A case study on grid integrated solar roof-top PV system

Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology ISSN: 2454-132X Impact factor: 4.295 (Volume 4, Issue 6) Available online at: www.ijariit.com A case study on grid integrated solar roof-top PV system Yash Ajgaonkar yashaj2014@yahoo.co.in Fr. Conceicao Rodrigues Institute of Technology, Mumbai, Maharashtra Mayuri Bhirud mayuri17b@gmail.com Fr. Conceicao Rodrigues Institute of Technology, Mumbai, Maharashtra Vinit Surve vinitsurve97@gmail.com Fr. Conceicao Rodrigues Institute of Technology, Mumbai, Maharashtra Poornima Rao punnag@yahoo.co.in Fr. Conceicao Rodrigues Institute of Technology, Mumbai, Maharashtra Sreehari S. sreeharidav@gmail.com Fr. Conceicao Rodrigues Institute of Technology, Mumbai, Maharashtra ABSTRACT With advances in technology and industrial development, there is an increase in the consumption of electrical energy. However, the rapid exhaustion of conventional fossil fuels to produce electrical energy has provoked the engineers to find sustainable means of electrical energy generation from renewable resources. Amongst all renewable resources, solar energy produces promising results. There has been a lot of research and development in the field of Solar PV systems. Hence with recent advancements in solar technologies, the PV systems have become more efficient and cost-effective. There are little awareness and knowledge about the implementation of Solar PV system amongst common people. The other main issue is the space required for installing solar panels for power generation. In this paper, efforts are made to create awareness and encourage people to adopt and implement solar roof-top PV system for sustainability and a better environment. This paper involves a case study on installation of roof-top solar PV system at RRR Laboratories Pvt. Ltd. Turbhe, Navi Mumbai. The paper provides a feasibility analysis in terms of both economics and design complexities using a Top-Down approach. The analysis suggests that grid integrated roof-top system is a more viable solution for city areas where available open space for the solar panels is the main constraint. If grid integrated PV systems are implemented on open rooftops in cities, it would become versatile utilization of rooftops which otherwise would have been left unutilized. So, the study concludes that a simple grid-tied solar PV system is feasible to be implemented on any roof-top area in cities at the individual level with affordable expenses. Thus, popularizing the implementation of grid-integrated solar roof-top PV system makes productive utilization of roof-tops as well as contributes substantially towards sustainability and environment. Keywords— Grid-connected system, Top-down and bottom-up approach, MPPT and Inverter, Payback period 1. INTRODUCTION Electrical energy has become the most vital resource for mankind in many ways. However; the rapid exhaustion of fossil fuels cannot suffice the increasing demand for energy. Another growing concern is the relativity of energy consumption to environmental degradation. In the past few decades’ considerable research has been conducted in the field of electricity generation from renewable resources. Energy generation from Solar PV systems has shown promising results and proves to be a viable option in most sun-belt rich countries like India. India being located within 20.593 0N [1] receives ample sunlight throughout the year thus proves an ideal location for energy generation from solar PV. The solar PV systems have different system methodologies that are grid integrated (with and without battery backup) and off-grid system which can be implemented according to the necessity and constraints. The solar PV panels have greatly improved in terms of its efficiency and manufacturing cost. In this paper, we have considered the most common simple and popular of all methodologies. There are three sections in the paper. Section ‘A’ is on the technical analysis and involves analysis on system components of solar rooftop PV systems. Section ‘B’ is on the Case study of the implementation of the Grid-tied system. Section ‘C’ is on the economic analysis of the proposed system design. 2. TECHNICAL ANALYSIS 2.1 PV Systems The two main methodologies involved in implementing Solar PV systems are Grid-Integrated system and standalone system. GridIntegrated Systems are further classified into two categories: 1. without battery backup 2. with battery backup. In Grid integrated systems without battery backup, the energy is being fed directly to system grid without using the battery storage. The feature of © 2018, www.IJARIIT.com All Rights Reserved Page | 40 Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology this type of the system is its simplicity in designing and cost-effectiveness. The disadvantage of the Grid-Integrated system is that it has to be islanded (an anti-islanding feature of the inverter) for the purpose of safety and to prevent the flow of reverse power during failure. The grid integrated systems with battery backup is a type of Hybrid systems which can supply energy to the grid as well charge the battery which in turn can be used to supply power to selected specific loads during the night or during grid failure. However, the design involved in this system is complex and require sophisticated control systems. Therefore, implementing the cost of this system is high. Off-grid systems are adopted in conditions where grid connection is either not possible or it is very costly. The feature of this system is that it is entirely self-sustaining without any grid supply. 