project number eie/05/011/si2.419343 microgrids...guide for teaching practices - microgrids project...

The sole responsibility for the content of this report lies with the authors. It does not necessarily reflect the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information contained therein.

MIC

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GR

IDS

PROJECT NUMBER: EIE/05/011/SI2.419343

MICROGRIDS PROMOTION OF MICROGRIDS AND RENEWABLE ENERGY SOURCES FOR

ELECTRIFICATION IN DEVELOPING COUNTRIES

Intelligent Energy – Europe (IEE)

Type of Action: 1

Key Action: Strengthening local energy expertise in developing countries

GUIDE FOR TEACHING PRACTICES

03 december 2007

GUIDE FOR TEACHING PRACTICES - MICROGRIDS PROJECT

EIE/05/011/SI2.419343 MICROGRIDS ii

ÍNDEX

page

ÍNDEX.......................................................................................................... ii

1. INTRODUCTION..................................................................................1

2. ARCHITECTURE OF THE SYSTEM ...................................................2

3. MODULES ...........................................................................................3

4. PRINCIPLES OF OPERATION............................................................4

5. HARDWARE DESCRIPTION...............................................................6 5.1. Photovoltaic module...................................................................6 5.2. Regulator ...................................................................................6 5.3. 200W inverter.............................................................................8 5.4. Trace battery monitor.................................................................9

6. FUNCTIONALITY...............................................................................11 6.1. PV Regulator............................................................................11

6.1.1 Installation......................................................................11 6.1.2 Features.........................................................................11 6.1.3 Operation modes ...........................................................11 6.1.4 Load connection and disconnection...............................12 6.1.5 Configuration .................................................................12 6.1.6 Indicators .......................................................................13

6.2. Battery monitor.........................................................................13 6.2.1 Battery parameter configuration.....................................13 6.2.2 Basic indicators..............................................................14 6.2.3 Additional indicators.......................................................14 6.2.4 Warnings........................................................................15


EIE/05/011/SI2.419343 MICROGRIDS iii

7. ELECTRICAL DIAGRAM...................................................................17

8. PHYSICAL CONSTRUCTION ...........................................................18

9. THE WIND TURBINE SYSTEM .........................................................20

10. TEACHING PRACTICES ...................................................................22 10.1. Practical Work1: Description of the photovoltaic trainer and

its components.........................................................................23 10.2. Practical Work 2: Verification of the open circuit voltage and

the short-circuit current ............................................................30 10.3. Practical Work 3: Verification of the PV panel quality ..............34 10.4. Practical Work 4: Verification of the PV panel quality ..............39 10.5. Practical Work 5: Connexion and start of a PV system

complete installation ................................................................44 10.6. Practical Work 6: PV panel behaviour during partial shades

on the PV cells. ........................................................................47 10.7. Practical Work 7: Inverter voltage, frequency and waveform

verification................................................................................51 10.8. Practical Work 8: Calculation of the section of the

conductors in a photovoltaic solar system. ..............................55


EIE/05/011/SI2.419343 MICROGRIDS 1

1. INTRODUCTION

An educational electrification kit has been developed in the context of the Microgrids project. This document is a guide to describe the architecture and functionalities of the system. A list of practices is also proposed in order to exploit all the capabilities of the kit for didactical purposes.



2. ARCHITECTURE OF THE SYSTEM

Next figure shows the architecture of the system:



3. MODULES

These are the modules included in the kit:

• 50 Wp Photovoltaic module.

• 10A Regulator system for the batteries.

• Battery monitor for DC monitoring.

• 200W Inverter 12VCC/220VCA 50 Hz.

• 12V 60A lead-acid battery.

• Two bipolar general switches 10A 220V.

• Programmer for automatic control of AC loads.

• Programmer for automatic control of DC loads.

• 12V DC lamp.

• 220V AC lamp.

The kit is completed with a 12V micro wind turbine system. It is formed by:

• 20 micro wind turbines.

• One DC generator.

• 1000W Inverter 12VCC/220VCA 50 Hz.

This wind system can be attached to the batteries of the educational kit for extra generation. In this case the output of the generator will be directly connected to the batteries. It can also work as an autonomous AC generating system by making use of the inverter.



4. PRINCIPLES OF OPERATION

The PV module is connected to the charge regulator through fuse protection F1. The regulator controls the flow of energy between the PV module, the battery and the loads to fulfill the following operations:

• Recharging the battery by means of the solar panel.

• Feeding the loads from the battery if there’s not enough solar energy.

• Feeding the loads from the PV panel if solar irradiation is sufficient for it.

The regulator offers information on current available from the PV module, current from the battery and current to the loads. It is also capable of switching the loads off and on.

In the connection from the regulator to the battery we can find:

• Protection fuse F2.

• Sensing shunt element. Voltage across this shunt is proportional to current that flows into/out of the battery. This information is sent to the battery monitor.

• The battery monitor collects the information of flowing current at any moment and shows a series of battery parameters that are described in section 5.4 (instantaneous current, voltage, state of charge, etc.)

