DC - Coupled system using Thinfilm Modules and Schneider Charge Controller

Hi,

I had a query about the design of a DC-coupled Solar PV System that incorporates the Solar Charge controller, Conext MPPT 60 150 along with Schnieder Conext XW+ 8548 E inverter/charger.

The maximum input voltage (temperature corrected), of the charge controller, is 150V as per the data sheet. We’re using First Solar 117.5W PV Modules (Thin film Cd-Te). The Open-circuit Voltage of one such module, at STC, is 88.2V (and 1.79A Isc) and after Temperature correction becomes 96V. This leads us to designing a string that only has one PV Module in series while around 27 PV modules in parallel – for one charge controller.

Physically, the PV Source circuit will require a combiner box where 27 Positive and 27 Negative wires from each module will be combined (parallel connection) to form a single positive and a single negative output that will be fed into the Charge controller.

The total Open-Circuit (temp corrected) Voltage of the string will then be 96V and the total Short-Circuit current will be (1.79 x 1.25 x 27) 60.4A.

My question about the mentioned design is, is this the standard way of designing a DC-coupled system with this Charge Controller and PV Module (Thin Film – CdTe), that results in such a high current and a huge number of conductors to be run through the conduits and combined at the Combiner Box? Is there any standard or Best practice in the industry that recommends Design and Implementation of the System using the mentioned methods?

I am looking for an international standard or a best practice to benchmark this design and its implementation so as to eliminate any efficiency and safety hazards.

Your help is much appreciated.

Regards

 

Jahanzeb Tariq

Comments

  • BB.BB. Super Moderators Posts: 26,758 admin
    This is one reason why it is really nice to use larger solar panels (>200 watt vs your 117 Watt panels). If you used ~300+ Watt panels, you would have almost 1/3rd the wiring connections (and using 4 amp circuit breakers/fuses at the combiner box, one per panel).

    Another question is what voltage is your battery bank? The Vmp rating of your panels is ~71 volts and ~66 volts NOCT (rated operating voltage at typical temperatures).

    http://www.firstsolar.com/-/media/First-Solar/Technical-Documents/Series-4-Datasheets/Series-4V2-Datasheet.ashx

    If you have a 48 volt battery bank and are in a hot climate (Islamabad Pakistan?), that is very close to not being high enough voltage to properly charge a 48 volt Lead Acid battery bank.

    There are other models of charge controllers with higher maximum input voltage (Schneider, and a couple other manufacturers, have 600 volt Max input voltage units which could take ~5 panels in series per string) which would reduce the number of parallel connection.

    Unless you have a 24 or 12 volt battery bank, I would be very concerned that your present design is not going to work out well for you.

    Also note that First Solar panels are a Cadmium based design. You (probably) will have to recycle them with somebody who can properly recycle them. Many countries are very concerned about Cadmium being dumped in garbage pits contaminating water supplies.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolraySolray Registered Users Posts: 246 ✭✭
    Can't you use some y connectors to join panels instead of feed all separately?
  • littleharbor2littleharbor2 Solar Expert Posts: 635 ✭✭✭✭
    A Midnite Classic 250 will handle 2 in series strings with room to spare. A Classic 200 would work on a 48 volt system with it's HyperVOC feature.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • BB.BB. Super Moderators Posts: 26,758 admin
    No, Y connectors will not work--Or at best, only work for the "return/common" side of the connection. The "hot side" will always need 4 amp fuse/breaker per panel (for safety). Typically used when 3 or more strings are in parallel).

    Plus the "down stream" side of the "4 amp" Y connection needs to manage >60 amps--Pretty specialized or needs a bus bar anyway (the Y connection is typically rated for 15 amps or so for MC4 connectors).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolraySolray Registered Users Posts: 246 ✭✭
    edited July 19 #6
    I think you missed the point there. If a panel can safely put 300 watts into a connector, can't you use a 'y' between 2 150 watt panels just as safely? Isn't the 300 watt panel just twice the power output of the 150 watt panels? By grouping 2 panels together into half as many double power panels, you cut the connections at the combiner in half. If it wasn't possible, a 300 watt panel would not be possible either.
    I am not suggesting to couple all the panels to a single line in.
  • BB.BB. Super Moderators Posts: 26,758 admin
    edited July 19 #7
    Solray,

    How did I miss the point? They are paralleling 27 panels at almost 2 amps each.

