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Solar Panel Spacing

06/22/2010 11:44 AM

Greetings All,

I'm trying to build a 1.5Mw solar farm, PV, fixed ground mount, and the engineers say that as a rule of thumb they just space the rows 2-3 times the max height of the panel (because of the shadow). I did the math and found I could space them 7 feet apart without causing shading, my engineers mumble "sounds awfully close" saying they wouldnt go closer than 12 feet, but they wont give me a good reason. Other than shading why would I go with wider spacing? Any opinions?

Spacecannon

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#1

Re: Solar Panel Spacing

06/22/2010 12:01 PM

To spend more money on connecting cable?

Sorry, couldn't resist.

I can't think of anything.

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#4
In reply to #1

Re: Solar Panel Spacing

06/22/2010 6:29 PM

Mikerho,

I consider SmartA** answers that make me laugh to be GAs

thx

Spacecannon

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#2

Re: Solar Panel Spacing

06/22/2010 12:13 PM

I am of the opinion that the cooler you keep your fixed panels, the more efficient they are relative to closely compacted arrays. It would not hurt to have them spaced wide enough to allow for green grass to grow underneath them and keep the over head panels cool. 12 feet seems like overkill for fixed arrays.

Some sheep or cows may come in handy to mow your grass.

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#5
In reply to #2

Re: Solar Panel Spacing

06/22/2010 6:32 PM

Ok, Ozzy nice thought and true answer but note my location, not many things live out here, let alone grass.

GA

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#7
In reply to #5

Re: Solar Panel Spacing

06/22/2010 10:12 PM

bugger...that really cracked me up when I payed attention to your location

Sorry mate

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#3

Re: Solar Panel Spacing

06/22/2010 12:15 PM

Are you referring to one row of panels shading the next row to the north, due to the rows of panels being tilted toward the celestial equator? Did you calculate the shade angle for the Sun at the winter solstice? If you did and there was no shading of the adjacent rows, then your closer spacing should be OK.

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#6
In reply to #3

Re: Solar Panel Spacing

06/22/2010 7:48 PM

Usbport,

Yes Im refering to the east-west rows of panels and the shadow that falls on the next row back to the north

yes thats how I did it, at winter soltice, I took my latitude (34.87) plus 23.5 equals 58.37,

then 90 - 58.37= 31.63 this equals the suns angle off the horizon on Dec.21 at solar noon,

then i did a scale drawing on profile and drew a line off the top at a 31.63 degree angle and it struck the ground a little less than 7 feet from the panel in front, ( if I hung a plumb bob off the back, 7' away shadow ended).

Did I miss any thing or make a mistake?

Spacecannon

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#8
In reply to #6

Re: Solar Panel Spacing

06/22/2010 10:13 PM

No, your math looks good. But of course you will get some shadowing before the sun reaches local noon at that time of year. There is a trade-off between how densely you pack the solar array to get the greatest number of solar panels within a given area, and how much shadowing you want to allow.

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#10
In reply to #6

Re: Solar Panel Spacing

06/22/2010 11:41 PM

You are perfectly right.

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#12
In reply to #6

Re: Solar Panel Spacing

06/23/2010 7:08 AM

As Usbport said you've done the calculation for mid day. What about the rest of the day?

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#19
In reply to #12

Re: Solar Panel Spacing

06/24/2010 6:21 PM

Randall, good question and GA for it

I went to the NOAA web site that calculates sun angles for various times of the year and found that at 7 feet spacing I had no shading 8-6pm, most of the day except near sunrise or sunset, for the sunny half of the year (march thru sept.), but the winter half I could get no shadows at noon, but the rest of the time some degree of shading.

Here's the rub, I just found out that some panels completely shut down production even if just a small part of them are shaded, I need to talk to my manufacture and see if mine are those kind. Even if they do shut down with shading there is a cost benefit analysis I have to do to compare the close spaced panels with shading and the extra cost to the far apart spaced panel and the less cost, ( far apart=fewer panels, but less energy production).

ah, the complexities of business decisions, do I go broke now or go broke later and bigger?

Spacecannon

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#22
In reply to #19

Re: Solar Panel Spacing

06/25/2010 3:19 AM

Can you put the panels on a slope (artificial or natural), or, make taller supports for the rear panels than the front ones?

If you dig a "trough" for the front panels, you can just move the soil a short distance to build a "mound" for the back panels.

I've shown the panels tilted to face the worst case sun scenario, I don't know if you intend to rotate them to "face" the sun.

Notice that the trough has to extend quite a long way in front of the front panel so that the side does not shade the panel.

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#23
In reply to #22

Re: Solar Panel Spacing

06/25/2010 1:58 PM

Randall, GA

Ive got a radical idea coming, mondaynite, that I want to share.

Is anybody familiar with double regression cost benefit analysis?

Spacecannon

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#32
In reply to #22

Re: Solar Panel Spacing

07/06/2010 12:32 AM

GA from me too.

In other words, if you make the floooring of your site inclined to degree equivalent to your latitude, the mount directly becomes equitorial. Now, the mounting mathematics becomes same irrespective of your location. (Locations at equators has advantages of not making anything, just get a plane ground.)

Some observatories like Ooty Radio Telescope in India are built on this principle.

The unique feature of the design is that the telescope has been constructed on a hill which has a natural slope of about 11 degrees, the same as the geographical latitude of Ooty. This makes the long axis of the telescope parallel to the Earth's rotation axis, giving it an equatorial mount. A celestial source in the sky can be tracked for about ten hours at a stretch by mechanical rotation of the parabolic cylinder in the east-west direction. In the north-south direction, the telescope response is steered electronically by introducing a suitable phase and delay gradient. along the dipole array.

This method is benefitial for solar panels also. Seasonal position change along with tracking the Sun over the day, will give maximum efficiency.

http://ncra.tifr.res.in/ncra_hpage/ort/ort.html

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#43
In reply to #6

Re: Solar Panel Spacing

01/18/2011 6:54 PM

What you have missed is that the array needs to be unshaded by its own shadows from 9 am to 3 pm on Dec 21....if you check, the sun angle on that day is only about 18 deg at those times...resulting in a longer shadow than at NOON, which is the wrong time to check for shadows...

Your drawing must show the length of the shadow at these times...and across the array at that angle...then you can see if the depth of the shadow shades the row behind...and guess what? It will, unless you are Min. 2 times the ht back....

The NREL has software packages that will show this, but if you can draw the top view of the array and the sun then you may be able to see what this is all about and AVOID a Costly error....

Normally, I would allow the Armchair Engineer to hang himself...but what the heck....you asked...but funny how the engineer you hired couldn't explain it...

If you can't see what I am talking about then you are not qualified to draft these geometric systems and should just do what everyone else does...which is usually called "industry standard" or "standard practices" and quit trying to be smarter than everyone else.

Ho, Ho, Ho.

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#44
In reply to #43

Re: Solar Panel Spacing

01/18/2011 10:02 PM

A little harsh dude, its all a learning experience, I ended up with a 20 degree slope. This is possible with thin film panels cause they still produce 60% of their output with the sun off perpendicular to the panel by 80 degrees. The front edge of the panel is about 8 inches off the ground and the back is about 3.5 feet, our spacing is 10 feet.

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#45
In reply to #44

Re: Solar Panel Spacing

01/18/2011 11:01 PM

You know my friend, I did want to respond myself. Not about the quiet useful information but the grandstanding on other peoples shoulders and making not only you look like some dill but possibly others on this thread. Very impertinent and simply bad style to come over like that.

How are things going Mate? Hope all is well and the gray matter keeps being teased to the hilt. A lot of people might think that it is only the technical parts that are of concern to anyone doing something new or newer but we know it is more to it than that. Even manners count to some extent.

Good luck and talk soon, Ky.

