MPPT charge controllers vs PWM for very small systems?

DumbdumbheadDumbdumbhead Solar Expert Posts: 28
Hi, I understand that MPPT charge controllers are superior in that they are more efficient but I am wondering how MPPTs perform in comparison to PWM controllers when applied to smaller solar arrays, say, under 200 watts?

Money is not the deciding factor for me in which controller I purchase, however, if an MPPT controller were to net me significant (relative of course) gains I'd be more inclined to purchase an MPPT controller.

I've heard somewhere, can't remember exactly that PWM controllers make noise? Is this true? How much noise? Is the noise annoying? Even a low decibel noise can be annoying if it is at a high frequency. This is an issue for me.

Does a PWM controller outperform an MPPT controller if applied to smaller systems (e.g. 110 watts of panels)? So I guess my main question is, is the advantage of an MPPT controller only seen if connected to larger arrays?

Thanx
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Comments

  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    MPPT will always yield more than PWM. Roughly this could be 20-30% more in winter and 10-20% more in summer.
    But for small systems the additional cost of the MPPT could be money better spent on more panels and a PWM. All depends on what the panel price is and what the price difference is between PWM and MPPT.
  • DumbdumbheadDumbdumbhead Solar Expert Posts: 28
    Re: MPPT charge controllers vs PWM for very small systems?
    stephendv wrote: »
    MPPT will always yield more than PWM. Roughly this could be 20-30% more in winter and 10-20% more in summer.
    But for small systems the additional cost of the MPPT could be money better spent on more panels and a PWM. All depends on what the panel price is and what the price difference is between PWM and MPPT.

    Stephendv, thanks for the reply. Cost is not a concern for me because the entry-level MPPT controllers, a few hundred bucks are in my price range. My only concern is performance in terms of outputted energy and noise. If what you say is correct, which I believe you are, then the MPPT controller is the way to go. I was just concerned that with an MPPT controller you will take a hit in regards to performance with smaller systems. Also, since I heard nothing about MPPT controllers making noise I am leaning toward the MPPT.

    Thanks again
  • BB.BB. Super Moderators, Administrators Posts: 32,204 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    Lots of questions---Lots of hand waving to follow:roll::
    Hi, I understand that MPPT charge controllers are superior in that they are more efficient but I am wondering how MPPTs perform in comparison to PWM controllers when applied to smaller solar arrays, say, under 200 watts?
    The smallest, well designed, MPPT charge controller I am aware of is the MorningStar 15 amp 12/24 volt MPPT controller.
    • 15 amps * 14.5 volts charging * 1/0.77 derating = 282 watt solar array @ 12 volts
    So, for a smaller 200 watt array--you do have a very nice controller available for $245 vs an inexpensive 20 amp PWM controller down to $90 or less.

    You could spend the $155 difference and throw another 50 watts or so of solar wattage out there...

    The advantages to MPPT (in my humble opinion by order of importance):
    1. Ability to run "high" Vmp-array for longer cable runs from the array to the battery shed/charge controller.
    2. Ability to run in wide temperature extremes efficiently. Hot Vmp=17.5 volt solar panels and cold battery banks means you may not get full voltage/current when charging/equalizing your battery bank. Run Vmp=35 volts on a 12 volt battery bank--and you have no worries about voltage drop (temperature, wiring, controller, or cold batteries requiring higher voltages to recharge).
    3. In cold weather (subfreezing), they can collect around 10-15% extra energy from Vmp increasing because of cold panels.
    MPPT controllers cost more and typically have more logging functions and computer interface options. Also, Remote Battery Temperature Sensors are usually an available options for MPPT controllers (monitoring battery temperature can optimize battery charging too).

    However, those options do cost money too--MorningStar probably makes a lot of money selling LCD displays for their units (Rogue offers theirs in the base unit).

    Instead of getting the extra LCD display option--I would consider spending that money towards a Battery Monitor. I believe, a much more useful piece of gear.
    Money is not the deciding factor for me in which controller I purchase, however, if an MPPT controller were to net me significant (relative of course) gains I'd be more inclined to purchase an MPPT controller.

    I've heard somewhere, can't remember exactly that PWM controllers make noise? Is this true? How much noise? Is the noise annoying? Even a low decibel noise can be annoying if it is at a high frequency. This is an issue for me.

    Two types of noise... Audio and Radio Frequency.

    There has been a few reports of audio clicking noises--but not too much that I remember.

    And RF noise. The more computers and MPPT hardware that is added, the more electrical noise that is created. Look for units that meet FCC class B (better) or Class A (not as good--but better than nothing).

    Many manufacturers have assumed they don't need to meet FCC limits for their controllers and, many times, people with AM radios, HAM, and other equipment have problems with interference.

    There is also a possibility of audio interference with PWM (and MPPT) controllers. Morning Star on some of their PWM units has a switch you can flip to change them from kHz of PWM switching to, I guess, a much slower seconds between "on/off" switching. This can reduce audio frequency audio noise (and RF noise too) on the battery bus.
    Does a PWM controller outperform an MPPT controller if applied to smaller systems (e.g. 110 watts of panels)? So I guess my main question is, is the advantage of an MPPT controller only seen if connected to larger arrays?

    PWM units are "less efficient" at taking 17.5 volt power and connecting it to 14.5 volt battery:
    • 14.5v/17.5v = 0.83 = 83% efficient at STC conditions
    In reality, solar panels get hot and Vmp drops by upwards of 2-3 volts--so the 83% efficiency goes up for PWM (because solar panel Volts/Watts goes down).

    A MPPT controller would have similar issues with temperature.

    A MPPT controller has much more computer processing and transistors/inductor internally--so they are naturally less efficient than "simple" PWM controllers. This extra power used to run the internal electronics makes running a small array on a larger MPPT controller less efficient.

    It is that difference between Vmp and Vbatt-charging where MPPT "picks up" the extra power... Remember:
    • Power = Voltage (array) * Current for a MPPT contoller
    • Power = Voltage (batt charging) * Current for a PWM controller
    The farther apart Vmp-array and Vbatt-charging are--the more efficient a MPPT controller is over a PWM controller.

    All About Charge Controllers
    Read this page about power tracking controllers

    Does this sort of make sense?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DumbdumbheadDumbdumbhead Solar Expert Posts: 28
    Re: MPPT charge controllers vs PWM for very small systems?
    BB. wrote: »

    Does this sort of make sense?

    -Bill

    Absolutely, basically what I get from you BB is that there is no perfect solution, just preferences. I like the idea of the MPPT because of its efficiency in respect to more energy output and better capture in more extreme conditions not to mention better performance when the solar arrays are further from the controller. One thing that did concern me about what you said, an MPPT has more complex circuitry thus increasing its power needs. All in all I think I want an MPPT controller even if it is for a measly 110w to 266w system. I want to start off with 110 watts of solar panels and see if I like it, then later down the road upgrade with more panels. I was just very concerned that MPPT controllers penalize smaller systems as they are generally marketed for larger systems.

    As usual, you have the answers. You should be getting paid for this stuff BB. I read over and absorb every last bit of your sage advice. :cool:
  • BB.BB. Super Moderators, Administrators Posts: 32,204 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    You are very welcome.

    One thing about solar PV systems--is they do not "grow" very well... If you expand by 2-4x the "energy" of your system (panels, batteries, inverters, etc.)--You almost need to start over.

    About the only devices that can scale well are the MPPT controllers. Because they typically have 12/24 or 12/24/48 volt output (at rated current)--so they can 2x - 4x their array handling capabilities just by changing battery bank voltage (downside, changing batteries, new inverter, etc.).

    What you normally do not want to do is run a "small" array on a MPPT controller... If you assume they are around 95% efficient, then that means the run with around 2.5% of rated output losses with "small arrays" (a bit of guessing on my part):
    • 15 amp * 14.5 volts * 0.025 tare losses = 5.4 watts estimated Tare losses
    With a 50 watt array, you would have about 10%+ losses just from running the MPPT contorller--and remember that ~5.4 watts is still there when the sun is not at peak but in morning or evening.

    So--my suggestion is to avoid "large MPPT controllers" with "small" arrays. The closer you get to the controller's rated input--the more efficient it will be for the overall system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • DumbdumbheadDumbdumbhead Solar Expert Posts: 28
    Re: MPPT charge controllers vs PWM for very small systems?

    BB, one last question for the day I promise :) Would this MPPT controller be good for a 110watt system? http://www.solar-electric.com/mosumpsochco.html

    Also, you mentioned that while the display meters that Morningstar sells with their controllers are useful, you suggested a true battery monitor. Listening closely to what you said about the power needs of the MPPT controller I am now concerned that an additional battery monitor would also have high power requirements. I know Trimetric makes battery monitoring systems, would the above mentioned MPPT controller by Morningstar and an additional battery monitor be a bad idea for a tiny solar array? I only want to mount two 55w panels on top of my trailer to basically help recharge a single 100AH deep cycle battery. I plan to utilize the 1,000watt genset to charge the battery up to 80% in the morning with the help of a 40amp Xantrex Truecharge2 battery charger allowing the 110 watts of panels to trickle charge the batteries the rest of the way.

    So...Battery Monitor+MPPT control=Power draw=poor choice for 110watt system?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    My opinion, for what it's worth:

    Don't bother with the MPPT controller. You've only got 110 Watts of panel, which likely won't produce more than 6 Amps. You'd be running at less than 50% of the capacity of the Sun Saver unit. You'd be spending $200 extra for an almost incalculable power advantage.

    Instead, use something like this: http://www.solar-electric.com/ss-6.html

    And yes, get a battery monitor as it will keep track of the state of charge regardless of charge source. Everything that goes in or out of the battery will be registered so you'll always know what shape your battery is in. Much more worthwhile investment in this case than the extra $ for an MPPT controller.

    Again; just my opinion.
  • BB.BB. Super Moderators, Administrators Posts: 32,204 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    I agree with Marc, Don't overspend for your first controller unless you are sure you are going to have ~200+ watts of solar panels in the near future.

    The Trimetic seems to make a lot of people happy here (although--programming is not intuitive). I don't believe the Battery Monitors use much energy... LCD are going to be lower power and able to display 100% of the time (with back light). LED displays are going to consume a little bit extra power (a quick skim of one manual talks about 16 millamps when the display is off => 0.016a*12v=0.2 watts).

    I do not use off-grid equipment--so realize I am just trying to guide you to some choices for you to make from my little knowledge of what is in use around our forum here (other people that can help you if you have questions).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    From what I know, the Morningstar is a great controller, but for about the same money, I would consider the Rogue MPPT. Great controller, nice metering, at a ver y competitive price. Small bu siness, but very customer freindly.

    http://www.roguepowertech.com/products/mpt3024.htm

    Tony
  • TheBackRoadsTheBackRoads Solar Expert Posts: 274 ✭✭✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    Also, if you want to add more panels later, they should be the exact same model as previously installed for maximum MPPT effectiveness, which can be hard if the panel went out of production.
  • BB.BB. Super Moderators, Administrators Posts: 32,204 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    The earlier Rogue controller was only rated for Voc = 60 vdc max.

    The MorningStar 15 amp MPPT is rated for Voc = 75 vdc max.

    The larger MPPT controllers are typically rated for 150 VDC Voc.

    Mixing and Matching of various Vmp/Imp panels is a pain in the butt... It is very difficult to predict what will be cost effective a year from now.

    Leads to even more difficulties in "growing" a PV power system over time.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    One consideration that helped me choose the Morningstar 15 amp MPPT for my small (200 watt) system over cheaper controllers was the programability of the unit (although you must buy a small meterbus adapter to program it; I think it was another $35).

    The programability is pretty deep for such a small unit; it not only lets you adjust battery settings, but you can also set all kinds of sophisticated timer functions for DC loads, thus avoiding the need for a DC timer if you have timed DC loads. The stand-alone DC timers that I found were north of $60 (although maybe I didn't find the cheap ones...). So that helped bring the cost difference of the MPPT vs. PWM controllers a little closer for me.
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    I got a picture of the inside of the controller that I was wondering if it was a mppt. and now im sure it is. Take a look at it and let me know what you think. TKS John.
    Its the 3 rd pictuer down the page.
    ZLPOWER SL-40A
    .
    http://www.diytrade.com/china/4/products/8042963/Mppt_Solar_Charge_Regulator_12v_24v_40amp_Parallel_Capability.html
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    One thing that hasn't been mentioned, unless I missed it, is that since the performance gains are greatest when the difference between array and battery voltage is greatest (as Bill pointed out), on a system which is designed to keep the battery above 50% depth of discharge, there will be less voltage differential for the MPPT to work with - and thus even less overall benefit will be realized.

    So personally, for a sub-200w system, I would agree with Coot that the "benefit" would be barely noticeable and not worth the money. MPPT might be worth it if I knew that the battery would be regularly discharged below 50% DoD or there were some other reason to use MPPT, for instance an oddball PV voltage.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?
    BB. wrote: »
    The advantages to MPPT (in my humble opinion by order of importance):
    1. Ability to run "high" Vmp-array for longer cable runs from the array to the battery shed/charge controller.
    2. Ability to run in wide temperature extremes efficiently. Hot Vmp=17.5 volt solar panels and cold battery banks means you may not get full voltage/current when charging/equalizing your battery bank. Run Vmp=35 volts on a 12 volt battery bank--and you have no worries about voltage drop (temperature, wiring, controller, or cold batteries requiring higher voltages to recharge).
    3. In cold weather (subfreezing), they can collect around 10-15% extra energy from Vmp increasing because of cold panels.

    Granted.

    But...how relevant are 1 and 2 in regards to an RV install? If the panels are 17.5vmp as per your example then the benefits of 1 and 2 would apply only if the modules were rigged in series.
  • BB.BB. Super Moderators, Administrators Posts: 32,204 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    dwh,

    Exactly. Correct (extra characters).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    Let's say that at best an MPPT charger will yield 30% more than a PWM controller, so you would need to buy 30% more PV with a PWM to get the same output.

    For a 110W system, that's 33W extra. Retail PV goes for about $3/Watt according to our hosts so that's $99 for the extra PV. If the difference between the price of an MPPT and PWM is less than $99, then it makes sense to go for the MPPT - if it's more, then rather get more PV and a PWM.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?
    stephendv wrote: »
    Let's say that at best an MPPT charger will yield 30% more than a PWM controller, so you would need to buy 30% more PV with a PWM to get the same output.

    For a 110W system, that's 33W extra. Retail PV goes for about $3/Watt according to our hosts so that's $99 for the extra PV. If the difference between the price of an MPPT and PWM is less than $99, then it makes sense to go for the MPPT - if it's more, then rather get more PV and a PWM.

    Not a bad rule of thumb, but I see a problem with it.

    The problem is the assumption of 30% higher yield than PWM. That's not accurate. There may be that much under certain conditions for a certain time, but it certainly won't be across the board. For there to be a 30% increase by using MPPT instead of PWM, there first has to be a 30% inefficiency loss for the MPPT to overcome. If the inefficiency is less than 30% to begin with, then there won't be a 30% gain from using MPPT.

    Hooking up a 24v nominal PV to a 12v nominal battery is going to create a greater inefficiency to give the MPPT something to work with, but if the PV is 12v nominal then there won't be nearly as much inefficiency to overcome.

    So the question is under what conditions and for how long will that 30% increased harvest occur (if ever)?


    If the actual gain of MPPT over PWM is say 15% -overall-, then your rule of thumb would say that if there is a $45 difference in price then the MPPT would be worth it.

    So this rule of thumb could be handy - IF the higher yield estimate is accurate.

    But I, for one, am not about to blindly accept the blanket statement that, "MPPT gets a 30% higher yield over PWM" when I know full well that, "it depends".
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    most times mppt will average about a 10% increase.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?
    dwh wrote: »
    So the question is under what conditions and for how long will that 30% increased harvest occur (if ever)?

    If the actual gain of MPPT over PWM is say 15% -overall-, then your rule of thumb would say that if there is a $45 difference in price then the MPPT would be worth it.

    So this rule of thumb could be handy - IF the higher yield estimate is accurate.

    But I, for one, am not about to blindly accept the blanket statement that, "MPPT gets a 30% higher yield over PWM" when I know full well that, "it depends".

    Agreed. To get to the bottom of the "it depends" part the important variables will be:
    - DoD of the battery
    - Panel temperature

    I'm also going to make a whole bunch of assumptions below to simplify this, because just those two variables could be quite different for different locations and systems.

    So firstly, let's assume that it's for a properly matched system 12V panels for 12V batteries and that the panels are crystalline. And to simplify the panel temperature part of the equation, I'm going to pick my location in Spain.

    I'm also going to assume that we have 2 magical seasons, where summer stays the same temperature for 6 months then we wake up one morning in winter which is also a constant temperature for 6 months. ;)

    Using this calculator to convert ambient temp to cell temp: http://pvcdrom.pveducation.org/MODULE/NOCT.htm

    The two cell temps for summer and winter are 55 and 20 degrees respectively. For a kyocera mono panel (KD135GX-LPU) with a 17.7Vmp (STC) that would be a Vmp of 15.3 in summer and 18.1V in winter, using the temp coefficient of -0.8V/C
    Another big assumption is that Imp stays constant (0.005A/C is not worth the hassle).
    Imp = 7.63A

    Assuming that average DoD for summer will be about 10% and for winter about 40%, so that's about 12.5V and 12.2V on the batteries. Again, to simplify, if the target charging voltage is 14.4V then I'll assume that the average charging voltage is 13.4V for summer and 13.3V for winter. Hmmm, so looks like DoD doesn't play such an important role in the difference.

