Author Options:

Reuse a solar panel from calculator? Answered

I have a solar panel from an old calculator, I'd like to use it to make a motor spin to make a junk bot.  It doesn't spin the motor when I hook it directly to the motor like I would a battery.  Do I need a capacitor or other electronics to make it work?  

I used a multimeter and the panel shows 2 volts in bright light, the motor does spin with a 1.5v battery.


The panel is only designed to run a small processor and LCD, which only require a tiny current to operate. Even a small motor needs a far larger current just to spin without a load. Even if you store the energy in a capacitor, I wouldn't expect a full second of operation from a full days charging.

You are ultimately limited by the power being received by the solar cell, which averages about 1400W per square meter from the sun, and indoors will be far less.

Try salvaging larger solar panels from old garden lights, these should at least give you enough power to charge a small battery pack.


That solar cell shows 2 volts at probably less than 5 milliamps...
2V * .005A = 0.01 watts.

almost any conceivable motor would draw orders of magnitude more power than 10 milliwatts.

Now I got a question - would it be possible to make larger cells out of a large pile of cells recycled from calculators and such items?

I mean I see calculators being thrown out all the time.

Replying to an old comment in case others have the same question: Yes, that is possible. But for 99 cents (USD) you can get a 600mW 6V panel off eBay. (Link below, and if that’s expired just search 0.6W solar, there are plenty for sale.)

At 5mA 2V it would take scavenging 60 old calculators for the same power output, them soldering them all together. If that takes you five hours congratulations: You just worked for 19.8 cents an hour. It’s likely to take far longer.


This panel will work for your junk bot. this website sells parts for "beam bots" also known as junk bots. The link I provided here gives plans for building a Miller Solar Engine and also lists the parts. Best of luck. also solarbotics has lots of parts and instructions so keep looking around that site.


one more thing... if you can't get enough voltage out of your panel just wire two of them in series (rather than parallel) and you should get 4-6vdc. if you motor doesnt want to move much try a few more capacitors to store up more energy. depending on your motor a 470 to 2000ufd is usually enough juice.