Panel Location

NorTracNY
NorTracNY Registered Users Posts: 13 ✭
in General Solar Power Topics #1
Hi, I found out my panels are being installed Friday. I found that the installer is willing to install them anywhere on the house. I don't have a fancy roof so it's all the same angle orientation and lack of shading. Is there any reason NOT to install on the roof of my garage? The installer said he's fine with it and that it's just up to me on looks. I figure if there are any problems, the roof of the garage would be less of an issue.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
    Re: Panel Location

    I found that panels reduced my attic temperature a lot (uninsulated attic, insulated ceiling).

    In general, you want the existing roofing materials to last 30-40 years so you don't have to pull the panels to replace the roofing after 12 years.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Panel Location

    if the garage is a farther distance from the controller then a heavier wiring may be needed otherwise it would be fine providing in either case as bill mentioned that you won't have need to change out the roof in less than 25yrs as that's the warranty of many pvs, but they can last longer.
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  • NorTracNY
    NorTracNY Registered Users Posts: 13 ✭
    #4
    Re: Panel Location

    OK, garage and house roofs are both 9yrs old, so no difference there. I'm figuring that I'm better off on the garage than the house because I wouldn't care about a leak as much. I'm doing a 20year lease (one time up front payment), so in 20 years whether the company gives me the panels or not, I'll have a new roof put on there. I also figure that I could reshingle the house when needed, and just do the roof separately, and the look would be ok.

    The run to the controler box is about 70' further by going to the garage as opposed to right on top of where the controler is.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Panel Location
    NorTracNY wrote: »
    The run to the controler box is about 70' further by going to the garage as opposed to right on top of where the controler is.

    That is a huge difference. You need to calculate the wire size very carefully. Or put all the equipment in the garage to shorten that run.

    Me, I would not intentionally add another 70' to a wire run if it could be avoided.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #6
    Re: Panel Location
    NorTracNY wrote: »
    OK, garage and house roofs are both 9yrs old, so no difference there. I'm figuring that I'm better off on the garage than the house because I wouldn't care about a leak as much.
    If your installer has you worried about causing leaks in your roof, then you need to look at other installers. They are liable for any water damage that your property suffers as a result of their incompetence in sealing your roof. I agree with 'coot, too; 70' added to the DC run is a major issue and may cost you significantly to get the wire size up to where voltage drop won't severely impact your production.
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  • NorTracNY
    NorTracNY Registered Users Posts: 13 ✭
    #7
    Re: Panel Location

    OK, let me clarify a few things.

    I don't know where the controlers would be placed. My panel box is 70'. Doesn't the inverter go on the roof and that converts it to AC? They can put whatever boxes they want in my basement where ever they want, so there shouldn't be any difference in the length DC is traveling. This is an attached garage on a single story ranch.

    The installer doesn't have me worried as much as some practicalities are better with the garage. The installer has a written guarentee which talks about so many inches around any penatration of the roof. If I can avoid having to worry about damage with the location, then all the better.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Panel Location

    I don't understand why 70 ft run to controller is such a big deal. Isn't this a grid tie? Isn't the voltage pretty high? --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Panel Location
    NorTracNY wrote: »
    OK, let me clarify a few things.

    I don't know where the controlers would be placed. My panel box is 70'. Doesn't the inverter go on the roof and that converts it to AC?

    Only mcro inverters go on the roof. Central GT and off-grid inverters need to be inside; they aren't weather proof.
    They can put whatever boxes they want in my basement where ever they want, so there shouldn't be any difference in the length DC is traveling. This is an attached garage on a single story ranch.

    That is good. The biggest problem with V-drop is from the array to the charge controller, as this is the longest DC wire run (or should be; it's really bad if the other two portions are longer).
    The installer doesn't have me worried as much as some practicalities are better with the garage. The installer has a written guarentee which talks about so many inches around any penatration of the roof. If I can avoid having to worry about damage with the location, then all the better.

