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7/31/2019 Distributed Generation Solar PV
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RENEWABLE ENERGY EDUCATION PROJECT
Grid-Connected Solar PV SystemDesign and Installation
Distributed Generation Solar PV
Ahmed O BAGRE
June 2009
KNUST SHORT COURSES PROGRAMME
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Part 1: Electricity fundamental
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Part 1 Learning Objectives
Explain water analogy applied to electricity
Compare AC and DC electrical current andunderstand their important differences
Explain the relationship between volts, amps,amp-hours, watts, watt-hours, and kilowatt-hours
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Hydraulic circuit
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Electrical circuit
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Pressure and Voltage
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Q = Q1 = Q2P = PT1 + PT2
I = I1 = I2U=U1 + U2
Resistances in series
T1
T2
R1
R2
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Resistances in parallel
T1 T2R1 R2
Q = Q1 + Q2PT1 = PT2 = P I = I1 + I2
UR1 = UR2 = U
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Synthesis: Water –
Electricity analogy
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Electricity Terminology Resistance (Ω)
The opposition of a material to the flow of anelectrical current
Depends on
Material
Cross sectional area
Length
Temperature
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Electricity Terminology
• L: Length (m)
• : Resistivity depending oncable material ( /m/mm²)
- cu = 0.0183 /m/mm² for copper (Cu)
- alu =
•A:Cross section area (mm²)
Resistance
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Electricity Terminology Voltage (E or V)
Unit of electromotive force
Can be thought of as electrical pressure
Ohm’s Law• V: Voltage (V)
• R: Resistance ( )
•I:Current flow (A)
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Electricity Terminology
Amps (I or A) Rate of electron flow
Electrical current
1 Amp = 1 coulomb/second = 6.3 x 1018
electrons/second
• V: Voltage (V)
• R: Resistance ( )
•I:Current flow (A)
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Electricity Terminology Watt (W) are a measure of Power
Amps x Volts = Watts
1 Kilowatt (kW) = 1000 watts
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Electricity Terminology
Watt-hour is the unit of Energy
Amp x Volts x hours = Watt-hours
1 Kilowatt-hour (kWh) = 1000 watts-hour (wh)
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Electricity Terminology Amp-hour (Ah)
Quantity of electron flow
Used for battery sizing (capacity) Amps x hours = Amp-hours
Amp-hours x Volts = Watt-hours
A 200 Ah Battery delivering 1A will last _____ hours
200 Ah Battery delivering10 A will last _____ hours 100 Ah Battery x 12 V = _____ Wh
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Types of Electrical Current
DC = Direct Current
PV panels produce DC Batteries store DC
AC = Alternating Current
Utility power Most consumer appliances
use AC
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Energy Conversion
Conversion efficiency
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Energy conversion
sun
Energy input
Solar irradiance1000 W/m²
Converter
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Part 2: BASIC OF PHOTOVOLTAIC
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Part 2 Learning Objectives
Learn how a PV cell produces electricity from
sunlight
Discuss the 3 basic types of PV cell technologies
Understand the effects of cell temperature and
solar insolation on PV performance Gain understanding of module specification
Identify the various parts of a module
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Utilisations indirectes de l’énergie thermique solaire (production de vapeur pour
l’entraînement d’un alternateur grâce à une turbine à vapeur
UTILISATIONDIRECTE DES
RAYONNEMENTSSOLAIRES
CENTRALE
ELECTRIQUE PHOTOVOLTAIQUE
SOLAIREPHOTOVOLTAIQUE
SOLAIRETHERMIQUE
CHAUFFAGE DESBATIMENTS
CUISINIERESOLAIRE
SECHOIR SOLAIRE PRODUCTION DEVAPEUR D’EAU
CENTRALEELECTRIQUE
THERMODYNAMIQUE
CLIMATISATIONSOLAIRE
SOLAIRE PASSIF
CHAUFFE EAUSOLAIRE
1
2
1 Utilisations directes de l’énergie thermique solaire
2
SOLEIL
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Got Sun?