    The panels need at least one over current protection per parallel connection (some recommend 2x OCP pet string (one on + and the second on - lead).

    They still need a combiner box for fusing anyway. And they usually have bus bars too.

    You can get variations of fused MC4 connectors. Not sure I have seen any fused Y connectors with the ability to parallel almost 30 connections with 30 strings.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolraySolray Registered Users Posts: 246 ✭✭
    That's the point you missed, only connect 2 panels, not all into a giant y connector. lol that would be foolish and I find it hard to believe you actually thought that would be suggested. Connect 2 panels and run those to a combiner, then 2 more together and run those into a combiner, etc. until all have been run to the combiner 2x2 to eliminate 1/2 of the wires to the combiner.
    Now do you see?
  • BB.BB. Super Moderators Posts: 26,758 admin
    edited July 19 #9
    It would reduce 1/4 of the wiring (assuming OCP per + lead and 1x Y connector per - lead).

    An Mc4 y connector is around $16 for connector + extra jumper cable (jumper from Y to bus bar, of that is what is wanted). Vs around 2x $6 for two jumpers (mc4 to bus bar).

    At best, about a wash (cheaper cabling + 2x more bus bar connections) vs Y solution.

    Of course, depends if installer will crimp their own connections or buy off the shelf.

    And the positive bus bar connections are still 27+ connections, and ground bus usually is the same size.

    I always suggest costing out several paper designs before buying/building the system.

    I believe the original poster is in Pakistan, so his local costs / availability may be different.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SolraySolray Registered Users Posts: 246 ✭✭
    edited July 19 #10
    I was thinking about easier, not cheaper. lol I don't normally do cheaper but I understand some people do. There are always other sources than buying all brand new parts as well, there are cheaper routes to the same gear if one is enterprising enough and has more time than money.
    Fair enough, it was just one possible suggestion, no need for you to try to shoot it down, it was out there for the OP, not you necessarily.

    Thanks anyways.
  • mike95490mike95490 Solar Expert Posts: 7,249 ✭✭✭✭
    Sadly, the lifetime of the Cd-Te cells is woefully short.   If it's at all possible, return them and rethink your design.  27 parallel panels is going to be a mess to wire safely with a lot of circuit breakers and enclosures.
    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 ,

  • SolraySolray Registered Users Posts: 246 ✭✭
    mike95490 said:
    Sadly, the lifetime of the Cd-Te cells is woefully short.   If it's at all possible, return them and rethink your design.  27 parallel panels is going to be a mess to wire safely with a lot of circuit breakers and enclosures.
    What is your source for this? Do you have any actual studies that confirm it?
  • mike95490mike95490 Solar Expert Posts: 7,249 ✭✭✭✭
    Thin film panels are cheap and have a quick payback period, but annual degradation is higher than mono or poly  panels.  All the ads talk about 20yr lifetimes, but what does the fine print on the warranty say - something like 80% of -2% of yearly loss, lots of wiggle room to not cover warranty.  Or just trust the salesman.

    http://www.nrel.gov/docs/fy12osti/51664.pdf   page 6, third table c   1-1.5% per year vs .5-.7% for Si.
    Thin-film degradation rates have improved significantly during the last decade, although they are statistically closer to 1%/year than to the 0·5%/year necessary to meet the 25-year commercial warranties.


    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 ,

  • SolraySolray Registered Users Posts: 246 ✭✭
    edited July 21 #14
    Did you happen to notice the disclaimer that basically says the information might or might not be accurate? In other words, it might just be a lot of nonsense.

    "This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof."

    It's also 5 years old and things in tech change a lot in that time.
    This is pretty much an irrelevant document now, even if it were true then, and there is nothing in it that says it was ever true.
  • SolraySolray Registered Users Posts: 246 ✭✭
    Solray said:
    I was thinking about easier, not cheaper. lol I don't normally do cheaper but I understand some people do. There are always other sources than buying all brand new parts as well, there are cheaper routes to the same gear if one is enterprising enough and has more time than money.
    Fair enough, it was just one possible suggestion, no need for you to try to shoot it down, it was out there for the OP, not you necessarily.

    Thanks anyways.
    LOL why would someone flag this post? Ridiculous. I have friends that go to wrecking yards for car parts and save a lot that way. There are also a lot of companies going out of business and selling solar gear for pennies on the dollar every day.
    Why would anyone be against people without a lot of money trying to save what they have?
    It boggles the mind.
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