Small Solar Panel

Construct a small, portable solar panel that will charge two AA rechargeable batteries in a day or two. Use the batteries to make any battery-powered device solar powered.

Step 1: Introduction

Construct a small, portable solar panel that will charge two AA rechargeable batteries in a day or two. Use the batteries to make any battery-powered device solar powered. Or use the panel to directly power small DC electronics.

The panel consists of eight 1"x3" solar cells wired in series with a blocking diode mounted on a board and protected by clear plastic. In this configuration the panel provides about 250 milliamps at 4 volts, which will charge two batteries in a day or two, depending on the weather and the batteries' capacity. Other solar cell configurations are possible to provide more or less power to, for instance, directly charge a 3.6 volt cell phone battery, or to provide a faster charge to AA batteries.

There are a number of off-the shelf small solar panels available on the web, but building one yourself gives you the flexibility to configure it to provide exactly the voltage and amperage your project needs. And it could be cheaper.

Comments

[softenersreviews]

There are many practical uses for this. Doing a DIY project while watching the how-to video?

[eyesee]

good

[eyesee]

good

[Schmidty16]

How many wats or volts does it produce

[dinesh007]

it's nice to improve the science knowledge

[the dashing hero]

dude, how did you do that!

[smallsolarpanels]

 This is a great instruction set.  I have some videos showing how to construct small solar panels

[Colonel88]

Nice job the adhesive looks like nose drops tho lol.

[mastover]

Nice Job! I love the idea!
You can get nice cheap solar cells at the electronic goldmine http://www.goldmine-elec.com/. I just ordered 4 of their small cells last week and they are in perfect condition even though it states "may have chipped edges".

[stevenh429]

well if you buy solar panels... there is no point on how to make them...

[ZOOBREAK]

that looks really cool,but where do you get the solar cells?

[CommanderBob]

Nickle metal hydride batteries can take up to 1/10 of there mAh rating and safely dissipate this as heat. This is the minimum and I am sure that if your batteries were charged and you left it there for say an hour, nothing would happen. Now if your batteries are lithium than it is a different story.

[Ausi319]

reverse diodes will make them so they dont drain into the panel.

[r.abdou]

How Old are you?

[Zimmerman]

You will need to add something to keep the batteries from over charging.

[Ausi319]

where do you buy a reverse diode?

[forte1994]

good instructible! but would you get more power if hooked up in parallel?

[Berserk87]

parallel would give you more amps. a lot of the solar cells ive been looking at are 0.5V output and 50-200mA output. so hes probably getting 4V @ 200mA. or around there.

[forte1994]

ok thanks

[hobbles]

Im gonna invest in getting better cells, you should make another panel and put it in series and it should cut the time in half. Im gonna try buying some from http://www.quadmodsusa.com/solarcells.html but i dont know how reliable they are.

[hobbles]

(removed by author or community request)

[ElectricMan1]

Didn't your solar cells break over time because, like its already hard to solder them correctly, how do you put them in a plexiglass container without them breaking?

[FaqMan]

This ible would help with our economy actually buying millions of none rechargeable batteries will pollute the Earth while rechargeable would not really. This can be the start of a cleaner earth.

[Tobita]

hello, i am kinda of new to solid state electronics and learned most of what i know now from my grandpa, and i was wondering, if i had solar cells connected in series, and they charge a bank of capacitors (also in series) and i have a switch separating the wire that connects the +and- sides of the capacitors, and i have a transformer on there to regulate it, will i be able to sustain a charge long enough for say charging and operating a notebook?

[kadris3]

probably not. charge and use batteries. it's much simpler. a laptop requires about 18 or 19 volts. 12 for some systems, and 5 for the others. its a dual voltage menace. some use a single battery so make up one to parallel the internal system in your laptop. watch polarity to save your electronics. good luck.

