Trees

CMcD · January 2012

Hi

I live in a forest setting in Canada, which means the sun gets very low in the sky during the winter. My panels are ground mounted on a hilltop. This allowed me to remove less trees, as the tree tops get progressively lower the further down the hill you go.

My question is: What is the value of the morning /afternoon sun?

Standing at my solar panels, is clearing the trees at a 45 degree angle in each direction too much? Or not enough?

Specifically, I am thinking about clearing more in the east and west, for the morning / afternoon sun. At high noon in the winter, the sun is clear of obstruction, but behind some tops when lower (morning/afternoon) in the sky (no leaves on trees, so I still get power, just not maximum).

I realize clearing a full 180 degree swath will maximize every possible amp available, but what is the optimal size of the clearing needed? i.e. degrees wider vs amps gained - taking into account that the sun's power will be decreasing, and that the angle of the sun to the panels will be increasing

Thank you.

westbranch · January 2012

Re: Trees

CMcD wrote: »

Hi
My question is: What is the value of the morning /afternoon sun?
At high noon in the winter, the sun is clear of obstruction, but behind some tops when lower (morning/afternoon) in the sky (no leaves on trees, so I still get power, just not maximum).

Thank you.

based on my experience, those little shadow lines will cut your pv output by at least 50%. Had an aspen tree with one branch shadow and we checked the MX60 in and output before and after whacking that Aspen... no brainier IMHO.
Early morning production (low) can be watched on your CC or battery monitor and you will be able to determine the time of day at which you 'need to have a clear shot at the sun' and full sun on the panels. Go for the 2 hour noon window ad expand from there.
what is your location?
hth

HTH

BB. · January 2012

Re: Trees

If you want, try PV Watts and pick a location "near you" (or at least similar latitude and weather conditions).

For Toronto, 2kW array and 0.52 derating for off grid, and fixed mount:

"Station Identification"
"City:","Toronto"
"State:","ON"
"Lat (deg N):", 43.67
"Long (deg W):", 79.63
"Elev (m): ", 173
"Weather Data:","CWEC"

"PV System Specifications"
"DC Rating:"," 2.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 43.7"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.1 CanB/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (CanB)"
1, 2.69, 88, 0.08
2, 3.51, 104, 0.09
3, 3.98, 127, 0.11
4, 4.68, 139, 0.12
5, 5.29, 156, 0.13
6, 5.48, 150, 0.13
7, 5.51, 152, 0.13
8, 5.23, 146, 0.13
9, 4.96, 139, 0.12
10, 3.61, 110, 0.09
11, 1.95, 54, 0.05
12, 1.97, 63, 0.05
"Year", 4.07, 1429, 1.23

2.69 hours of noon-time equivalent sun per day (fixed array, average weather conditions) and 88 kWH per month of off grid AC power (again daily long term average).

It has an option to "output hourly performance data":

1969, 1, 10, 09:00, 0
1969, 1, 10, 10:00, 215
1969, 1, 10, 11:00, 375
1969, 1, 10, 12:00, 334
1969, 1, 10, 13:00, 323
1969, 1, 10, 14:00, 455
1969, 1, 10, 15:00, 318
1969, 1, 10, 16:00, 110
1969, 1, 10, 17:00, 47
1969, 1, 10, 18:00, 0

So for a typical January 10th (1969 was the "typical" day), if you lost 10 to 11 am worth of sun, you would lose 215 Watt*Hours worth of energy.

-Bill

waynefromnscanada · January 2012

Re: Trees

Get out and see where the sun comes up this time of year, and where it sets this time of year. That will tell you how wide the swath of trees need be cut.
In my location, the winter sun pokes it's face up off the horizon and in less than 10 minutes I'm getting major charge rate - - with my panels mounted vertical for Winter. Snow doesn't collect on them and sun reflecting off the snow covered ground boosts output similar to that experienced with cloud edge effect in Summer, except it tends to last all day.

TnAndy · January 2012

Re: Trees

It will also depend on how you have the panels in the array wired. If you string panels in series, and ANY shade hits any one panel in the string, the whole string goes WAY down in production. I have two arrays on trackers that, unfortunately, I put too close together......late afternoon, the west array begins to shade the east array on one edge, and boy, can you see the results on the two charge controllers.....the west array will still be doing 1200-1400w, the east array falls off to 300-400.....and it's only shading the panels by maybe 6" on one side.

CMcD · January 2012

Re: Trees

Thank you everyone

Bill this is exactly what I was looking for - a hard number in watts:

"So for a typical January 10th (1969 was the "typical" day), if you lost 10 to 11 am worth of sun, you would lose 215 Watt*Hours worth of energy."

By what you have provided, I should clear all winter obstacles from 10 am to 4 pm., to get the best return on my investment.

I need the firewood anyways - I was just looking for some guidance on where and how far to cut. Thank you again.

niel · January 2012

Re: Trees

actually, it goes by solar noon as the center point of time. i would say from solar noon on the winter solstice +/-3hrs as beyond that the incidence angle is more detrimental and further attenuates the pv output. ideally, there should not be anything from sunrise to sunset interfering, but we all don't have ideal circumstances.

i cited the winter solstice because that is the lowest point the sun will track across the sky. the deepest cuts into the trees will occur in the southeast and southwest directions as that is the sunrise and sunset points that are on the horizon. the trees farther out to the east and west will also interfere with the sunrise and sunset, but at that point the sun is in the sky a bit longer and is higher up so you will get more power even with the trees in the east and west interfering at sunrise and sunset.

hope i didn't confuse you any, but it is pretty much like wayne said, go out and look and you will see it.

BB. · January 2012

Re: Trees

CMcD,

Notice the actual value is based on a 2,000 Watt fixed array for an off grid system... If yours is different, you will need to plug in your numbers (like 5kW array and 0.77 derating for on-grid system).

And, as always, look at your system--The website may not agree with Reality. :roll:

-Bill

Trees

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