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Load characteristics of the Solar cell

Apparatus – measuring principle

This experiment is based on the basic principle of measuring the load characteristic, which is based on a standard procedure for measuring the dependence of the output voltage on the current taken. In this task, a solar cell is used as a source of electricity. Its source of electromotive voltage is the light energy that falls on it. In order to monitor the dependence of the output electrical quantities on the light, the solar cell is artificially illuminated by a light bulb. The output light output of the bulb can be set to four preset levels. The scheme of the experiment shows figure 1.

schema zapojeni zatezovaci charakteristiky fotoclanku
Fig. 1 – Wiring diagram for measuring the load characteristics of a solar cell

In our remote experiment, a K8055 USB board (Velleman) is used to control the measuring apparatus, which is controlled by our K8055-MARIE application. The bulb circuit uses the DA output of the K8055 board converter, the output current of which is amplified by the DIY ISES Booster (only Czech). The luminous flux is directed by a reflector to the used solar cell – the system is created on a 3D printer (see Fig. 2).

zatezovaci charakteristiky fotoclanku - osvit
Fig. 2 – Bulb-solar cell configuration (before applying the reflective layer inside the reflector)

The ISES system modules (voltmeter and ammeter) are used to obtain the values of electrical quantities in the detection part of the apparatus, ie in the voltage and current sensing circuit. For this purpose, the ISES-ZOMBIE (only Czech) connection is used, which allows the connection of two ISES measuring modules to the K8055 board.

The circuit of the lighting bulb is supplemented by a reed relay, which detects the current flowing through the circuit of the bulb. The status of the relay is read by one of the digital inputs of the K8055 board. If the filament of the bulb burns out, this condition is detected on the measuring panel of the apparatus.

ISES zombie
Fig. 3 – ISES ZOMBIE module used to connect two ISES modules

A digital resistance decade is used in the role of a remotely adjustable load rheostat, which is controlled by eight digital outputs of the K8055 board. It is a power-adapted resistance decade, the resistors of which can be connected and disconnected by means of eight relays, which are controlled by the mentioned digital outputs of the control board. Thanks to this, it is possible to set 256 possible values for the load rheostat. This is a sufficient number of values to measure different output currents.

odporova dekada
Fig. 4 – Resistance decade module for source load (consisting of a pair of boards with four relays)

The above-mentioned functional blocks of the measuring apparatus are connected to the K8055 control board according to the block diagram in Fig. 5. The BK126 school power supply is used to power the power parts of the task. The coils of the eight digital rheostat relays are also supplied with this source. On the contrary, the ISES ZOMBIE input module is powered from the modified K8055 board – a description of this modification is given in the article: ISES – Z.O.M.B.I.E. on our publication website Fyzikální kabinet GymKT. (both links only in Czech)

blokove schema experimnetu
Fig. 5 – Block diagram of the measuring apparatus of the experiment D.E.V.I.L.

The measured experimental values (electrical voltage Ucell and current Icell) are read and displayed on the control panel in a web browser on the client side. The values measured in this way can be stored in a table and continuously displayed in a graph. This display is used primarily for an approximate check of the accuracy of the measured data, or to find the places of the characteristic where it is necessary to measure the necessary data. For complete processing according to the assigned work task, it can be downloaded to a computer and processed in any spreadsheet.

Control of the experiment

ovládání experimentu - Remote-LAB GymKT - DEVIL
  1. solar cell illumination – for measurement you can choose one of four levels of exposure solar cell

  2. solar cell load – for adjusting the electric current drawn from the solar cell serves rheostat, which can be controlled by this slider

  3. experimental data – there are shown the measured values of voltage and current that can be stored in the table

  4. table of exp. data – a table of experimental values (electric current, voltage) that can be further worked with

  5. table data processing – the data in the table can be displayed in a graph, saved to a computer for further processing, or the table can be deleted and measured again