[Tobita]

oh my, dual voltage cells? well, if the problem would be shorting my battery or not having enough/too much voltage/amperage what if i simply connected the charging cable, if i stay in the operating amperage and voltage, i SHOULD be able to charge it, even for the smallest moment, right? if not, i could simply be the most hopeless person at this =P

[kadris3]

the internal battery cells usually aren't dual voltage. they are higher than the 12vdc systems available everywhere. the computer breaks the voltage down for the various systems it requires. if you are building a system for running the computer, you need two in series: a 12vdc jell cell and a 6vdc gel cell to give you the 18vdc that the computer uses. charge the battery array with about 20 vdc at low amperage. watch polarity carefully. a starting point would be to measure the dc voltage on the output of the 117 vac charger that came with the computer. this will tell you the charging voltage. this is what you will need from the solar array. you can then design the solar array to charge the internal battery. you can then run it from the charged internal battery or the outboard 18 volt jell cells you made up. when charging it might be better to have the computer off to prevent an over voltage as the cells get near full charge. the other alternative and much simplier is use an inverter on a 12 vdc system to provide 117 vac to the charger which came with the computer.i have done this in the truck when i have been on the road and it worked well. i used a 140 watt msw inverter from harbor freight $17.xx on sale. a 70 watt unit as available from wally world for $14.xx and this also worked as well. i also did cell phones and electric razors in the manner. if you need more explanation please feel free to contact me directly to save bandwidth. go to unclecytheledguy.com and click on the contact uncle Cy. i will be happy to provide any electronic help i can at no cost to you. good luck

[Tobita]

cool, but i am gonna keep most of my project for the winter months when it's too cold to go outside and have nothing else to do :D but hot damn, i can't wait !!!!

[kadris3]

good for you. many of us northerners do the same. i have several radios to build and i pile them up until winter. lots of projects: electronic and otherwise. i meant to mention earlier, a transformer is for alternating current, but a solar panel generates direct current. you might be successful at charging some capacitors but they would only provide tiny amounts of current. you need much more than that for the needs you described. good luck with your project

[Tobita]

it's winter now! and i put away most other things waiting for this one, first i need to reformulate the goal (charge things using the classic 2/3 prong North America plug) the power source (solar) and storage (pending, worst case is some capacitors in series with a high-end resistor at the end (i wouldn't do that)) so, if i get everything on paper/wetware/digital, i could start an instructable if i had someone capable of fixing the errors and putting things into effect (short on cash since a while, bought a tad too many gifts) then it doesn't seem too mind-meltingly massive.

[kadris3]

with average intelligence, which you have already demonstrated, getting wired is no problem. as i have said before, forget capacitors. they will not work. get a couple of golf cart batteries at wally world. they are deep cycle 6vdc and more amperage than three trolling motor batteries. series up the two batteries for the 12vdc you need. keep everything on 12vdc and use an inverter to charge the computer. automotive lights(12v) work well and you don't need to convert anything. RV lights from an old RV, junk yard, RV store are easy to get, and work well. heed the cautions above and go for it. good luck.

[Tobita]

i think now i would need to get the solar panels, but if we could use something that could diffuse the sunlight for more exposure and mount it on the panels it should chare faster, correct? and, when i visit saudi in march, should i dare attempt to bring it in the plane? xD (i wasn't serious, i would mail it instead)

[kadris3]

incorrect. diffusing sunlight cuts down on your output from the cells. this is especially true for crystalline, or polycrystalline. slightly less true for amorphous silicone. there are some semi bullet proof(i.e. well built) panels out there but they are expensive. D.I.Y. is the only way to go if you are broke. if all you are doing id recharge a laptop, you may be able to go directly to an inverter and forget the battery bank. you need enough power to drive the inverter, so there is a downside to everything. have a safe trip.

[Tobita]

cool, but either way, unless i move back to saudi arabia for good, i think this will stay as a novelty item xD

[kadris3]

that's o.k. too. even casual use may save a drop or two of foreign oil. as the whole nation does it, these little drops add up. besides being fun to play with, you have a back up system when the power fails. let the experiments begin.

[Tobita]

yeap!

[numenius]

This looks useful. I have a boat which has various battery needs so this would be a good soloution. Ready made panels seem overpriced here (UK) How much did this particular project cost?

[liam01]

yeah, solar panels are really expensive in the uk. Might try ebay.

