Solar power supply...
Matt White
Posts: 60
Maybe someone can help me with an idea.· I have a solar panel that can generate anywhere up to about 3v.· I'd like to use an OpAmp to increase the voltage to 5v so it can charge a Cap·and be used as a power source.· I figured I could use an ADC to monitor the voltage and when the voltage was high enough to power something I could switch on the solar panel power and switch off the battery power for part of the circuit.· I·don't know how practical it·is..·but I thought it would be fun to try and build.
Matt
Matt
Comments
·· The Op-Amp will require more than the voltage you're trying to get to in order to "boost" the voltage.· In a sense you'd already be providing the power from another source anyway and the solar cell wouldn't really be doing the charging in this setup.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
·· Correct me if I'm wrong but, I think Matt is thinking the Op-Amp will boost the voltage on it's own (without outside power).· About the only way that's going to happen is with a DC/DC converter or charge pump and you're going to lose current in the process.· Considering how little a solar cell provides to start, it's really not going to work.
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Ryan
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Ryan Clarke
Parallax Tech Support
RClarke@Parallax.com
Post Edited (Ryan Clarke (Parallax)) : 6/15/2006 3:50:11 PM GMT
· A battery that runs down (because of a bad panel or excessive draw) cannot be charged by the solar because the charger is a trickle charger which supplies slightly·more than the electronics take up.
· Efficiency is everything -- ·and you'll find in these situations, as few others,·that there truly is no such thing as a free lunch.
Ryan
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Ryan Clarke
Parallax Tech Support
RClarke@Parallax.com
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Chris Savage
Parallax Tech Support
csavage@parallax.com
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Well well, I'm seeing things, three of them.
-Stanley Blystone
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Chris Savage
Parallax Tech Support
csavage@parallax.com
Ryan
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Ryan Clarke
Parallax Tech Support
RClarke@Parallax.com
The second problem is that converters waste a lot [noparse][[/noparse]at least 10 to 20%, some much higher] of your power.
A third problem is that you have to determine your available power as a fraction of the actual sunlight because the solar panels are not very efficient [noparse][[/noparse]likely less than 10% of the solar energy] and get less efficent as they become hotter. A big solar panel will provide more than a tiny one. Just high voltage is not enough as Amps x Volts = Power.
And for a fourth problem, you have to look at the actual weather and location. The maximum output of the solar panel may never be achieved. How many days of clear sunshine do you have? Overcast cuts the amount of energy by a great deal. How long is your day? If you live in Alaska, you get a lot during the summer - nothing during the winter. Are you in a shady valley?
If you can get through all that, some applications just will never work.
Don't try to provide solar powered lighting for an Alaskan winter.
But a solar powered radio or computer for summer use in Alaska might be excellent.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
we use solar panels for lots of our remote weather stations (there's just no other form of energy that would work).
We've done tests in the Rockies on how much snowfall affects solar panels....and you'd be surprised (maybe not) to see that they are not affected very much at all.
Anyhow, solar panels are a current source. So, throughout the day you'll typically see the same voltage from the panel, it's the current from it that changes with solar intensity.
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·
Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
If you have the time, I, for one, would love to hear more about your experiences with current vs. voltage considerations in photo-voltaic arrays (PVA's) both in terms of external influences (rain, snow, angle of the sun, environmental contaminants, etc) and in terms of using individual solar cells or sets of solar cells in parallel and//or series configurations. My own "reality" is based only on my own experiences, and not by virture of any PVA research I've done. As you will see in a moment, ours was an empirical, but not terribly scientific approach.
Just as a general matter, we would hook up a small "test" PVA and dummy load, to a recording volt-amp meter (two parameters), to gather local data for a few days and attempt to extrapolate from that "test" PVA aproximately how much larger (voltage-wise and current-wise) a PVA panel might be appropriate for this particular geographic location. Generally, doubling the current extrapolation and multiplying the voltage extrapolation by 1.5, would give us a PVA which would work throughout the year with a safe margin. I'm SURE there were many times when larger than needed panels were employed. This was a PVA => storage battery application, and not a pure PVA application, so the considerations concerned might well vary because of that.
TIA
Regards,
Bruce Bates
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3 V, 200 mA at full sun outdoors
3 V, 100 mA at full sun indoors through window
2.5 V, 8 mA with light from 60 W incandescent lamp with 25 cm distance to solar cell (2000 lx)
2.5 V, 40 mA with light from 60 W incandescent lamp with 8 cm distance to solar cell (10,000 lx)
Thanks!
