Design of LED lighting system using solar powered PV cells for a proposed business complex

The paper outlines the concepts and design of an upcoming stand-alone solar photovoltaic system to supply the energy needs of a new proposed business complex. The purpose of this study is to develop a prediction method for the use of solar energy for commercial purposes. Firstly, the annual energy demand for the illumination and utilities in a business complex is calculated. LED lights are considered in the complex for the illumination to minimize the cost of energy. Based on the load estimation, the number of solar panels are predicted as 6097, to generate the power for the proposed area. Secondly, the important part of the design in the estimation of solar radiation and optimal tilt angle of a photovoltaic panel has been calculated for the maximum energy harvest. In this case the optimal tilt angle is 49.34°. The installation of PV panels for optimal and feasible operation is also predicted. The calculated parameters are used in a simulation with a software to test their practicality in the business complex. The technique is used to determine the amount of energy produced and system’s performance ratio. A cost estimate is also provided for the solar PV system. In the end, an analysis of these simulations and estimations is presented.


Design of LED lighting system using solar powered PV cells for a proposed business complex Sayan Kumar Nag * & Tarun Kumar Gangopadhyay
The paper outlines the concepts and design of an upcoming stand-alone solar photovoltaic system to supply the energy needs of a new proposed business complex. The purpose of this study is to develop a prediction method for the use of solar energy for commercial purposes. Firstly, the annual energy demand for the illumination and utilities in a business complex is calculated. LED lights are considered in the complex for the illumination to minimize the cost of energy. Based on the load estimation, the number of solar panels are predicted as 6097, to generate the power for the proposed area. Secondly, the important part of the design in the estimation of solar radiation and optimal tilt angle of a photovoltaic panel has been calculated for the maximum energy harvest. In this case the optimal tilt angle is 49.34°. The installation of PV panels for optimal and feasible operation is also predicted. The calculated parameters are used in a simulation with a software to test their practicality in the business complex. The technique is used to determine the amount of energy produced and system's performance ratio. A cost estimate is also provided for the solar PV system. In the end, an analysis of these simulations and estimations is presented.
A solar photovoltaic power plant converts sunlight into electricity by using photovoltaic cells, also known as PV or solar cells 1 . Alloys of silicon are used to make these cells 2 . Solar energy is directly converted into electricity by photovoltaic cells. They work according to the principle of photovoltaics 3 . Photons are absorbed by certain elements when exposed to light, which releases free electrons. The photoelectric effect is the term used to describe this phenomenon 4 . The photovoltaic effect is the process of producing direct current electricity using the principle of photoelectric effect 5 .
Based on the principle of photovoltaic effect, solar cells or photovoltaic cells are created 6 . Sunlight is converted by them into direct current (DC) electricity 7 . But the amount of electricity generated by one solar cell is not adequate 8 . Hence, solar modules or solar panels are comprised of several solar cells mounted onto a support frame and electrically connected to one another 7 .
In general, solar panels are available in a range of sizes and power outputs, ranging from several hundred watts up to several kilowatts 9 . While panels or modules deliver power at a certain voltage, the current they produce is determined by the intensity of the incident light 10 . In most cases, however, solar power systems are also equipped with inverters to provide AC power 11 .
India consumes about 6% of global energy 12 . India has an installed generation capacity of 365 GW of which 55.8% is coal powered, 13.7% is hydroelectricity, 10.1% is wind powered, solar PV is of 8.8%, 6.8% is of natural gas, bio energy and waste is of 2.7%, 2% is nuclear powered, 0.1% is oil powered 13 .
Solar energy makes up of about 8.8% of the electricity generated 14 . This is because solar power plants cannot be deployed in regions having inconsistent sunlight or because of the large surface area required to capture solar energy 15 . However, in solar-rich nations and regions electricity produced from solar panels is cheaper than electricity produced commercially 16 . In the recent years, use of solar energy has seen an exponential rise in India 17 . Advances in solar panel efficiency are expected to make solar energy more readily available for use in home and office buildings 18 .
The present project is aimed to focus on the study of an energy efficient illumination and utilities system using LED lamps, for a business complex. Utilizing systems like light-emitting diode (LED) instead of traditional lamps can reduce electricity consumption 19 . The scope of the work is to design an effective solar photovoltaic system which would meet the complete energy demand of a proposed business complex without consuming conventional energy supply.
A block diagram of the tentative process is shown in Fig. 1.

