SOLAR SIZING

BYPREMKUMAR E

Sizing – Major Parameters

■ Availability of Load.

■ Availability of Shadow free Area.

■ Climatic Conditions.

■ Availability of products.

■ Site Survey.

■ Cost of Project.

Client Requirement Technology Selection

Electrical Design Layout and Shading

The PV System Design

Technology Selection Solar PV Panel

■ PV Panels converts sunlight directly into electricity. PV gets its name from the process of converting

light (photons) to electricity (voltage), which is called the PV effect.

■ Types

– Multi/Poly Crystalline Modules (Efficiency of 14%-16%)

– Mono Crystalline Modules (Efficiency of 15% -17%),High Efficiency Cell (17% to 20%)

– Thin Film Modules (Efficiency of 10%-12%)

■ It is always selected based upon site and client requirement.

■ Temperature coefficient of power plays an important role in hot climates.

■ PV panels will generate its Rated power (As Mentioned in Datasheets) only at Standard Test

Condition (STC).

Efficiency of the Solar PV Module

■ High efficiency doesn’t mean better, it just means your panels use less space on your roof.

■ Efficiency isn’t usually a critical concern unless you have an enough space on your roof to install

PV Panels.

■ The most efficient solar panels cost a little more, so they’re a less common choice.

■ When the Efficiency of the Solar panel is high means the area required to achieve Required

power will be less

■ Example : I am Considering 38.4 kWp System with 120 Nos of 320Wp Modules

■ PV Module 1 - 320Wp with 19.60% Efficiency

■ PV Module 2 - 320Wp with 16.47% Efficiency

Modules with 19.6% Modules with 16.47%

Inverter Selection

■ Inverter capacity selected based on Solar PV Panel capacity.

■ First, determine the PV array’s location. The available area for the modules, shading issues, the

need for using multiple roof orientations, These site limitations will also play a role in determining

what inverter is appropriate for your location.

■ PV arrays produce less than their STC rating, due mostly to conditions that differ from STC—like higher

cell temperatures, lower irradiance, and module soiling.

■ When predictable system losses are taken into account, a PV array expect to operate at around 70% to

80% of the STC rating, So the size of the PV array can be designed to exceed the inverter’s power rating.

■ Many inverter manufacturers specify simply that a PV array’s STC rating should be no more than 125% of

the inverter’s continuous output rating - known as the “sizing ratio”.

■ Sizing Ratio = DC Capacity / AC Capacity = 37.5 kWp / 30 KW = 1.25

■ For utility-scale power plants, central inverters are preferred over String Inverters.

■ For different module specification, string inverters are recommended for minimizing

the mismatch losses.

■ For sites with different shading conditions or orientations, string inverters are more

suitable.

■ In cases where the panels are all oriented and angled the same way, Central

inverters offer the best optimal production with lower DC Watt unit cost.

Inverter Selection

String Inverter Advantage (Avoiding Mismatch Losses)

Losses Associated with Solar PV System

Pre Photovoltaic Losses

Module and Thermal Losses

System Losses

Reflection Loss

Soiling Loss Losses due to Shadow

Conversion Loss

Thermal Loss

Loss due to Irradiation

Wiring Loss Inverter Loss

Transformer Loss

Mismatch Losses

Sample DC and AC Cable Loss Calculation

DC Voltage Drop Calculation

DC Side Voltage Drop should be maintained Less than 2%

Example :

• Voltage of the system = 730V

• Current of the system = 8.22A

• Resistance of 4Sqmm Cu Cable = 5.090 Ohm/Km

• Distance between PV Array and Inverter = 180Meter

• Voltage Drop (V= I x R) = (I x L x 2 x R)/1000= (8.22 x 180 x 2 x 5.090)/1000 = 15.06V

• Voltage Drop in % = (15.06/730) *100 = 2.063% ( Which is greater than 2 %)

• Resistance of 6Sqmm Cu Cable = 3.390 Ohm/Km

• Voltage Drop (V= I x R) = (I x L x 2 x R)/1000= (8.22 x 180 x 2 x 3.390)/1000 = 10.031V

