LED Solar cell and its working


Ever thought of using LED as a solar cell? Do this experiment to find that out how it works. In this article, I will tell about LEDs. Circuit configuration required is necessary to convert LEDs into solar panel. Read the article to know about LED solar cells, their configuration and applications.

Solar cells are used to convert sun light into electrical energy. LED is capable of doing the same.

About Light Emitting Diode (LED)


An LED is a semiconductor optoelectronic device which emits a narrow bandwidth of visible or invisible radiations (light). LEDs operate on electroluminescence (emission of light from a semiconductor under the influence of an electric field).

Internal Structure of a typical LED

Internal structure of LED

Working of LED


In any normal PN junction diode, when a recombination occurs, the energy produced at the junction is released in the form of heat. These radiations are invisible. Unlike a PN junction diode, semiconductor materials like GaAsP and GaP are used in case of LED. If these materials are used, then recombination at the junction results in production of photons. Thus, the junction can act as a source of light.

In the figure shown below, anode is given a more positive potential than the cathode. This makes P region more positive than the n region. This positive potential at P region repels holes to the n side and the negative potential at the n side repels electrons to the P side. So, holes and electrons recombine at the PN junction and this produces energy. In case of an LED, this energy will be released in form of photons. These photons escape through the window provided on the anode and hence, the LED acts as a light source.

Colours & constructions
Depending on the type of material used to make the PN junction, the wavelength of light produced varies. Different colours are produced for different materials used in the construction.

Amber - AllnGaP
Blue - GaN
Green - GaP
Yellow - GaAsP
Red - GaAsP
White - GaN

How LED works as a solar cell?


Red LEDs act as solar cells when irradiated by solar energy.

LED as solar cell

When solar light is allowed to fall through the window of an LED, the photons in the light which has wavelength equal to the band gap of LED penetrates deep into the PN junction. On absorbing energy from these photons, the electron hole bond at the PN junction breaks and result in accumulation of electrons in the n side and holes in the p side. So, p side will be more positive than n side. This makes anode positive and cathode negative. Hence, LED acts as a cell.

LED solar panel


The voltage produced by a single red LED is around 0.7 to 1.3 volts but its output current is very low. So, a single LED cannot be used for powering any device. To increase its output current and voltage, we will use a combination of LEDs which are connected both in parallel and in series. The advantage of this is that the parallel combination increases current rating while the series combination increases voltage rating.

If the current output of a single LED is around 100uA, then 2 LEDs in parallel can produce 200uA. Similarly, if the voltage produced by a single LED is around 1.3 volts, then 2LEDs in series can produce 2.6 volts.

LED solar panel circuit diagram

led solar cell circuit diagram

Home-made LED solar panel capable of producing 12 V 50mA

Home made LED solar panel

LED solar panel side view

Home made LED solar panel back view
If the number of LEDs in this circuit is increased, more volts and higher current rating can be obtained.

Typical applications


1. They can be used to construct cheap solar cells.
2. They can be used for mobile phone charging.
3. They can power double voltage oscillators used for low power devices like mosquito repellents , calculators and digital watches.

Advantages


1. The cost incurred is low. They are economical in use.
2. They are easily available.

Disadvantages


1. If it is exposed to sunlight for long period, the LED can damage. In order to prevent this, high power LEDs can be used.
2. All the LEDs should face the sun at the same angle. This can be done by mounting all the LEDs on a common PCB.
3. Since the output current is low, for high power applications, more number of LEDs must be used but this makes the circuit bulky.

Read New inventions in Solar cells of Photo voltaic technology


Attachments

More articles: Solar Power

Comments

Author: ihsan04 Aug 2014 Member Level: Bronze   Points : 0

Hi Vineeth,
If using yellow led, does it have different output voltage? I am very interested about led as solar cell. I want to exchange opinions with you, can I know your email?

Guest Author: A.K.Das.28 Dec 2014

Well, I would like to construct one, for my self,and then confirm, OK,But however, I must congratulate the auther for, his brain wave.Thanks.

Guest Author: arun02 Apr 2015

How many LED are required to make a mobile charger. Please send me the circuit diagram with 5vd c1000mA. I need it for my mobile.

Guest Author: sampson22 Jun 2015

How many LED's should I put such that it will generate 12V?

Guest Author: Eddy21 Oct 2015

This just doesn't work. At least not at the voltage level described. I just tried about 4 different kinds of LEDs. All were about the same results. With a single LED reading V on my multimeter with my iphone light touching the LED I get about 1.3-1.6 Vs. With 2 in series I get about 3V after that things go down hill fast. Adding LEDs in series from that point forward decreases voltage instead of increasing.

Next I tried to measure current. I couldn't read any current on a very nice Fluke DMM. I tried using another LED as a load or a little mini filament light bulb that I use on my breadboard. No current registered.

So I said what the hell I will solder up a board like in the article. I made 8 rows series each with 7 LEDs in parallel. The most Voltage I could get was .6 Volts and still couldn't read any current draw when I attached a load.

I thought maybe the current output was super small so I tried tripping the gate of a very sensitive SCR. No luck.

I think the problem is that the LEDs are a super weak power source but an easier load. How does this circuit keep from just draining its self trying to power the LEDs? It is like a free energy machine it just doesn't work even with external energy (light) applied.

Guest Author: Sherri14 Jan 2016

The theory is good, one I've been working on but cannot solve. I'm guessing each LED needs it's own circuit so that it's not losing power trying to energize it's neighbor. Does anyone have a solution for that?



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