Component Selection Criteria & Sizing of Solar PV System

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Component Selection Criteria & Sizing of Solar PV System

Japen Gor

GORenewable Technology Ahmedabad, India

AbstractThe paper focuses on explanation of Solar PV System Designing, Component sizing and selection based on the practical experience as a consultant in Solar PV industry. Designing of On-Grid-Grid-Tied Solar PV System is taken into consideration for complete system designing.

Keywords Solar Photovoltaic Systems, On-grid Solar System, Grid-Tied Solar PV Systems, System Designing, Component Sizing, Component Selection.

  1. INTRODUCTION

    Use of solar photovoltaic systems is increasing day-by-day. It is one of the best portable renewable energy solutions in modern times. Due to lack of understating of functioning and critical design parameters installers often end up installing incorrect size of components together. The paper focuses on delivering the details understanding component selection including and not limited to solar PV Modules, inverters, cables and safety switches. The method explained in the paper is completely based on the practical experience of an author.

  2. TYPES OF SOLAR SYSTEMS

    Types of Solar Systems

    B. Practice Question 1: System sizing for 4 kWp (DC)

    Step 1: Module Calculations

    There are many solar module manufacturers.

    It is important to select appropriate module manufacturer/supplier.

    Ever module manufacturer makes different ratings of modules. i.e., 250Wp, 300Wp, 320Wp, 325Wp, 335Wp etc

    It is important to receive updated datasheet from manufacturer/supplier and keep it handy while doing the system sizing.

    Off-Grid

    Stand Alone Off-Grid Hybrid

    On-Grid

    Grid-Tied or Grid- Connected

    Grid-Interactive or On-Grid Hybrid

    (Source: https://www.adanisolar.com/Downloads)

  3. SIZING OF GRID-TIED OR GRID-CONNECTED (ON-GRID) SOLAR PV SYSTEMS

    Components to be sized/calculated

    1. Solar Modules/Panels

    2. Inverter (Selection)

    3. DCDB (DC Fuse, DC MCB, DC SPD)

    4. ACDB (AC Fuse, AC MCB, AC SPD)

    5. DC Cable

    6. AC Cable

      1. Steps of System Sizing

        Step 1: Module Calculations Step 2: Inverter Selection

        Step 3: Strings and Arrays of Modules

        Step 4: Calculations of Balance of System (BOS) Step 5: Simple Single Line Diagram (SLD)

        (Source: https://www.adanisolar.com/Downloads)

        Out of above options let us assume we select 325Wp modules as modules to be used for our project.

        Hence Isc @45 Deg. C. = 9.40 + (9.40 x 0.0138) =

        ~9.53A

        Please remember Pm = Im x Vm and same calculation are to be done for Vm and Im instead Voc and Isc to determine the loss in power due to rise in temperature.

        For the purpose of sizing of the system we are not going to consider above calculations in this method of sizing of system.

        Now,

        Total No. of Solar Modules required = System Size (DC)/Wp of Chosen Modules

        = System Size (DC)/Wp of Chosen Modules

        So Now, Parameters of selected modules are as follows

        • Wp = 325Wp

      Voc = 45.69V

      Vm = 36.81V

      Isc = 9.40A

      Im = 8.83A

      Temperature has vital effect on performance of PV modules. Output and life of PV modules have direct connection with the surrounding temperature, however for sizing of system we are not going to consider the effect of temperature in such method of sizing.

      Effect of Temperature

      Temperature has vital effect on performance of PV modules. Output and life of PV modules have direct connection with the surrounding temperature.

      All Solar Modules are tested at 25 Deg. C.

      With increase in temperature, Voltage of Module decreases and current increases. However, % decrease of V is higher than % increase of I hence overall power output decreases. Eg.

      For selected 325 Wp panel, performance of module at 45 Deg. C is expected as follows.

      Rise in surrounding temperature is 45 25 Deg. C. = 20 Deg. C

      Deduction in Voltage would be = 0.31% x 20 Deg.

      C. = 6.2%

      Rated Voc (@25 Deg. C.) = 45.87V

      Hence Voc @45 Deg. C = 45.87 (45.87 x 0.062)

      = ~43.03V

      Rise in surrounding temperature is 45 25 Deg. C. = 20 Deg. C

      Rise in Current would be = 0.069% x 20 Deg. C. =

        1. %

          Rated Isc (@25 Deg. C.) = 9.40A

          = 4000Wp (DC)/325Wp

          = ~12.31 Nos.

