Mppt vs pwm

2

Comments

  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    *sigh*

    A PWM type controller will only pass the maximum current available from the panel(s): Imp

    No, that's absolutely wrong. You need to learn how pv works.

    Are you going to close this thread down now too?

    Cal
  • PhotowhitPhotowhit Solar Expert Posts: 5,323 ✭✭✭✭✭
    Re: Mppt vs pwm
    calbiker wrote: »
    No, that's absolutely wrong. You need to learn how pv works.

    Are you going to close this thread down now too?

    Might want to explain your statement, right now most everyone reading this is saying,...

    ...Do YOU understand how PV works?
    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
  • Jigme UrgyenJigme Urgyen Registered Users Posts: 13
    Re: Mppt vs pwm

    what really needs to be said is that your talking about charge controllers that have MPPT against charge controllers that dont have MPPT. PWM is a technology that the charge controller uses when hooked up to batteries. MPPT is something that is used by the charge controller on the PV side to track the array's power point. Everyone knows the benefits, and it isnt just about power gains or dealing with hotter weather, although those are some benefits.

    I think its almost not worth talking about anymore, Unless you building a very specific system, something small or with a fixed static load.

    If you think your batteries will be charged back to 99% SOC by midday with your array, save the money on a PWM charge controller and buy some tigo gear. You get some management and a whole lots of metrics from your array that is very interesting and useful. plus each module unit will give you some MPPT at the panel. One thing that sucks with cheap solar systems is lack of management of the array and the batteries.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Mppt vs pwm
    calbiker wrote: »
    No, that's absolutely wrong. You need to learn how pv works.

    Are you going to close this thread down now too?

    Cal

    I might suggest you consider your tone a bit. Folks here are all to wiling to share thier knowledge, and most of it from most posters (especially the mods (excepting me)) is very learned, educated and experienced. Some of these guys are EEs, and PV design engineers so suggeting " they learn how PV works" is a bit cheeky to say the least. I sugget that if you have an opinion, please fee free to proffer it, but also undertnd that you will need to back that opinion up with some fact. Post some side by side comparisons bolstering your opinions on MPPT vs PWM and then we CN have a discussion.

    Very early on, I flippantly commented that I "got double production at very cold temps". When met with skeptisim as to the amount of cold weather gin, I was forced to look at the numbers and modify my "claim. In fact I got much better production in the cold, but not twice as much. So like I said, folks here are very smart, many of whom have forgotten more about RE/PV than most of us will know. They are here Ito help, and shae tht vast knowledge freely, but being (wrongly) arrogant will only irritate folks that know way more than you.

    Icarus
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Mppt vs pwm
    I think its almost not worth talking about anymore, Unless you building a very specific system, something small or with a fixed static load.

    I hear you.. I got all confused with my proposed system.. (PWM vs. MPPT)

    Ended up going with a bigger PWM Controller (Morningstar TS45).. Granted initial outlay ($150) is smaller vs the MPPT type ($400).. but I'll always wonder what if..

    780w of 12v panels 130w (17.xxV) on a 45 amp PWM controller (3 parallel strings of 2).. the good news (IMHO) is I have room to double my wattage on the same setup..

    The sun is good in the south where my cabin is near.. (30.69 lat & -104.85 long).. all panels facing south and nothing in there way..

    It does hit 0' F down here and we got 1 1/2" of snow in the winter.. so I may not gain as much with the MPPT on those days.. but I won't be using much juice in the winter either.. (LP heater and wood stove).

    The PV costs is a toss up at the end of the day.. $1400 for 24v panels (for 760w) or $1250 for 12v panels (for 780w).. the 12v panels are easier to handle by myself as well..

    I went 12v as untill I get all the panels setup and mounted I can use the 12/24v controller and a single 12v battery, and at least get juice flowing for my drill.. then when all is setup I get my battery bank (24v), flip a few DIPS (to switch to 24v) and be GTG..

    ETA: This was added for you folks to discuss and analyze.. I'm not changing my setup..
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm
    calbiker wrote: »
    No, that's absolutely wrong. You need to learn how pv works.

    I may not be the sharpest knife in the drawer, but I do know how PV works.

    Moreover, I know better than to deliberately antagonize the moderators of a discussion forum.

    You need to learn a lot more than just how PV's work.
    Are you going to close this thread down now too?

    Cal

    No, I'm going to wait for you to explain to us all how PV's work and how it's possible for them to output more current than the panels themselves can produce.

    In fact we're all waiting for you to back up even one of your claims with some real data.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm
    Photowhit wrote: »
    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.

    when the controller (any controller) hits absorb, then and only then will the controller start to cut back on the current. so going by my example, if this is an actual voltage before the absorb setpoint then my example does hold true and by the downconverting of the mppt cc it would output more than the pwm which the pwm is only outputting the imp before it goes to absorb at the same setpoint.

    now if the current being delivered to the battery is large % of the charge then the battery may start to setback the current as it would self regulate, but a higher ah battery may take on all of the available current before absorb. this higher ah battery would fit the standard range we often cite in the 5% to 13% charge rate range. imo if the current does fold back in bulk then it may be overcharging as that foldback is supposed to occur in absorb and not bulk.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Mppt vs pwm
    calbiker wrote: »
    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
    15% is a typical average, as most spec sheets etc will tell you, and has been stated here several times. We have seen gains as low as 2% in Phoenix in the summer, and as high as 42% in Flagstaff in the winter.

    And I think you are missing the 2nd most important factor in MPPT controllers, which is that it allows the use of much higher voltages feeding the controller and thus much smaller wire.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm
    what really needs to be said is that your talking about charge controllers that have MPPT against charge controllers that dont have MPPT. PWM is a technology that the charge controller uses when hooked up to batteries. MPPT is something that is used by the charge controller on the PV side to track the array's power point. Everyone knows the benefits, and it isnt just about power gains or dealing with hotter weather, although those are some benefits.

    I think its almost not worth talking about anymore, Unless you building a very specific system, something small or with a fixed static load.

    If you think your batteries will be charged back to 99% SOC by midday with your array, save the money on a PWM charge controller and buy some tigo gear. You get some management and a whole lots of metrics from your array that is very interesting and useful. plus each module unit will give you some MPPT at the panel. One thing that sucks with cheap solar systems is lack of management of the array and the batteries.

    do understand in general that i have nothing against pwm controllers and have had a few of them myself. also, understand that mppt does not create a power gain as i would better describe it as a power recovery from that which would've been normally lost just using a pwm style of cc. the controller is not creating anything, but rather is working with what it is presented with to be better utilized in charging the batteries through more current available from said power.

    as to how you describe mppt is not quite accurate as you make it sound as if it is an addon to a pwm controller and that's just not quite right. it is, at the risk of oversimplifying, a dc to dc converter that has provision to self adjust for the changing input conditions it's presented with during the bulk stage. now during absorb or float it may act more like a pwm.

    in operation the mppt wins hands down, but in the real world it may not always be cost effective for a small system as mppt costs quite a bit more than pwm. this cost aspect was not the aspect of the discussion i was addressing, however, it is worth considering. there are always factors that may sway one individual over another under the same general system setup. things like future expansion and long wire runs can be 2 of the influencing factors that i believe were mentioned already by bb, but often it will boil down to an individual's personal preferences and decision on what is good for them to go with.
  • Jim45DJim45D Solar Expert Posts: 102 ✭✭
    Re: Mppt vs pwm
    ywhic wrote: »
    I hear you.. I got all confused with my proposed system.. (PWM vs. MPPT)Ended up going with a bigger PWM Controller (Morningstar TS45). I'm not changing my setup..

    I know exactly where you're coming from. I have used MPPT, of course "Old Technology" as I"m using Blue Sky, and have been for nerly 8 years now. Yes, I have saw a over exagerrated increase in that 8 years of no greater than 4% increases. Why? By trying to let moma nature replicate STC of 77°. That does happen in January, but very few days.I have gone with exactly what you have, as far as the controller. Morningstar PWM 45 CC. When the MPPT leaves the bulk mode....it changes it's name to PWM anyway. and my bulk is over by 9:45 am, at the latest. Increase, you bet. None. At present time of this post 8:35am it's only 90° in the shade. Who knows what it is temp. wise on the roof. However, I will soon place a remote thermometer up there.

    Whatever it is, MPPT isn't going to help. No doubt they work swell in the milder, cooler parts of the country. But here in the remote desert of S.W. Arizona any increase is lost due to heat on the wiring and panels. I will get one of those, just as soon as they modify them to supply a mist of semi-cool water on, and around the panel placements....it must be on demand though. Stick with what you have. These guys here will, and from what I've seen will help all they possibably can. To you and everyone else. Seldom does one get wrong advise. However, it does and will happen again.

    I have spent close to what you have, and mine is on a RV....and, I'm not done yet. Just simply go with more panels if the ambient heat is against you. I'm ashamed to post what I've spent, and I can't stop in mid-stream now. Too much invested, and more to be invested. A larger array than what we both are contemplating, more batteries, (and I'm limited here due to space) 40° cooler, batteries ran below 60% DOD, irresponsibility concerning conservation...this senario would beg for MPPT. All of this is why I canned MPPT, and went with PWM. Those STC's that were done in a controlled labratory doesn't apply to the real world. At least not to the real one here in Az. Moma nature can change that whole sales gimmick pitch in a matter of 2 to 3 minutesr rendering MPPT worthless here. You may get a few more day's use in your S.W. Texas location. However, is it enough to justify the extra monies?

    Hide and watch, as soon as this newer technology wears off a new one will crop up. Say did you hear of the new panel in production. A bright new company forming in S. China. The Sun-Hung-Low Mfg. Co. A up and coming solar corporation due to lay-offs of employees from Yingli & Toyomit. They gotta keep going....if they don't other competition will drive them out. Hang in there Al.

    Remember: Salesmen gotta eat like everyone else,....including lawyers.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm

    "But here in the remote desert of S.W. Arizona any increase is lost due to heat on the wiring and panels."

    just so you understand, this will represent a loss to any controller and not just an mppt. those described losses occur prior to getting to the cc and no matter what type of cc you are using you will suffer these losses. this does not mean mppt is wrong for hot areas of the country as it means you need a higher vmp to overcome temp losses. the wiring losses are similar as a higher vmp is the answer there too if you can't change the wire gauge or the length used. these losses are a bad thing for any controller.

    i am not trying to persuade you to change your controller either for if your system works well for your requirements even with the losses then why change it?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    One of the reasons it was suggested to Al to stay with the PWM controller: heat, enemy of all things (especially PV's).

    Since heat knocks a panel's Voltage down, the Voltage difference between battery and Vmp for the panel becomes less and less. It is that difference (times the current) that is the power which "goes missing" with PWM controllers and that MPPT (as Niel so correctly stated) can recover. If that power isn't there to begin with, there's nothing to recover. Nothing can make up for that.

    Although related to the cold temperature superconducting that can greatly increase the panel's Voltage and thus the maximum current available through an MPPT controller, the two situations are not identical. Under normal operating conditions the MPPT can recover that V-difference * Imp power. Remove the V-difference with heat and you remove the power. Increase the V-difference with cold and you increase the power potential.

    But in a side-by-side comparison you would look at neither temperature extreme when comparing the amount of maximum power available from the same panels using the two different controller types. In that instance the MPPT does have an advantage. But as has been stated repeatedly on this forum it is usually not worth the extra money for a smaller system; the controller price difference would buy another panel which would equate to more power gain.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm

    not so sure coot is splaining things quite right.:confused: a bit of power is lost at high temps, but it's not as much as you might think if you read and calculate for individual pvs under a certain hot temps. the real problem is the voltage reduction can fall below the point where the batteries can get a proper charge and this is a problem no matter what cc type is used. when a pv rated at say 16.9v vpm is used and present a hot temp in conjunction with batteries that would require near 15v and it may stop doing anything as the cc itself may require a buffer or minimum voltage above that of the battery's voltage in order to operate. this requirement no doubt varies considerably from cc to cc and often is not mentioned in specs for it.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    Yes, I was rambling a bit. :blush:

    Just trying to point out that if you're comparing the maximum power available from any given array with the two different types of controller you can't go throwing high or low temperatures in because it skews the results due to the change in Voltage of the panels.
  • Jim45DJim45D Solar Expert Posts: 102 ✭✭
    Re: Mppt vs pwm
    Jim45D wrote: »
    Whatever it is, MPPT isn't going to help. No doubt they work swell in the milder, cooler parts of the country. But here in the remote desert of S.W. Arizona any increase is lost due to heat on the wiring and panels.

    Please let me rephrase that...."Whether it's PWM or MPPT" it will not do anything....as there's nothing there to do anything with. Why? It only gets worse as the day progresses. I do understand guys. Heat is the culprit. I just simply phrased it wrong. Thanks. Presently, at 9:45 with ambient temp at 96.3 in the shade. My ole trusty MPPT is doing a tap dance of 13.7 V on the meter. Batts fully charged. Therefore it will just flicker the rest of the day between 13.5 & 13.8 V.
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Mppt vs pwm

    For the Morningstar Ts-45 PWM the manual says:

    PWM Battery Charge Algorithim settings are configurable for..

    14.0
    14.15
    14.35
    14.4
    14.6
    14.8
    15.0

    I don't know if thats the numbers your referring to or not.. Does say lowest battery charging voltage in the notes for those settings..
  • Jim45DJim45D Solar Expert Posts: 102 ✭✭
    Re: Mppt vs pwm

    No Al. I'm not refering to the PWM cc. I'm still using the BS MPPT. I don't have the new cc or meters installed yet.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    Niel's point, btw, was that with an MPPT controller you can put panels in series so that even under high temp conditions that could cause the available single panel Voltage to drop below a level capable of charging the batteries there would (with the series connection and MPPT controller) be enough Voltage to maintain battery charging.

    Man, that gets cumbersome no matter how you try to say it. :roll:
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Mppt vs pwm
    ywhic wrote: »
    For the Morningstar Ts-45 PWM the manual says:

    PWM Battery Charge Algorithim settings are configurable for..

    14.0
    14.15
    14.35
    14.4
    14.6
    14.8
    15.0

    I don't know if thats the numbers your referring to or not.. Does say lowest battery charging voltage in the notes for those settings..

    no. those i believe are controller output voltage presets and if the controller needs say a minimum of 16v to operate (not sure for the cc) then a heated pv could fall below the minimum input voltage it needs to operate. i am guessing on the minimum input voltage and this will vary from cc to cc. there may be some out there that will operate without a higher input requirement as i'm thinking the shunt types here on this like stecca has. series controllers will need more voltage in than the desired voltage and may be as low as the v drop loss at the mosfets which is often a fraction of a volt. this is in fact an area not very much talked of and might be interesting if someone could do some tests to get approximate minimum voltage leeways for various controllers.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    Along those lines, I dug through some Outback data and found no definite mention of minimum input Voltages per se.
    However, their charge efficiency graphs indicate 17 Volts for a 12 Volt system, 34 Volts for a 24 Volt system, and 68 Volts for a 48 Volt system.
    Other controllers could of course have different specs.
    This is why you can have trouble with '12 Volt' panels whose Vmp is '16.9' or the very common '24 Volt' panels whose Vmp is '30'.
    The usual problem with Voltage causing "no charge" on MPPT controllers is batteries drained below the minimum to fire up the controller. Seen it more than once on this forum.
  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    Photowhit wrote: »
    Might want to explain your statement, right now most everyone reading this is saying,...

    ...Do YOU understand how PV works?

    LOL, yes I do! I was hoping someone here does also. Perhaps someone will step up and explain PV to you guys. I can certainly understand why you think mppt is so much better. It's just that your underlying conception how pwm works is incorrect.

    Cal
  • calbikercalbiker Banned Posts: 50 ✭✭✭✭
    Re: Mppt vs pwm
    No, I'm going to wait for you to explain to us all how PV's work and how it's possible for them to output more current than the panels themselves can produce.

    In fact we're all waiting for you to back up even one of your claims with some real data.

