Picture of Non-PV Solar Power
Edit: Sweet, I'm on hackaday!

Hello, in this Instructable I will show you how to generate solar power using inexpensive solid state parts and without PV (photovoltaic) cells or panels. I wanted to make this project to see if I could beat the dollars per watt costs of commercially available solar panels.

You only need a few inexpensive parts to build one. It is pretty easy to build and very simple. As far as I know, my idea for the combination of thermoelectric coolers and Fresnel lenses is original... but it's probably not.

Sorry about the rubber bands and foam but remember this is an experiment on my part. Rubber bands are just the best thing for me! Likewise, I recommend you also build a prototype and if (when) it works you should go on to more fancy enclosures. Remember this is just a rough guideline and you can modify it however!

How it works:
This generation method uses a Peltier cell to generate electricity. Peltier cells are designed to be used as heat pumps. When you apply power to a Peltier cell, it begins pumping heat, and one side becomes cold and the other, hot. However, you can do the opposite and generate power from a temperature differential on the sides. To generate this differential, a Fresnel lense focuses light onto one side of the Peltier, and it becomes hot. The other side has a heatsink attached along with a fan that is powered by the Peltier.

Lenses concentrate light, which is absorbed by everything, and when light is absorbed, heat is created. You can easily burn yourself and other things with the lens. Don't leave this out uncovered because the sun moves and it might focus on something. I disclaim all responsibility for anything ever.
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Step 1: Parts and Tools

Picture of Parts and Tools
For this project you will need:
a Peltier cell (I got a 50W one for $5 off of eBay, they are still there)
a Fresnel lense (mine's about the size of a sheet of printer paper, there are a whole lot on ebay)
a CPU heatsink (any type of heatsink will work, as long as it's big enough. I got mine at a garage sale for $2.50)
a 5V fan (more info on that later)

Tools/other materials:
Thermal grease
Black paint (I used semi-flat spray paint and it didn't burn)
Soldering stuff
Wire cutters
Reflective material

Note on the peltier: The wattage doesn't affect the power output, but it does affect the internal resistance, which in turn affects the voltage output. Higher wattage = lower voltage, higher amperage. You want a lower wattage peltier so the voltage output is high enough.

My dad built a DIY projector and one of the Fresnel lenses he bought was scratched so he gave it to me.

Warning about the Fresnel! Don't go much bigger than the sheet-magnifier size because you will fry your Peltier. We are probably already running it over it's heat limit, which means it may not last as long.

We have a bunch of foam lying around from building RC foamy airplanes.

The heatsink used to have a fan on it but it was 12v and barely ran off of 5v, so I hunted for 5 volt fans. I was impatient and couldn't find one that I could purchase locally, so I went to Fry's electronics and picked up a laptop cooling pad for $10. There is another one there for $5 that will work fine. It had two fans built in, so I took out the 6 screws, pulled it apart, and pried off the two fan blades/circuit boards. As you can see, they were smart and made the fan axles built into the case instead of standalone fans... so I outsmarted them and dremeled out the axles! You could go my route and use a band/jig saw or dremel, but I highly recommend buying a 5v fan online to save yourself the trouble.

Step 2: Prepare the Peltier

Picture of Prepare the Peltier
First, you need to get your stuff ready. You want to have maximum thermal conductance between the non-hot side of the peltier and the heatsink. You should first remove any mounting equipment the heatsink might have, and while you are at it if it has a fan, take it off too. It might come with a bit of thermal goo on the bottom. This probably isn't the right size for your peltier. Go ahead and scrape it off, and then clean the surface of the heatsink with alcohol and a paper towel.

Put the peltier on some newspaper and put a coat of black paint on one side of it. I used semi-flat spray paint, when I did the first coat it congealed into blobs on the surface, but the second coat covered all of it. I did put on too much though and it's a bit thick.

Now, put enough thermal grease onto the peltier to *just* cover the whole thing. You don't want to use too much.

Figure out where on the heatsink you want your peltier, and stick it on. I recommend putting it in the center. Stick it straight on and wiggle it around a bit to make sure the grease is spread properly.

