MPPT stepdown efficiency

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Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: MPPT stepdown efficiency

    You will get over an 18% Voc hike at -30 deg C.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: MPPT stepdown efficiency

    RC, If I am reading the online version of Outbacks calculator, I get 112V Vtoc from a 72 v configuration. a 55% increase! Is it possible to go over that ?

    OB now wants you to send them the spec sheet for your panel(s) :cry: and they will grind the numbers... and , I hope email a report. Sent in Sat. , waiting for it to come ...

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: MPPT stepdown efficiency

    funny I actually logged on today to start a thread about the efficiency of my flexmax, but I find the discussion already in progress. my brother is looking into getting 4 pallets of the kaneka panels that I just bought, so he had me running mine in various configurations through my flexmax 80, so he could get some numbers to crunch for his system. I noticed that my efficiency seemed low, and so today i finally got around to actually checking it out more thoroughly.

    in order to be sure I got the numbers right I took my camera and snapped some pics of the display
    then I crunched the numbers to determine my controllers efficiency

    boy was I disappointed!

    in 64.6v 12.7a = 820.42w
    out 13.1v 53.8a = 704.78w

    85.904% eff

    in 63.2v 12.8a = 808.96w
    out 13.0v 53.8a = 699.4w

    86.456% eff

    in 64.4v 12.8a = 824.32w
    out 13.1v 53.8a = 704.78w

    85.498% eff

    in 64.0v 13.0a = 832w
    out 13.1v 53.0a = 694.3w

    83.449% eff

    the power curve in the owners manual lists 68volts input at 850 watts at or above 93% efficient.

    fyi my controller was in a room that was 50 degrees f at the time the pics were taken and the cooling fan on the controller was not running

    I AM REALLY GETTING TIRED OF BEING LIED TO BY MANUFACTURES!!

    I would love to see real world numbers from all the controllers out there, so if anyone has the time (and camera) please snap some pics and crunch some numbers, lets get some real stats. not pr firm bs.

    also if anyone else has a similar setup flexmax, lets compare numbers, I would love to know if my experience is a fluke.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MPPT stepdown efficiency

    wild01, you're putting 60 V in at the array to charge a 12 V system, right? In Outback's defense I have to point out that they do mention efficiency dropping with greater difference between array and system Voltage. The rule-of-thumb is to use an nominal array Voltage 'one step up' from the system Voltage. For 12V, that's a 24V array.

    But you're quite right about efficiencies not being up-to-snuff. Part of it is the lab conditions that things are rated under don't exist in the real world. The manufacturers (and not just OB) will go on about temp, humidity, wire sizing, even torque on connectors as being factors. This is why we think we're doing good to get 50% equivalent power out the AC end. :cry:

    What's worse is that those numbers on your FM's screen aren't accurate. Solar Guppy can tell you just how 'optimistic' OB readings can be.

    But we do the best we can with what we've got, eh?
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: MPPT stepdown efficiency
    wild01, you're putting 60 V in at the array to charge a 12 V system, right? In Outback's defense I have to point out that they do mention efficiency dropping with greater difference between array and system Voltage. The rule-of-thumb is to use an nominal array Voltage 'one step up' from the system Voltage. For 12V, that's a 24V array.

    But you're quite right about efficiencies not being up-to-snuff. Part of it is the lab conditions that things are rated under don't exist in the real world. The manufacturers (and not just OB) will go on about temp, humidity, wire sizing, even torque on connectors as being factors. This is why we think we're doing good to get 50% equivalent power out the AC end. :cry:

    What's worse is that those numbers on your FM's screen aren't accurate. Solar Guppy can tell you just how 'optimistic' OB readings can be.

    But we do the best we can with what we've got, eh?


    oh I get that I won't get great efficency going from 60 to 12, I don't expect "great" efficiency, I do however expect my controller to perform as well as the manual says it will. (the manual shows that if I went with a 24v(34v) nom sys, my eff would be 94-95% and at a 48v (68v) 93-94%)

    as far as the readings on the screen being off, while I realize that the fm isn't known for being calibrated all that great, the calibration should be the same for input and output, so while yes I may not actually be getting 50 amps etc, the % eff should be the same (or so I understand it)


    I realize that the industry inflates certain claims, but at least with panels it's predictable, there are charts to tell you what is actually likely for your installation and the panel will actually put out what it says it will in the light intensity that it was tested at! granted most us locations don't receive that kind of light but some do (at 7800ft where I live the panels actually perform as rated if not better, of course I can also get a sunburn in 10 minutes on a cloudy day here)

    There's no reason for a controller to not perform up to it's listed efficiency. either the controllers being sold aren't made as well as the ones being tested, or the tests are being faked. (or I got a crummy controller that is performing at less than spec) this is INTERNAL efficiency we're talking about, so nothing about the install should effect it. granted temp could as could humidity, but neither of those were a factor this morning when I snapped those pictures.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: MPPT stepdown efficiency
    wild01 wrote: »
    as far as the readings on the screen being off, while I realize that the fm isn't known for being calibrated all that great, the calibration should be the same for input and output, so while yes I may not actually be getting 50 amps etc, the % eff should be the same (or so I understand it)

    Nope, there is NO current measurement on the input on either the MX or FM Outback chargers. The values shown on the LCD for input are 100% made up by the software.

    The Xantrex XW-Mppt is the only controller with 1% shunts and current measurement for input and output current.

    The MorningStar Has both input and output current, but the input is not very accurate as it only intended use is for the software for calculating vmp , a relative task, not absolute in accuracy required ( reported current )
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: MPPT stepdown efficiency
    Nope, there is NO current measurement on the input on either the MX or FM Outback chargers. The values shown on the LCD for input are 100% made up by the software.

    The Xantrex XW-Mppt is the only controller with 1% shunts and current measurement for input and output current.

    The MorningStar Has both input and output current, but the input is not very accurate as it only intended use is for the software for calculating vmp , a relative task, no absolute in accuracy required.
    Wow, another thing I did not know about the XW - I should read this forum more often ;)

    It is my understanding that the Morningstar controllers use a computed only value for the input current display ?
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: MPPT stepdown efficiency
    Nope, there is NO current measurement on the input on either the MX or FM Outback chargers. The values shown on the LCD for input are 100% made up by the software.

    The Xantrex XW-Mppt is the only controller with 1% shunts and current measurement for input and output current.

    The MorningStar Has both input and output current, but the input is not very accurate as it only intended use is for the software for calculating vmp , a relative task, not absolute in accuracy required ( reported current )

    huh, wow, now I'm really confused!
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: MPPT stepdown efficiency

    The TriStar does not display input current on the LCD, its a real measured value, just not high tolerance. This is noted in the manual

    On the MorningStar TriStar Mppt, the resistance of the input FETs is measured for the input current sense, this saves the power loss of a shunt, lower internal heat and short paths into and out of the PCB. Since the MS units do full sweeps in 300ms to find the vmp point, the tolerance isn't an issue and allows very accurate performance with even severe AC ripple on the output ( the dsp in realtime compensates and yields a near DC input current value )
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: MPPT stepdown efficiency
    Windsun wrote: »
    Wow, another thing I did not know about the XW - I should read this forum more often ;)

    It is my understanding that the Morningstar controllers use a computed only value for the input current display ?

    The XW-CC shunts (resistors) are also low side sensing, which is the "easy" way out of measuring input and output current. Doesn't matter if the resistors or shunts are 1%, 0.1% or 10%... As long as they don't drift with temperature or current, the circuitry can (theoretically) be adjusted to be accurate (as long as the circuitry around it allows it)

    PS, never rely on the controllers' meters themselves to measure converter efficiency. Efficiency is very hard to measure accurately, let alone using meters on a product, I don't care who's controller they are.

    Those MF/MX efficiencies are also done at higher power rather than lower power levels.

    boB
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: MPPT stepdown efficiency
    The TriStar does not display input current on the LCD, its a real measured value, just not high tolerance. This is noted in the manual

    On the MorningStar TriStar Mppt, the resistance of the input FETs is measured for the input current sense, this saves the power loss of a shunt, lower internal heat and short paths into and out of the PCB. Since the MS units do full sweeps in 300ms to find the vmp point, the tolerance isn't an issue and allows very accurate performance with even severe AC ripple on the output ( the dsp in realtime compensates and yields a near DC input current value )

    This is the display I was referring to, not the LCD obe, I was not very clear
    http://www.morningstarcorp.com/en/demos/tsmppt/liveview.html
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: MPPT stepdown efficiency

    Well, I've often wondered how anyone could develop solar equipment in the pacific nw and have any idea how it would perform if hooked up to something that was actually exposed to sunlight. :roll:

    when I'm working up there people always ask me what I think about them putting in solar, and I have to explain to them the concept of sunlight being a necessary element in the equation.
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: MPPT stepdown efficiency
    wild01 wrote: »
    Well, I've often wondered how anyone could develop solar equipment in the pacific nw and have any idea how it would perform if hooked up to something that was actually exposed to sunlight. :roll:

    This is why boB came out to my place in Maine for a while to find some sun.
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: MPPT stepdown efficiency

    yeah I guess I just don't understand why solar equipment developers don't just move here and develop their products in an environment suited to solar. I mean I'm 20 miles from the largest solar power plant in north america and I have literally hundreds of offgrid neighbors, and most of the percision electronics that control my system were designed in one of the cloudiest rainiest places in the world.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: MPPT stepdown efficiency
    wild01 wrote: »
    yeah I guess I just don't understand why solar equipment developers don't just move here and develop their products in an environment suited to solar. I mean I'm 20 miles from the largest solar power plant in north america and I have literally hundreds of offgrid neighbors, and most of the percision electronics that control my system were designed in one of the cloudiest rainiest places in the world.

    I think that's called a "Labor of Love" and craftsmanship.
    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 ,

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: MPPT stepdown efficiency

    But you want to design solar equipment in places where sunlight is rare; it gives the designers a challenge!
    I hear Midnight Solar is planning an R&D department on the dark side of the moon. :p
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: MPPT stepdown efficiency
    On the MorningStar TriStar Mppt, the resistance of the input FETs is measured for the input current sense, this saves the power loss of a shunt, lower internal heat and short paths into and out of the PCB.

    I'm surprised that route was taken, given the resistance variance even between FETs from the same lot...and not taking into account the 2:1 difference (or worse) that temperature changes may cause. Does than mean that the calculated Vmp is going to drift with temperature, or is there compensation?

    Marc
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: MPPT stepdown efficiency
    lorelec wrote: »
    I'm surprised that route was taken, given the resistance variance even between FETs from the same lot...and not taking into account the 2:1 difference (or worse) that temperature changes may cause. Does than mean that the calculated Vmp is going to drift with temperature, or is there compensation?

    Marc


    I think that Henry meant to say that they measure the voltage across the FETs, rather than the actual resistance of the FETs. That should work just fine since they don't need it for an accurate current they are going to report back to the user.

    boB
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: MPPT stepdown efficiency

    You both have it right, its the voltage drop and its a relative value. Accuracy does change over temperature, but the vmp sweeps are done every few minutes and it is only during the sweep ( which is only three tenths of one second ) the current value is used, so changing over time has no effect. I'll check on the webpage value reported for input current, but I'm pretty sure its a software computed value, not measured. Even if the MS unit had a precision input current sense, with its performance capable of better than 99% efficiency its beyond measuring unless you have calibrated power analyzers, it was a major pain for me even testing with the Yokogawa's

    There are other things done that are proprietary in the mppt as for intervals, triggers and such, but MorningStar has the benefits dynamic tracking ( small harvest loss ) without any of the problems ( ac ripple , partial shading , getting stuck in a secondary vmp hump ) for some examples.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: MPPT stepdown efficiency
    wild01 wrote: »
    yeah I guess I just don't understand why solar equipment developers don't just move here and develop their products in an environment suited to solar. I mean I'm 20 miles from the largest solar power plant in north america and I have literally hundreds of offgrid neighbors, and most of the percision electronics that control my system were designed in one of the cloudiest rainiest places in the world.

    For Development, its diversity of weather, Florida has it all , cold to hot, clear to cloudy and everything in between ... I find stuff all the time, even with mature products due to my local weather
  • System2
    System2 Posts: 6,290 admin
    Re: MPPT stepdown efficiency
    westbranch wrote: »
    Marc, thanks for the Vtoc caution. The Outback calculator came up with
    112V Vtoc from a 4 in series string and
    84V Vtoc from a 3 in series string

    with the temp set to - 30 C, mind you the temp button did not seem to change anything when moved.

    looks like you were getting > 11% more output. Even adding 15 % to the above would keep me below 141 V max...


    EJ

    I was just trying to understand this concept today - I am considering 72v config on several projects, but with cold temps I am afraid of exceeding 150V. So I called both Outback and MStar tech support to try to better understand the situation.... one of them told me that to figure my cold temp max voltage, I just take my Voc (43.6) times 3 (130.80) and then add the extra voltage only once.... [I am figuring 40 degrees less than 25C, with Coeff of -.16v/degC (6.4V)], for a total cold voltage of 137.2..... the other company told me, no you add the 6.4v three times, for a total voltage of 150V....then he suggested with a "hmmmmm" maybe you could add a transorb or something to limit the voltage on cold days. Now, which one gave me the correct advice.... and I did not say which company gave which answer....

    for those of you who have had the "over 150v" problem on 72V array, what actually happens to the CC? One manufacturer told me "anything over 150v will damage the unit" and the other told me "well, it will be OK at 151v, but maybe around 160v it could get damaged".....???
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MPPT stepdown efficiency

    .16v/degree c would be for each pv and being in series it is x3 and is either added to or subtracted from the 25 degree c base for the total. add if colder as you know.
    that is a bit on the high side so i'd be curious what pvs you are talking of?
  • System2
    System2 Posts: 6,290 admin
    Re: MPPT stepdown efficiency
    niel wrote: »
    .16v/degree c would be for each pv and being in series it is x3 and is either added to or subtracted from the 25 degree c base for the total. add if colder as you know.
    that is a bit on the high side so i'd be curious what pvs you are talking of?

    They are BP solar BP4160S. (obtained from an oddball source) I think they were built for test purposes, so they are not on the BP website, so I called and asked for the specific temp coeff for these panels

    again - what happens with the CC when the voltage exceeds 150? and when will this happen? only at "wakeup" before the load comes on?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: MPPT stepdown efficiency

    I have this from Xantrex site for BP 4160:
    Pmax @ STC 160 W
    Pmax @ PTC 142 W
    Vmp at Pmax 35.4 V
    Imp at Pmax 4.52 A
    Voc @ STC 44.2 V
    Voltage change -160 mV/C

    Remember that all Solar Charge Controllers (and any DC power supply) have switches that turn things on and off... So what you are looking at is the voltage level, which exceeded, will damage or punch through the insulation (or jump the air gap in a mechanical switch).

    The thing to remember is that the thickness of the insulation in digital electronics is extremely thin--So the voltages across the insulation/switching elements is very high. When you exceed the recommended maximum voltage--you are into the manufacturer's safety margin (design and manufacturing tolerances).

    Will you kill the device if you go to 151 Volts... Probably not. However, many solar charge controller manufacturer's log the maximum voltage and will void your warranty if Vmax is exceeded.

    With any charge controller, there are times when the battery is full and they do not need to take anymore energy from the panel--effectively, the panel is turned off and is at Voc (cold/hot/whatever).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset