Introduction: Repairing Polymer Degradation on Solar Cells

Picture of Repairing Polymer Degradation on Solar Cells

I love my neighbor’s garbage; I call their garbage my parts department. My neighbors buy solar garden lights, put them in the garden or along their walkways, and forget about them. Then every spring like clockwork, while they replant their garden or fix up the yard, they discover the lights don’t work, and toss the lights in the waste bin, this is where I come in.

On garbage day I would go around to my neighbor’s garbage and pick the things I might find useful like garden lights, and electronics. Many of the things I get are in need of repair or only salvageable for parts.

One of the repairs needed to some of the solar lights is polymer degradation of the solar cells. This can be caused by UV light from the sun, exposure to chemicals, or oxidation from the oxygen in the air. To fix exposure or oxidation that leaves the surface of the solar cell covered in white residue you need to clean the residue off the cell and clear coat it. Test the solar cell and make sure they work to some useful degree.

As an added green project, all the components in this Instructable are salvaged and repurposed.

Step 1: Tools & Supplies

Picture of Tools & Supplies

Multi Meter




Soldering Iron

51Ω Resistor

Newspaper or Drop Cloth


Clear Coat

To start, dissemble all the unrepairable solar lights.

Step 2: Dissemble the Solar Lights

Picture of Dissemble the Solar Lights

Many of the solar lights I get just need to be cleaned or a new battery, others need a new switch or a wire replaced. Then there are the ones that are only salvageable for parts.

Start by dissembling the solar light, this is a good time to reverse engineer the circuit board and make a schematic. This is important because later when you are looking for a charging circuit you will already have one for that solar cell and a battery. A charging circuit for that solar cell and a battery is the solar light circuit with the LED removed.

Strip out all the useful components and the solar cells.

Keep all the solar cells, many damaged cells can be repaired or refurbished for use in other solar lights and projects.

Step 3: Refurbishing the Solar Cells

Picture of Refurbishing the Solar Cells

After gathering up a number of solar cells separate them into the repairs needed, for this Instructable you want the ones with Polymer Degradation.

This is one you can add to your 101 uses for toothpaste; dab a little toothpaste on the solar cell and add a little water, then buff. The abrasives in the toothpaste acts like the abrasive in polishing compound, this scuffs the surface so the clear coat will stick to the solar cells surface and it buffs out the scratches high spots.

Rinse and repeat as necessary to remove the poly oxide and high spots from scratches.

Step 4: Clear Coat

Picture of Clear Coat

Here is one you can add to my Instructable Plastic Coat, repairing solar cells.

When the solar cell is completely dry after buffing and rinsing, lay down some newspaper or some other drop cloth.

Place the solar cell on something to raise the cell off the drop cloth, and using a small paint brush, coat the cell with the clear plastic coat.

In a couple minutes the plastic coat is dry and you are ready to test the solar cell.

Step 5: Testing Voltage

Picture of Testing Voltage

Now that you have refurbished the solar cells it is time to find out what you can do with them. You do this by checking the voltage and the amperage produced by the solar cell. A good sunny day is best for testing the solar cell, just a small cloud across the sun or the cell not being 90⁰ angle to the sun can affect the output.

Never check the voltage of the solar cell unloaded, that means do not just attach meter leads to the solar cells leads. Unloaded the meter misinterprets the current going through it as voltage and gives you a much higher voltage than the solar cell is producing, as in this case 10.55 volts.

Start by connecting the solar cell to a resistor, the resistor can be any size. I chose a 51Ω resistor because I wanted to use the same resistor for checking the current. Then measure the voltage across the resistor, now you get a much more accurate output voltage of 6.174 volts.

Step 6: Testing Amperage

Picture of Testing Amperage

It is always good practice to never test a power source’s current without a load, dead shorts tend to be detrimental to electronics. With the 51Ω resistor attached to my circuit I got a current of 121.9 mA.

Solar cells are less affected by dead shorts; most solar cells convert less than 8% of the suns energy to electricity. If you dead short a battery the current will climb until something blows, if you dead short a power supply the current will climb until something blows.

