Understanding and using solar energy in 20 steps
Contents 1.
Step: The preparations................................................................................................................. 1
THE BREADBOARD ................................................................................................................................. 1
SOLAR MODULE ..................................................................................................................................... 2
SOLAR MOTOR....................................................................................................................................... 2
DIODE ................................................................................................................................................... 2
LEDS.................................................................................................................................................... 2
RESISTORS ........................................................................................................................................... 2
ELECTROLYTIC CAPACITORS .................................................................................................................. 3
HOOK-UP WIRE ...................................................................................................................................... 3
2.
Step: Connection and functioning of the solar module............................................................ 3
CONNECTING THE SOLAR MODULE AT THE PATCH PANEL .......................................................................... 3
THE FUNCTIONING OF THE SOLAR MODULE AND A SUITABLE LIGHT SOURCE ............................................... 4
3.
Step: Determining the polarity of the solar current .................................................................. 4
4.
Step: Using solar power directly with LEDs .............................................................................. 4
5.
Step: Series and parallel connection.......................................................................................... 5
6.
Step: Solar power with intermediate storage ............................................................................ 5
7.
Step: Solar power – high energy?............................................................................................... 6
8.
Step: Preparing the solar drive ................................................................................................... 6
9.
Step: Converting solar energy into motion................................................................................ 6
10.
Step: Solar kinetic energy with starting help ........................................................................ 7
11.
Step: Shading on the solar module – causes and effects.................................................... 7
12.
Step: Orientation of the module toward the light source..................................................... 8
13.
Step: Influence of the temperature on the solar module...................................................... 9
14.
Step: More solar energy through mirror technology............................................................ 9
15.
Step: Storing solar energy..................................................................................................... 10
16.
Step: Stored energy and mechanical energy ...................................................................... 11
17.
Step: Solar energy, charge monitoring and fuel gauge ..................................................... 11
18.
Step: Solar energy and non-return valve ............................................................................. 11
19.
Step: Charging batteries with solar energy......................................................................... 12
20.
Step: Chemical processes with solar energy...................................................................... 12
1.
Step: The preparations
The breadboard
With the breadboard, the experiments can be configured without a soldering iron. Also called a patch
panel, on the inside it consists of contact springs that are connected to one another in a system of
rows. The electronic components and connection wires can be repeatedly inserted in the contacts and
thus allow a circuit to be designed without soldering or screws. Connection wires pinched off
diagonally with the wire cutter make insertion easier.
The patch panel included with the educational kit has 270 contacts altogether in a 2.54 mm grid. The
230 contacts in the middle range are each connected by vertical strips in rows of five. At each edge of
the wide side there is a row with 20 contacts which are horizontally connected to a bar. These “upper”
and “lower” rows are well suited for use as power supply bars.
Fig. 1: Inner principle of the patch panel
Solar module
The solar module included consists of several polycrystalline solar cells. The silicon material, made of
several crystals, is contaminated by intentional doping, which gives a negative and a positive layer.
The N-layer (negatively doped) is coated dark blue on top, for better absorption of light. The lower
layer is the P-layer. The electrons are set in motion by impinging light and a voltage arises between
the two layers described. We can use this voltage and the flowing current. A single crystalline silicon
solar cell gets ca. 0.5 V per cell. The current depends on the size of the cell.
Fig. 2: Schematic symbol: solar module
Solar motor
There is a solar motor in the educational kit that starts up with just a small amount of current and a
little voltage. The motor in the educational kit is a low-voltage DC motor.
Fig. 3: Schematic symbol: motor
Diode
Diodes let the current pass in only one direction. For that reason, they are used to rectify AC voltages
and to block undesirable polarity with DC voltage, among other things. You can picture the functioning
of a diode in normal operation most easily as a non-return valve (water installations).
Fig. 4: Silicon diode, type 1N 4148. The cathode of the diode is identified by the imprinted stripe; the
other connection wire is the anode. The technical current direction goes from the anode to the
cathode.
In forward direction (schematic symbol: arrow), with a silicon diode such as the 1N 4148, significant
current only begins to flow at a voltage of ca. 0.6 to 0.7 V.