Solar photovoltaic power plant types
Depending on the power requirements, several solar modules are electrically connected to form a PV array and achieve more power 20 . There are different types of PV systems depending on their application: i. PV direct systems This system only supplies the load when the sun is shining. There is no battery as the generated power is not stored 21 . A diagram of PV direct system is shown in Fig. 2. ii. Off-grid Systems Systems of this type are usually used in locations where the power of the grid is not available or reliable. There is no electrical grid connection for off-grid solar power systems. It has a solar panel array, storage battery and inverter circuit 21 . A diagram of off-grid system is shown in Fig. 3.   www.nature.com/scientificreports/ iii. Grid connected systems Taking advantage of the grid connection, additional energy can be obtained from the grid for these solar power systems. It may or may not be backed by batteries 21 . A diagram of grid connected system is shown in Fig. 4.

Construction of a solar PV power plant
The process of building a solar PV power plant is a complex effort that requires considerable time cost and expertise.
It can be divided into following stages: i. Identification of the location. ii. Determination of the grid connection point. iii. Pre-construction documentation and negotiations. iv. Building the infrastructure i.e., roads, fence, security, etc. v. Equipment and logistics purchase. vi. Installation of supporting structures. vii. Installation of the transformer substation. viii. Connection with the grid.

Scheme of the present research
A layout of proposed area of illumination in the business complex. The proposed layout of the building or structure is shown in Fig. 5. It is established according to the foundation plan drawings and specifications provided by the engineer or architect. Presently, building design focuses on maximizing sustainability, environmental impact and energy efficiency. All these factors have a direct effect on the power distribution in the building. In practice, electrical engineers must work with architects and mechanical engineers to achieve the most accurate estimates of demand.

Calculation of loads for illumination and appliances used in this business complex.
The projected electricity demand identifies the building's requirements in terms of power supply and distribution. Therefore, an accurate estimate of the amount of power required for a building to function successfully is an essential step in planning and designing a system. Appliances used in the business complex with their power rating is shown in Table 1. Finally, total load of the proposed business complex is shown in Table 2.
The required value of the annual solar incidence of the area. Solar PV systems must be designed based on how much sunlight can be harnessed at any given time and place. Solar radiation (or radiation) and solar isolation are the two most predominant methods of solar radiation. Solar radiance is described as the instantaneous power density in the units of kW/m 2 . Solar radiance varies, from 0 kW/m 2 at night up to 1 kW/m 2 during the daytime 27 . Location and local weather are also crucial factors affecting solar radiance. Pyranometers (for measuring global radiation) and pyrheliometers (for measuring direct radiation) are used for the measurements. These data have been collected for over two decades at a well-established location 28 .
Sunshine recorders are also an inexpensive and less accurate method of measuring solar radiation. Sunshine recorders (also known as Campbell-Stokes recorders) measure how many hours during the day sunlight is above a certain level (usually 200 mW/cm 2 ) 27 . Data collected in this manner can be used to calculate insolation as a function of the hours of sunshine measured with a value calculated using several correction factors 28 . Finally, www.nature.com/scientificreports/ cloud cover data collected from existing satellite images can be used to estimate solar insolation as illustrated in Fig. 6. A solar radiation map of India is shown in Fig. 6. 29 .
Designing of the PV system. From   31 . Therefore, we would require approximately 6097 panels to supply complete power to the proposed business complex.

