Author Topic: First steps in using the Sun's energy  (Read 28099 times)

birrbert

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First steps in using the Sun's energy
« on: January 04, 2013, 06:29:18 AM »
Hello!

So, it's not much, but I finally managed to put my solar panels to work. I bought six panels (6 Volts x 100 mA = 0.6 Watts each). Dimensions: 12 cm x 4.5 cm x 0.5 cm. They look like the ones this guy uses in his video. First photo attached (excuse the glare).

I wired them in series two by two, this way I got three 12 Volt/100 mA panels. Then I wired these three in parallel to get 12 Volts/300 mA. Second photo attached.

It's winter now and it was overcast all day, but without a load I measured 9-10 Volts coming out of my creation. Now, as I put a load on it, the voltage drops dramatically:
- attached a 12 Volt/200 mA fan and it goes down to ~1.7 Volts, the fan starts spinning only if I spin it first;
- attached a green LED and it goes down to ~2 Volts, the LED lights up;
- attached a green LED and it goes down to ~3 Volts, the LED lights up.

As noob this might sound, please try to explain to me what's the case here: is something wrong with my panels or just there isn't enough sunlight? :)

Thanks!

PS: my goal is to build some kind of charger with these panels, but I don't know yet what for.
"Dubito ergo cogito, cogito ergo sum." Descartes

SeanB

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Re: First steps in using the Sun's energy
« Reply #1 on: January 04, 2013, 07:29:54 AM »
You are in Romania, roughly 45 degrees north. Thus the sun at noon is roughly at 45 degrees from the vertical. Solar panel ratings are quoted at a standard illumination, roughly 2kW per square meter of panel, or basically high noon at the equator give or take. At your latitude the sun is roughly half that in summer, and being winter it will be even less, probably half again. Thus the panels will give at noon when held normal to the sun ( facing the sun at no angle at all, so they get all the sun) around 25% of the rated output. Thus you will get around 3V per panel but the maximum current will be around 25mA per panel, depending on the load. You will be able to charge a small flat lithium cell with each panel at current, but will need some form of charge controller for a small panel to regulate the power into the cell.

birrbert

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Re: First steps in using the Sun's energy
« Reply #2 on: January 04, 2013, 08:44:19 AM »
Thanks for the info SeanB!

So, when talking about a solar panel or cell there's a huge difference in performance between two states: loaded and not loaded. Why is that?

With the current wiring (three double cells in parallel), I can get a maximum loaded performance of 6 Volts x 75mA = 0.45 Watts, is that correct? If yes, that would be enough to slowly charge cell phones that have a 3.7 Volt rechargeable battery.

Could you please recommend a charge controller? Are there any for such a small panel/power? Could I make one myself? I see a nice little project developing here (interesting for me at least). :)

edit: I recovered a 5 Volt regulator (LM340T-5) from an old satellite receiver so I could use that, but probably 5 Volts is too much for a 3.7 Volt Li-Ion cell phone battery and it will damage it; maybe damage the phone too; please correct me if I'm wrong.
« Last Edit: January 04, 2013, 08:54:11 AM by birrbert »
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kibi

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Re: First steps in using the Sun's energy
« Reply #3 on: January 04, 2013, 09:58:30 AM »
I would recommend watching this video. Shahriar explains and demonstrates the experiment very well. The video is an hour long,  but very interesting. Watching this video should answer a lot of your questions.

http://www.youtube.com/watch?v=lrELRVFEx_s

birrbert

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Re: First steps in using the Sun's energy
« Reply #4 on: January 04, 2013, 12:48:11 PM »
Thank you kibi for the link!

I watched the whole presentation and I liked it. It answered a few of my questions, plus gave me many new pieces of information, but that particular IC device is out of my reach... it's either sold in large quantities or shipping to Romania would cost a fortune; plus I'd love to try out a the demo board but that costs a fortune too, I mean way too much for a beginner hobbyist like me. Rhetorical: when will stuff like this be available for people like me?

Regarding solar panels: what I still don't understand is where does that big difference come from when they don't have a load and when they do have a load? Is the voltage dropping because my loads (fan and LED) are pulling all the current and current is low because of light conditions? How can I determine/measure the true capacity of my solar panels? Without knowing this information I can't really do anything, can I?

Regarding my idea of a solar charger: how about using a step-up converter? I found quite a few types on eBay at an affordable price. I could experiment with one that has a wider input, let's say 1-5 Volts and a 5 Volt fixed output (with a potentiometer I could set the right voltage to charge a specific battery). What do you think?

