experiment manual 14thnov2011

1

© Insight Solar, 2011 Ecosense. [email protected]

Experiment ManualIncludes 9 experiment with step-by-step guidance

2


Develop an in-depth understanding of a Solar PV plant through a real-life hands on experience.

A B

Collapsible stand

Adustable PV Panel

Regulated lamps

Concealed meters

DC load indicator

AC load indicator

Compact Solar Photovoltaic Module Stand

It consists of two faced Photovoltaic panel, which can be folded and reassembled at use. The module also contains a uniquely designed support stand with adjustable gears for micro-tilting the PV panel for accurate experiments and readings. This module also carries two lamps which can be regulated for variable radiation.

Main Controller

This has been designed keeping in view the user interactivity while connecting the terminals and simultaneously taking the corresponding readings. The main load indicator has been kept at the bottom to avoid the glare in the eye while conducting the experiments.

A B

Protective shield

3


two experiments explains the working of stand-alone PV system with either DC and AC load. Experiment 3 explores the complete stand alone PV system with both DC and AC load. Experiment 4 focuses on the charging and discharging characteristics of battery. This experiment is about voltage and current variation with charging and discharging.

This experimental manual is prepared specifically for the users of “Insight Solar PV training kit”. This manual covers the fundamentals of solar PV system which would be helpful to the engineering students of both undergraduate and postgraduate level. The manual is divided in two parts. Part I focuses on the characteristics of PV module at different conditions. Part II focuses on the characteristics of PV system and power flow analysis.

Part I comprises five experiments. Experiment 1 helps to evaluate current-voltage characteristics of single PV module while Experiment 2 focuses on evaluating current-voltage characteristics of combination of two PV modules in series and parallel. These two experiments also help to evaluate fill factor of PV module. Experiment 3 explains how incident radiation and power output of module gets changed with change in tilt angle of PV module. Experiment 4 shows the effect of shading of cells of PV module. This experiment uses some shading blades for shading the solar cells. Experiment 5 helps to explains the working of diode as blocking and bypass diode.

Part II consists of four experiments. Experiment 1 demonstrates and explains the power flow of PV system when DC load connected to it. Similarly, Experiment 2 does the same when AC load is connected. These

Insight Solar Experiment Introduction

IntroductionInsight Solar

DOs

• Alwaysperformtheexperimentwithatleasttwostudents.

• AlwaysstarttheexperimentwithPVmodulecleaning.

• Makesureallconnectionsaretight.

• Noteallreadingsofdifferentmeterssimultaneously.

• Conductonesetofeachexperimentwithin2-3minutes.

• Followalltheprecautionsgivenattheendofexperiment.

DON’Ts

• Don’texposethecontrollerunitinwater.

• Don’tshortthebatteryterminalsoranyothersourceterminals.

• Don’tmovethehalogenorPVmodulewhiletheexperimentisgoingon.

• Don’tconnectthemoduleo/ptothechargecontrollerbeforeconnectingthebatterywithchargecontroller.

• Don’tallowthemoduletemperatureabove700C.

4


Objective To demonstrate the I-V and P-V characteristics of PV module with varying radiation and temperature level.

Theory PV module is characterized by its I-V and P-V characteristics. At a particular solar insolation and temperature, module characteristic curves are shown in Fig. 1.1(a) and 1.1(b) respectively.

Characteristic curves of solar cellIn I-V characteristic maximum current at zero voltage is the short circuit current (Isc) which can be measured by shorting the PV module and maximum voltage at zero current is the open circuit voltage (Voc). In P-V curve the maximum power is achieved only at a single point which is called MPP (maximum power point) and the voltage and current corresponding to this point are referred as Vmp and Imp. On increasing the temperature, Voc of module decreases as shown in Fig. 1.2, while Isc remains the same which in turn reduces the power. For most crystalline silicon solar cells modules the reduction is about 0.50%/°C.