2.2 PV Panels Basically, the most common types of panels used are monocrystalline and polycrystalline. The Monocrystalline Solar Panels uses high purity silicon and therefore considered to be highly efficient (reaching above 20%). Whereas a low-cost silicon is used to fabricate polycrystalline cells, their efficiency is typically in the range of 12%-14%. Monocrystalline solar panels last the longest they tend to be slightly less affected by high temperatures compared to polycrystalline panels 25-35 years. Monocrystalline panels have a high-power output, occupy less space, and last the longest. For the case study, Monocrystalline panels are considered. 2.3 Sizing of the panels and its specification If small, shaded or unusually shaped roofs are available the solar panel sizing is of major considerations where we need to go for few panels but of higher efficiency. In case of large usable roof area, there can be a compromise made between efficiency and number of panels to achieve the targeted output. For the case study, we have selected the following data. Terminology 1. STC- Standard Test Condition when 1000W/m2 irradiance, 25°C cell temperature. 2. Open Circuit Voltage (Voc): Voltage measured across two terminals of a solar panel at no load. 3. Maximum Voltage (Vmpp): The Vmpp is the voltage when the power output is the maximum. 4. Maximum Current (Impp): The Impp is the current when the power output is the maximum. 5. Short Circuit Current (Isc): Current flowing when both the terminals are shorted. Table 1: Electrical and mechanical data Electrical Data Mechanical Data Specifications 1.Peak Power (Wp) STC 350 355 360 1. Dimensions (L X W X H) 1956 X 992 X 36 (mm) 2.Maximumvoltage (Vmpp) 38.11 38.19 38.32 2. Weight Of each panel 3. Maximum current (Impp) 9.17 9.30 3. Bypass diodes 3 4. Open circuit voltage (Voc) 47.41 47.49 47.68 4. Number of Cells 72 5.Short circuit current (Isc) 9.71 9.82 5. Frame 6. Efficiency (%) 18.03 18.31 18.82 9.40 9.96 6. Safety Class 22Kg Anodized aluminum frame Class II 2.4 String connections of PV Panels Connecting solar panels together depends on overall system size, solar module output and system optimization between the solar modules and the inverter rating. Strings Connections can be done in two ways either in Parallel connections or in Series connections. If the inverter operates with the low input voltage, the modules can be connected in parallel to the inverter. The advantage is that the voltage on the DC side will be lower, safer installation, operation and system maintenance. In parallel, the shadow caused which covers the surface affects only that particular module. But the disadvantage of connecting solar panels in parallel is, low voltage implies large currents and therefore cables of larger diameter, higher cost, or greater electrical losses. In Series connection required cable size reduces, resulting in cost saving & improved efficiency due to lower inverter & cable loss. Therefore, a combination of series and parallel connection of PV panels are selected for optimum results. 2.5 Inverter The inverter is an important component of the PV system. As the generated electrical power by PV panels is DC and hence they it is to be converted to AC. One of the most important features for the grid-tied feature is the Anti-Islanding. Islanding is defined as the situation in which the energy generation source remains energized while the grid to which its feeding remains isolated due to failure. This situation is dangerous as the energized source is connected to the other equipment connected to the grid which can pose threat not only to the equipment but also to the maintenance personnel working. Thus, in event of grid failure or isolation of a Solar PV system, the inverter should be capable of sensing that it is isolated from the grid and should immediately de-energize and stop feeding the grid. The anti-islanding can be done by passive and active methods; however, the reliability of passive methods is very poor and hence modern inverters are equipped with the active anti-islanding feature. The protection system in the inverter involves 1. Ground fault monitoring. 2. Surge arrester (DC). 3. DC side reverses polarity, Galvanic isolation, and AC short circuit current detection capability. 