1 - OVERVIEW
The Solar Energy Mini-Laboratory was designed and constructed to enable experiments related to the use of silicon photovoltaic cells as alternative energy sources.
The equipment consists of two silicon solar cells and a solarimeter mounted on an azimuth-elevation platform, together with three digital meters and a variable resistive load.
The mounting platform allows the solar cells and solarimeter to be pointed in any direction above the horizon.
A termination panel is provided with binding posts to allow various connection of the solar cells (eg isolated, series, parallel) together with connection of the measuring instruments and the variable resistive load as desired.
2 - PARTS LIST
1 Mounting platform with an azimuth turntable and an elevation surface on which may be mounted up to two solar cells and a solarimeter. This platform also contains a terminating panel (strip) with 8 colour coded binding posts (terminals), and one 125 ohm 10W variable resistive load.
2 Silicon photvoltaic solar cells type SP500-2V (or ETM500-2V)
1 Solarimeter type DSR-1
3 Digital multimeters type Q-1500 or equivalent
2 sets of DMM test probes
2 patch cords (red) with banana plug terminations
2 patch cords (black) with banana plug terminations
3 - MANUFACTURER
Australian Space Academy
4 - LABELLED FRONT VIEW OF MINI-LABORATORY
5 - LABELLED REAR VIEW OF MINI-LABORATORY
6 - DETAILS OF TERMINATION PANEL WIRING
Note that the adjustment for the variable resistance load (rheostat) is on one of the elevation platform supports. This is not calibrated, but its actual resistance may be measured at any time with one of the digital multimeters (usually the one marked V, which is used to measure voltage).
To do this, be sure to disconnect all solar cells from the LOAD terminals, and turn the DMM selector control to the 200 ohm range.
7 - ALIGNMENT TOOL
To aid in pointing the elevation platform so that the solar cells and the solarimeter are normal to direct light from the Sun, an alignment tool has been provided on the platform. This consists of a long screw projecting at right angles to the platform, and which has a washer at its base. The platform is aligned normally (perpendicular) to direct sunlight when no shadow of this screw is visible. If the shadow is visible but lies within the washer, then the instrument is aligned within 10 degrees. This is usually regarded as sufficient for average precision measurements. However, as the Sun moves across the sky by about one degree every 4 minutes, it is necessary to continually align the platform for the highest accuracy measurements.
8 - USE OF THE DIGITAL MULTIMETERS
Three DMM's are provided in the mini-laboratory. These are marked A, V and S. The usual assignments of the meters are as follows:
S permanently connected to the output of the solarimeter. The scale selected should be the 200 milliamp range.
A used to meaure the current that the solar cells provide to the variable load. Note that this meter should be in series with both the cells and the load. The scale selected should be 10 amps, and the red probe terminal used should be the special 10A terminal (note: This is the only range that uses this terminal).
V used to measure the output voltage produced by the solar cells. This meter may be connected across the load terminals, except in the case when it is desired to measure the open circuit voltage of a solar cell. It is then connected directly across the solar cell terminals, in parallel with cell, and all load should be disconnected from that cell or cells. The scale selected for these measurements will generally be the 20 volt range.
Do not forget to turn off all digital multimeters when measurements are not being made, and at the conclusion of the experiment.
9 - NOTES ON SOLAR CELLS
MODEL SP500-2V (or ETM500-2V)
MANUFACTURER Not Available
COUNTRY OF MANUFACTURE China
PART NUMBER O - 2017 [Dick Smith Electronics]
POWER OUTPUT 1/4 Watt (full Sun) [nominal]
OPEN CIRCUIT OUTPUT VOLTAGE Voc = 2 V [nominal]
SHORT CIRCUIT OUTPUT CURRENT Isc = 500 mA [nominal]
10 - NOTES on SOLARIMETER
NAME Diffuse-light Solar Radiometer
MANUFACTURER Australian Space Academy
This solarimeter is designed to measure both the direct solar energy and the diffused or scattered sunlight incident upon the solarimeter. It consists of a small silicon photovoltaic cell mounted on a baseboard above which a white hemispheroidal diffusing surface (translucent) has been placed.
The instrument is designed to be used in conjunction with a type Q-1500 or equivalent digital multimeter set on the 200 mA current range. Although the instrument may be used with other indicating meters, it has only been calibrated under the above specified conditions.
The calibration for this solarimeter has been performed against a calibrated Qualimetrics, Inc Silcon Cell Pyranometer model 3120.
Solarimeter calibrations are only useful when comparing similar instruments. In the calibration curve it will be seen that the DSR-1 points diverge above the 3120 curve at lower solar elevation angles. This is because the translucent screen of the DSR-1 makes it more sensitive to diffuse light than is the 3120 which employs a transparent screen above the photocell.
Different solarimeters may thus have different angular responses (and it should be noted that the DSR-1 does display some azimuthal sensitivity), and different spectral responses.
However, the cell used in the DSR-1 solarimeter is very similar to the solar cells provided with the Solar Energy Mini-Laboratory, and thus the DSR-1 output can be used to determine the efficiency of these cells.
Note also that for accurate readings the solarimeter should be operated well away from any other structures (eg buildings), particularly brightly coloured structures. This also includes the operator with light coloured clothing (which can add a diffuse component to the reading).
With all the above factors taken into consideration, the estimated solar flux will in general be within 10% of the true value.