Step 3: Attach things

Picture of Attach things
Now you will want to firmly attach your peltier to your heat sink. I used iron wire to hold it on and keep it from sliding as you can see, but really, any thin material that can resist the high temperatures and you can wrap around will work fine. Gluing or taping is not recommended because it will not stick to the smooth heat sink surface.

After this you should attach the fan. What I did is like I did with the "baseplate" as you can see in the next step. I put rubber bands on the base of the fan and around to keep it on. I had to put a bit of cardboard between the base and the heatsink fins to keep the fan blades from hitting the sides of the heatsink. I bent the cardboard so part of it would slide into the fins and this worked perfectly, almost holding the fan in on it's own!

Step 4: Frame Creation

Picture of Frame Creation
The first thing I did before making my frame is I cut a baseplate from foam that surrounds the Peltier and goes on the bottom of the heatsink. Measure the size of your peltier, and cut a hole in a piece of foam as big as the bottom of your heatsink. Make sure to cut holes for any wires or anything to come out!

I had to attach the baseplate with rubber bands, which works fine for me. I recommend, if you can, using any mounting hardware that is usable. Just make sure the bands don't go over where the light will be focused! The baseplate is important because it's really hard to mount the peltier/heatsink anywhere without it. Glue/tape just doesn't stick to heatsinks... It also makes it so you can put a reflective box around the Peltier. We'll talk about this once we've made our frame and figured out our focal point.

Now you will want to make a frame/enclosure for everything. In the pictures you can see what I did, feel free to improvise. There are many ways to make one. You could make a box, or a foldable stand, or do what I did, which is sort of a combination. The strategy is the same for all of them. Figure out the rough range of measurements between the peltier cell and the lense for the focal point, because you will want the peltier-lense distance to be adjustable.

Don't measure the focal point where the light is at the smallest point, that will just burn off the paint. Flip around the lense until you are pointing the side at your "measuring surface" (I used a napkin so it wouldn't burn) that creates a square sized spot, and measure it where the spot is a bit smaller than the total size of the Peltier - remember, there are two points where the spot is the size of the Peltier. Use the farther one or the reflective shroud will actually block light!

Once you have figured out the focal-point range, cut your frame. Mine has a slit that you can move a foam panel back and forth on, to adjust the focal length. The light-collecting assembly sits on this. See the photos for more details.

One thing to remember when making your frame/enclosure etc. is that heat management is EVERYTHING, because this generates using heat. If somehow the heatsink is getting heat that is not through the peltier (maybe light is falling onto it) then you will be losing a lot of power.

Step 5: Finishing Up

Picture of Finishing Up
Now that you have your frame and everything built, we will make that reflective shroud I mentioned. I did this by cutting four pieces of foam that were half as wide and a bit longer than a side of the Peltier, gluing them on in the formation that you can see, and double-sided-taping aluminum foil to the inside. Hint: Mylar from the inside of potato chip bags is a better reflector.

I actually extended it so I could put a plexiglas window to trap the heat, but it was right at the focal point so it distorted the lense... maybe I'll drill a hole.

To give the fan some extra power, I wired together a 3v 150ma solar panel for $3 and used skewers to hold it up, and put it in series with the Peltier. Power for usable applications can still be drawn from the + and - of the peltier because the solar panel is just for the fan.

I used springy-wire splicy things to connect the wires. The circuit has the peltier and solar cells in series to generate ~5V for the fan.

Step 6: Notes

Picture of Notes
From my setup, my highest recorded voltage is exactly 2.7v. The internal resistance of the Peltier is ~3 ohms because at 7.5v input it draws ~2.5A. This means I could get 2.7/3 = .9A out, and 2.7*0.9 = 2.43W.
So, now I will figure out the cost for the average person to build it.
Heatsink = $5
Peltier = $5
Lens = $5
Fan = $5

Solar Cells = $3

Total: $20-25

This is equal to right around $10/W, which is on par with the cost of commercial solar panels. Pretty good for an untested experiment. However, some disadvantages of this are:
-My enclosure is too flimsy to be held vertical so it can harvest power at the middle of the day
- Needs to be well aimed to be effective
-Less efficient than PV

Yeah, this technology probably isn't ready for prime time. But it is interesting and very fun/cheap to make.

One thing you might be wondering, is why is the power output so low?
Well, first of all, the wattage of a Peltier is not the power it will output. It is the power it will draw at it's rated voltage. Another thing, Peltiers are not designed to generate electricity. They are optimized to pump heat. To really take advantage of the energy available, you will want to get a Seebeck unit. These are the same thing, but optimized to generate. With a seebeck unit, power output would go up by many times. Same with price.
So, I will continue working to improve the output. There are a lot of things I can and will be trying. Make this project your own!

Here are ideas I had:

Use something like the LM2623, LM2371, Mintyboost circuit, or LVBoost to get this up to 5v to charge/power USB devices and Li batteries. You probably will have to parallel a couple of whatever you use to get full output and decent efficiency.

Use one of the projector-TV fresnels and focus it onto a 3-by-3 grid of Peltiers. Put them in series and no inefficient boost converter needed.

Build a solar tracker to harness the output all day.

Get sheet aluminum about 10" by 10", put peltier+heatsink in center, paint other side black, insulate it and put plexiglas over it and it will be a lot like PV.
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I would like to see someone build a 3-stage solar power generator: a photovoltaic cell connected to a peltier/seebeck unit connected to a stirling engine. Actually, the peltier/su could go on either end of the stirling engine. I wonder how much power one could get out of such a setup.

Reviewing you comments of 5 years ago, I know that the back of solar panels gets very hot and that heat diminishes the output of the panel....great idea to use the back of the panels to generate power and thereby cool the panels.

I know I'm replying to myself, but oh well. I had a rethink of my idea, and came up with this setup: take an old satellite dish, line the concave side with small photovoltaic cells (1st power source). The pv cells, being shiny, would reflect some light, and being mounted in a satellite dish, would focus the reflected light onto a seebeck unit (2nd power source) which is mounted on the stirling engine (3rd power source). Would this not work?

go here if u want decent prices.


Dhakian1 year ago

I don't know much at all about optics. Would it be feasible to use a hook up a series of lenses and heat pumps into an array? Would there be any advantage to this? (I'm new to the DIY-energy community.) Along with that, would it be possible to use a more more concave lens, closer to the Peltier cell?

im getting interested in peltiers as backup, not replacement to solar.i think your math is off tho, you stated $10/watt is on par with solar. i can get solar for .70 to $2.00 a watt (depending on panel manufacturer) anywhere (ex. home depot 105 watt 12v panel for $159.00= approx. $1.60/watt)

maovi2 years ago
jomac_uk4 years ago
Just a thought, if you use a peltier cell and a freshnel lens to generate electricity and you have a bank of them in say a 1m X 2m area, will the set up generate more or less electricity per given area compared to solar PV's?
Depending of the elements you will be using -You can expect more or less 1Kwh per 1m X 2m area of peltier.
But the problem is - You willl need a pretty BIG freshnel lens or BIG solar oven and 1m X 2M heat sink too.... that's a huge thingy.
Nice job - I've been thinking of heating a peltier element with my solar oven to generate a little electricity, but haven't tried it yet.
carey1245784 years ago
i bought a fresnel lens as a magnifer at Barns and Noble
likewho4 years ago
I’ve tried standard peltier modules with limited success and very short service life. They cannot hold up to the higher temperatures necessary for good power generation performance. I found a terrific supplier with both standard temperature and high temperature TEG modules designed specifically for power generation. They sell a lot of devices on eBay and you can also buy from them direct. The company is Thermal Enterprises and here is are links to a couple of their eBay items.


bananafred (author)  likewho4 years ago
They don't even provide the chemistry... whats to prove their better or different from normal TEC modules? And wow, you look a lot like a shill, with all of your comments being promoting these items.
arbit3r5 years ago
 Hey interesting project. First thing I've heard of peltier cells and they look pretty interesting. I'm thinking maybe a bank of peltier cells heatsunk one side and fed with a heated liquid from a solar panel (liquid type not  pv).
nice job on ur project,
i got an ideer:  if u focus the light on a black container or can filled with water coundt u make a solar powerd sterling engine???
(see sterling on instructables)
I saw something similar in concept to this on Daily Planet, once.  A company in the southern states makes big parabolic mirrors that focus light onto a single point, and run high efficiency stirling engines from the heat generated at that point.  The stirling engines are then used to generate electricity.
scubascooby5 years ago
How hot do PV cells get in sunlight ?

Is there any benefit in putting a peltier on the back of a PV cells to harvest the heat that would otherwise be wasted ?

Kaiven5 years ago
Ooooh! Brilliant! So in theory, anything that uses electricity to produce heat can use heat to produce electricity?
Padlock Kaiven5 years ago
No. Theoretically, heating an oven will not produce electricity. Logically, heating an oven will not produce electricity. Period, heating an oven will not produce electricity. Ever.
Kaiven Padlock5 years ago
Oh, well I have a gas stove, not electric, so I wouldn't think that :P
Padlock Kaiven5 years ago
;-) Theoretically, heating a toaster will not produce electricity. Logically, heating a toaster will not produce electricity. Period, heating a toaster will not produce electricity. Ever. I've never seen a gas toaster...
Kaiven Padlock5 years ago
But I don't own a toaster.
Padlock Kaiven5 years ago
Work with me here...
Kaiven Padlock5 years ago
Heating an incandescent lightbulb won't create light?
Padlock Kaiven5 years ago
I'd think that if you heated an entire incandesent lightbulb to somewhere along the range of 2000 to 2500 degrees celcius, it woundn't produce any light. Why? The pressure differentials from the vaccuum in the bulb and the atmospheric pressure might be just enough to break the glass at 2000 degrees. Anything above 2300 and the bulb will melt. If you could somehow heat just the filament, then it would create light. Thus, they run on electricity.

 if you put an incandesent lightbulb in a microwave it will light up
I wouldn't think so. I'm too afraid to try it, though; I have an expensive microwave.
 no, it really does. It does not, however, make the filament glow, the microwave radiation interacts with the inert Argon gas, making the gas sort of arc to itself, sort of. The effect is that the gas inside the bulb glows in a wide array of colours, but the reaction of the microwaves with the gas also generates quite a lot of heat, which, after about 30 second to a minute, causes the glass to heat up to the point at which it melts and fails, with a bang of sorts...then you are left to explain this very strange looking melted light bulb :)
Actually the cause of the lighting is arcing between various points of metal within the bulb. You can get the same effect with a small piece of crumpled tinfoil (or aluminum foil for you purists) The microwaves create electrical potential differentials that cause arcing from one pointy spot to another all over the place. There is actually a low grade vacuum inside an incandescent light bulb not gas. Argon, Neon and other "Noble" or inert gases are used inside plasma balls to create the colors. Even a fluorescent bulb has a vacuum and any colors seen are the reaction of the fluorescing powder inside the bulb to UV radiation from the arcing.
And this is the brilliance of collective knowledge. I have provided the evidence, you have provided the explanation and those who read these streams of comments and investigate the evidence provided before them will benefit from our melding of minds. I thank you for your information. :)
It's like a mini-Wikipedia. Don't ya love crowd-sourcing?
That's a more sensible explanation. I was trying to figure how microwaves reacting with the filament could heat it up past 1200 degrees. That would have to be one heck of a microwave.
 did you watch the video :D
Yes. Not with the sound, though. So if he said something that I missed, well, i missed it.
 lol...that's ME! woo! I microwaved a light bulb and recorded itjust for you :P

in the video I give a brief analogy of the process takingeffect...nothing you can't gain from the post above (Oct 12, 2009. 10:01 PM)

this is the way it is :P the photos show the aftermath.
I know what I'm doing tonight.
youve never gone camping i take it there you would have seen a gas toaster there a funny round thing with closehanger looking things to hold the bread in place an they sit ontop your gas burners like a pan would  but these have holes in them wich arnt very good for cooking the egg at the same time but if you take a small coffee can an trim off the bottum art leaveing a lip you can place that inside the toaster provided theres still room for the heat to get past it to the breadslice .  also theres the sqware wire racks you can get at any store were you put bread inside fold it over locking it shut that can be used to cook your steak as well an if your gas runs out its awsum over a fire pit.
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