Introduction: High Power Solar Day Lamp

Background:  This article is continuation of earlier article entitled “Simple Solar Day Lamp which lasts for 15 years” available at following link:

In the earlier article, construction of a small 5W day lamp was described. Here, how to make a high power solar day lamp is described. Apart from providing more light this design also offers following advantages:

1. 10% more light.
2. For increased power output, current still remains same as that for 5W version. Thus it still uses the same cheaper cable.
3. Improved construction, which provides better light reflection and safety to LEDs from damage.

Step 1: Material Required:

1. Aluminum U Channel
2. Wooden batten
3. Wood screws 0.5” long
4. Plastic or fiber washers 3 mm inner diameter
5. 23 White LEDs 1W rating
6. 3 Way terminal strip and mounting screw/nut.
7. Four Solar PV panels of 12V 5 W rating  (OR Two 24V 10W panels)
8. Wires

Please see the earlier article which provides step by step guidelines for making the LED array. Only different here is that we are making a bigger array with 23 LEDs.

Step 2: Circuit Diagram:

Circuit diagram of high power day lamp is shown in Fig. 1.

It consists of 23, 1W white LEDs (LED1 to LED23) connected in series. A current limiting resistor of 33 ohms 2W rating is connected to the LED array. Four solar PV panels of 12V 5W rating are connected in series as shown in the figure. The positive terminal of PV array is connected to the resistor and the negative terminal of the PV array is connected to the cathode of LED23.

Step 3:

Alternatively, in place of 4 panels we can connect two PV panels of 24V 10W rating. The circuit diagram for this alternate design is shown in Fig. 2.

Step 4: Improved Construction

As compared with the earlier design, slight improvement in the construction of LED array is suggested here. The LEDs are moved to the inner side of the aluminum channel as shown in the close up photograph in Fig. 3.

Step 5:

Similarly, the wooden batten is moved to the outer side of the aluminum channel as shown in the side view in Fig. 4.

Step 6:

Fig 5 shows the finished LED array with translucent plastic cover. This cover protects the LEDs from dust and also, reduces the glare coming from LEDs.

Step 7: Final Integration

Figure 6 shows the completed unit. Four PV panels of 12V 5W rating are attached to each other to make a single array of panels. This will make the mounting of PV panels on the roof easier. Cable is connected from the panels to the LED array.

Step 8:

Figure 7 shows the LED array when it turned ON during a sunny day. Even on cloudy days it provides fairly good amount of light. This day lamp can be used where ever lights need to be turned ON in the day time. As millions of lights are used during day time, this lamp will find use in offices, homes, malls factories etc.

Step 9: Multiple LED Arrays

Circuit diagram for connecting multiple LED arrays is shown in Fig. 8. Here two PV panels of 24V 30W ratings are connected in series. To the output of this PV array, three LED arrays of 23 LEDs each are connected in parallel. Current limiting resistor of 33 ohm 2W rating is connected in series with each LED array.

This will provide light equivalent to 3 tube lights. The advantage of this circuit is that, it needs less wiring, as, only one cable needs to be routed from the PV panels to the inside of the building. This wire should support current drawn by 3 LED arrays (about 1 amp). Inside the building, each LED array can be connected in parallel by using thinner wires. By increasing power rating of the PV panels, we can connect more LED arrays in parallel.

Step 10:

Finally, even though day lamp can not provide light during night, still it has the advantage of not using the batteries. The batteries have very short life. By avoiding use of batteries, the life of day lamp obtained is more than 15 years. It offers maintenance free operation and not even a switch to be flipped by the user. Need is to identify suitable locations where it can be used very effectively.

Abhijeet Deshpande
Bangalore, INDIA