DC loads are organized as follows:

• One fitting for a 12V bulb.

• One 12V output to be connected to a pair of wires.

• One 12V timed output to be connected to a pair of wires. In this case it is possible to program the state of the load (on/off) for a period of time. This period can be one day (programmable each 15min) or one week (programmable every 2 hours). The programming operation is done in a mechanical way. There’s a series of miniature levers in a circular configuration. Each lever can be independently moved to the left or to the right. This position defines the state of the load (on/off) for the corresponding period of time).



The connection to the inverter is protected by the fuse F3. The output of the inverter is AC 220V and it is configured in the following way:

• A residual current device to protect the people in case somebody touches an energized points.

• A magneto-thermal circuit breaker to protect the system from short-circuits and over-voltages.

• One 12V output to be connected to a pair of wires.

The AC loads are distributed this way:

• One fitting for a 220V bulb.

• One socket for a 220V load.

• One socket with a 220V AC timed output. In this case it is possible to program the state of the load (on/off) for a period of time. This period can be one day (programmable each 15min) or one week (programmable every 2 hours). The programming operation is done in a mechanical way. There’s a series of miniature levers in a circular configuration. Each lever can be independently moved to the left or to the right. This position defines the state of the load (on/off) for the corresponding period of time).



5. HARDWARE DESCRIPTION

5.1. Photovoltaic module

These are the characteristics of the generating module:

• Maximum power voltage: 16.7 V.

• Maximum power current: 3A.

• Open circuit voltage: 21,5V.

Next figure shows current (amperes) versus voltage (volts) according to the different levels of solar radiation:

I/V graph of the PV module at 25ºC

5.2. Regulator

The regulator is used to control the flux of energy between the PV module, the battery and the DC loads. This product includes a LCD which shows accurately the state of charge (SOC) in percent and as a battery gauge symbol.



Charge regulator

The main features are:

• PWM shunt battery charging.

• State of charge (SOC) battery regulation.

• Built in Ah counter.

• Boost charging.

• Equalizing charge.

• Float charging.

• Automatic load reconnection.



• Manual load switch.

• Automatic selection of voltage (12 V / 24 V).

• Temperature compensation.

• Positive grounding (or) negative grounding on one terminal.

• Field adjustable parameters by two buttons.

• Lighting control options during night time.

5.3. 200W inverter

The sine wave inverters of the AJ series have been designed to meet industrial and domestic needs. They meet the highest requirements of comfort, safety and reliability. Any device designed for the public electrical network of 230 V 50 Hz can be connected to them (up to the nominal power of the inverter).

The AJ series is the perfect source of voltage in any place where the public network is not available. The main features are:

• Pure sine wave output.

• A high and steady efficiency.

• An outstanding overload capacity, thanks to the combined use of a toroidal transformer and a MOS power stage.

• A digital regulation and microprocessor controlled.

• An electrical supply to any kind of electrical appliance.

• A complete internal protection of the inverter (overload, overheat, short-circuit, reverse polarity).

• An adjustable stand-by level on a large range and from a very low level .



Power inverter

5.4. Trace battery monitor

The TM500A features six data monitoring functions and three indicators including:

• State of charge/amp-hour content (full or percent of capacity)

• State of charge/voltage (real-time voltage level, historical high and low system voltage)

• Amps (real-time amps, total charging amps, total load amps)

• Amp hours removed

• Days since fully charged

• Cumulative amp hours

• Recharge indicator

• Low-voltage indicator

• Full-charge indicator

The unit is configurable for specific system or application functions such as setting the CHARGED indication parameters, battery capacity, charging efficiency, low-battery warning conditions and a recharge reminder. The TM500A can monitor any battery supply from approximately 8 to 65 volts, track energy consumption and estimate remaining battery life.



In addition to its status monitoring features, the unit can act as a remote control, switching the inverter OFF or ON (only on inverters incorporating an RC4/RC8 compatible remote control jack). The TM500A operates on 12-, 24-, or 48-volt battery systems (48-volt systems require an optional shunt board).

Battery monitor



6. FUNCTIONALITY

Next the capabilities of the system will be explained by specifying the features of the two main control modules: PV regulator and battery monitor.

6.1. PV Regulator

6.1.1 Installation

It is directly connected to the battery. It automatically detects whether it is 24 or 48V. Order for connection must be:

1. Battery.

2. PV module.

3. User loads.

For disconnection the inverse sequence must be executed.

6.1.2 Features

1. Calculation of SOC (State of Charge) from the I/V characteristics of the battery.

2. Charge regulation. Constant voltage charge is done using all the current supplied by the PV module until final voltage is reached. Current regulation is done by PWM modulation at the PV module input. There are three different charge modes (depending on the type of battery and regulation): normal, reinforced or compensated.

3. Protection against deep discharge. If the battery goes beyond a configurable minimum value the regulator disconnects the output in order to avoid the discharge.