[stevezone]

seller fred480v on ebay sells the individual solar cells that you can inexpensively make your own solar panels with.

[Ausi319]

yea you can make your own. i'm looking for a seller that will sell me some for a good price. (and that i can just send the money in the mail or something.) But how do you know how many milliamps you are getting? i know the volts. But how do you know how much your panel is putting into the battery(milliamps) at a time?

[frontier]

http://www.allelectronics.com/index.php?page=search&search_query=solar&x=0&y=0
thats the cheapest place in the internet i've found for small solar panels anyway, i dont know about bigger ones :O

[claire!]

this is great, but how big is each cell?

[kadris3]

here i am running my keyboard, and failing to complement the author. i am sorry. this is exactly the thing which will free us from foreign oil. neither right away nor overnight, but every time we succeed in less oil generated power being used we contribute to moving away from this house of cards. we will win. it will be the students experimenting after school, the self directing mad scientist in his garage or basement, or the tinkerer in his shop that will eventually free us. keep up the good work. thank you.

[eggplanthunter]

If I use 3v@200mA panel with a 1N5819 diode(drop=.34v@100mA), can I charge 2 AA NiMH(1.2v@2800-2900mA) batteries? Or will i need to go to a higher voltage, ie. 3.6v@200mA to charge the AAs.

[kadris3]

the 3.6 vdc would be better. you should be a volt or two over the voltage of the cells. at 2.4 vdc and a .34 vdc voltage drop across the diode you are about as low as you can go and still obtain a charge. even higher than 3.6 might be better as it will take longer to charge as the cells approach full charge. it will take 2 days of full sun to charge them up as winter usually has less sun than summer time. good luck. be sure to tell everyone how it worked for you. we learn from the success of others. good luck

[eggplanthunter]

Thanks, I decided to go with the 3.6s. Just one question. When you said a higher voltage would make it charge faster, I was under the impression the amperage affected charging speeds more than the voltage....

[kadris3]

both are related. if you are charging a 2.4vdc battery bank with 3 vdc array and have a diode in there, it may hardly ever get to full charge or take forever. you need a few volts over that which you are charging. 13.8 is used in car alternators to charge 12vdc batteries. 8vdc generators charge 6vdc batteries in older cars. if 6.2 vdc were charging a 6vdc battery the time constant would be almost infinite. once the proper voltage is established, get the amps you need by paralleling up more cells. you are correct in that amperage determines the length of charge, but this is only true once the proper voltage is established. you configuration will take about 2 days in bright sunlight. good luck with your array. please let us know how you do. thank you.

[jackusage]

If you link the cheap solar light panels together in an array is there a limit to the amount of panels/voltage/amps that the array or each individual panel can take without getting damaged? If you could private message me the answer I would appreciate it.

[iman]

this may sound extremely stupid, but what does a diode do ? :(

[kinz1jg]

A diode allows electrical current to flow in only one direction. For this solar panel, the electricity should flow from the solar cells to the batteries or device, but not the other direction, thus the diode.

[besilly]

Would you have any directions on how to connect such a diode? I am trying to hook-in some solar panels into my electric car batteries. I have bought some diodes. How would they be connected between the battery and the panel wires?

[Ian01]

kadris3's explanation confuses even me, and I'm very hard to confuse. The diodes should have a line around one end. That end is the cathode. The other end is the anode. On a schematic, the cathode is the line at the tip of the triangle, and the triangle is the anode. Current can flow through the diode from the anode (positive end) to cathode (negative end) only. If you try to put a current through the other way, it will be blocked. There is a small reverse leakage current in all diodes. Diodes also have a forward voltage drop, meaning that the voltage at the cathode is always about 0.7 volts less (for a silicon diode) than the voltage at the anode. What this means for charging batteries is that if you use a 12 volt solar cell with a diode, the batteries will only get about 11.3 volts. 12 volt batteries need about 14 volts to charge, so you will need a ~15V solar panel. If you use a germanium or Schottky diode, you will have a forward voltage drop of 0.2 volts or 0.15 to 0.46 volts respectively. With these diodes, the batteries get more voltage, but there is more reverse leakage in the diode, but that's not very important, as there is not enough leakage to damage the solar cell. (Solar cells can be damaged by reverse current, because they are diodes, but they have a low breakdown voltage.)

[kadris3]

sorry, i didn't mean to confuse. by chasing electrons on paper it is easier to understand the direct short/infinate open of the diode.

[kadris3]

u should use a shottky diode as the forward voltage is about .2vdc. germanium is next w abt .4vdc. a silicon one has .7vdc. small voltage loss is better. the line is cathode and the arrow is anode. current flows against the arrow positive to negative. if u don't get this(many of my students don't), place the diode in one of the lines of the solar cell. take a reading w a volt meter. if u have voltage, it's in correct : solder it quick to insure it stays right. if u get nothing on the voltmeter, the doide is backwards. turn it around and check it again. if u get a reading solder it quick. if not ur diode is bad. get another diode and start again. when u get a volt reading, solder quick. if u don't have a voltmeter, use an led. solder a 680 ohm resistor in series. long lead is plus on the led. good luck. X

[kadris3]

major mistake: current flows NEGATIVE to positive. sorry

[Ian01]

Current flows from positive to negative, electrons flow from negative to positive.

[iman]

Thanks :) Matt

[iectyx3c]

Good presentation, +1 points. Practical, easy to understand. The link to Plastecs is now 404, try cutting it down to http://www.plastecs.com/ and it should work.

[projects2]

I want to make food heater for one plate of food at a time. The food plate will be plced in a tightly sealed casing that is covered with aluminium foil in the inside. The project is for a school project. I also intend using a heater fan of the following ratings heater 115/230V fan 24Va.c./d.c.

[ajparag]

this is a nice instructable. thank you! I suggest you update this instructable when u get more ideas.

[static]

Some of the "solar yard lights" do have battery holders and charge a pair of AA nicads in a day. They have to be the most inexpensive solar battery charger I know of.

[denassdidu]

A poly backing work's great for placsing on top when you won't to flip them over!

[denassdidu]

Great info. It work's best if you solder the tap's first' and then solder the tab's to the cell!!!1

[denassdidu]

Good info!!! RECsilicon.com, realy has got my notice on quul's and supply.

[denassdidu]

do not over heat the tab wire's, or they become frail.

[diehlman]

During the day the process is
Sun > Solar Panel > Battery = charging
During the night the process reverses
Battery > Solar Panel = discharge
The panel will discharge a battery over night.
The diode is used to stop the discharge at night.

zener diodes regulate voltage and are rated in watts. a 1/2 watt circuit will burn out a 1/4 watt zener diode.
15 volt zener
25 volts in> 15 volt zener > 15 volts out

Regulators can be used to control voltage, and or current depends on the design. To figure watts multiply voltage times the amperage.
watts = Voltage X amperage.

A 64 watt solar panel say at 15 volts = 4.25 amps
a regulator would drop the voltage to 14volts and regulate the current to below 1 amp to safely charge a car battery. It should also include a blocking diode to prevent discharge.

[denassdidu]

Where to buy???

[aureliansh]

you should join my group alternitive energy

[PCvsMac]

Hello. If I removed the panel from a solar light, let's say, and wired them to a AA double battery holder (with batteries) and a blocking diode: a) Would this work? b) How long would it take power 2x AA batteries? c) Is there a risk of leaking etc. in the batteries?

[kinz1jg]

Good questions. I've tried doing the same thing -- removing solar panels from solar lights to charge two AA batteries. The answers to your questions are: 1) yes, it is possible, but see my comments below, 2) the time to charge two AA batteries depends on how powerful the solar panel is, how much sunlight there is, and how much charge (milliamp-hour or mAh) the batteries hold, and 3) if the panels are really powerful or if the batteries get really hot, then there is a risk of leaking, but personally I worry more about them getting wet and shorting out or corroding. There is some discussion in the other comments in this instructable about overcharging. The solar panels from solar lights that I used were originally set up to charge a single AA battery, so each panel produced a little less than 2 volts. Solar panels need to produce more voltage than the battery or batteries you are charging, therefore the individual panels worked fine with one battery but wouldn't charge two. Also, the panels were not very powerful, producing about 50-60 milliamps each. Charging a 2000 milliamp-hour (mAh) battery with one panel would require about 40 hours of direct sunlight (2000 mAh / 50 mA), assuming there was no loss of power between the panel and battery, which is not a reasonable assumption. To work around the voltage and power limitations, I wired four solar light panels to generate 4 volts and about 110 milliamps. This setup works OK, but it doesn't charge as fast as the solar panel in this instructable, taking two or three days.

