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heynow999 · September 2008

http://www.lilith-ezine.com/articles/environmental/The-Solar-Powered-Myth.html

It seems to me the guy is way off with the numbers. Here is an example. The whole atricle is full of statemnets like this.

"Smaller units are ideal for cottages by the lake and can charge cell-phones, laptop batteries and even power a small microwave. Larger solar panels are used to provide ample supply for even large homes. Two to three large solar panels plus a battery system will cost a person roughly $2500 to $3500 CDN, will provide most all their energy needs, and will feed surplus electricity back into the grid. "

I sent him an email saying he was a bit off. He stands by his numbers.

BB. · September 2008

Re: Look at this article

Well--that is why we all are here... To help explain to people that just because it is written somewhere (FTA above):

[SIZE=-1]There are about 4 hours of peak sunlight per day, but don't let that fool you. Solar panels still continue working even at night soaking up minute amounts of energy from starlight (or if you're in the city from the constant glow of street lights), even in the winter, whenever. (There is a lot of people out there who believe that solar panels cease working completely at night.)[/SIZE]

Does not make it true...

-Bill

Windsun · September 2008

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That article is one of the worst and least factual that I have seen for quite some time. It is full of so many errors that it would be impossible to list them all, but just the idea that you get any usable power at night should throw up red flags.

icarus · September 2008

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Yep,,, Canadian Tire is where I will buy all my solar stuff in the future. The expert sales person (if you can find one with his finger out of his nose!) was selling paint earlier today, and curtain rods before that. Just the kind of experience I want!

Tony

wxh3 · September 2008

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Starlight? Is this a joke?

BB. · September 2008

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Well, just to put a cap on the starlight myth...

Solar panels do not develop enough voltage under starlight to even begin supplying any real power (self discharge or what--don't know the physics).

Anyway, assuming that they "worked" under starlight--some numbers:

• sunlight on an average day ranges from 32 000 to 100 000 lux
• TV studios are lit at about 1 000 lux [i.e. 1000 lumens
per square metre]
• a bright office has about 400 lux of illumination
• At sunset and sunrise, ambient outdoor light is also about
400 lux (if the sky is clear).
• moonlight represents about 1 lux
• starlight measures a mere 0.00005 lux

Since solar panel power output is proportional to the energy hitting the surface... Then for a 10 kWatt array in sunlight vs starlight:

10,000 watts (peak) * 0.00005 lux (star) / 100,000 lux (sun) = 0.000005 watts

5 millionths of a watt for a 10 kWatt array--Gather all of that power for 12 hours per night 365 days per year (assuming no moon) = 0.02 watt*hours per year... Yea--that will power my microwave.

Assume that this is a grid tied system, so about $10 per watt installed price.

10,000 watt * $10 per watt / 0.02 WH * 0.001 kW/W * 20 years = $250,000,000 per kW*Hour

Yep--good return on my investment there for my Star Powered Grid Tied solar array. Quarter of a Billion Dollars per kWhr--sounds like a government project to me.

-Bill

BB. · May 2009

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In reviewing this article--I just noticed another part that I missed last year:

[SIZE=-1]The myth that solar panels don't work in the winter or a northern (Canadian) climate is completely false. The fact is that solar panels actually work even better during the winter, because of the huge temperature change between night and day. It doesn't even need to be sunny. Solar panels use the changes in air temperature to provide electricity. The more dramatic the temperature change the more energy produced.
[/SIZE]
[SIZE=-1]Thanks to the temperature changes at night solar panels still provide a trickle of energy during the wee hours of the morning, combined with a battery system that hooks into your fuse box, it provides electricity at all times of the day and night. [/SIZE]

No--solar panels do not generate electricity because of changes in air temperature.

Yes--solar panels can work better in winter because of cold weather (increases Vmp which increases Power=I*V) and reflection from snow onto the panels (acting like a set of mirrors).

-Bill

nigtomdaw · May 2009

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Well maybe not starlight but I have seen 3/4 amps coming off my array on a clear night and a full moon, :cool:

BB. · May 2009

Re: Look at this article

nigtomdaw wrote: »

Well maybe not starlight but I have seen 3/4 amps coming off my array on a clear night and a full moon, :cool:

Really???

If full sun is 100,000 lux, and full moon is about 1 lux... That would, on my 3.5 kW worth of solar panels output:

3,500 watts * 1/100,000 = 0.035 watts under full moon

And, to me, that makes sense... I can get a few tens of watts from my array when they are in full shade (sun rise / sun set) -- and when looking at the Moon in the sky--It is just there, sort of blended into the sky. The moon is such a small source of light vs the total sky--I just don't see how it can provide any significant source of power.

Another comparison--I have a 50 milli-Watt LED flashlight (1x AAA battery that lasts 8+ hours). And under a full Moon--the LED will outshine the mood when the beam is less than ~10' in diameter...

To get ~35 watts from my panel--I would need ~1,000 lux. Which is a bit more than a bright office.

I remember somebody (you?) before said they got some power under a full moon... Many times, I have looked at my system to see if it "woke" at night under a full moon--And it never has--even though it should if there were 20 watts (or less?) available from the panels (I have seen my GT inverter in "voltage fault" at 180 volts and 0.1 amps = 18 watts).

3/4 of an Amp at 12 volts would be 9 watts (yours is probably a 24 or 48 volt system?)--I just don't see how this could happen under a full moon.

There are reports that one vendor's new MPPT controller shows power being generated at night due to a firmware/hardware fault (don't know if the problem has been fixed yet or not)...

-Bill

niel · May 2009

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gee, i feel jipped then as my pvs are in line of sight from a street light directly across the street whos light far exceeds the brightest full moon here and i don't see anything on my meter.:grr

nigtomdaw · May 2009

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guess i have no smog sorry guys but living in nowhere has its advantages no maths here or street lights:roll:

lorelec · May 2009

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Solar cells (any p-n junction) do produce charge carriers that increase with temperature at anything above absolute zero. The thing is that the current is so small (nanoamps or less) that the physics of the junction make sure that it never "escapes." Definitely doesn't produce any usable current, but maybe this is what the author of that article was somehow misinterpreting. This thermal generation is what's responsible for the change in Voc(and Vmp) as a solar panel heats.

Marc

BB. · May 2009

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OK--now to do the calculation a few different ways for Street Lamps...

Googling around, a 250 watt HPS lamp will "light" a 7 meter x 25 meter stretch of road at about 35 lux (roughly matched several other sites I found too).

3,500 watt of solar panels * 35lux/100,000lux = 0.875 watts

Assume that 100% of the 250 watts is converted into light (not happening):

250 watts / (7m*25m)= 1.43 watts per sq. meter

Assume that full sun is ~1,000 watts per sq. meter.

1.43 w/sqm * 1/1,000 w/sqm * 3,500 watts = 5 watts

Assuming conversion of energy to light is less than 100% efficient, and transmission of light from the bulb through the lumenar to the ground is less than 100% efficient, then the ratio of 0.875w/5w=0.175 seems to be pretty reasonable for overall losses (ratio of "light" to "total power into lamp to ground/solar cell").

I just don't see the "moon", or street lamps, providing any useful amounts of energy (not even enough to turn-on the controller with a 3,500 watt array).

Disclamer: The above are pure guesses... your results may vary if you have AGM batteries and/or more efficient TSW vs MSW inverters. Also, thin film arrays, vs poly/mono crystalline panels or space rated gallium arsenide solar panels from earth re-entry scavenging of old deep space probes may affect your results by +/- 10%. :roll:

-Bill

niel · May 2009

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well my pvs do not sit directly under the street light on the road, but the light from it is far brighter than any moonlight here.
as to smog, i don't experience that here and the particulate matter experienced here certainly wouldn't be bad enough to stop either the moonlight or street light's light. pittsburgh is not a smokey city like it once was about a century ago because most of those mills and industries had closed down during the regan era. even with them it wasn't that bad as the 60s did institute polution controls that did work to improve the air quality drastically in this area. if it was that bad i certainly would not have invested in pv, but i'm certain the air is somewhat better where you are.

nigtomdaw · May 2009

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Well next time i have a full moon on a clear night ill take a picture of the C40 display im only reporting what i see, remember i live in an area with no light pollution on a night with no moon or stars you can outstretch your arm and not see your hand , dark is dark in the middle of nowhere

Plus Ive only seen this on the C40 not the XW considering that the C40 is an older design made when there where no rules on hours worked time off sleeping and so on, it never sleeps then it therefore doesnt need to wake up like mppt units do so here Niel is maybe why i see a reading on my plain older vanilla PWM C40 that I or you do not on our Tutti Frutti flavored MPPT units.:p Probablly the same on Bills grid tied MPPT too busy sleeping to do the Wearwolf shift,

I will get the time dated photographic evidence for you give me up to 6 months I cant exactly remember at what time of year it happens but we do get a very bright large moon through out the year, i promise no fiddling Bill its not worth it for the amps level we are discussing, but then you can re assess your maths or ill eat humble pie,

Plus the C40 display isnt actually DVM accurate

niel · May 2009

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just to be sure you understand that all i said was i feel jipped and did not call you a liar even though i am skeptical. you are correct that i use mppt though. hmmm. if i remember i may just take a look during a full moon and see what the voltage off of my pvs are with my dmm. there also could be problems with some people using blocking diodes in measuring the voltage. some are built into the pvs so you can't always blame somebody for them being there, but the point is the v drop needs overcome in said cases. i think i did this once long ago and saw nothing.
bill if you haven't any blocking diodes in your pvs, maybe you should measure the voltage next full moon. i know there's a howling good joke in here somewhere.:D

BB. · May 2009

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Guys--just having fun. (engineers are boring

).

I don't think my panels have blocking diodes--maybe I will pop the cover off of my GT inverter sometime and see what it reads--but there is no way that I can see getting 10 watts from a full moon. The math just does not add up.

-Bill

niel · May 2009

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i know bill and i agree with you, but there may be some flukey thing going on we aren't aware of just to keep an open mind.

lorelec · May 2009

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I don't see this working, either. In the dark (moonlight, starlight, whatever) you're not going be getting anywhere near 12 volts out of that array anyhow. Would be interesting to see some measurments, though.

Come to think of it, even if you managed to produce something out of a "dark" array, any load attached to it would immediately drop the voltage to nothing, resulting in no usable power.

Marc

niel · May 2009

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i don't believe he claimed 12v, but only cited a current output. at what voltage did you observe the 3/4 amp i believe you said nigel?

nigtomdaw · May 2009

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I assume the voltage in was the nominal battery bank voltage as the c40 is tied to the battery bank voltage unlike mppt and the readings on the c40 display match the bb voltage in otherwords i can remember

lorelec · May 2009

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I checked my 500W array yesterday evening while there was still a bit of twilight left in the sky -- something I thought might approximate the light of a full moon. Short circuit current was 75 microamps, open circuit voltage was 120 millivolts. I'd need an array 10,000 times this size to get three quarters of an amp out of it. Of course, a full moon positioned above the array might produce a little more output.

Marc

niel · May 2009

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sounds about right to me.:D

BB. · May 2009

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If you want to generate power regardless of the sky conditions, day or night, then Google "heteroelectric"...

A Russian "invention" that is >90% efficient and is either a new photo sensitive material and/or their version of a super capacitor. Reports have been around since ~2006 (that I see). Very hush-hush...

Obvious issue is that even 100% conversion efficiency is only ~8x more power than a "standard" silicon solar cell. To be useful, would need to be a 100-1,000x more efficient--and there we get into perpetual motion machines. :roll:

-Bill

nigtomdaw · June 2009

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ok guys message sent, so then let me be and leave me to it i quiet fancy humble pie

nigtomdaw · June 2009

Re: Look at this article

not:cool:................18 charactors met

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