# Solar Cells?

Is this a good set up for a series/parallel configuration? when I test it with a multimeter the voltage was around 2.5 v each cell produces 3v@40ma. so something is wrong here.

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2 years ago

As Pointed out 3 volts only occurs when facing noon day overhead sun and perpendicular to it. No clouds. dust or fog...

What you have are two pairs of cells in series and then the pairs are wired in parallel..

-max-2 years ago

The output power, voltage, and current for solar panels can be a very tricky business. Generally, there are 3 main ratings for output of the panel, short circuit current in max sunlight, the optimum current/voltage in max sunlight, and the open-circuit voltage, again, in max sunlight.

Here are some real world figures I have for one of those CIS panels that is in the photo, measured with a 60W incandescent lamp indoors:

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3.32V @ 0A, 0W open-circuit (well, just a 10Mohm load, from the multimeter)

0.435V @ 81mA, 26.5mW near-short (7 ohms impedance load)

(sadly I do not have data for short-circuit current, but the voltage would be approaching 0, and the current would probably be close to 100mA, but 0W since 0*anything finite. I think the reason for that was that last one being 7 ohms is because the current shunt resistors inside my multimeter. The mA/uA range on a standard multimeter has lots of burden voltage compared to the current because the current shnt resistors are pretty high resistance.)

2 years ago

Those are wonderful data numbers.

Shows there is no need for tricky regulators when charging a battery as the internal resistance in a solar cell will adjust to trickle charge a battery in a simple direct way.

You do have to reasonably select the array to match the load...

2 years ago

Thanks! I learned after further research about impedance matching, and how to maximize power transfer, and efficiency in this case, that I need to match the 'internal impedance' of the panel. I guess it is close to 50 ohms output impedance, interestingly enough, lots of signal terminations work with 50 ohm termination! I wonder if that was by design... I doubt it.

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I was thinking about designing a custom switch mode power supply that would charge a battery or supercapacitor at a continuos power, and instead of regulating the current or voltage on the output (other than to turn off the charging when the battery is topped off) actually use the negative feedback loop to control the amount of current drawn from the solar cells, to force them to stay within the optional range of power. However, I do not know if that optimum voltage/current will change with sunlight, temperature, color of the light, age of the panels, etc. It get exponentially more difficult to design something like that the more things you try to consider :P

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I like to think about impedance matching like a waterwheel. If you build one, and do not use it or connect anything to it, then it freewheels fast as possible, and does not do anything useful, since there is no load, no torque force from it to rotate a load, like a corn miller or generator. Likewise, if you connect too much load to it, it pretty much grinds to a halt, (In the most literal sense possible, of course! http://www.phrases.org.uk/meanings/grind-to-a-halt...) and again, you get no power output, since it is all force, but no RPMs! There is a sweet spot, halfway in between the 2 extremes, that is the optimal for power extraction!

2 years ago

Now I know you will like the Sola voltage regulating transformer because it is the bridge between those extremes you understand.

A Sola is a ferresonant 97vac to 135vac line input while 120vac line output with minimal waveform distortion. A useful product for sensitive electrical equipment at the end of a long easily disturbed power line.

But not generally known is the fact that you can overload the Sola and instead of burning up it goes into current limit mode because it is an air gap magnetic device.

A wonderful application is charging a battery car overnight.

When first plugged in, a heavy charging draw limits the damaging battery current by the inherent sola current limit :-) Then by early morning as the battery has reached full charge the sola is holding the voltage at a final terminating easy charge rate...

BTW this Sola really works on winding up a flywheel power system.

2 years ago

I have heard about those things, Although I have not heard it called that. Wikipeda calls them Constant Voltage transformers, or CVT's. http://en.wikipedia.org/wiki/Voltage_regulator

2 years ago

Correct.... Sola is a brand name we old guys prefer to CTV.

2 years ago

And CTVs work like a power load shedding device where power generation plants dink \$\$\$ out of you ... if you accidentally peak a power load price point even for a second they can bill you the higher rate for the next 8hrs.

2 years ago

Gees, that sucks. Do the newer meters not account for reactive power? What if you had a load that only used reactive power, could you cheat out the power companies? (I do not really understand how AC reactive loads work, I like DC much better ;) It's simpler)

2 years ago

All power companies watch and charge more for power factor ie reactive power because the current flow is real as far as the power lines and impacts the other users who share that power line.

BTW plans are afoot to use HV DC power lines to transmit electricity, they loose less to the surrounding environment. Electronics is able to up and down convert to local AC without the need of old style power transformers.

2 years ago

Great! Although I would think it would take a really long time for that to become standard and the transition will probably be slow and painful, and might even require a strong government forcing it, like the digital TV revolution a few years ago. :(

2 years ago

See map provided of existing dc transmission lines and proposed superconducting DC power lines.

2 years ago

Understandingly so! BTW, where do these sola's get used? Industrial purposes for soft-starting motors, preventing inrush, or in UPS supply's of some sort? sensitive hospital equipment??

2 years ago

I use one to keep the air-conditioner running during state sponsored brown outs as many others can do. The sola works power like any other step-up xfmr by sucking more current to raise the operating voltage above brown ;)

2 years ago

Lol yup! I have actually used solar cells connected directly to a 2 NiMh in series batteries to charge them, worked fine, but really, really slow. I was using a relatively small solar cell, and it powered a digital watch which I took apart, a 6 LEDs from a flashlight I took apart, and a metronome, which I again, took apart when I was young! (I wonder where all my toys are... or the part from them, anyway... :P)

-max-2 years ago

So do NOT make the mistake of multiplying the short circuit current, or absolute maximum current to the open circuit voltage or absolute maximum voltage, you will get a decepticly high and useless number, that in some cases severly overestimates the power output.

dominick.j.pezza (author) 2 years ago

So.... in reality since its series and parallel I am looking at 6v @80ma correct?

2 years ago

Exactly !

the cells producing 2.5 instead of 3 is probably because the sun wasn't bright enough

i think you put them in parallel because you have a positive and a positive connected

and a negative and a negative

2 years ago

It's two parallel strands of two serial cells. Configuration looks sane. Of course the voltage should double that of a single cell. Try to measure the voltage of every cell by itself. Of course in approximately the same light condition.

2 years ago

instead of a 2 by 2 change it so the it is 1 by 4 and make sure it is positive negative positive negative positive negative positive negative