Theory of solar angles
Air mass. Considering the vertical path of the sea surface as unity, the path length of the sun's rays through the atmosphere is described in terms of "Air Mass" 32 .
Alternatively, the air mass "m" is the ratio of the path length of the sun's rays through the atmosphere to the length of the path when the sun's position is directly overhead (i.e., the zenith position) 32 .
Thus, m = The length of the path transversed by the beam radiation Atmospheric vertical path length Figure 7 shows the solar radiation geometry and the various angles formed which will be explained in next sub-sections.
According to Fig. 8  www.nature.com/scientificreports/ Zenith angle. It is the angle between the rays of the sun and the vertical plane. It is denoted by "θ z " 32 .
According to Fig. 8, According to Eq. (1), the air mass is equal to the cosecant of the altitude angle (α). Therefore, at sea level m = 1. m = 1 when the sun is at zenith position (i.e., overhead). m = sec θ z , when m > 3. m = 0, Just above the Earth's atmosphere.

Angle of latitude.
Latitude is the angle formed by the radial line connecting a given location to the centre of the Earth. This line is projected onto the equatorial plane to determine the latitude of the vertical space on the surface of the Earth 32 .
From the centre of the earth, it is the number of degrees of angle north-south of the equator 32 . A positive latitude indicates the northern hemisphere and a negative one indicates the southern hemisphere. It is denoted by ϕ L .
As per Fig. 9, angle of latitude is the angle between the line OA and the projection line OA' , on the equator plane. Point A, depicts the location on the earth's surface, Point O, depicts the centre of the earth. By convention, the latitude will be + ve for the North Hemisphere.
Therefore, according to Fig. 9, ϕ L is ∠AOA' .  It can also be defined as the angle between the line running from the centre of the Sun to the centre of the Earth and the projection of this line on the equatorial plane of the earth 32 . It is shown in Fig. 10.
When measured from above the equatorial plane declination angle is positive in the northern hemisphere 32 . This is the direct consequence of the tilt and it would vary between 23.5° on June 22 to − 23.5° on December 22. For minimum or maximum declination, the sun appears in a stand still condition. This condition is called a solstice. During winter solstice, the sun rays would be 23.5° south of earth's equator i.e., δ is − 23.5°. During summer solstice, the sun rays would be 23.5° north of earth's equator i.e., δ is 23.5°. The variation of sun's declination is shown in Fig. 11.
The declination of the angle can be determined from Cooper's approximate equation.   www.nature.com/scientificreports/ where, "n" is the day of the year counted from 1st January.
Hour angle. The angle at which the Earth must rotate to get the meridian of a particular point (or the observer point) directly in line with the sun's rays is called the hour angle at that moment. It is denoted by ω 32 . In other words, at any moment, it is the angular displacement of the sun towards East or West of local meridian (due to rotation of the earth on its axis) 32 . The Hour angle (ω) is shown in Fig. 12.
On considering Fig. 11, to calculate Hour angle (ω) is the angle measured in the Earth's equatorial plane, between the projection of OA and the projection of a line from the centre of the sun to the centre of the earth.
Altitude angle or inclination angle. The altitude angle indicates how high the sun appears in the sky.
The angle is measured between the imaginary line between the observer and the sun and the horizontal plane on which the observer is standing 32 . When the sun falls below the horizon, the altitude angle is negative. It is also known as inclination angle and solar elevation angle. It is denoted by "α". According to Fig. 8, α = Inclination angle or Altitude angle = ∠QPS. According to Fig. 13, α = ∠CAB = Inclination angle or Altitude angle.  www.nature.com/scientificreports/ As (α + θ z ) = 90° = π 2 Therefore, Again, θ z = π 2 -α. The value of this angle could be calculated directly from software using the latitude and longitude values.

Solar azimuth angle.
It is the solar angle on a horizontal plane, in degrees, between the line due south and the projection of sun's rays on the horizontal plane. It is denoted by r s 32 .
In other words, it is a horizontal angle measured from North to the horizontal projection of sun's rays. When measured from South towards West the solar azimuth angle is positive. From the Fig. 13, Solar Azimuth Angle, r s is ∠BAS. AS is Line due on the South and BA is Horizontal projection line of Sun's ray towards West. Therefore, r s is ∠BAS. The value of this angle could also be calculated directly from software using the latitude and longitude values.