Matt
Matt
I've played around with charge pump circuits in the past,utilizing the 555 timer chip.It is certainly not ideal for some purposes,as stated by the other guys.But,for the purpose of learning new things,it would be a worthwhile area to experiment with and expand your knowledge.The voltage and current produced might suit your needs,all you can do is try.
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Thanks, Parallax!
I hope I'm not accused of hijacking this thread, but I wasn't sure if a separate thread was needed for this.
I'm afraid I don't have the actual data from the "snow depth test"....The panel was tested at different angels (vertical) but was primarily pointing due south (mag or true...I'm not sure).
We had to setup 4x100Watt panels (in series) to supply power to a wind tower on a rock shoal in the middle of a harbour.· The line that was there had been damaged due to anchors.· So we went wireless....the transport authority has float planes there and require 5second wind updates, so the average power being used was fairly good.· I went to Soltek to spec out a solar system and they came back with 4deep cycle batteries and 6panels....theoretically this would keep us backed up for 20+days....cripes!!· So we downsized it to 4panels and 3batteries to keep costs down.
I've included a pic.· Those panels are on a 25degree angle....partly to keep the bird guano from sitting and hardening on the panels (that seems to be the worse for blockage).
Our guys use the same panels on ocean buoys....but they're so concerned about power consumption that, as soon as one panel gets weak, they replace it.· So I was able to pick up a panel for a simple setup here at work (see pic)....just powering a campbell scientific logger.· Been working fine...is set at a 45deg angle and although it does ice up, the metal and colour tend to warm up quickly in the sunlight and the ice slides right off (of course, the ice still lets light in).
I do not have any temperature vs. panel output data though.· I suppose I could just look at the logger data over the year (records temp and battery voltage) but I'd suspect that the change in temperature also affects the deep cycle battery, which would present a changing load and would skew the readings.
I've even taken a few batteries and a solar panel camping...needed to recharge the trolling motor.· Have to say that it wasn't great...but still worked!
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·
Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
On the other hand, fog or overcast really cut down on the sun's output. Point Reyes, California has 300 days of fog per year. Solar power would be quite limited there.
Regarding the Voltage/Current limitations, having a stable voltage is nice for charging batteries. But, NiMh also perfer not to be charged at a rate in excess of 1/10th of their amp-hours as they have heat damage, over 1/3rd of their amp-hours is quite damaging. Also, if they are charged below a certain rate [noparse][[/noparse]something like 1/30th or 1/50th], the may suffer less eventual output. So there seems to be an optimal current range for long battery life. I suppose one could impliment a low side cutoff to protect the battery.
Another dilemma in snow country is that a cold battery just won't put out as much as a warm one. So the solar panel might best work secondly as battery warmer.
If you really want to use a 555 charge pump, there are low-power varieties of the 555 that can make the whole thing a lot more efficient.· The Art of Electronics has a listing that compares types.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 6/16/2006 4:03:10 PM GMT
Matt
Post Edited (Matt White) : 6/16/2006 6:48:26 PM GMT
Please realize that most of the inefficiencies in charging a battery end up as heat INSIDE the battery. So best to put the solar power there to achieve charging while the "waste" will generate some heat to improve the battery's performance. All this is quite useless of course unless you insulate the Smile out of it.
The practical side of things in "snow country": solar (electrical) and batteries are a real stretch to be used when there is absolutely no other way, or if the power requirements are VERY low.
Cheers,
Peter (pjv)
The risk is that if your solar charger fails, it only take one cold night to render your system useless.
And you can insulate your battery with some thermos type of foam/padding. Keep it out of the elements and off the ground.
Battery blankets are great, but will kill a weak battery anyhow!
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·
Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Actually, in northern Alberta the batteries are often burried as frost does not penetrate to 6 feet down. And in the deep northern winter, one needs to design for counting on only 2 hrs sun per day average. So that can sure put some demand on battery requirements.
For northern oilfield applications, thermo electric generators are usually employed. They provide power (50 Watts starting to kilowatts) as well as "waste" heat to keep equipment warm.
I shudder everytime I hear or read about someone believing that solar power is practical. In the desert, sure it may be reasonable, but up north at minus 30 C·or minus 40 C·batteries temporarily loose 75% or more of their deliverable capacity, it·becomes the last choice. And only then if the power needs are very modest.
I realize we have gotten off topic a bit as I'm sure Matt's interests are in a different direction.
Cheers,
Peter (pjv)
Post Edited (pjv) : 6/16/2006 9:44:18 PM GMT
I hadn't realized they buried the batteries....no doubt that's work you ONLY do during a thaw!
I agree....WAY off topic...but good tidbits nevertheless!
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·
Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Matt