How much power will I loose using these panels for 12 volt?

Leehamrick
Leehamrick Registered Users Posts: 17
I have two panels that I think are for grid tie in but I need to use them for a 12 volt system.
I know I will loose some power but how much?
What will be the max watts on these when use for 12 volt?
This is why in another post I was asking about 2 separate systems on one battery bank

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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    For a PWM controller:
    • Imp*Vbatt-charging = Watts in to battery bank
    • 8.2 amps * 14.5 volts charging = 118 Watts

    For a typical MPPT installation:
    • Imp*Vmp*derating= Watts into battery bank
    • 8.2 amps * 29.44 volts * 0.77 panel+controller derating = 186 Watts

    Rough but reasonable numbers. And MPPT system in subfreezing weather will do ~10-20% better. No real change either way for a PWM controller.

    $100-$150 for a PWM controller vs $300-$600 for a MPPT controller--Sometimes hard to justify the extra costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?

    Simple rule-of-thumb: multiply Imp of the panel times "standard" Vmp for "12 Volt" panels of 17.5 and you get the approximate panel equivalent. So in this case 8 * 17.5 or roughly the same performance as a 140 Watt panel. In essence that is losing 95 Watts per panel.

    Looking at it from an economics POV with two panels you'd be down 190 Watts, or "one of these" http://www.solar-electric.com/et-solar-190-watt-monocrystalline-solar-panel.html which is worth $262.

    To handle the current with a PWM controller you need 20 Amp capacity, like this: http://www.solar-electric.com/ss-20l.html

    Add the $80 price of that to the $262 worth of loss Watts and you get $342.

    You could expect to get 30 Amps out of those two panels with an MPPT controller on a 12 Volt system. If you could buy one of those for $342 you're right at break-even, so to speak.

    Unfortunately we're still waiting on availability of the Rogue 3024 and MidNite Kid 30 Amp MPPT controllers. Otherwise the MS 45 MPPT is $400 so not quite worth the expense.

    One way of looking at it anyway.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    BB. wrote: »
    For a PWM controller:
    • Imp*Vbatt-charging = Watts in to battery bank
    • 8.2 amps * 14.5 volts charging = 118 Watts

    For a typical MPPT installation:
    • Imp*Vmp*derating= Watts into battery bank
    • 8.2 amps * 29.44 volts * 0.77 panel+controller derating = 186 Watts

    Bill,

    Why did you include derating in MPPT, but not PWM? If it is for temperature and conditions for the panels, it should mostly affect Imp, so it should affect PWM controller as well.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    Vmp is affected by temperature about 10x that of Imp--and is in the opposite directions (Vmp falls pretty quickly as panels get hot... Imp rises slightly as panels get hot).

    PWM controllers are, in general, pretty efficient (very little in the way of electronics to waste power as heat).

    And as long as Vmp array is > Vbattery charging, there is no "voltage drop" losses to worry about "subtracting" energy from the battery. That is one "advantage" of Current Mode power sources--Virtually 100% of the current out of the panel ends up at the battery... And from ~15 volts to near 0 volts, Imp is relatively proportional to the sun light.

    And notice that the Watts in to the battery varies with respect to voltage--if the battery is "near dead" at 11.5 volts, watts in is less than if the voltage is near fully charged at 14.5 to 15.0 volts...

    So, for Watts In, PWM controllers deliver (slightly) more Watts for the 80% to 100% state of charge. Whereas MPPT controllers (for the most part) reliever constant Watts In to the battery regardless of battery voltage (power=Volt*Amp -- As voltage goes up, amps falls for MPPT charge controller).

    So--When I do "Volts*Amps" where Vbatt is the voltage--I have basically taken all of the deratings for Vmp to Vbatt losses (i.e., Vmp=17.5 volts at the array vs Vbatt~14.5 volts at the battery). Or:
    • 14.5 volt batt / 17.5 volt Vmp = 0.83 = ~ 83% "efficiency" for "PWM" controller

    The differences in operation between MPPT and PWM controllers is "so different" that it is not really "fair" to try and compare the differences in controllers with one "derating" number...