• Voltage Drop in % = (10.031/730) *100 = 1.374% ( Which is Less than 2 %)

AC Voltage Drop Calculation

AC Side Voltage Drop should be maintained Less than 3%

Example :

• Full Load Current = 152 A

• Resistance = 0.198

• Power Factor = 1 (Unity)

• Reactance = 0.0744

• SinQ = 0.6

• Length = 300 Mtr

• Line Voltage = 400V

• Voltage Drop= 1.732 x (Current)x(RCosØ+j SinØ)xLengthx100) / Line VoltagexNo of Runx1000

• Voltage Drop in % = (1.732 x 152 x (0.198x1 + 0.0744x0.6)x300x100)/415x1x1000 = 2.30%

Layout and Shading

■ The PV Module Layout helps us to arrive Total PV Capacity can be installed, cable length

and What kind of Module Mounting structure can be used.

■ A Shadow from a pipe, tree or any other object that comes between the sun and PV

system decreases the power Output.

■ The continuous shadow will create a Hotspot and damage the PV Modules.

■ If the rows of tilted modules are too close to each other, one row will cause a shadow on

the next, causing additional losses. If the modules are spaced out a lot, there are fewer

shadows, but that comes at the cost of space optimization.

Shadow Caused by Water tank

How The Shadow Affects Panel Output

Case-1 (Power Output = 100%) Case-2 (Power Output = 66%)

Case-3 (Power Output = 33%) Case-4 (Power Output = 0%)

Module Inter-row Shadow

Case-1

Case-2

Output power = 0 %

Output power = 66 %

Weight and Space Occupied by PV System.

■ Area Required (1 kWp) – Multi And Mono Crystalline Modules

Rooftop - 90 to 110 Sq.Ft

Sheet Roof – 75 to 90 Sq.Ft

■ The mounting structure should be designed to handle cyclones where wind speeds can reach 100 to 200 km/

■ Rooftop plants weight – 4.5 to 5 kgs/Sq.Ft (Module, Structures , PCC Foundation)

– Elevated Structure - 8 to 10 kgs/Sq.Ft (Module, Structures , PCC Foundation)

■ Sheet Roof weight – 2.5 t0 3 kgs /Sq.Ft (Module, Structures )

IEC Standard to be followedSystem Standard Standard Description

SPV Modules

IEC 61215 "Design qualification and type approval” includes the examination of all parameters which are responsible for the ageing of PV modules.

IEC 61730 “Photovoltaic (PV) module safety qualification” has been issued to further examinations about the PV modules safety against electrical

shock hazard, fire hazard, mechanical and structural safety.

IEC 61701 IEC 61701 has been issued for testing the salt mist corrosion with sodium chloride moisture

Inverters

IEC 61683 Procedure for Measuring EfficiencyIEC 60068 Environmental testing

IEC 62116 Test procedure to evaluate the performance of islanding prevention measures used with utility-interconnected PV systems.

IEC 62109 Safety of power converters for use in photovoltaic power systems

Junction Box/Enclosure for Inverter IEC 529 Classifying the degrees of protection provided by the

enclosures of electrical equipment, IP 54 for Outdoor, IP 21 for Indoor.

Cables IEC 60502

This specification covers single core cables and three core armoured or

unarmoured cables, Which tests Insulation, Armour, Sheath and Assembly

How To Decide Capacity of Gridtie System.

■ Space available for SPV Installation.– Rooftop - 90 to 110 Sqft per kWp– Sheet Roof – 75 to 90 Sqft per kWp

■ Electricity Usage

■ Load Details– Base Load– Peak Load

■ Case :1 = Enough Roof Space to Install -100kWp, But the base load is around 60kW, Net Metering is not

applicable. – PV Capacity should be based on Base LOAD only.

■ Case :2 = Enough Roof Space to Install – 40 kWp, But the base load is around 60kW, Net Metering is

applicable - PV Capacity should be based on Free Space availability.