    Always a consideration. One of the unknowns with this is how the roof is constructed (in respect to both load bearing and leak resistance). It may be easier to determine that on the garage if it does not have a ceiling.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Panel Location
    vtmaps wrote: »
    I don't understand why 70 ft run to controller is such a big deal. Isn't this a grid tie? Isn't the voltage pretty high? --vtMaps

    If the word "controller" is involved then that means it's either off-grid or a hybrid GT system, either of which use "low Voltage" arrays (under 150 VDC for most MPPT type controllers).

    Otherwise, straight GT inverters do use "high Voltage" arrays in excess of 250 Volts where long wire runs are less of a concern. Micro inverters (the good ones) put out 240 VAC, so again the wiring length is less of an issue.

    I admit to being confused as to which type of system we're discussing at the moment. In any case, 70' can be a significant amount of wire even on higher Voltage systems. Use any V-drop calculator and see what happens when you add 70' to the length of any given wire size at any given Voltage and current. Even on >240 it can be the difference between an acceptable loss and an unacceptable one (or the need to increase wire size).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #11
    Re: Panel Location

    The problem with placing a Grid Tied system inverter "far" away from the main panel is that if you have high average line voltage (say >255 VAC), when you add voltage drop (actually voltage rise) from the GT inverter outputting maximum current--The voltage rise can cause the GT inverter to "read" excessive line voltage and shut down (5 minute timeout, no damage/safety issues). GT inverter cutout is typically 264 VAC maximum (and probably as low as 260 VAC).

    Some power companies will adjust the final transformer tap to bring the voltage down to "nominal" of ~240 VAC... However, in many areas, you will see "variable" line voltage (jack up in summer because of well pumping/Air Conditioning loads)--So you may have seasonal variation too.

    Anyway, before you do anything, make a paper design and spec. the cabling, voltage drop/rise, and other issues first.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • NorTracNY
    NorTracNY Registered Users Posts: 13 ✭
    #12
    Re: Panel Location

    This is a straight grid tie system. Sorry if the lingo was confusing with me using controler. Another potential company had discussed panels on post off the ground. This would have been 150' from the house. They had said that wasn't an issue, so I'm definitely a little confused. I've looked more into the financials of this system (rediculously good) much more than the technical ones. There are no micro inverters.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
    Re: Panel Location

    If you use a central GT inverter, place the inverter near the AC mains panel, and run DC from the array to the GT inverter (typically around 300-400 VDC nominal). Wire gauge stays relatively small and voltage drop/rise is not an issue with respect to AC line voltage.

    Usually, most drop is around 1% to 3% of line voltage... (that is about 4 steps in wire awg size--i.e., 10 vs 6 awg wiring). Below 1% is usually not economically worth the costs.

    What size solar array are you looking at?

    Also, have you reviewed the billing/rate plan(s)? That can make or break a solar PV GT system (especially if you are a commercial power user).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Panel Location

    Straight grid-tie systems run arrays in the 250 to 500 VDC range. As such there is plenty of Voltage for overcoming wire resistance on long runs. For example, a 5.6kW array using 24 235 Watt 30 Volt panels may run two strings of twelve each: 360 Volts @ <8 Amps per string (16 total). About 10 AWG could handle that up to 150 feet.

    The same power size on micro inverters would be 28 of them (one per panel, slightly smaller panels) and the output from the lot would be 240 VAC @ 24 Amps. For 10 AWG over 150' the loss would now be slightly over 3% and larger wire or two runs might be necessary.

    Put the same 5.6kW array into an off-grid situation and you have a nightmare unless you use one of MidNite's high Voltage controllers. Even then the limit is 250 VDC and it won't operate that efficiently with that conversion ration.

    Sorry for veering off track; just trying to explain the concerns vis-a-vis wire lengths and different system types. Carry on.
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  • NorTracNY
    NorTracNY Registered Users Posts: 13 ✭
    #15
    Re: Panel Location

    It's 21 Sunpower panels with a SunPower inverter. SPR-327NE-WHT-D and SPR-6000m (240V)
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