Experiment no. 1Insight Solar

Insight Solar Experiment no. 1

Fig. 1.2. Variation in Voc with change in temperatureFig. 1.1(b). P-V characteristic of PV module

Fig. 1.1(a). I-V characteristic of PV module

2,500

2,000

1,500

1,000

0,500

0,00000 .050 .1 0.15 0.20 .250 .3 0.35 0.40 .5 0.55 0.60.45

Voltage (V)

Cur

ren

t(A

)

1,200

1,000

0,800

0,600

0,400

0,200

0,00000 .050 .1 0.15 0.20 .250 .3 0.35 0.40 .5 0.55 0.60.45

Voltage (V)

Pow

er(W

)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.000 .1 0.20 .3 0.40 .5 0.60 .7

Voltage (V)

Cur

rent

(A)

045 C

025 C0T = 60 C

5


Experimental set-upThe circuit diagram to evaluate I-V and P-V characteristics of a module is shown in Fig.1.5. Form a PV system which includes PV module and a variable resistor (pot meter) with ammeter and voltmeter for measurement. Pot meter in this circuit works as a variable load for the module. When load on the module is varied by pot meter the current and voltage of the module gets changed which shift the operating point on I-V and P-V characteristics.

PV characteristics evaluation can be achieved by following connections in control board (as shown in Fig.1.6).

On changing the solar insolation Isc of the module increases while the Voc increases very slightly as shown in Fig. 1.3.

Fill factor: The Fill Factor (FF) is essentially a measure of quality of the solar cell. It is the ratio of the actual achievable maximum power to the theoretical maximum power (PT)that would be achieved with open circuit voltage and short circuit current together. FF can also be interpreted graphically as the ratio of the rectangular areas depicted in Fig.1.4. A larger fill factor is desirable, and corresponds to an I-V sweep that is more square-like. Typical fill factors range from 0.5 to 0.82. Fill factor is also often represented as a percentage.


V

PT

MP OC

PMAX

IMP

ISC

I

V V

Fig. 1.3. Variation in I-V characteristic with insolation

2

1

0

Voltage in V

Cu

rren

tin

A

00 ,1 0,20 ,3 0,40 ,5

21000W /m

2600 W/m

2200 W/m

Fig. 1.5. Circuit diagram for evaluation of I-V and P-V characteristics

V Pot meter

A

Fig. 1.4. Graphical interpretation of the Fill factor (FF)

FF = PMAX

PT

= IMP • VMP

ISC • VOC

Module TemperatureLED

Diode 1 Diode 2

Inverter I/P Inverter O/P

Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage

Solar Charge Controller

Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

6


Observations: Table for I-V and P-V characteristics of PV module :

These 4 sets are for different radiation and temperature levels but in one set the values of radiation and temperature will be constant.

Results: 1. Draw the I-V curves of all the sets

on a single graph and show the characteristics at different radiation and temperature levels.


Controller connections

Fig. 1.6. Control board connections to get I-V and P-V characteristics

7



2. Draw the P-V curves of all sets on a single graph and show the characteristics at different radiation and temperature levels.

3. Calculate the fill factor for the given module.

Precautions:1. Readings for one set should be

taken within 1-2 minutes (for indoor

experiment) otherwise temperature of the module may vary as radiation source used is halogen lamp.

2. Halogen lamp position should not be changed during one set otherwise radiation on modules will change.

3. Connections should be tight.

Notes

8


Objective To demonstrate the I-V and P-V characteristics of series and parallel combination of PV modules.

Theory PV module is characterized by its I-V and P-V characteristics. At a particular level of solar insolation and temperature it will show a unique I-V and P-V characteristics. These characteristics can be altered as per requirement by connecting both modules in series or parallel to get higher voltage or higher current as shown in Fig. 2.1(a) and 2.1(b) respectively.

On increasing the temperature, Voc of modules decrease while Isc remains same which in turn reduces the power.

Therefore, if modules are connected in series then power reduction is twice when connected in parallel.

On changing the solar insolation, Isc of the module increases while the Voc increases very slightly, therefore there is overall power increase. In parallel connection power increment is twice than when connected in series.

Experimental set-up The circuit diagram to evaluate I-V and P-V characteristics of modules connected in series and parallel are shown in Fig. 2.2(a) and 2.2(b) respectively.


