Need help with breakers, combiners

cbourascbouras Registered Users Posts: 11
I need advice on constructing a 5 KW grid-tied solar panel array. Here's some details:

20 Solar panels, Kyocera KD245GX-LPB
- Vmax 29.8 V
- Imp 8.23 A

Planning to connect into two strings of 10 panels each, so 2 strings
- String Vmax = 298 V

Planning to use #6 AWG cable since the panels are far away from the utility's breaker box and I want to minimize losses

Planning to use a 2 pole breaker/switch then a combiner box to produce 16.5 A at 298 V to go into a Sunny Boy 3800-US inverter in the following fashion:

*---< string 1>
* [pole1]*----| combiner |
| Sunny boy |
| utility |
*---< string 1>
* [pole2]*----| box |
| inverter |
| box |
| ^
|___________________________|

Questions:
1) Does this arrangement make sense?
2) What breakers would you recommend. I can only find one from Eaton that fits the bill and takes a #6 AWG cable. ABB breakers are available, but specifications for them hard to find and their site impossible to navigate.

Carlos

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with breakers, combiners

    Welcome to the forum, Carlos.

    Sorry your post seems to have slipped through the cracks a bit; we do try to get responses in quickly, even if it's just "I don't know; let's see what others say".

    There are commercially available combiner/breaker boxes which are suited to this type of application:
    http://www.solar-electric.com/sopawiinco.html
    Trying to adapt other technology to it isn't a good idea, both due to the Voltage involved and the fact it is DC which is more difficult to control. For this high Voltage you'd be using the 600 VDC fuses, not 150 VDC breakers.
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Re: Need help with breakers, combiners

    Have you gone to the sunny boy website and put your data into the input calculator/system sizer ?

    I ask, because I think the 298V you plan, seems low for a grid tie inverter, most like 350 - 500VDC for full MPPT action.

    Or maybe I'm out of date.
    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 ,

  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    I avoided the whole panel configuration issue as I am not really that familiar with SMA's products... But, from their website:

    Min/Start Voltage: 250 / 285 V
    MPPT Range 250 – 480 V

    Using a MPPT string sizing tool (not SMA's)--It appears that 10 modules in series for a 90F day (assuming San Diego CA?), panels on a windless roof mount works out to a Vmp-hot~242 volts--So it falls out of maximum power band by a bit (don't know SMA--may not be a big issue--it is close).

    And, in any case, 20x245watts=4,900watts of array--Adding two more panels may be less than cost effective--You could look at going with a larger GT inverter if you add more panel to bring Vmp-array voltage up.

    San Diego tends to be cooler (on coast)--So you might not want to derate the charge controller so much anyway (if you can get a slight larger one at similar pricing). Of course, this also goes into the home/main panel sizing too--So, there may be other reasons for a 3.8kW maximum GT inverter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    Thanks all for your valuable advice, let me summarize what key points I got, to see if I'm getting it right;

    Concern #1 Start voltage for a string of 10 modules appears to be low, at Vmp of 298 nominal for a string of 10 modules, and minumum start up voltage of 250 / 285 V for the inverter selected, the inverter will not work well during a good portion of the day when the sun is not hiting the modules directly. Solutions are to increase the voltage by adding panels or select a different inverter that can start at a lower voltage.

    Question: Given the Sunny Boy's MPP voltage range of 250 – 480 V, sounds like I should be aiming to be closer to the top of the range (480) right?

    Question: will the inverter stop working altogether at 250 V or will it's performance be degraded?


    Concern#2 Breakers are not the way to go, rather use fuses in a combiner box and a manual switch box that can handle the voltage and currents available. Above all, do not use AC breakers and try to adapt to DC.

    Question: I could do this, but would rather have a breaker solution than fuses. Is there any company (other than Eaton) that supplies a breaker solution for a system running at about 45V and 20 amps ? Eaton seems to have solutions on their web site, but I can't find any place to order their components.


    Thanks again for your quick replies.

    Carlos
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    Got to go--but the website says nominal Vmp is ~ 310 volts or so...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    How about this plan instead:
    - add 2 panels per string, for a total of 12 pannels and a VMPP of 358V.
    - Use a Sunny boy 5000-US with minimum start voltage of 250 to 300 V. OVersized in terms of current capacity, but OK

    Is this voltage more in line to what you all would expect for this inverter?

    By the way the location for this project is Puerto Vallarta Mexico.

    Carlos
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with breakers, combiners

    I'll suggest you look over the plans from all angles, starting with what the existing service is. That should give you the information needed to determine how large a GT inverter you can use, then size the array accordingly. In Puerto Vallarta you are definitely going to have some significant heat derating of the panels. You may find you need to switch to more panels but of a lower Wattage in order to bring both the Vmp and total Watts in line with the inverter's operating needs.

    You might try SMA's string sizing tool too: http://america.sma.de/newstringsizing.aspx
    Some have reported it having glitches, but give it a shot.
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    It looks like Puerto Vallarta is a pretty temperate to warm climate (10C to maybe 40C min/max)?

    You don't want to run the voltage up either without checking the SMA sizing tools (and/or checking with the local SMA rep where you will be purchasing the system).

    If I used Cariboocoot's link correctly, this is the result I get (using 240 instead of 245 watt panels which where not listed--but probably make no difference):
    Results

    1string configurations
    • 8 in series
    • 9 in series
    • 10 in series
    • 11 in series
    • 12 in series
    • 13 in series
    2string configurations
    • 8 in series
    • 9 in series

    Eight to nine modules on a 40C day should be around Vmp-array of (Using Xantrex GT Sizing Tools):
    • 8x = 185.2 volts
    • 9x = 208.35 volts
    Sounds low--but perhaps that is how it rolls. :confused:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with breakers, combiners

    Bill;

    I tried this the "manual" way and for the 3kW inverter got 16 of the 245 Watt panels in one series string.
    :confused:

    Makes me wonder about SMA's sizing tool - or my brain. :p
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    A completely different question, does your local power company allow Grid Tied/Net Metered solar PV systems?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with breakers, combiners
    cbouras wrote: »
    I need advice on constructing a 5 KW grid-tied solar panel array. Here's some details:

    20 Solar panels, Kyocera KD245GX-LPB
    - Vmax 29.8 V
    - Imp 8.23 A

    Planning to connect into two strings of 10 panels each, so 2 strings
    - String Vmax = 298 V

    Planning to use #6 AWG cable since the panels are far away from the utility's breaker box and I want to minimize losses

    Planning to use a 2 pole breaker/switch then a combiner box to produce 16.5 A at 298 V to go into a Sunny Boy 3800-US inverter in the following fashion:

    *---< string 1>
    * [pole1]*----| combiner |
    | Sunny boy |
    | utility |
    *---< string 1>
    * [pole2]*----| box |
    | inverter |
    | box |
    | ^
    |___________________________|

    Questions:
    1) Does this arrangement make sense?
    2) What breakers would you recommend. I can only find one from Eaton that fits the bill and takes a #6 AWG cable. ABB breakers are available, but specifications for them hard to find and their site impossible to navigate.

    Carlos
    For one thing, Vmax is not just string length times Voc; you need to adjust Voc upwards for the lowest temperature you will see (usually the record low for your location). Use the temperature coefficient on the data sheet for the module to calculate the "real" Vmax for your module.

    Next, you need to look at the minimum voltage you can expect. You do that by adjusting Vmp downwards with the same coefficient (if a separate one is not published for Vmp, which it usually isn't) for the expected highest cell temperature you will likely see for extended periods of time. You must also add 20-35 degrees to the high ambient temperature (usually the highest average monthly high for your location) to get cell temperature, depending on the type of mounting your modules will have.

    At that point you will have a module Vmax and a Vmin. Use these numbers to find your best match of string length to the operating window of your inverter, taking care that your voltage never will exceed the maximum allowed by the inverter under the coldest possible temperature. If that happens, even for a short time, the inverter is at risk of failure and your warranty is voided. Most inverters now have a "black box" recorder that will tattle on you to the manufacturer when you send the blown inverter back to them.

    Have fun!
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    This is extremely helpful and logical, thank you. I wonder why this is not in any of the literature I acquired for this project.

    Carlos
    ggunn wrote: »
    For one thing, Vmax is not just string length times Voc; you need to adjust Voc upwards for the lowest temperature you will see (usually the record low for your location). Use the temperature coefficient on the data sheet for the module to calculate the "real" Vmax for your module.

    Next, you need to look at the minimum voltage you can expect. You do that by adjusting Vmp downwards with the same coefficient (if a separate one is not published for Vmp, which it usually isn't) for the expected highest cell temperature you will likely see for extended periods of time. You must also add 20-35 degrees to the high ambient temperature (usually the highest average monthly high for your location) to get cell temperature, depending on the type of mounting your modules will have.

    At that point you will have a module Vmax and a Vmin. Use these numbers to find your best match of string length to the operating window of your inverter, taking care that your voltage never will exceed the maximum allowed by the inverter under the coldest possible temperature. If that happens, even for a short time, the inverter is at risk of failure and your warranty is voided. Most inverters now have a "black box" recorder that will tattle on you to the manufacturer when you send the blown inverter back to them.

    Have fun!
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    Yes, I did check that before starting. The Mexican utility company CFE, government owned, allows and encourages use of PV and other alternative energy sources.
    Also the CFE has tarifs that will blow your mind. Zones that fall in tourist areas pay many times higher rates than other zones, making PV very attractive. As an ezample I can expect this house in Puerto Vallarta to clock in $2,000 US a month in electric power for the hot months, so I'm installing the most efficient everythings I can find and enough PV power to break even. I should be able to pay for this project in three year tops, including import taxes.

    BB. wrote: »
    A completely different question, does your local power company allow Grid Tied/Net Metered solar PV systems?

    -Bill
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    :confused: is right. Not sure how the inverter would ever work with the values you got from the calculations. I'll do this manually and see where the discrepancy is coming from. Thanks for the tips.
    BB. wrote: »
    It looks like Puerto Vallarta is a pretty temperate to warm climate (10C to maybe 40C min/max)?

    You don't want to run the voltage up either without checking the SMA sizing tools (and/or checking with the local SMA rep where you will be purchasing the system).

    If I used Cariboocoot's link correctly, this is the result I get (using 240 instead of 245 watt panels which where not listed--but probably make no difference):



    Eight to nine modules on a 40C day should be around Vmp-array of (Using Xantrex GT Sizing Tools):
    • 8x = 185.2 volts
    • 9x = 208.35 volts
    Sounds low--but perhaps that is how it rolls. :confused:

    -Bill
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    So it looks like SMA's tool recommends a Sunny Boy 4000-US with a two string, 10X configuration. The tool states I can use from 8 to 11 modules in a 2- string configuration and from 8 to 16 modules in a one sring configuration.

    Puerto Vallarta's temperature ranges from a low of 60F at night in the frigid winter to 90F during the day on August. Temperate is an understatement. ;)

    Ouside of manual calculations which would indicate I have not enough voltage to make the inverter work all the time (I have to check with the SMA rep) looks like my original plan would work. Complete beginner's luck.

    Any words of advice on the SMA tool other than check with the rep?

    Again to all, grateful doesn't begin to express how I feel about your rapid response.

    Carlos
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with breakers, combiners
    cbouras wrote: »
    So it looks like SMA's tool recommends a Sunny Boy 4000-US with a two string, 10X configuration. The tool states I can use from 8 to 11 modules in a 2- string configuration and from 8 to 16 modules in a one sring configuration.

    Puerto Vallarta's temperature ranges from a low of 60F at night in the frigid winter to 90F during the day on August. Temperate is an understatement. ;)

    Ouside of manual calculations which would indicate I have not enough voltage to make the inverter work all the time (I have to check with the SMA rep) looks like my original plan would work. Complete beginner's luck.

    Any words of advice on the SMA tool other than check with the rep?

    Again to all, grateful doesn't begin to express how I feel about your rapid response.

    Carlos
    Are you using the on-line string calculator or their free downloadable Sunny Design tool? Sunny Design is the better tool, though it is a PC only (no Mac version).

    When a string calculator gives you a range of choices for string length, it is generally better to go with a higher number, since inverters run more efficiently with higher DC voltages. Also, as long as you don't (ever!) hit the upper voltage limit, a higher STC voltage will help keep you operating on hot days, which is especially important in climates like yours which have a lot more hot days than cold.
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    Thanks again for the tip. I just downloadad the tool Sunny Design V1.57. Puerto Vallarta is not available at as a location, so I used Honolulu, very close in climate and altitude (15 degrees versus 20 degrees for Puerto Vallarta)
    Same results. Sunny Boy 4000US-208V works.

    Here's what it spits out:
    Nominal power ratio: 89% (check mark)
    String power (input): 4.8 kW
    Power ratio (input): 100%
    String MPP Voltage at 41C : 290V (check mark)
    String MPP Voltage at 25 C: 298V (check mark)
    String MPP Voltage at 60 C: 281V (check mark)
    min. MPP voltage, set grid voltage 208V : 218V
    String open circuit voltage at 16C: 374 V (check mark)
    max. allowed DC voltage (inv): 600V
    Max. currnet of PV-generator: 16.1 A (check mark)
    the modules available to select are slightly smaller than what I have, so I used the difference in current rating to proportion and came up with 16.4 A
    Max DC current permitted 18.0A
    Number of strings (2 inputs) : 2
    Number of modules per sring min = 8 max = 16: 10
    Playing with the number of modules, the program gives no warning with 9/string and with 11/ string, but starts warnings at 8/string and 12/string

    It seems to all check out. Any comments?
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    What is your line voltage--208 or 240 vac?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need help with breakers, combiners
    cbouras wrote: »

    Max. current of PV-generator: 16.1 A (check mark)
    the modules available to select are slightly smaller than what I have, so I used the difference in current rating to proportion and came up with 16.4 A
    Max DC current permitted 18.0A

    In Sunny Design, if the specific module you want to use is not among your choices, you can add it to the database. Under the "Module type" field, click the "New module" button. That will take you to a screen where you can enter all the parameters for the module from the data sheet, and after that it will be a choice in the Module block on the PV-plant page. What you did may very well be OK, but I would run SD for the specific module just to be sure.
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    The line voltage in Mexico is 127V and is configured in star-star-delta with the stars connected to ground on the source and load sides and the delta in the terciary used for the control of harmonics and to feed distribution transformers for the sustation services and/or reactors to aid in voltage regulation. this hould yield line to line voltage of 220V
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with breakers, combiners
    cbouras wrote: »
    Mexico's line voltage is listed as 120VAC or 127VAC depending on which web site you look at.

    That would be the North American "standard" 240 VAC split.

    "Official" household Voltage standards I've seen listed in my lifetime:
    105, 107, 110, 115, 117, 120, 125, 127

    Sort of sounds like "whatever ends up coming from your outlets by the time it gets there", eh? :roll:
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    Followed advice and entered the Kyocera module in question, Sunny Design states it will work.

    The problem now is whether or not I can connect it to the Mexican grid at 127V single phase, 220V line to line. This is worth a call to SMA. It appears to support he configuration, but it auto senses 240V versus 208V, and it may just barf at 220V.

    Stay tuned
  • BB.BB. Super Moderators Posts: 26,872 admin
    Re: Need help with breakers, combiners

    127/220 does not make sense for Split phase lines... The high should be 2x the low voltage (127/254 or 110/220).

    Most US GT inverters work from 216-264 volts or so... 220 would be on the low side but still work (5 minute timeout if a heavy motor starting current drops the line below ~216 volts).

    Should be configurable by the installer to local requirements (ask SMA?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Need help with breakers, combiners

    Bill;

    Being curious I started looking in to the Mexican Voltage question. It seems it varies from place to place - and time to time. As a general rule it's the same as U.S.A. and Canada, but with some "local differences". Some of the outlets are new, 3-prong and some are old 2-prong (no ground, no polarity).

    If the Voltage is too low the inverter may decide the grid is down and disconnect.
  • cbourascbouras Registered Users Posts: 11
    Re: Need help with breakers, combiners

    I checked with SMA. They have several distributors that sell to Mexico. Sunwise in Rancho Cucamonga, CA was the one they recommended.
    The unit will work, but it needs to be adjusted by loading software into a PC and connecting through a cable, part# SB-232.
    They stated I should connect the unit and power it up, then call the distributor and they'll walk me through the process of adjusting it.
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