STAND-ALONE PHOTOVOLTAIC SYSTEMCOMPONENTS

• Objective– to know components (balance of system) required to design

stand alone system

• Learning Out come :–After this lecture, you will be able to…

Identify components required during design of stand alone system

Know Working principle and types of inverter , maximum power point tracker

Know storage type (battery) required for stand alone system , their type and characterstics

Know general lay out of installation , protection , distribution box , etc

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Learning Out come :

• Appreciate application areas of PV system• Design stand alone Pv system for single home,

institutions (school, health center etc)• Know criteria in selection of pv module, battery, charge

controller and inverter• Explain different types of inverter based on out put wave

form• Regarding batteries DOD and SOC, gassing, sulphation

and stratification • Use of charge controller in stand alone Pv system

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Application of PV

• Photovoltaic cells and systems have a wide variety of applications, including

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Application of PV 4

Basic components stand alone5

Basic components grid connected6

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Thin film or amorphous solar photovoltaic

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Example of pv system9

basic components

• Module (Array)- the basic component that convert solar energy directly to electricity i.e. the very source of electricity

• Battery :where the energy from the module stored for later use

• Charge controller; the device which controls the energy produced by the module, the level of battery charge and energy consumed by the equipment

• Load ; energy consuming appliance ( TV, radio ,fridge ,computer etc)

• Inverter ; to convert DC to AC when required

• Connecting wires , combiner boxes and protective devices such as circuit breaker ,Dc and AC disconnect switch , fuse etc

solar PV system in Direct current

• the pv module produce Dc current and voltage and the battery stores DC

• This type of system generally works in very small Dc voltage ,12V,24Vor 48V. And primarily for Dc lighting and for Dc equipment with low energy requirement

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SPV with DC and AC12

• In order to use AC appliance with PV system we need DC to AC converter called Inverter.

1. Module /Array13

• Module/array is Electric generator in PV system• Electric characteristic of module

• all module specification is based on STC (standard test condition ) which is industry standard which allows to compare the performance of different module from different manufacturers. STC test is done at

In reality the working condition of the module is different fromSTC and the manufacturers give standard operating condition(SOC) data as well.

STC specification of some modules14

NOCT spec of some module15

1. Module /Array16

The electrical characteristics includes:• Pmax= maximum power the module can produce at MPP• Imax= maximum current at MPP • Vmax= maximum voltage at MPP• Voc= open circuit voltage• Isc= short circuit current

1. Module /Array17

• Choosing module ; the following points have to be taken into account when choosing /buying module

• Module characteristics and application- check module IV curve rather than data

• Warranty – usually 20-25 year • Cost per watt• Module certification

Series connected modules 18

Parallel connected modules19

Series-parallel connected modules

• In high power applications, the array usually consists of a combination of series and parallel modules for which the total I –V curve is the sum of the individual module I –V curves.

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2. Batteries

• Used to store electricity generated by module during the day time to be used by appliance during night time or cloudy days.

• Most sensitive part of spv system and needs the most care and attention

• Its life time is 2-8 years and after which needs replacement –therefore represent the highest cost the user will have over the life time of the system

• There are many types of batteries potentially available for use in stand-alone PV systems, including lead-acid, nickel-cadmium, nickel-metal-hydride, rechargeable alkaline manganese (RAM), lithium-ion, lithium-polymer and redox batteries

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Common batteries in pv system22

Battery (lead acid)23

Type of Lead-acid Batteries24

battery25

Profile of Battery Voltage26

Indicator of State Of Charge27

Charging Efficiency28

2. Batteries

• Among the many possible battery technologies, it is the lead-acid battery that continues to be the workhorse of PV systems.

• Battery maintenance can be a major limitation for stand-alone PV systems.

• Typical requirements for a battery system to be used for long term storage are:

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2. Batteries

• Conventional car batteries (SLI) are not designed for deep discharge; therefore, they are inappropriate for PV systems.

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2. Batteries

• EfficiencyBattery efficiency can be characterized as follows:

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Battery energy efficiency 32

2. Batteries 33

• Power rating and capacity

• At the other extreme, • however, high temperatures accelerate aging,

selfdischarge and electrolyte use. • The battery capacity is measured in kilowatt-hours (kWh)

or ampere-hours (Ah), at a constant discharge rate. • The rate of discharge affects capacity

• Battery capacity is affected by temperature, falling by about 1% per degree below about 20°C.

• At the other extreme, however, high temperatures accelerate aging, self-discharge and electrolyte use.

2. Batteries 34

• Depth of discharge(DOD) / state of charge (SOC)• Depth-of-discharge is the percentage of the rated

capacity withdrawn from the battery. Shallow cycling batteries should not be discharged more than 25% of rated, while up to 80% of the capacity of deep cycling batteries may be discharged

Sate of charge =1-DOD

Lead Acid batteries35

• A lead acid battery consists of a negative electrode made of porous lead and a positive electrode which consists of lead oxide.

• Both electrodes are immersed in a electrolytic solution of sulfuric acid and water.