    However, if you do try--That 0.77 panel+controller losses is as good as any... Hot solar panels have upwards of 15%-20% Vmp losses, and MPPT controllers have ~5% losses when operated at their "optimum" operation current/voltages. And for PWM, most of their "losses" is the Vmp to Vbatt conversion losses.

    Assuming panels are, for the most part hot, and batteries are, mostly, operated at the ~80%+ state of charge--The derating numbers are not that different (for different reasons) between PWM and MPPT (and I usually do not try to differentiate).

    If you are in very cold climate (well below freezing), you can get 10-15+% higher Vmp and a MPPT controller will do better than spec. in summer. However, if you have 6+ hours of sun in summer and 2 hours or less sun in winter, 10% more of 2 hour sun day is not that big of increase--So, usually worth ignoring in back of the envelope planning.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    That is right, temperature mostly affects Vmp, but things like non-optimal angle or hazy atmosphere do affect Imp, so there has to be sme (smaller) derating for PWM controllers too. Would you give 10%? Such as

    8.2 amps * 14.5 volts charging * 0.9 derating = 106 Watts
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?
    NorthGuy wrote: »
    That is right, temperature mostly affects Vmp, but things like non-optimal angle or hazy atmosphere do affect Imp, so there has to be sme (smaller) derating for PWM controllers too. Would you give 10%? Such as

    8.2 amps * 14.5 volts charging * 0.9 derating = 106 Watts

    No, because in both cases you're talking about starting from an Imp * Vmp "ideal" - real or not. The actual power difference is found in the Voltage; the MPPT has the ability to take whatever Voltage "overhead" is available above battery Voltage and turn it into current. The PWM controller can only pass Imp.

    So then you get into the difference found in individual systems with insolation variations, temperature variations, and wiring loss variations all affecting the efficiency difference between the two types of controller. With panels in a hot climate, for example, the Voltage overhead may become zero and the MPPT loses any advantage it may have.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    Don't know why then those companies paid me as a senior systems design engineer/architect for all those years...

    Anyway, do you want a "real discussion"?

    What I typed is all true. And I would never tell anyone to only purchase an MPPT charge controller as they are eleventy million times better than a PWM controller.

    Right tool for the jobs... For smaller system (less than ~200-400 watts) a PWM controller may be the better solution (on cost/complexity).

    For larger systems (>800 Watts), a MPPT charge controller is probably better--Both because you can get large format (>200 watt solar panels) and use a MPPT controller to down convert from high voltage/low current panels to the low voltage/high current for charging the battery bank. This allows you to use less copper (less costs) for running from the Solar array to the charge controller+battery bank. And for very hot climates (where Vmp can sag well below the Vmp~17.5 volts), you will still be able to equalize a 12 volt battery bank at ~15-16 volts on a hot summer afternoon (where a Vmp 17.5 volt panel on PWM controller may not be able too).

    So--I have typed this explanation a 1,000 times here before (PWM for small systems and usually MPPT for larger systems). If you want to pay ~$300-$600+ for a 120 watt solar panel system--Be my guest.

    I show my work and always recommend folks to do a couple paper designs (MPPT, PWM, Conservation, whatever) and see what works out for them before the spend the first $$$... Want to show your work?

    -Bill

    PS: Another moderator deleted and banned a poster that was very upset about my explanation that for an "average"/"correctly designed" solar PV system, MPPT and PWM controllers have similar efficiencies at normal "summer temperatures".

    He was not happy. Anyway--As we always state here--Do the paper design first before you start buying parts. There is no one size fits all solution in solar power.

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?

    To be absolutely clear he was banned for using foul language - and then replacing when it had been edited out the first time. Such behaviour will not be tolerated.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    BB. wrote: »
    PS: Another moderator deleted and banned a poster that was very upset about my explanation that for an "average"/"correctly designed" solar PV system, MPPT and PWM controllers have similar efficiencies at normal "summer temperatures".

    I actually think that PWM controllers are much better for even bigger systems. As the prices are stacked now, for the price difference between MPPT and PWM you can buy a big solar panel, which will add much more production to your system than the MPPT controller can.

    However, I seriously doubt that PWM controllers are 100% efficient.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    Not 100%--But >98% is pretty easy (notice that most PWM controllers have no cooling fans/large heat sinks vs MPPT type controllers).

    But the big issue is still the voltage drop from Vmp-Vbatt:

    14.5 volt batt / 17.5 volt Vmp = 0.83 = ~ 83% "efficiency"

    Plug in a 30 volt Vmp panel, and the "non" conversion losses go way up:

    14.5 volt batt / 30 volt Vmp = 0.48 = ~ 48% "efficiency"

    Remembering that Power = Volts * Amps ... And if you are using 1/2 of the available output voltage of a solar array, you are only pumping ~50% of the Panel available wattage into the battery bank.

    Note as solar panels get hot, Vmp falls towards battery voltage... And Imp remains the same (actually very slightly increases) so the PWM system becomes more efficient.

    However, overall, the panels are still outputting less wattage when because of the falling Vmp voltage. A very hot panel + PWM may actually put more wattage into a battery bank vs a MPPT controller on the same array.

    Certianly, there are other issues (Vmp>Vbatt to move current, Pmax is not a sharp peak but rounded, so there is a bit of +/- slop around the peak before power/current falls off dramatically, differences between tare losses between PWM (low) and MPPT (higher).

    -Bill

    PS: And note, MPPT efficiencies "Fall" at dawn and dusk... They have less output at low light because they still need the 3-6+ watts to run the micro processor, switching converter, etc.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?
    NorthGuy wrote: »
    I actually think that PWM controllers are much better for even bigger systems. As the prices are stacked now, for the price difference between MPPT and PWM you can buy a big solar panel, which will add much more production to your system than the MPPT controller can.

    However, I seriously doubt that PWM controllers are 100% efficient.

    It's more the other way around: the biggest advantage to MPPT is the flexibility in array design it allows. So you can get the equivalent power from "GT" panels with an MPPT controller for less money than the same using "standard" panels and a PWM controller due to the lower per Watt cost of the GT panels making up for the increased cost in the charge controller. This is providing the array is large enough.

    The "big" solar panels tend to be the GT ones with Vmp of 30 or so, which is not right for any battery system Voltage. As such when used with a PWM controller there is a significant power loss.

    If you examine the two using one panel and "ideal" illumination you get this sort of result:
    140 Watt KD panel, Vmp 17.7 Imp 7.9
    The PWM controller will pass 7.9 Amps maximum, regardless of battery Voltage. So at low of 12 Volts you have (12 * 7.9) 94.8 Watts and at a high of 15 Volts you have (15 * 7.9) 118.5 Watts.
    The MPPT controller is trickier to estimate the current output from as the Voltage of the panels can turn into extra charge current. If the wiring is efficient there is more Voltage available. But essentially you get 77% of the panel's rated power divided by the battery Voltage. So at 12 Volts you'd have 8.9 Amps whereas with the PWM only 7.9. This is that "10% more current" they tout in advertising. But as the Voltage goes up the current goes down and the MPPT controller's heavier self-consumption over PWM; you can actually lose a bit of current potential. Since the most current is usually needed at the lowest battery Voltage this is not a practical problem.

    You are correct that PWM controllers are not 100% efficient; nothing is. The confusing bit is that a solar panel can put out its Imp at any Voltage between practical zero and Vmp; the power used by a controller comes from some of this power overhead (the V difference between battery and real panel Volts * current). The MPPT's power demand is greater because it is a more complex circuit.

    Even so, the amount of power lost to either type of controller is miniscule to the big picture. That's why arguing about an apparent 2% efficiency difference between two different MPPT controllers is pointless. Efficiency will vary on any part of any system depending on the operating conditions at that particular time.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    It's more the other way around: the biggest advantage to MPPT is the flexibility in array design it allows. So you can get the equivalent power from "GT" panels with an MPPT controller for less money than the same using "standard" panels and a PWM controller due to the lower per Watt cost of the GT panels making up for the increased cost in the charge controller. This is providing the array is large enough.

    The "big" solar panels tend to be the GT ones with Vmp of 30 or so, which is not right for any battery system Voltage. As such when used with a PWM controller there is a significant power loss.

    They are not that bad. If you have a panel with Vmp of 30, this is only 2V higher than 28V that you would need to charge 24V batteries. I think this is not a bad match. These panels will perform with PWM not much worse than with MPPT. If you think of them as 200W panel as opposed to 250W and compare their prices with standard 140W panels designed to 24V batteries, you'll see that they're actually cheaper, at least at NAWS.

    4 big 250W 30 Vmp panels + PWM may turn out to be cheaper than 3 of the same panels with MPPT, and will produce more. You can look at this as wasted energy, or you can look at this as saved money.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?
    NorthGuy wrote: »
    They are not that bad. If you have a panel with Vmp of 30, this is only 2V higher than 28V that you would need to charge 24V batteries. I think this is not a bad match. These panels will perform with PWM not much worse than with MPPT. If you think of them as 200W panel as opposed to 250W and compare their prices with standard 140W panels designed to 24V batteries, you'll see that they're actually cheaper, at least at NAWS.

    4 big 250W 30 Vmp panels + PWM may turn out to be cheaper than 3 of the same panels with MPPT, and will produce more. You can look at this as wasted energy, or you can look at this as saved money.

    Ah, but no: if you have a panel with a Vmp of 30 it will probably be quite a bit less than the 28.8 typically used on a 24 Volt system by the time it gets to the battery. "True" 24 Volt panels have a Vmp of around 35 to compensate for heating and wiring losses and controller consumption. Without that the batteries may never see enough Voltage from the panel to fully charge. You'd be amazed how easily 2 Volts can disappear in panel heat and wiring resistance.

    140 Watt panels tend to be "true 12 Volt" panels with a Vmp of 17-18. Put two in series to charge a 24 Volt system and you have an array Vmp of 34-36. Much higher than 30.

    The trick with the "GT" panels is to have the array Vmp up above what is needed for the system Voltage. So whereas a 30 Vmp panel can charge a 12 Volt system it can't do so without significant power loss, and it may not fully charge a 24 Volt system at all. Trying to cut the margins to a minimum results in a poor performing system: charging conditions are not the same every day of the year.

    The economics works like this:
    140 Watt Solartech panel goes for $1.96 per Watt.
    240 Watt Trina panel goes for $1.00 per Watt.
    Need >400 Watts of panel and you save over $384. Together with the cost of the PWM controller you'd have to have anyway and there's the price of the MPPT unit. The larger the array, the more practical this becomes.
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    Ah, but no: if you have a panel with a Vmp of 30 it will probably be quite a bit less than the 28.8 typically used on a 24 Volt system by the time it gets to the battery. "True" 24 Volt panels have a Vmp of around 35 to compensate for heating and wiring losses and controller consumption. Without that the batteries may never see enough Voltage from the panel to fully charge. You'd be amazed how easily 2 Volts can disappear in panel heat and wiring resistance.

    You're probably right.

    Here's the standard 140W panel for 24V, 130W actually. Vmp = 34V.

    Here's the big panel. Vmp = 32V.

    It is twice as much capacity for the same price. Unfortunately, I don't have any experience running panels with PWM controllers, but with all my inexperience I would bite and go with the big panel for my PWM. May be that's a trap and I would have to break my PWM controller, rewire the panels, and go with MPPT. Fortunately, I needed a bigger array, so I didn't fall for this trap :p
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?

    That's why you need to plan these things out before you buy anything! :D

    In some cases it would work, in others it wouldn't. Cool temps, short wires = works fine. Texas heat, 50' between array and controller = whoops! :p
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    Great discussion.

    FWIW - it looks like the new Rogue CC and Midnite's "The Kid" will both be about $400. Not cheaper than the Tristar MPPT45 but certainly more features for the money. The higher VOC of The Kid is going to give it a big advantage over the Rogue since it will allow 3 of the typical lower cost "grid tie" (VOC around 35) panels to be put in series for a 48 volt system or 2 for a 24 volt system. The Rogues VOC input limit isn't going to allow that.

    Bill's point about the efficiency of PWM controllers is a good one. My only PWM experience is a 10 amp Stecca used in a small 12V shed system. No heat sink or fan and it stays cool. I do have a used Tristar 45 PWM controller I picked up for a small garage 12V system but I haven't installed it yet. Interestingly it has the same large cooling fins their MPPT controller has but this may just be due to standardization of form factor - I suspect they're not needed.

    I find it very interesting that Midnite's soon to be released pwm controller (The Brat) is in a polycarbonate case - so clearly heat sinking is not needed. And it can put out up to 30 amps! - and for $100 it's going ot make the cost equation of mppt vs pwm for medium sized systems interesting!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    The new Rogue is a higher voltage rated unit:
    • High efficiency (in/out): 98.4%(68v/54.3v), 98.2%(51v/40.8v), 98.1%(34v/27.2v), 97.5%(17v/13.6v)
    • Ultra-low standby power consumption: 135mW typical in rest
    • 30-amp output
    • Will accommodate 12, 24, 36, or 48-volt battery banks
    • Use with PV arrays up to 100-volt maximum
    • Extensive fault protection, including reverse battery, with no mechanical contacts/relays
    • Automatic fault resolution allows return to normal operation after a fault is removed
    • Fast and fully automatic dynamic maximum power point tracking - no adjustments to make
    • Automatic slow-stepped MPP sweep triggered by fast-rising battery voltage minimizes overshoot
    • 20x4 backlit LCD display with intuitive, easy-to-use interface
    • Dual microprocessors allow dedicated power conversion management
    • Setpoints can be retrieved, viewed, and adjusted at any time with the front panel controls
    • 31-day internal data logging records vital parameters for assessing system performance
    • Remote battery voltage sensing for more accurate charging
    • Auxiliary output/relay can be configured to turn on at a preset battery voltage
    • Rogue PowerNet communications port for interface with a PC or remote monitoring device
    • Six-stage charge routine ensures long battery life with minimal user maintenance
    • Super-easy battery equalization, initiated at the press of a button from the front panel
    • User-upgradable firmware (requires optional DCV-0001 data converter)
    • User-adjustable battery temperature compensation
    • User-adjustable setpoint calibration
    • Top-of-the-line electronic components chosen with reliability and efficiency in mind
    • Heavy-duty convection cooled design allows ambients of up to 60 degrees Celsius
    • Durable white powder coated steel enclosure
    • Conformal coated circuit board
    • Designed and built in the USA
    • 5-year warranty
    Included:

    • Remote battery temperature sensor and cable
    • Remote battery voltage sense cable
    • User's manual
    • Mounting screws
    • Ground lug

    Last status from his website:
    June 28, 2013 - Got some controllers shipped out this week for evaluation. The website has also now been updated for the MPT-3048. If you're looking for some light reading, you can find a spec sheet and user's manual here.
    June 13, 2013 - Just got the first article off of the production line for inspection. Looking at another ~week now before test units are available.
    If you'd like to be one of the first to own the MPT-3048, and if you're willing to let me know how it works for you, send an email to sales@roguepowertech.com with details of your system's capabilities (array size and voltage capability, battery bank voltage capability, type of batteries), and also what area of the world you're located in and where the unit will be installed (building, RV, boat, etc).

    In return for your help, you'll get a good discount off of the $395 retail price of the controller, and a free DCV-0001 data converter package so that you can use the software utility to monitor the controller and test its functionality.
    I'll leave the opportunity open until Friday, June 21, at which point I'll send a reply back to a few people who meet what I'm looking for. You should have a reply by the following Monday (the 24th) if you've been selected.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    BB. wrote: »
    The new Rogue is a higher voltage rated unit:
    l


    Right- but with a max input voltage of 100 Volts, 3 of the typical 35+V VOC "grid tie" panels is a no go - and 2 will not be enough for a 48V system

    Midnite's "The Kid" has a max input voltage of 120V - plus their HyperVOC on top of that.

    So with the Rogue - if you want a 48V system you're stuck using 4 12V panel or 2 24V panel series and can't use the less expensive "grid tie" type panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: How much power will I loose using these panels for 12 volt?

    I did not look closely at the Rouge specs yet... If that is Vmp-stc max of ~100 volts--That is pretty good (close to Voc-cold of 140-150 VDC). If that is Vpanel-input max = 100 Volts--Yea, that is a bit tight for running a 48 volt battery bank with "GT Panels" (as in, may not work for most GT panels).

