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Smog and panel output
By sandovalch, Section Solar Posted on Tue Dec 20, 2005 at 03:52:07 PM MST
any data? or info?

I was just wondering if anyone has data or info on solar panel output and smog buildup. I live in a city and have my panels at my home. But it seems like when there is no wind at all and you can literally "see" the smog in the air, my panels output drops drastically even though there are no clouds in the sky?
Has anyone any ideas or perhaps first hand experience on this?

Smog and panel output | 11 comments (11 topical)

Re: Smog and panel output (3.00 / 0) (#1)
by DanB on Tue Dec 20, 2005 at 08:55:02 AM MST

lack of wind helps your panels heat up a good bit, I expect that affects them perhaps more than the smog - but it's an interesting question.

Re: Smog and panel output (3.00 / 0) (#2)
by johnlm on Tue Dec 20, 2005 at 09:27:46 AM MST

On a day with no wind and no smog (if this occurs) measure the current output of one of your panels and compare it to the current out on a day with smog and no wind. That will eliminate the temperature variable that Dan suggested and will give you and idea of the effect of the smog. Luckily I never see smog problems where I live but I have been in the large cities on the west coast on days that the smog was so bad I would suspect the output of a solar panel was likely reduced to 1/2 the output. I built myself a small solar insolation meter using a small solar cell calibrated with a few resistors and feeding an old analog meter movement. The output reading is calibrated against published solar insolation tables so I can read the solar insolation directly. Its real handy to check out the loss through glazing or at various angles from normal, or when there are thin clouds, or just plain readthe solar intensity at any given time that would be going into a solar collector. The output can be calibrated to read Langleys or BTU/hr. The design is pretty simple as the output current of a critically loaded (electronic term for loaded to a maximum power point) solar cell is pretty linear with variation in sunlight intensity.

Johnlm

Re: Smog and panel output (3.00 / 0) (#7)
by sandovalch on Tue Dec 20, 2005 at 10:45:49 AM MST

Johnlm, would it be possible for you to post a simple drawing for your gadget?

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#8)
by johnlm on Tue Dec 20, 2005 at 04:43:31 PM MST

Give me a day or 2 and I will do that.
John

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#9)
by johnlm on Wed Dec 21, 2005 at 11:17:00 AM MST

Here is the info on my Solar Insolation Meter.
First a few explainations. The easiest way to get relative measurements is to just connect a solar cell to a meter set to measure current in the range that the output of the solar cellis capable of. ie a small cell that puts out 0.55V at 0.5 amp would have you set the meter on say a 2000mA scale. Note the reading in full clear day sunlight and compare that to one of your smoggy days with the cell oriented the same way at about the same time of day to determine a relative measurement of the two readings. This approach is shown in the first schematic on one of the pics below.
The second schematic on the page shows how to make relative measurements using the meter in voltage measure mode. Note that the value of the resistor across the solar cell needs to be low enough in value to get the solar cell in a current source condition. That means the resistor is loading the cell so much that the output voltage has dropped from its normal 0.55V down to around 0.1 to 0.2 Volts and any change in light intensity shows up as a linear change in output current which is read as a linear change in voltage across the resistor. If you don't have the cell loaded enough the output will not be linear, but dont load it so much that it totally kills the output. For my small 10 X 20 MM cell I used on my meter which can probably only put out maybe 50 mA max the value of the load resistor was 15 Ohms. I experimented with a larger 20 X 40 MM cell that is rated at 0.55V and 0.3A this morning I found it needed about 2 ohms of load resistor. I bought the cell at Radio Shack about 15 years ago.

To make a meter that reads actual values of solar insolation is a bit more complicated as you will need to use solar insolation tables to get an idea of what kind of intensity (usually in the USA measured in BTU/Ft^2/Hr) you can expect. Now if you live in an area that always has some smog or hazy skys then these tables will not be correct as you will always measure less than what should be available.
I have put in a picture (below) of one example of these tables that works for me as where I live in Colorado totally clear skys (other than when its cloudy) with no haze or smog are the norm. There are other tables that give approximate values of BTU/Ft^2/Hr or Watts /Meter^2 on map contours for the USA. Possibly these are available for all over the world if you find the right sites on the internet.
If you use the approach in the second schematic you could make up a table of output voltage readings for various availability listings on the table to have a somewhat calibrated measurement. I have found that calibrating these is best done with the cell in the horizontal position as you get less reflected light onto the cell.

Schematic three shows the actual circuit in my meter using an old analog meter movement I had laying around. The meter is set up to read voltage and the corresponding variable resistor in series with the meter is of a value that works with my particular analog meter movement. The potentiometer was adjusted to calibrate the output reading on the meter scale with the known incoming sunlight intensity.

Johnlm

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#10)
by johnlm on Wed Dec 21, 2005 at 11:18:51 AM MST

Sorry the pics are kind of fuzzy - poor scan.

John

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#11)
by sandovalch on Thu Dec 22, 2005 at 06:20:44 AM MST

Thanks I´ll give it a try!

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#3)
by ghurd on Tue Dec 20, 2005 at 09:32:25 AM MST

To actually 'see' the smog must be holding back some sun. High humidity here makes a visible haze, and that cuts back power quite a bit, but not drastically.

I'm with Dan that heat is most of it.
Low angle panels, hot sun, hot roof, no wind, warm climate...

Maybe try to get the panels another 15 - 20cm higher on both ends for better circulation?

G-
Ghurd.info

Re: Smog and panel output (3.00 / 0) (#4)
by johnlm on Tue Dec 20, 2005 at 09:45:09 AM MST

Or if the back side of your panels are accessable, just take a large fan and blow air across it while you have a smoggy condition and no wind and see if that gets the panel back up to normal. What is the definition of "drastically reduces the output"?
What is the ambient temperature? If the smog is thick enough to start making the sun look orange, its causing a reasonable amount of loss. Lower sun angles (earlier in the morning or later in the afternoon combined with smog will make it even worse.

John

Re: Smog and panel output (3.00 / 0) (#6)
by sandovalch on Tue Dec 20, 2005 at 10:44:26 AM MST

My ambient temperature is about 25°C. It gets down to about 19°C on colder days, but to 30°C on days without wind.
This question arised, because in this time of year I always have lower current output from my panels even though I rise the angle to compensate for the sun.
I also have noticed that on windy days the output is higher and there is no visible smog in the air. I would like to do a temperature test.

[ Parent ]

Re: Smog and panel output (3.00 / 0) (#5)
by Gordy on Tue Dec 20, 2005 at 10:33:30 AM MST

My thoughts are that the smog is a low lying "dirty" cloud which will absorb and defract some of the sun lite. The defracted light will not hit your panel directly (at an angle) and some of it will reflect off the glazing.

To test the heating Dan mentioned you could mount a remote thermomiter to the under side of your panel, and compair readings for differant days.

Another test you could do is to mount a large (say 20") box fan near the bottom of your panel. When you get one of those smogy days and output has droped turn the fan on to cool the panel and see what the output does. This would only be a test, as the fan would more than likely use more power than it would help generate.

A few years ago I read that someone was haveing heat buildup problems with his panels. The talk was about building a solar chimeny to draw air under the panel to cool it. Chimeny was to be a basic hot air solar colector (box painted black on inside with glazing, open at top and bottom). The bottom of the chimeny was to be sealed to the top of the panel, and scirting mounted to the side of the panel down to the roof (to control air flow under the whole panel. And I think reflective material on the shingles below the panel to keep them from heating up, and that heat being drawn to the panel.

Good luck, Gordy

Smog and panel output | 11 comments (11 topical)

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