I know I ask a lot of questions, but please bear with me. I set out achievable goals for myself, but without explanation from more experienced people I can't progress. For example if I purchase something from eBay, it will take 4-6 weeks until it arrives to me and if I get the wrong item I will have to wait another 4-6 weeks for the next one to arrive.
« Last Edit: January 04, 2013, 12:55:47 PM by birrbert »
"Dubito ergo cogito, cogito ergo sum." Descartes

SeanB

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Re: First steps in using the Sun's energy
« Reply #5 on: January 04, 2013, 01:26:28 PM »
A solar panel can be thought of as a voltage source with a series internal resistor. The voltage is essentially constant when exposed to light ( not really true but when lit by outdoor light it is pretty much true) but the resistor value is dependant on the amount of light on the front of the panel. Thus open circuit the panel will deliver 6V over a pretty big light range, from morning dawn to noon. The current available though depends on the light on the cell. If you short the cell with a ammeter you get the short circuit current ( 100mA max in your case) which is proportional to the light incident on the panel. Thus the current you can draw is somewhere between zero and the full amount. You choose the load to fall somewhere in that line. If you want to charge a simple cellphone cell with a built in charge controller then all you need is the simple 5V LDO you have to limit the voltage presented to the cell when it disconnects when fully charged. A simple shottky diode between the panel and the diode works for most cases, if you have some working cellphone battery units they can be connected across the panel to charge them slowly, probably will take a single panel 3 days to fully charge a battery by you.

birrbert

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Re: First steps in using the Sun's energy
« Reply #6 on: January 06, 2013, 06:07:29 AM »
Today is Sunday and my last free day. Tomorrow it's back to work so I decided to do something new and exciting on my last holiday. So I made a short video clip while playing with solar panels and a DC fan. For me it was a groundbreaking activity; I enjoyed it a lot. :)

The sun shone, no clouds close-by so I decided to hook up the solar panels I have in my window to a DC fan and play around a bit. As you will see at first I had to give the fan a little spin, but by noon the sun was high enough and strong enough to power the fan without me having to intervene. Also, at noon the fan was able to draw 100 mA at around 10-11 Volts from my little solar array.

Moreover, I gave a chance for the 5 Volt voltage regulator and it worked nicely. It's not burned or damaged, at least I know that now. :)

Please excuse the camerawork. My Canon SD1000 can film at a maximum resolution of 640x480 and the quality dropped a little more after uploading it to YouTube.

Link to video: https://www.youtube.com/watch?v=560G6E2G1NQ
Link to photo album: http://www.flickr.com/photos/birrbert/sets/72157632451440224/

It was a good little exercise - for me as a beginner - to learn about solar panels, wiring in series and parallel, setting up a multimeter to take volt and current measurements, implementing a voltage regulator in the circuit and finally very basic stuff like the use of crocodile clips. For the next step I ordered some analog volt and milliamp meters because with just one multimeter I can't keep an eye on all the factors in the same time. I will test a DC to DC step-up converter in low light/low voltage conditions.

In the long run my goal is to make a simple, relatively small size, yet precise and safe cell phone charger which is able to charge both on sunny and cloudy days.
Secondary goal: to learn and have fun along the way (and maybe to inspire beginners to start experimenting, just like Martin inspired me).
« Last Edit: January 06, 2013, 06:28:14 AM by birrbert »
"Dubito ergo cogito, cogito ergo sum." Descartes

MJLorton

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Re: First steps in using the Sun's energy
« Reply #7 on: January 09, 2013, 05:56:28 AM »
I would recommend watching this video. Shahriar explains and demonstrates the experiment very well. The video is an hour long,  but very interesting. Watching this video should answer a lot of your questions.

http://www.youtube.com/watch?v=lrELRVFEx_s

Another viewer also brought this one to my attention.
This is an excellent video...of great value to me...I have shared it on G+, FB, etc....
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

MJLorton

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Re: First steps in using the Sun's energy
« Reply #8 on: January 09, 2013, 06:07:49 AM »
Hats off to you Birrbert! What you are doing will certainly help others and it's a fun way to learn. I look forward to following your experiments.

Cheers, Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

birrbert

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Re: First steps in using the Sun's energy
« Reply #9 on: January 09, 2013, 04:41:34 PM »
I appreciate your support! Thank you!

The irony of fate: I'm stuck right now because the Sun's up a very short period of the day during which I'm in the office working. :-\
"Dubito ergo cogito, cogito ergo sum." Descartes

birrbert

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Re: First steps in using the Sun's energy
« Reply #10 on: January 15, 2013, 03:52:41 PM »
While I wait for the components to arrive I thought I'll raise a few questions or issues.

