To easily make a homemade/DIY solar cell, get a power transistor like the
2N3055 and carefully cut open the case. That exposes the semiconductor
material inside to light. Hook up some wires and you're done! Doing this
I managed to get around 500 millivolts and 5.5 milliamps which is
2.7 milliwatts. To power a 15 watt compact fluorescent lightbulb I'd
need at least 5555 of them. However, just 5 of them in series will
power a small 1.5 volt calculator in good indoor lighting conditions.
Be sure to also check out the
solar panel
I made using multiple of these transistor solar cells for powering
a calculator as well as
this more powerful
one enclosed in a box.
The transistor solar cell wired up...
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... and being tested.
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In the photo on the left below is the transistor.
Use a hacksaw to cut off the front of the metal case as in the photo
on the right. There are thin delicate wires inside so when you cut, do
many short cuts all around the case being careful to not let the blade
go deeply inside the case. Don't do just one cut all the way
through.
The 2N3055 power transistor - top view.
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Cutting open the case.
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In the photo on the left, below the case has been cut all the way to the
backing and the thin, delicate wires are completely unprotected. In the
photo on the right only the front part of the case has been cut off,
leaving a protective, cylindrical wall around the insides, giving some
protection for the wires.
The solar cell and thin wires.
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Case cut to leave a protective wall.
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As shown in the photo and illustration, there are three points to make
electrical contact with in a transistor unlike with a typical solar
cell.
Bottom view showing where to connect wires.
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Comparison of transistor and typical solar cell.
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To know how to connect to the transistor to get the best output I
set up a testing station where the transistor would be fixed firmly
in place while I tried all the possible ways of connecting to it
and measured the output for each way. The results are on the right,
below. This was done indoors to get constant lighting conditions.
Two cool white compact fluorescent lightbulbs were used.
This means that the values are low and may scale differently
in sunlight since sunlight has a different range of frequencies.
Setup for testing the efficiency of the different ways of
connecting.
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Test results
| Test |
Voltage |
Current |
Power |
| Base+, Emitter- |
370mV |
94uA |
35uW |
| Base & Emitter+, Collector- |
325mV |
215uA |
70uW |
| Collector-, Base+ |
340mV |
265uA |
90uW |
| Collector+, Emitter- |
28mV |
65uA |
1uW |
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As you can see from the table above, using the Collector as negative
(i.e. connecting to the metal case) and the Base as positive (i.e.
connecting to the Base pin) while ignoring the Emitter gave the best
results.
And lastly, for fun, I played around with focusing light on the solar
cell using a small Fresnel lens to see the difference it made. I
got around 520 millivolts and over 5.5 milliamps (measured on the
microamps scale, the milliamps scale on my meter is broken.)
Focusing sunlight on the transistor solar cell using a
Fresnel lens.
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Video all about the 2N3055 transistor solar cell
Here's a video I made about my experimenting with this 2N3055 transistor
solar cell.
Making a solar panel from these transistor solar cells
