FlexMax 80 and High Voc

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RWB
RWB Solar Expert Posts: 168 ✭✭✭✭✭
Hey guys and TallGirl................

I am hear to dig into the gold mine of info about off grid solar systems and equipment that is stored in your brains from years of research and experience.

My first of many questions is this:

What is your guys opinion on what the Highest Voc I should run a FlexMax80 Charge Controller without causing any known problems. I read somewhere on there that the FlexMax's had an issue with high Voc or the high end of the Panel Input Voltages. Is this true? What can you tell me?

I am going to use the FlexMax 80 in 2 configurations, one is a 24V Battery Bank, and another system will be a 48V Battery Bank. They will be completed 1 inverter Outback systems, Inverter to match the battery bank voltage, FlexNet DC, FlexMax80, Midnight Solar Epanel, Mate 2.

With the 24V System we will be running 2 1140w Think Film Panel Arrays. The 48V System will be running 4 1140W Thin Film Arrays. I'll get you the specs later and the panels can be wired to almost any voltage range. What I need to know is what can you guys tell me about the Flex Max 80 and any known issues with higher panel voltages.

The goal is to reduce wiring size from the panel arrays as much as possible. The panels will outside and the wire will be ran to a tent where the electronics will be.

Any advice would be appreciated.................

Comments

  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    Post datasheet for your panels, what their Voc and Vmp voltages are. Are they Kanekas from sunelec by any chance? I figured they may be, because your array wattages are divisible by 60.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    Here are the Solar Cell Specs:

    Nominal Power (Pmax) 47W
    Voltage at Pmax (Vmp) 32.2V
    Current at Pmax (Imp) 1.5A
    Short Circuit Current (Isc) 1.8A
    Open Circuit Voltage (Voc) 47.5
    Temperature Coefficient 0.45%/ C

    There will be 24 of these modules per panel.

    There will be 2 Panels per 24v Battery Bank and 24v Outback Inverter/Flexmax 80

    There will be 4 panels per 48v Battery Bank and 48V Outback Inverter/Flexmax 80

    What advice can all you experts give me on wiring these panels to the Flexmax 80 to achieve the smallest wire from panels to BOS.

    Or should I say what can you tell me about the pros and cons of running a High Voc panel setup.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    Bummer. Can't run 2 in series, because after thermal derating your Vmp will be too low for 48V battery. Can't run 3 in series, because your Voc will be right at maximum operating voltage of controller. If you can get away with only using 24V battery system voltage, then 2 panels in series will work fine, but then you are limited to only about 2200W of PV power through each FM-80, as opposed to 4400W at 48V system.

    There is a way to limit Voc of 3 panels in series from reaching above 140V limit by making a voltage clamp circut. It's a pretty simple device that uses zener diode driving a high powered pass transistor that is connected in series with large power resistor for heat dissipation. It connects in parallel with solar array. Because Vmp of 3 panels in series will be 32.2V * 3 * 0.8 = 77.3V the clamp circuit will never see maximum power point current, so there is no need to size the circuit to handle full PV power. There is a way to measure how much current the panels will produce at 140V. That current will be dissipated by clamp circuit.

    In the same way, you can now put 4 panels in series for approximate temperature derated Vmp of 32.2V * 4 * 0.8 = 103V But now, the Voc will be 190V and you better really hope that clamp circuit does not fail and allow that voltage to pass to your FM-80. There would have to be triple redundant voltage clamp protection setup, to make sure if one stage fails, your FM-80 is not an instant toast.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    Does it matter that the 24 Cells on each panel can be wired in any configuration we want them to be. So we can do anything with those 24 cells per panel to run at max Voltage with the FlexMax 80 keeping in mind we want to use 4 panels on a 48v System and 2 panels with a 24v system.

    I want to make sure everybody understands exactly what the options are here.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    Oh, you're saying that you can have each 47W panel wired to any cell configuration you need? If so, then wire them to have total Voc of everything in series on the coldest day be at about 120 - 130V, while Vmp on hottest day be above 58.4V
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc
    AntronX wrote: »
    Oh, you're saying that you can have each 47W panel wired to any cell configuration you need? If so, then wire them to have total Voc of everything in series on the coldest day be at about 120 - 130V, while Vmp on hottest day be above 58.4V

    Yes that is what I am saying.