6.1.3 Operation modes

There are two operation modes:

1. SOC regulation (State Of Charge). The bar indicates the percentage of SOC.

2. Voltage regulation. SOC bar disappears and it is replaced by the voltage value.



If there’s any other user connected to the battery, then the SOC calculation is not correct because there’s a current that is not being measured. In the case of the kit, the inverter is directly connected to the battery. Therefore if Ac loads are being used the voltage control must be used.

6.1.4 Load connection and disconnection

By pressing right button DC loads can be successively connected and disconnected.

6.1.5 Configuration

Configuration mode is entered by pressing the left button for at least three seconds. It is possible to go through different menus in the following way:

1. To modify current value, press the right button. The value flashes and the left button can be used to change it. To finish the operation the right button must be pressed again..

2. Press the left button to go to the following menu.

These are the configuration menus in the appearance order:

1. Regulation mode: SOC or voltage..

2. Battery type: gel or lithium.

3. Night light: this feature activates the output load only when it is dark. This mode can de configured to be activated for a certain number of hours. When the light comes back the output is disabled.

4. Default configuration: When the option PRE is called the default configuration is activated (SOC control / Gel battery / Night light off).

5. Self test. It carries out an automatic test to verify that the regulator is working properly. Preparation; connect a light DC load and disconnect it with the right button. Execution: press the left button (the display flashes) and afterwards the right button. If everything is OK, 000 can be read in the display. Otherwise an error number can be seen.



6. Serial number(SN). By pressing the right button the SN starts flashing. Press the left button to successively see the figures of the SN.

6.1.6 Indicators

Press the left button to go through the different indicators in the display:

1. Battery voltage (V).

2. Output current in PV panel (A).

3. Charge current to the battery (A).

4. Load current (A).

5. Load counter (Ah) from last reset (simultaneously press the two buttons).

6. Discharge counter (Ah) from last reset (simultaneously press the two buttons).

Other indications:

1. Disconnection warning: flashing of SOC or voltage value.

2. Voltage disconnection: if the minimum advisable limit for the battery is surpassed, the output is disconnected as a protection against deep discharge. The face appears to be sad and SOC/voltage value flashes. Disconnection values are prefixed and are not configurable (warning: 11.7V, disconnection 11.1V, reconnection 12.6V).

6.2. Battery monitor

6.2.1 Battery parameter configuration

Battery behaviour is described through two parameters: efficiency and capacity (amperes-hour).

Battery efficiency

1. Press SELECT until BATTERY LEVEL indicator is activated.

2. Press simultaneously RESET-SELECT.

3. Select with RESET the desired value and confirm with SELECT the value.



Capacity

1. Press SELECT until Ah indicator is activated.


3. Select with RESET the desired value and confirm with SELECT the value.

6.2.2 Basic indicators

Press SELECT to go through all the indicators in the display:

1. Battery level: FULL (>92,5%), LO (<27,5%), numeric values between 30% y 90% with 5% steps.

2. Batttery voltage: Volts (accuracy: 0,1V).

3. Instantaneous charge/discharge current: amperes(accuracy: ±1,5%).

4. Charged/discharged energy from last reset (Ah). If the decimal point flashes, value must be multiplied by 1000. This value is cleared when the indicator CHARGED is permanently on.

5. Energy saving mode (no illumination in the display).

6.2.3 Additional indicators

Thay can be accessed by pressing ELECT button until the message dSF can be seen in the display:

1. dSF: Days from the last complete charge of the battery. It is cleared when the CHARGED indicator is flashing. It can be manually cleared.

2. cAH. Cumulated amperes-hour. When the decimal point is flashing, the value must be multiplied by 1000. It can be manually cleared.

3. bHI. Maximum voltage detected in the battery.

4. bLO. Minimum voltage detected in the battery. It is cleared to current value by pressing RESET.

To clear the values RESET must be pressed for 5 seconds. The value flashes three times and it is then updated.



6.2.4 Warnings

Battery recharging

The Ah led can be configured so it flashes some time after the last recharge (off or 1 to 99 days). This is a way to remind that batteries must be charged. These are the steps to be followed:

1. Press SELECT until dSF can be seen in the display. Press simultaneously SELECT-RESET and release them.

2. Use RESET to select the desired value and SELECT to confirm.

Low battery voltage indicator

A minimum value can be configured for the battery voltage between 10 and 35V, so the V indicator flashes if the battery is under that level. The default value is 11.2V. These are the steps to be followed:

1. Press SELECT until bLO can be seen in the display. Press simultaneously SELECT-RESET and release them.

2. Use RESET to select the desired value and SELECT to confirm.

Charged indicator

The charged indicator can be programmed so that if flashes whenever certain charging criteria are fulfilled. These criteria can be: only voltage, voltage and current or current and time. The charged indicator stops flashing (permanent illumination) whenever certain conditions are not fulfilled. In that moment the Ah counter is cleared.

The charged indicator is cleared by pressing RESET while the active indicator is %, V or A.

The default charge voltage is 14.4V.

