Introduction: Cheap Solar Panel for Under $30

Picture of Cheap Solar Panel for Under $30

Right now, it seems that someday we will all be charging our cars with solar power. Solar power is both awesome and sustainable, and is a hot topic in social media. I was given the opportunity to lead a tech workshop, so I decided it would be a good idea to teach people about solar power.

This instructable teaches readers how to make a weather proof portable solar panels for under $30. It's a rudimentary panel, not including all the downstream gizmos of the panel's output such as regulators, inverters, energy storage methods, etc. The panel is constructed by chaining 10 solar cells in series (with bypass diodes - more on this later). The solar cells I purchased were listed at a 0.5 Vdc output with an ideal max 8 amp output (this is an ebay listing). So, for 10 cells in series, the panel's output is ideally 5 Vdc with a 40 W power output.

This is all well and good, but in practice, the panel I made produced about 5 Vdc at 72 mW on an overcast day. So I question the ebay listing's specifications. However, if you want to learn about basic solar panel design, this instructable is worth a glance.

Step 1: Solar Cell Theory - Elevator Pitch Version

Picture of Solar Cell Theory - Elevator Pitch Version

Solar cells are made of photovoltaic (PV) materials. This long name is intentional: when PV materials are exposed to solar radiation (photons --> photo), the material outputs a voltage (voltaic). What voltage means, in layman terms, is the electrons in the material are excited. If you funnel these excited electrons through a wire, you have electrical current. One can harness this current to do work downstream of the PV material.

PV materials are made of P-N junction semiconductors (not explained in this instructable). A classic example of a P-N junction is a diode. A P-N junction optimized to be light sensitive is more or less a PV material. Thus, a solar cell is essentially a light sensitive diode, or a photodiode. Thus, when thinking about solar cells, one can think of them as photodiodes.

One interesting fact about solar cells is that their PV material works even when shattered. In the above images, you can find the front and back view of a shattered solar cell. When one electrically connects the fragments of the cell, they collectively produce the same amount of power as the solar cell originally did, while still in one piece.

Step 2: Solar Panel Circuit and Theory

Picture of Solar Panel Circuit and Theory

The circuit for a solar panel is rather simple. It helped me to imagine the solar cells as voltage sources, because that's essentially what they become under sunlight. A simple solar panel schematic places the solar cells in series.

Another interesting fact about solar panels is that when shade drapes across one cell, the cell actually acts as an open circuit. This is a problem, because if even just one cell becomes shaded, it cuts power from the entire solar panel. This problem is solved by adding 'bypass' diodes. Bypass diodes are diodes oriented in parallel with the solar cells that enable current to flow around a particular chain of cells when it becomes shaded. In this panel, I have incorporated four bypass diodes, thus enabling the panel to function if multiple quadrants of the panel become shaded. This is shown in the video for this step, which shows how shadows reduce output voltage, but never reduce it to zero.

One last thing to note is that when it's dark outside, solar cells can actually sink current, acting as a resistor. Thus, in front of the circuit, I have included a blocking diode to ensure that solar panel never acts as a power drain.

Step 3: BOM

Picture of BOM

Here is a list of the materials you will need. The prices listed are on a per panel basis. I bought in bulk because it was a workshop:

  • 10 Solar Cells - $ 13
    • I used 10/panel, feel free to add more
    • Note: you will probably break about 5, so make sure to buy plenty extra
    • Ebay Link
  • Solar Tab + Bus Wire - $3
    • Tab wire - used connect panels to panels
    • Bus wire - used to connect rows together
      • Wider and thicker than tab wire
    • Ebay Link
  • Test Lead Clips - $2
    • Don't buy the ones I did, they were overkill
    • Ebay Link
  • 14 gauge wire - less than $1
  • Diodes - less than $1
    • I chose 10A10 because I knew they could handle the ideal current and were very cheap on ebay
    • Ebay Link
  • Plastic Film - $2
    • This will weather proof the panel, more on this later
  • Zip Ties (optional) - $1
    • Used to secure the solar panel to the backing material

Soldering materials:

  • Solder core wire (I used one pre-impregnated with flux)
  • Soldering iron
  • Wire cutters + strippers
  • Helping hands

Circuit debugging tools:

  • Multimeter
  • Alligator clips

The remainder of the materials are common arts and crafts materials

  • Scissors
  • Cardboard
    • This will be the backing material
  • Tape
  • Hot glue gun (optional)
  • Plastic gloves

Step 4: Solder Order

Picture of Solder Order

On my solar cells, the current flowed from the front of the cell to the back (conventional current). Thus, the front can be regarded as "-" and the back can be "+".

