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Looking for details on trackers

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eeprom

Electrical
May 16, 2007
482
Hello,
On a solar tracker, single axis, what is the typical angle of operation? The sun moves 180 degrees at the equator, and much less near the poles. But there is so little energy in the sun at the ends of the day that it may not be worth chasing it. So what would be the maximum required angle for a tracker to reach? At 45 degrees north? Any links to papers on this would be great.

thanks,
EEPROM
 
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One offbeat place to start might be naval or astronomical almanacs. They can give sunrise & sunset time & azimuth for a full year at any latitude.
 
Thanks. But I guess what I'm looking for is how many degrees are required of an effective tracker. Let's say a tracker has a range of -90 to +90 degrees. So in the morning, it sits at -90 waiting for the sun to rise. Then through the day the tracker follows the sun until it sets. So, theoretically the tracker has traveled 180 degrees through the day. I'd like to know how much of that travel was wasted. For example, if the same tracker was limited to -50 to +50 degrees, would there be a significant difference in power production by a solar panel mounted on the tracker? It costs energy to move the tracker, and so I want to minimize the range of travel to the most effective area. I'm looking for papers which describe this.
 
You are looking for the insolation curve during the day. To all intents and purposes it resembles a sine wave ^.6, if you have perfect tracking, and ^.9 if you have a fixed array optimised for noon.

There is some attenuation due to increased path length as well.

Plus weather.



Cheers

Greg Locock

SIG:please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
Thank you for the insolation data. I did find some code on the internet which will help me to develop a program to determine the sun's positions as a function of time and date. But specifically what I need is some research data showing solar cell power output based on sun angle, given the assumption that the cell is tracking perfectly. There is a point at the beginning (and end) of the day when the solar cell is not going to generate enough kW to justify the energy used by the tracker. I am looking for that data, and I know someone has already done this. I just haven't been able to find it yet. Any help would be appreciated.

eeprom
 
The sun angles are enough to determine the instantaneous insolation at any given time of the day, relative to the peak value.

TTFN

FAQ731-376
 
The solar insolation tables for a given latitude have that included already. In other words, 5 hours per day value given for, say 21 June is the sumation of all insolation for that day falling on 1 m2, which = 5 x 1000 W/m2 = 5,000 W/m2-Day Since solar panels have a rated output based on an insolation of 1000 W/m2, that's all you need for that.

If you are in the EU area, here is the best online calculator,
You eventually even get to choose a 2 axis tracker option to have it calculate those insolation values.

In most cases, except perhaps if you are using concentrated PV, or at the north pole, A 1-axis tracker will give a good solution. For panels with concentrator lenses, 2-axis is a must. 1 axis tracking can get you around 25% more power, 2 axis can up that to about 32-35%.

Search for Bird's Clear Sky Insolation Model.
I tried to attach it 3 times, but couldn't do it.

I think you'll find most of the rest of the info you want here,

Modeling sys performance

If not, just type in whatever in Google and you'll get way too much info.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
I'd been searching on Google for two days before I tried for solutions here. But you mention a point very directly related to my question. You state that with a concentrator a 2-axis tracker is a must. Therefore the amount of error is of obvious importance. What is a typical tolerance for targeting error?

thanks
 
There's this, but probably overkill:

since the sun is about 0.5° subtense to start with, I can't imagine anyone designing something that would require any tighter than a few degrees of positional accuracy. Clearly, timekeeping and initial alignment is more critical.

TTFN

FAQ731-376
 
The high efficiency concentrated cells, esp. those with 3 layers of elements at different depths within the cell enclosure supposedly must have it to get to 34% efficiency.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)
 
I found some NREL documentation in a paper which states that for a concentrator panel, they were using acceptance angles from 0.5 to 2 degrees. They had included gear backlash at 0.05 degrees. This seems extremely tight to me. The acceptance angle may be unique to each design.
 
If you're pointed near the sun, you're only off by the cosine of the pointing error. That'll be minor, compared to the losses due to dust settlement on the panel itself.

TTFN

FAQ731-376
 
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