Incident angle (θ OR θ i ).
It is the angle between the incident sun rays on the plane surface and the normal on that surface. It is denoted by θ i 32 . The angle of incidence is shown in Fig. 14. In general, the angle of incidence can be expressed as The slope (optimal tilt angle) (β). It is the angle between inclined plane surface with the horizontal. It is denoted by β 32 .
It is taken to be positive for the surface slopping towards the south and negative for the surface slopping towards the south 32 . β is the angle between inclined surface and the horizontal plane with respect to the collector surface.

Calculation of solar angles required for the present business complex
Calculation of the solar angles for the location of the business complex i.e., Kolkata (Longitude is 88.363895° E, Latitude is 22.572646° N) at a given time i.e., 12:00 noon on 18 April 2021 is done. To calculate solar elevation angle and azimuth angle the software Keisan Online Calculator will be used. Figure 15 shows the given specifications of Kolkata presented in software. Figure 16 shows the variation of solar elevation angle with respect to time at Kolkata on 18 April 2021. Here, X axis represents time and Y axis is the variation of solar elevation angle. It is observed from the graph that the value of elevation angle steadily begins to increase from negative at 00:00 h after that it becomes positive at around 05:00 h then reach its peak around 11:30 h and after that it steadily decreases to again become negative around 18:00 h. As the solar elevation angle represents how high sun appears in the sky. So, it could be concluded from the graph that the sun is below the horizon before 05:00 h and after 18:00 h and it reaches its highest at 11:30 h. Hence, the solar energy could be harvested between 05:00 h to 18:00 h. The values of the solar elevation angle (α) and azimuth angle (r s ) of a given location, here, Kolkata and at a given day, here, 18 April 2021 can be directly cos θ i = cos δ cos ω (cos φ cos β + sin φ sin β cos r) + cos δ sin ω sin β sin r + sin δ( sin φ cos β − cos φ sin β cos r) Figure 14. Angle of incidence (θ i ), tilt angle (β) and angle of latitude (ϕ L ) 32 .  Table 3.

Performance ratio and daily power output of the PV system
Now, in order to determine the performance ratio of the PV system of the business complex the values of the solar angles that were calculated till now will be put in the software PVSyst. The city being considered is Kolkata, India, the location of the business complex. Some of the important screenshots of simulation are as follows: Figure 17 shows the tilt angle and azimuth angle of the solar PV system. The plane considered here is a fixed tilted plane. The optimization is done with respect to the yearly irradiation yield. The X axis of the graph (a) represents the plane tilt whereas the X axis of the graph (b) represents the plane orientation and the Y axis of   www.nature.com/scientificreports/ both the graphs represents the yearly irradiation yield. From the simulation the values obtained of transposition factor (TF) is 0.98, losses with respect to optimum is -8.2% and irradiation on collector plate is 1713 kWh/m 2 . Figure 18 represents in the input of the total Load of the business complex in a year which is found out to be 1,90,830.760 Kilowatt-hours/year.  www.nature.com/scientificreports/ Figure 19 shows the battery specifications used in the solar PV plant. The battery used here is an adjustable lithium-ion battery. The total no. of cells used here is 512 of which 16 are connected in series and 32 are connected in parallel. Figure 20 defines the number of solar modules used here. As calculated previously the required number of solar modules to meet the complete energy demand of the business complex is 6097. But here 6102 modules have been considered in order to maintain the series and parallel symmetry. But it would also be beneficial as  www.nature.com/scientificreports/ it will serve as a backup whenever there is some extra energy demand. Among the 6102 modules 6 modules will be connected in series row and 1017 modules would be connected in parallel row. It also shows the battery operation specifications used in the solar PV plant. The battery is to be operated at standard room temperature at 24 °C in a fixed air-conditioned room. It is because battery temperature is crucial for the aging of the battery. Figure 21 defines the specifications of PV cell used. As defined is the calculation the PV cell used here is a 150 W polycrystalline silicon cell. The PV array design is also given here. The array would have 41 stings and 24 modules in series. It is done so that there is optimum used of space i.e., minimum area used for maximum electricity generation. The figure also shows that the controller used in the system is a universal controller which will operate in DC-DC converter mode. Figure 22 shows the circuit diagram of the stand-alone solar PV system for the proposed business complex. Figure 23 shows the final software generated results for the stand-alone PV system.  www.nature.com/scientificreports/ Considering first graph, 23(a), the daily input/output diagram, the X axis represents the global incident on collector plate in kWh/m 2 /day and the Y axis represents the effective energy at the output of the array in kWh/ day. It is observed that the output energy increases with the increase in incident solar radiation.
The graph 23(b) is the performance ratio (PF) and solar fraction (SF) graph. Here, the X axis represents the performance ratio (PF) and the Y axis represents the time in months. From the simulation, the PF value is obtained as 0.569 and the solar fraction (SF) is 0.740.
The graph 23(c) is the array of power distribution. The X axis represents the effective power at the output of the array in kW and the Y axis represents the effective energy at the output of the array in kWh. The present curve drawn here is for the entire year, from 1st January to 30th December, 2021.
The graph 23(d) is the array temperature versus effective irradiance. The X axis represents the effective irradiance in W/m 2 of the array in kW and the Y axis represents the average module temperature during running in °C. It is estimated for the entire year from 1st January to 30th December, 2021. From the graph, it is established that the temperature of the module increases with increase in solar irradiation but the performance decreases. The parameters obtained from the simulation are shown in Table 4.