    Even with Voc~140-150 VDC range, there were some GT panels with Vmp~50-70 volt range that could not be configured for use with a typical Outback/Midnite/etc. 140-150 Vpanel max controller. One panel was too low of voltage, and two panels in series was too high (mostly this was with Dupont Thin Film panels that had the "difficult" Vmp-stc range).

    Waiting and watching.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    Yeah- I guess when I saw the Specs I assumed that array "up to 100-volt maximum" was referring to Voc - but maybe not.

    If it is - then it is a curious design choice since it will be a turn off for those who want to use the lowest price/watt panels. Perhaps the components needed to push it up to 120 V are much more expensive?

    I will soon be in the market for a mid sized controller - and the lower input voltage max (if it means Voc) would be a deal breaker for me since I already have panels with a VOC of 36V.

    I immediately noticed the higher input voltage listed on "The Kid" spec sheet. We'll have to see how the street prices compare but I've seen $400 mentioned by both manufacturers.

    BTW if you look at the sub $1/watt panels out there - almost all of them have Vmps of 29-30 and Vocs of 35-37. There are a few with Vocs in the 50V range but those can be combined in 2 series strings for 48 V systems so not a problem for a 120V max input controller.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?

    You wouldn't pick a Rogue for a 48 Volt system: it's model number "3024" refers to it handling 30 Amps @ 24 Volts. Not meant for higher Voltage systems. But a great choice for numerous smaller systems as at 30 Amps it's just the right size for a single set of GC2's. The Kid is similar, but typical of MidNite has higher input Voltage limit. I think they are familiar with the problem of cold weather raising Voc. ;)
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    You wouldn't pick a Rogue for a 48 Volt system: it's model number "3024" refers to it handling 30 Amps @ 24 Volts. Not meant for higher Voltage systems. But a great choice for numerous smaller systems as at 30 Amps it's just the right size for a single set of GC2's. The Kid is similar, but typical of MidNite has higher input Voltage limit. I think they are familiar with the problem of cold weather raising Voc. ;)

    'Coot, the new - soon to be for sale- Rouge controller is also for 48V systems. See the link and specs that Bill posted.

    Also - their discontinued 3024 controller had a max input V of 60 which also was a problem if you wanted to combine 2 typical "grid tie" panels in a string for a 24 volt system
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: How much power will I loose using these panels for 12 volt?

    So are they going to call it a 3048? I haven't seen an update since their last "almost in production" in June. :roll:

    If the Voc can't handle 120 Volts like the Kid then there's going to be limited ability to use it for just the reasons you mention. You need 70 Vmp array for a 48 Volt system, and that means the Voc will be 86 without any cold temp adjustment. This narrows the panel choices considerably. :blush:
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    Yep - the 3048 Price is $395. If you want to keep up with the latest on Rogue - ya gotta check out their facebook page!:roll:
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    That is a 100v Voc limit, and I realize that's going to be a deal-breaker for some of the GT panels...but it's so hard to make everyone happy. All of the components are already rated >100v for a margin of safety. The FETs, for example, are 120v. The caps 160v. I'm sure there are manufacturers that like to advertise a "150v max" controller...and use 150v FETs. I'm not comfortable with that. So to make a 120v controller I'd be using 150v FETs, which have a significantly greater on-resistance resulting in less efficiency and more heat. The inductor is another one of those parts that you have to select carefully. Higher voltages would require a larger inductor, more copper, more space, and greater cost. An increase in cost is definitely a deal-breaker when you're already close to $400. So for those and other reasons, I decided to stop at 100v and retain all of the other features that cost money, but which I wanted to make sure were included. There are tradeoffs in every design. While Midnite's controller might have a 120v limit, the spec sheet says it derates above 25degC, so how much current are you going to get out of it when it gets hotter than room temp?

    Stay tuned for availability on the 3048. Should be another week or two.

    Marc
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: How much power will I loose using these panels for 12 volt?

    Thanks for the added info Marc. I guess there are always design trade offs - no free lunch!

