Polycrystalline Solar Cell Report by -mjl359

**H&J: The cell can be used to either detect or harness light. The author of the main sensor report covers the solar cell as an energy harnesser, but there is a link to a project utilizing the cell as a light detector. It's a bit pricey for what it offers as a detector (you can detect light with a 50 cent photodiode).

See also John Schimmel's datalogging assignment for notes on using a solar cell as a light sensor.
tigoe

The model is SCC2433a - 24 x 33mm. Purchased from solarbotics for $5. ***H&J: Solarbotics appears to no longer manufacture/sell the polycrystalline cell, but offers a monocrystalline version: (monocrystalline and polycrystaliline refer to the silicon used in the solar cell; the first being purer, more efficient, and a bit more pricey than the latter.)

***H&J: Short Circuit Current = maximum current that can be drawn from the solar cell; Open Circuit Voltage = maximum voltage available from the solar cell

This solar cell is an effective light sensor as well as power source for small scale robotics. This particular solar cell measures 24 x 33mm and generates .3V and 16mA in normal sun and in strong sunlight, up to 2.9V (open circuit) and 30mA (short circuit). Put in a circuit with a capacitor, and even one of these cells can power a small robot to move around, draw, shake, and generally amuse. This cell, as with most polycrystalline cells, excels in outdoor applications, however it can be used indoors for lower power needs.

Applications

The typical use of this solar cell is to power small robotics, calculators, cute desk accessories and of course art projects.

Electrical

Characteristics solar cell data sheet

'''**H&J: Neither Solarbotics or either ITP author mentions specific wavelength ranges for the solar cell. The specs from Solarbotics show a power,voltage,current load chart for a sunny solstice day at noon somewhere in Canada. This seems pretty typical for a solar cell, as they are, after all, manufactured to be used with a very specific type of radiation (solar). The authors tested the solar cell indoors, using those awful ITP fluorescent lights. Solar cells are PN (positive negative)'''

Solar cells are junction light detectors otherwise known as photonic semiconductors. They are made of silicone and have exceptionally large light sensitive areas. Typically, a single silicone solar cell (about an inch square) generates 0.5 volt in bright sunlight.

**H&J: This is a bit unclear. Light hits the surface, where a photon will create a hole electron pair at the PN junction. A current will flow if two sides of the junction are connected.

**H&J: Cute picture, but may not be helpful. Picture from Forest M. Mim's book: Getting started in Electronics. forrest mims website

***H&J: Clearer explanation of linking multiple solar cells together. The solar panels can be put in series for sum of voltage, or in parallel circuits for sum of current. they are often wired to rechargeable cells and batteries.

For more easy to read and very through information on the development and physics operating the solar cell, you can check out wikipedia: solarcells

This chart shows the load, average voltage, current (micro Amps) and power (micro Watts) out put of this model solar cell. Although this isn't part of it's light sensing data I collected. It is interesting to see the relationship between the output. it's important to know what combination of Average and Voltage you will need for your project in order to use this cell most efficiently. This is able to output 2.6 volts, but no amps. It is only at lower voltages is the cell able to output a combination of volts and amps. 2.56 volts and 4.56 amps is the highest volt to lowest amp ratio.

For more information about the relationship between Volts, Amps, and Current...

wikipedia: voltage

wikipedia: ampere

Pin Descriptions

There at positive and negative output pins at the back of the solar cell. Positive goes into an input pin for the micro-controller. Negative goes to ground. This will create an analog light sensor circuit. It's not a way to measure voltage as accurately as another instrument like a multi-meter, however you can now use the data to power data visualization or small robots with as great of precision as you can get data range from your solar cell.

Microcontroller Connections

This shows the pic circuit, with a 10K resistor on the solar cell, which i decided to abandon after testing the circuit. i got the best number range without any resistor.

**H&J: The microcontroller shot should include the connection to the sensor (the PIC code needs to be updated to Arduino analog in code:

Schematic of the photograph you see above (without a 10k resistor on the solar cell input

Code Sample

Give a code sample for the microcontroller you developed the example on. Link it to the Code group of the wiki, formatting the link like this:

pic ADC in code

Processing code

Typical Behavior

***H&J: The visualization's amplitude could be increased (via the processing sketch) to clarify the output. What is this output? What is the microcontroller reading? The descriptions of the screen shots could be clearer.

This solar cell doesn't have a large voltage output. The Range of number I was able to measure in the lab under indoor low light conditions was between 0-20. I expect this number range would triple in full sunlight.

The graph on the image above is low, do to the indoor low light condition of the lab, where i did these measurements. None the less you can see the visual differential of the solar cell in it's detection of light. In this image there is an incline in the data image as I turn the solar cell towards the light.

In this image there is an decline in the data as I turn the solar cell towards away from the light. The voltage the solar cells sends the pic drops.

Application Notes

I will use this solar cell to create a decorative personal warning device. The device will be triggered by full sun activating a mechanical movement of a decorative feature, letting the person wearing it know when it's time for sun protection. It also functions a kinetic ornamentation. The inspiration for this project comes from a current social fascination with safety, and a whimsical exploration into solar energy. Coincidentally at MoMa safety exhibit.

Edit Hannah & Jen

Solarbotics appears to no longer manufacture/sell the polycrystalline cell, but offers a monocrystalline version: (monocrystalline and polycrystaliline refer to the silicon used in the solar cell; the first being purer, more efficient, and a bit more pricey than the latter.)

The cell can be used to either detect or harness light. The author of the main sensor report covers the solar cell as an energy harnesser, but there is a link to a project utilizing the cell as a light detector. It's a bit pricey for what it offers as a detector (you can detect light with a 50 cent photodiode).

Neither Solarbotics or either ITP author mentions specific wavelength ranges for the solar cell. The specs from Solarbotics show a power,voltage,current/load chart for a sunny solstice day at noon somewhere in Canada. This seems pretty typical for a solar cell, as they are, after all, manufactured to be used with a very specific type of radiation (solar). The authors tested the solar cell indoors, using those awful ITP fluorescent lights.

The microcontroller shot should include the connection to the sensor (the PIC code needs to be updated to Arduino analog in code:

A simple description of what the solar cell is doing and how that relates to the output, might be more helpful than links to wikipedia. The wikipedia links might be helpful for more advanced explanation of electron holes and pn junctions.

The visualization's amplitude could be increased (via the processing sketch) to clarify the output.

The descriptions of the screen shots of the processing code could be clearer.

Clearer explanation of linking multiple solar cells together.

difference between open circuit and short circuit - why is one in volts and one in mA?

-Short Circuit Current = maximum current that can be drawn from the solar cell
-Open Circuit Voltage = maximum voltage available from the solar cell