Compact Sunlight Simulator for Photovoltaic Panels

While designing solar photovoltaic (PV) systems, we need sunlight for testing our design. For that purpose we may have to do many trips outdoors. This consumes lot of time and efforts. Also, testing stops, once the Sun sets. We often come across cloudy weather for days together. In such cases, the testing gets delayed.

Here, design and construction of a compact sunlight simulator is presented. It should be noted that, it is not a substitute for sunlight. The simulator generates only about 10 to 20% of rated power. This much power is sufficient to do initial development and testing of the system. Once the system is designed properly, then, it can be taken out in sunlight for full power testing. In this way, simulator will reduce the delays which are caused by cloudy weather. Further, initial development and testing can be done in the night as well. It will be useful in college laboratories, for demonstration. As sunlight may not be always available, during lab experiments.

In order to make the simulator compact, the panels are arranged around the light source. Hence, using single source of light, all panels receive light and thus very less light energy gets wasted. For this design, using 5 PV panels, a cube is designed. If more panels are needed, we can think of a pentagon or a hexagon shape for the top panels assembly.

Following is the bill of material: See Figures 1, 2, 3 and 4.

Solar Photovoltaic panels 12 V 10 W (36 cells) – 5 panels

Wooden Batten (20 mm x 10 mm) - 4 ft long

Flat Aluminum strip (24 mm x 2 mm) – 2 feet long

Teflon wires – 2 meters

Copper cables 1 sq mm – 6 feet

Connector with 12 terminals – 1

Plastic Legs, 1” height – 6

M4 x 15 mm screws, washers and nuts – 8 sets

Lamp Holder – 1

Two pin plug – 1

Metal clip “U” type - 1

Lamp 200 W – 1

Aluminum “U” channel 2 feet

Reflector made using Aluminum foil and cardboard 1.5 sq ft

Selection of PV panels is very important to get maximum power output. For this purpose, the characteristics of all five panels should be matching. This can be done by checking the power output of individual panels, for given light intensity and for a given load. All panels should generate the same voltage. This will ensure all panels are matched. The PV panels selected here, are 10 W rating, having size of 13” x 12” with thickness of 1”.

Cut the flat Aluminum strip in 4 small pieces of about 3 inches in length as shown in Fig. 5. The exact length of these pieces will depend upon the PV panel thickness. Make two holes at the ends of these pieces. Put marking at 1/3rd distance from both ends, so that the piece is divided into three sections. With respect to the middle section, bend the other sections by 45 degrees.

Using bent Aluminum strips, assemble the four panels as a hollow cube as shown in Fig. 6. Use the mounting holes provided on the PV panels. DONOT do any drilling or cutting operations on the PV panels. This may damage the PV panels.

Cut two pieces from the wooden batten, having length equal to that of the panel (Fig 7). Cut Aluminum “U” channel equal to the width of the PV panel, plus twice thickness of wooden batten. The “U” channel and batten are fixed to the PV panel using screws as shown in Fig. 7. Mount four legs on the panel and two legs at the middle of the wooden battens. Figure 8 shows the assembled bottom panel resting on the 6 legs.

Cut the wooden batten to about 1.5 feet. Make hole at the center of batten, to pass the Teflon wire, as shown in Fig. 9. Interconnect the lamp holder and the two pin plug.

Keep the assembled bottom PV panel on a flat surface. Place the 4 panel assembly over it. Mount 12 way connector on a wooden batten and fix the assembly on one of the PV panels as shown in Fig. 10. Connect wires to all the 5 PV panels and connect them on the 12 terminal connector. Place the lamp assembly on the top side in the middle. Break the U clip and fix on both sides of the wooden batten of the lamp assembly. This will secure the lamp assembly to the panels.

For testing the unit, an array of LEDs has been made as shown in Fig. 11. It consists of 4 LED PCBs (total 27 White LEDs) connected in series. Also, current limiting resistor of 14.8 ohm has been connected in series to limit the current. User can use any other type of load for measuring power output.

Connect the load to the panels. In this test procedure, all PV panels PV1 to PV5 have been connected in series. Put the 200 W incandescent bulb in the holder and switch ON the power. Place the reflector above the PV panels. Ensure there is gap between the PV panels and the reflector, to allow hot air to escape (Fig. 12).

Series & Parallel connections of PV Panels. In the above testing, all PV panels were put in series. If required, all PV panels could also be connected in parallel. In this case, it may be advisable to put a schottky diode in series with each panels.

PRECAUTIONS:

1) While connecting bulb to the power supply, if necessary, take professional help to avoid electric shock.

2) When the lamp is ON, avoid touching or moving the unit. Keep the unit in a secured place.

3) If lamp has to be removed, wait for some time after turning OFF, as lamp will be hot.

4) Between panels and the reflector, there should be sufficient gap for the hot air to escape.

Figure 12 shows the unit turned ON. The PV power generated has been fed to the LED load, and the load is also ON. Figure 13 shows the readings taken using multi-meters.

PV voltage generated = 80.8 V

Drop across resistor = 1.578 V

Current through load = 1.578/14.8 = 0.106 A

PV Power generated = 80.8 * 0.106 = 8.56 W

If it is required to increase the PV power output, then, we have to increase the bulb wattage. In that case, instead of single bulb, we can use multiple bulbs to increase the input power. There are many possibilities for multiple bulb design. Here one optimum design is presented.

We need following material as shown in Fig. 14:

Wooden Block (40 mm x 40 mm x 60 mm) – 1

Lamp Holders – 4

Lamps 60 W – 4

Teflon wire – 2 feet

Copper cable 1 sq mm – 2 meters

Self-threading screws – 8 Wooden

Batten (20 mm x 10 mm) – 1.5 feet long

The cable assembly is shown in Fig. 15. First, fix four lamp holders on the four faces of the wooden block. Connect all lamp holders in parallel using Teflon wire. To the fourth lamp holder, also connect the 1sq mm copper wire. Pass it through the central hole of the wooden batten. Then fix the 3 pin top.

Place the cable assembly on the top side of the panels as shown in Fig. 16. The unit is ready for use. Instead of incandescent bulbs, LED flood lights could be used, to reduce the power consumption and to reduce the heat.