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object lesson: wearable solar energy

One of my nerdier pastimes ;) is listening to science podcasts. Each week, The Naked Scientists features a "Kitchen Science" DIY experiment to try at home. This one shows how to make your own (very tiny) photovoltaic-solar-cell out of a diode!

When I saw it, I immediately thought of all those 3V coin cell batteries I go through with my small projects. It's possible to buy rechargeable versions of these batteries, so I decided to see if I could recharge them with solar energy - even better if it's wearable, extra points for including recycled components.

progress: testing

the batteries

I II III
description Rechargeable Ni-MH Button MS Lithium Rechargeable Battery Rechargeable Ni-MH Button
photo Rechargeable Ni-MH Button MS Lithium Rechargeable Battery Rechargeable Ni-MH Button
spec sheet V 6 HR MS621FE V 18 HR
nominal voltage 1.2V 3V 3.6V (3 x 1.2V)
start charge 1.27V 2.65V 3.63V
after powering an LED for 24h 1.27V 2.45V 2.5V
after charging 4.5h with solar panel C 1.36V
after charging 4.5h with solar panel B 2.63V
after charging 4.5h with solar panel A 3.41V

the panels

solar panel A solar panel B solar panel C
description 11 naked diodes in series 12 shrinkwrapped diodes in series Commercial solar panel
photo Rechargeable Ni-MH Button MS Lithium Rechargeable Battery Rechargeable Ni-MH Button
charge in full sun 3V 2.5V 4.6V

progress: restart

Okay, okay, at the bottom of this page it might say I'll post my findings here July 2010 once I finish testing. Well it's the end of July and I haven't had time to do any testing! As of today, I'm restarting the project. I have hooked up all my batteries to LEDs to drain them, so that I can do a bit of (ghetto) testing. Meanwhile, I've been busy researching, and have found a bunch of interesting stuff about solar energy and rechargers, etc.

solar charging

There are quite a few instructions for building solar chargers online. Instructables has a bunch of very informative ones, including an Instructable for a basic solar panel using diodes! This Instructable uses different diodes to the ones I'm using, and they look much better, simply because they're more stable. I will definitely be including these in my tests. Very exciting!

I especially like these instructions as they start with the very basics and then adapt the designs to add more features. My solar charging circuits will start at the basic level for testing.

Over the next few weeks, I'm going to find out more about the things I've seen mentioned in my solar studies. When to use germanium diodes, how capacitors can help the recharging process, and if any of this even makes sense as applied to wearables.

first findings: naked diodes

I had a bunch of salvaged diodes that I had cut out of old TV sets, etc. I crushed the black plastic off them and then soldered crimping beads onto the legs. This was pretty time-consuming and created IMO particularly ugly little beads.

In the spirit of experimentation, I bought some new diodes and crushed the black plastic off them and bent the legs to be sewn. I also happened to have a small solar panel that I decided to test as well.

Here are my findings so far:

Things to test: