MPPT for high Power and high voltage in & out

wire_weaver
wire_weaver Registered Users Posts: 10 ✭
in Advanced Solar Electric Technical Forum #1
Before I set out to design my own MPPT boost/buck solar charge controller, can anyone please tell me if the following is commercially available ?

An MPPT boost/buck solar charge controller with:
400<Vin<600
0<Iin<12A
400<Vout<600
0<Iout<12A
Power rating at least 4500kW
Efficiency>98%

I have searched for quite a few hours and found NOTHING. The application is simply to add another MPPT to my SMA SMC 9000TL inverter which only has one MPPT in it. I would place it between one string and the inverter's input. At that input to the inverter there would also be another string in parallel. Currently the two strings are in parallel but aren't sufficiently well balanced for my liking despite having identical conditions and panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #2
    Re: MPPT for high Power and high voltage in & out

    About the nearest I can imagine would be to use a Grid Tied inverter connected to a pure sine wave battery connected inverter. The GT inverter would "back drive" the Off Grid inverter and recharge the battery bank. You could use step up and step down transformers (as needed) to match voltages/send power much longer distances.

    This is not a difficult setup--But there are issues with controlling the GT connection and battery charging as most back driven Off Grid Inverters will not control the battery state of charge while doing this. Xantrex/Schneider XW hybrid inverter and SMA Sunny Island do perform this function by altering the Off-Grid inverter's output frequency. The Sunny Island is probably more sophisticated in its frequency control/integration.

    Are you really looking to recharge at 480 VDC battery bank?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: MPPT for high Power and high voltage in & out

    Sounds to me like he's got two mismatched strings on a GT inverter and wants to improve things by building a separate MPPT unit to optimize panel output to the inverter.

    Personally I don't see much success coming from this. It'd be far simpler and probably cheaper and certainly less headache to change out the inverter for one with two separate inputs. Or simply add a second inverter for the other string. Or change the panels so the two strings' output was more closely matched. Or getting some of those "magic boxes" that pick an MPPT point per panel.

    Almost anything would be better than trying to build your own high Voltage buck converter and adapt it to the existing controller.

    But then I'm old and lazy. :p
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #4
    Re: MPPT for high Power and high voltage in & out

    If it is matching DC strings for a single GT inverter... I wonder if a:

    SolarMagic™ Technology Home

    or similar product would work?

    Thank you Marc, I completely misread the question.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: MPPT for high Power and high voltage in & out
    BB. wrote: »
    If it is matching DC strings for a single GT inverter... I wonder if a:

    SolarMagic™ Technology Home

    or similar product would work?

    Thank you Marc, I completely misread the question.

    -Bill

    That's the "magic box" I was trying to think of!

    Thanks, Bill; between us we have almost one whole brain. :p
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #6
    Re: MPPT for high Power and high voltage in & out

    Thanks Cariboocoot, yes you understood my requirements, my existing inverted is GT with two strings but only on MPPT (not a huge battery bank Bill :D )

    >change out the inverter for one with two separate inputs.
    I have 8.9kW of panels. A dual MPPT inverter at such high power isnt cheap.

    >Or simply add a second inverter for the other string.
    Also not cheap -at least $3500 for a 4.5kW inverter.

    >Or change the panels so the two strings' output was more closely matched.
    Not a bad idea. Even though each panel and string are the same in every respect, there is something different that must be due to mfg. tolerances.

    >Or getting some of those "magic boxes" that pick an MPPT point per panel.
    Great solution but too costly. There are 42 panels in total.

    >Almost anything would be better than trying to build your own high Voltage buck converter and adapt it to the existing controller
    these high voltage in and out MPPT tracker are at the front of every GT inverted with MPPT. THere must be many reference design circuits in the public domain. Of course I would prefer to buy than build, but nobody seems to make them - unless I cannibalise the PCBA from an existing GT inverter.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #7
    Re: MPPT for high Power and high voltage in & out

    The strings should not be that much different if they meet manufacturer's specifications.

    You may have a poor connection or bad panel somewhere.

    Are the strings mounted differently (east / west roof; one string mounted flush to roof, the other mounted off roof by >5 inches)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #8
    Re: MPPT for high Power and high voltage in & out

    There are supposed to be high-voltage MPPT charge controllers coming from 2 manufacturers. Useful for taking the high voltage input for a PV array designed for GT and using it to charge a battery bank. Someone here announced one coming from Xantrex/Schneider probably 6 months ago.

    But I just noticed you also want 400<Vout<600, which these aren't designed to do. I think they will have the usual low-voltage battery output (12/24/48 ). Do you really need a high-voltage battery bank? I have one that is 192 volts nominal and that's highly unusual even for the crowd that hangs out around here.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #9
    Re: MPPT for high Power and high voltage in & out

    wire_weaver,

    While designing and building one of these high power switchers you desire might be a very interesting and fun project, my opinion is that this is not an easy task.

    You may well have experience doing this, and have all of the test equipment needed, but, these circuits are a bit difficult to get running well enough to even see what must be done to make them better. The power levels often result in many burned-up parts, and the designer left wondering just what happened !?!!

    AND, as you probably well know, the DC voltage levels that you would be dealing with are some of the most lethal for humans.

    I agree with BB, that trying to find the problem with imbalance in the PV DC into the inverter, and correcting it seems a much better use of time. However, with 42 panels on a (or some) roof(s), trying to sort and balance the strings is no simple matter either.

    And, yes, the new Schneider XW MPPT 80 600 (did I get that right ?) is designed for 24 or 48 volt battery charging from 350-500 V PV array.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #10
    Re: MPPT for high Power and high voltage in & out
    techntrek wrote: »
    There are supposed to be high-voltage MPPT charge controllers coming from 2 manufacturers. .... I think they will have the usual low-voltage battery output (12/24/48 ). Do you really need a high-voltage battery bank? I have one that is 192 volts nominal and that's highly unusual even for the crowd that hangs out around here.

    Hi techntrek, please read my other replies, the inverter is GT, I am not going into a battery bank.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #11
    Re: MPPT for high Power and high voltage in & out
    BB. wrote: »
    If it is matching DC strings for a single GT inverter... I wonder if a:

    SolarMagic™ Technology Home

    or similar product would work?

    -Bill

    These are designed to be used one per panel. However I wanted one per string putting the voltage, current and power specs up much higher, but keeping the H/W costs much lower (should one exist commercially). In fact I'm surprised one doesn't exist in a standalone 'sub system' style design to be used for say a new inverter design by a company who doesn't want to design every subsytem of their new inverter from the ground up. This kind of MPPT is replicated millions of times over being the front end to every GT MPPT inverter on the market right now.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #12
    Re: MPPT for high Power and high voltage in & out
    Vic wrote: »
    wire_weaver,

    While designing and building one of these high power switchers you desire might be a very interesting and fun project, my opinion is that this is not an easy task.

    Good Luck, Vic

    Valid points Vic which is why I'd really like to find a commercially available one ! 2nd option is to cannibalise a 5000kW GT inverter, removing its MPPT and using that.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #13
    Re: MPPT for high Power and high voltage in & out
    BB. wrote: »
    The strings should not be that much different if they meet manufacturer's specifications.

    You may have a poor connection or bad panel somewhere.

    Are the strings mounted differently (east / west roof; one string mounted flush to roof, the other mounted off roof by >5 inches)?

    -Bill
    Good point Bill. Strings are identical in every respect. Orientation, height of roof, angle of inclination, mfg part number, amount of sun.

    17 of the panels were purchased about 8 months after the first 25 panels so there might be minor mfg differences being amplified by the sheer quantity of panels I have.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #14
    Re: MPPT for high Power and high voltage in & out

    What is the electrical/miss-match problem as you see it?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #15
    Re: MPPT for high Power and high voltage in & out
    BB. wrote: »
    What is the electrical/miss-match problem as you see it?