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#46
In reply to #45

Re: Solar Panel Spacing

01/18/2011 11:13 PM

agreed!

I think it takes a very dedicated person to do what spacecannon (Lynn) has done and is doing... dealing with politics of energy products in california is enough to test a saint, from what I hear. Some people are action people, and really get things done... others just watch... others say 'what happened' and then others just criticize for no reason.. or sense. but perhaps we are misundersstanding our 'guest'

Chris

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#47
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Re: Solar Panel Spacing

01/18/2011 11:20 PM
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#9

Re: Solar Panel Spacing

06/22/2010 11:13 PM

Maths always beats rules of thumb.

My rule of thumb is - An engineer that can't give a cogent reason for what he does, doesn't really know what he's doing. Is he a real engineer?

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#11

Re: Solar Panel Spacing

06/23/2010 12:57 AM

If all panels are on one plane, how can there be shading?

They can be touching each other without any problem. The issue may be that some space is required for routine maintenance.

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#13

Re: Solar Panel Spacing

06/23/2010 9:03 AM

it is going to be a function your latitude. But remember that shadows get longer the farther away from zenith the sun is and shadows are even longer than that in the winter. so calculating your angle based on the zenith in summer will leave the panels shaded in early morning or late afternoon and in the winter. so you need to calculate your angles based on the worst case in winter.

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#18
In reply to #13

Re: Solar Panel Spacing

06/23/2010 9:39 PM

Agreed. My mistake. Being in the tropics, where the angular variation is small (as is cos), I misjudged. For any large power collector it is not possible to have all panels in one plane. In this situation, in high latitudes there will be shading between column elements. Not applicable to row elements. Thanks for correcting. Bioramani

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#14

Re: Solar Panel Spacing

06/23/2010 10:36 AM

Bill,

GA, thx for the link. I went to the NOAA web site and they have a cool program for sun orientation. I'd put the link on here if I knew how.

Spacecannon

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#15
In reply to #14

Re: Solar Panel Spacing

06/23/2010 11:02 AM

This link?

just copy the URL to the clipboard, highlight the text you want to be the hyperlink and click on the little picture of the globe with a bit of chain in front of it and paste the url in the appropriate window....

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#20
In reply to #15

Re: Solar Panel Spacing

06/24/2010 6:26 PM

Rorschach,

nice link, and GA for it, but no I ment the NOAA sun tracking site below, hope this works

http://www.esrl.noaa.gov/gmd/grad/solcalc/

Spacecannon

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#21
In reply to #20

Re: Solar Panel Spacing

06/24/2010 6:31 PM

This one shows solar position angle, azmuth and elevation on any day at any time,

the previous one I sent ya'll to would mark the sunrise and sunset angles on the map if you checked the boxes at the bottom of the page, its also very helpful to figure out panel orientation.

http://www.srrb.noaa.gov/highlights/sunrise/azel.html

Spacecannon

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#16

Re: Solar Panel Spacing

06/23/2010 12:41 PM

Since we are considering fixed ground support, probably set at the optimum winter angle there can be no shading provided all panels are at the same height. Essentially we have a plane with the source of light having a diurnal movement and a seasonal variation. There can be no shading in this geometry. Bioramani

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#17
In reply to #16

Re: Solar Panel Spacing

06/23/2010 12:55 PM

uh, no, you are completely wrong.

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#24

Re: Solar Panel Spacing

07/04/2010 7:59 PM

What about leaving enough room to drive a maintenance / cleaning truck between the rows?

Good luck!

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#25
In reply to #24

Re: Solar Panel Spacing

07/04/2010 10:09 PM

I'll probably have to use a golf cart.

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#26

Re: Solar Panel Spacing

07/04/2010 10:50 PM

Greetings all,

The radicall idea was a long time comming and cost a few hundred dollars for an engineer to analize.