With a solar cell if you connect the amp meter to the cell without a load, the current will climb like a battery or a power supply but the current will stop climbing once it reaches 8% of the energy of the sun. That doesn’t mean this is safe to do in all cases, just some solar cells will not be damaged by it. Without a load the current only went up by 2.1 mA to 124.0 mA.

Step 7: Charging NiCad Batteries

Picture of Charging NiCad Batteries

Now you have a solar cell, a charging circuit for batteries and the basic specks of the solar cell:

6 volts

120 mA

720 mW

To charge the high capacity of a NiCad battery or battery pack it is recommended to charge the battery at the rate listed on the battery label.

To achieve a complete charge of a NiCad battery it must be charged at a rate equal to or greater than C/10. Where C = cell capacity in mAh. For example: A 1000 mAh cell requires 1000/10 or a minim 100 mA charge rate or greater. Charging at a lower rate than C/10 will not result in a completely charged battery.

So this solar cell should be able to charge four, 1.2 volt, 1000 mAh batteries in series.

Step 8: Powering a Motor

Picture of Powering a Motor

Powering an electric motor with a solar cell can be challenging; the startup surge current of a motor can be twice the running current, so this 720 mW solar cell may not start a 720 mW motor when the motor is connected directly to the solar cell. You would need a charged capacitor or battery between the solar cell and the motor for the added startup current.

However smaller motors like this 175 mW motor can be powered directly from the solar cell since it only needs 35 mA to run, it is less than 1/3 of the of the solar cells output.


sitnah (author)2016-06-25

I took tons of pictures as I was taking the lights apart since I knew almost nothing about what I was doing.

Attaching a picture of a couple of the solar cells after they've been in the AZ sun for 2 years. Think there is any hope for them?

Josehf Murchison (author)sitnah2017-06-05

I think I may have found a way to fix polymer degradation that bad.

Put the cells in the sun until the polymer or resin completely cracks off the silica.

Then remove the old polymer resin and replace it with new polymer resin.

sitnah (author)Josehf Murchison2017-07-17

You are a genius ! I had tried toothpaste before and it didn't work.

After being in the sun for a few weeks, something got burned loose (?), and voila !

I'll repeat sun exposure again after the monsoon season ends and see if it improves them some more.

sitnah (author)Josehf Murchison2017-07-17

Great idea !

I put 3 of them on a table that gets sun for most of the day. Since we had temperatures of about 100, it didn't take long to show some results. It looks like the coating sort of re-melted, It isn't perfect, but the crack lines are no longer showing as "edge standing up" cracks, they are smoothed over.

Putting out abt. 50mA now. I was hoping the weather would hold, but rainy season is here now, will leave them out to see how they handle the rain, and some more sun when the rainy season is over.

Will try to remember to take a picture of them tomorrow!

sitnah (author)sitnah2017-07-17

Forgot to ask - do you use the top plastic/metal part of the case (path lights)

I made a few mobile solar lights from some I had, and now my friends want me to make them some, but I find it hard to find the bigger ones - 5" or more diameter.

So was just wondering if you don't use them, if you'd be willing to sell me some empty cases? If they need cleaning or spray painting, etc, that's OK.

Josehf Murchison (author)sitnah2017-07-17

Love to see the pic when you post it.

Good ones I rebuild so I don't have any to give away or sell.

Josehf Murchison (author)sitnah2016-06-25

Those are toast, I wonder how well this stuff would work at protecting the polymer solar cells from UV.

sitnah (author)Josehf Murchison2016-06-25

I've tried a few things, uv protect spray paint, car headlight repair, nothing worked. As an example, we have a sliding glass door that only gets the morning sun. It is tinted, and the narrow strip of carpet between the door and the vertical blinds faded. I put a strip of dark car tint on the bottom of the door, it still faded the new carpet a bit. Maybe I'll try that on the solar panels, if they don't light up all night, it's easy to take it off, lol.

DarrenO2 (author)2016-05-20

This great! How do you get to dig around in the neighbors trash without being shot or arressted.

Yonatan24 (author)DarrenO22016-05-24

Why would you get arrested?