4. Overvoltage protection along with all pole sensitive residual current monitoring. © 2018, www.IJARIIT.com All Rights Reserved Page | 41 Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology 2.6 MPPT (Maximum Power Point Tracking) The inverter also incorporates a feature called MPPT (Maximum Power Point Tracking). It generally comprises Buck-Boost Converters that automatically adjusts itself to give maximum power condition in cases where there are changes in insolation level, temperature rises etc. MPPT control system has a basic principle of controlling the duty cycle D of the converter with changes in system parameters. With MPPT it is ensured that maximum power is extracted from the panels. 2.7 Protection system With increasing plant capacity of solar PV system, the parameters like voltage, current and power increases. Thus there is a need for a sophisticated protection system to prevent damage to equipment as well as human life. The protection system in a Solar PV system involves protection against Overload, short circuit current, and Lightning Surges. DC fault current is associated with lower rate of rising of current under short circuit condition when compared to the same magnitude of AC short circuit current (Typically, the short circuit current for a 325 W solar panel ranges from 8.5 to 9.8 A). As the rate of rising of current is low the arcing time is high and fuse link melts slower than for similar AC fault currents. DC semiconductor fuses are a special type of fuses which act very fast within milliseconds and isolate the system to prevent further damage. Since the solar PV system is situated majorly on open building rooftops or open ground areas are highly vulnerable to lightning strokes which can enter the system. These high voltage transients can damage the equipment connected and may even put human life in danger. To protect the PV system from lightning surges Lightning arrestors and Lightning rods are used. 3. THE CASE STUDY ON SYSTEM IMPLEMENTATION AT RRR LABS The proposed PV system is to be implemented on the RRR labs a Surface metal finishing company. The building is 2 storeyed and located in Turbhe, MIDC area, Navi Mumbai, India. The site latitude and longitude are 19.070710 N, 73.016210E [1]. The irradiance is defined as the ratio of average insolation to average daily sunshine hours. For the given site annual irradiance is 5.37 kWh/m2/day [2] . For the northern hemisphere, the panels should be facing south and the tilt angle for the panel can be generally taken as the site latitude and for the given location tilt angle is 19.070. The average solar radiation incident is around 5.67 kWh/m 2 [1]. During summers i.e. in months of February to May the radiation is as high as 7.2 kWh/m2 [1], whereas in monsoon the radiation drops to 4.5 kWh/m2 [1]. In winter i.e. from October to January the radiation is around 5 kWh/m2 [1]. Along with good solar radiation, the amount of active sunshine is also vital. More the sunshine more amount of time the system can generate. For year around the average number of active sunshine hours is greater than 190hours each month with the highest amount of 320 sunshine hours in summer months [1]. Thus, the above statistical data shows that the site location is suitable for effective solar PV generation. For design implementation, the following approaches are followed: A. Top-down approach: In a top-down approach, the solar system is implemented based on resource constraints. In this method, the number of panels required is calculated considering the available area in which the system can be implemented. Therefore, this method considers the practical viability of system implementation. After calculating the number of panels that can be fitted in the required area the annual system energy generation is calculated. Thus, the amount of savings is the difference between load energy consumption and energy generation by the PV system. The advantage of this system is that it can be easily implemented especially in cities. B. Bottom-up approach: In the bottom approach, the energy generation by the PV system should be equal or greater than load consumption. After considering the energy generation required, accordingly, the number of solar PV panels is calculated. The major disadvantage of this method is the requirement of adequate space to accommodate that many panels. Hence may not be viable with space and other constraints. For a present case study, the Top-down approach is adopted as the available area is limited. The Layout of the Rooftop area available for installing the PV panels is given below in Fig1. While measuring the rooftop, two important factors are to be considered: 1) Exclude the area where the shadow is present 2) Space around each panel for cleaning and maintenance. From the roof layout after excluding the shading areas the available rooftop areas are marked as rooftop 1 and rooftop 2 where the PV panels can be installed. Since the available area is very small we follow Topdown approach of implementation of a solar PV system in which we calculate the number of