The tab wires will be soldered from the back of one cell onto the front of the next cell, in order for current to flow through them. It's important to stick to this pattern, because remember solar cells are like photodiodes, and if you orient one incorrectly it will mess up the panel.

Any mistakes made before soldering are easy to fix, but mistakes after soldering are hard to fix. My advice to you is to plan out everything and check your work using alligator clips and a multimeter. Ignore the diodes for this step.

Step 5: Cut Tab Wire

Picture of Cut Tab Wire

My solar cells were 6" x 6", so I cut the tab wire to fit these cells. It helps to make a hand sketch to get an idea of where each length of wire will be used.

Tab Wire

  • Meant to join two cells: 12.5" lengths
    • 18 segments
  • Meant to connect a cell to a bus: 6.5" lengths.
    • 24 segments

Bus Wire

  • Ends of panel: 13" lengths
    • 2 segments
  • Join series rows together: 7" lengths
    • 4 segments

Step 6: Soldering the Backs

Picture of Soldering the Backs

Before starting soldering, you need to know a few things:

  • The solar cells are very brittle, so it will take some getting used to
    • I broke many cells before getting procedure down for repeatable success
  • Do not solder the cells over a bumpy surface. Either solder over a metal sheet, glass plate, or cardboard
    • If you solder over a bumpy surface you will probably break your cells
    • I used cardboard because it has a little bit of 'give' to it
  • The tab and bus wire are pre-tinned (usually), which means you don't have to add any solder. In practice, I found this tabbing to be insufficient, so I would add some solder.
    • The less you use the better, because solder on the backing acts like bumps underneath the panel when soldering the front, which increases your chances of cracking the solar cell

Note: the soldering was a very hard thing and came with a learning curve. Here is what I can say to do:

  • Place a small amount of flux on tab wire before soldering
    • Some people use flux pens, I did not have access to one
  • Use a chisel tip soldering iron
    • I had my iron on 380°C
    • Keep a clean tip
  • Use a just dab of solder to initiate wicking but not too much more beyond that
  • Try to drag the iron with light pressure on the panel and at a constant rate
  • Use a weight to hold the tab wire in place initially

Step 7: Solder the Fronts

Picture of Solder the Fronts

Soldering the front of the cells is the hardest part. I have included a couple pictures of my failures to show you that this step can be frustrating. It took some practice to get the soldering methodology down. Here are some tips:

  • Wear gloves, because your finger prints stay on the cells
  • Use little pressure, because using more will crack the cells
  • Try to drag the iron faster here, but test throughout the process that the tab wire is actually properly soldered onto the panel
    • This creates a smoother finish, and the front solder job is what will be seen on the final panel
  • Use little flux
    • The flux spills off the sides and leaves dark marks on the solar cell. I am not sure if this residual decreases the cell's power output
  • Try to solder cell pairs before combining them into chains

Step 8: Solder the Bus Wire

Picture of Solder the Bus Wire

Congratulations, you have made it past the hardest part! Up next is to combine the ends of the tab wire onto the bus wire, forming several voltage nodes. I would advise to solder the shorter bus wires first, and leave the long wires for last. Soldering the bus wire can be dangerous because it is so close to the fragile solar cells. Be careful on this step.

After the bus wires are soldered, congratulations, you should have a fully functioning solar panel! Next step is to add in the diodes and test lead clips for the finishing touches.

Step 9: Solder Test Lead Clips Onto the Panel's Terminals

Picture of Solder Test Lead Clips Onto the Panel's Terminals

This is an easy step. Cut two segments of wire, each with whatever length you desire. I chose 2'. Strip about 0.5" of insulation of both ends of the wire, and tin the exposed copper.

Next is to attach the test lead clips. I pulled one of the handle covers off, and underneath it were three thin tabs. The wire should be placed between the tabs and then have the tabs bent onto the wire, holding it in place. Solder the test lead clips to the wire, permanently securing the connection. End by sliding the handle cover back on, this time having to feed it along the wire you just attached.

Step 10: Solder the Diodes

Picture of Solder the Diodes

Now the next step is to solder the diodes. Helping hands or a weight are particularly useful in this step. In my case, I soldered the diode directly to the bus wire, and then used the 14 gauge wire to connect other end to the next bus. Any time there is potential for a short, be sure to use electrical tape to cover any exposed leads.

Note: each time you solder a bypass diode, be sure to test it with a multimeter. One time, I soldered a diode in the wrong direction and then broke a cell (and had to replace it's whole chain) while trying to de-solder of the diode.

Step 11: Test Your Panel

Picture of Test Your Panel

Now that the panel should be electrically connected, you are all done! Hopefully you have been testing your panel throughout the process. Before mounting any of the cells firmly on your backing material, I would test all of the cells to ensure they are producing a reasonable voltage.

If you are testing it indoors, I found the cells produced very little current and also did not quite reach their specified 0.5 Vdc production. Keep this in mind.

I used a multimeter and idealized the solar panel as a thevenin equivalent circuit (even though this probably isn't a correct practice because the panel behaves nonlinearly). I found the ideal resistance to get a max power draw to be about 36 Ω.

Step 12: Finishing Touch: Secure Cells to Backing Material and Add Plastic Covering

Now that you are confident your panel works, go ahead and hard mount and weather proof it. The mounting is simple: use electrical tape, zip ties, or hot glue to firmly attach the panels to the backing material. Note, any glue used may melt on hot days or if the solar cells heat up.

Weather proofing the panel entails cutting out two equal sized plastic sheets, and placing them above and below the panel. Now get your soldering iron, and follow a procedure similar to this one: Fusing Plastic Sheets. I can no longer find it, but another instructable had suggested sandwiching wax paper between the soldering iron and the two plastic sheets to prevent yourself from totally caking plastic onto the iron.

Note: if you are concerned about ruining your solder tip, this is a very valid concern, as it will probably bake the plastic onto the tip. If you are smart, clean the tip often throughout the process and use a fan to blow away all smoke (as plastic fumes are bad to breathe).

You can't perfectly seal the wires because you can't easily melt the plastic film onto the wires. If you want an airtight seal, use clear packing tape to seal any openings. In my case, I left some openings for air to escape. However, in moist climates, this might have been a bad call.

The corners are hard to perfectly seal. My advice would be to start in one spot and make a clockwise lap around the panel. Otherwise, wrinkles may form which ruin and air tightness you had.

The plastic film slightly interferes with the solar cell's efficiency, as it's reflective. However, compared with the trade off of weatherproofing, which enables one to take the panel into the great outdoors (to endure wind/rain/dust), I thought it was worthy. The video shows the slight detrimental effect of the plastic film on the open circuit voltage of the panel.

Step 13: Conclusion

Picture of Conclusion

In conclusion, one can gain a respect for solar panel manufacturers when constructing a solar panel. The panel I made produced only about 72 mW of power in overcast weather. While this is not that much power, it would make a half decent trickle charger for under $30.

Advantages:

  • Low cost
  • Requires only simple tools to make
  • Can be made in about 5 hours
  • Highly customizable
  • Works even if partially shaded

Disadvantages:

  • Very fragile
  • Low power production
  • Not perfectly weather proof

Areas for improvement:

  • Spend the money on a hard backing material such as MDF
  • Potentially make a 'cookie cutter' for the solar cells to hold them in place
    • Also could restrain loose wires away from front of cells to maximize power production
  • Spend more $$$ on higher quality solar cells
  • Standardize a method to melt plastic film into a protective seal around panels
    • Potentially use different housing material that is more 'optically clear' to let in more sunlight
    • Figure out how to prevent condensation, which again would block sunlight and also can introduce shorts
  • Don't touch the solar cells without gloves as it's easy to leave finger prints
  • Add more cells in series to get a higher voltage output
    • 5 V is only useful for small electronics, whereas 12 V can be used to charge a car battery
  • Find some mirrors to reflect sunlight onto the cells, increasing the intensity of light on the cells --> more power!
    • Make sure you think about heat dissipation in this case
  • Become better at soldering

I am always looking for recommendations, please post your comments if you see any gaps in the electronics/theory section, or have general advice. Thanks for reading!

Comments

gm280 (author)2017-04-26

I am certainly all for FREE electricity. But solar panels are so inefficient and the cost will never provide a benefit over buying electrical power off the grid presently. However, I don't think we need to throw in the towel yet either on solar power. If there were a simple way to directly convert HEAT to electricity, our energy problems would be totally solved. If you can just imagine the amount of BTU's it takes to warm up our days from a low temperature in the morning, to a much higher temperature in the afternoon times, that is beyond belief. And the day we can convert that immense amount BTU energy to electricity, is the day we are energy free. However your primer on solar panels was interesting to follow along anyways.

efh52 (author)gm2802017-05-09

Inefficiency requires that you specify the scope. 17% of the solar radiation that strikes a market ready solar panel is converted into electricity. 98% of the generated electricity is intact as it passes through a good inverter. So let's round the total output to your home as 16%.

As to your grid purchased electricity, to be fair we need to count it from the same source; the sun. As most electricity is in the US is from coal (though the logica applies to all fossil fuels), I'll follow a coal generation path of efficiency. Plants capture about 5% of the solar radiation they are exposed to and make it into biomass that MAY become coal. (I'll not guess at how much plant does not become coal). The process of converting coal to electricity as about 30% efficiency. Distribution of electricity runs about 95% efficient. .05 x .30 x .95 = .014 or 1.4%.

Coal (fossil fuel) generated electricity is certainly more cost effective at this time, but i is about 10x (1.4% v 16%) less efficient than off-the-shelf solar generation.

Please don't call my 17.63% efficient solar panels inefficient! Feel free to say they are expensive though!

zanod (author)gm2802017-04-29

"the cost will never provide a benefit over buying electrical power off the grid"

... so all these huge solar farms covering hectares of land, are running at a loss?

I don't think so.

Powerpinluc (author)gm2802017-04-27

Great Instructable. Energy storage is also a huge issue in the "Free" energy world. I still want to use electricity at night ;-) Also, it would be great to convert BTU to electricity efficiently. It would be a game changer...but entropy "degenerate" the quality of the energy at each conversion from btu to watt to btu. Simply put, 100% efficiency conversion is physically impossible. You will always need a source, a new input of power.

EthanL6 (author)gm2802017-04-27

Look up the peltier device

Robert McGregor (author)gm2802017-04-27

Thermisters are great.Get 12vdc from your furnace or gas hot water tank chimney!Rob

NKemp (author)gm2802017-04-27

Efficiency is only part of the equation. The cost per watt is the other part. The cost per watt has dropped so much that it is a viable alternative. Multiple PV farms have been installed ... by the utilities! ... and that is in MN! And similar is occuring all over the country. Time, volume and experience will bring the costs down lower.

The only question is which country will take the lead and end up being the low cost producer.

KatherineW3 (author)gm2802017-04-27

Thanks for posting this comment. It prompted me to read up on cost-benefit analysis of "going solar." While it is perhaps true in some areas that there's little short-term benefit from the capital outlay, that's not true everywhere, and the value to society and ecosystems can be quite high. Here's a good article: http://planetsave.com/2015/06/27/solar-power-pros-and-cons-is-solar-power-worth-it/

david.roseman (author)gm2802017-04-27

You are kidding, right? Not only is solar cheap, large scale farms are helping with this, but there are also MANY solar thermal power generators. You might want to hang out on Wiki for awhile and read up.

zanod (author)2017-04-29

When speaking about sealing the panels in plastic, you say "compared
with the trade off of weatherproofing, which enables one to take the
panel into real sunlight, I thought it was worthy". Does this indicate
that sealing them in plastic precludes taking them into direct
sunlight? It's confusing, because you later speak about using mirrors
to focus more sunlight onto them.

How hot can they get in direct
sunlight? It should be noted that items assembled with hot-melt glue
will come apart if left locked in a car in Summer.

BrotherJames8765 (author)zanod2017-05-02

To clarify: one can take the solar cells into the sunlight whenever, but at the risk damaging/scratching them if they sit on the roof, where they will have dirt blown against it and potentially be rained on. I just meant the plastic covering protected the cells from things like wind/rain, I was talking long term.

As to how hot they can get in direct sunlight, that depends on the backing material. This instructable was not designed to be fully practical, just educational, so I didn't bother thinking about heat dissipation. If you are curious about solar cells in general, then I would google it.

