# Solar Panel Angle



## Rick (May 10, 2002)

Should our panels be set at latitude plus 8 degrees?

We saw this mentioned in an older book, and Ann wanted me to get a second opinion.

Thanks,

Rick


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## wy_white_wolf (Oct 14, 2004)

I have 3 settings for mine. Lat.-15 for summer, lat. for spring and fall, lat.+15 for winter. If I was to have only 1 setting it would be at lat+8 to compensate for less available sun in the winter.

Most people seem to go with 2 settings Lat.+/-15. They change on the first day of spring and first day of fall. I change 6 weeks before and after them.


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## SolarGary (Sep 8, 2005)

Hi,

The NREL Redbook gives actual radiation collected by month for panels tilted at +15, 0 , and -15 from latitude.
Just download the volume for your sate, and look at the table for a city near you -- you can see how much you get for each of these angles each month, and decide if its worth making them adjustable.

The Redbook also give numbers for collectors that track the sun through the day.

http://rredc.nrel.gov/solar/pubs/redbook/

Gary


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## wy_white_wolf (Oct 14, 2004)

Thanks Gary, I haven't seen that before.


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## idahodave (Jan 20, 2005)

Good data. 

I looked at Billings, and found the 0 deg and 90 deg tilt outputs interesting. 
My off-grid place is about as far north as Billings and I find changing the tilt angle twice a year makes a difference.

Thanks for the reference.


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## fishhead (Jul 19, 2006)

I've got 2 questions. 

Where is 0 degrees? Vertical?

On that chart does the larger the number mean more heat output?


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## wy_white_wolf (Oct 14, 2004)

0 is horizontal
90 is vertical

The chart is killawatts per square meter daily


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## Explorer (Dec 2, 2003)

My solar retailer advised me to set mine at +15 year around, but I have a small system.


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## SolarGary (Sep 8, 2005)

Hi,
I think that one thing that is probably not included in the NREL Redbook numbers is reflection off the ground, or better yet a snowfield in front of the collector.
In the winter, this can help a vertical panel quite a bit -- maybe as much as 30%.

For thermal panels used for winter space heating, I think vertical really has a lot of advantages. I guess it might make sense to go vertical on PV panels in the winter if you are seasonally adjusting them anyway?

Gary


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## fishhead (Jul 19, 2006)

wy_white_wolf said:


> 0 is horizontal
> 90 is vertical
> 
> The chart is killawatts per square meter daily



Thanks.


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## WisJim (Jan 14, 2004)

I adjust the angle on my main array about 6 or 7 times a year. I have a little chart that I made up showing me the optimum angle for each change on the back and the positions marked on the adjustable braces so I get close to optimum output most of the year. I decided when to change the angle by using the output charts for PVs and plugging in lots of values to see how much I would gain by adjusting the angle, and decided it was worth doing. It also gets me close to the panels to check wiring, dirt, etc.


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## idahodave (Jan 20, 2005)

The higher the angle the better the snow sheds.


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## wy_white_wolf (Oct 14, 2004)

RainEx works wonders on helping solar panels shed snow. Don't know if it decreases there output though.


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## SolarGary (Sep 8, 2005)

wy_white_wolf said:


> RainEx works wonders on helping solar panels shed snow. Don't know if it decreases there output though.


Thanks -- I'll have to try that.

I don't suppose the RainX would damage twinwall polycarbonate panels?

Gary


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## wy_white_wolf (Oct 14, 2004)

SolarGary said:


> Thanks -- I'll have to try that.
> 
> I don't suppose the RainX would damage twinwall polycarbonate panels?
> 
> Gary


Car waxes work good too. Just alot more work. They do seem to last about twice as long as rainx before they need reapplied.


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## Rick (May 10, 2002)

Thanks a heap for the input, folks.

Rick


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## WisJim (Jan 14, 2004)

I just reread some of this thread and realized that Rick didn't say if these are PVs or air or water heating panels.


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## Rick (May 10, 2002)

WisJim said:


> I just reread some of this thread and realized that Rick didn't say if these are PVs or air or water heating panels.


Greetings Jim

They are PV....... We have what appears to be an aluminum water heater in the barn. It is rectangular, and used to have a glass insert.

Any idea if plastic or plexi-glass wood do a reasonable job of heating water for showers?

Rick


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## SolarGary (Sep 8, 2005)

Rick said:


> Greetings Jim
> 
> They are PV....... We have what appears to be an aluminum water heater in the barn. It is rectangular, and used to have a glass insert.
> 
> ...


Hi,
If you are looking for a waterproof liner for a tank that is to hold hot water, I'd look into EPDM. This is available a lot of places as pond liner. Its good for about 180F and lasts a long time.
Plexiglass (Acrylic) does not have a very good temperature capability.

Gary


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## mondakkid (Oct 17, 2006)

Good Morning: I found this thread very interesting. There is so much info out there, some of it is hard to find. I have a question and wonder if anyone has seen any data on it. I am in the process of building near Kingman, Az. I will be using air type heat collectors for my winter heat. Since I will not be using these during the summer, I am putting a cover(has aluminum reflective metal on the inside of cover) that hinges on the bottom of each collector. When I use the collectors during the winter I will drop the cover down. Has anyone seen any data on the amount of extra solar energy that these covers could give and at at what angle with the horizontal would give the max. Solar Gary mentioned that up north the snow on the ground would help with the efficency. I think using covers would prolong the use of collectors and protect them from hail, rocks, etc. when not in use.


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## wy_white_wolf (Oct 14, 2004)

Rick,

PV - Photovoltaic (electric)

Forget everything I said as it doesn't apply to heat panels. 

Sorry

Set them at Lat+15 to 20 for ideals. Many have good luck and less maintance (depending on style) with setting them vertical (90)


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## SolarGary (Sep 8, 2005)

mondakkid said:


> Good Morning: I found this thread very interesting. There is so much info out there, some of it is hard to find. I have a question and wonder if anyone has seen any data on it. I am in the process of building near Kingman, Az. I will be using air type heat collectors for my winter heat. Since I will not be using these during the summer, I am putting a cover(has aluminum reflective metal on the inside of cover) that hinges on the bottom of each collector. When I use the collectors during the winter I will drop the cover down. Has anyone seen any data on the amount of extra solar energy that these covers could give and at at what angle with the horizontal would give the max. Solar Gary mentioned that up north the snow on the ground would help with the efficency. I think using covers would prolong the use of collectors and protect them from hail, rocks, etc. when not in use.


Hi,
The Passive Solar Energy Handbook by Mazria has a table that show the benefit of reflectors in front of collector. 
For the case where the length of the reflector equals the height of the collector, and at 40 deg latitude, and with a reflector reflectance of 0.8, the winter time average benefit of the reflector is about 35 to 40%. The best angle appears to be about a 5 degree down slope on the reflector. Reflectors are doubly good in that they increase energy input from the sun without increasing losses (as adding more collector area would). But, you need to be more careful with overheating when the collector is stagnated.

This book has a lot of good solar design info, and is available cheap on Amazon used books and the like -- the expanded version is better, but harder to find.

One caution. I read of an actual case where a crank down reflector was being used. It was left in a position where the far end was off the ground, and since it was only supported at the ends, it bent into a curved shape. The shape turned out to the just right to concentrate the sun on the wood eave structure and it started a fire. Sort of a one in a million thing, but something to watch out for.


Steve Baer pioneered using crank down reflectors in front of solar windows. This is a paper he wrote on using reflectors:
http://zomeworks.com/files/sunbenderTM/reflector-shades.pdf

Gary


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## mondakkid (Oct 17, 2006)

Solar Gary....That is some good info...am excited to see if I can find that book on the net. You have been a great help to many of us on this forum...thanks again for your time and efforts. We really do appreciate it. mondakkid(jerry)


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