Fig. 2.1(b). I-V characteristic of parallel connected modules


Fig. 2.1(a). I-V characteristic of series connected modules

Voltage(v)

Voc

I(A)

Voc

Pmax Pmax

I(A)

Voltage(v)

Voc

Pmax

Pmax

9


Form a PV system with modules in either series or parallel and a variable resistor (Pot meter) with ammeter and voltmeter for measurement. Modules in series or parallel are connected to variable load (pot meter). The effect of load change on output voltage and current of the modules connected in series or parallel can be seen by varying load resistance (pot meter).

I-V and P-V characteristics of the modules connected in series or parallel can be achieved by connections shown in Fig. 2.3(a) and (b) respectively.

Series connected modules

Fig. 2.3(a). Control board connections for modules connected in series



Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

Fig. 2.2(a). Circuit diagram for evaluation of I-V and P-V characteristics of series connected modules

V Pot meter

A

V Pot meter

A

Fig. 2.2(b). Circuit diagram for evaluation of I-V and P-V characteristics of parallel connected modules

10


Observations:Table for I-V and P-V characteristics of PV modules in series:


Table for I-V and P-V characteristics of PV modules in parallel:


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

Parallel connected modules


Fig. 2.3(b). Control board connections for parallel connected modules

11



Results: 1. Draw the I-V curves of all the 3 sets

on a single graph for the modules

connected in series and parallel and show the characteristics at different radiation and temperature levels.

2. Draw the P-V curves of all the 3 sets on a single graph for the modules connected in series and parallel and show the characteristics at different radiation and temperature levels.

Precautions:1. Readings for one set should be taken

within 1-2 minutes (for indoor exp.) otherwise temperature of the module may change as radiation source used is halogen lamp.

2. Halogen lamp position should not be changed during one set otherwise radiation on modules will change.



Notes

12


Objective To show the effect of variation in tilt angle on PV module power.

Theory Tilt is the angle between the plane surface under consideration and the horizontal plane. It varies between 0-900. PV arrays work best when the sun’s rays shine perpendicular to the cells. When the cells are directly facing the sun in both azimuth and altitude, the angle of incidence is normal. Therefore, tilt angle should be such that it faces the sun rays normally for maximum number of hours.


The tilt angle settings for different seasons are shown in Fig. 3.1. PV systems that are designed to perform best in the winter, array should be tilted at an angle of equal to latitude +15°. If the array is designed to perform best in the summer, then the array needs to be tilted at an angle of equal to latitude−15°. In this way the array surface becomes perpendicular of the sun rays. For best performance throughout the year, tilt should be equal to the latitude angle.


Summer

Tilt angle is setat latitude minus15 degrees

Spring & Fall

Tilt angle is setat latitude

Winter

Tilt angle is setat latitude plus15 degrees

Fig. 3.1. Tilt angle settings for different seasons

13


Experimental set-upThe tilt angle of the module can be changed by rotating the lever below the module. Lit the halogen lamp and change the tilt of the module by rotating the lever.

To evaluate effect of tilt on power output of the module, following connections are to be done in the control board as shown in Fig. 3.3. The pot meter in this case has to be fixed at constant position so that the effect of tilt can be seen.



Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Fig. 3.2. Arrangement to vary tilt of the module

Fig. 3.3. Control board connections to evaluate effect of tilt

14


Observations:Tables for evaluating effect of tilt: Each set is for the different positions of pot-meter but during one set its position will be fixed. Radiation on module will be calculated by taking an average of the radiations recorded at three difference locations on the module (viz. upper end, middle and lower end).

ResultsDraw the graph between tilt (as x-axis) and Radiation and Power (on left and right y-axis). Relation between radiation and power o/p will be linear.

Precautions:1. Readings for one set should be taken

within 1-2 minutes (for indoor exp.) otherwise temperature of the module may vary as radiation source used is halogen lamp.

2. Observations for tilt angle should be taken as correct as possible.

3. Always take radiation reading after module current and voltage readings.



Notes

15


Objective To demonstrate the effect of shading on module output power.

Theory There are 36 solar cells in a module. These 36 solar cells are in series as shown in Fig. 4.1 which makes the module as series connected solar cells.


These cells are in series without bypass diode so shading of one cell will be sufficient to reduce the power to zero. This arrangement gives zero power if the entire row of cells gets shaded.

Experimental set-up There are some shading elements of the string size which can cover the string of module completely. For executing this experiment, put one of these shading elements on one string to shade it completely. After this shade two parallel connected strings. For conducting this experiment do the connections as shown in Fig. 4.2.


Fig. 4.1. Internal structure of the module

16




Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

Results: 1. Demonstrate the power output of

module with one string shaded.

2. Demonstrate the power output of module with two strings shaded.

Precautions:1. Shading of string should be exactly on

that string only.


Observations:Table for evaluating the effect of shading on cells:


Fig. 4.2. Control board connections

17


Objective To demonstrate the working of diode as Bypass diode and blocking diode.

Theory Diode is very important element in the PV system. This element can work as a blocking diode or as a bypass diode. Diodes connected in series with cells or modules are called blocking diodes and diodes connected across cells or modules are called bypass diodes. There are two situations where these diodes can help.

Bypass action of diode

If two modules are in series then the current in circuit will be decided by the module which is generating less current. Hence if one module is completely shaded then the current in the circuit will be zero. If there is a diode in parallel with the shaded module then power output of non-shaded module gets bypassed by diode and will be available at load terminals.

Blocking reverse flow of current from the battery through the module at night.

In battery charging systems, the module potential drops to zero at night when


sunlight is not available. The battery could discharge at night time by flowing current backwards through the module. This would not be harmful to the module, but would result in loss of precious energy from the battery bank. To prevent the current flow from the battery to the module at night time blocking diode is placed in the circuit between the module and the battery. Circuits with and without diodes are shown in following figures.

Blocking reverse flow down through damaged module from parallel connected modules during the day.

Blocking diodes placed at the head of separate series wired strings in high voltage systems can perform yet another


Fig. 5.1. Diode in blocking mode in series connected modules

+

18


Experimental set-up There are two diodes which can be used as a blocking diode as well as bypass diode.

a) Diode in bypass mode in series connected modules

Shade one module completely and connect the diode in parallel with shaded module terminals (as shown in Fig. 5.3.).

b) Diode in blocking mode in series connected modules with batteries

In blocking action of series connected modules a diode is connected in series with series connected modules. This protects the module from reverse current flow from battery. Connections as shown in Fig. 5.4.

c) Diode in blocking mode in parallel connected modules

In parallel connected modules the diode is connected in series with the shaded module and this protects the shaded module from reverse current flow (generated by other module). Connections as shown in Fig. 5.5.

function during daylight conditions. If one string becomes severely shaded, or if there is a short circuit in one of the modules, the blocking diode prevents the other strings from loosing current backwards down the shaded or damaged string. The shaded or damaged string is “isolated” from the others, and more current is sent on to the load. In this configuration, the blocking diodes are sometimes called “isolation diodes”.


V+

-

Shaded diode

A

Fig. 5.2. Diode in blocking mode in parallel connected modules

19


Fig. 5.3a. Series connected modules without bypass diode

Fig. 5.3b. Series connected modules with bypass diode


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load



20




Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Fig. 5.4a. Series connected modules with batteries and without blocking diode

Fig. 5.4b. Series connected modules with batteries and with blocking diode

21



Fig. 5.5a. Parallel connected modules without blocking diode

Fig. 5.5b. Parallel connected modules with blocking diode



Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

22


Observations:1. Power output of series connected

modules before using bypass diode with shaded module will be close to zero. After using bypass diode with shaded module, power output of series connected modules gets increased from nearly zero to higher value.


2. Connections with two configurations of blocking mode without using diode, LED will glow in these two cases showing reverse current flow.

3. Connections with two configurations of blocking mode using diode, LED will not glow in these two cases.

Notes

23



Objective Workout power flow calculations of stand-alone PV system of DC load with battery.