MauricioO4 (author)2017-04-28

I think this is a good start, it shows how solar power is made, one thing you are misinterpreting the specs of the panels it say 0,5 V 8 A that multiplied gives the roughly 4W ( not 40W as you say), good job anyhow,

Thanks for your input, however, I was listing 40 W for 10 cells in series. I will clarify that in the description!

halciber (author)2017-04-27

I really enjoyed this Instructable. I especially appreciate the detail in both the photographs along with the diagrams. Thank you for posting this.

One question for you, could you please post the sources of the materials? At least the source for the solar panels?

Thanks!

Hi halciber, I added them into the instructable as other requested them as well.

Thank you James,

I really appreciate it!

Regards,
Mike

Captain_Nemo (author)2017-04-28

The myth that solar is sustainable is pretty common now days, it is in fact not sustainable. The cells need to be make from something in the first place, which we will run out of if we make enough panels (that'd be a lot, but will happen eventually), damaged cells need to be replaced, you can probably recycle the material, but you will never get 100% back from recycling. Aside from damage, panels also degrade with age. Between those three factors, we will eventually run out of materials to make solar panels, and all solar panels will eventually fail, therefore, solar panels are not sustainable.

Solar panels are also not a feasible source of power, being that there is a fixed amount of energy they could possibly harvest, which is in turn dampened significantly by their efficiency (lack there of) which peaks at 22% with most systems in use around 11%.

david.roseman (author)2017-04-27

1: You need to keep all the wires away from the front of the cells. If the cells get any shade from the wire, their efficiency of the entire module goes down.

2: Covering it loosely in a plastic bag that is not optically clear, also causes a great deal of power loss. You are also introducing condensation, which will corrode both the cells and the wiring.

3: Why only produce 5v output? You won't be able to trickle charge much with that. If you wire large cells together in series then you can up the voltage per the wattage of the cells

Thank you for your input, I added this into the areas for improvement section!

I chose 5 V because that is enough for small electronics. If I were to do this for a house, it would have been at least 12 V. What do you mean by 'large cells'? Also, what is 'voltage per wattage'?

YLBright (author)2017-04-27

PLEASE provide an Ebay link. Could not find.

joeken1 (author)2017-04-27

Thank you for posting this Instructable. I am from India, and will have to research suppliers of the parts. Great photographs that accompany this article

BrotherJames8765 (author)joeken12017-04-27

I found all of my parts on ebay because that's where the cheapest components are. However, usually cheap means low quality as well. It would be worthwhile to invest more in the solar cells.

Robert McGregor (author)2017-04-27

Like your article.ive been off grid since the new year!Yahoo! Im working on wind,heat through thermisters and water turbines.House is going to be all 12vdc and usb! Rob

Wow I want to get there someday, that is amazing! I hope your panels are of higher quality than this one haha

meanblackbike (author)2017-04-27

Really great instructable for newbies. Good job.

I'm wondering on some ideas to increase the power of a PV by using mirrors, is it worth it and so on?

However I haven't got any PV of the mentioned size.

Also if you decide to use mirrors you might need to coo the PV using something like aluminum heat sink and even cooler/fan, so this PV remain intact.

I might be possible to gain more then 10x more power from the PV using mirrors with a area of 15x the area of PV or some.

If you don't mind to try I will be appreciated.

Hello! Thanks for your input. That is actually a documented method of getting more power out of solar panels is my understanding. Modern panels can absorb a higher spectrum of light, which requires higher quality PV material. Due to higher costs for this PV material, they use less of it and send more sunlight onto the smaller cells with mirrors. It's pretty cool!

However, for me to do it, the point of my setup was to be a very inexpensive workshop for beginners. To add on cooling and mirrors, I would buy higher quality cells to make it worthwhile.

GonzaloR2 (author)2017-04-27

Me parece que su didáctica grafica es admirable,muy asimilable .Gracias por su aporte tan interesante porque asi vamos teniendo idea de lo que será la energía solar asia el futuro.Desde Manizales Caldas Colombia

De Silva (author)2017-04-27

very, very good!!

Startx04 (author)2017-04-27

I think TESLA shows that Solar works ;-)

Add a battery pack and you are good to go.

EcoExpatMike (author)2017-04-25

I really like how you explain the electrical issues. Lots of us are kinda clueless in that...

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