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Solar Energy Has Great Potential
80,000 Terawatts of Solar Power fall on the Earth constantly
Compare to 14.5 Terawatts current human power use
Every country has it
No one can embargo it or raise the price
As an alternative to fossil fuels, solar energy reduces air
and water pollution and global warming
It’s becoming more and more cost effective, especially
when you include these ‘external’ costs
Already the best value in remote areas
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What is a solar cell? Solid state device that converts incident
solar energy directly into electrical energy
Efficiencies from a few percent up to 20-30%
No moving parts
No noise
Lifetimes of 20-30 years or more
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Cross Section of Solar Cell
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How Does It Work? The junction of dissimilar materials (n and p type
silicon) creates a voltage
Energy from sunlight knocks out electrons, creatinga electron and a hole in the junction
Connecting both sides to an external circuit causes
current to flow In essence, sunlight on a solar cell creates a small
battery with voltages typically 0.5 V. DC
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Available Cell Technologies Single-crystal or Mono-crystalline Silicon
Polycrystalline or Multi-crystalline Silicon
Thin film
Amorphous silicon
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Monocrystalline Silicon Modules
Most efficient
commercially available
module (11% - 15%)
Most expensive to
produce
Circular (square-round)
cell creates wasted
space on module
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Polycrystalline Silicon Modules Less expensive to make
than single crystalline
modules
Cells slightly less
efficient than a single
crystalline (10% - 12%)
Square shape cells fitinto module efficiently
using the entire space
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Amorphous Thin Film
Most inexpensivetechnology to produce
Metal grid replaced withtransparent oxides
Efficiency = 6 – 8 %
Can be deposited onflexible substrates
Less susceptible toshading problems
Better performance in lowlight conditions that withcrystalline modules
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Photovoltaic terminology:
Cell to Array
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Photovoltaic therminology
Solar cells(0.5V)
(0.3 - 2 watt) Modules(10-300 Watt)
Array (largest area > 5 MW)
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Standard Test Conditions (STC)
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Current-Voltage (I-V) CurveMaximum Power
(Vco: Open circuit voltage)
(Short circuit current)
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Terminology Isc: Short circuit current, maximum current a module
can produce under given conditions (V= 0; P=0)
Voc: Open circuit voltage, maximum voltage under
given conditions (Isc = 0; P= 0) Imp: Current that results in maximum power under
given condition (V= Vmp; P = Pmp)
Vmp: Voltage that results in maximum power under
given condition (I= Imp; P = Pmp) Pmp = Imp x Vmp
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Effects of irradiance As insolationdecreases:
• Current decreases
• Voltage dropsslowly
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Effects of irradiance
Example: The module MSX-83 from BP Solar has a rated Isc of 5.27 A at STC. What will be the Isc at 800 W/m²?
- STC irradiance is 1000 W/m² = G1- G2 = 800 W/m² - ISC1 = 5.27A- ISC2 = ?
• Isc is directly proportional to irradiance
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Effects of irradiance
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Effects of Temperature
As the PV cell temperature
increases:
The current increases
slightly
The voltage decreases, the
change of voltage is
directly proportional to
temperature rise
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Effects of temperature
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Effects of temperature
Voltage change
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Effects of temperature
Voltage change example 1 : The module SM55 from
Siemens has at STC Vmp of 17.3 V. If the module operates outdoor and heat up to 50°C, the Vmp at 50°C will be:
ΔV(50°C) = - 0.079 V/ °C x (50 - 25)
= - 1.975 V
Vmp (50°C) = 17.3 - 1.97
= 15.325V
15.325 V is still enough to fully charge a typical "12 volt" battery that actually needs up to 15 volts to reach full
charge. 43
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Effects of temperatureVoltage change example 2 : The module POLY 175 from SCHOTT Solar has at STC Vmp of 44.3 V. Find out the Voc at 50°C.