          Here

          If we select 12nos of 325Wp modules total system size would be = 325Wp x 12 = 3900Wp = 3.9kWp

          And

          If We select 13nos of 325Wp modules total system size would be = 325Wp x 13 = 4225Wp = 4.225kWp

          In practical scenario the selection of number of modules depends on various factors like

          1. State policy

          2. Space available

          3. Energy required

          4. Budget

          5. Designers ideology

      Here for sake of calculations we select 13nos of 325Wp panels and hence our updated system size would be 13nos x 325Wp = 4.225kWp

      Step 2: Inverter Selection

      (Souce: https://ksolare.com/product-4/)

      For On-Grid Systems, generally the DC capacity and AC capacity (of inverter) are very much similar.

      Hence here we shall look for inverter which can take min. 4.225kWp (DC) input.

      Looking at datasheet, 4.0kW inverter (Model: KSY 4kW) has Max Peak DC Input Power of 4.8kWp and hence that inverter serves the purpose.

      Here we select KSY 4kW inverter for our calculations and make note of important parameters next.

      Note: every single detail mentioned on datasheet are important however for the purpose of calculations and demonstration we shall focus on few as follows.

      • Nominal Input Power: 4kW

      • Nominal AC output power: 4kW

      • Max Peak DC Input Power: 4.8kW

      • Max Peak Output Power: 4.4kW

      • MPPT Tracking Voltage: 100-500V

      • Max output current AC: 19.1A

      • Min. Start Voltage: 120V

      • No. of MPPT Trackers: 2

      • Strings per MPPT Trackers: 1

      • Max MPPT I/P Current: 10A

      • MPPT Short Circuit Current: 15A

      One of the most important point in datasheet is to identify the maximum DC input that can be connected to Inverter, and this detail can be decided based on

      No. of MPPT Trackers and Strings per MPPT

      (Source: https://www.indiamart.com/proddetail/ksolar-15kw-3-phase- solar-grid-tie-inverter-22785960633.html)

      Inverter with 2 MPPTs and 1 string in each MPPT Total possible string connection: 2

      Tracker

      No. of Total Inputs (Total Strings) Available

      = No. of MPPT Tracker x Strings per MPPT Tracker

      in our case

      No. of Total Inputs (Total Strings) Available

      = 2 x 1 = 2.

      (Source: https://ksolare.com/)

      Inverter with 2 MPPTs and 1 string in each MPPT, Total possible string connection: 2

      (Source: https://vhil.in/ksolare-2-kw-single-phase-solar-on-grid-inverter/)

      Inverter with 1 MPPTs and 2 strings in each MPPT Total possible string connection: 2

      (Source:https://www.deyeinverter.com/product/three-phase-string- inverter/sun30-33-35-40-50kg03.html)

      Inverter with 4 MPPTs and 4 string in each MPPT Total possible string connection: 16

      Step 3: Strings & Arrays of Modules

      For On-Grid Systems we try to keep voltage of DC and AC as high as possible (with in inverter and grid permissible limits).

      Hence here we shall try to make as many series connection as possible among the modules since in series connections voltage adds up.

      Remember:

      Series connction of any electrical component is known as STRING

      &

      Parallel connection of any electrical component is known as ARRAY

      Max. No. of Modules in a Series

      = Max. MPPT (I/P DC) Voltage of Inverter/Voc of Module

      = 500/45.69

      = 10.94

      =~ 10 (Always Round Down)

      AC SPD Rating = Type II

      DC Cable

      As per government regulations, DC Cable must be minimum 4sq.mm.

      Hence here we shall consider Cu. 1C 4sq.mm. DC Cable

      No. of Strings (Input to Inverter)

      = Total No. of Modules/Max. No. of Modules per string

      = 13/10

      = 1.3

      = ~ 2 (Always Round Up)

      Hence arranging 13 modules in 2 strings

      = 13/2

      Hence arranging 13 modules in 2 strings

      = 13/2

      S1 = 7 Modules S2 = 6 Modules Or

      S1 = 6 Modules S2 = 7 Modules

      Step 4: Calculations of BOS SPDs

      There are mainly three types of SPDs as follows

      Type I Permanently Connected, Hard-Wired, intended for installation between secondary of the service transformer and line side of main service equipment.

      Type II Permanently Connected, Hard-Wired, intended for installation on load side of the main service equipment Type III Called Point of Utilization SPDs, to be installed at a minimum conductor length of 10 meter from electrical service panels.

      DCDB (DC Fuse, DC MCB, DC SPD)

      Ratings of DC Fuse and DC MCB

      = Isc (of string) x 1.25

      = 9.4A x 1.25

      = 11.75A

      =~15A

      Hence

      DC Fuse Rating = 15A

      DC MCB Rating = 15ADC SPD Rating = Type II

      ACDB (AC Fuse, AC MCB, AC SPD)

      Ratings of AC Fuse and AC MCB

      = Imax (AC output of Inverter) x 1.56

      = 19.1A x 1.56

      = 29.796A

      =~30A

      Hence

      AC Fuse Rating = 30A AC MCB Rating = 30A

      (Source: https://deekayelectricals.com/polycab-solar-dc-cable/)

      AC Cable

      Core of AC is determined based on AC-Phase output of inverter

      i.e.