[!Andrew_Modder!]

do cells have little + and - connectors built on em?

[chuckr44]

Doing a search on google for +"solar cell" +DIY seemed to yield some promising results of making your own solar cell. But I thought I read somewhere that it's a complicated process to make usuable solar cells. One reason why the good ones are still expensive.

[onetoremember]

It is possible we sell a book/pamphlet by a guy called noon who shows you how to amke a solar cell. www.onetoremember.co.uk

[Ian01]

That guy shows you how to build a cuprous oxide solar cell, in a book that you have to buy. Scitoys shows you how to do it for free.
http://sci-toys.com/scitoys/scitoys/echem/echem2.html#solarcell
http://sci-toys.com/scitoys/scitoys/echem/echem3.html - flat version

[Loveofchaos]

i can see a smart person making millions from rich people with my awesome idea.... solar mosaic, a cool looking, clean source of energy

[godsdog]

Nice instrucable. For ultimate efficiency, consider utilizing a regulator (maybe a cheap ol' 5v reg)instead of the zener. Perhaps the backing could be black and attached to a tripod so you can angle perpendicularly to the sun.

[Ian01]

What zener? I see no zener. Aren't all linear regulators lossy? So wouldn't using a regulator decrease the efficiency?

[servant74]

A zener is a type of diode. It typically has less 'loss' than a regular diode. Think of a diode as a one way valve, but it takes some pressure, to make the valve allow flow through it the 'right' way, and it protects from there being any flow the wrong way. A zener version of the valve requires less 'pressure' to allow it to open up to allow flow going the right way. To get the electricity to water flow allusion right think of: the 'pressure' is voltage, and the 'volume' of flow is the amperage. It makes a lot of sense (and possibly a quarter volt of electricity additionally available). In solar that can be a lot of power!

[Ian01]

I knew all of that, I meant that is a regular diode, not a zener. The word "zener" is not mentioned once in the instructable, that is a regular diode used to stop the battery from discharging through the solar cells.

Your explanation of zener diodes is incorrect. A zener diode functions like a regular diode, but allows current to flow the wrong way if the voltage applied to the diode is greater than the zener voltage. A regular diode will do the same thing, but this will damage the diode. A zener is designed to allow reverse flow, and then recover when the voltage is applied the 'right' way. Your explanation, "A zener version of the valve requires less 'pressure' to allow it to open up to allow flow going the right way. " seems to be for Germanium or Schottky diodes, not Zener diodes.

[godsdog]

Looks like a zener diode to me...I like how you hack regulators and get so excited about your 'notion' that it would be less efficient than the current setup. Chill.

[Ian01]

The diode is to protect the solar cells from reverse polarity, so the battery doesn't discharge into the cells and damage them.

[kadris3]

.............so it doesn't discharge into the cells and drain the battery bank. rarely are the cells damaged in this configuration. they have enough internal resistance that cell damage is most rare.

[Ian01]

I didn't mean the battery could be damaged by discharging (though it can), I meant that the solar cells might get damaged by the reverse current, and the diode is to protect them, not the battery.

[kinz1jg]

I like the idea about attaching the panel to a tripod to angle it to the sun, although I'd worry about the tripod tipping over in high wind. Right now mine is propped against a brick. I'm not familiar with regulators, how would that increase the efficiency?

[kadris3]

it wouldn't increase efficency. it would prevent overcharge if u went off for a period of time and weren't tending the batteries. these are necessary in larger arrays where there is a large solar array and not quite enough battery capacity.