Cost estimation
Each energy-producing organization has their own cost per unit of electricity. However, here we will determine the unit rate without considering debits, capital and taxes. On considering our stand-alone solar PV plant for the business complex, the breakup of the capital cost is shown in Table 5.

Conclusion
Based on the findings of this paper, the feasibility of designing a stand-alone solar photovoltaic (PV) system is evaluated which can meet the entire energy requirement of a proposed business complex. It has been carried out without the support of any conventional supply of energy, i.e., conventional power plant.
The paper starts with a brief theory of solar photovoltaic power plant, its working principle, application and percentage share in energy sector. Then descriptions of different solar plants along with their working principle is presented in a brief but compact manner. Construction of a solar plant is also specified in the study as they play an important role. In the second phase, a typical layout of a business complex is shown and the annual energy demand of the business complex is calculated. Specific attention was paid to the usage of LED lights for illumination purposes as they play an important role in energy conservation. It also contains the solar radiation map of India. The crucial factors including designing the PV system is that the theory and calculation of the solar angles. The properties of the various solar angles are described for certain important applications. The calculated  www.nature.com/scientificreports/ value of Optimal Tilt Angle is 49.3153814° considering the business complex in Kolkata (India). The simulation technique and practicality of the system is also described in a step by step process. The paper concludes with a cost estimation of the solar PV system for a particular building.
The main conclusions from this study are as follows: i. The stand-alone solar photovoltaic (PV) system would be able to supply complete energy independence for any individual building. Hence, the non-conventional energy (here solar energy) may be the alternative source of illumination and utilities for an office complex or a residential building. ii. The value of Transposition Factor (0.98) establishes the efficiency of the PV system, the Solar Fraction (0.740) value establishes the effectiveness of the system and the Performance Ratio (0.569) shows that energy independence is a possibility in the future. Furthermore, it could also be emphasized that as the efficiency of the PV cells increases so it would be the value of Performance Ratio and Solar Fraction of the system. iii. The cost estimation shows that the acquisition and installation cost of PV system is economically feasible for a typical business complex.
The maintenance needed for solar power plants is very less and therefore, it can be installed at any given space where sufficient sun light is available. It can be easily installed on the rooftop of high-rise buildings. Hence, it is concluded that solar energy generated through solar PV modules is the energy of the future. This system will reduce pollution significantly. It is very much possible to use them in individual building to attain complete energy independence in the future.

Data availability
All data generated or analysed during this study are included in this published article [and its supplementary information files].  The total cost ₹ 12,84,08,304