      1. Phase output 2 Core AC Cable 3-Phase output 4 Core AC Cable

        Here since our inverter is single core, we should consider Cu 2C sq.mm. AC Cable

        (Source: https://pdf4pro.com/view/details-make-the-difference- indiancables-net-5b17c3.html)

        In above table

        Look into column of Current Ratings. Look into In Air

        Find out AC output current of inverter in that column i.e. 19.1A

        Keep eye on that raw and look into first column of that corresponding raw.

        In our case that Ans is 4

        Hence our AC Cable would be Cu 2C 4 sq.mm. AC Cable

        Step 5: Single Line Diagram

  4. CRITERIA FOR SELECTION OF MODULE

    • Cost: What is the rate in terms of Rs. per Watt?

    • Power: Range OR Specific?

    • Size: (Mono/ Poly-crystalline silicon) 60 OR 72 Cell OR smaller?

    • Type: Mono/ Poly-crystalline silicon OR thin-film?

    • Bypass Diodes in Junction Box: 3 OR 6 OR 12 OR other?

    • IEC Certification available?

    • Warranty on Performance and Workmanship available?

Important Parameters of PCU

  • DC Nominal and Maximum Power

  • Efficiency Maximum and European

  • Total Harmonic Distortion (THD)

  • MPPT Range

  • Aux. power consumption

  • Grid voltage and frequency tolerances

  • Protection Features

  • Ingress Protection (IP) rating

  • Operating range of temperature

  • Dimensions and Weight

  • Remote & Local controlling and monitoring

VI. REFERENCES

  1. Adanisolar.com. 2021. [online] Available at:

    <https://www.adanisolar.com/Downloads> [Accessed 8 May 2021].

  2. KSolar. (2021, May 3). Solar Inverter Manufacturers in India. KSolar | Indias Best Solar Inverter Manufacturer. https://ksolare.com/product-4/

  3. KSolare.com. 2021. [online] Available at:< https://ksolare.com/> [Accessed 8 May 2021]. https://ksolare.com/

  4. No Name (2021) https://vhil.in/ksolare-2-kw-single-phase-solar- on-grid-inverter/, Available at: https://vhil.in/ksolare-2-kw-single- phase-solar-on-grid-inverter/ (Accessed: 08th May 2021).

  5. No Name (2021) https://www.indiamart.com/proddetail/ksolar- 15kw-3-phase-solar-grid-tie-inverter-

    22785960633.html, Available

    at: https://www.indiamart.com/proddetail/ksolar-15kw-3-phase- solar-grid-tie-inverter-22785960633.html (Accessed: 08th May 2021).

  6. No Name (2021) https://www.deyeinverter.com/product/three- phase-string-inverter/sun30-33-35-40-50kg03.html, Available

    at: https://www.deyeinverter.com/product/three-phase-string- inverter/sun30-33-35-40-50kg03.html (Accessed: 08th May 2021).

  7. No Name (2021) https://deekayelectricals.com/polycab-solar-dc- cable/, Available at: https://deekayelectricals.com/polycab-solar- dc-cable/ (Accessed: 08th May 2021).

  8. No Name (2021) https://pdf4pro.com/view/details-make-the- difference-indiancables-net-5b17c3.html, Available

    Payment terms: How much advance? Delivery time: Readily available or months? Reputation and Bankability of Manufacturer

    [9]

    V.

    CRITERIA FOR SELECTION OF INVERTER

    Payment terms: How much advance? Delivery time: Readily available or months? Reputation and Bankability of Manufacturer

    [9]

    V.

    CRITERIA FOR SELECTION OF INVERTER

    at: https://pdf4pro.com/view/details-make-the-difference- indiancables-net-5b17c3.html (Accessed: 08th May 2021). GERMI (2016) 26. Component Selection and Sizing, 1 edn., Gandhinagar: Presentation.

    Main Components of PCU

    • IGBTs

    • Gate Driver Cards

    • Snubber Capacitors & Discharge Resistors

    • Heat sink with blower fans

    • DC Bus Capacitor

    • L-C-L Filter

    • Grid Synchronizing Contactor

    • DC and AC Isolators

    • Fuses for DC inputs

    • Cabinet and L-C-L filter cooling fans

    • Transformer (Only for PCUs with transformer isolation)

    • EMI & EMC Filters

    • Surge Protection Devices (SPDs)

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