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Effect of temperaturePower change
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Effects of temperature
Power change Example 1: The module SM55 from Siemens has at STC Pmax of 55 W. If the module operates outdoor and heat up to 50°C,the Pmax at 50°C will be:
Power change ΔP(50°C) = - 0.255 W/ °C x (50 - 25)
= - 6.375W
Pmax (50°C) = 55 - 6.375
= 48.625 W
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Effects of temperaturePower change Example 1 : The module POLY 175 from SCHOTT Solar has at STC Pmax of 175 W. Find out the Pmax at 50°C.
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Orientation and Tilt Angle
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Site Selection –
Tilt AngleBest annual performance:
• Orientation: South
• Tilt angle : Latitude of thesite
Azimuth:
• South : 0°
• North : 180Max performance is
achieved when panels
are perpendicular to the
sun’s rays
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Part 3: Modules connection
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Part 3 Learning Objectives List the characteristics of series circuits
List the characteristics of parallel circuits
List the characteristics of series/parallel circuits (mix-
circuits)
Understand the shading effects on modules
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Series Connections
Loads/sources wired in series
VOLTAGES ARE ADDITIVE
CURRENT IS EQUAL
One interconnection wire is usedbetween two components (negativeconnects with positive)
Combined modules make seriesstring
Leave the series string from aterminal not used in the seriesconnection
Principle
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Series Connections:
Electrical circuit
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Series Connections:Curve I(V)
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Parallel Connections
Loads/sources wired in parallel: VOLTAGE REMAINS CONSTANT
CURRENTS ARE ADDITIVE
Two interconnection wires are used between twocomponents (positive to positive and negative tonegative)
Leave off of either terminal
Modules exiting to next
component can happenat any parallel terminal
Principle
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Parallel ConnectionsElectrical circuit
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Parallel Connections
Curve I(V)
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Series/Parallel Connections
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Series/Parallel Connections
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Series/Parallel Connections
The module MSX-83 from BP solar is used in the following configuration to make a PV array:
4 modules in series 2 strings (of 4 modules in series) in parallel
The electric characteristics at STC are given below: Maximum power (Pmax) = 83W Short-circuit current (Isc) = 5.27A Voltage at Pmax (Vmp) = 17.1V
Open-circuit voltage (Voc) = 21.2V Current at Pmax (Imp) = 4.85A
What will be the electric characteristics of the PV array?
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Ns = 4 ⇒ VTmp =17.1V x 4 = 68.4 V and VTOC = 21.2Vx4= 84.8V
Np = 2 ⇒ ITmp = 4.85A x 2 = 9.70A and ITSC = 5.27A x 2 = 10.54A
PTmax = VTmp X ITmp = 68.4 x 9.70 = 663.48 W
PTmax = Pmax X 8 = 83 x 8 = 664 W
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Series/Parallel Connections For PV array, the electric characteristics are:
Maximum power (Pmax) = 664W Short-circuit current(Isc) = 10.54A
Voltage at Pmax (Vmp) = 68.4V Open-circuit voltage(Voc) = 84.8V
Current at Pmax (Imp = 9.70A.
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Series/Parallel Connections
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Quiz TimeIf you have 4 module of 12V / 3A in an array what
would the power output be if that array were
wired in series?
What if it were wired in parallel?
Is it possible to have a configuration that would
produce 24 V / 6 A? Why?
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Dissimilar modules in series Voltage remains additive
If module A is 30V / 6A and module B is 15V / 3A the
resulting voltage will be?
Current taken on the lowest value
For modules A and B wired in series what would be
the current level of the array?
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Dissimilar Modules in Parallel Amperage remains additive
For the same modules A and B what would the voltagebe?
Voltage takes on the lower value.
What would the voltage level of A and B wired in
parallel be?
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Shading on Modules Depends on orientation of internal module
circuitry relative to the orientation of the shading.
SHADING can half
or even completely
eliminate the output
of a solar array!