Theory Stand alone PV system (Fig. 6.1) is the one which can be used for both AC and DC loads and installed near the location of load. These systems are easy to install and understand. These systems can be used without batteries also, but these systems perform best with battery bank. These systems are best suited for the locations


where grid connectivity is not present and these systems fulfill the requirements of these locations.

Stand alone PV system of DC type is used when local loads consist of DC equipments and battery storage only. This system consists of PV module, charge controller, battery and DC load.

Charge controller regulates the module voltage at 12V or any other value of voltage, required by the battery bank or load and then powered the load. In this system there is no need of Inverter so efficiency of system is high because DC to AC conversion stage is absent.

Experimental set-up

The demonstration of stand alone PV system with only DC load can be done in the following ways:

a) Using only single module (Fig.6.2a)

b) Using modules in parallel (Fig.6.2b)

c) Using modules in series (Fig.6.2c)Fig. 6.1. Stand alone PV system

24





Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

Fig. 6.2a. Demonstration of DC load with single module (12 V system)

Fig. 6.2b. Demonstration of DC load with parallel connected modules (12 V system)

25




Fig. 6.2c. Demonstration of DC load with series connected modules (24 V system)


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

26



Observations The parameters to be observed are DC load current, DC load voltage, battery current and battery voltage with different series/parallel combinations of modules.

Tables for Stand-alone PV system calculation:

Results

Show the power balance by following formula:

Array power = load power + battery power + Power loss by charge controller

Note:Batterypowerwillbewith–vesignifbatteryisdischargingthroughload.CurrentconsumptionofChargecontrolleris4mA.

Precautions

1. Readings should be taken carefully.

2. Always plug-in the module power lead at the input of charge controller, after connecting the battery terminals with charge controller output terminals.


Notes

27



Objective Workout power flow calculations of stand-alone PV system of AC load with battery.

Theory Stand alone PV system (Fig. 7.1) is the one which can be used for both AC and DC loads and installed near the location of load. These systems are easy to install and understand. These systems can be used without batteries also, but these systems perform best with battery bank. These


systems are best suited for the locations where grid connectivity is not present and these systems fulfill the requirements of these locations.

Stand alone PV system of AC type requires inverter to convert DC voltage available at the charge controller output to controlled AC voltage of required magnitude to supply AC type of load.

This system consists of Modules, charge controller, battery and inverter. Charge controller regulates the module voltage to 12 volt and charge the battery and then this regulated DC power is converted to AC by means of inverter. Inverter efficiency is approximately 95%.

Experimental set-up

The demonstration of stand alone PV system with only AC load can be done in the following ways:



Fig. 7.1. Stand alone PV system

28




Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Fig. 7.2a. Demonstration of AC load with single module

Fig. 7.2b. Demonstration of AC load with parallel connected modules

29



Observations The quantities to be observed are AC load current, AC load voltage, inverter input voltage, current, battery current and battery voltage with different parallel combinations of modules.

Tables for Stand-alone PV system calculation:

Results

Show the power balance in both the sets by following formulae:

1. Array power = Inverter i/p power + battery power + loss due to charge controller

2. Inverter efficiency = AC load power*100/Inverter input power (DC)


Precautions1. Readings should be taken carefully.



Table for inverter efficiency:

30



Objective Workout power flow calculations of stand-alone PV system of DC and AC load with battery.

Theory Stand alone system (Fig. 8.1) is the one which can be used for both AC and DC loads and installed near the location of load. These systems are easy to install and understand. These systems can be used without batteries also but these systems


perform best with battery bank. These systems are best suited for the locations where grid connectivity is not present and these systems fulfill the requirements of these locations.

This system use DC power to charge the battery and run the DC load but, use AC power to run the AC load. There are modules, charge controller, batteries, DC load, inverter and AC load in this system. This system runs the AC and DC load simultaneously and can fulfill the demand of the both types of loads.

Experimental set-up

The demonstration of stand alone PV system with AC & DC load can be done in the following ways:



Fig. 8.1. Stand alone PV system

31




Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Fig. 8.2a. Demonstration of AC & DC load with single module

Fig. 8.2b. Demonstration of AC & DC load with parallel connected modules

32


Observations Tables for Stand-alone PV system calculation:

Results

Show the power balance in both the sets by following formulae:

1. Array power = DC load power +AC load power + battery power+ loss due to charge controller.

2. Inverter efficiency = AC load power*100/Inverter input power


Precautions

1. Readings should be taken carefully.



Table for inverter efficiency:


33



Objective To draw the charging and discharging characteristics of battery.

Theory Battery discharging

Battery discharging depends on magnitude of current drawn and the time for which this current is drawn. Rate of charge flowing determined the steepness of discharge characteristic. At higher current i.e. at higher rate of discharge, voltage variation becomes more steeper and battery discharge up to much low voltage. Similarly, at lower rate


of discharging voltage variation becomes less steeper and battery discharge up to somewhat higher voltage. The typical 12V, 3Ah battery discharge characteristic is shown in Fig. 9.1.

Battery charging

Starting current of charging is much higher because the voltage of the discharged battery is low. Initially battery draws almost constant charging current while battery voltage increases rapidly, as soon as battery voltage reaches rated voltage, charging current start reducing rapidly and battery voltage becomes constant. After fully charging, the battery charging current reduces to vary low value required to trickle charge the battery. The typical charge characteristic of 12V battery is shown in Fig. 9.2.

23 5 10 20 30

13.0

12.0

11.0

10.0

9.0

0

0Discharge characteristic (25C )

1.23A

h

0.77A 0.44A 0.225A

140

120

100

80

60

40

20

0

0.25

0.20

0.15

0.10

0.05

0

15

14

13

12

11

Charge Volume

Charge Voltage

Charge Current

Charge Time (H)

Cha

rge

Volu

me

Cur

rent

Volt

age

Volt

age

(%)( CA) ( 12V)

Fig. 9.1. Battery discharging characteristics Fig. 9.2. Battery charging characteristics

34




Battery charging

Battery discharging


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load


Diode 1 Diode 2


Module Current

Module Voltage

Inv. Input Voltage

Inv. Input Current

Batt. Input Current

Gen. AC Current

DC Load Current

Batt. Input Voltage

POT Meter

Gen. AC Voltage

DC Load Voltage


Battery 1 2

Module Output 1

Battery / Inverter

DC Load

DC I/P

Module Output 2

AC Load

DC Load

Experimental set-up To demonstrate charge and discharge characteristics of the battery connections, do the connections in control board as shown in Fig. 9.3(a) and 9.3(b).

Fig. 9.3 (a). Fig. 9.3 (b).

35



Observations Discharging experiment can be done at different current values. This can be achieved by changing the load.

Table for discharging of battery:

Results

1. Draw charging and discharging curves by taking time (in hrs) on x-axis and voltage and current on y-axis..

Precautions1. Connections of battery should be

made carefully.


3. Connections should be tight

Table for charging of battery:

36


Insight Solar Notes

Notes

37


Insight Solar Notes

Notes

38


Insight Solar NotesInsight Solar Notes

Notes

39


Insight Solar Notes

Insight Solar Notes

Notes

40


About Ecosense Ecosense is a group of engineers, designers and researchers from various IITs of India, which work towards bringing sustainable transformation in the lives of common people by providing basic infrastructure solutions for clean water, sanitation, energy and green habitat. We work with government, private organizations and civil societies to sensitize and help them adopt development mechanisms that are environment friendly. We expertise in integrated water management, renewable energy, irrigation, environmental planning & management, rural & urban development, training & capacity building.

We operate with a commitment to integrity and hold ourselves to the highest standards of ethics, quality, and accountability. Our team shares a genuine sense of respect and stewardship for the places where we work and the people whose lives we impact.

Delivering environment friendly mechanisms

Ecosense Sustainable Solutions Pvt. Ltd.Correspondence Address: D-44, 2nd Floor, East of Kailash, New Delhi – 110065Regd. Address: 124, Himgiri Apartment, Vikaspuri, New Delhi – 110018Phone: +91 11 41097435, +91 9910477840, +91 9910166999Email: [email protected] • Web: www.ecosenseworld.com

experiment manual 14thnov2011

Documents