Polymorph (author)Yonatan242016-06-12

In some towns, they've made it illegal to even lift the lid on someone else's trash can.

I used to live in a city where twice a year the city trash would do curb pickups of things like appliances and boxes full of stuff. It had to be in boxes or self-contained. People put out washers and dryers, refrigerators, TVs, stereos, wheelbarrows, etc. It was great! A city-wide dumpster dive. Often by the time they did the pickup, less than half of what had been put out was still there.

I got TVs, stereos, VCRs, a wheelbarrow, etc. that all just needed minor repairs.

But the city didn't like that people were taking that stuff. I think because the company that contracted to do the trash pickup got paid by how much they picked up.

So they changed it - you can call in twice a year to have a pickup like this done at your house, but that means everyone does it at different times. And they are REALLY strict now about only putting it out a max of 48 hours before the pickup.

What a waste. More for the landfill.

There might be another reason for banning scavenging, Vancouver BC band it to stop black market income. People on government income were making extra income salvaging stuff from the garbage and not clamming the income. After protests they allowed it with a permit.

I guess that makes sense...

There are probably a lot of people that empty your trash, take what they want, and leave all of the other junk on the sidewalk... No one wants that.

BardaWolf89 (author)Yonatan242017-06-03

That would be covered under littering/vandalism laws though. There's no reason to ban dumpster diving in general. In fact, because the store I work for likes to save money, we always put metals in back of the building outside the dumpster. They'll be picked up usually within a day or two by scrappers. We save space in the dumpster, less litter to fill the landfills, and the scrapper makes some money. Everybody wins.

There are a lot of stupid laws on the books. In some places its illegal to even put up a clothesline or start a vegetable garden. Don't underestimate the stupidity of a law just because of perceived unproven benefits.

I don't even know if trash picking is illegal here, but I still do it. And I would continue even if it were illegal. Its one of the few things I really enjoy, and I cant afford to buy all the things new that I find in the trash.

Its not just the government people are weird.

Years ago when I made my living as a TV repair man I saw a color console TV being put out for pickup.

I asked the guy if he minded if I took it.

He said just a moment went back to the hose and returned with a hammer and smashed the picture tube. Then he said now you can have it.

Yikes. I've repaired a lot of TVs, stereos, VCRs, turntables, etc. that have been left by the side of the road. Repair and reuse is a better way to recycle than melt down and reuse some of the raw materials.

The sad part you can't give away a CTR TV or monitor today even if they work perfectly.

Dr.Bill (author)Josehf Murchison2016-07-11

Yeah, government always has to get their greasy little fingers into your business.

Josehf Murchison (author)Dr.Bill2016-07-11

And it is easy to pick on the poor.

Yonatan24 (author)Polymorph2016-06-12


I live in a place that there are a ton of buildings, so there's a way higher chance of finding junk (gold) :)

We have our trash picked up several times a week, I think twice for big things, once for regular trash, and once for recycling. Something like that...

Polymorph (author)Yonatan242017-06-04

I don't mean regular trash pickup. I mean twice a year you can call for amounts that would normally cost money to have them pick up. Lots of boxes, too many to fit in the trash container. Furniture, appliances, that sort of thing.

Once a week here compostables recyclables and garbage in a clear bag, $1.00 for every bag over 1 payed in advance. then yard waste 1 day and large items once a month called in and payed for in advance.

There are people out there that are just mean.

Back when I was a TV repair man I saw a chap putting a color TV out to the curb and asked him if he minded if I took it. He said no problem and put a hammer through the picture tube.

WOW! yes there are some out there like that.

Hmmm... At least you had some other parts to salvage...

I find all sorts of junk on the curb, And I always take it. Most of my projects are made with junk I find outside...

Almost all of my projects come from the curb, after all how can you call it free energy if you bought the machine.

DarrenO2 (author)Yonatan242016-05-24

Because some people or officers are too quick to say a person would be stealing their stuff even if it were trash. Just depends on the person and neighbor.