■ Case :3 = Enough Roof Space to Install -100kWp, Base load is around 250kW, Net Metering is applicable.

But the Client Requirement is 50kWp - PV Capacity should be based on Client Requirement.

Load vs System Sizing

• Base Load is = 40KW

• Injecting power into Grid is not

allowed

• Enough Roof Space to Install

50kWp System

• PV Capacity sized based on

Base Load & Space Availability

• PV System Capacity = 36kWp

Site Inputs ReceivedSITE INPUTS

• Total PV Capacity required = 36 kWp

• Roof Space Available = 31 Mtr x 15.9Mtr(Shadow

Area)

• SPV to Inverter Distance = 30 Mtr

• Inverter to Existing LT Panel Distance = 80 Mtr.

• Earthing Conductor Required = 40 Mtr

• Spare Feeder Available- Yes 100A

• Inverter Placement on roof.

PV Panel Layout

Designing of Grid tied System

■ The maximum Voc in the coldest daytime temperature must be less than the inverter

maximum DC input voltage.

– VOC < Inverter Max DC Voltage

■ The Minimum Vmp in the hottest daytime temperature must be greater than the minimum

MPPT range of Inverter.

– Vmp > Min MPPT range of Inverter.

■ The inverter must be able to safely withstand the maximum array current.

■ DC PV Array Capacity should Exceed 125% of Inverter output capacity.

Inverter SpecificationInput Side (DC) Output Side (AC)

Maximum DC Power – 37.5 kWp Rated Output Power - 30KVA

Maximum Input Voltage - 1000V Max Output Current - 50A

DC Voltage Range - 200-1000V Nominal Voltage - 3 Ph,400V

MPPT Voltage Range - 520V -800V AC Voltage Range – 400V (+/- 20%) – (320V-480V)

Number of MPPT- 2 Nos Nominal Frequency – 50Hz

Max Input current per MPPT – 30A Frequency - 45Hz – 55Hz

Total Input Current - 60A Power Factor @ Rated Power - Unity

Number of Input – 6 pair of MC4

Efficiency – 98.20%

Solar PV Panel Specification

■ Module Power – 300 Wp at STC

■ Type – Multi crystalline (HHV)

■ Output Tolerance of Power – 0/+4.99

■ Open Circuit Voltage – 45.5 V

■ Maximum Power Voltage – 36.5 V

■ Short Circuit Current - 8.65 A

■ Maximum power Current – 8.22 A

■ Cells per Module – 72 Nos

■ Bypass Diodes - 3 Nos

■ Efficiency– 15.44 %

■ Maximum System Voltage – 1000 V DC

Effect of Change in Temperature■ Minimum Site Temperature considered = 5 deg C

■ Maximum Site Temperature considered = 50 deg C

■ Maximum power voltage – Vmp of 300Wp is 36.5 V.

■ Temperature Coefficient of Vmp = -0.45%

■ 0.45% of 36.5 V is = 0.16425V

■ Change in Operating Voltage due to Temp rise(50 Deg) is = 50 – 25(STC)= 25 Deg

= 25 * 0.164 = 4.1V

= 36.5 - 4.1V = 32.4V

■ Open Circuit Voltage– Voc of 300Wp is 45.5 V.

■ Temperature Coefficient of Voc = -0.34%

■ 0.35% of 45.5 V is = 0.1547 V

■ Change in Operating Voltage due to Temp rise(50 Deg) is = 25(STC) – 5 = 20 Deg

= 20 * 0.1547 = 3.094V

= 45.5+3.094 = 48.594V

Change In Temperature Change In Irradiance

Single Line Diagram

■ Total PV Capacity Required = 36 kWp

■ Module selected to meet required Capacity = 300 Wp

■ Total Number of Modules required = 36000/300 Wp = 120

■ Minimum Number of Modules can be used in series = 520 V / 32.4V = 16.02 Nos

= 17 Nos.

■ Maximum Number of Modules can be used in series = 1000 V / 48.59V = 20.2 Nos

= 20 Nos.

■ To achieve desired capacity and to operate within MPPT range 20 nos Modules connected in

series

■ Total Number of Modules = 6 String x 20 Series = 120 Nos x 300Wp = 36kWp

PV Array Design

■ Number of MPPT per Inverter = 2 Nos

■ Total Number of strings = 6 Nos ( 3 Strings/MPPT ).

■ 3 String in 1st Mppt & 3 string in 2 MPPT.

■ Maximum String Current per MPPT = 8 x 3 =24 A (Inverter Capability-30 A/MPPT)

Balance of System SelectionMODULE MOUNTING STRUCTURES

■ Type of Structure

• RCC Roof (Normal/Elevated).

• Galvalume Shed.

• Ground Mount System.

• Material of the Structure ( Hot Dip Galvanised / Pre Galvanised Structures)

• Min Clearance between Roof/Ground to Panel.

AJB – ( 3 WAY IN / 3 WAY OUT) – 2 Nos

■ Fuse Rating/MCB.

■ Maximum Continuous Current = Short Circuit Current * 125 %

= 8.4 A * 125 %

= 10.5 A =12 A,

= 1000V,12A,2P Fuse/MCB.

DC Cables ( SPV Interconnection and SPV to AJB & AJB to INVERTER )

■ String Current – 8.5 A

■ String Voltage – 630 V

■ Minimum DC Cable Size should be used is 4 mm2

■ Current Carrying capacity of 4 mm2 Cable = 25 amps to 35 amps.

■ For Longer distance 6 mm2 Cable may be used to reduce DC Cabling Loss.

INVERTER to ACDB

■ Maximum Output Current from Inverter – 50 A

■ Current carrying capacity of Copper cable / Sqmm – 4 A/mm2

■ 50 A / 4 A = 12.5 Sqmm

■ Current carrying capacity of 16 Sqmm Copper Cable = 80 amps – 90 amps.

■ 4 C, 16 Sq.mm Flexible Copper Cable.

ACDB Switching

Maximum output Power = 50 A x 1.25 A continuous current

= 62.5 A = 63 A.

Preferably 4p 63 A,415 Vac MCB- 1 Nos

OFF GRID SYSTEM DESIGN

■ Load Calculation :

– Computer - 250W x 3 Nos x 4 Hours = 3000Wh

– CFL lamp - 20W x 10 Nos x 6 Hours = 1200Wh

– Fan - 60W x 5 Nos x 4 Hours = 1200Wh

– Television - 150W x 2 Nos x 4 Hours = 1200Wh

Total Load = 6600Wh /Day

■ Total Sun Hours Considered = 4 Hours

■ Total PV Capacity Required = 6600/4 = 1650 x 1.3 = 2145 Wp

■ Number of Modules Required = 2145/285 = 7.52 Nos = 8 Nos x 285Wp = 2280 Wp

■ Inverter Selected = Peak Load x 1.3 = 1550 x 1.3 = 2015W = 2KVA Inverter Selected.

■ Inverter Specification

– Max VOC = 180V.

– Min Vmp = 62 V.

– Battery Voltage = 48 Vdc.

■ Min Number of Panels can be connected in series = 62V/35.7V = 1.73 = 2 Nos

■ PV Array Configuration = 2 Panels in Series x 4 String = 8 Nos x 285Wp = 2280Wp

■ AJB Required = 4 In/1 Out

Battery Sizing vs Backup time

■ Backup time required = 4 Hours.

■ Total Load = 1550W

■ System Voltage = 48Vdc

■ Battery Sizing = Total Load x no of backup hours /(System Voltage x DOD x inverter Efficiency)

■ Battery = 1550 x 4 /( 48 V x 0.6 x 0.85) = 316 Ah =300 Ah

■ Required Battery = 48 V,300 Ah ( 12 ,150 Ah -8 Nos)

Single Line Diagram of Off Grid System

Battery DOD vs Life Cycles

THANK YOU