Panel from Scrap Cells

[taylorp035]

My friend had 11 solar cells from a school project that had been sitting around for 10+ years, so I decided to solder the cells up to charge my 18650 battery bank to go along with my windmill project "Christmas Windmill".

The cells were rated at 0.5v @ 3.5 amps, which sounded like a lot of current to me.  I found an old glass oven door and a nice clear top piece of glass.  Watched a video on how to properly use tabbing wire and then wired it all up.  Added two layers of caulk to the edges of the glass to seal it all in and to prevent any motion that might break the super delicate cells.

In parallel (figuratively and literally), I finished up the wiring to go through the 1S BMS units, the parallel pack connectors, the DC-DC converter for the power meter and the power meter.  The setup will be good for 20A continuous and easily upgradable to 40A.  The windmill will hook up to the input posts on my wiring board with the panel.

Today I put the panel out in the sun for a few hours for the first time with all the wiring hooked up.  It peaked at 2.71 A while charging at 4.02 v.  By the end of the day, I had 6.3 Ah into the 124.8 Ah pack per the meter.  The panel was super sensitive to any shade from tree branches and orientation to the sun (~1.2A if the panel was flat on the ground).  The sun isn't super strong this time of year in NW PA, so I was very happy with this result.  I used to have a 15w amorphous panel that was 2-3 times the size of my homemade panel and it only ever put 11W in the middle of summer.... this panel was pushing 10.4w for most of the day.  No load voltage was about 6.4v. 

My goal is to get to the point where I can power two cell phones and my laptop with relative ease.  I ended up using the battery pack to power my work laptop during a 14hr power outage (super rare since they upgraded the local substation 15 years ago).

[Bruce S]

Nice!
Question:
Do you counter sink the holes for those bolts in the wood too?
I have a indoor setup similar , I used counter sunk holes to keep them from shorting on the tables.

Cheers
Bruce S

[SparWeb]

Hi Taylor
Great idea.

Since you like testing, you could try a test like this to find the peak power points for sunny and hazy conditions:
https://www.fieldlines.com/index.php/topic,150102.msg1051364.html#msg1051364

[taylorp035]

Question:
Do you counter sink the holes for those bolts in the wood too?
I have a indoor setup similar , I used counter sunk holes to keep them from shorting on the tables.

Yes, I counter sunk the 10-32 bolts.  I hadn't considered the possibility of them shorting out, so I might go a bit deeper...

Since you like testing, you could try a test like this to find the peak power points for sunny and hazy conditions:
https://www.fieldlines.com/index.php/topic,150102.msg1051364.html#msg1051364

I will have to find some different loads to see what the max power I can get out of the panel.  It's supposed to be sunny tomorrow and I have the day off.  Based on your voltage graph, I'm guessing I have a bit more to go if the charging voltage gets closer to 5-5.5 volts. 


I also want to figure out if I need a diode on the solar panel.  I wasn't sure if it was going to drain my battery without one.

[richhagen]

Ghurd used to power his Christmas lights with a small wind or solar project.  It is nice when you can use something you built in a pinch.  Where I am at we also do not often have power outages.  I got up one morning to find my computer not working.  The lights were on as they switch to solar when there is power automatically.  It took me a bit longer than it should have to realize that the mains power was actually out.  It did not stay off long enough for me to rig a cord for the computer and monitor to the inverter though.  I use DPDT relays to switch stuff and I was concerned that the computer might not like the power blip when it switched, so I did not have its circuit switch to solar like the lights and some other stuff.  I like your little panel.  I made some similar, got condensation in them when left out, so I switched to encapsulating them.  I have a small vacuum oven, so the last panel I made - a few years back now - was an EVA, Tedlar sandwich, ended up with some air bubbles in it from when baked under vacuum, but that does not seem to impact it when left out.  I like that construction method and suspect that one will last a long time even with all of its imperfections.  Incidentally, I find that my BMS's let my 18650's charge a bit higher than I would like and discharge quite a bit lower. I have taken to adding LVD's to my powered circuits separate from the BMS to prevent over discharge.  On my larger setup with these type batteries, I can use the charge controller to limit the overall voltage, though the BMS is the only cell level protection.  So far so good, but my learning with Lithium Ion is still a work in progress.  Rich

[taylorp035]

I've made a tracking sheet to see how much power I make with the windmill (once running) and solar panel.  I experimented with a few different positions for the panel and levels of commitment on adjusting it over 7 different days since it's been unusually warm and sunny during November in NW PA (it was 78-80F the other day, breaking the record high by 11F).

I've discovered any kind of shading by a single twig from 100 feet can drastically reduce power.  Light wispy clouds are less of an issue, but still put a sizeable damper on the power.

With a peak of 2.2-2.45 amps most days, I set my record daily production 4 times, with a maximum of 11.2 Ah.  On that day, I put it out at 10:15 AM and brought it in around 5 PM.  Generally full sun can only be realized from 10-3 PM.

Two days I decided to leave it in one position.  The first was leaving it flat on my deck all day.  It only made 0.295 Ah that day.  The second was tilted up in a sunnier location and I managed 5.1 Ah.

I've also found a 6 throw - double pole switch that I want to use to make my battery go from 1s to 3s with the flick of a switch instead of pulling (12) 45A power pole connectors on a set of fragile batteries and BMS board.

I'm up to 43.7 Ah so far in total.  It's definitely worth my effort to put it outside since I can charge my phone 4 or so times from empty with one day's production.  The windmill should do much, much better, so I've been hard at work on that on the many upgraded components that I hope to have a nice update for soon.  Given the last week, I could easily make 20-40 Ah in one day, if not more.

[taylorp035]

So the end of the line came for the panel.

When I soldered the cells together, I used regular pipe solder flux instead of the right stuff for electronics.  It ended up eating through all the connections in the cells.  It was making about 10% of the power it should of after 3 months while exposed to full sun with a perfect layer of snow reflecting in front of it.

[SparWeb]

Uh oh.
Don't scrimp on your solder!

[Mary B]

So the end of the line came for the panel.

When I soldered the cells together, I used regular pipe solder flux instead of the right stuff for electronics.  It ended up eating through all the connections in the cells.  It was making about 10% of the power it should of after 3 months while exposed to full sun with a perfect layer of snow reflecting in front of it.

Never use acid core solder on electronics! Rosin core only!