Looking to go solar...everything looking good, am I missing something?

Options
2»

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #32
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    The micro inverters may be better in that over-all they may produce more total power than a central inverter if there are any shading issues. As Bill said it's hard to tell if there are any from your picture.

    For a GT system price per Watt isn't the whole story, because the different systems may produce different amounts of Watt hours at different times which will apply to your billing in different ways depending on your usage plan. Yes, it's confusing.

    You should try the various configurations you've been offered on PV Watts and see if the production differences will be significant.
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #33
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    I'm shying away from the micro-inverters as an installer told me that out here in the super hot Phoenix sun, those inverters bake at 150+ degrees which isn't really something you want. Probably best to just go with a regular unit in the garage and call it a day.

    As for the different configurations, that's the thing...the ones I've been offered say it takes a 12.24kW Canadian Solar setup to make the same power as a 11.2kW setup so can I really trust the monthly numbers they are telling me? The PVWatts site only allows me to enter the system size, DC-to-AC Derate Factor (which I don't know what that factor is, was told by someone else to use 0.84) and that's it so it wouldn't know the difference between different brands and what they produce when.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #34
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    Curiously you seem to be getting quotes all using the same inverter; the Fronius 10kW.
    That eliminates one factor in comparing quotes as they will all have 96% conversion efficiency. The difference seems to be in how much panel you put behind it and how well those panels will produce in a day.

    Normally if you want full 10kW output from the GTI you'd have 13kW of panel on it. No one has quoted for that much so it's a moot point.

    There may be minor difference in the panel temperature coefficients but yes the heat will be killer for Voltage. The companies that make the micro inverters claim they will stand up to it. Many of us have had the same doubts as you about that.

    If the shading issue is unknown it can't be figured in. PV Watts has input for panel angles which may make a difference with arrays not all facing the same direction or at the same elevation angle.

    Why is this looking like it's coming down to price per Watt? :roll:
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #35
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    Is it bad if it's coming down to price per Watt? :) Should it not?

    The more I look at the numbers, the more I'm leaning toward a Canadian Solar 11.2kW system which would be $24,001 net cost vs the Sun Power 11.2kW which would be $29,732 net.

    Shading isn't an issue, they can put the panels to where there will be zero shade all year. Angle wise it's 14º - 18º between all surfaces.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #36
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    Are they all facing "south" (same compass direction, or do you have some facing East/West)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #37
    Options
    Re: Looking to go solar...everything looking good, am I missing something?
    HX_Guy wrote: »
    Is it bad if it's coming down to price per Watt? :) Should it not?
    While the equipment is a ok measure of the value you'll receive, I'v not seen anything about the racking and Installation. The quality of the Instillation has to be of a 25 year quality. The racking and roof penetrations were more than 20 % of my total costs. Some here like the " L Bracket / Lag bolt " screw down, Personally it wouldn't fly with me. Some things may depend on where you live, all of mine were flashed with standoff's.
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #38
    Options
    Re: Looking to go solar...everything looking good, am I missing something?
    BB. wrote: »
    Are they all facing "south" (same compass direction, or do you have some facing East/West)?

    -Bill

    I believe the SunPower guy said they could fit all 35 panels facing south (though they haven't actually been on-site to measure). The Canadian Solar would require 44 panels so some would have to face east. Maybe that's where he is getting that we would need a 12.24kW system to produce the same 11.2kW that the SunPower does?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #39
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    In general, for optimum generation, each "plane" of solar panels should be on its own MPPT input... There is at least one GT Inverter that has several (?) independent MPPT inputs.

    Most GT Inverters have a single MPPT input and should all be connected to the same plane of arrays. Normally, if you have different planes, you would use several smaller central controllers or use Micro Inverters on this type of system.

    MPPT tracks the Vmp-array voltage... And this voltage is variable based on the temperature of the physical cell... In theory, you could get upwards of 10-20% or so difference in Vmp between an East/South/West facing array. Miss-matching Vmp-array-string voltages will give you some losses... How much--I do not know (could be 5% or it could be 20% or more--it all depends).

    Sorry--giving more questions than answers.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #40
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    I have no idea what you just said. :D But, I am getting a more clear picture on why the difference in system size and output.

    Another quote I received was for LG panels (very similar wattage and size to the Canadian Solar). The system size though was 10.92kw producing 18,121 kWh per year. The layout would be identical to the Canadian panels with 14 panels facing east and 28 panels facing south. Going off those numbers, it would in fact take a 12.2X kW to produce the 20,000+ kWh that I was quoted, which if they were all south facing, it would take 11.2kW. So if I'm wanting to compare apples to apples, I need to look at the cost of the 11.2 SunPower, which is $29,732 vs $26,670 for Canadian Solar.

    Is the SunPower brand worth the extra $3,000?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #41
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    Basically, solar panel arrays facing different directions will have different operating temperatures (panel facing south may run hotter than a panel facing east/west at noon). So, one array will have Vmp-temp~350 volts, and the other array may have Vmp-temp~300 volts.

    Remembering that power=voltage*current... So when you connect both together in parallel, the MPPT controller will pick the max power at Vmp 300 volts or 350 volts or somewhere in the middle.... In any case there is no "optimum maximum" point that gets all the available power. One of the strings (at least) has to operate at non-optimum Vmp voltage that that condition.

    Note that at noon, the south facing array will be collecting the most energy, and the east facing array, not so much... And running the east array at less efficiency is a lesser amount * percentage loss--So it is not "that bad" of losses.

    But this is why folks sometimes use two smaller GT central inverters or micro inverters or multiple input MPPT central inverters for mixed array installations.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #42
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    We'll this is turning out to not be quite as rosey as I initially thought, the shade issues seems to be much bigger.

    The guy who was pushing SunPower and the micro-inverters(the brand is Solar Bridge BTW) came by and did measurements and a shade analysis himself and according to him, we have full shade on the majority if the south roof in Nov/Dec/Jam so he recommended not putting any panels there at all. So with that, filling up all south facing non-shades parts AND the east facing side, we could only get about a 9kW system with the bigger cheaper panels like Canadian Solar. Even with the 327W SunPower panels, we wouldn't get full 100% coverage. Incidentally, and seems like BS, be said with the 240W micro-inverter panels we could get full coverage because the panels are so much smaller and he can more/different layout.

    That's at least how I remember it, waiting on actual quotes. I'm pretty skeptical on the shade thing though, I don't recall the neighbors 2 story house shading out house that much and the other guy's analysis said otherwise. I may just wait until winter and see for myself before going forward.
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #43
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    It looks like the guy was pretty spot on. I figured out how to turn on Shadows in Sketchup (this program is pretty damn powerful and useful!) and just with a rough box to represent the neighbor's 2 story house (I guesstimated 23' to the roof, could be less) but it looks to confirm what the guy found today using the SunEye...

    10:00 am
    solar10am.jpg

    1:00 pm
    solar1pm.jpg

    3:00pm
    solar3pm.jpg
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #44
    Options
    Re: Looking to go solar...everything looking good, am I missing something?
    HX_Guy wrote: »
    As for the different configurations, that's the thing...the ones I've been offered say it takes a 12.24kW Canadian Solar setup to make the same power as a 11.2kW setup so can I really trust the monthly numbers they are telling me?

    Just be sure they are explaining where they are getting their figures, it may be that the NOCT values (normal operating cell temperature values) are that different, This might well be very important in a hot environment , like Phoenix.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #45
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    If you limited on space you should look into the most efficient panels, I thought SunPower tended to be more efficient though with a positive ground limiting inverter choices...

    ...I haven't been active for a while so perhaps one of the Mod's will have this info at hand...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #46
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    As far as I know (very little)--you are correct, Sun Power still needs positive grounding for string/central inverters.

    Many (most/all?) central GT inverters are configurable (or available) in both positive and negative ground.

    There are the new transformerless GT inverters--Not sure if they are correct to use with the Sun Power panels.

    I believe Sun Power still sells the panels+inverter through their distribution channel--So any Sun Power systems could be properly configured.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    #47
    Options
    Re: Looking to go solar...everything looking good, am I missing something?

    So there's still some hope for optimal south facing panels.

    Someone on another forum told me about this app for the iPhone called SkyView. You set a date and time and then point the phone in a direction and it simulates where the sun will be in the viewfinder. Crazy impressive technology for a "phone".

    Of course I got up on my roof and did some testing really quick. I took the photo from as low down as I could while still being able to see the screen and tap the photo button. One thing I'm not sure of though is the angle and how does that affect things? I mean sure I can see the sky, but wouldn't the building's shadow get longer as the sun is lower? These photos were taken with the phone basically at a 45º angle while the roof is at a 14º angle, if I took the picture at 14º, all I would see if sky of course.

    Here are the pictures, I set it to December 21st at 12:30pm.

    First photo is from 3' down from the roof edge which is where a panel could start...
    solar17.jpg

    Second picture is from 5' lower, figuring a 3x5 panel (and also 5' from the roof bottom, roof width is 13').
    solar18.jpg

    Based on these, what's your guys' take? And again, what kind of affect does the angle that the phone was at while taking the picture play into it?
    · Share on Twitter

Categories