My plan is to build the charger using the components below in the following order:
- 12 Volts x 0.3 Amps = 3.6 Watt solar panels;
- one LM340T-5 voltage regulator;
- one DC-DC Converter Step Up Module (0.9-5V to 5V 600mA) with USB port.

The solar panels would provide 12 Volts in full sunlight to the voltage regulator -> the voltage regulator would be connected to the solar panels to feed only 5 Volts maximum into the step-up module; in other words it would act as a safety device to protect the step-up module from receiving too much voltage  -> with a USB cable the cell phone would be connected directly to the step-up module and hopefully accept a charge.

I have two things in my head right now:

1) SeanB mentioned this already and I also read it somewhere that cell phones have some kind of built-in charge regulating circuit so 5 Volts would be OK and I shouldn't be able to damage the phone or the battery because this circuit will 'adapt' the 5 Volts according to its needs. This is great if it's true because the battery is 3.7 Volts only. So is this really true? Let me tell you why I'm asking. I'm still a bit confused because I have two cell phones which have two different chargers. One is a Nokia 1112 and it came with a charger that puts out 3.7 Volts/355 mA. The second is a Nokia X1-01 which came with a charger that puts out 5 Volts/350 mA. Both have 3.7 Volt Lithium-Ion batteries, they only differ in capacity. So what gives? Why does the Nokia 1112 charger put out only 3.7 Volts? How can you charge a 3.7 Volt battery with only 3.7 Volts? Or the two phones have different built-in charge controllers?

2) What would happen if in low light conditions the voltage regulator received less than 7.5 Volts from the solar panels? I'm asking this because I read in the LM340T-5 datasheet that 7.5 Volts is the minimum input to put out 5 Volts. I'm guessing that the LM340T-5 would gradually put out less than 5 Volts, but the step-up converter wouldn't mind because it can work with input voltages as low as 0.9 Volts. The only thing is that there will be current fluctuations. This is only theoretical, but could the fluctuating current damage the cell phone or its battery?

It's a very simple concept using just a few components, but unless I burn myself (i.e. blow up a Li-Ion battery) I believe I can learn a lot. :)
"Dubito ergo cogito, cogito ergo sum." Descartes

MJLorton

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Re: First steps in using the Sun's energy
« Reply #11 on: January 16, 2013, 03:31:01 PM »
I won't add much value to the current thread....but I came across this site with some really handy info related to electronics, solar, multimeters, etc: http://www.robotroom.com/

Reading this regarding small solar projects may be helpful: http://www.robotroom.com/Solar-Recharging.html
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

birrbert

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Re: First steps in using the Sun's energy
« Reply #12 on: January 17, 2013, 02:46:59 AM »
Great website. It feels good to read because it confirms some of my findings and concerns. Please keep them coming! :)
"Dubito ergo cogito, cogito ergo sum." Descartes

birrbert

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Re: First steps in using the Sun's energy
« Reply #13 on: March 03, 2013, 06:54:12 AM »
Hello! Long time no see. :)

This little project of mine was idle for a while, because I had to wait about 4 weeks for the step-up converters (1 | 2) to arrive and then I needed a free day with sunshine to experiment. Luckily, today everything came together. Please allow me to summarize my findings.

Test subjects: Nokia 1112, Nokia X1-01, Samsung GT-E2120 and Apple iPhone 3GS.

Main components used: 12V/300mA solar array, LM340T-5 voltage regulator, cable with female USB sockets and another cable with a male USB plug on the input side and 10 different plugs on the output side for various mobile phones.

Prior to this solar charge test I tried to charge all four mobile phones with the USB cable from eBay plugged into my laptop's USB port (which we know that supplies stable 5 Volts and 500 mA). All of them were charging fine except for the Nokia 1112; I'm guessing that 5 Volts was too high for him. Also, all tests were conducted with bright sunlight reaching the solar cells.

