Summer wrap-up part 2 (The problem with shade)

If you’ve noticed in the image of the solar panels in their natural habitat (my backyard) you’ll see that much of it is shaded.  This isn’t always the case, however it’s very much the case after mid-August once the sun has declined enough in the sky and the foliage from the trees is in its fullest bloom.

This presents a problem for those that might be in slightly more wooded areas that still would want to use the power of the sun to gather electricity.  So how does one get around that?

Cells could be mounted higher, certainly, but that might be an impossibility for land that’s surrounded by very tall trees.  Cells could be spread out to various sunny areas, but they’re not going to be efficient as they’ll most likely only be in sunny areas for part of the year.  Additionally, spreading them out means longer wires being run and an increase in power loss along this wiring.  Plus, solar panels get pretty gross over time and they need to be accessible enough to give a good cleaning.

So let’s make a solar panel that goes where the sun is. The concept goes like this:

  1. An array of batteries is stored in a housing, all of equal physical size and capacity
  2. A robotic arm takes a discharged battery out of the housing and places it on a mobile bot
  3. The robot navigates the land using GPS, radio communication to a central server, and various sonar/infrared sensors to avoid obstacles and find a nice sunny spot.
  4. It parks on the spot and deploys a solar panel to charge the battery it’s been assigned, along with its internal power source.
  5. Once charged, it navigates back home where the robotic arm takes the fully charged battery and places it back in the bank.
  6. It then loads another discharged battery onto the bot and the cycle repeats.

Seems simple enough, right?  Doesn’t seem economically practical at all unless the swarm of bots doing this is big enough.  Probably still isn’t a break-even point in there.  Don’t care, it’s neat.  So let’s get started.

 This is the basic construct for a platform that will bear the weight of the battery.  It will not have a motorized drive-train as there would be a huge draw of power just bearing the weight of what is above it.  It’s made up of a few parts from a Tamiya Tracked Vehicle Chassis.  For this project I used a total of three of them.  They’re about $15 a pop on eBay.

Through this base I run two 3/16″ smooth and one 1/8″ threaded rods.  This will connect to the drive trains and allow it to move closer and further from them, allowing the power of the chassis and the weight of the battery as an anchor to articulate the panel.

 

Here it is tied to the chassis, each of these have a drive train and motors attached.

 

 

 

A motor is attached to the back with gearing to turn the threaded rod which is held in place at the connection point to the drive train chassis, articulating back and forth respective to the circuit’s polarity.

 

The wiring is snugged inside of some acrylic tubing and housed above to keep things nice and neat.  What isn’t pictured at this point is an additional drive-train attached to the front and mounting brackets for the panel.  Because I’m lazy and didn’t take any more pics.

The battery you’ll notice has securing brackets.  These are spring-loaded so that lifting the battery swings them away from the terminals and lowering the battery connects it to the terminals automatically.  Once complete, the system will detect a power-on with the connection of the battery, secure it with additional articulating power-driven latches (not pictured, but done) and run some self-tests.

Time to see how this thing handles the backyard terrain.  As I’m writing this I know the results of said tests but you’ll just have to wait until I get around to telling you about them.

 

Summer wrap-up part 1 (No more blues)

It’s that time of year where working outside is shortened in hours.  And the chill causes your nipples to pierce your shirt.  So much of my work space has been consolidated, but the projects are in full force.  Here’s an overall update and a promise to keep the posts more frequent and a little funnier.

The solar panel succumbed to a nice blast of wind that sent it shattering.  The problem here was the construction more than the wind.  Without fully encapsulating the panels in an epoxy-like substrate they were subject to flex upon impact.  Being silicon-based and 0.2mm thick it doesn’t take much of a jar for them to shatter.  Trying to repair by removing the broken cells proved impossible as more and more kept cracking.  So time to redo:

As I’ve described the gist of how to put this together in a prior post I’ll skip the gruesome details.  The major difference here is that the panels are attached to glass, they’re closer together, and fully encapsulated with a clear-drying epoxy.  This makes them water-tight and gives them much more support.  Basically you can hit the thing and as long as you can’t shatter the glass, which is now also enforced with epoxy, you’re not going to hurt them.  The glass was unnecessary and I’d probably recommend doing it with plexi next time, but the glass was much cheaper.

As a result of the spacing changes and the dimension changes of the cells (4×5 with a single tab line to 3×6 with dual tabs) this panel is 25% smaller but still kicks out the same power of nearly 100 watts.  It has a short circuit voltage of approximately 25v.  This is an awkward voltage for a panel as they’re typically hovering around 12v, however there’s a reason for this.

The final wiring for the panel includes a high-power schottky diode that prevents any reverse voltage from frying the cells if their output dips below the voltage levels of anything they’re charging.  Basically it stops a battery it’s charging from discharging back into the panel once the sun goes away or the battery becomes fully charged.  This drops down the voltage by 0.9v.  The closed circuit voltage also naturally drops slightly leaving me with a little over 23v.  With this voltage I am able to split it into two voltages of 15v and 8v which are then used to charge 12v SLA batteries and sets of 3.65v Li-Ion batteries wired in series.  An interesting note about batteries is that even though they’re labeled with a specific voltage, they only run at that voltage for a specific instant in their discharge cycle.  12v batteries that are run through heavy deep-discharge cycles should be charged to 14.8v and discharged to approximately 11v.  Li-Ions should be charged to 4.2v and considered discharged at 3.2v for maximum life.  The speed of charge and discharge is also important and there’s a whole bunch of other crap that needs to be taken into account to maximize their health.  So I’ve implemented a software-based charger that monitors the batteries and optimizes their output.  So far it’s the only “ultra-smart” solar-based charger I’ve seen in existence.  Maybe it doesn’t even work.  Probably it’s a lot of extra overhead for something that’s not that important.  But I don’t care really, it’s neat.  More on that in future posts.

Also, the panel has to find the sun so it’s mounted to a make-shift rotating tracker that’s made out of scraps of an old desk (nothing greener than re-use):

That’s all for now.

Coming soon:

  • The problem with shade
  • The problem with wheels
  • Closing the feedback loop on CNC milling
  • Green garage gardening greatness
  • Zombie apocalypse weather preparedness
  • Watching the watchers

Yes, those are vague.  You’ll see.