    We can take those 24 panels and wire them anyway we want. Then Combine the Output from the first set of 24 cells with the 2nd set of 24 panels. For the 48V system we have the same option except we have 4 sets of 24 cells.

    The panels will be facing the same direction in the same location.

    Lets go off the weather in Haiti where the disaster happened.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    Argh, I got confused. We probably got some language barrier going on as well.

    Here is what you can do right now. For your 48V system, go ahead and try to wire two panels in series and 4 in parallel or so. That would be 8 panels total, or 4 series pairs in parallel. This is just a test to see how well 48V system will work with only 2 panels in series. Pay attention to your maximum power point voltage your FM-80 will park at. Then see what is your output power is. Compare it to total rated power of your panels. Also, forget about running high voltage to avoid too much copper wire between panels and FM-80. Try to position your panels as close to FM-80 and batteries as you can.

    Edit: Do NOT connect more than 2 panels in series. Connecting 3 in series may damage your FM-80.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    Wire your panels like on this picture. There are only 4 pairs of panels pictured there. You need to wire 48 pairs just like that. If you can, put 5A fuse in series with every pair of panels.
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: FlexMax 80 and High Voc

    The max I would feed the FM is 140 vdc the problem is you have to know the coldest day and plan for that. Funny boB and I will be feeding a Classic over 250 volts today or tomorrow to bad they where not shipping you could do 5 panels in series.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
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    Re: FlexMax 80 and High Voc
    halfcrazy wrote: »
    Funny boB and I will be feeding a Classic over 250 volts today or tomorrow to bad they where not shipping you could do 5 panels in series.

    Too bad we'll all be powering our homes from fusion-reactor-plasma-warp-drives by the time it's released. ;) <nudge> <nudge> <wink> <wink>
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc
    AntronX wrote: »
    Wire your panels like on this picture. There are only 4 pairs of panels pictured there. You need to wire 48 pairs just like that. If you can, put 5A fuse in series with every pair of panels.

    Thanks for your work on this AntronX, so what will this give me by your calculations?

    Also what is the coldest temp that these panels can be run when wired in this configuration and hooked up to the FM80 without causing problems.

    .
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc
    stephendv wrote: »
    Too bad we'll all be powering our homes from fusion-reactor-plasma-warp-drives by the time it's released. ;) <nudge> <nudge> <wink> <wink>

    Yes I wish that Classic was available now also :) It sure would help.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
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    Re: FlexMax 80 and High Voc

    RWB, as to the coldest temp, you need to identify where your are going to site the panels and then check the long term weather records, or plan for - 40 * F or C. doesn't matter cause at that temp they are the same... better to not play the margins...

    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
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc
    westbranch wrote: »
    RWB, as to the coldest temp, you need to identify where your are going to site the panels and then check the long term weather records, or plan for - 40 * F or C. doesn't matter cause at that temp they are the same... better to not play the margins...

    Eric

    Yes so I guess its best to figure out the max voltage config based off a -40 Max temp.

    AntronX does you calculations factor in the max cold temp so the Voc is ok even at -40?

    Later I'll ask more about how to best figure out all this on my own, but I'd ask you guys for advice regardless.
  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
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    Re: FlexMax 80 and High Voc

    I did not specifically calculate what panels will do at -40 C, but you are not going to have that in Haiti anytime soon. Two in series will be totally safe. Like I said, 2 in series may even not be enough on very hot day and when batteries are near absorbtion voltage. Tell me more about this setup. Will it be permanent or temporary? What you guys powering with it? How soon you need to have it running?
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
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    Re: FlexMax 80 and High Voc

    RWB, where are your panels going to be mounted?
     
    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
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    Yes In Haiti I'm sure there will not be any snow soon.

    But I'm trying to figure a wiring configuration that will work in all conditions and still allow me the highest Reliable panel voltage. This is the best way to work the numbers considering the systems can be moved to other locations in the world.

    So instead of designing the system to work with Haiti's warmer climate its better to design the system so that it works anywhere in the world cold or hot.

    The panels are laminated on Fabric that is stretched under tension on angle towards the sun. They are tested for up to 65 Mph Winds.
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    Is there a program or spread sheet I can plug these panel numbers into and get the max and minimum data for the panels under different weather conditions?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: FlexMax 80 and High Voc

    RWB,

    Not quite sure what you are asking... The formulas for panel voltages should be:
    • Voc (cold) = Tcold * Tcoeff V/°C + Voc @ 25C
    • Vmp (hot) = Thot * Tcoeff V/°C + Vmp @ 25C
    Using a standard BP solar BP-4175 (175 watt) mono-crystalline panel:
    Max Power Voltage - Vmp 35.7 Vdc
    Open Circuit Voltage - Voc 44 Vdc
    Voltage Temp Coeff - Vtoc -0.16 V/°C
    STC Rating - Pmp 175 Wstcdc
    Max Power Current - Imp 4.9 Adc
    PTC Rating 155.2 Wptc

    Say -10 C for cold and +45 C for Hot.

    Assume worst case temperatures... Assume Tcold=ambient temperatures for Voc (maximum array output voltage). Assume Thot is ambient temperature +35C temperature rise (little wind, hot day). Remember STC temperature is 25C, so all values have to be adjusted by -25C:
    • Voc (cold) = Tcold * Tcoeff V/°C + Voc @ 25C
    • Vmp (hot) = Thot * Tcoeff V/°C + Vmp @ 25C
    • Voc (cold) = (-10C-25C) * -0.16 V/°C + 44 Volts = 49.6 Volts (@-10C)
    • Vmp (hot) = (45C-25C+35C) * -0.16 V/°C + 35.7 Volts = 26.9 volts (at 45C ambient + 35C rise)
    Note that current does not change much with temperature so can be ignored for calculating minimum/maximum controller current.

    Notice that you almost need a 2:1 voltage range (Voc cold to Vmp hot)... So, if you have a battery bank that needs 60 volts to charge, plus 2 volts for controller wiring drop--your Vmp min of 62 volts would require a controller with a Voc max of almost 124 volts...

    Concidering that the "standard" MPPT controller will operate only to round 140 VDC--that gives you a pretty narrow range of optimum Vmp to hit...

    Note that the Power Curves for a solar panel are fairly flat at Vmp--So even if your Vmp is a bit low--for charging/equalizing in your very hottest weather--the system will still work OK.

    data sheet for a crystalline silicon panel

    If your required Vmp is within ~10% of your panels actual Vmp (temperature corrected)--you will not lose very much energy (10% off of Vmp would probably lose around 10% or a bit less in power output).

    Running 10% off of Vmp is not great--but your panels will not spend all of their summer at 45C + 35C rise either...

    If you want to estimate the other panel output characteristics based on cell temperature (and solar irradiation) you can use these numbers from the generic crystalline panel information (they are all about the same, even amorphous should be close to the numbers below--they are still all physics based on silicon). Note, the below are % voltage and current changes, not absolute like the BP Solar numbers above were:
    Temperature Coefficients:

    Nominal Operating Cell Temperature (NOCT) 45ºC±2ºC
    Temperature Coefficient of Pmax = -0.34 %/ºC
    Temperature Coefficient of Voc= -0.48 %/ºC
    Temperature Coefficient of Isc= 0.017 %/ºC

    Notice that the current Temp Coeff is positive "+"... The voltage coefficient and power coefficients are negative.

    As for calculating power output--just measure (with your solar irradiation monitor/assume various Watts per Sq. Meter. The panels are usually rated at 1,000 Watts per Sq. Meter.

    There are "edge of cloud effects" and such where your panels could output more power than expected (broken clouds can focus sunlight, panels can cool off when shaded by clouds, then bright sun hits before panels heat up, etc.).

    Amorphous panels can have a rapid falloff in output efficiency in the first 6 months of sunlight--after that period, they should level off.

    From the PV Watts program, you can see what they assume for generic system values/losses for derating. They use 0.77 for Grid Tied systems.

    For off grid systems, I use 0.77 (panel and MPPT GT inverter efficiency--very similar for MPPT DC solar charge controllers) and a couple more:
    • 0.80 for Flooded Cell Batteries
    • 0.90 for AGM Batteries
    • 0.85 for TSW (true sine wave inverter)
    • Derating = 0.77 * 0.80 flooded cell bat * 0.85 invrt = 0.52 overall derating
    You can use a program like PV Watts Website and get monthly or even hourly output data from ~20 years of measurements of solar irradiation data for various sites around the US and World. Plug in your array size (1kW is smallest number--if your system is smaller, just multiply by the size in kWatts--like 400 watts would be * 0.4kW).

    Note, if you are in coastal areas or other locations with lots of humidity and/or variable cloud cover--there can be significant year to year variations (over 10%). For the US, you can use the "Red Book" and look at PDF printouts for various locations (they have a small charge with the average and high/low ranges). High deserts tend to have low year to year variability. Coastal areas tend to have higher variations.
    I will stop here--because I am not quite sure where you want to take this.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: FlexMax 80 and High Voc

    The FM80 will operate at up to 145 Voc. Above that, it'll suspend operation, but it'll automatically resume operation once the Voc has fallen below ~145 V.

    The "official" absolute max input spec is 150 V.

    Link to spec sheet.

    HTH,
    Jim/crewzer
  • RWB
    RWB Solar Expert Posts: 168 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    Hey guys I am looking for your input on this solar panel design.

    My question is how do you think the curve of the panel will effect the output of the panel and the cells with all the cells at a different angle and not having all of the cells on the same flat tilt.

    I am thinking that having various cells at different angles will cause most cells to have a different Vmp thus causing a MPPT Charge Controller to pick a MPPT Voltage that is good for the string as a whole but will not produce anwhere near what all the cells could if the panel was stretched flat so all the cells were on the same tilt/angle.

    Right now the angle of the panel is tilted 22 degrees above horizontal.

    What are your thoughts on this design?

    I say if the panels could be stretched flat and the panel could be adjusted for the correct angle that the output from this panel could be greatly increased. Looking for others input on this.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: FlexMax 80 and High Voc

    I've heard roughly: Each degree off perpendicular to the sun = 1% power loss

    The panels will all have about the same voltage in sun, the intensity will be what affects the amps output. If they are 12V (18VMP) panels, all wired in parallel, should work. If you need to start putting them in series for more voltage, your amps will be limited by the most off axis panel.
    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, Administrators Posts: 33,479 admin
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    Re: FlexMax 80 and High Voc

    A single axis offset with the sun is simply Cos (angle)... If you are 10 degrees off angle, you are Cos (10) = 0.98 (98% of power).

    If you are Cos 20 = 0.94 (94% of power)--Cos 45 = 0.70 etc...

    The Vmp is, more or less, dependent on cell temperature--so if the cells are all roughly equivalent sun and wind--the Vmp's will be very similar...

    However, your big problem may be Imp and Vbatt vs Vmp of a "panel"... Normally, you want to match Vmp to Vmp for parallel connections within 10% or so--not too much energy lost. And you want to do the same thing with Imp--match them to 10% or better--Or, you will lose a lot of power in your series strings. The "worst" ideal single angle mismatch:
    • InvCos 0.90 = 26 degrees
    If any of your series solar panels are off plane by 26 degrees or more--you will have a greater than 10% (SWAG) power loss.

    And at morning/evening with the sun low in the sky--you will have panels getting near zero direct sun--so those strings will stop producing.

    To be honest, your angles (just from looking at the pictures) seem to not cause that large of power drop (at least during mid-day).

    If you want to see what the ideal setup (a set of parallel panels each with their own polar orientation--such as a "12 volt panel" charging a 12 volt battery--Really Vmp>17 volts on a MPPT or PWM controller and no Imp series connection issues)--You could use the PV Watts program and calculate the average output for each panel WRT to panel tilt and azimuth (pick three panels to start with middle and two end points). And see what the "hit in production" maybe. If you want, assuming this is an off-grid system, use 0.52 as a derating factor (battery and inverter losses included).

    If you need high array voltage (48 volt battery bank or for Grid Tied inverter of 200-600 VDC)--then the series current issues may be a bigger problem (but I don't think that much for such a "gentle" set of angles). (not too much is on the order of 10% losses or so maximum).

    Just my two cents.

    -Bill

    PS: The Shade on the Carport from the home's roof is probably much more of a problem.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset