Ground mount - Tree line distance

[mmcgady]

I am in the very beginning stages of planning to go off grid. Probably start in 2 or 3 years. As one of the first steps will be to obtain property, I want to determine my constraints for size and shape of the property. I want to build a ground mount structure for solar panels.

I am planning this build to be US - North or South Carolina. I am interested in maximizing (within reason) my ability to generate solar power and be able to rely on it during the entire year. With this in mind, the biggest challenge seems to be how much sunshine can the panels be exposed to on the shortest daylight hours of the year - 12/21. My thinking is that if the system can generate enough energy for my needs on 12/21, the rest of the year should not be a problem. With this in mind, as I search for suitable property, my question is one about the tree line. How far should the ground mount structure be from the tree line and how tall can the trees be (they may not belong to me) for me to feel good about power generation on 12/21?

I have a diagram to illustrate this issue (I know it is a terrible drawing. No skills here. Please excuse this). Please consider the bottom to be geo south and top geo north. Realizing that as the sun will be lowest in the southeast (morning) and southwest (afternoon), the trees should be further from the panel structure in these directions. And when the sun is coming from due south, the trees can be closer. With this in mind the tree line can be a curved shape as shown. The questions are what is the required distance for the south-north arrow, southeast arrow, southwest arrow? Given these answers what is the tallest the trees can be. There must be a calculator out there for this. But I cant find one with the specificity that I want. Any input is appreciated.

 

[Symbioquine]

Nobody is going to be able to give you a number for those distances with the information above.

Couple points:

* Elevation of the bottoms of the panels and tops of the trees is also relevant
* Different kinds of trees grow to different heights
* Trees grow (and different kinds grow at different rates), so you should leave yourself enough buffer for at least 25 years of tree growth - maybe more since a well-built panel mounting system might be re-usable for the next set of panels once the first ones age out
* Some trees don't have leaves in the winter so might produce marginally less shading then (though maybe not enough less to matter)

There must be a calculator out there for this. But I cant find one with the specificity that I want.

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)

re.jrc.ec.europa.eu

You can upload a data file for your horizon - which could include the trees. (The default dataset does not consider trees)

 

[400bird]

There isn't a hard line. It's going to be an angle that depends on your location (further north = more acute) angle.

If the trees are 20' from the panel they could prob be line 6' tall
At 200' away, maybe 60' tall.
That's going directly south.
The math gets more complicated when you want to start calculating the east to west traverse across the sky.

If there's a tree line, you'd be best to be on the south of it. Makes the math easy! Trees to the north can't block the sun.

 

[mmcgady]

Thanks for the calculator. Using this will take a good bit of study. I will try to learn it. As far as my distances and trees, I am not looking for data on types of trees and such. I am only looking for geometric figures - distance and height. For the elevation of panels off the ground, somewhere between 2 and 4 feet is a good enough estimation. I am only interested in fairly rough numbers. Is it 100 ft or 600 ft? How does the height of the trees impact the distance? How many sun hours can I expect given those metrics. Again, I am looking for rough precision.

 

[400bird]

You can use this calculator to determine the sun angles on specific dates/times.

NOAA Solar Position Calculator

 

[OffGridInTheCity]

I use this site - https://www.suncalc.org/#/40.1789,-3.5156,3/2022.12.17/10:53/1/3 - to get sun/angles for any time of day of the year right down to you're home/location/street.

For example, my neighbor put up a pool shade right next to our shared fence (in violation of setback rules) that causes shadows on my array in Dec/Jan. The angle from the edge of my array to the edge of the pool shade structure is 27deg - and in fact the app above shows that this start's occurring about 6 weeks prior to Dec 21st. Today at 12:08 the sun will be 24.31deg - the highest all day - which means a shadow will be on my array all day and I've verified this by observation.


I'd suggest shooting an angle from the lower edge of you're array (or planned array) to the top of the trees and then use this app to click days/times at you're exact location to see how you're affected.

 

[mmcgady]

I use this site - https://www.suncalc.org/#/40.1789,-3.5156,3/2022.12.17/10:53/1/3 - to get sun/angles for any time of day of the year right down to you're home/location/street.

Offgridincity - This looks promising. I will get it a try.

 

[mmcgady]

Offgridincity - suncalc.org is exactly what I need. Thanks so much. I am sorry for the issue with you neighbor. Perhaps you should get the authorities involved to enforce the setback rules.

 

[OffGridInTheCity]

Offgridincity - suncalc.org is exactly what I need. Thanks so much. I am sorry for the issue with you neighbor.

Great! And thanks for the kind thought

Perhaps you should get the authorities involved to enforce the setback rules.

No need for that- live/let-live. It's interesting as I was bothered by it last July when he put it up but my wise wife said 'let it go' as it's not a friendly situation. It turns out that in my area, it's mostly cloudy Dec/Jan and the overcast mitigates the 'shadow' so I'm not actually loosing all that much. The other 10 months it's not an issue.