It can be configured by:

4. Pressing SELECT until indicator V is activated.




6. Select with RESET the desired level and press SELECT to confirm.



7. ELECTRICAL DIAGRAM

The next figure shows the electrical connections of the system:



8. PHYSICAL CONSTRUCTION

The kit has been designed in order to be easily transportable. This way it can be used for educational purposes in tours around the rural areas. As it can be seen in the following figures, the system is a case containing all the elements. When it is closed it can be easily handled and transported. When it is open, the left side shows all the DC elements and the right side shows all the AC elements.

Case containing the kit



Educational Kit



9. THE WIND TURBINE SYSTEM

The wind turbine is specially suited to low wind speeds, such as those of the target areas in Senegal. The generating system is a group of 20 microturbines with generator rated 165 W for 10m/s wind.

The following table indicates power versus wind speed:

Wind speed (m/s) 4 5 6 7 8 9 10 11

Power (w) 10 20 35 57 85 120 165 220

The following photographs show the configuration of the microturbines and the connection to the generator:

20 microturbines group



Connection to the generator



10. TEACHING PRACTICES

In this chapter a series of teaching practices will be proposed for the educational application of the kit.



10.1. Practical Work1: Description of the photovoltaic trainer and its components

PURPOSE: Analyze a PV panel used in a basic installation in order to obtain photovoltaic

solar energy.

OBJECTIVES: Know the basic components of a photovoltaic installation.

Identify and know each one of the parts of the solar trainer photovoltaic SIDAC.

DESCRIPTION • The Training KIT is a modular system, where each module has a group of connectors

to facilitate the connexion between the different components (see attached). So, the experiences are realized very easy.

• The flexibility of the system facilitates its orientation and the displacement. So, we can look for the best conditions to illuminate the panel.

• In the figure of the next page, it can be seen the distribution of the different elements of the modular system: connectors, power electronic interfaces, location of the panel, the modules and the battery.

• The inter-connexion of the components are made by cables for high security currents.

• The load can be DC or AC.



Training KIT components

Solar panel • Solar PV Panel mono-crystalline with the following characteristic: Maximal power 55 W,

voltage (for maximal power) 16.7V, current (for maximal power) 3 A, open circuit voltage 21.5, short-circuit current 3.10.

Solar Charge Regulators (Steca PR)

Features:

• PWM shunt battery charging.

• State of charge (SOC) battery regulation.

• Built in Ah counter.

• Boost charging.

• Equalizing charge.

• Float charging.

• Automatic load reconnection.

• Manual load switch.



• Automatic selection of voltage (12 V / 24 V).

• Temperature compensation.

• Positive grounding (or) negative grounding on one terminal.

• Field adjustable parameters by two buttons.

• Lighting control options during night time.

Stationary battery ESF 70471 • Stationary cast in one piece battery of 108 Ah. Discharged in 5h.

Inverter (AJ 275 sin wave inverter)



EXECUTION SEQUENCE

With a continuity tester, the following tests will be done:

• Connections of the PV panel and the battery.

• Its corresponding connections in the charge regulator.

An ohmmeter will be used to measure the loads in the DC side and AC side.

QUESTIONNAIRE

1) How many cells are in a PV panel?

2) Calculate the surface of one of the PV cells.

3) Calculate the intensity and the electrical power that a cell of the PV panel would generate when the maximum solar irradiance intensity is 100 MW/cm2 and the voltage maximum of the cell is 0,5 V and its efficiency is 12%.

4) How many 2 volts stationary batteries should be interconnected to obtain a work voltage of 48 Vcc? How should the batteries be connected, in series or parallel?



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SOLUTIONS

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2. ........................................................................................................................................

3. ........................................................................................................................................

4. ........................................................................................................................................



APPENDIX

Photovoltaic panels

PV panels are composed by a variable number of connected photovoltaic cells in series and/or parallel in order to be able to produce a nominal voltage of 12 volts. Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. Cells require protection from the environment and are packaged usually behind a glass sheet.

The photovoltaic panels should always be oriented towards the South.

Regulator

The regulator is equipped with various devices to protect its electronics, battery and load. If the maximum permitted data of the regulator are exceeded, the regulator can break down despite the protective functions. Never improperly connect more than one component to the regulator! The protective function is automatically reset after remedying the error.

• Protection against reverse polarity of solar modules. The power of the solar module may not exceed the nominal power of the regulator!

• Protection against reverse polarity of the connected consumer at the load output. Protects the regulator, not the consumer.

• Protection against reverse polarity of the connected battery. Charging and discharging the battery is prevented.

• Short-circuiting at the module input.

• Short-circuiting at the load output.

• Protection against over charging. The regulator disconnects the connection to the battery and turns off the consumer.

• Open circuit-proof during operation without battery or consumer. Load output is protected from high module open circuit voltage directly flowing to load side.

• Reverse current protection at night. Prevents reverse current in the solar module at night. An additional reverse current diode is not necessary!



• Overvoltage and undervoltage protection. Immediately turns off the load output during insufficient or excessive battery voltage.

• Excess temperature protection. If the temperature inside the regulator is too high, the load output of the regulator is turned off to reduce power loss.

• Overload protection at load output. If the permitted load current is exceeded, the load output is turned off.

• Transient overvoltage protection. A varistor at the module input protects against overvoltage >47 V. The component limits the diverted energy to 4.4 joules.

• Deep discharging protection / low voltage disconnect.

• Prevents excessive deep discharging or overloading the battery.

A good system of regulation not only allows to take maximum advantage of the energy provided by the photovoltaic system but, in addition, is essential to guarantee a good protection and use of the batteries.

Batteries

As the solar intensity varies during the day it is necessary to store the generated electrical energy. The batteries are generally used, which is the most effective and economic system. The photovoltaic equipment normally uses stationary batteries with independent connection of 2 V, which offer the suitable voltage when connected in series. The capacity of storage is calculated on the base of the considered daily consumption and the number of days of autonomy that is determined considering the maximum number of cloudy days in the normal climate of the zone.

The active life of the battery will depend on the good use and the quality of the regulation system of load and unloading. The battery should never be discharged below 80%.

Converter

The great majority of household electric system is designed to work in sinusoidal AC of 50 Hertz and 220 V. Usually the batteries DC current conversion from (12, 24 or 48 V) to alternating (220 V) is made by means of an inverter producing a sine wave.



10.2. Practical Work 2: Verification of the open circuit voltage and the short-circuit current


solar energy.

OBJECTIVES: Verify the short-circuit current of the solar panel.

Verify the open circuit voltage of the solar panel.

DESCRIPTION

In order to obtain the Icc, the current intensity should be measured with an ammeter connected directly on the output of the panel, without load.

In order to obtain the Vo, the voltage should be measured with a voltmeter connected directly on the output of the panel, without load.

EXECUTION SEQUENCE a. Orient the PV panel towards the solar irradiance.

b. Connect the PV panel to the KIT without load.

c. Connect the ammeter to the output of the panel.

d. Take the measurement.

e. Connect the voltmeter to the output of the panel without load

f. Take the measurement.



QUESTIONNAIRE

1) What efficiency (%) will have a PV cell of 100 mm of diameter whose maximum intensity produced is 2.5 A and which is exposed to a solar irradiation of 100mW/cm2?

2) What intensity can produce a PV cell of 150 mm of diameter, whose efficiency is 12% and which is exposed to a solar irradiation of 75 mW/cm2?

3) Which will be the voltage of two groups of three cells in series that have been connected in parallel?

4) Knowing the open voltage of the PV panel, calculate how many panels would be necessary to generate 150 Vcc. How would they be connected?



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SOLUTIONS

Values of Icc and Vo of the panel nameplate: • Icc= • Vo=

ANSWERS TO THE QUESTIONNAIRE

(For all the cases the voltage of a PV cell is considered 0.5 V)

1. ........................................................................................................................................

2. ........................................................................................................................................

3. ........................................................................................................................................

4. ........................................................................................................................................

WORK PROPOSAL • Obtain Icc and Vo with different values of irradiation. Draw conclusions.



APPENDIX

Short Circuit Intensity Icc

It occurs to zero voltage and it can be measured with an ammeter connected directly to the output of the photovoltaic panel. Its value can vary with the surface of the PV cells and with received solar irradiation.

For PV cells of 100 mm of diameter, Icc value is next to 2.5 A for a radiation of 100 mW/cm2.

Open Circuit Voltage Vo

It is the maximum resulting voltage without load connected to the panel. Its measurement is realized connecting directly a voltmeter to the terminals of the photovoltaic panel. The open voltage value oscillates around 0.5 V for each PV cell of the panel and the total voltage will depend on the number of cells.



10.3. Practical Work 3: Verification of the PV panel quality


solar energy.

OBJECTIVES: Calculate the maximum power point of the PV panel.

Obtain the index of panel quality on the basis of the fill factor parameter.

DESCRIPTION

In order to calculate the maximum power point of the PV panel, a curve (I,V) should be drawn using the pairs of values obtained for different loads until short circuit. Once the point of maximum power obtained, the fill factor indicating the quality of PV panel cells can be calculated.

EXECUTION SEQUENCE a. Orient the PV panel towards the solar irradiance.

b. Connect the PV panel to the KIT without load.

c. Add a variable resistor of 3,3 Ω to 100 Ω/4 A at the PV panel terminals. Connect a voltmeter and an ammeter to these terminals.

d. Change the resistance, from its maximum value to its minimum, making gradually 15 or more measurements (I,V).

e. With the obtained values, draw the graph in the section.

f. Use the practical work 2 to recover the short circuit-current value of the PV panel.

g. Use the practical work 2 to recover the open voltage value of the PV panel.

h. Get the product of the pairs of values (I,V).

i. Get the pair of values (I,V) of the curve, whose product is maximum.



j. Find the fill factor (FF ) from the obtained values and the recovered ones using the formula: FF=IpVp/IccVo (See the appendix)

k. Verify if the obtained value fits to the fill factor value of the commercial cells.

QUESTIONNAIRE 1) Compare the fill factor of the used PV panel with 0.7 value of another PV panel and

deduce which one has better quality.

2) Without the variable resistor, which values of constant resistance may be chosen to draw the graph?

3) If the resistance takes zero value, could it damage the PV panel? Justify the answer.

4) Does the PV panel quality change with the solar radiation?



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I-V curve

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SOLUTIONS


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2. ........................................................................................................................................

3. ........................................................................................................................................

4. ........................................................................................................................................

WORK PROPOSAL

Get the FF for different values of radiation. Compare the results.

APPENDIX

Power tip Wp

It is the highest electrical power that can provide a PV cell or solar PV panel for a specific radiation value. It is defined by the I,V curve point where the product of the current and the voltage are maximum. All the other points of the curve generate smaller values of this product. Wp=Vp•Ip

Fill factor FF

It is a variable value between zero and one. The cell has a better quality when the value is

close to one. The expression of fill factor is: 0

p p

cc

I VFF

I V=

Where:

FF = Fill factor

Ip = Current for maximum power point



Vp = Voltage for maximum power point

Icc = short circuit current of the PV panel

Vo= Open circuit voltage of the PV panel

Usually for the commercial PV cells, the FF is between 0.7 and 0.8. The FF for the monocrystalline silicon has a better value than the polycrystalline silicon. The fill factor is a very useful parameter since it gives an idea of PV panels quality.



10.4. Practical Work 4: Verification of the PV panel quality


solar energy.

OBJECTIVES: Obtain the panel efficiency.

Differentiate PV cells quality and efficiency.

Convert the incident radiation of calorie/cm2 minute to W/m2

DESCRIPTION • In order to calculate the efficiency of a PV cell or a PV the maximum power and the

incident irradiation power must be related.

• The incident irradiation power value(fara virgula) can be found in tables(fara virgula) or graphs that reflect the place, the time of the year and the hour of the measures. Also it is possible to measure incident irradiation power with perimeter. See appendix.

EXECUTION SEQUENCE a. Use the practical work 3 to recover the maximum power Wp.

b. Use the practical work 1 to recover the PV panel surface maximum power Wp. Recover from the practical work 1 the value of the panel useful surface.

c. Look for the power of incident irradiation

d. Make the units conversions, if it is necessary.

e. Find the efficiency (η) from the obtained values and the calculated ones by means

of the formula 100p

r

WW

η = ⋅ . See appendix.

f. Verify if the obtained value corresponds to the efficiency values of the commercial PV cells.



QUESTIONNAIRE

a) An efficiency of 25% is a high or a low value for a monocrystalline cell? Justify the answer.

b) Could a cell with very high quality have an efficiency superior to one? Justify the answer.

c) The efficiency depends on:

The time of exposition?

The surface of the panel? Justify the answers.

d) Classify the different types of PV cells according to their? efficiency. Justify the answers.

e) Has the panel temperature some influence on the efficiency ?



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INSTRUMENTATION

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WORK PROPOSAL

Get the FF for different values of radiation. Compare the results.



APPENDIX

Incident Radiation. The incident radiation would be obtain at the same moment as the pairs of values (I,V) for the calculation of the FF. If the incident radiation is taken from the tables, the indicated values can not reflect the real radiation of that moment, because they are calculated on the Maxima average of every indicated period. The most appropriate way to make the measurement would be the use of the perimeter..

Efficiency of a PV cell. It is a factor that relates the power produced by the PV panel to the incident irradiation power or. This variable is a function of the irradiation. Efficiency

It is a variable value between zero and one. The PV cell has a better efficiency when its value is close to one. Efficiency is defined:

100p

r

WW

η =

Where: η = efficiency Wp = maximum power Wr = power of the incident radiation on the useful surface of the panel Normally, for the commercial PV cells η is between 10% (polycrystalline silicon) and 14% (monocrystalline silicon). Gallium arsenide has an efficiency of around 27%. It seems logical to think that the latter would be the most indicated to manufacture panels because of their high performance. But the main problem is that this material is rare and few abundant. Nowadays, it is in an experimentation phase and it is not industrially manufactured.

T ransformation of units It is usual to evaluate the incident radiation value in cal/cm2min and also in W/m2 with the



following relation among them: a)Transformation of the values from W/m2 to cal/cm2·min 1 Joule = 0.24 cal.

1 0.24 0.24 601min

J cal calWs s

⋅= = =

2 2 4 2

1 0.24 60 0.24 60min min 10

W cal calm m cm

⋅ ⋅= =

⋅ ⋅ and therefore: 2 2

1 694,4min

cal Wcm m

=⋅

and

2 2

1 0.00144min

W calm cm

=⋅

b)Transformation from J/m2 to W.h/m2 1 Julio = 1W·s 3600 H = 1W·h



10.5. Practical Work 5: Connexion and start of a PV system complete installation

PURPOSE: Connexion of all the equipment and verification of its good operation.

Reading and interpretation of catalogues provided by the manufacturers.

OBJECTIVES: To know the function of each one of the elements that composes the

equipment.

To be able to interconnect all the elements supporting the described sequence.

To be able to start and to check the equipment operation.

To become familiar with the interpretation of the technical information.

EXECUTION SEQUENCE a) Connexion of the equipment by executing the following sequence:

1) Connect the solar panel and the battery to its corresponding module.

2) Connect the output of the regulator to the battery. Always check the polarity.

3) Press the regulator button and confirm if it indicates a voltage near to that of the

battery.

4) Connect the load output of the regulator to the input of the inverter and to the

connector of DC load. Check the CA and CC operation.

5) Connect the input of the regulator to the PV panel. If there’s sufficient solar

irradiation, press the button (it corresponds to the push-button of load current) to

confirm that there’s an input current whenever is not any connected load.

b) Check the good operation of the whole system.

Read voltage and current displayed by the regulator.



Check that the battery charging using regulator buttons . Check the current by monitoring the A .

c) Connect a CC or CA load of 100W and check in the regulator the magnitude of the current by pressing A (it corresponds to the button load current).

d) Reading of the regulator technical information. e) Reading of the inverter technical information.

QUESTIONNAIRE 1) Would it be correct to directly connect the input of the regulator to the terminals of the

battery? Justify the answer.

2) What would it happen in the case that the PV panel wouldn’t give a sufficient current to

charge the battery and the load is also connected? And if, the load weren’t connected?

3) Would it be possible to connect a TV with a consumption of 230W to the output of the

inverter? Why?

4) It is at night and the load consumption is 20W, in case the battery was discharged at

70% of its capacity:

a) How would act the regulator?

b) And in the case that it was in the daytime with a maximum solar irradiation?

5) Would it be correct to connect at the output of the inverter an open voltage transformer

in which would represent a load of 50 W?




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INSTRUMENTATION

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WORK PROPOSAL • Check with an oscilloscope the waveform in the output of the inverter supplying a

resistive load.

• Repeat the operation with an inductive load.

• Draw conclusions.



10.6. Practical Work 6: PV panel behaviour during partial shades on the PV cells.

PURPOSE: To analyze the solar energy production of a PV system.

OBJECTIVES: To observe the behaviour of the PV panel when shades appear on one or

more cells.

Analyze the balance of voltage, current and powers for different situations with shade on the cells.

Observe the increase of temperature in a cell partially covered.

DESCRIPTION • Experimental tests by covering gradually a part of the PV panel cells.

• Check the values of the voltage, current and power for the different situations of shade for the cells.

• Check the increase of temperature of a cell affected by shade.

• Conclusions.

EXECUTION SEQUENCE a) In order to cover the cells, some pieces of paper can be used ( for ½, 1, 2, 3 and 4

cells). b) Connect the output of the PV panel directly to the adjustable resistance adapted to 5

ohms: 1) Cover 4 cells and take measure of voltage and current for the PV panel. 2) Repeat the first step for 3, 2, 1 and ½ cell. In the last test, observe that the partially

covered cell experiences an increase of temperature.

c) Perform all sections b) in three different zones of the PV panel:

• In the input cells, in those of the centre and in those of exit of the panel.

d) Draw a table (see annex) with all the obtained values and establish conclusions.



e) Wrapping with tinfoil the a laboratory thermometer which reaches 100ºC, take the

superficial temperature of each one of the cells and note it. Cover now half of each one

of the cells and on the covered part, take again the temperature. Check if is a

substantial increase of the last one.

QUESTIONNAIRE 1) Having the panel connected to the KIT which works correctly, in which situation it is not

correct to do the proposed tests. Why?

2) If a cell is totally covered, could it be damaged due to the heat generated by the power

dissipated in the assumption that the panel was in short circuit? 3) In an system in which there were several PV panels connected in series to increase the

output voltage, the shade effect could be diminished on a PV panel?




MATERIALS………………………………………………………………………………………

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INSTRUMENTATION

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WORK PROPOSAL

Instead of doing tests by connecting the PV panel to the resistance, perform them with the all mounted KIT.



APPENDIX

Usually the PV cells which compose a solar panel have been selected with respect to their electrical behaviour in order to have quite similar characteristics. If the PV cells have different characteristics, the behaviour of the module would be deficient and the efficiency low.

Supposing that all the PV cells are similar, the possibility that one of them does not generate the same current, if is not damaged, will be due to the total or partial shades on it.

When one or several cells will generate less current, the total current trough the PV cells connected in series are affected. The PV cells that perceive shade instead of behaving as a generator, behave as load which dissipates a certain power, and consequently increase the PV panel heat. This dissipated power is the product of the voltage and the current along all its behaviour curve, therefore the worst condition, with regard to the heat, will occur when the PV panel is in short circuit.

Tables for the tests.

4 cells 3 cells 2 cell 1 cell ½ cellTension Intensity First test

Power

4 cells 3 cells 2 cells 1 cell ½ cellTension Intensity Second test

Power

4 cells 3 cells 2 cells 1 cell ½ cellTension Intensity Third test

Power



10.7. Practical Work 7: Inverter voltage, frequency and waveform verification

PURPOSE: Behaviour analyses of the DC/CC converter: Voltage I/O, frequency and

waveform.