We pay to have our trash taken away by the township or to take it to the dump, so my neighbors love scrapers. A refrigerator costs $100.00 for the township to take away, or free if a scraper takes it. My neighbors put stuff out to the side of the road and it is gone by garbage day.

I guess once the neighbors know you are saving them money or helping them then they are more likely to help you.

Some of them even put a sign on it, "Free to Good Home."

Cool. Maybe I will start trying that.

sitnah (author)2016-06-25

I'm so glad I found your posts with GOOD information.

So much misinformation on the web !

I read that "when a solar light doesn't work, it's almost never the solar panel"

Ha! Tell that to the AZ sun. They begin to degrade the minute you set them out.

Second, "solar panel must only put out 10% of the battery mA capacity ..."

In less than one summer, the panel on some string lights degraded so much they only lit for an hour at night. 20 lights, 1 AA 300 mA battery.

Thinking "what the heck, they are not working now", I took a chance, and replaced the solar panel on one set with a 3V 220 mA panel, and put in a 600mA battery. Been 3 months now, and they are still running all night long. I'm thinking the light has some protection to stop charging when battery is fully charged?

I am now, thanks to your advice, scavenging parts from all the solar lights I threw in a box in the shed.

Thanks again !

Josehf Murchison (author)sitnah2016-06-25

Nice charge rate 220 mA for a 600 mAh battery, the battery should be fully charged every day even on low light days.

NiCad batteries have over charge protection in the battery, so they are hard to over charge.

If you get the chance to read the directions on garden lights it tells you to place the light in a location where the solar cell will get 10 hours of full sun daily. Good luck finding that, where I live we get less the 60 hours of full sun a month for 6 months most years. That is a lot less than the 300 hours of full sun a month the light needs.

The way these lights are made you need full sun just to reach a charge rate of C/10, (The minimum charge rate for NiCad batteries.) Unless you live in the tropics you are not going to get that much sun every day, so most of these lights are under charging the batteries.

Your choice of a larger solar cells is a good solution to the under charging of the batteries.

If you have lots of these lights you might be interested in these Instructables.

sitnah (author)Josehf Murchison2016-06-25

We get plenty of sun here in AZ. Too much maybe for the coating on the panels.

I put the solar panels are on the patio roof, because anywhere else they only had direct sun part of the day, and I thought that was why they didn't light up for very long. The lights are strung from cup hooks under the patio roof.

Maybe I'll get brave and add an instructable for how I set them up to be easy to repair.

Josehf Murchison (author)sitnah2016-06-25

An Instructable on installing solar lights is a good idea.

Do the cactus fruit grow where you live?

Every time I had a load for Laredo TX I would spend the weekend at the Love's Travel Stop in Encinal. I would take walks in the desert eating the wild cactus fruit.

sitnah (author)Josehf Murchison2016-06-25

I'll give it a try. I think my installation & modifications are unique, but I'm probably wrong, lol.

We are in southern AZ, Sierra Vista Ft Huachuca area. It's cooler here because of the altitude, so we don't have too much of the fancy cactus unless they are in a yard. Hit 100 last week though.

bcampbell23 (author)2016-05-24

People are way too quick to throw stuff away. Excellent way to get free light.

They are way too quick.

I got a T-Fal broiler brand new in the box yesterday it did not go in their yard sale so I got it.

Mjtrinihobby (author)2016-05-23

I like your style especially with hunting for goodies from the neighbors! So cool. Great instructable as always.


This weekend is a holiday there was a hundred yard sales and tonight what didn't sell will be at the curb.


Mjtrinihobby (author)2016-05-23

I like your style especially with hunting for goodies from the neighbors! So cool. Great instructable as always.

Jockywilson11 (author)2016-05-22

Nice one, I'm off to repair my garden lights now!

Good luck and Thanks.

dianakbrown (author)2016-05-21

I am glad to see you on Instructables! Love to see you turn trash into solar useables.


Meglymoo87 (author)2016-05-19

Cool :)

Did you like how I even make my own clear coat?

Yes! Great job :)


About This Instructable




Bio: I am a photographer, a tinker, an electronics technology engineer, and author; I write short stories and poetry for the love of writing. I started ... More »
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