Strings in different orientations?

mwalsh
mwalsh Registered Users Posts: 7
I have a situation where I can have 18-22 panels on a south facing roof, but that doesn't give me a system of sufficient size (at least that's what my brain keeps telling me).

I have discussed putting a further 8 panels on an easterly facing roof, but my installer hasn't discussed panel orientation and inverter behavior with the single inverter based system he's recommended (Sunny Boy SB5000US). In fact, I don't think he believes we even need to consider a second inverter, whereas I have my doubts.

Could anyone give me some feedback when it comes to the pros and cons of either:

a) Settling on the smaller system, with all panels facing south
b) A one inverter system with strings in multiple orientations
c) A dual inverter system with strings in multiple orientations

Could you try to keep it a bit "Dummies guide to...." please? I'm not a solar guy, or even really that intelligent to be completely truthful. :blush:

Oh, and how comes multi-tracker inverters aren't more common here in the States?

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Strings in different orientations?

    i don't know the particulars of what your pv capacity is or what your power consumption typically is, but i think you can probably go with the installer's recommendation if he is aware of and allows for some way to expand upon the system if need be even if it comes to a totally separate system being added with the proposed one. it can get very costly even for a few more pvs and may even mean revamping the electrical service box. discuss all options and requirements and weigh it out and if you want to you can just get another opinion from another installer. who knows as more may get cheaper?:D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Strings in different orientations?

    You can "play" with the PV Watts website and see how much you are "hurt" with non-southerly facing arrays.

    Lets take all of the defaults for a 4kW solar array for Long Beach California (Grid Tie System):
    "Station Identification"
    "City:","Long_Beach"
    "State:","California"
    "Lat (deg N):", 33.82
    "Long (deg W):", 118.15
    "Elev (m): ", 17
    "PV System Specifications"
    "DC Rating:"," 4.0 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 3.1 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 33.8"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","12.5 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 4.43, 395, 49.38
    2, 5.00, 406, 50.75
    3, 5.52, 491, 61.38
    4, 6.21, 528, 66.00
    5, 6.12, 533, 66.62
    6, 6.09, 512, 64.00
    7, 6.63, 565, 70.62
    8, 6.79, 575, 71.88
    9, 6.18, 514, 64.25
    10, 5.46, 477, 59.62
    11, 4.81, 413, 51.62
    12, 4.34, 386, 48.25
    "Year", 5.63, 5795, 724.38

    The above is Hours of Sun; kWH per month; $$ amount per month of electricity based on $0.125 per kWH.

    Do the same thing now facing East:
    "Array Azimuth:"," 90.0"

    1, 2.63, 223, 27.88
    2, 3.24, 255, 31.88
    3, 4.07, 355, 44.38
    4, 5.06, 424, 53.00
    5, 5.45, 470, 58.75
    6, 5.51, 457, 57.12
    7, 6.17, 523, 65.38
    8, 5.61, 466, 58.25
    9, 4.51, 365, 45.62
    10, 3.66, 310, 38.75
    11, 2.87, 235, 29.38
    12, 2.50, 210, 26.25
    "Year", 4.28, 4293, 536.62

    About a 26% reduction in output over 1 year.

    Now--something else to think about--at least in Northern California, we are forced to use a Time of Use rate plan for our billing.

    For me, base tier during the summer is $0.09 per kWH off peak and $0.27/kW peak (summer, noon-6pm week days).

    So--for me, the power I generate in the "morning is only worth $0.09/kWH but the power I generate in the afternoons is worth 3x more (during winter, the spread is $0.09 off peak and $0.12 for peak).

    So, you may have other economic reasons to not bother with easterly facing arrays.

    However--If you have a tiered power system--even offsetting off-peak power can keep you in lower tiers (PG&E has horrendously complex TOU/Tiered billing--and my old plan is much simpler than the current TOU plan for new solar GT customers).

    You may have to ask an installer or even your power company to give you a better idea of the issues with when you generate your power.

    There has been a lot of discussions about sharing one GT Inverter with 2 or more directions of orientation... The end result will probably be that you are best served with two separate GT inverters (or one inverter with multiple discrete MPPT inputs). Or using the Micro Inverters like Enphase (one inverter per panel--Micro inverters are also a topic with lots of ongoing discussions here).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Strings in different orientations?

    Use a seperate inverter for each orientation.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Strings in different orientations?

    I am not the techie here, i am just putting this in on my experience on east facing panels, mine are roof mounted facing east as the sun rises (4 kc 130 panels) it catches the morning sun and starts charging early, but at about 4:30 in the summer afternoon it drops to just a few amps of out put, but in winter time it puts out fairly good until the sun sets, like I stated earlier I am not a "tech" and I get my readings from a morningstar 30 w/digital meter, that I look at during different times of the day. But it seems like I get more charge time during the winter months than the summer months because the panels are facing east? I guess I need to keep a chart, but I am allergic to pen and paper. In other words east facing panels will jump start your charging (out-put) early, but in the latter part of the day, they wont do much good. But your mileage will vary, to your location and type of panels??? Hope I made some sense here. :D
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Strings in different orientations?

    Here's an extremely detailed thread from someone who did it:

    http://forum.solar-electric.com/showthread.php?t=6394

    Might answer some questions for you.
  • mwalsh
    mwalsh Registered Users Posts: 7
    Re: Strings in different orientations?

    PV capacity with just the south array is 4.5kw, though I can get up to 5.01 with the space available. However there is some shadowing with 2 of the panels on one string in the afternoon during winter, from a neighbors chimney.

    With additional panels to the east I add another 1.8kw, and we get closer to my desire to have a system that is ~6kw in size. 5.75kw would either zero (or be very close to zeroing) my utility bill every year, based on current and anticipated use (EV coming in December). 6kw will give me some surplus where I don't have to worry about whether I need to charge the car an extra once or twice, or use the house A/C a bit more during a heat-wave. Plus it will allow me to sell back surplus to the utility when the new law comes in January 1st!

    The vendor is fundamentally opposed to micro inverters on the basis of introducing multiple potential sources of failure and his reckoning that in the not too distant future micro-inverters will be built into panels, making separate ones obsolete and difficult to obtain replacements for.

    With a single inverter and strings in different orientations, please help me understand what happens when they are corrected in series......am I correct in thinking that performance of the entire array diminishes to that of the worst performing string? This is what I'm worried about most. I get some really nice sun on the south facing roof at a time when I'm worried significant shadowing will fall on the panels to the east (though I must say that I have yet to go up on the roof late in the day to see what actually happens).

    The following image from Google Earth was taken in the wintertime, sometime in the early afternoon:

    winter.jpg
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Strings in different orientations?

    I sort of recall one brand of inverter that has seperate MPPT circuits inside, but I've got no idea who makes it. I'd strongly push for each face to have it's own inverter, it gives a little reduncancy if one goes down, but doubles the chance one may go down..... But I'd never put 2 different arrays into one MPPT, late afternoon when the east gets shaded, I'd think it would drive the MPPT nuts.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    Re: Strings in different orientations?

    Assuming satellite picture was taken on winter solstice, here is my panel placement idea. Red = Enphase, Green = gtid-tie inverter 1, Blue = grid-tie inverter 2.

    Make sure there is no shadows on bottom green row during winter, othervise extend Enphase into entire bottom row. Different panel orientations should be on separate inverters.
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    Re: Strings in different orientations?

    Definitely go with two separate inverters. You'll lose a lot of power from the south facing array once in the afternoons once the sun stops hitting the east facing array.

    If you really want to opt for only one inverter, just install on the south facing roof and forgo the panels on the east facing roof.

    If you later decide that you still want more power, then you can add panels to the east facing roof on a separate inverter then.

    How many kW can you fit on the south roof? (what panels are you looking at?)
  • mwalsh
    mwalsh Registered Users Posts: 7
    Re: Strings in different orientations?
    AntronX wrote: »
    Make sure there is no shadows on bottom green row during winter, othervise extend Enphase into entire bottom row. Different panel orientations should be on separate inverters.

    Ooh, thanks for that. Interesting concept. I never thought of putting just a few micro-inverters specifically on panels that might be impacted by shadowing. I was just going to leave space where you have those and go with three rows having eight, eight, and four.

    How do those tie in with the other regular inverters on an array?

    Sunny Boy in Europe has an inverter series that features separate MPPTs. I don't know if they are available here or not:

    http://download.sma.de/smaprosa/dateien/5693/SBHCMS-DEN083125.pdf
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    Re: Strings in different orientations?

    IMO, either stick with a central inverter or go all the way with micro-inverters. You need to have separate electrical runs for each which will drive up costs.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Strings in different orientations?

    Do a PV watts calculation using both array array facets to see what the likely difference will be. http://rredc.nrel.gov/solar/calculators/PVWATTS/version2/

    Personally I would consider using at least two inverters, but I am not a grid tie expert.

    Welcome to the forum,

    Tony
  • mwalsh
    mwalsh Registered Users Posts: 7
    Re: Strings in different orientations?

    My installer and I are going to have a chat this next week. During that chat, I'm going to insist that we do the job with micro-inverters. I've just watched some of the Enphase training videos and it looks like a really elegant solution to the problem we have.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Strings in different orientations?

    Just to let you know, I'm not thrilled with the idea of 20 or 30 little inverters. From a realibality standpoint, it's a lot of AC connections in the weather, and lots of electronics modules in about the worst enviroment, other than under a car hood.
    Enphase claims a unbeliveable reliability #, and they have not had a long history to look back on. And you have to subscribe annually to their monitor service, as the data from each module is encrypted.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mwalsh
    mwalsh Registered Users Posts: 7
    Re: Strings in different orientations?

    Well, those things did occur to me too, and I think these are the same objections my contractor has.

    The only other thing I could do is the second inverter. But with the small number of panels I can get facing east ( 6-8 ), then we'd have to find some that would put out enough voltage to start the inverter (SB3000 starts @ 228v)
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Strings in different orientations?

    Then just use the enphaase for the east , and maybe the little chimeny shaded section.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Strings in different orientations?
    mike90045 wrote: »
    Then just use the enphaase for the east , and maybe the little chimeny shaded section.

    that's what i was thinking too and there's no reason why you couldn't mix systems. be sure of the dawn/dusk shadowed areas during the warmer months too as those shadows can be appreciable as you wouldn't want the strings to be shadowed, just the enphase.
  • mwalsh
    mwalsh Registered Users Posts: 7
    Re: Strings in different orientations?

    OK, I think I got this all worked out. The only problem now....I think it's gonna cost me!

    18 x Sunpower 315 panels on the south facing roof with a single SB5000 inverter.

    So, yes, the Sunpower panels are probably going to be hugely expensive. But compared to 26 or 28 lesser output panels, plus a bunch of micro-inverters or a two-inverter system,...unless the cost is obscene or the panels are made of unobtainium, I think it might just be the way to go. Plus it might be easier to get these panels right now as government agencies and non-profits across CA cancel their orders because the incentives are on hold.

    I don't suppose anyone has priced these before and could give me an idea of the cost? I have my wife ready with the smelling salts!
  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Strings in different orientations?
    mwalsh wrote: »
    18 x Sunpower 315 panels on the south facing roof with a single SB5000 inverter.

    Hi, we talked about your project over on PriusChat, too.

    My contractor guesstimated that SunPower would cost $1/watt
    more than the other vendors.

    If you work for a major corporation, you might want to check
    if they have a corporate discount with SunPower. The
    company I worked for did, $.45/watt. After you add in the
    Fed's 30% rebate, that puts SunPower back into the
    competitive range.

    In my case, SunPower would have given me a 10% greater
    capacity potential due to their smaller size panels. But, I
    would have lost some yield because I needed Enphase
    inverters for my particular two-facet set up and Enphase
    was not supported for the SunPower panels of interest to me.

    John
  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    Re: Strings in different orientations?

    FWIW, A number of Sunpower panels do work with the M210-84 Enphase inverter, they have this this strange disclaimer:
    Although electrically compatible with the M210-84, Enphase Energy does not currently have a business relationship with Sunpower. If installed with a Sunpower module, the Enphase warranty will be supported on all Enphase products.

    I think this is because when you go Sunpower, you typically go with their panels and inverters, no?

    Anyway, Enphase can cost about $0.50/watt more than a central inverter... You can do the math in comparison to Sunpower system...
  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Strings in different orientations?
    drees wrote: »
    FWIW, A number of Sunpower panels do work with the M210-84 Enphase inverter, they have this this strange disclaimer...

    My contractor became an authorized Sunpower installer
    on the very week he arrived to install my Sharp panels!
    The contractor's lead tech explained to me "between the
    lines" what he felt was happening.

    Sunpower is endeavoring to provide a complete Sunpower-
    branded solution. For example, you can buy a Sunpower
    branded central inverter from them. If they offer a complete,
    fully integrated solution, presumably that type of solution
    will work better out of the box. This allows Sunpower to
    exert more control over the quality of the total solution,
    increase its revenues by selling more than just the PV
    modules, and offer added value that elevates them above
    other vendors who only have PV panels to offer. My
    contractor sensed that the offered Sunpower inverter
    is actually from a well known industry standard vendor,
    but relabeled as a Sunpower unit. In any case, with this
    kind of marketing strategy, Sunpower will want to
    dissuade prospective customers from looking outside the
    Sunpower suite of products, even if they theoretically
    should work. By introducing FUD about the certification,
    it can force Enphase to back off their warranty (which
    is what happened when I originally asked my contractor
    to contact Enphase about Sunpower support).

    John
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Strings in different orientations?

    john,
    your installer is correct about sunpower as they want to be unto themselves and their inverters are rebranded from xantrex i believe. it may seem better to sunpower and they believe they can force only their equipment onto a customer in this way. it can be good in some ways and bad in others i suppose for the little guy getting his feet wet with up to a few pvs from sunpower will not be able to utilize off grid arrangements totally through sunpower seeing as how they think everybody is connected to the grid. few of their pvs made it into the arena without the rest of the system they would sell to the customer with the pvs. this off grid arena they are missing out on and won't sell just the pvs in such a case so they are losing some $ in the off grid market.
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Strings in different orientations?
    jcgee88 wrote: »
    My contractor became an authorized Sunpower installer
    on the very week he arrived to install my Sharp panels!
    The contractor's lead tech explained to me "between the
    lines" what he felt was happening.

    Sunpower is endeavoring to provide a complete Sunpower-
    branded solution. For example, you can buy a Sunpower
    branded central inverter from them. If they offer a complete,
    fully integrated solution, presumably that type of solution
    will work better out of the box. This allows Sunpower to
    exert more control over the quality of the total solution,
    increase its revenues by selling more than just the PV
    modules, and offer added value that elevates them above
    other vendors who only have PV panels to offer. My
    contractor sensed that the offered Sunpower inverter
    is actually from a well known industry standard vendor,
    but relabeled as a Sunpower unit. In any case, with this
    kind of marketing strategy, Sunpower will want to
    dissuade prospective customers from looking outside the
    Sunpower suite of products, even if they theoretically
    should work. By introducing FUD about the certification,
    it can force Enphase to back off their warranty (which
    is what happened when I originally asked my contractor
    to contact Enphase about Sunpower support).

    John

    John,

    Many years ago, Lennox A/C tried to do the same thing with their line of A/C and heat furnaces when the popularity of their "Pulse Heat" system was getting in the high 90's in efficiency and they came out with a "Two speed compressor". Their systems were known for being "built like a tank" and they back-tracked to day one and offered a "Lifetime Warranty" on the gas furnance's heat exchanger. With such a hearty line of products, then they tried to lock down dealers, repair parts, and installations to have a super large and controlled product in a public market.

    I think they almost lost their shirt with their "Locked-Step" approach. Small Lennox installers became tied to this "control" and began to suffer. Plus, when the "Pulse Heat" exchangers began to crack, the recalls and company paid pressure checks caused them to stop production....

    Having, and requiring use, of a full array of products under one brand was a slippery slope back then, not to mention in this day and time. All it takes, like Lennox, is one troubled product in their line to cause the whole house of cards to topple...

    Just a thought,
    Bill
    Bill
  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    Re: Strings in different orientations?

    I thought SunPower was rebranded SMAs? I have a client who is a SunPower dealer, but they've never let me touch one of those systems (I've worked on their OutBack and Xantrex installs). A potential client in New Orleans said the same thing -- re-branded SMA -- and offered to sell me leftover communications cards from some of their installs.

    I agree that the "total control" approach can backfire. But having seen hybrid / mixed / "evolved" systems, a turnkey, single vendor isn't such a bad idea.