solar panels that can be fitted on rooftops 1 and 2. After considering the shadows and spacing between the panels to ensure maintenance and cleaning 10 solar PV panels can be implemented. Fig. 1: Roof layout for the RRR labs © 2018, www.IJARIIT.com All Rights Reserved Page | 42 Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology 3.1 System components 3.1.1 Panel selection: As the available area for present location is limited the system should be able to generate maximum possible output. Thus, high efficiency 72 cells Monocrystalline solar panels are used even though they cost more than other solar panels. Based on the available roof area number of solar panels that can be installed are 10. If 10 panels of 72 cells monocrystalline panels each of 350 W each are used, then total plant capacity is 3.5 kW. Fig. 2: The system configuration 3.1.2 Inverter and MPPT: After considering the panels, the next major component is the Inverter. A 4.6 kW dual MPPT inverter is used equipped with the anti-islanding feature. Generally, a single MPPT controller is enough, but with dual MPPT controller, the reliability of the system increases. The protection system can be categorized as DC side and AC side protection. At DC side highspeed DC Semiconductor fuses are used instead of HRC fuses. At AC side immediately after Inverter, a 4 pole MCB is used and at the substation, MCCB is used. The inverter has inbuilt overvoltage, ground fault detection circuit along with the anti-islanding feature. To prevent lightning surges each string will have 2 lightning arrestors on each side with effective grounding. In proposed design 10 panels are used of 350 W nominal power rating and 5 panels are connected in series and two such strings are connected in parallel. In series connection voltage across each panel gets added up and currently remains same whereas in parallel connection currents get added up and voltage remains same. 4. THE ECONOMIC ANALYSIS The consumer always quantifies the product in terms of its cost and benefit in terms of profit and hence economics is governing factor. In earlier days the initial investment in solar PV system was very high and its returns were very low and hence at residential level consumers were reluctant to implement the solar PV system. With increasing technological advancements in Solar PV systems, the manufacturing cost has come down drastically and even on the residential level, it is now affordable. In Grid-Tied PV system due to the absence of batteries and other control systems, the initial investment is very less as compared to stand alone system and hence largely implemented at residential and small-scale commercial industries. For a Grid-tied PV system following components are used 4.1 Solar PV Panel The panel chosen has the following specification which can be referred from Table 1. 4.2 Irradiance calculations To calculate irradiance levels, the sunlight is available for 9 hours is assumed. 4.2.1 During summer 4.2.2 During Monsoon 4.2.3 During Winter Average irradiation is 6.75 kWh/m2 [2] 6.75 × 103 Irradiance = = 750 W/m2 9 Average Irradiation is 4.83 kWh/m2 [2] 4.85 × 103 = 538 W/m2 Irradiance = 9 Average Irradiation is 5.31 kWh/m2 [2] 5.31 × 103 Irradiance = = 590 W/m2 9  Vmpp and Vocremains same for irradiance levels  Voc = 47.4v  Vmpp =38.2 V © 2018, www.IJARIIT.com All Rights Reserved Page | 43 Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology 4.2.4 During Summer (Feb– May) Irradiance =750 W/m2and Sunshine available for 8 hours 750 750 × Isc at 1000 W⁄m2 = × 9.76 = 7.32 A 1000 1000 W Impp at 1000 W/m2 9.24 Impp at 750 2 = × Isc at 750 W⁄m2 = × 7.32 = 6.93 A m Isc at 1000 W/m2 9.76 Isc at 750 W⁄m2 = Pmp at 750 W⁄m2 = Impp at 750 W⁄m2 × Vmpp at 750 W⁄m2 = 264.72 W Units generated during summer per panel = Power × No. of hours for which sunshine is available × No. of days = 264.72 × 8 × 120 = 254.18 units⁄panel Total units Generated during Summer = units generated per panel × No. of panels = 254.18 × 10 = 2541.8 units 4.2.5 Monsoon (June–September) Irradiance =538 W/m2and Sunshine available for 4 hours 538W 538 W 538 = × Isc at 1000 2 = × 9.76 = 5.25A 2 m 1000 m 1000 W Impp at 1000 W/m2 W 9.24 Impp at 538 2 = × Isc at 538 2 = × 5.25 = 4.97A m Isc at 1000 W/m2 m 9.76 Isc at Pmp at 538 W⁄m2 = Vmpp at 538W/m2 × Impp at 538W/m2 = 189.85W Units generated during monsoon per panel = Power × No. of hours for which sunshine is available × No. of days = 189.85 × 4 × 122 = 92.648 units/panel Total units Generated during Monsoon = units generated per panel × No. of panels = 92.648 × 10 = 926.48 units 4.2.6 In Winter (October – Jan) Irradiance =590 W/m2and Sunshine available for 7 hours Isc at 590 Impp at 590 W m2 W m2 = = 590 1000 × Isc at 1000 W m2 W Isc at 1000 m2 Impp at 1000 W m2 = × Isc at 590 590 1000 W m2 × 9.76 = 5.75 A = 9.24 9.76 × 5.75 = 5.44 A Pmp at 590 W/m2 = Vmpp at 590 W/m2 × Impp at 590 W/m2 = 207.8 W Units generated during winter per panel = Power × No. of hours for which sunshine is available × No. of days = 207.8 × 7 × 123 = 178.91units/panel Total units Generated during winter = units generated per panel × No. of panels = 178.19 × 10 = 1781.9 units 4.2.7 Annual unit generation by the System Total Units generated by the System in a year = 2541.31 + 926.48 + 1781.9 = 5.249Mwh/year Total Load consumption = 12.645Mwh/year 𝐒𝐚𝐯𝐢𝐧𝐠𝐬 𝐢𝐧 𝐮𝐧𝐢𝐭𝐬 = 𝟓. 