Charge Controller Rating Selection

mereldamerelda Registered Users Posts: 7
Hi All,

I have a 30kW solar array, and a bunch of 12V, 680Ah batteries for a standalone PV system. The array to battery controller distance should be less than 30m.
I thought of two configurations to connect the battery charger controller, but not sure which one is better:

1. 240Vdc, 140A = 1 30kW charger controller
2. 48Vdc, 50A = 16 2.4kW charger controller

For option 1, the controller I found is Phocos SPS 48D300
http://www.sunshineworks.com/charge-controllers/sps/phocos_datasheet_SPS_series_e.pdf

For option 2, the controller I found is SMA Charger 50
http://files.sma.de/dl/14117/SICHARGER50-DEN122511W.pdf

I am trying to base my design decision on price, efficiency and safety, but I'm struggling to find the price for either one, so the above is all the information I have currently.

Any input is appreciated, thanks so much!

Merelda.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge Controller Rating Selection

    Merelda;

    The terminology you're using is a bit off for the way charge controllers are evaluated. A controller will have these important specifications:

    Maximum Output Current
    Nominal System Voltage(s)
    Maximum Input Voltage
    Function type (MPPT or PWM)

    If your total battery bank is 680 Amp hours @ 48 Volts nominal you'd be looking for a controller capable of around 68 Amps output. This would be something like an Outback FM80 or MidNite Classic 150. Both of these are able to do up to 80 Amps on 12, 24, or 48 Volt systems, have a maximum input of 150 VDC (with the Classic capable of handling more), and are of the MPPT type.

    Let's look at the two you've linked to:
    1). Insufficient information available. It only lists output specs of up to 300 Amps on 12 Volts, which is incredibly high. This is evidently a special-application controller.
    2). Output current is 50 Amps (low for 680 Amp hour batteries) @ 12, 24, or 48 Volts, maximum input Voltage 140, is an MPPT type controller.

    I don't think you'd be happy with either of these controllers. It may be necessary for you to go the extra mile and import a MidNite from the USA.

    That 30 meters from array to charge controller will be a problem; you will definitely want to run a higher array Voltage to overcome this. BTW, you are looking at about a 4kW array for that size battery bank.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Charge Controller Rating Selection

    Hi again Merelda,

    Based on the information in your other thread, you're talking about a 30kW PV system and a consumption of 150kWh/day. Most battery based inverters can't handle a battery with a higher voltage than 48V (*). So you're limited to using 48V for the battery. For 1 day of storage and a 50% Depth of Discharge you're looking at 6250Ah battery. What's more is that it's not really recommended to parallel batteries, so much better if you can get 24 x 2V cells with a capacity of 6200Ah, now those might be hard to find, so you could parallel 2 strings of 24 x 2V 3100Ah cells. If you search for "OPzS batteries" you'll find manufacturers who sell batteries of this size.

    If you have a 48V battery, then your charge controller will also be limited to 48V.
    Popular choices are: 90 Amp midnite solar classic charge controller, 80A Outback FM charge controller. The SMA charger is really unreasonably priced compared to it's size and the competition.
    With 30kW of PV and charging at 48V that'll be 625A, so if you went with the 90A midnite you'd need 7 of them.

    (*) I only know of 1 off-grid system that works with a higher than 48V battery, which is the Ingecon Hybrid: http://www.ingeteam.com/EN/ProductsandServices/Energy/Photovoltaic/Products.aspx?TIPO=PTD&ITEMID=22&IDIOMA=EN&PRT=SBP&PRTID=2 from a Spanish company. It has everything included, MPPT, inverter and charger as a single unit all you need to add is batteries and panels.
  • mereldamerelda Registered Users Posts: 7
    Re: Charge Controller Rating Selection

    Hi,

    Thanks for the detailed response :)

    If I use a midnite classic 150, with the 3100Ah OPzS batteries you recommend then it should be alright?
    I found that for C120 batteries the charging current can vary between 0.5 - 50 A, does the charge controller regulate the charging current and voltage together, so I won't have to worry about slow charging or even unable to charge the batteries at all?

    And also, from the diagram I got from the midnite website, the inverter and mppt are combined.
    http://www.midnitesolar.com/pdfs/offGrid.pdf
    How come in my application I need to separate the two?

    Please see the photo for my understanding of my system topology...
    https://www.dropbox.com/s/76fqtigpoo9anfx/toplogy.jpg
    Apologies for the bad hand-drawn quality..

    Thanks very much!
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Charge Controller Rating Selection
    merelda wrote: »
    If I use a midnite classic 150, with the 3100Ah OPzS batteries you recommend then it should be alright?

    Yep, 7 of them should do the trick. Before you dive in, check with the techs at midnite solar (they have a forum) whether you can expect any issues with 7 of them in parallel. In theory it should be fine, but their controller is relatively new so best to double check. If this is just for economic viability analysis then you can assume they'll work, 'cause if they don't then you can just put 8 x outback 80A controllers :)
    merelda wrote: »
    I found that for C120 batteries the charging current can vary between 0.5 - 50 A, does the charge controller regulate the charging current and voltage together, so I won't have to worry about slow charging or even unable to charge the batteries at all?

    Yep, the charge controllers will take care of regulating voltage and current automatically.
    In your diagram looks like you have a 20kW generator, but then 19.5kW available on each of the phases? So I assume it's a 60kW gen with 20kW on each phase(?) Looks like you only want the sunny islands to provide 15kW on one of the phases? The SI's support 3 phase operation so you can stick one on each phase if you like.

    The 5kW SI's have a 56A internal transfer relay, so each can accept 12kW from a generator phase connected behind this relay. Which would leave you a bit short. So the options are:
    a) Use 6 x 5kW SI's, 2 per phase then connect the generator through the transfer relay.
    b) Do it as you've done in the diagram with the SI's on only a single phase
    c) Use 1 x 5kW per phase, and use a synchronous generator on the AC output side. The generator must disconnect from the AC bus if there's overfrequency on the bus! and it MUST be able to synch to an existing grid. SMA have examples of this setup in their literature but is by no means "standard".

    In all the options, the SI's can support the gen power. So for option a) you'll have 2 x 5kW + 20kW available on each phase. Option b) with the generator on, you'll have 15kW + 20kW available on phase 1 and 20kW on the other phases.

    Since you're not AC coupling the solar panels, you can also use any of the modern inverters that can be paralleled, e.g. Xantrex XW, Victron Multiplus/Quatro, Studer XTM, maybe outback (don't know if they can scale to 15kW?) - instead of the SI. Given the size of the gen, the victron quatro inverters could be interesting because they have 2 x 100A internal relays each, so you could connect up to a 138kW genset behind 3 of them and still use their internal transfer relays.
    Nice brochure of some of their setups: http://www.victronenergy.com/upload/documents/Brochure%20-%20Off-Grid,%20back-up%20and%20island%20systems_rev%2006_EN_web.pdf
    merelda wrote: »
    And also, from the diagram I got from the midnite website, the inverter and mppt are combined.
    http://www.midnitesolar.com/pdfs/offGrid.pdf
    How come in my application I need to separate the two?

    The unit on the left is an outback inverter, the one on the right is a midnite charge controller, they're just both mounted together on a midnite E-panel. You'd have to buy them as separate units and do the mounting.
  • mereldamerelda Registered Users Posts: 7
    Re: Charge Controller Rating Selection

    Oh yes, I need to have 20kW on each phase.
    But when I'm reading another thread on this forum I realised that the generator needs to supply high enough current to charge the battery.
    And the charging current is suggested to be 10% of the battery Ah.
    But since I have 90A charge controllers, does it mean that the current to charge the battery is "shared" between the charger?
    So how do I select my generator then?

    I actually want to have a balanced three phase, with each phase having 19.5kW.
    So I want all three phases to be powered by the panels (and batteries) majority of the time, but if it isn't enough then the generators come into help.
    If I'm not mistaken, only sunny tripower support three phase with a single unit? But their MPP voltage is at 320V.
    In the datasheet of SI 5048, for 3 phase operations they have 3 SI5048 units?

    I looked at the brochure, and I think Quatro goes up to 10kVA, so I need to parallel two to get 20kVA, and further parallel 3 for 3 phase (6 in total)?
    And for 10kVA quartro the charging current is 140A, so go back to my first question... Will this be enough?

    Would it be possible for you to point out what kind of diesel generator I should be looking at?

    Thank you for the detailed explaination!!!
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Charge Controller Rating Selection
    merelda wrote: »
    Oh yes, I need to have 20kW on each phase.
    But when I'm reading another thread on this forum I realised that the generator needs to supply high enough current to charge the battery.
    And the charging current is suggested to be 10% of the battery Ah.
    But since I have 90A charge controllers, does it mean that the current to charge the battery is "shared" between the charger?

    The generator charges the batteries through the inverter/charger unit (Sunny Island or Victron quatro, etc). The midnite charge controllers are just used to charge from the solar panels. You should size the generator based on the maximum expected peak power expected and the average charging current of the inverter/charger. Each 5kW sunny island has a 100A charger, so 4800W each (140A charger in the 10kW quatros). You have some leeway in deciding on the genset, too small and it'll have to run for a long time to charge the batts- too large and it becomes inefficient and a money pit. There have been some discussions on this forum about it, try a search for "generator sizing".
    merelda wrote: »
    I actually want to have a balanced three phase, with each phase having 19.5kW.
    So I want all three phases to be powered by the panels (and batteries) majority of the time, but if it isn't enough then the generators come into help.
    If I'm not mistaken, only sunny tripower support three phase with a single unit? But their MPP voltage is at 320V.
    In the datasheet of SI 5048, for 3 phase operations they have 3 SI5048 units?

    First things first, the sunny tripower is a grid tied inverter, not a battery inverter. If you're going for a DC system like this with midnite controllers then you don't need a grid tied inverter. All battery inverters can support more than their rated output for a given period of time, e.g. the 5kW sunny island can do 12000W for 3 seconds and 8400W for 1 minute. So you can think about your 20kW load and work out how many inverters you'll need per-phase to support that. If it's 20kW peak for 1 second then you just need 2 SI per phase, if it's 20kW constant output, then you'll need 4 per phase.
    merelda wrote: »
    I looked at the brochure, and I think Quatro goes up to 10kVA, so I need to parallel two to get 20kVA, and further parallel 3 for 3 phase (6 in total)?
    And for 10kVA quartro the charging current is 140A, so go back to my first question... Will this be enough?

    Yep, 6 in total if you want 20kW constant on each phase, but as I said above if the 20kW isn't constant but very short peaks then you might be able to get away with just 1 per phase.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charge Controller Rating Selection

    Well let's see.
    You need 3 phase power, 20kW per phase.
    A Sunny Island is 5kW, so it falls a bit short. In fact most inverters do. This looks like a question to ask companies like Outback to see if their Radian 8kW inverters can be in a stacked configuration of 3 x 3 for 24kW 3 phase AC out (they're fairly new and I'm not familiar with them).
    If I'm not mistaken, only sunny tripower support three phase with a single unit? But their MPP voltage is at 320V.

    Sounds like you're confusing GT inverters with OG inverters again. A battery-based inverter doesn't have a MPP Voltage.

    As for charging, don't get the charge controllers for the PV's confused with the chargers built-in to some inverters. Generator would power the inverter/charger; this has nothing to do with the charge controller (except for having the same charge set points).

    You can connect multiple charge sources to the same battery bank. In the case of the two 90 Amp charge controllers, the array is divided up with each controller handling 1/2 the panels. Don't connect the controller inputs together; only the outputs.

    You are going to need a generator capable of power loads plus the charging circuits as needed. This will be a very big generator along the lines of 20kW 208 VAC 3-phase. That is way out of my range of experience, but there's probably someone here familiar with such units.
  • mereldamerelda Registered Users Posts: 7
    Re: Charge Controller Rating Selection

    Hi,

    Thanks for the reply, sorry that I got OG and GT inverters confused again..

    The thread I read concluded that sizing the generator depends on:
    (a) Load Consumption, which according to my 15-min interval logger is 16kW for a maximum of 15 minutes.
    (b) Charging current, which is either 100A (SI) or 140A (Quatro)

    I found this 3 phase, 20kW (230V, 50Hz) Perkins generator for just over $8000
    http://www.hardydiesel.com/downloads/perkins-404d-22g.pdf
    It will be alright though?

    And lastly, would it be better to use sunny island or quatro?
    Quatro comes out to be about 8% cheaper than SI.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Charge Controller Rating Selection

    I thought you said 20kW per phase? So then you need a 60kW gen. Don't really know much about these industrial sized units, other than you should get a 1500rpm version and motor from a well known manufacturer like Perkins, Cummins, Volvo.

    Regarding SI or quatro, 8% is not much.
    Investigate who will give you better service for warranty, how long will replacements take, can you phone up and talk to an engineer quickly etc.
    SMA also do a pre-wired pre-configured box with multiple SI's in it, called a multicluster which could be another option (no idea about pricing): http://www.sma.de/en/products/off-grid-inverters/multicluster-boxes-for-sunny-island.html
  • BB.BB. Super Moderators, Administrators Posts: 29,511 admin
    Re: Charge Controller Rating Selection

    Check the features and support for any major product you purchase... 8% is not a big enough number (in my humble opinion) vs your overall costs to make that a top reason for A or B product.

    One thing to check with about integrated inverter/chargers... Many will let you program the maximum input current (say 30 amps) from the generator--Then vary the charger current and cut back on battery charging if your overall AC loads nears the 30 amp (AC input current) limit. This could help keep the generator size down and let you run at >50% rated power for more of the running time.

    By the way, this is a large system--And while we are all ready to help, in the end, you might need the help of a knowledgeable system engineer/integrator to make sure your final system will operate reliably and meet your needs.

    Asking questions here can help you when talking with the various suppliers so that you are all speaking the same language and you have most of your needs already documented.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Charge Controller Rating Selection
    BB. wrote: »
    By the way, this is a large system--And while we are all ready to help, in the end, you might need the help of a knowledgeable system engineer/integrator to make sure your final system will operate reliably and meet your needs.
    Asking questions here can help you when talking with the various suppliers so that you are all speaking the same language and you have most of your needs already documented.

    2 x what Bill said 8)
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