Marginal HyperVOC - should I risk it?

Susido
Susido Registered Users Posts: 32 ✭✭
in Solar Beginners Corner #1
I want to buy another four 130W 12V panels (while I can still find them) to combine with my existing 8 similar panels. I have a MidNite Solar Classic 150 controller and if I install them in a 2 string 6 panel each configuration MidNite Solar's panel configuration tool shows that Max VOC on my controller will be "MARGINAL":

VOC @ -35 C°: 155V
Max Non operating VOC (HyperVOC) @ 24V Nominal Battery Voltage: 174V
Maximum Number Of Modules In Series: 5
Max Number Of Modules In Series (Using HyperVOC): 6
Temperature The Classic Will Enter HyperVOC: -23 C°

Does it make sense that my VOC at -35C is only 155V yet the Classic enters HyperVOC at -23C?

In any event I would like to keep my panel configuration as 2 strings to avoid having to put circuit protection on each of 3 strings. It is unlikely I would be using these solar panels in very cold winter conditions anyway (I have a couple of smaller panels I use with a PWM controller to trickle charge my battery bank over winter.)

But are there other drawbacks to going with 2 strings like poor charging efficiency? And if I do go with 3 strings, approximately what size fusing should I use for each? Currently I just combine the output of my 2 existing stings and send that through a 60 amp circuit breaker before it goes to the Classic.
Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Marginal HyperVOC - should I risk it?
    Susido wrote: »
    I want to buy another four 130W 12V panels (while I can still find them) to combine with my existing 8 similar panels. I have a MidNite Solar Classic 150 controller and if I install them in a 2 string 6 panel each configuration MidNite Solar's panel configuration tool shows that Max VOC on my controller will be "MARGINAL":

    VOC @ -35 C°: 155V
    Max Non operating VOC (HyperVOC) @ 24V Nominal Battery Voltage: 174V
    Maximum Number Of Modules In Series: 5
    Max Number Of Modules In Series (Using HyperVOC): 6
    Temperature The Classic Will Enter HyperVOC: -23 C°

    Does it make sense that my VOC at -35C is only 155V yet the Classic enters HyperVOC at -23C?

    Yes, because of the temperature coefficient of the panel the 12C temperature difference between -23 and -35 may be 5 Volts.
    In any event I would like to keep my panel configuration as 2 strings to avoid having to put circuit protection on each of 3 strings. It is unlikely I would be using these solar panels in very cold winter conditions anyway (I have a couple of smaller panels I use with a PWM controller to trickle charge my battery bank over winter.)

    But are there other drawbacks to going with 2 strings like poor charging efficiency? And if I do go with 3 strings, approximately what size fusing should I use for each? Currently I just combine the output of my 2 existing stings and send that through a 60 amp circuit breaker before it goes to the Classic.

    I believe what they are warning you about is that the controller is likely to enter HyperVoc and shut down as the Voc of the array under the expected temps is likely to exceed the 150 Volt operating maximum.

    The higher your PV array Vmp is in relation to your system nominal Voltage the lower the controller efficiency. You are running a 24 Volt system and it looks like your array Vmp is >100. That is a pretty wide stretch.

    Were it me I'd configure the twelve panels as four parallel strings of three, giving a Vmp around 52 and eliminating the Voc issue entirely. Of course for that you'd need a combiner box and circuit protection per string as well as checking the wiring against the increased current. But it would work better.
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  • Susido
    Susido Registered Users Posts: 32 ✭✭
    #3
    Re: Marginal HyperVOC - should I risk it?

    Thanks very much for your advice. So 4 strings of 3 panels each will be the goal.

    The questions I have relate to appropriate circuit breakers for this configuration. There is no series fuse ratings (maximum or otherwise) given for my panels. Would (4 - one for each string) 10 amp Midnite Solar MNEPV 150VDC breakers work best here? Or 12 amp? Or 15 amp? And do I need, or is it recommended, an additional breaker after combining the output of the 4 strings (i.e. between the combiner box and the controller)? That would be handy as a kind of master on/off PV switch. Thanks for your help.
    Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Marginal HyperVOC - should I risk it?
    Susido wrote: »
    4 strings of 3 panels each will be the goal.

    The questions I have relate to appropriate circuit breakers for this configuration. There is no series fuse ratings (maximum or otherwise) given for my panels. Would (4 - one for each string) 10 amp Midnite Solar MNEPV 150VDC breakers work best here? Or 12 amp? Or 15 amp?

    The breakers should be Isc multiplied by 1.56 Round up to next available size. I would guess that your Isc is at least 7 amps. If so, you should use the 12 amp breakers.

    btw, you can buy a Midnite combiner with built-in MC4 connectors on the bottom of the box. The one in the catalog has 600 volt fuses, but they're happy to make them up with 150 volt breakers. Note: the fuses are 1.5 times larger than the breakers. Thus a 4 fuse combiner can be a 6 breaker combiner.
    Susido wrote: »
    And do I need, or is it recommended, an additional breaker after combining the output of the 4 strings (i.e. between the combiner box and the controller)? That would be handy as a kind of master on/off PV switch.

    Yes, you should have a breaker close to the controller to act as a switch. When you power up a controller, switch the battery on BEFORE the PV. When you power down, switch off the PV BEFORE you switch off the battery. You should also have a breaker between the controller and the battery. If it is a polarized breaker, be sure the (+) on the breaker goes to the battery (+), not to the (+) battery connection on the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Susido
    Susido Registered Users Posts: 32 ✭✭
    #5
    Re: Marginal HyperVOC - should I risk it?

    Thank you. That 1.56 * Isc formula is very helpful - I didn't see it in the first 30 threads I read using a search on "breaker size". My Isc is 7.98A which multiplied by 1.56 = 12.49. So in my case I should go with 15A breakers correct?

    I believe I'll just need an additional Big Baby box to the one I have now, MC4 connectors are not an issue by the time wiring enters by shed (thank goodness). Already have the other two input/output breakers. I do not believe MidNite's MNEPV breakers are polarized?
    Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #6
    Re: Marginal HyperVOC - should I risk it?

    Big baby ok for indoors. Combiner usually at array, hence use the 3 or 6 breaker combiners which are weather proof, the price is not too bad.

    I havent tried it but it may be possible by the look of it to fit 4 breakers in the 3 breaker combiner.
    http://www.solar-electric.com/mnpv3.html
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
    Re: Marginal HyperVOC - should I risk it?
    Susido wrote: »
    I do not believe MidNite's MNEPV breakers are polarized?

    Those breakers are polarized. All Midnite's din rail breakers are polarized. The panel mount breakers are not polarized.
    zoneblue wrote:
    Big baby ok for indoors. Combiner usually at array, hence use the 3 or 6 breaker combiners which are weather proof, the price is not too bad.

    I haven't tried it but it may be possible by the look of it to fit 4 breakers in the 3 breaker combiner.

    I agree. Use a weatherproof combiner box to combine. You cannot fit 4 breakers in the MNPV3.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #8
    Re: Marginal HyperVOC - should I risk it?
    vtmaps wrote: »
    You cannot fit 4 breakers in the MNPV3.
    --vtMaps

    Out of curiosity, why not?
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #9
    Re: Marginal HyperVOC - should I risk it?
    zoneblue wrote: »
    vtMaps wrote:
    You cannot fit 4 breakers in the MNPV3.
    Out of curiosity, why not?

    Why not? Well, very few things are impossible... with enough machining I suppose you could do it. The buses and din rails are designed to accommodate three 150 volt breakers or two 600 volt fuses.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #10
    Re: Marginal HyperVOC - should I risk it?

    Im trying to be obtuse, take a look at the picture here:

    http://www.solar-electric.com/mnpv3.html

    The din rail is wide enough to hold at least 5 breakers. Yes the Pos bus will need replacing, and the neg bus, will start to get a bit congested, and overall cable mgmt ditto. But the deadfront will be the only real thing that stops it working.

    Unless they have changed the design from that picture...
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #11
    Re: Marginal HyperVOC - should I risk it?

    Don't know exactly the NEC code section but you will start exceeding the box fill ratio, number of terminations and wires that are allowed in a specific size cu/in box. Heat dissipation issues etc.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #12
    Re: Marginal HyperVOC - should I risk it?
    zoneblue wrote: »
    Im trying to be obtuse, take a look at the picture here:

    http://www.solar-electric.com/mnpv3.html

    The din rail is wide enough to hold at least 5 breakers. Yes the Pos bus will need replacing, and the neg bus, will start to get a bit congested, and overall cable mgmt ditto. But the deadfront will be the only real thing that stops it working.

    Unless they have changed the design from that picture...

    But for $14.75 more you can have a Midnite Solar MNPV6 Solar Panel Array Combiner with 6 slots and not have to play with anything.
    http://www.solar-electric.com/mnpv6.html
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