Best direction?

BoFuller · July 2011

I am going to build a cabin on my forty acres, which is totally off-grid. I plan to install solar panels on the south facing roof. My question is, before I start digging the foundation, what is the optimal direction for the best solar usage? Is it exactly 180 degrees due South? Or slightly SE or slightly SW? Up to 30 degrees either way is fine for my layout, so I should just use the optimal sun exposure for determinig the final positioning.
I looked at some site that gave me a declination of 22.3 but it didn't explain it very well. Do I add that number? or subtract it? or what?
I'm sure that someday I will think this is a stupid question, but I need some help before I turn in my final site plan for my permit. This will be a 35 X 35 log cabin with two stories and a 6/12 roof, most likely seamless metal.
Thanks for any assistance.

BB. · July 2011

Re: Best direction?

You can plug various numbers into PV Watts website... The data is based on actually solar measurements (including weather).

Estimate your load by seasons (summer fans, winter lights) and look at the PV Watts results--You may have quite a bit of summer energy, but need more energy for winter (as an example)--so tilt the panels up a bit (or put them on the ground and make them adjustable).

"Dave Sparks" here is in an off-grid installer in the Sierras and likes 2-axis trackers very much and has good luck with them (as long as they are greased on a regular basis). So you might try PV Watts with the 2-axis trackers and see what happens in your region.

If you have fixed mount and evening thunderstorms/high heat--pointing the panels more towards the southeast may be better... If you have morning valley fog--perhaps pointing more southwesterly would be better... PV Watts can help with those decisions.

-Bill

petertearai · July 2011

Re: Best direction?

You dont have to mount the panels on your roof. You have 40 acres !
My panels are mounted on a frame behind the house. Easy to install and easy to clean and check. You can also make your frame to be adjustable for angle to sun .
I have mine set to best winter angle as this is the time that you need to have the most efficient solar harvest.

waynefromnscanada · July 2011

Re: Best direction?

BoFuller wrote: »

I looked at some site that gave me a declination of 22.3 but it didn't explain it very well. Do I add that number? or subtract it? or what?

I'm assuming you live in North America? If so, the following will apply.
Add or subtract - - depends on which coast you are on. Magnetic North is always on the move, all-be-it slowly. It's now somewhere west of Ellesmere Island in Canada, and moving at about 40 KM/Yr and presently heading in the direction of Siberia, but that direction is expected to change in the years/decades ahead.
If you live on the East coast of North America and look North, True geographical North will be to the right of Magnetic North, so you would ADD to the magnetic bearing, whatever declination is applicable to your location. If you're on the West Coast of North America, True North would be left of Magnetic, so you would subtract the declination # from your magnetic compass bearing. If you live somewhere in the central area of the continent where True and Magnetic are in a straight line from where you live, then there would be no declination to deal with, they'd both be in exactly the same direction from your point of view. You didn't mention your latitude, but if you live in snow country, you may very well get best overall results by shifting the wintertime tilt of your panels to vertical, which pretty much eliminates snow covering them, and provides reflected light from the snow covered ground, as well as from the sun which at that time of year will be low on the Southern horizon. Wintertime vertical works really well for me in Nova Scotia, no more constant cleaning snow off the panels, and lots of production within 10 minutes of the sun poking it's nose up over the South-East horizon every sunny morning. What better way to start the day.

BoFuller · July 2011

Re: Best direction?

waynefromnscanada wrote: »

I'm assuming you live in North America? If so, the following will apply.
Add or subtract - - depends on which coast you are on. Magnetic North is always on the move, all-be-it slowly. It's now somewhere west of Ellesmere Island in Canada, and moving at about 40 KM/Yr and presently heading in the direction of Siberia, but that direction is expected to change in the years/decades ahead.
If you live on the East coast of North America and look North, True geographical North will be to the right of Magnetic North, so you would ADD to the magnetic bearing, whatever declination is applicable to your location. If you're on the West Coast of North America, True North would be left of Magnetic, so you would subtract the declination # from your magnetic compass bearing. If you live somewhere in the central area of the continent where True and Magnetic are in a straight line from where you live, then there would be no declination to deal with, they'd both be in exactly the same direction from your point of view. You didn't mention your latitude, but if you live in snow country, you may very well get best overall results by shifting the wintertime tilt of your panels to vertical, which pretty much eliminates snow covering them, and provides reflected light from the snow covered ground, as well as from the sun which at that time of year will be low on the Southern horizon. Wintertime vertical works really well for me in Nova Scotia, no more constant cleaning snow off the panels, and lots of production within 10 minutes of the sun poking it's nose up over the South-East horizon every sunny morning. What better way to start the day.

I thought I covered all the necessary information. I didn't mention location as it is the Northern AZ website and I live in Northern AZ. Not thinking about people all over the country asking questions. Sorry.
Location - Northern AZ, just SW of Seligman.
N 35 degrees, 11.239 minutes
W 113 degrees, 2.197 minutes
Elevation of 6160 feet. Very light snow and only ocassionally.
I suppose I like the idea of facing slightly SE to catch the early morning rays.

BoFuller · July 2011

Re: Best direction?

petertearai wrote: »

You dont have to mount the panels on your roof. You have 40 acres !
My panels are mounted on a frame behind the house. Easy to install and easy to clean and check. You can also make your frame to be adjustable for angle to sun .
I have mine set to best winter angle as this is the time that you need to have the most efficient solar harvest.

I have 40 acres but it is all covered with trees. I have pulled out plenty just to make a space for the cabin. It just seemed to me that putting them on the roof would be easier than making a tower to maount them on.

But then I'm not experienced here. It may be that the cons of roof mount outweigh cutting a few more trees. Does roof mount lead to roof leaks? Is it going to be a lot harder to adjust them on the roof?

BB. · July 2011

Re: Best direction?

Trees grow--So you will (probably) be back trimming/cutting in a few years down the road anyway.

Unless you have problems with theft, or a spouse who has a well developed sense of style (not me)... I would avoid placing on a roof (leaks, more money spent on structure engineering, difficult to clean and manually tilt panels, etc.).

You are, hopefully, going to be living with these guys on your roof for the next 25-40+ years... And you will need to get up there once in a while to clean, remove windblown materials, watch for animals nesting, protect against animals eating the wiring, etc...

Having a separate structure with no roof/"living space" underneath for critters (i.e., the area between the panels and building roof where small rodents and such like to live)--could be a big help in the woods.

-Bill

Best direction?

Comments

Categories