Results without step-up converters (only voltage regulator with 4.99 Volts stable output)
- Nokia 1112: didn't accept a charge at all; I couldn't make it to charge in any configuration so I won't talk about it anymore in the following paragraphs.
- Nokia X1-01: accepted a charge, but voltage was oscillating; it was dropping every second to 3.6 Volts which was too low for the phone and stopped the charging process; then it came back to 4.99 Volts for another second, started to charge, but it dropped to 3.6 Volts again and the process was in a loop.
- Samsung GT-E2120: accepted a charge and it was steadily charging at around 3.9-4 Volts.
- Apple iPhone 3GS: at first it accepted a charge and it was steadily charging at around 4.5 Volts, then I unplugged it to try another phone and when I plugged it back in it wouldn't accept a charge; it was weird, but I tried it a third time too and after plugging it in I got the message that 'Charging is not supported with this accessory'. I gave it a try with the original USB cable which came with the phone, but no luck there either. A bit later I plugged it again and it was accepting a charge.

Results with step-up converters
I kept the voltage regulator in the circuit to keep the step-up converters safe. The converter with the blue PCB (made by LC Technologies) put out 4.93 Volts open circuit, the converter with the green PCB (no manufacturer) put out 5.35 Volts.

Basically I got the same results as without the step-up converters with a slight difference in the case of the Apple iPhone 3GS:
- Nokia X1-01: oscillating charge, 4.93 Volts dropping to 3.53 Volts with the blue converter and 5.35 Volts dropping to 3.55 Volts with the green converter.
- Samsung GT-E2120: steadily charging at around 3.88 Volts with the blue converter and 3.85 Volts with the green converter.
- Apple iPhone 3GS: didn't accept a charge with the blue converter at 4.36 Volts and accepted a steady charge at 4.80-5.08 Volts with the green converter (4.56 with the screen on).

Conclusions based on individual mobile phones:
- Nokia 1112: needs more research to find out how much voltage it needs to accept a charge; this value is most likely around the 3.7 Volt mark since the original Nokia charger puts out that much.
- Nokia X1-01: needs more research to find out why the voltage keeps dropping and what can be done to avoid this.
- Samsung GT-E2120: very easy to charge since it's accepting a relatively wide range of input voltages.
- Apple iPhone 3GS: relatively easy to charge, but with my current configuration and current sunlight conditions it was on the edge between accepting a charge or not accepting a charge.

Conclusions valid to all mobile phones:
- I had the feeling that with good sunlight charging was worse with the step-up converters compared to using just the regulator. The main reason I wanted a step-up converter was to be able to charge mobile phones in low light conditions too, but in low light conditions this configuration wouldn't work because this particular regulator would supply too low voltage to the converters. In that case these converters would work if instead of a voltage regulator I used a component that regulates only above 5 Volts; under 5 Volts this component should turn off and allow all the voltage and current to pass through and reach the converter freely. Questions is: which electronic component can do this? :)
- There are huge differences in voltage across different components of the circuit when under load and open circuit and this confuses me the most. I'm aware of the fact that the under load voltages count only; somehow these should be stabilized because charging any mobile phone can be achieved only with stable DC.

To-do list:
- Determining the minimum voltage at which mobile phones still accept a charge.
- It would be great to somehow determine the amount of current that my solar charger can put out while charging different mobile phones, because in this case I only measured the voltages. That way I could learn about the relationship between volts and amps.
- The input voltage of the step-up converters (received from the 5V regulator) was varying greatly. I guess that the converters act as a load too (to a certain degree) and the regulator can't put out a stable 5 Volts as it does without the converters in the circuit. It would be nice to log for a while and calculate min, max and average.

Also, I would appreciate any feedback from you guys who are more experienced to improve this little solar mobile phone charger. I would like to keep it as simple as possible, but at this stage it clearly needs some improvement. Just a side note here: I made a few test with a capacitor (4700uF/50V) and the Nokia X1-01 to check if the oscillation stops, but it didn't help; in some cases the voltage even dropped with the capacitor in the circuit. Maybe a super or hybrid capacitor would do a better job and then my to-do list would be irrelevant because there would probably be no need to have regulators and step-up converters in the circuit. :)
« Last Edit: March 03, 2013, 07:12:55 AM by birrbert »
"Dubito ergo cogito, cogito ergo sum." Descartes

SeanB

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Re: First steps in using the Sun's energy
« Reply #14 on: March 03, 2013, 07:21:32 AM »
You probably will need to have some appreciable capacitance in parallel with the solar panel as well, 6700uF or more, rated at about 16V will do, and this will stop the oscillation, which is most likely the phone charger attempting to draw too much current from the converter. The convertrs do need a supply capable of supplying large current pulses, which the solar panel is not capable of doing, you need the big capacitor to do so. As well you need to use a connecting cable with low drop, so a minimum of 1.5mm cable for a small panel capable of 2A is not uncommon. I have used 4mm cable to connect mine, as it is on the roof and is connected by 40m of cable.