Fig. 5: Schematic symbol: diode
As a rule, there are two kinds of diodes used in photovoltaic systems: blocking diodes and bypass
diodes. Blocking diodes prevent the battery from discharging through the photovoltaic modules when
sunlight is lacking. The bypass diodes protect the solar cells and the panel from possible damage
which could be caused by partial shading.
LEDs
The LED (light emitting diode) has one further characteristic: it shines when voltage is applied.
Normally, LEDs should always be operated with a series resistor for current limiting. Red LEDs require
the least voltage (1.8 V). After them are the yellow, green, blue and finally white LEDs with the highest
voltage (up to 3.6 V).
Fig. 6: Pin assignment of LEDs: the anode (+) with the longer connection wire and the cathode (-)
additionally marked with a flat area (6a) on the enclosure
Fig. 7: Schematic symbol: LED
Along with the “normal” LEDs there are also special designs such as a flashing LED. You can identify
a flashing LED by the small black spot within the red enclosure. This spot contains a tiny electronic
system in the form of an integrated circuit which causes the LED to flash as soon as the correct
voltage is applied.
Resistors
A resistor is a passive component in electric and electronic circuits. Its main task is reduction of the
flowing current to “reasonable” values. The resistance values are imprinted in the form of coded
coloured rings. The first four coloured rings indicate the resistance value according to the following
table. The fifth (narrower) coloured ring stands for the tolerance of the resistance value. A tip for easy
differentiation of the resistors in the educational kit: The 10 Ω type is thicker than the others. There are
two of the 100 Ω type.
There are metal film resistors in the educational kit with the following values:
Resistance
value
10 Ω
100 Ω
1 kΩ
2.2 kΩ
1st Ring
2nd Ring
3rd Ring
4th Ring
5th Ring
brown
brown
brown
red
black
black
black
red
black
black
black
black
gold
black
brown
brown
brown
brown
brown
brown
Fig. 8: Schematic symbol: resistor
Electrolytic capacitors
Electrolytic capacitors have a high capacity compared to normal capacitors. Due to the electrolyte, an
electrolytic capacitor is polarity-dependent and the connections are designated with a positive pole
and a negative pole. If the component is connected “the wrong way around” over a longer period, the
electrolyte of the capacitor is thereby destroyed. Do not exceed the imprinted maximum voltage
indication, because otherwise the insulation layer could be destroyed.
µF means “microfarad”; the unit µ is one millionth of the basic unit.
Fig. 9: Electrolytic capacitors with connections; the positive pole is the longer connection. In addition,
the negative pole on the enclosure is designated by a bright stripe.
Fig. 10: Schematic symbol: electrolytic capacitor
For the sake of simplicity, the term “electrolytic capacitor” is sometimes shortened to “electrolytic.” This
abbreviation is mainly used in the US.
Hook-up wire
You can make jumpers with the hook-up wire that is included. To do this, you have to estimate or
measure the approximate length of the jumper (plus the length for the wire ends that are to be inserted
into the plug contacts). The ends are stripped of insulation for ca. 8 mm. Connection wires pinched off
diagonally with the wire cutter make insertion in the patch panel contacts easier. Once the jumpers
have been made, they can be used again and again.
2.
Step: Connection and functioning of the solar module
You will learn about the characteristics and functions of a solar module through practical experiments
in the following sections. You will learn how solar modules can be used and what to take into account
in order to obtain optimal energy yields.
Connecting the solar module at the patch panel
Experimental set-up: solar module, patch panel, pin contact strip
On the back of the module there are soldered connections with cables soldered on. The kind of current
the module delivers is DC. Thus, as with a battery, there is a positive pole and a negative pole.
Connect the black and the red cables to the patch panel. It is recommended that you insert the black
connection into the lower bar and the red one into the upper bar, as shown in Fig. 11. The solar
module can remain plugged in for almost all of the following experiments.
Fig. 11: The connection lines of the solar module (flex ends) can also be directly inserted in the patch
panel, but pins can stabilise the connection.
Place the solar module so that a sufficiently bright source of light shines on it.
There are various measurement methods for determining the power values around the solar modules:
•
Display with LEDs
•
Measurements with a consumer, e.g., a motor
•
Measurements with a multimeter (additionally required)
•
Measurements and analysis with the PC (not provided)
Simple measuring tasks such as the polarity display or basic functional displays can be handled well
with LEDs. If detailed measurements are desired, a multimeter is a good aid. In the educational kit,
simple measurements and functional displays are carried out with LEDs and with the motor.
