWh

Net Present Costs

Component Capital
Replacement

O&M
Fuel Salvage

Total

 

Generic flatplatePV 24,877

 

0

 

1

 

0

 

0

 

24,879

HOMERCombinedDispatch 0

0
0
0
0
0

Discover AES2.8kWh24VDC 13,232

3,027
6,301
0
­506
22,055

SystemConverter 1,421

798
0
0
­181
2,038

System 39,531

3,826
6,302
0
­687
48,972

Annualized Costs

Component Capital Replacement O&M Fuel Salvage Total

Generic flatplatePV 1,579 0 0 0 0 1,579

HOMERCombinedDispatch 0 0 0 0 0 0

Discover AES2.8kWh24VDC 840 192 400 0 ­32 1,400

SystemConverter 90 51 0 0 ­11 129

System 2,509 243 400 0 ­44 3,109

Power(kW)

 

Quantity Value Units

Ratedcapacity 8kW

Meanoutput 2kW

Meanoutput 43.23kWh/d

Capacity factor 21.72%

Totalproduction 15778kWh/yr.

Minimumoutput 0.00kW

Maximumoutput 8.08kW

PVpenetration 172.91%

Hoursofoperation 4361hrs/yr.

HourofDay

Leveledcost 0.100$/kWh

Quantity Value

Stringsize 1

Stringsinparallel 4

Batteries 4

Busvoltage 24

Quantity Value Units

Converter

Quantity Inverter Rectifier Units

Capacity 5 5kW

Meanoutput 0 0kW

Minimumoutput 0 0kW

Maximumoutput 3 4kW

Capacity factor 5 6%

Hoursofoperation 5,135 3,416hrs/yr.

Energyin 2,218 2,452kWh/yr.

Energyout 2,107 2,330kWh/yr.

HourofDay

Losses 111 123kWh/yr.

24

RectifierOutputPower

4.14

18

12

6

0

0.00

HourofDay

 

18

12

6

0

0.00

Pollutant Emissions Units

Carbondioxide 0kg/yr.

Carbonmonoxide 0kg/yr.

Unburnedhydrocarbons 0kg/yr.

Particulatematter 0kg/yr.

Sulfurdioxide 0kg/yr.

Nitrogenoxides 0kg/yr.

References

About HOMER Energy – Creators of Hybrid Renewable Microgrid System Design Software. (n.d.). Retrieved September 30, 2018, from http://www.homerenergy.com/company/index.html

Ian, B. (2004). HOMER, the micropower optimization model, helps you design off-grid and grid connected systems. National Renewable Energy Laboratory. doi:https://www.nrel.gov/docs/fy04osti/35406.pdf

Raji, A. K. (2017). Techno-Economic Feasibility Study of Autonomous Hybrid AC/DC Microgrid System. System Reliability.