pwm vs mppt?

BrianinsocalBrianinsocal Registered Users Posts: 13
I was reading a thread that came up from 2011 (Googled) So I am sure the info was outdated, then realized that this was a forum site and registered. Looking forward to learning a lot.

I tried using the search for this question but was having trouble finding it. I will be using 2 100 watt Renogy panels for a small system for my shed. Will have a 125 AH battery and an inverter. In the thread I was reading there was a question weather it was worth the cost to buy a MPPT controller over a PWM controller.

Can someone help me with this question. Sorry I am sure it has been asked many times but I would appreciate the help immensely.

Thanks in advance,
Brian

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: pwm vs mppt?

    Welcome to the forum Brian.

    For two 100 Watt panels that will put out about 11 Amps and be a short distance from a 125 Amp hour battery buying a $300+ charge controller makes no sense whatsoever.

    Caveats: the panels need to be proper Vmp for the battery Voltage, as in 17-18 for a 12 Volt system and the distance does need to be fairly short or else the wires end up being very large.

    Usually MPPT type controllers do not make economic sense until you get into >400 Watt arrays, wherein buying the "odd Voltage" GT panels is so much cheaper than standard panels that it pays for the added cost of the controller. There are a few exceptions to this, as with some RV applications where you need to squeeze out every bit of power you can.
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?

    Thank you Cariboocoot,

    You have saved me some money. I see that NAWS sells controllers. Could you possibly suggest one for me to purchase for this application.

    Thanks
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: pwm vs mppt?

    There are also times when MPPT controllers can be cost effective... Large panels (>~200 watts) are typically "non-standard" for battery charging Vmp voltages (~17.5 for 12 volt battery, ~35 volts for a 25 volt battery, ~70 volts for a 48 volt battery bank).

    The larger format panels tend to be Vmp~30/40 volts... An MPPT (Maximum Power Point Tracking) charge controller can take high voltage/low current from the array and efficiently (~95%) down convert it to low voltage/high current for charging the battery bank. (sort of like the DC version of a step-down AC transformer).

    And these large format panels can be ~1/2 the price of the smaller (140 watt or less) panels that are Vmp Battery "Friendly" voltages.

    So--You end up with less expensive PWM controller and expensive panels, or more expensive MPPT controller with cheaper panels (and the very large panels over ~140 Watts can be very expensive to ship--unless you are buying a pallets worth at a time).

    That is why we suggest doing a couple paper designs first. It does not take long to pencil out the requirements and pricing of the major components to see what will work best for your application.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?

    Thank you BB for the great info.

    Good idea to pencil out some paper designs first. That way I know what exactly I am going to be using the system for. I can then make a better choice at what I will need and use. I will be eventually be doing a bigger system on a room in the back area so the drawings will come in handy. I have a habit of jumping the gun and buying things then realizing there was a better solution.

    Thanks
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: pwm vs mppt?

    Several good quality "lower cost" MPPT controllers to look at:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller (always get the Remote Battery Temp Sensor option)
    MidNite Solar Kid MPPT Solar Charge Controller
    www.roguepowertech.com/products/chargecontrollers/mppt/mpt3048.htm

    You would be happy with any of the above. Look at options that may interest you (remote meters, networking, logging, etc.).

    The 15 amp SunSaver will handle just under 300 Watts "cost effectively". If you want more panels, you would need a 30+ amp controller and/or go higher than 12 volt battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: pwm vs mppt?
    Thank you Cariboocoot,

    You have saved me some money. I see that NAWS sells controllers. Could you possibly suggest one for me to purchase for this application.

    Thanks

    Do you have the exact panel specs for Vmp and Imp?
    It's going to be around 10-12 Amps I'm sure.

    This is the tiny Morningstar MPPT 15: http://www.solar-electric.com/mosumpsochco.html
    At $225 I don't see that being cost-effective compared to a 20 Amp PWM controller from the same company: http://www.solar-electric.com/ss-20l.html for $76 or a slightly fancier ProStar @ $89 http://www.solar-electric.com/pros15solcha.html

    In fact the ProStar 15 with meter is $137: http://www.solar-electric.com/pros30solcha.html
    Still cheaper than the MPPT 15, and you're looking at a power output difference of about 1 Amp if there's no problem with distance. Not worth spending another $100 for 1 Amp in my opinion.
  • ILFEILFE Solar Expert Posts: 364 ✭✭
    Re: pwm vs mppt?

