Help me make wise decisions - First timer

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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #62
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    It's a matter of "now vs. later"; he plans to start with four, and then add the additional panels with an increase in system Voltage later (expand the two strings to three panels each and add a third string of three). At least that was the plan until the last post inquiring about GT systems.

    That is absolutely correct, my last post regarding grid tied systems was merely to take advantage of unused power. The difference in inverters alone is so substantial that the ROI of selling power back to them with this sized system is completely impractical.

    I'll go back to the 24v with 2x2 panel setup for now, and later change to the 48v 3x3 setup. That seams realistic to me
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  • SolInvictus
    SolInvictus Solar Expert Posts: 138 ✭
    #63
    Re: Help me make wise decisions - First timer

    Please correct me if I am wrong. The Midnight Classic KID has a maximum input voltage of 150 VDC. With 9 PV panels connected in 3 series strings, the open circuit voltage would be 44 V * 3 = 132 V which is too close to the maximum voltage of the charge controller. On cold days the Voc could exceed 150 VDC and destroy the charge controller. Expanding your system to a 48 V battery array with 9 PV panels would require a new charge controller with a higher input voltage rating. For the 48 V battery array, you could use 8 PV in 4 series strings with a combiner box and fuses on each series string.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #64
    Re: Help me make wise decisions - First timer
    SolInvictus wrote: »
    Please correct me if I am wrong. The Midnight Classic KID has a maximum input voltage of 150 VDC. With 9 PV panels connected in 3 series strings, the open circuit voltage would be 44 V * 3 = 132 V which is too close to the maximum voltage of the charge controller. On cold days the Voc could exceed 150 VDC and destroy the charge controller. Expanding your system to a 48 V battery array with 9 PV panels would require a new charge controller with a higher input voltage rating. For the 48 V battery array, you could use 8 PV in 4 series strings with a combiner box and fuses on each series string.

    I agree it is close however doesn't the kid have hyper voc allowing it to push to 162v safely??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #65
    Re: Help me make wise decisions - First timer

    Straight from Ryan:
    *150 volt input operational, 162 volt safety limit. Controller will not run above 150 but it is safe to 162vdc

    Now if you live in a really cold location (like I do) that panel Voc could go above that. But for most people it's unlikely. Otherwise you'd would need a Classic 150 to run the panels like that just to cover the potential hyper Voc (Classic could take 198 Voc).

    But it does point out why you need to check all the details against your particular application.
    For example we are assuming that the 36 Volt rating of the panels is indeed Vmp and not Voc (if the latter then the Vmp would be around 30). Exact specs can make a difference, but it looks safe either way in this case.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #66
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Straight from Ryan:



    Now if you live in a really cold location (like I do) that panel Voc could go above that. But for most people it's unlikely. Otherwise you'd would need a Classic 150 to run the panels like that just to cover the potential hyper Voc (Classic could take 198 Voc).

    But it does point out why you need to check all the details against your particular application.
    For example we are assuming that the 36 Volt rating of the panels is indeed Vmp and not Voc (if the latter then the Vmp would be around 30). Exact specs can make a difference, but it looks safe either way in this case.


    Well here are the exact specs:

    unnamed1.jpg

    unnamed.jpg
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #67
    Re: Help me make wise decisions - First timer

    Nice to know I was right - although that's hardly unusual :D

    So the Vmp is indeed "36" and the Voc "45" for all intents and purposes.
    As such three in series would give a string Voc of 135, and when cold that could indeed approach the Kid's maximum 162 but it would need a 1.2X increase. So then we ask the magic question of what is the coldest temp you will see at the location?
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #68
    Re: Help me make wise decisions - First timer

    Well that sounds like a loaded question lol. Per wikipedia average lows in the winder are mid 20's. This year we saw lots of ~0 degree lows. Says the record is -17

    So, pretty cold??

    Maybe just smarter to go the Classic 150 route? I've also wondered about the Classic 200/250, why not pick those up?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #69
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Well that sounds like a loaded question lol. Per wikipedia average lows in the winder are mid 20's. This year we saw lots of ~0 degree lows. Says the record is -17

    So, pretty cold??

    Maybe just smarter to go the Classic 150 route? I've also wondered about the Classic 200/250, why not pick those up?

    Yes, you're flirting with danger at 0 Fahrenheit.
    The Classic has a limit of 150/200/250 +nominal system Voltage or 198 Volts for a 150 on a 48 Volt system. That you probably will not breach as it would require a 1.4X temp factor - that's Snag, Yukon Territory temperatures. :D
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #70
    Re: Help me make wise decisions - First timer

    Sounds like I'll be ordering the Classic 150. Any reason to pick the Outback Flexmax over it?

    Additionally at what point does it make sense to buy the larger inverters like the Outback inverter chargers instead of just the plain old pure sine wave inverters?? I assume quality is a factor, beyond that??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #71
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Sounds like I'll be ordering the Classic 150. Any reason to pick the Outback Flexmax over it?

    The Outback is slightly cheaper but it does not have the hyperVoc function the Classic has. As such I wouldn't choose it in this case.
    Additionally at what point does it make sense to buy the larger inverters like the Outback inverter chargers instead of just the plain old pure sine wave inverters?? I assume quality is a factor, beyond that??

    When you need to add the features they have, such as that built-in charger, programmable functions (LVD, HVD, auto gen start), stackability, 240 VAC output, and so forth.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #72
    Re: Help me make wise decisions - First timer

    I imagine without doing any research you can indeed use one without using the built in charger functionality? IE you could use one while remaining completely "off grid".
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #73
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    I imagine without doing any research you can indeed use one without using the built in charger functionality? IE you could use one while remaining completely "off grid".

    I think you misunderstand the reason for the built-in charger. Sometimes the sun doesn't shine and you need to start the generator, which recharges the batteries through the inverter's built-in charger.

    Of course it can also be used as a back-up system for grid power, where the utility keeps the batteries charged this way and they take over to power critical systems when the grid goes down. Solar panels & controller are optional in that case.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #74
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    I think you misunderstand the reason for the built-in charger. Sometimes the sun doesn't shine and you need to start the generator, which recharges the batteries through the inverter's built-in charger.

    Of course it can also be used as a back-up system for grid power, where the utility keeps the batteries charged this way and they take over to power critical systems when the grid goes down. Solar panels & controller are optional in that case.

    Oh yes I fully understand that, I just wanted to make sure it would still function without seeing ac power on it's charging port.

    I just checked my kill a watt meter and my 8.8cu/ft beer fridge used just shy of .25kwh over a 24 hour period!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #75
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Oh yes I fully understand that, I just wanted to make sure it would still function without seeing ac power on it's charging port.

    Even the XW will function without AC IN active. Although it draws current any time it is, needed or not. :p But in short they are designed to work without AC IN, and when they detect it automatically switch over.
    I just checked my kill a watt meter and my 8.8cu/ft beer fridge used just shy of .25kwh over a 24 hour period!

    Averaging a bit over 10 Watts per hour is pretty good. Have you seen the thread under Energy Use and Conservation about small refrigerators? Some are pretty bad indeed!
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #76
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Even the XW will function without AC IN active. Although it draws current any time it is, needed or not. :p But in short they are designed to work without AC IN, and when they detect it automatically switch over.



    Averaging a bit over 1 Watt per hour is pretty good. Have you seen the thread under Energy Use and Conservation about small refrigerators? Some are pretty bad indeed!

    Good deal, I think I'd set the inverter up to a transfer switch. One allowing grid power, the other allowing me to hook up an inverter generator.

    As for the one watt per hour, did you mean 10??
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  • SolInvictus
    SolInvictus Solar Expert Posts: 138 ✭
    #77
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Well that sounds like a loaded question lol. Per wikipedia average lows in the winder are mid 20's. This year we saw lots of ~0 degree lows. Says the record is -17

    Temp. Coefficient of Voltage of BP4175B: -0.16V/K = -.16 V/C
    NOCT is usually 25 C
    Maximum voltage on the KID: 162 V

    The KID would break when the temperature of the PV panels are:

    (44.5 V + (T - 25 C) * -.16 V/C) * 3 = 162 V
    T = -34.4 C = -29.9 F

    The KID would stop operating when the temperature of the PV panels are:

    (44.5 V + (T - 25 C) * -.16 V/C) * 3 = 150 V
    T = -9.4 C = 15 F

    If your lowest temperature is -17 F, it looks like the KID is okay with three in series.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #78
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Good deal, I think I'd set the inverter up to a transfer switch. One allowing grid power, the other allowing me to hook up an inverter generator.

    There's them that has done that two. It can get complicated with multiple AC sources for a single input. The XW has two AC inputs for just that reason.
    As for the one watt per hour, did you mean 10??

    Yup. Typo. Fixed it. :D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #79
    Re: Help me make wise decisions - First timer
    SolInvictus wrote: »
    Temp. Coefficient of Voltage of BP4175B: -0.16V/K = -.16 V/C
    NOCT is usually 25 C
    Maximum voltage on the KID: 162 V

    The KID would break when the temperature of the PV panels are:

    (44.5 V + (T - 25 C) * -.16 V/C) * 3 = 162 V
    T = -34.4 C = -29.9 F

    The KID would stop operating when the temperature of the PV panels are:

    (44.5 V + (T - 25 C) * -.16 V/C) * 3 = 150 V
    T = -9.4 C = 15 F

    If your lowest temperature is -17 F, it looks like the KID is okay with three in series.

    Well I get 158 Volts for three in series which is too close to 162 for my tastes.
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  • SolInvictus
    SolInvictus Solar Expert Posts: 138 ✭
    #80
    Re: Help me make wise decisions - First timer

    Yes, it is close. Personally, to save $200 to $300 on the charge controller with an expected lifetime of 10 years, I would risk it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #81
    Re: Help me make wise decisions - First timer
    SolInvictus wrote: »
    Yes, it is close. Personally, to save $200 to $300 on the charge controller with an expected lifetime of 10 years, I would risk it.

    Especially if he ends up not expanding. :D
    And there are alternative expansion options as well.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #82
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Especially if he ends up not expanding. :D
    And there are alternative expansion options as well.

    Ok maybe a dumb question.... But if you knew it was going to be really cold, and may hit that limit, couldn't you just cover a panel with a cloth for the day??? What would be the negatives of that???

    Yes, its a ghetto fix, but I just am wondering..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #83
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Ok maybe a dumb question.... But if you knew it was going to be really cold, and may hit that limit, couldn't you just cover a panel with a cloth for the day??? What would be the negatives of that???

    Yes, its a ghetto fix, but I just am wondering..

    The problem comes first thing in the morning when the panel is as cold as it will get and then there's enough light on it to cause it to produce Voc. It does not take much light to do this. In theory you could cover the panels with something opaque to prevent the light from activating it if you knew it was going to be cold, or you could just disconnect them. But at some point you'll have to reconnect them, which means making sure the panel Voc is not above the controller limit. This could be done by measuring the Voc from the disconnected array before connecting it.

    But most people want it as automatic as possible. For quite some time many of us (especially up here) have toyed with plans to 'clamp' high Voc to where it can't hurt the controller, but they all run into the "if it fails you get a fried controller" problem. Manually you could short the array output through a resistor, say, and then remove that short when there's enough power to provide charging.

    Lots of ways around it, but all of them with a chance for failure. MidNite's HyperVoc function is the most sure-fire safety for this. That and planning the array so it doesn't go above the max input.
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #84
    Re: Help me make wise decisions - First timer

    Do you think I'd be relatively safe with the Kid??

    I'm just debating which to go with, I don't want to waste money but I also don't want to wish I had
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #85
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Do you think I'd be relatively safe with the Kid??

    I'm just debating which to go with, I don't want to waste money but I also don't want to wish I had

    There is no question it would work on the 24 Volt system with two panels in series.

    From the calculations I did if/when you run up to 48 Volts and three panels in series the maximum Voc would be 158 at your coldest temperature which is under the Kid's 162 maximum input. So it should work. The only other suggestion I would have is to ask the folks at MidNite what they think, and what would happen if the 162 Volts is exceeded.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #86
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    From the calculations I did if/when you run up to 48 Volts and three panels in series the maximum Voc would be 158 at your coldest temperature which is under the Kid's 162 maximum input. So it should work

    That's too close for (my) comfort. Don't forget: record low temperatures in any region are based on air temperature a few feet above ground. The reason the air gets so cold on clear, still nights is because surfaces get COLDER than the air, and it is conduction from those colder surfaces that makes the air cold. It's called "radiative cooling".

    Therefore, when calculating max Voc, you must plan for several degrees cooler than the record low temp.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #87
    Re: Help me make wise decisions - First timer

    Am I crazy or did a bunch of replies disappear???
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #88
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Am I crazy or did a bunch of replies disappear???

    Yes. It has something to do with this: http://forum.solar-electric.com/showthread.php?22572

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #89
    Re: Help me make wise decisions - First timer

    What size breakers should I go with? I'll be using 2 strings of 2 panels to start, later I'll go to 4 strings of 2. Amperage should stay the same
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #90
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    What size breakers should I go with? I'll be using 2 strings of 2 panels to start, later I'll go to 4 strings of 2. Amperage should stay the same

    Yes: the breakers or fuses for panel protection remain the same because there is no change in the current carrying ability of a panel string. You're just adding more in parallel.

    This is not true of the wiring from the combiner to the controller which should be sized to handle all four strings to start with (and thus avoid having to change it out at the time of expansion).
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  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #91
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Yes: the breakers or fuses for panel protection remain the same because there is no change in the current carrying ability of a panel string. You're just adding more in parallel.

    This is not true of the wiring from the combiner to the controller which should be sized to handle all four strings to start with (and thus avoid having to change it out at the time of expansion).

    That being said with the first system at 24 volts and under 30 amps, would you buy a true "combiner box" or would you just wire nut the two strings inside a box near the charge controller then one run to the controller? When I see the combiner boxes they all seem to be using fuses rather than breakers, any reason to that? Seems like I could even just run both strings through a 40 amp breaker (assuming that sounds correctly sized) then into the charge controller. Do they really need to be individually fused?? I can certainly do it, just seems a bit over the top for a small system like this will start at.

    Again I can buy a box, but it just seems a bit much to spend $150 or so on what two wire nuts could accomplish unless there truly is a 'need', thats half the cost of a new controller in this case.
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