The functioning of the solar module and a suitable light source
Experimental set-up: solar module, patch panel, 100 Ω resistor, red LED
This experiment also works with little light (cloudy sky); with a lot of light (full sun) the visible
effects are more noticeable.
Insert the connections of a red LED (light-emitting diode) and the 100 Ω series resistor in the patch
panel. The longer connection of the LED is to be connected to the red “side” (+). Depending on the
radiation intensity, the LED shines more or less brightly. If the LED does not shine, either there is too
little “light energy” available or the LED was connected using the wrong polarity. If the LED flashes,
you used the flashing red LED.
Fig. 12: Simple functional test with a red LED
Fig. 13: Patch panel set-up
You can do the experiment with various light sources, e.g., with direct sunlight, a halogen lamp, an
incandescent lamp, an electric torch, an energy-saving lamp, a fluorescent lamp, an LED torch, etc. If
the LED shines brightly, the light source is suitable.
3.
Step: Determining the polarity of the solar current
Experimental set-up: solar module, patch panel, 100 Ω resistor, red LED, orange LED or green LED
You need a bright light source for the following experiment.
The next thing we will do is set up a polarity checker with which you can comfortably determine the
polarity (positive or negative pole) of the solar module and other voltage sources without having to
unplug and/or plug in anything. From the upper bar the connection to the row of five is made with a
100 Ω resistor and from there across to another row of five. From the lower bar two LEDs are
connected to the rows of five. The LEDs indicate the polarity. As an example, the LEDs can be
inserted so that the red LED lights up when the polarity is wrong and the orange-coloured one lights
up when the polarity is correct. Instead of the orange-coloured LED, the green one can also be used,
but its functioning is harder to see in daylight.
The connection wires of the solar module can now be connected to the patch panel – without paying
attention to the polarity. The LEDs signal what the polarities are.
Fig. 14: Patch panel with polarity checker using LEDs
Fig. 15: Detail of wiring
If the polarity checker is to be used for higher battery voltages (e.g., 9 V), the series resistor is to be
replaced by one with 1 K, so that the LEDs are not destroyed.
4.
Step: Using solar power directly with LEDs
Experimental set-up: solar module, patch panel, 100 Ω series resistor, red, green, orange LED,
flashing LED
This experiment also works with little light (cloudy sky).
Fig. 16: Insert the green, red, orange-coloured LEDs and the flashing LED one after the other in the
patch panel. The longer connection wire of the LED is the positive pole.
Fig. 17: The associated circuit diagram; first insert the green, the red and then the flashing LED in the
patch panel to close the circuit.
Unplug a connection of the solar module. What happens? The LEDS no longer shine. Plug it in again
– the LEDs shine again.
5.
Step: Series and parallel connection
Experimental set-up: solar module, patch panel, red, green and orange LEDs, two 100 Ω resistors
This experiment also works with little light (cloudy sky).
Fig. 18: a) Principle behind series connection of individual solar cells; b) string of crystalline cells with
connections of individual solar cells by means of flat connectors.
The principle of series and parallel connection can be studied with the help of LEDs.
Series connection of solar cells as it was done in the case of the module included in the educational
kit:
•
The voltages are added when solar cells are connected to one another in series.
•
The short circuit current corresponds to that of a single solar cell – i.e., to that of the
weakest one (the weakest link in the chain).
•
If a solar cell is shaded, the output of the entire solar module drops by the degree of
shading.
•
With partial shading of a cell, the illuminated solar cells feed their current into the shaded
solar cell; the latter heats up and in an extreme case can be destroyed.
•
What does series connection mean? So as to be able to practically understand this, do the following
experiment with the LEDs:
Fig. 19: Insert the red and the orange-coloured (or green) LED in the patch panel so that both LEDs
are connected in series. The longer connection wire of the LEDs is the positive pole.
Fig. 20: The associated circuit diagram
No series resistor has to be used with this set-up. How brightly do the LEDs shine?
Individual solar cells (or solar modules) can also be connected electrically in parallel. In this case, all
negative pole and all positive pole connections of the solar cells are connected to one another. The
result:
•
The voltage of the solar cells connected in parallel corresponds to that of a single cell.
•
The short circuit current is increased by the amounts of current from the individual cells.
With solar cells that are equally strong, the short circuit current is increased by the number of cells.
•
It is possible to connect cells together with different outputs (short circuit current).
With partial shading of a cell, the illuminated solar cells feed the added current into the shaded cell.
The latter heats up and can in an extreme case be destroyed.
Fig. 21a: Parallel connection of several solar cells
Fig. 21b: Parallel connection of two LEDs
6.
Step: Solar power with intermediate storage
Experimental set-up: solar module, patch panel, 100 Ω series resistor, flashing LED, 4,700 µF
electrolytic capacitor
This experiment also works with little light (cloudy sky).
Insert the flashing LED and the series resistor in the patch panel.
Fig. 22: Circuit diagram: series resistor and flashing LED
Fig. 23: Patch panel set-up
Depending on the light shining on the solar module, the LED flashes more or less brightly. With little
incidence of light, the flashing can barely be seen. Now insert the electrolytic capacitor as well. At first,
the LED no longer flashes for some time, but also more brightly with little light.
Additional experiment: Insert another LED, e.g., the red one, instead of the series resistor in series to
the flashing LED. Now you suddenly have two flashing LEDs.
Fig. 24a: Circuit diagram: flashing LED and red LED in series connection
Fig. 24b: Patch panel set-up: flashing LED and red LED in series connection
7.
Step: Solar power – high energy?
Experimental set-up: Solar module, patch panel, bright orange LED, 100 µF electrolytic capacitor,
4,700 µF electrolytic capacitor
This experiment also works with little light (cloudy sky); the charging times are shortened
with a strong light source.
The LED solar flashing light can be set up with the simplest means. Depending on the light available,
when pressing the switch-key the LED produces a bright flashing light after a charging time of a few
seconds.
Fig. 25: Set-up of the LED solar flashing light
You can make the switch-key yourself from the wire included.
Fig. 26: Wire switch or switch-key from the hook-up wire of the educational kit
Fig. 27: Circuit diagram: solar flashing light, alternatively with the small and the larger electrolytic
capacitor
First experiment with the small 100 μF electrolytic capacitor and replace it in the second experiment
with the larger 4,700 µF electrolytic capacitor. Due to the low voltage, the flash energy amounts to only
about two mWs. A relatively small charging current is required, which the solar module can supply
without any problem. Depending on the light source, the electrolytic capacitor is sufficiently charged
after a few seconds. Now cover the solar module and afterward briefly press the switch-key. The LEDs
flash briefly. Only a little residual brightness remains if low current continues to be supplied through
the solar module.
8.
Step: Preparing the solar drive
Experimental set-up: 1 solar motor, patch panel, pin contact strip, disc
As with the solar module, the connection lines of the motor are made of flex. Connect the black and
the red cable to the patch panel. It is recommended that the black connection be inserted in the lower
bar and the red connection (+) be inserted into a contact in the row of five, as shown in Fig. 28.
Fig. 28: The connection lines of the solar motor (flex ends) can also be directly inserted in the patch
panel, but pins can stabilise the connection.
In order to be able to tell whether the motor shaft is turning during the experiments, it makes sense to
mount the disc included on the motor shaft. For this, pre-drill a hole in the centre with a needle. Put the
cardboard disc on the axle of the motor.
Fig. 29: Preparing cardboard disc for mounting
Fig. 30: Cardboard disc mounted on motor axle: a) from above, b) from the side
9.
Step: Converting solar energy into motion
Experimental set-up: solar module, patch panel, motor with disc
For the following experiments, you need a bright light source or full, direct sunlight for the solar
module.
Fig. 31: Experimental set-up with the solar module, patch panel and motor
Fig. 32: Circuit diagram: solar module and motor
You can also attach the motor to a cardboard box with a piece of double-sided adhesive tape.
Fig. 33: The disc is turning
If sufficient light shines on the solar module, the motor axle begins to turn by itself. If there is too little
light, you may also need to turn the motor a little with your finger to set it in motion. This is due to the
fact that the motor’s starting current can be more than double the operating current in continuous
operation.
Fig. 34: “Starting” the motor with the index finger with too little light incidence; reason: the motor’s
starting current is greater than its current in continuous operation.
This experiment also shows the different operational modes of solar power and power that comes from
batteries. The current requirement when starting the motor is completely supplied by batteries without
any problem. The solar module in direct operation can only supply to the consumer current that is
converted by means of the momentary irradiation of light (and the efficiency of the solar cells). If you
have a 1.5 V battery or accumulator cell handy, just for fun connect it to the motor.
10. Step: Solar kinetic energy with starting help
Experimental set-up: solar module, patch panel, motor, 4,700 µF electrolytic capacitor, flashing LED
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
The electrolytic capacitor is charged by the solar module in this circuit. The flashing LED and the solar
motor are connected in series with the capacitor storage. The LED flashes with increasing charge in
the electrolytic capacitor. If sufficient light and energy flow are available, the solar motor receives
current pulses by means of which a pulsating rotary motion can take place.
Fig. 35: Patch panel set-up with wire switch
Fig. 36: Circuit diagram
With a wire switch, you can now connect the motor directly to the electrolytic capacitor. If the
electrolytic capacitor is charged, the disc rotates at high speed.
Additional experiments: Experiment both with and without a wire switch and with a 10 Ω, 100 Ω and 1
kΩ resistor in each case. What changes with the motor speed and how it functions?
Fig 36a: Additional experiment with resistors
The additional experiments as illustrated in Fig. 36a show that with the resistors the current flow to the
motor can be changed by means of the resistors and thus the speed is affected.
11. Step: Shading on the solar module – causes and effects
Experimental set-up: solar module, patch panel, motor or LEDs with series resistor
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
Fig. 39 shows the experimental set-up. The LEDs (alternatively, the motor) are connected to the
module, the module is oriented toward the light source and the motor shaft turns. If you do the
experiments outdoors with bright sunshine, the motor is better than the LEDs as a consumption
indicator. The shining of the LEDs can hardly be seen in bright ambient light. In a room it is also
possible to shield the LEDs with a piece of cardboard.
Fig. 37: (omitted)
Fig. 38: Shading with a) film and b) cardboard
Now slowly shade part of the module with your hand. The speed of the motor becomes slower, or the
motor totally ceases to turn.
Fig. 39: The motor or alternatively the LEDs with the 100 Ω series resistor can be connected to the
solar module.
Now you can do further experiments of this kind:
Produce a slight shadow by means of an additional glass disc or a matt film that is held between the
light source and the solar module.
Produce a heavy shadow by means of a piece of cardboard that you hold directly over the solar
module.
Shade individual solar cells of the solar module by placing a piece of cardboard directly on one or
several solar cell(s) of the solar module.
Fig. 40: Individual solar cells shaded
In the case of large PV systems that are equipped with crystalline solar modules, the topic of shading
is an important one. So that the entire solar generator does not fail in case of partial shading, e.g.,
due to a leaf, Schottky diodes are used as “current bypass” around the shaded solar cell. With
defective diodes, a hot spot can develop in an extreme case, with individual solar cells being
destroyed.
12. Step: Orientation of the module toward the light source
Experimental set-up: solar module, patch panel, motor
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
Fig. 41: Experiment with orientation of the module toward the light source
Fig. 42: Circuit diagram with two main orientations
Take the solar module between thumb and index finger (without shading the surface) and orient the
surface of the module as much as possible at a right angle to the light source. How fast does the
motor axle turn? Now vary the orientation toward the light source by moving the solar module back
and forth and observe the motor.
The more perpendicularly the light beams strike the solar module, the more light energy the solar cells
can transform into electric current and thus supply the motor.
Fig. 43: Schematic diagram of the inclination angle toward the light source. The number of arrows
striking the solar module stands for the light intensity.
Orient the solar module precisely toward the sun or another light source by placing cardboard, blocks
of wood, etc., underneath the solar module. Observe the motor. As described further above, the motor
axle turns. Now you have earned a break. Wait about an hour (or several hours) and then look at your
experimental set-up again. The sun is no longer precisely perpendicular to the solar module; the motor
turns more slowly or has even stopped. Since the light source, i.e., the sun in the sky, moves from
east to west (of course only seemingly), optimally the solar module ought to be guided in its orientation
toward the sun.
13. Step: Influence of the temperature on the solar module
Experimental set-up: solar module, patch panel, motor or LEDs, 100 Ω resistor, black film or
cardboard, thermometer
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
In this experiment you can deal with the influence of the ambient temperature on the output of the
solar module.
The solar module should be oriented directly toward the sun; the motor or an LED can be used as
output indicator. Black paper or cardboard temporarily placed on the solar module will heat it more
intensely. If no thermometer is available, you can also feel the temperature with your finger.
Fig. 44: Experimental set-up – what influence does the temperature have on the solar module? The
temperature sensor of a surface thermometer was attached to the back of the module with an
adhesive strip.
If you do this experiment on a warm, sunny summer day (favourably), of course you don’t need any
black cardboard. It would intensify the warming effect. A black surface absorbs the heat more quickly.
Construct this experimental set-up in direct sunlight and pay attention to the output of the motor or the
plugged-in LED. Feel the surface temperature of the solar module with your hand.
The reason for the blue surface coating of the solar module is that as much light as possible is
absorbed and as little as possible is reflected. The disadvantage: the surface accordingly heats up
intensely. With direct sunlight, heating on the top of the module to over 60 °C is no rarity.
By means of the experiment you can learn the following: the consumer connected to the solar module
runs somewhat slower with increasing heating of the solar module. Put the module in the refrigerator
for half an hour and repeat the experiment with the solar module at the same solar intensity and with
the same connected motor.
14. Step: More solar energy through mirror technology
Experimental set-up: solar module, patch panel, mirrors (e.g., reflective metal, reflective tiles, cosmetic
mirrors, reflective foil, etc. – the mirror should be at least as large as the solar module).
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
The experimental set-up with the solar module and the motor is identical to those in the previous
experiments. When positioning the mirrors, you can see the reflected light on the table, on the wall or
on the solar module, depending on the orientation of the mirror. The solar module should not be
shaded by the mirror. If the reflected light also directly strikes the solar module, observe what the
motor does.
a)
Mirror position in front, below the solar module. By changing the inclination angle of the mirror
to the module, twice the amount of light can be directed onto the module.
Fig. 45: A reflective tile was placed below the solar module in the experiment.
b)
With two mirrors on the right and left sides and with good orientation of the mirror to the
module, up to three times the amount of light can be directed onto the module.
Fig. 46: The mirror principle: The light beams reflected by the mirror onto the solar module bring
additional energy. Note that the angle of incidence onto the mirror is the same as the angle of
emergence to the solar module.
If the mirror is oriented to the solar module at the correct angle, the light output to the solar module is
increased by the reflected portion. The electric output of the solar module can thus be increased in a
simple manner.
15. Step: Storing solar energy
Experimental set-up: solar module, patch panel, 100 Ω series resistor, red, green, orange, flashing
LED, 100 µF and 4,700 µF electrolytic capacitors
This experiment also works with little light (shadows, cloudy sky).
Is it true that the low output of your solar module can yield a large amount of energy over a long time
through reasonable storage of power? The principle of electrical power, invisible for our senses, can
be compared to and explained by a principle which we can observe with water:
a water tap (your solar module) that drips over many hours gradually fills a ten-litre bucket with water.
Fig. 47: The principle of energy storage explained on the basis of the dripping water tap: small
amounts over an entire day fill a large basin.
Over the course of a day with sunshine, a solar module with low output “drips” the power converted
from the sun milliampere hour for milliampere hour (mAh) into the energy storage.
The unit mAh quantifies the power per hour, in contrast to mA, which signifies the momentary current
flow.
There are electrolytic capacitors in the educational kit that can store power. The advantage of the
capacitor storage is that it has a very long service life. But compared to a battery the storage capacity
is only slight, which for the experiments has the advantage that the principle of storage can be
observed over a manageably short period of time. The connection wires of the electrolytic capacitor
must be connected briefly (short-circuited) before the experiment so that the charging function can be
experienced.
This experiment also works with little light (shadows, cloudy sky).
Fig. 48: Patch panel set-up – use the flashing LED. a) First plug in the small 100 µF electrolytic
capacitor (the longer connection wire is the positive pole). b) Then replace it with the 4,700 µF
electrolytic capacitor. What happens after the replacement? The LED doesn’t flash anymore; it takes
some time after plugging the electrolytic capacitors in before the LED shines or flashes again. If the
solar module is covered, the LED continues to flash.
Fig. 49: The electrolytic capacitors C1 and C2 and the LEDs can be replaced for the experiments.
Think of the series resistor R1 when connecting the LEDs.
Series of experiments:
a)
Plug the 100 µF electrolytic capacitor in; note the polarity. What happens?
The flashing LED pauses briefly, then flashes again.
b)
Plug the 4,700 µF electrolytic capacitor in. What happens?
The flashing LED pauses for a longer time, then flashes again.
c)
Leave the experimental set-up as in b) until the LED flashes. Then pull the 4,700 µF
electrolytic capacitor out of the patch panel. Next, shade the solar module. The LED immediately stops
flashing. Now plug the electrolytic capacitor back into the previous contact rows and continue to shade
the solar module. The LED flashes although no power is coming from the solar module.
Fig. 50: Experimental set-up: the electrolytic capacitor is replaced.
Ergo: the charge in the “energy storage” electrolytic capacitor is preserved over a longer period.
d)
If the electrolytic capacitor is charged, the LED flashes. Now disconnect the solar module.
Observe how long the LED flashes and draws its power only from the storage electrolytic capacitor.
The larger the capacitor storage is, the longer the LED flashes, even without power from the solar
module. With a Gold Cap, the missing power supply (e.g., during darkness) could thus be bridged over
a long period.
e)
Now leave the previously charged electrolytic capacitor connected to the solar module over
night (without LED) so that no more light strikes it. The next day, check with a flashing LED how much
charge is still in the capacitor. The flashing LED shows little or no reaction. What happened? The
electrolytic capacitor discharged “backwards” via the solar module.
16. Step: Stored energy and mechanical energy
Experimental set-up: solar module, patch panel, 4,700 µF electrolytic capacitor, motor, flashing LED
This experiment also works with little light (cloudy sky).
If you connect the motor directly to the solar module, it can be that the amount of energy coming from
the solar module is not sufficient to make the motor start up automatically.
Fig. 51: Circuit diagram – use the flashing LED as power indicator. First plug the 100 µF electrolytic
capacitor in and then the 4,700 µF electrolytic capacitor parallel to the connections of the solar
module.
If the motor is connected to the capacitor, the motor shaft turns several revolutions. Under some
conditions, the start-up held of the electrolytic capacitor is already sufficient, so that the motor can
continue to run with the slight power of the solar module.
Fig. 52: The motor is temporarily connected at the same contact points as the electrolytic capacitor.
The motor turns a few revolutions, the LED does not flash anymore and it takes a few seconds until
the LED starts to flash again if the motor is again disconnected. The motor completely discharged the
electrolytic capacitor.
17. Step: Solar energy, charge monitoring and fuel gauge
Experimental set-up: solar module, patch panel, flashing LED, red LED, 1N4148 diode, green LED,
4,700 µF electrolytic capacitor, 1 K resistor, 2.2 K resistor, wire switch; additional experiment:
rechargeable battery
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
Is the energy storage now empty, half-full or full? For this, we need a display, similar to a fuel gauge in
an automobile. But the fuel gauge of a rechargeable battery is a lot more complicated. In order to get
all the factors under control, there are clever monitoring electronics with microprocessors and
elaborate software.
In Fig. 53, you see the experimental set-up of a simple charge level indicator which you can assemble
with the parts in your educational kit. The upper red LED indicates the charging current to the energy
storage and shines as long as the electrolytic capacitor is being charged. The middle flashing LED
begins to shine in connection with the diode and the green (or orange-coloured) LED when the
electrolytic capacitor (or rechargeable battery) is completely charged. Due to the fact that D2, D3 and
D4 are connected in series, the LED starts to flash only with a voltage of ca. 4 V. This voltage is
suitable for the “battery full” display in the case of a lithium battery. If D3 is bypassed, the voltage is
reduced at which D2 flashes.
Fig. 53: Experimental set-up on the patch panel
Fig. 54: Circuit diagram of the charge level indicator (test circuit whether solar module is suitable)
The simple battery fuel gauge is implemented via voltage measurement of the battery. It would be an
improvement to do the voltage measurement under load. The load ought to have a current
consumption that is 10% of the battery’s capacity and could be activated at the moment of
measurement by a button.