𝟐𝟒𝟗𝐌𝐰𝐡/𝐲𝐞𝐚𝐫 4.3 Load consumption and cost analysis The RRR labs in Turbhe Navi Mumbai has a 3 phase connection from MSEB (Maharashtra state electricity board). The annual energy consumption by the RRR l labs is obtained from the Bill generated by the MSEB along with the billing amount. Following figures show annual energy consumption along with the amount. Fig. 3: Monthly Consumption © 2018, www.IJARIIT.com All Rights Reserved Fig. 4: Monthly Expenditure Page | 44 Ajgaonkar Yash et al.; International Journal of Advance Research, Ideas and Innovations in Technology Figure 3, depicts that mean consumption of energy is around 900 units with a peak consumption of 1300 units in summer months and lowest consumption of 600 units in winter. From figure 4, the consumption rates are greater than Rs. 6000 with highest and lowest rates of Rs. 9000 and Rs.4000. 4.4 Cost calculations Table 2: Cost calculations S. no Equipment 1. Solar Panels 2. Inverter (2MPPT) 3. Cabling 4. Protection 4. Structure 5. Peripherals 6. Design and Installation Total Cost Including 5% GST Quantity 10 1 Unit Cost 12,000 56,000 Rs 2/watt for 3.5 kW plant Rs 3.5/watt for 3.5 kW Rs 4/watt for 3.5 kW Rs 5/watt for 3.5 kW Cost 120,000 56,000 7000 8000 12250 14000 17500 246488 4.5 Incentives and Government subsidies Government Schemes for solar rooftop PV systems 1. Rajiv Gandhi Gramin Vidyut Karan Yojana (RGGVY) 2. Subsidy by MNRE on Total System Cost Therefore, By 30% Subsidy from MNRE = 30% of Total cost = Rs 73946 Initial Investment = Total Cost – Subsidy = Rs 172542 172542 = Rs 49297.7/kilowatt 3.5 Initial Investment 172542 Pay Back Period = = = 3.008 Years Electricity bill cost 57354 Cost per kilowatt = 5. CONCLUSION In this paper, a 3.5 KW grid-tied solar PV system is designed for RRR labs, Turbhe Navi Mumbai. The Top-down approach is adapted for carrying out the technical and economic analysis of the system. After considering the available area for installation, excluding the shading areas, the proposed system has a plant capacity of 3.5 KW. The annual system generation is calculated to be 5.249 MWh. The initial investment for the proposed system is projected to be Rs 246,488 which includes system components, installation, and other miscellaneous accessories and taxes. The system can acquire a 30% subsidy on total cost from MNRE (as per their current policy). After considering the subsidy, the total investment reduces down to Rs 172,542. The cost per kilowatt for the system is Rs 49,297. The payback period for the system is calculated to be 3.13 years without MNRE subsidy and 2.19 years considering 30% subsidy. In this work, emphasis is given on the need and importance for installing Grid-tied Solar Rooftop PV system in city areas. The paper strives to create awareness and promote the use of renewable resources especially solar PV system. With the implementation of the Solar Rooftop PV system, apart from financial benefits, the major payback in long run is the contribution towards sustainability and environment thereby promoting sustainable development. 6. REFERENCES [1] Meteo Data. [Online]. Available: www.synergyenviron.com [2] (2018) Google Earth website. earth.google.com [3] A. Al-Salaymeh et al. Technical and economic assessment of the utilization of photovoltaic systems in residential buildings: The case of Jordan Energy Conversion and Management 51 (2010) 1719–1726. [4] Al-Salaymeh A. A general model for the prediction of global daily solar radiation on horizontal surfaces for Amman city. Emirates J Eng Res (EJER) 2006; 11(1):49–56. [5] A. Muntasib Chowdhury et al./Design and Cost-Benefit Analysis of Grid Connected Solar PV System for the AUST Campus.6th International Conference on Electrical and Computer Engineering ICECE 2010, 18-20 December 2010, Dhaka, Bangladesh [6] Monthly electricity bill, Maharashtra State Electricity Board (MSEB), RRR labs (Turbhe, Navi Mumbai). [7] Wang, Y., Zhou, S. &Huo, H., 2014. Cost and CO2 reductions of solar photovoltaic power generation in China: Perspectives for 2020. Renewable and Sustainable Energy Reviews, 39, pp.370-80 [8] Hamed ALLaham et al./Technical and Economical Analysis Of Photovoltaic System Applied To A Uae Data Centre [9] S.S. Alrwashdeh/ Resource-Efficient Technologies 3(2017) 4 40-4 45 [10] B. Marion, J. Adelstein, K. Boyle, H. Hayden, B. Hammond, T. Fletcher, B. Canada, D. Narang, A. Kimber, L. Mitchell, G. Rich, and T. Townsend, “Performance parameters for grid-connected PV systems,” in Photovoltaic Specialists Conference, 2005. Conference Record of the Thirty-first IEEE, 2005, pp. 1601–1606 © 2018, www.IJARIIT.com All Rights Reserved Page | 45