Mppt vs pwm

I am building a small solar system which will put out around 300 watts. Im trying to decide what kind of charge controller to get. My system is rated to use around 500 watts a day so effeicency is not that much of a problem because i have plunty coming in. Would you reccomend going with the more expensive MPPT or go with the cheap PWM.
Will the PWM be able to take in 33 volts from the solar panel?
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Comments

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Mppt vs pwm

    is it a 12v or 24v system?

    What do you mean "your system uses 500w per day"???
  • alexassyiaalexassyia Registered Users Posts: 3
    Re: Mppt vs pwm

    sorry for the confusion i had to type this post in a rush. I mean that i added up a estimate value for my energy use for all my devices and got around 500 watts of power consumption per day. So with my 300 watt solar panels i dont think efficency for me is that much of an issues by losing 20 % by going with the PWM.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    Welcome to the forum.

    So your looking at a 300 Watt array and power consumption of 500 Watt hours per day?

    In addition to the system Voltage john p asked about, you need to know how far the array will be from the charge controller.

    The issues are:

    A PWM controller can not down-convert Voltage, so if the panels are "33 Volt" (Vmp?) they will not work well on a 12 Volt system. Frankly they will not work well on a 24 Volt system either; it's too low for proper charging.

    If the distance from the panels to the controller is long you can have a problem with too much Voltage drop before reaching the controller. In that case running the panels in series (or a combination of series/parallel depending on the exact specs) will give you higher Voltage to overcome the extra wire resistance. And then you're back to issue #1.

    Otherwise you'll lose about 140 Watts of power from your 300 Watt array, or about 46% not 20%.

    More details will help us help you. :D
  • PhotowhitPhotowhit Solar Expert Posts: 5,358 ✭✭✭✭✭
    Re: Mppt vs pwm

    Are your panels rated 33 voc (voltage open curuit) 33 vmp(voltage under load)?

    Either way, if you have a 12 volt system, likely you'll need an mppt type, or more panels. Looks like you have panels designed for grid tied systems or MPPT type controller. A slim chance if you have a 24v system and 33vmp panels your fine.

    This is due to loosing more tha your 20% closer to 50%.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • alexassyiaalexassyia Registered Users Posts: 3
    Mppt vs pwm

    Thank you for all the help, its looking like MPPT will be the better chocie here
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: Mppt vs pwm

    A couple of good 12/24 volt battery bank MPPT charge controllers to look at in that power range:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller
    Rogue 12/24 volt 30 amp MPPT controller

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • firerescue712firerescue712 Solar Expert Posts: 93 ✭✭
    Re: Mppt vs pwm
    BB. wrote: »
    A couple of good 12/24 volt battery bank MPPT charge controllers to look at in that power range:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller
    Rogue 12/24 volt 30 amp MPPT controller

    -Bill

    I use both of these charge controllers and highly recommend them.
  • BillBlakeBillBlake Solar Expert Posts: 49
    Re: Mppt vs pwm
    alexassyia wrote: »
    I am building a small solar system which will put out around 300 watts. Im trying to decide what kind of charge controller to get. My system is rated to use around 500 watts a day so effeicency is not that much of a problem because i have plunty coming in. Would you reccomend going with the more expensive MPPT or go with the cheap PWM.
    Will the PWM be able to take in 33 volts from the solar panel?

    Traditional PWM vs. Morningstar’s TrakStar™ MPPT Technology

    Introduction:

    Morningstar MPPT (Maximum Power Point Tracking) controllers utilize Morningstar’s own
    advanced TrakStar™ Maximum Power Point Tracking technology to harvest the maximum amount of
    power from your solar array. It is generally accepted that even the most basic MPPT controllers will
    provide an additional 10‐15% of charging capability compared to a standard PWM regulator.

    In addition to efficiency, there are several important differences between PWM and MPPT technology and unique
    advantages to each. These basic differences are outlined below and an explanation is given on how to
    properly size solar arrays for each type of controller.

    <snip>

    http://www.morningstarcorp.com/en/support/library/MS.WP.MPPTvPWM.01.EN.pdf


    This Morningstar paper isn't going to address your particular situation like the slick old (and young)
    Daddies on this forum can :-) However I thought you might enjoy it.

    I've been looking through a lot of old posts and one recurring theme seems to be paramount.
    'Plenty of Solar Power (on average) - not enough Charging Time.'

    The 'Too Much solar, a Good problem' thread is an example.

    Wonder what the average (supplemental) generator fuel costs are running over a 10 year period?
    Including maintenance, repairs and replacement.

    Some riddles take a long time and some can crack pretty quick.
    niel will crack this riddle of all Solar riddles this month :p

    Bill Blake
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: Mppt vs pwm

    I have a Morningstar MPPT controller and a Steca PMW, folks here do not appear to be familiar with a well made German PMW controller that will handle up to 47V, this is an option. http://www.stecasolar.com/index.php?Solar_charge_controllers
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: Mppt vs pwm

    Actually, our host carries a couple (6 and 10 amp PWM versions?):

    Steca Charge Controllers for Solar Electric Systems

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Mppt vs pwm

    With my proposed scenerio I'm getting beat up on other forums from choosing a MorningStar TS-45 PWM w/meter ($240).. over an MPPT one..

    Do you have a decent MPPT controller for under $275 that can handle one of these 2 possible scenerios??

    My proposed panels are either going to be Kyocera 12v 130 w panels (17.4 VMP, 7.75 IMP) x 6 (2 in series (34.8 VMP, 7.75, VOC would be 43.4) then the 3 in parallel) (23.25 IMP together) (780 watts of PV)

    or possibly 3 280 w panels (35.5 VMP, 7.89 IMP, VOC 45) in parallel.. (23.67 IMP together) (840 watts of PV)

    Both PV scenerios are over the normal 29-30 VMP (GT panels), with 34.8-35.5 VMP respectively..

    I'm just trying to charge a 24v battery bank (though thats changable I guess).. so some persons here stated with 34+ VMP panels I could stick with PWM controller and be fine..

    Possible choices I like(d) are:
    MorningStar 15 MPPT.. but it looks as though I am ABOVE the max rating on that..
    Stecca 2010 is rated at 20 amps max as well..
    BlueSky SB3024IL or DIL (with display) (30 amp) looks good but the price is over $325..
    Rogue MPT-3024 (30 amp) is nice too but again $325

    Whats your take on that BB??
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: Mppt vs pwm

    Albert, there are people with much more experience than I with those controller choices (I have none--so that was easy :roll:)...

    From my limited knowledge, I would suggest MPPT controllers for:
    1. Long distances between Array and charge controller/battery shed (reduce copper wire costs)
    2. High power installations (over ~400-800 watts--again, reduce copper wire costs for array to controller)
    3. Ability to use "non-standard" Vmp solar panels (>>100 watts, typically much less expensive $$/watt)
    4. Wide temperature extremes (very hot panels can depress Vmp-array enough to make equalization charging a bit iffy--where you want >15.0 volts for equalization)
    5. Logging/Ethernet/Computer logging and connectivity (typically, the more expensive/modern MPPT controllers have more of these functions).
    6. Some MPPT controllers have more sophisticated charging algorithms that may allow you to better/faster charge your battery bank with custom parameters (timed/low current float transition, remote battery temperature sensors/remote voltage sense leads, etc.).

    Advantages for PWM controllers:
    1. Much cheaper. You want an extra 10% more power, get more panels with the savings
    2. Some PWM controllers do offer remote battery temp sensors and even remote voltage sense (MorningStar TS PWM models).
    3. Did I say cheaper?
    4. With Vmp~17.5 volt panels connected in parallel vs series or parallel connected MPPT controllers--There is really not that much power increase (10%) unless you have lots of sub-freezing weather.

    With many of these controllers, PWM or MPPT, you may want to purchase a digital display (not cheap), a computer converter interface (not cheap), or even some sort of gateway for network connectivity (not cheap).

    Some MPPT controllers come with a native LCD Display (Rogue, Outback, Midnite Classic). Some do not need computer interface adapters (Rogue, Midnite). And a few even come with Ethernet native connectivity (MorningStar TS MPPT 60 amp; Midnite Classics).

    The above list is not comprehensive--More of a suggestion of where/what to look for.

    If the PWM controller will meet your needs and price point--Why not.

    If the MPPT with non-standard Vmp panels can come close to meeting your price point and give you additional functions that you would like--Why not...

    In the end, I would suggest a rough design/costing to see where your price points will end up.

    And make sure to include shipping/insurance... >~135 watt solar panels may have to ship truck, and both can cost an arm and a leg to ship (especially if these are partial pallet shipments that need to be repacked). Also, panel over ~175 watts usually need two people to handle safely during installation.

    Hope this helps rather than confusing you more...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CATravelerCATraveler Solar Expert Posts: 98 ✭✭✭✭
    Re: Mppt vs pwm

    Check the limits of whatever CC you're considering. With 840W you're pushing 30A. I know that the Rogue will take more watts and derate on 12V, but don't know about 24V. Temperature etc. should be considered.

    Morningstar has a nice calculator for their products to help with the limits.
  • PhotowhitPhotowhit Solar Expert Posts: 5,358 ✭✭✭✭✭
    Re: Mppt vs pwm

    Your right at the limits for the Rogue, Why don't you write Marc and ask him what he thinks? I found him to be very personable. I have a Rogue, but really only use it to check out panels, If your going to get a PWM with a display, there isn't a huge difference.

    If 'SunKing' is giving you problems I'll gladly go debate him... So long as you explained that your primary heavy load is in South Texas in the Summertime!

    He tried to have me thrown off one forum, when I explained to the Admin how silly he was getting they asked if I'd like to Moderate. God bless the moderators! it really is a time comsuming, often thankless job. So he's there and the forum is nearly dead...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Mppt vs pwm

    Photowit I spent many many hours trying to help people on the site Sunking is on but his arrogance just got me in the end. Even when I would prove him wrong he would never admit it. The final straw was when he lost the arguement he was having with me he had the whole thread deleted. His theory figures sometimes bear no resemblance to what you get with real items.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Mppt vs pwm
    ywhic wrote: »
    I'm getting beat up on other forums from choosing a MorningStar TS-45 PWM w/meter ($240).. over an MPPT one..
    <snip>
    so some persons here stated with 34+ VMP panels I could stick with PWM controller and be fine..

    Depends on how you define 'fine'. If you need to have the most efficient and expandable system possible in order to be fine, then no, you will not be fine with a PWM controller. If you want a system that performs well for less money, then yes, you will be fine.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Mppt vs pwm

    Well after checking the MS website last night.. the TS-45 PWM can get me 1560 watts of 12v (17.7 7.39) panels if needed (aka 12)..

    Since I am starting at 6 (780 watts of PV) and figure no more than 10 I should be be GTG for my intended setup.. its good to know I could go up to 1560..
  • PhotowhitPhotowhit Solar Expert Posts: 5,358 ✭✭✭✭✭
    Re: Mppt vs pwm
    john p wrote: »
    Photowit I spent many many hours trying to help people on the site Sunking is on but his arrogance just got me in the end. Even when I would prove him wrong he would never admit it. The final straw was when he lost the arguement he was having with me he had the whole thread deleted. His theory figures sometimes bear no resemblance to what you get with real items.

    FWIW - He is still listed as moderator at the original site, but it's clearly no longer moderated and over run with ads, as it turns out it was on a different site, but it was SunKing...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    BillBlake wrote: »
    Traditional PWM vs. Morningstar’s TrakStar™ MPPT Technology

    Introduction:

    Morningstar MPPT (Maximum Power Point Tracking) controllers utilize Morningstar’s own
    advanced TrakStar™ Maximum Power Point Tracking technology to harvest the maximum amount of
    power from your solar array. It is generally accepted that even the most basic MPPT controllers will
    provide an additional 10‐15% of charging capability compared to a standard PWM regulator.

    MPPT is overrated. My testing has shown under normal conditions using 12V battery and 17.4V Vmp panels, mppt gains over pwm is in the range 3 to 6%. Gain is dependent on battery voltage and PV temperature. 15% is a gross exageration.

    Cal
  • BB.BB. Super Moderators, Administrators Posts: 31,038 admin
    Re: Mppt vs pwm

    I agree, the 15-20%+ "increase" by MPPT is only present during (for the most part) subzero weather (cold panels). On warm days, MPPT and PWM will output pretty much the same (assuming Vmp-array is ~17.5 volts for both units).

    However--Given that there are few "true" 12 volt panels (Vmp~17.5-18.5 volts or so), MPPT controllers are pretty much a requirement as PWM controllers will have very poor solar panel efficiency... For example a Vmp~30 volt panel on a 12 volt battery system:

    17.5 volts / 30 volts = 0.58 = 58% efficiency

    The large panels are pretty nice... Generally the $$$/Watt price is lower, fewer electrical connections, and fewer mounting points. The downside is they do pretty much require a MPPT controller and for panels >~175 watts, it takes two people to safely move them around and install.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm

    the vmp and battery state of charge ratio also can make wide swings allowing the mppt controller to provide far more current when the pwm is wasting more power. this can even exceed the gains cold weather provides. it does generally take more power to run an mppt controller, but the gains are great enough over pwm to make them worthwhile even with the smaller pv prices we've been seeing.

    calbiker,
    i would also be interested to know what mppt controllers you were testing, lay out the test parameters, and to publish the results here.
  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    niel wrote: »
    the vmp and battery state of charge ratio also can make wide swings allowing the mppt controller to provide far more current when the pwm is wasting more power.

    You speak in platitudes. What do you mean by "far more" current? 3%, 5%, 10%, 30%? To me, far more sounds like 30%. That would be a gross exaggeration when using 17.5V panels.

    My comparison is between a BS 2512iX and a direct panel (130w Kyrocera) connection to battery. Not sure how much data I have access to as I'm in Maui for 3 weeks.

    Cal
  • PhotowhitPhotowhit Solar Expert Posts: 5,358 ✭✭✭✭✭
    Re: Mppt vs pwm

    I think Niel, and myself, are interested in what conditions the testing was carried out.

    When asked in detail, or if you read closely most of the MPPT builders will not claim more than a 10% gain during warm weather, and that only when the controller is acting as an MPPT controller, so gains would be modest, I don't doubt 3 - 5% and less if your not drawing down the battery much.

    Winter time with a heavy use system, and more MPPT time, I'd say it's likely to see double digits.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm

    platitudes eh? it is a well known fact that with lower battery soc that more current will be realized by the downconverting action of an mppt controller. for example if you have a charged up battery at say 14.6v and a good guess it may need .3v leeway to operate from a pv with a wmp of 200w that this could loosely translate into 200w/14.9v=13.4228a. let's also take 200ma off for its operational current (only as example) giving us 13.2228a realized to the battery.

    now when the battery has been discharged to a much lower soc that the same voltage leeway will be needed by the mppt cc and if down to say 12v that this will translate to 200w/12.3v=16.2602a. subtracting the 200ma tar now gives 16.0602a. this is from one extreme to another, but is representative of what can happen with mppt. this does not happen with pwm as the excess voltage present will not add to the power fed into the battery as it is more or less the imp-tar loss=net pwm current. now 16.2602a/13.2228a=1.2971 or a 29.71% increase.:p

    now about your test parameters and results for what mppt controllers? one mppt cc does not apply to all and blue sky is using older mppt technology.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Mppt vs pwm

    Couple of things,,

    The BS controller is a fairly old design. I own a Bs controller, as well as a Rogue, and I can monitor them side by side. The Rogue out performs the Bs hands down in all conditions. As has been suggested, MPPT gain is much greater with lower battery voltages, and begins to ebb as batteries come close to full.

    The question is,, for a single panel installation on an RV MPPT might not be worth the duded money, but as an array and battery banks gets bigger it becomes more advantageous. I love the MPPT controllers, but since my battery gets charged fully by mid day most days, I would probably. Be fine with a PWM controller.

    Tony
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm

    well we weren't talking of what it is cost wise in all circumstances as we were going into the real meat of what an mppt cc will typically operate like. even though the gains are less at near full charge it will still be more than the output current of a pwm cc. that's even true of blue sky's mppt controllers. in that example i gave for a 200w pv if that pv had a 17.5v vmp that would give a imp of 200w/17.5v=11.4286a. now 13.2228a - 11.4286a (didn't account for pwm tar losses) = 1.7942a over the pwm.
  • PhotowhitPhotowhit Solar Expert Posts: 5,358 ✭✭✭✭✭
    Re: Mppt vs pwm
    niel wrote: »
    ...even though the gains are less at near full charge it will still be more than the output current of a pwm cc.....

    I'd challenge this, as a charge controller nears full charge on the batteries it reduces the amount of current flowing, hence once it reduces to the point of the PWM CC there is no benefit.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    niel wrote: »
    platitudes eh? it is a well known fact that with lower battery soc that more current will be realized by the downconverting action of an mppt controller. for example if you have a charged up battery at say 14.6v and a good guess it may need .3v leeway to operate from a pv with a wmp of 200w that this could loosely translate into 200w/14.9v=13.4228a. let's also take 200ma off for its operational current (only as example) giving us 13.2228a realized to the battery.

    No way! Let's get real. Temperature is the great equalizer. Your 200W panel will never produce 200W in the real world.

    That's the main difference between mppt and pwm. MPPT is extremely affected by temperature while pwm isn't.

    As far as BS being old technology, that may be. But I doubt there's a significant difference. I know someone here claims the Rogue provides 15% more current over BS. I call that absurd.

    Cal
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Mppt vs pwm

    To be clear, neither controller is effects by temperature per we, only the PV is. PV out put varies considerably with temp, up with lower temps, down with higher ones. MPPT controllers can take advantge of the higher outputs at lower temps in ways that PWM controllers simply can't.


    I can tell you, having both the Bs controller and the Rogue , the Rogue out performs the BS in all conditions. That is not to say the Bs is a bad controller, but the Rogue is simply better. I am away from home for a bit so I can't give you a side by side for a while, but using the Trimetric to do a side by side, it it pretty significant.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    *sigh*

    A PWM type controller will only pass the maximum current available from the panel(s): Imp
    An MPPT controller can convert the "extra" Voltage available (if any) into additional charging current.
    This difference is prevalent at maximum charging current, id est minimal battery Voltage.

    To understand the claims made by manufacturers you only have to look at the difference using one panel. For this we'll choose the KD 135 which operates at Vmp 17.7 and Imp 7.63 (17.7 * 7.63 = 135 Watts).
    With the PWM controller the Vmp will be reduced to battery Voltage, so at a minimal 12 Volts you get 7.63 Amps maximum or 91.56 Watts: about 67.8% of panel rating.
    With the MPPT controller the maximum current has the Voltage difference added to it. Thus we use the typical 77% derating for panel + controller efficiency. The 135 Watt panel effectively becomes 103.95 Watts, and the potential maximum current 103.95/12 or 8.66 Amps.
    If you look at the difference between the MPPT's 8.66 Amps and the PWM's 7.63 you get get 1.03 Amps more from MPPT. Do the percentage calculation and you see (1.03 * 100 / 7.63) 13.49% more peak charge current with the MPPT controller.
    Pretty much what manufacturers claim, although I'd take issue with that being 13% increase in efficiency as it only applies to the maximum current potential. When Absorb or Float stage is in play, the current difference is not relevant as these stages are both Voltage dependent.

    The real advantage to the MPPT controller shows when you need larger arrays and have to find some way of moving greater amounts of power from the panels to the batteries without having to buy massive wiring to reduce V-drop (and thus power loss). If you needed six of those 135 Watt panels because you wanted 40+ Amps of charge current (45.78 with the PWM) you'd find yourself faced with the dilemma of trying to push all that current at system Voltage through, say, 20 feet of wire and end up needing about 2 AWG to keep the V-drop under 3% on a 12 Volt system. On the other hand the MPPT will allow you to double the Voltage and halve the current so the same charge rate delivered to the battery need only have 8 AWG from the array to the controller. A significant savings. The longer the wire run, the more current needed, the greater the MPPT advantage.

    It is not only about temperature.
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