    I'll make you a deal. Fix the battery FAQ and I'll school you on PV.

    Cal
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm
    calbiker wrote: »
    I'll make you a deal. Fix the battery FAQ and I'll school you on PV.

    Cal

    Here's the deal: put up or shut up.

    It's all very well for you to come on here and shout "You're wrong!" at everyone, but so far you've only offered your unfounded opinion as to why. Not one word of explanation nor a single fact to support your opinion. And in the interim you've done nothing but antagonize.

    We're still waiting for you to contribute something positive instead of just wasting server space.
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Mppt vs pwm

    He came in on 4/22 asking a question.. & now he knows it all.. (I thought I was special..)

    Rule #1 don't insult mod's on ANY FORUM..

    You said your in Maui.. so just repeat that and don't post till you get home then WITH data..
  • BB.BB. Super Moderators, Administrators Posts: 30,940 admin
    Re: Mppt vs pwm

    Calbiker,

    Just so you are aware--None of us moderators have any business relationship with our host NAWS (other than, possibly, as a customer once in a while). We are all volunteers here and all we do is try to keep spam under control and help keep posts on "theme" (i.e., we will split off posts to new threads. Helps keep threads "on track" for the original discussion/poster's intent).

    Anything with NAWS, their store, website, FAQ's, etc. are not in our control. Windsun and Rick are both the admins here from NAWS and keep the forum software running and pay the bills (thank you again NAWS!:D) and operate the forum to help spread useful information to all (customers or not).

    Windsun and Rick do read and post here on occasion. If you have a concern about a FAQ--Please feel free to PM Windsun directly with your suggested changes. They do not read/monitor all posts here (that is the job of us moderators) and it is very easy for them to miss anything directed towards them.

    Take care,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Jim45DJim45D Solar Expert Posts: 102 ✭✭
    Re: Mppt vs pwm

    CalBiker: What's wrong with the battery FAQ's? Also please explain why the underlying concept of how a PWM CC does work, vs MPPT. I personally don't need more incorrect information. Not that I've been given any thus far, but please spell it out.
  • CATravelerCATraveler Solar Expert Posts: 98 ✭✭✭✭
    Re: Mppt vs pwm

    I favor mppt because of panel costs and to a lessor degree limited panel space on a RV. The sweet spot for panels today is the larger lower $/W panels with the trade off for a more costly CC. And with 12V I'm at the lower end of the CC maximum power than say a smaller 24V CC which might have a little less cost.

    I'm still trying to sort through more detail concerning serial vs parallel panel shading. Shading is a given for a RV, just a fact of being mobile.
  • CATravelerCATraveler Solar Expert Posts: 98 ✭✭✭✭
    Re: Mppt vs pwm

    Where can I find more detail on how mppt actually works? I've read some generalized descriptions about searching for the max power point, etc. but how to get there? Constrain/enhance voltage and/or current? Technically I should be OK in the understanding arena but this not an area that that I'm skilled. Thanks in advance.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Mppt vs pwm

    Basically it's a microprocessor controlled buck converter. http://en.wikipedia.org/wiki/Buck_converter
  • PhotowhitPhotowhit Solar Expert Posts: 5,323 ✭✭✭✭✭
    Re: Mppt vs pwm
    niel wrote: »
    when the controller (any controller) hits absorb, then and only then will the controller start to cut back on the current. so going by my example, if this is an actual voltage before the absorb setpoint then my example does hold true and by the downconverting of the mppt cc it would output more than the pwm which the pwm is only outputting the imp before it goes to absorb at the same setpoint.

    In a discussion of "MPPT vs PWM" if your leaving out that the last 10% of charging is the same, What some(I) would call "...nears full charge ..." ...

    And, as a group, we typically recomend not discharging more than 20%...

    It is important in the understanding of the adavntages of MPPT charge controllers.

    Most of the posts relate to a momentary or "point in time" advantage. Not the overall advantage which this fact is very important in the comparison of MPPT vs PWM.

    Hope you agree with all this, unlike others here, I'm trying to add to the understanding, not trolling...
    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
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