    One thing I have learned since becoming a member of this forum is, ask yourself this question. "Is there any chance you will be expanding your system in the future?" If there is, I would suggest the more efficient (MPPT) controller. The Midnite Kid is the hottest new item on the market today. For a bit more money than a similarly sized PWM controller, you get a much better quality unit. The features are no comparison.

    EDIT: I see BB posted the same suggestion while I was working on my post. BMTA. :) Anyway, an accessory that will not be too costly to add to the Kid, is a WhizBang Jr battery monitor.

    My two cents,
    Paul
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?
    BB. wrote: »
    Several good quality "lower cost" MPPT controllers to look at:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller (always get the Remote Battery Temp Sensor option)
    MidNite Solar Kid MPPT Solar Charge Controller
    www.roguepowertech.com/products/chargecontrollers/mppt/mpt3048.htm

    You would be happy with any of the above. Look at options that may interest you (remote meters, networking, logging, etc.).

    The 15 amp SunSaver will handle just under 300 Watts "cost effectively". If you want more panels, you would need a 30+ amp controller and/or go higher than 12 volt battery bank.

    -Bill

    Thanks BB for that info. I probably will go with the Morningstar pwm for now just because I won't be expanding this system. Though I will be going at least 400 watts for the room outback and will use one of the MPPT controllers you recommended. Thanks again, Brian
    ILFE wrote: »
    One thing I have learned since becoming a member of this forum is, ask yourself this question. "Is there any chance you will be expanding your system in the future?" If there is, I would suggest the more efficient (MPPT) controller. The Midnite Kid is the hottest new item on the market today. For a bit more money than a similarly sized PWM controller, you get a much better quality unit. The features are no comparison.

    EDIT: I see BB posted the same suggestion while I was working on my post. BMTA. :) Anyway, an accessory that will not be too costly to add to the Kid, is a WhizBang Jr battery monitor.

    My two cents,

    Thanks ILFE, I won't be expanding this system due to the fact it is only for a smaller shed. Only will be running lights and an occasional drill motor. I will however be wanting something I can expand on for the room out back. Thanks for the info and the link to the Midnight Kid MPPT controller. I will keep it in mind for future applications.
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?
    Do you have the exact panel specs for Vmp and Imp?
    It's going to be around 10-12 Amps I'm sure.

    This is the tiny Morningstar MPPT 15: http://www.solar-electric.com/mosumpsochco.html
    At $225 I don't see that being cost-effective compared to a 20 Amp PWM controller from the same company: http://www.solar-electric.com/ss-20l.html for $76 or a slightly fancier ProStar @ $89 http://www.solar-electric.com/pros15solcha.html

    In fact the ProStar 15 with meter is $137: http://www.solar-electric.com/pros30solcha.html
    Still cheaper than the MPPT 15, and you're looking at a power output difference of about 1 Amp if there's no problem with distance. Not worth spending another $100 for 1 Amp in my opinion.

    Thanks Cariboocoot,

    I will go with either the ProStar @ $89 or the ProStar 15 with meter $137. Just going to go back to your store and compare the two items.

    Thanks again for your help with this. Can't wait to get the system up and running.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: pwm vs mppt?
    ILFE wrote: »
    One thing I have learned since becoming a member of this forum is, ask yourself this question. "Is there any chance you will be expanding your system in the future?"

    In this case I think expansion would be a totally different system, as he seems to be running 12 Volts with 'standard' panels and a small battery.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: pwm vs mppt?
    Thanks Cariboocoot,

    I will go with either the ProStar @ $89 or the ProStar 15 with meter $137. Just going to go back to your store and compare the two items.

    Thanks again for your help with this. Can't wait to get the system up and running.


    Um, not my store. :D
    We moderators are volunteers and do not work for NAWS nor any of the companies that make the equipment. It helps keep the information unbiased. We link to NAWS because they pay for the forum and it is a good retail outlet with decent prices and service.

    I don't even live in the same country. :D
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?

    LOL!! Small world, I just took it for granted you lived in the states.
  • BB.BB. Super Moderators, Administrators Posts: 32,318 admin
    Re: pwm vs mppt?

    I think Canada is a State of Mind... :-)

    Cololorado is a State of Intoxication... :-)

    -Bill "state of confusion" B. :p
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrianinsocalBrianinsocal Registered Users Posts: 13
    Re: pwm vs mppt?
    BB. wrote: »
    I think Canada is a State of Mind... :-)

    Cololorado is a State of Intoxication... :-)

    -Bill "state of confusion" B. :p

    LMBO!! To funny!! :D
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