    -Bill

    I re-checked my readings. I incorrectly suggested that direct sun on all panels resulted in a large mismatch btwn strings. With full sun the most I see is one string down by about 5% (e.g. one string supplies 8A, the other 8.4A (both at say 400V).) I can probably live with that. (considering I have a very generous gross FIT right now of A$0.60/kWh for the next 5.5 years)

    However at certain times of the day a tree shades about 1/3rd of three of the 21 panels of one string. This produces a much greater mismatch where the shaded string is down by at least 20% from memory. when at most it should be down ((3/21)*100)/2 % =7% because there are two bypass diodes per panel and the shade is on the lower third when the panels are in portrait orientation.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #16
    Re: MPPT for high Power and high voltage in & out
    wire_weaver wrote: »
    I re-checked my readings. I incorrectly suggested that direct sun on all panels resulted in a large mismatch btwn strings. With full sun the most I see is one string down by about 5% (e.g. one string supplies 8A, the other 8.4A (both at say 400V).) I can probably live with that. (considering I have a very generous gross FIT right now of A$0.60/kWh for the next 5.5 years)

    However at certain times of the day a tree shades about 1/3rd of three of the 21 panels of one string. This produces a much greater mismatch where the shaded string is down by at least 20% from memory. when at most it should be down ((3/21)*100)/2 % =7% because there are two bypass diodes per panel and the shade is on the lower third when the panels are in portrait orientation.
    Cut down the tree or move the array. Too obvious? :p
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #17
    Re: MPPT for high Power and high voltage in & out
    wire_weaver wrote: »
    Hi techntrek, please read my other replies, the inverter is GT, I am not going into a battery bank.

    Your original post is ambiguous, you mention GT but you also say "MPPT boost/buck solar charge controller". A charge controller is only for batteries, so that's the direction I went. 8)
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #18
    Re: MPPT for high Power and high voltage in & out

    As you can see, shading causes serious power losses for a solar PV array--especially shading panels in a parallel string setup.

    You could rewire the strings so that each string shares the shading. Or, you should really consider cutting the tree(s). The shading will will probably only get worse over time as the tree(s) continue to grow.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #19
    Re: MPPT for high Power and high voltage in & out
    ggunn wrote: »
    Cut down the tree or move the array. Too obvious? :p

    Local laws prohibit me from cutting down more than 15% of a tree each year ! It would only re-grow by at least that amount anyway. Furthermore it is a council owned tree, not one I planted, making it harder to justify lopping it. You can see it at the top middle of the attached photo. Believe it or not, when I designed the PV sytem, I used Google Sketchup to simulate the shadows from that tree falling onto the panels and it didn't prove a problem. Then I discovered a bug in Google Sketchup which meant the timestamp it used was 2 hours out !! Grrr.... At least the problem only exists for a few months of the year each winter time. Note I pre-emptively trimmed some of my pergola to remove shadows based on the simulation using sketchup.

    As for the idea of moving the panels - no chance !! I have maxed out all the available space on my home's roof facing NNE !

    Attachment not found.

    Attachment not found.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #20
    Re: MPPT for high Power and high voltage in & out
    BB. wrote: »
    As you can see, shading causes serious power losses for a solar PV array--especially shading panels in a parallel string setup.

    -Bill

    Thanks Bill, see my last post with photos.
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  • wire_weaver
    wire_weaver Registered Users Posts: 10 ✭
    #21
    Re: MPPT for high Power and high voltage in & out
    techntrek wrote: »
    Your original post is ambiguous, you mention GT but you also say "MPPT boost/buck solar charge controller". A charge controller is only for batteries, so that's the direction I went. 8)

    Mmm.. I understand the confusion. sorry, my fault. I should have deleted the words "charge controller". the buck/boost is still applicable.
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