With thin-film PV I can have the the panels at zero tilt (flat) and in january they'll produce 87.482Kw, in june they'll produce 219.9.... if the tilt in January was at 60 degrees they would produce 160.396Kw and in june produce 118.244Kw. This shows that thin film still produces ~50% of max optimum even when the panels are set off from the suns angle by 60 degrees.

The total Kw produced over a year with the tilt at 10 degrees, (highest the sun gets at my Lat.), is 1975.436Kw. The total Kw produced at 30 degrees tilt over the year is 2091.600 Kw. 30 degrees was the optimum for this computer study done by the Mfg, but the study was done with no shading year round.

I had an engineer do a study a few weeks back that didnt seem right, his spacing was 2 times the height but then was shaded by the panel in front of it for half the time during the winter equinox. So because of the suns low angle in winter I would loose ~15-20 of total production.

My idea, cause thin film works well with the sun at off angles, is to set it at 20 degrees tilt (nearly optimum for summer) which will produce more power in summer when its peak pay. Leave the spacing at double the height and have less shading in winter and more producion, making up for the low suns angle and lower production with the lower tilt.

The reasoning for this is that when they did the study at my Lat. optimal efficientcy was 30 degrees but with no shading calcualted in. In truth 20 degree tilt is only 1.33 percent less in efficiency than 30 degree tilt, (still they didnt figure in any shading).

I feel that if the tilt were set to 20 degrees, the less shading in winter, would make up for the 1.33% loss in overall production efficiency.

Granted the money men are real sensative to 1 % differences on return, so I better be right, what do ya'll think, am I off my rocker?

Spacecannon

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#27
In reply to #26

Re: Solar Panel Spacing

07/04/2010 11:26 PM

Hi Lynn,

What is the square area that these kw numbers are for? (again if I missed it pls)

I think that what you are proposing is a valid engineering optimisation or compromise, due to the increased cost of motorizing (sun tracking) a large array. I would think this would be standard for large arrays. If your solar elevation in summer is 80 degrees, and in winter is 20 degrees, but your warmer seasons are longer than your cold ones, then an average collector tilt of 10 to 20 degrees (up from horizontal) seems optimal to me.

Chris

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#29
In reply to #27

Re: Solar Panel Spacing

07/04/2010 11:31 PM

Chris,

The study was based on a 1MWp plant, what ever that means.

Spacecannon

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#38
In reply to #27

Re: Solar Panel Spacing

07/07/2010 2:47 AM

Chris,

They did the study for a 1Mw farm.

Spacecannon

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#28
In reply to #26

Re: Solar Panel Spacing

07/04/2010 11:28 PM

Note: The latest study I had done the engineer came back with a recomendation of 12 Degree tilt using the thin-film PV.

I dont think the money men will go for that radcal a change.

Spacecannon

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#33
In reply to #26

Re: Solar Panel Spacing

07/06/2010 8:49 AM

SC, I would suggest that the way to improve efficiency would be to mount the panels in thermal contact on the back side with a heat exchanger and use the heat to spin a turbine for additional power generation. You may have to use something like ammonia or an HCFC as the working fluid since the thermal differential will be relatively low but it should work. It will also keep the PV cells cooler which improves their efficiency enormously. PV cell's efficiency drops off BIG TIME when they get hot. The cooler you can keep them the better.

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#34
In reply to #33

Re: Solar Panel Spacing

07/06/2010 9:08 PM

Here is a UL listed set-up doing just that. The concept is very good and you do get the benefits of both water and electric. You just have to protect against galvanic reaction of moving fluids and dissmilar metals. The one drawback is you still have the temp correction factor of the panel above 25C. But I don't see getting around that in the Mohave forest.

Side note, most panels state not to expose to excess moisture. Might invade the panel and cause issues. Moisture, delamination, etc.

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#35
In reply to #34

Re: Solar Panel Spacing

07/06/2010 11:58 PM

so what happens if they get too hot? is there a graph somewhere? (general)

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#36
In reply to #35

Re: Solar Panel Spacing

07/07/2010 1:57 AM

have not seen one, BUT the efficiency of the conductor and the cell drop bunches. "technical term"

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#37
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Re: Solar Panel Spacing

07/07/2010 2:06 AM

thanks.

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#39
In reply to #35

Re: Solar Panel Spacing

07/07/2010 2:51 AM

Chris

The Mfg says the thin film perform better in hot areas, soby did some comparisons but couldnt find it.

Spacecannon

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#40
In reply to #39

Re: Solar Panel Spacing

07/11/2010 6:16 PM

Hi spacecannon

We seem to have the same disease, not finding things I mean. (Chris to the rescue) I am on a very similar subject, in some ways, and I will get in touch with you at some later stage. Depends on when this little chicken will hatch.

I will talk to Chris about involving you a bit down the track. Your experience and interests in this subject makes collaboration something worth while investigating.

Good luck with what you are doing and sorry I can't help much at the moment. I am on a very steep learning curve my self and it is getting steeper by the day.

I've been watching that storm brewing since a while now. Not looking very promising but then again, storms are here to stay and for us to weather, whatever happens.

Talk to you soon, Ky.

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#41
In reply to #40

Re: Solar Panel Spacing

07/12/2010 12:52 AM

Good luck Ky

Chris is exceptional

Spacecannon

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#42
In reply to #41

Re: Solar Panel Spacing

07/12/2010 1:11 AM

We all are Mate, this whole bunch of fantastic people here in CR4. We'll talk later, once projects are a bit more in place.

Have a great day, Ky.

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#30

Re: Solar Panel Spacing

07/05/2010 1:08 AM

sorry I am late,

just getting to emails. Here is my two cents

I don't have my toys with me to see actual percentages of loss but an overview at http://www.solarpathfinder.com/formulasnts

It is a handy site because it can be imported to excel.

AS for your dilema, your math seems good, and as far as spacing a cooling. Read the panel manufacturers fine installation notes. As some panels can not be installed in areas over 104 degrees F. Most only require a couple of inches of air gap for cooling, but each panel is different. Also pay attention to temperature correction factors for conductors in conduits exposed to direct sun.

http://www.copper.org/applications/electrical/building/pdf/derating.pdf

Hope this helps, I will try to keep up to date. So if you have questions, just update discussion

Happy 4th and Bless the USA

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#31
In reply to #30

Re: Solar Panel Spacing

07/05/2010 12:17 PM

GA to the EV1guy,

There is always something ya forget to think about, just too much to cover, BRILLIANT suggestion on the temperature of conduit, I totally forgot to figure it in.

Mfg doesn't say anything about 104 F being a top temp.

they say cooler the better but...

nothing spacific

Spacecannon

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#48

Re: Solar Panel Spacing

01/19/2011 1:10 PM

Hi Ky & Chris,

On the subject of technical difficulties, we have had a lot of difficulties with the local utility God. We set up our meter panel in a way that appears appropriate, but they want it done differently. Ours was set up with the meter panel on one side of a post and the main switch with the breakers attached to the opposite side of the post, so they were back to back, with the post inbetween. Their paperwork says the panels need to be adjacent, isnt back to back adjacent? Anyway they said we had to remount on treated plywood with 2 posts so that they are side by side facing the same direction. This meter is out in the middle of the desert, and we have been trying to get this installed for 10 months. According to their policy you have to have a meter on the property and a customer number before they will consider your intertie application for a solar farm. In Dec. the Calif. Public Utilitilies Commission said they can no longer make that a requirment, but it hasnt filtered through the system yet and they are still requiring it. Time is precious so i cant wait for it to filter down, so I must go change it for the 3rd time.

Monopolies of any kind are bad.

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#49
In reply to #48

Re: Solar Panel Spacing

01/19/2011 2:47 PM

Wish I could help Lynn. Roll with the punches and stay diplomatic. It's what survival is all about. The last will be the first, like in any game of cat and mouse. I know the time wasted hurts but you (we) will catch up.

Good luck, Ky.

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