    I'm sure it will be a great product and you will sell a bunch. It must be tough competing with the big guys! - much respect.:cool:
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    lorelec wrote: »
    That is a 100v Voc limit, and I realize that's going to be a deal-breaker for some of the GT panels...but it's so hard to make everyone happy. All of the components are already rated >100v for a margin of safety. The FETs, for example, are 120v. The caps 160v. I'm sure there are manufacturers that like to advertise a "150v max" controller...and use 150v FETs. I'm not comfortable with that. So to make a 120v controller I'd be using 150v FETs, which have a significantly greater on-resistance resulting in less efficiency and more heat. The inductor is another one of those parts that you have to select carefully. Higher voltages would require a larger inductor, more copper, more space, and greater cost. An increase in cost is definitely a deal-breaker when you're already close to $400. So for those and other reasons, I decided to stop at 100v and retain all of the other features that cost money, but which I wanted to make sure were included. There are tradeoffs in every design. While Midnite's controller might have a 120v limit, the spec sheet says it derates above 25degC, so how much current are you going to get out of it when it gets hotter than room temp?

    In standard buck design, FET only sees the difference in voltage between battery and PV, so in 48V configuration FET rated for 120V will work for 120+48 = 168V. Same goes for the inductor. The capacitors are already rated at 160V. Most people would rate it at 150V if not 160V! 60V safety margin is really good. People won't be afraid of higher VOC during cold winter days. No doubts this could've worked for 3-panel strings, which usually have VOC around 110V.
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    NorthGuy wrote: »
    In standard buck design, FET only sees the difference in voltage between battery and PV, so in 48V configuration FET rated for 120V will work for 120+48 = 168V. Same goes for the inductor. The capacitors are already rated at 160V. Most people would rate it at 150V if not 160V! 60V safety margin is really good. People won't be afraid of higher VOC during cold winter days. No doubts this could've worked for 3-panel strings, which usually have VOC around 110V.

    You always have to take worst-case into consideration. With a 120v input and a 120v FET, and perhaps a 12v battery that drops down to 10v for some reason -- you have only a 10v margin remaining. Parasitics could cause a little ringing that would narrow even that margin considerably. That would be a poor design choice. What happens if someone shorts the battery? All of a sudden you have full Vin across the FET and POOF! If you want to keep Ip-p ripple on the inductor under some maximum, then you'd have to increase inductance with a higher Von, which will require more turns/larger core. If you don't, then you'll have to see if the resulting temp rise from the higher ripple is manageable.

    Marc
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    lorelec wrote: »
    You always have to take worst-case into consideration. With a 120v input and a 120v FET, and perhaps a 12v battery that drops down to 10v for some reason -- you have only a 10v margin remaining. Parasitics could cause a little ringing that would narrow even that margin considerably. That would be a poor design choice. What happens if someone shorts the battery? All of a sudden you have full Vin across the FET and POOF! If you want to keep Ip-p ripple on the inductor under some maximum, then you'd have to increase inductance with a higher Von, which will require more turns/larger core. If you don't, then you'll have to see if the resulting temp rise from the higher ripple is manageable.

    Of course when you design an inverter you need to make it fool-proof and take into account the guys who's going to short batteries, make wrong connectins, etc. Given enough copies sold, there will be a multitude of user errors, some of which are even impossible to predict. When I connect something wrong and it survives, I'm always very grateful to the engineers who thought about all the stupid mistakes I can make :D
  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    Re: How much power will I loose using these panels for 12 volt?
    NorthGuy wrote: »
    Of course when you design an inverter you need to make it fool-proof and take into account the guys who's going to short batteries, make wrong connectins, etc. Given enough copies sold, there will be a multitude of user errors, some of which are even impossible to predict. When I connect something wrong and it survives, I'm always very grateful to the engineers who thought about all the stupid mistakes I can make :D

    Trying to make a product bulletproof as well as foolproof is a major challenge. Reverse battery connections are a more common occurrence than I imagined. Short circuits happen. People use products in ways that they're not designed to be used. I tried to predict as much as that as possible when designing the 3048. I'm sure someone will find a way to use it that I had not thought of, though!

    Marc