Fig. 54a: Additional “load” with orange-coloured LED or Motor (sample circuit)
18. Step: Solar energy and non-return valve
Experimental set-up: solar module, patch panel, electrolytic capacitor, button, silicon diode, series
resistor, red LED
This experiment should be done with uniformly bright sunshine (or desk lamp).
Fig. 55: Principle of the circuit with blocking diode
With solar charging of an electrolytic capacitor, Gold Cap or rechargeable battery, the charge would be
discharged again at night via the solar module (see 14th step). Therefore a non-return valve must be
added in the form of a diode. The diode functions like a valve that only allows the energy to flow in one
direction and prevents it from flowing in the other direction.
Turn the diode in the patch panel around. The LED doesn’t flash anymore since the current coming
from the solar module is blocked.
Blocking diodes prevent the storage battery from discharging via an unilluminated solar cell.
Fig. 56: omitted
Fig. 57: Patch panel set-up
19. Step: Charging batteries with solar energy
To stay with the comparison to water: for the collection tank – and thus the energy storage – an
experiment is now done with a battery. A rechargeable battery can replace primary batteries and be
used in nearly all portable electronic devices.
Fig. 58: The Micro AAA and Mignon AA rechargeable battery types can easily be used for many
portable electronic devices.
Experimental set-up: solar module, patch panel, resistor, LED and also a rechargeable battery
For the following experiments, you need a bright light source (or full, direct sunlight) for the solar
module.
The simplest possibility for charging is constant current charging. The battery is charged over a certain
period with a defined current. With simple constant current charging of a battery, the usual practice is
to charge it with 1/10th the current of the capacity specification for 14 hours.
With simple mains chargers, limitation of the charging current is achieved by a resistor which is
inserted between the power supply unit and the battery. But with solar chargers this approach would
be absurd. Here, the charging current can be achieved without loss by means of dimensioning (size)
of the solar cells or the solar module.
Thus not even a series resistor is needed with suitable dimensioning of the solar module. The solar
module in the educational kit, which delivers a 35 mA current with full sunshine, can safely charge a
battery cell. This proportionality changes with “larger” solar modules (producing more output) which
can deliver more current. Then limitation of the charging current or a charging electronic device is
urgently needed; otherwise, the battery would be destroyed.
Fig. 59: Circuit diagram and experimental set-up of a simple solar charger; the diode was inserted so
that the battery doesn’t discharge via the solar module at night.
Fig. 60: Patch panel set-up: Charging current display with an LED
20. Step: Chemical processes with solar energy
Experimental set-up: solar module, patch panel, dish, water, sodium bicarbonate or common salt, red
LED, 4,700 µF electrolytic capacitor
This experiment also works with little light (cloudy sky); the visible reaction in the water
becomes clearer with full sunlight or a strong light source.
Fig. 61: Experimental set-up: splitting water up. The solar radiation is additionally enhanced by a
mirror.
Fig. 62: Basic circuit diagram for splitting water up shows a solar module and the electrodes.
Experimental set-up: a dish with water and some sodium bicarbonate or common salt Plain water
conducts current very poorly. If sodium bicarbonate is added to the water, oxygen and hydrogen come
about through the electrical splitting up. If common salt is used, oxygen and chlorine gas come about.
You can use two wires as electrodes, ca. 10 cm long, the ends of which were stripped about 2 cm.
a)
Arrange the bare ends of the wires vertically in the dish beneath the surface of the liquid at the
maximum distance from one another and secure them with clothes pegs to the dish. The solar direct
current is conducted into the liquid through the two wires as electrodes. (By means of electrolysis,
reaction products come about at the electrodes from the substances contained in the liquid.)
b)
Connect the wire electrodes to the solar module. When beams of sunlight shine on the solar
module, you can see that little bubbles rise at the two wire ends in the liquid – at the negative pole
about twice as much as at the positive pole.
c)
An additional LED is series indicates the flow of current. Since the current is very slight, you
can perceive the weak shining of the LED more or less.
Fig. 63: In order to additionally show the flow of current, an LED is inserted in the circuit. The
additional electrolytic capacitor C1 is not obligatory for the functioning of the circuit, but it stabilises the
functioning.