OBJECTIVES: Check of input and output voltage of the converter comparing to its nominal

voltage and accepted variations.

Check of the output frequency of the converter by taking into account accepted variations.

Check the converter output waveform.

EXECUTION SEQUENCE a) Input and output converter voltage:

1) With a DC voltmeter, check the input voltage of the converter, considering that its

nominal voltage is 12 V CC and that the accepted variations oscillate between +25 %

and - 15 %. Note the values in the table (see the appendix).

2) With a CA voltmeter verify the output voltage of the converter, considering that its

nominal voltage is 220 V CA and that the voltage variations are + - 7%. Note the

values in the table (see the appendix).

b) Output frequency of the converter.

With a frequencymetre verify the frequency in the output of the converter considering that

the variation is + - 2%, for a frequency of 50 Hertz. Note the values in the table (see the

appendix).

c) Waveform of the converter.

With an oscilloscope, verify the waveform in the output of the converter.



QUESTIONNAIRE 1) How is better to place a DC / CA (12 V / 220 V) converter in order to avoid high

voltage drop?

a) As close as possible of the batteries

b) As close as possible of the load

c) Is not important

2) How is better to place a DC / DC (24 V / 12 V) converter so that high falls of tension

don’t occur?

a) As close as possible of the batteries

b) As close as possible of the load

c) Is not important



DIAGRAM / ELECTRIC CIRCUIT…………………………………………………………….

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WORK PROPOSAL • Perform the same verifications by adding different loads to the output of the converter.

Compare the results with the measurements conducted in open circuit.

• Execute all the measurements only with the oscilloscope.



APPENDIX

The solar photovoltaic systems generate DC power while practically all the electrical domestic devices are designed for AC power.

The converters or investors are devices destined to transform DC power in AC power(Figure ). The converters create a square waveform that can be filtered to obtain a sine waveform like that of the grid.

Figure ?: Equivalent schema

For many applications with solar energy, it is sufficient to use converters of square wave because it can supply perfectly different loads like incandescent lights, small motors, etc. These converters, when there is not filter, have an inferior cost and present a higher efficiency because the losses are smaller.

Table for the I/O converter values:

CONVERTER

INPUT V VARIATION (%) OUTPUT V VARIATION

(%) FREQUENCY VARIATION (%)

rated registered accepted registered rated registrada accepted registered rated registered accepted registered

12 V CC +25% -15% 220 V CA +- 7% 50Hz +- 2%



10.8. Practical Work 8: Calculation of the section of the conductors in a photovoltaic solar system.

PURPOSE: How to calculate the section of the conductors in a photovoltaic solar

system..

OBJECTIVES: Calculate of the conductors section is very important when working with DC

low voltage (12V) because the voltage drop in the conductors can be very important if the size is not well evaluated.

Verify the existing conductor sections of the photovoltaic panel and compare with theoretical calculation, verify if the section is correct.

Verify the existing conductor sections of battery and make a theoretical calculation of conductor sections supposing that this is located at 2 meters from the converter.

EXECUTION SEQUENCE

a) Calculation of conductor sections of the connection between the PV panel and the KIT 1. Verify the existing conductor sections of the PV panel. Measure the length of the cable

2. Calculate the minimum section required for a maximum voltage drop of 0.1 V, thanks to

the formula:

( )Vb-Va56LI2S

⋅⋅⋅

=

With:

I = maximum short circuit current of the PV panel (see practical work 2), in Amperes

L = length of the cable from the panel to the KIT, in meters

Va-Vb = maximum voltage drop (0.1 v)

Compare if the section found it fit with the conductors of the equipment



b) Calculation of the conductor sections in the output of the battery 1. Verify the existing conductor sections of the battery

2. Calculate the minimum section required so that cables present a maximum voltage drop

of 0.2 V, using the same formula, and considering that the power output of the converter is

150 W for 12 V input voltage and is located at 2 meters from the battery:

( )Vb-Va56LI2S

⋅⋅⋅

=

With: I = power of the converter/input voltage L = 2 meters Va-Vb = maximum voltage drop (0.2 V) Compare if the section found it fit with the conductors of the equipment.

QUESTIONNAIRE

What is the value of maximum voltage drop between the PV panel and the training KIT if the conductor section is of 4mm2. Calculate the minimum section required by the training KIT conductors if the battery is 20 meters far from the converter, accepting a maximum voltage drop of 0.2 V. What would be the maximum current that could circulate in a 4 mm2 section line and 30 meters length in order to avoid a voltage drop superior to 5% of the nominal voltage (12V).




MATERIALS………………………………………………………………………………………

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INSTRUMENTATION

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WORK PROPOSAL

Calculate the sizing of an system that could supply with electrical energy the classroom or the laboratory that is being occupied. Size the equipment and make the calculation of the conductor sections.

project number eie/05/011/si2.419343 microgrids...guide for teaching practices - microgrids project...

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