    The 4 scenarios then are:
    - MPPT in summer: 15.3V x 7.63A =~ 116W
    - PWM in summer: 13.4V x 7.63A =~ 102W
    - MPPT in winter: 18.1V x 7.63A =~ 138W
    - PWM in winter: 13.3V x 7.63A =~ 102W

    MPPT gain in summer = 12%
    MPPT gain in winter = 26%

    Average gain over an imaginary 2 season year = 19%

    So yes, 30% seems to be on the optimistic side. Temp effects in winter play the biggest role so there will be a more pronounced difference in more northern latitudes.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    for what its worth . On my 240w system daily harvest wen up from 78 ahr to 81 ahr. BUT the cost difference was PWM $120 MPPT $360
  • System2System2 Posts: 6,290 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    hi every body

    it is nice discussion to clear many thing,

    I am planning for a 500w load grid tie system but temperature very 25 to 50c in my area but I think MPPT still a good choice
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    fawd. Most of the solar controllers have the temp stated on them that I read about.Or just email the company/or call them.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?
    john p wrote: »
    for what its worth . On my 240w system daily harvest wen up from 78 ahr to 81 ahr. BUT the cost difference was PWM $120 MPPT $360

    If your mppt cost is a one time only, and you know that over it's life it is going to produce an additional 10,000 AHs(1000 AH/Yr for 10 years), is that worth the difference of $240?
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    bmet.
    you asked if the controller is worth the money if it is made back by the work it dose. I would have to say yes.> But why spend twice the amount of money if you don't have to! Just because one cost the most dosen't always mean you are getting the best for your money. I could buy one apple in one store for one dollar, and buy another apple in a different store for two dollars, same brand,same taste, same color, same weight, off the same tree.
    John
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    And both apples will give you the exact same output (taste, fiber, nutrients, water content), so obviously paying $1 is a better deal. However, after spending the big money for an entire PV system an extra $240 for such a large performance boost is a no-brainer.

    There are similar gains found elsewhere in the PV world. With a grid-tied system a grid-tied inverter which costs slightly more but outputs a few percentage points more.... that difference means an entire year's worth of output for free by the end of the system's life.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • conntaxmanconntaxman Solar Expert Posts: 125 ✭✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    But did the two apples fall the same distance? :blush:
    Also i was reading that their is a new type of controller.Instead of having only one, they now use one for I think each panel and then they all plug into each other.This is suppose to be better then using only one controller.
    Everything get out dated fast now.
    Im only going to be running about 1000 watts of solar panels. and Im just starting and want to see if it will pay for itself, and I really don't think the payback is their, until panels come WAY DOWN in price, and they will , just like every thing else. But it's fun..
    I forgot, what color was the apple. ha ha ha :cry:
  • System2System2 Posts: 6,290 admin
    Re: MPPT charge controllers vs PWM for very small systems?

    Hi Guys,

    I have been offered a small PV system for a yacht and I am struggling with the same problems that has been discussed in this thread:

    It's 2 x 70 W Sunware 3266, 24V panels with the following data:

    Pmax = 70W
    Voc = 48 V
    Vmp = 42,4V
    Isc = 1,75 A
    Imp = 1,65 A
    NOCT = 46 degree C
    Pmax Coefficient = -0,34 %/K
    Voc Coefficient = -0,34 %/K
    Isc Coefficient = +0,03 %/K (K = Kelvin)

    The controller offered is the Morningstar TS-MPPT-60 or the TS-MPPT-45.

    The battery bank is 24 V, 1000 Amps/hours.
    The PV system is only used to keep up / top up the batteries.

    Is it worth to buy this system?
    Is it worth with the MPPT controller?
    Should the PV panels be connected in series or in parallel?

    Thanks.
  • SevenSeven Solar Expert Posts: 292 ✭✭
    Re: MPPT charge controllers vs PWM for very small systems?

    Please tell us you put an extra zero on the battery ah number. 1000ah is way too much for your panels and cc
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: MPPT charge controllers vs PWM for very small systems?
    Seven wrote: »
    Please tell us you put an extra zero on the battery ah number. 1000ah is way too much for your panels and cc

    "The PV system is only used to keep up / top up the batteries."
    Which to me indicates the battery primary charging system could be engine alternator? and the solar is just to top things off.

    Is it worth buying the system? Depends on the price I guess. The TS MPPT controllers are awesome units, and while perhaps overkill on this installation (again depending on price) they would definitely allow future expansion, if not on the boat, then at a cottage or home installation. If going with the MPPT, for the relatively small difference in price, I'd go with the 60 instead of the 45. I needed a new controller for part of my system, and although for immediate need the 60 is overkill, I went with it anyway as if the main controller failed, this one could take over. I'm glad I went that way, it's efficiency is very high indeed, with lots of room for added future installations or upgrades.
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