Understanding and using solar energy in 20 steps

Transcription

1 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 Step: Connection and functioning of the solar... 3 CONNECTING THE SOLAR MODULE AT THE PATCH PANEL... 3 THE FUNCTIONING OF THE SOLAR MODULE AND A SUITABLE LIGHT SOURCE Step: Determining the polarity of the solar current Step: Using solar power directly with LEDs Step: Series and parallel connection Step: Solar power with intermediate storage Step: Solar power high energy? Step: Preparing the solar drive Step: Converting solar energy into motion Step: Solar kinetic energy with starting help Step: Shading on the solar module causes and effects Step: Orientation of the module toward the light source Step: Influence of the temperature on the solar Step: More solar energy through mirror technology Step: Storing solar energy Step: Stored energy and mechanical energy Step: Solar energy, charge monitoring and fuel gauge Step: Solar energy and non-return valve Step: Charging batteries with solar energy Step: Chemical processes with solar energy 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.

2 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 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.

3 There are metal film resistors in the educational kit with the following values: Resistance 1st Ring 2nd Ring 3rd Ring 4th Ring 5th Ring value 10 Ω brown black black gold brown 100 Ω brown black black black brown 1 kω brown black black brown brown 2.2 kω red red black 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)

4 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.

5 Unplug a connection of the solar 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

6 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 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

7 For the following experiments, you need a bright light source or full, direct sunlight for the solar 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 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 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

8 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 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 Produce a heavy shadow by means of a piece of cardboard that you hold directly over the solar 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 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 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 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.

9 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 In this experiment you can deal with the influence of the ambient temperature on the output of the solar 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 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). 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 By changing the inclination angle of the mirror to the module, twice the amount of light can be directed onto the 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 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 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.

10 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 The LED immediately stops flashing. Now plug the electrolytic capacitor back into the previous contact rows and continue to shade the solar The LED flashes although no power is coming from the solar 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 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 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

11 charge is still in the capacitor. The flashing LED shows little or no reaction. What happened? The electrolytic capacitor discharged backwards via the solar 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 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 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 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

12 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 14 th 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 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 1/10 th 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 Thus not even a series resistor is needed with suitable dimensioning of the solar 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.

13 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 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.