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Part 4: Photovoltaic System
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Part 4: Learning Objectives
Understand the functions of PV components
Identify different system types
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Direct coupled system
• No storage (batteries)
• Needs MPPT to maximize the energy feed par the PV generator
• Operates only during sunlight hours
• Better for water pumping, refrigeration system
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Standalone system
Battery – stores DC energy Charger/Controller – senses battery
voltage and regulates charging Inverter – converts direct current (DC )
energy to alternating current (AC) energy Loads – anything that consumes energy
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Hybrid System DC Bus
• Diesel generator cannot supplythe load directly
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Hybrid System AC Bus
• Flexible system with modular components• PV and Diesel Generator can worksimultaneously• Battery to increase the availability ofenergy
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Grid-Tied System(Without Batteries)
Complexity
Low: Easy to install(less components)
Grid Interaction
Grid cansupplement power
No power whengrid goes down
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Part 5: BATTERIES
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Part 4: Learning Objectives
Battery basics
Battery functions
Types of batteries
Charging/discharging
Depth of discharge
Battery safety
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Batteries in Series and Parallel Series connections
Builds voltage
Parallel connections Builds amp-hour capacity
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Battery Basics
Battery
A device that stores electrical energy (chemical energy to electrical
energy and vice-versa)
Capacity
Amount of electrical energy the battery will contain
State of Charge (SOC)
Available battery capacity
Depth of Discharge (DOD)
Energy taken out of the battery
Efficiency
Energy out/Energy in (typically 80-85%)
The Terms:
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Functions of a Battery
Storage for the night
Storage during cloudy weather
Portable power
Surge for starting motors
**Due to the expense and inherit inefficiencies of batteries it isrecommended that they only be used when absolutely necessary (i.e.in remote locations or as battery backup for grid-tied applications ifpower failures are common/lengthy)
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Batteries: The Details
Primary (single use)
Secondary (recharged)
Shallow Cycle (20% DOD)Deep Cycle (50-80% DOD)
Types:
Unless lead-acid batteries are charged up to 100%, they will
loose capacity over time
Batteries should be equalized on a regular basis
Charging/Discharging:
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Rate of Charge or Discharge
Rate = C/T
C = Battery’s rated capacity (Amp-hours)T = The cycle time period (hours)
Maximum recommend charge/discharge rate = C/3to C/5
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Cycle Life vs. Depth of Discharge
Depth Of Discharge (DOD) %
# of Cycles
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Part 6: Controllers and inverters
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Part 5: Learning Objectives Controller basics
Controller features
Inverter basics
Specifying an inverter
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Controller Basics
To protect batteries from being overchargedFunction:
Maximum Power PointTracking
– Tracks the peak
power point of the
array (can improve
power production by
20%)!!
Features:
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Additional Controller Features
Voltage Stepdown Controller: compensates for differingvoltages between array and batteries (ex. 48V array
charging 12V battery)
By using a higher voltage array, smaller wire can be
used from the array to the batteries Temperature Compensation: adjusts the charging of
batteries according to ambient temperature
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Other Controller Considerations
When specifying a controller you must consider:
DC input and output voltage
Input and output current
Any optional features you need
Controller redundancy: On a stand-alone system it might
be desirable to have more then one controller per array in
the event of a failure
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Inverter Basics
An electronic device used to convert direct current
(DC) electricity into alternating current (AC) electricity
Function:
Efficiency penalty
Complexity (read: a component which can fail)
Cost!!
Drawbacks:
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Specifying an Inverter
What type of system are you designing? Stand-alone Stand-alone with back-up source (generator) Grid-Tied (without batteries) Grid-Tied (with battery back-up)
Specifics: AC Output (watts) Input voltage (based on modules and wiring) Output voltage (120V/240V residential) Input current (based on modules and wiring)
Surge Capacity Efficiency Weather protection Metering/programming
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The sun is the primary energy source for almost all energy flows on the planet. It’s time
we started using it.