Lead Acid batteries36

Gassing :

Lead Acid batteries37

Type of Lead-acid Batteries38

Indicator of State Of Charge39

Cycle life40

Do you know? (Voltage)

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Lead Acid batteries42

• Impact of depth of discharge on number of cycles

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Grid connected PV44

Battery Capacity45

Stand alone or roof mount PV46

How to read capacity47

Battery capacity vs discharge rate48

Maintenance of Electrolyte( To keep Level )

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Maintenance of Electrolyte( To Prevent Stratification )

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Maintenance of Electrode( To Prevent Sulfation )

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Maintenance of Cell Voltage( To Equal voltage )

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Solar spectrum

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Parallel conection58

battery storage days59

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3. Charge controller61

• Charge controller placed between batteries and solar module . And have the following function;

3. Charge controller62

3. Charge controller

• :

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Charging phases of charge controller64

Charging phases of charge controller65

Type of Charge Controller66

Type of Charge Controller67

Types of charge controller68

Series and shunt charge controller69

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Steca mppt controller71

Electrical characteristics of charge controller

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Choosing charge controller73

Set point voltages74

Connecting Sequence to cc75

Additional functions of CC76

4. Inverter 77

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Type of inverter79

inverter80

Output Waveform of inverter81

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Characteristics of Typical lnverters83

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Inverter efficiency 85

Worldwide Annual Insolation86

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Continued..89

Choosing an inverter 90

Choosing an inverter 91

When to use inverter?92

Connection to inverter93

Single inverter plant (small plant)94

Plant with one inverter for each string95

Multi-inverter plant96

5. Lighting and appliance97

characteristics of different light98

Choosing appliances99

Choosing appliances100

Dc lights101

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Interconnection 103

For stand-alone PV systems the PV array charges the battery, and the battery provides dc power to the inverter which can produce ac power output at any time.

Interconnection 104

For simple interactive PV systems, the PV array is connected to the dc input of inverters, and there is no energy storage.

Selecting and sizing cables105

Selecting and sizing cables

• When sizing the cables, three essential criteria should be observed:

• the cable voltage ratings, • the current carrying capacity of the cable and • the minimizing of cable losses.

• With large PV systems and long module strings, the voltage rating of the cable should be checked, taking into account the maximum open-circuit voltage (at -10°C) of the PV string or array to which it is to be connected.

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Maintenance107

General Cleaning108

Measuring Points (Centralized)109

Common Troubles in a PV System110

Common Troubles in a PV System111

Troubleshooting Procedures112

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COSTS ESTIMATE AND PRICING115

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Design of stand alone system

Design of stand alone system

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PSH129

• Learning Out come :• After this lecture, you will be able to…• Design stand alone photovoltaic system for

residential ,commercial center and institution such as school, health center etc.

• Understand design procedures for spv system • Identify and select components required during

design time• Make appropriate assumptions during design time• Know selection criteria for battery, inverter, cables

and etc

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step 1. measure /estimate daily electric consumption wh/day

• The most important and complex stage in sizing a stand-alone PV system is providing a carefully worked out breakdown of the daily electricity consumption. This is listed in Table below using the example of a small holiday home.

• First of all we need to estimate the consumption of all the individual electric loads. All intended electric loads and their respective power consumption are listed with their probable daily operating times and their daily consumption amounts.

• The calculation of the radiation energy is based each time on the weakest month, taking into account the location, inclination and temperature

Example of step1132

.Sizing PV array

• The size of the PV array should be selected to take account of:

• seasonal variation of solar radiation • seasonal variation of the load • battery efficiency • manufacturing tolerance of modules • dirt • temperature of array (the effective cell temperature)

• In order to determine the energy required from the PV array, it is necessary to increase the energy from the battery bank to account for battery efficiency. It around 90% or 0.9

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Step2 .Sizing PV array134

• After the daily electricity demand has been ascertained, the correct size of the PV array needs to be determined.

• There are different approaches to determining the yields of the diverse solar module types available on the market.

• The most sensible procedure would be to base this on the nominal power of a module at STC

Sizing methods

• There are two types of sizing method for stand alone PV system

1. Ampere hour method (Ah method)2. Watt hour method (wh method )

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Steps in Ah method1. determine total load Ah /day total load Ah/day= 1.2 2. Determine Battery size Ah(batt)= no. of batt in series = no. of parallel string =total no. of batt= no. of batt in series x no. of parallel string

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Steps in Ah method

• Total Ah of battery bank=( Ah single batt) x( no. of parallel string)

• System voltage = no. of batt in series x (voltage of selected battery)

3.Determine Pv array sizeTotal Ampere required from pv=1.2 xNo.of module in series=No.of parallel string=Total number of module=no.series x no. parallel

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Steps in Ah method

4. determine charge controllerThe current of charge controller= 1.3 xInput voltage of charge controller = voltage of the array 5. Determine inverter wattage =1.3 x total wattage of the applianceInput voltage window=bus voltage 6. Determine wire sizeDetermine the distance fromArray to CCCC to battery

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Steps in Ah method

• From battery to inverter• From inverter to sub distribution box• From sub distribution box to load• Assume 5% voltage drop in distribution system

AC side • 2-3% voltage drop in DC Side• 1% drop from charge controller to battery.Area of the wire=r Resistivity of copper 0.0179 L – single length of wire

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Watt hour method

1, get total wh of the load (E)2. PV power (peak)= where Q is for quality factor of the system ranges from 0.1-0.4Total number of= Pv module No. of series connected module=No. of parallel string=

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• Area required = 3. Determine battery sizeKwh of battery =

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no. of batt in series = no. of parallel string =

total no. of batt= no. of batt in series x no. of parallel string

• Total Ah of battery bank=( Ah single batt) x( no. of parallel string)

• System voltage = no. of batt in series x (voltage of selected battery)

4 &5. other steps are the same to that of Ah method.

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