Solar array getting activated soon....tree question...

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Geek
Geek Solar Expert Posts: 32
I have a couple trees in front of the house that provide some shadow to the roof in certain hours of the days.
Now in winter both trees are 'naked' without leaves. Will the thin branches cause the array to reduce its performance, I mean even if the branch's shadow on the roof is 'tiny" and long will this create an obstruction and reduce production?

How bad?

I will trim the top off or cut the trees off but it's too cold now and want to wait 'till Spring.......

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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Solar array getting activated soon....tree question...

    The answer is,, depending on how your array is wired,, ANY small shading can have a huge impact on performance. Any series string will be affected by the shading. Even the shadow of a utility wire is enough to degrade performance.

    Do everything you can do to keep the shadows off the panels. Beware topping trees however, especially evergreens as they tend to re-grow multiple growing points that in fa few years adds even more to the problem.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Solar array getting activated soon....tree question...

    The answer is probably "more than likely" the shadows will greatly reduce the output during the time the shade is present.

    You can estimate the loss several ways... One would be to, during the time the array is in full sun, take a broken branch and shade some panels while somebody else watches the display. Everybody's situation is different, but even the shading from a couple power lines across a large array can cut output by 50%.

    Another would be to use the solar calculator and compare your output (daily, or hour by hour--option on the results page) and see how much you are losing.

    Part of what determines how great the shadows will affect your output is how many parallel strings you have and if the shadows block one or several strings worth of panels.

    Generally, if one panel has significant shading on on string, the output of that entire string may be lost. For example, two strings, then 1/2 of the output may drop out.

    On the other hand, even if you lose 1kW worth of production for 20 minutes (as an example, using $0.10 per kWhr)

    1kW*20 min / 60min per hour * $0.10 per kWhr = $0.03 cents worth of electricity

    So--while you want the panels to always receive an optimum amount of power, partial shading during part of the year may not be the worst thing in the world.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Geek
    Geek Solar Expert Posts: 32
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    Re: Solar array getting activated soon....tree question...

    Ok, thanks.

    These are oak trees and I was told they will die if I cut the top off......and I didn't want to cut the trees either....:cry: but I guess that will be the option.......
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Solar array getting activated soon....tree question...

    It is amazing--once a person gets $$$$ of solar panels bolted to their roof, how anti-tree NIMBY (Not In My Back Yard) they can become (been there, done that).

    As a kid we had huge trees around our coastal valleys, and having cars and home crushed is not unusual. What really turned me against trees in my back yard is when the cities started telling me when and how we could prune and if we could remove them... And then started charging us some $200-$500 for permits and tree fees when we wanted to take out trees that had outgrown the yard and/or became a threat to structures.

    Now, when trees die, I don't replace them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Solar array getting activated soon....tree question...

    Find a good tree guy. You should be able to limb/ top an oak without killing it. Just depends on how much you have to do.

    To test how much you are losing with a shadow, do this test if you can. Assuming you have someway of measuring PV output, look at the meter while the panels are in full sun. Then take a broom handle and throw a shadow over one panel, and watch the meter. Then cast that shadow over two panels. If the panels are wired in series, you will see a decline with the first shadow, but not too much more with the second.

    Pretty interesting to discover.

    Tony
  • Geek
    Geek Solar Expert Posts: 32
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    Re: Solar array getting activated soon....tree question...

    will ice also reduce production?

    we have some ice left on the array from a storm a couple days ago.
    They activated the system yesterday and the guy said it was producing 140 watts only because of the ice accumulation.

    Lastly, do I just read the inverter numbers, what about the new meter outside? I'm not sure how to interpret the meter because it keeps changing to all 8888888 and then it shows a "net" word to the left and then a small number with arrows that appear pointing to the left, my company is CL&P in CT.

    If I only need to worry about the readings on the inverter, then when/how/what time do you capture this and will it reset daily or what??

    Need to understand so I start placing these number into an Excel spreadsheet (only there's one already posted in the forum I can use).

    Thanks....
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: Solar array getting activated soon....tree question...

    Anything that blocks the sun from the panels will have a significant effect on output. Panels should warm up enough to shed ice however,,, eventually.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Solar array getting activated soon....tree question...

    Regarding the Inverter readings... Depends on the brand and what interface(s) you may have avaiable.

    I have a Xantrex GT 3.0 and the LCD display shows the current power output and today's kWhr (reset to zero every morning), the total kWhrs since built, the line voltage/frequency, and the Current/Voltage from the array.

    And, if you have the computer interface--some more information is available.

    Regarding the meter that goes 88888 every so often... Is this connected just to the Inverter output, or is this the whole house billing meter?

    Also, with electronic utility meters, the frequently have a very sophisticated power monitoring system inside... And, perhaps, a way that the consumer can switch between modes (mine uses a magnet held to the right side of the meter face for 1 or 10+ seconds to access two other series of screens).

    For mine, roughly it goes:

    88 88888 88
    02 date
    03 time
    05 00001.40 = 1.40 kWatts (current watts used/generated in last few seconds)
    98 48054 kWhrs since installed (total Peak TOU kWhrs used/generated)
    99 49343 kWhrs since installed (total Peak+Off-Peak TOU kWhrs used/generated)
    88 88888 88

    For mine, I have peak and off peak billing, hence two "registers" (98 and 99). The meter started at 50,000 kWhrs ("zero") and if 50,001 it means that I consumed 1 kWhr. If it reads 49,999 I generated 1 kWhr (all since the meter was installed--and it is read ~once per month for billing).

    There is an "LCD" dial at the bottom, and if the arrow points left and the dial "spins" to left, then I am generating excess power to the utility. If the arrow points right and spins right, then I am consuming power from the utility.

    If I hold a magnet next to the meter, I can see the voltage and current measurements, power factors, distortion, etc.

    All of the basic functions were described in a manual I could download from General Electric.

    Sort of the missing piece of information that I miss with my setup (kWhr meter in inverter, and kWhr net billing meter) is that I have to read my kWhr reading on the Inveter roughly when my meter is read (or read both meters myself) and basically do the math (Difference of meter readings from month to month, then subtract the monthly billing meter reading from the inverter reading--the result is how much power my home used in one month--watch signs).

    Depending on how your meters are connected (inverter, house load, or combined net metering) and how the meters are programmed (cumulative, or one register for how much power you use, another for how much power you generated, etc.) you will have to adjust the math accordingly (my utility is a net meter billing--so simply the meter turns forwards or backwards based on the total power going through my electric service--not everyone is the same).

    Just as a note, if you have net metering and they change your meter when the solar system is first connected--you may get an erroneous bill (not uncommon with PG&E--at least a few years ago). Instead of showing a 100 kWhr credit, I got a 900 kWhr bill (why more than our normal, non-solar assisted bill). So check the first couple of bills closely to ensure they are correct.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Geek
    Geek Solar Expert Posts: 32
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    Re: Solar array getting activated soon....tree question...

    I forgot to mention my inverter is a sunnyboy 5000 with a tiny display, I was actually wondering how I can get readings through my wireless router and my laptop, there's gotta be a way because Akeena offers a website for me to get the readings if I pay an annual fee, so they have a way to feed this to my router somehow.....

    do you know?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Solar array getting activated soon....tree question...

    This is all I know (link to Mfg. website about monitoring products)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Geek
    Geek Solar Expert Posts: 32
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    Re: Solar array getting activated soon....tree question...

    thanks Bill, but the options seem a little confusing somewhat, I will check with the installer for a better explanation.

    thanks guys for your great support.