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Old 27-06-2016, 20:19   #1
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MPPT or PWM Solar Charge Controller

So I have been doing a lot of reading on Solar, and charge controllers and am a bit confused as to what the best option for me might be. I am thinking of adding a number of Solar panels to my sailboat, but similar to most sailboats, a lot of the areas I can put panels will get some shading. So to limit issues with some panels being shaded, I assume I will need to run most of my panels in parallel.

Ultimately I think I can add 5 solar panels
1 large panel on the arch (300 watts)
2 medium sized panels one on each rail which could be tilted (2 x 120 watts)
2 medium sized flexible panels on top of the bimini (2 x 120 watts)

So the questions I have
1. Would I be better to put 2-3 smaller panels on the arch and run them in series versus having 1 bigger panel?
2. Since I assume most of my panels will be shaded at different intervals, with exception to those on the arch, I assume that I am best of running the panels in parallel, or am I wrong about this?
3. Reading up, it appears most of the benefit to MPPT Charge Controllers is their ability to handle and increase efficiency based on running panels in series, instead of parallel, or am i missing something, which means if most of my panels are in series am I really missing anything to go with the cheaper option of an PWM controller?
4. Most PWM controllers appear to be smaller 12v 390w / 24v 780w assuming all my panels were outputting at 100% that puts me around 780w while its unlikely I would ever hit that, would I need 2 PWM controllers, and is there any issue with multiple controllers charging the same battery bank? Or would this be another reason to go with an MPPT controller?

Cost really isn't a huge consideration at this point, as I don't expect the setup to be overly expensive no matter which option I take on the panels or controller.

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Old 27-06-2016, 21:33   #2
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Re: MPPT or PWM Solar Charge Controller

I think lots of small panels is the way to go but not in series unless you have a huge array and the fancy controller.

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Old 27-06-2016, 21:51   #3
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Re: MPPT or PWM Solar Charge Controller

First off if you have 300 watt panel those are 24V. If you have a 24V system that is fine. Otherwise you will need a MPPT controller to convert the 24V to 12V. If you have a 24V system, then you would need 12V panels wired series in groups of two. Otherwise parallel is fine.

A MPPT controller will work in parallel or serial. If you have an arch on the back. I might put two (or three) 300 watts on that and call it good.

Myself I like 12V panels and PWM, but that's because I'm pinching pennys. Plus you can cheat and connect 12V panels to a 12V system if the controller dumps. OK, you can do that with 24V panels too, but much easier to fry the batteries with 24V running without a controller.

If you have the money go with the large panels and MPPT.

One fun fact: MPPT only works in Bulk change mode. Once you switch to absorption, your working in PWM anyway.
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Old 03-07-2016, 02:48   #4
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Re: MPPT or PWM Solar Charge Controller

My 300 watt panels are 12 VDC with maximum 17 VDC output.

The main purpose of an MPPT is:
A. Reduce wiring and breaker costs when running panels in series
B. Maximize production of solar output to charge batteries.
C. Control battery charging.

Okay!!! Now flip out now and don't read this if you are into solar for houses.

If on the other hand you are a sailor remember:

#1 Simplicity simplicity simplicity!

#2 Redundancy and more redundancy!

With this in mind.


Install one wire to your circuit panel to individual breakers for each panel. It is not like panels will be very far away. With this arrangement you can individually shut off panels, make repairs, and don't have eggs all in one basket.

The few batteries on a boat are cheap compared to a big MPPT. Where is that cool dry place to mount an MPPT or other solar controller?

Further don't you already have two or more other automatic battery chargers? On my boat I have a smart inverter when running a generator, a smart alternator when running the engine, and the wind generator is smart too. Why install another smart device when battery charging and equalization is best done with a dependable supply? Big battery banks take many hours to charge. How are you going to charge batteries and equalize when the sun goes down?

I can hear you all whining all the way out here. "But you will cook your batteries!"

Well perhaps if you are the type to leave your hatch covers open in the rain or when you leave the boat.

If on the otherhand you know how to close your hatch covers to prevent water damage, you are the type that simply can disconnect at the circuit breaker panel most of your solar if leaving the boat.

While on board you can monitor the weather yourself and can notice when it is bright and sunny.

Further, you may already have an automatic dump mechanism to prevent overcharging. My smart inverter will turn off the AC when battery voltage is low. I have it set for 13.7 Volts. Huh? If I leave the boat a longer period, I can safely have on more solar power since I know when batteries are nearly charged my AC power goes on. That load includes fan, lights, and stereo.

Important don't shed load by running the blower to your engine room. That load introduces moisture to a cold engine and increases corrosion.

Another really simple thing is an analog thermostat. I have one next to my batteries. When the batteries are charging hard they get hot and a 12 VDC computer fan blows air on them. This keeps them cooler and reminds anyone aboard that hears the fan to check if too many solars are on.

Slightly more complex is my high voltage alarm and relay. When I am running my fridge and electric watermaker, they go on at 13.3 VDC. This means they automatically shut off at night and automatically turn on during the day. This device acts like a load shedding device too.

Finally there is the battery selector panel. You do have house and engine battery separate? My solar panels normally only charge house bank. This is a safety ensuring the engine bank is protected. When voltage is high enough from the solars I manually start charging the engine bank by turning my selector switch to BOTH. Around 4 pm I turn it back. In this manner I have manually charged engine batteries for years. Works fine.

Note: Do not do what I am doing if you have a giant solar array and a tiny battery bank.

In my case I am running 900 watts of solar and 400 AHr house, and 150 AHr engine battery.

That BTW was enough solar that today I ran a large orbital grinder for four hours, and still finished the day with fully charged house and engine bank.

I set the low voltage cutoff on the inverter at 12.3 VDC. This was necessary because of high power draw on startup. All three 300 Watt panels began the day in on position and I didn't have to change them despite bright clear sky since I used the power sanding. I did change the selector switch manually to charge the engine bank and turned it back in the afternoon.
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Old 03-07-2016, 04:01   #5
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Re: MPPT or PWM Solar Charge Controller

A 130W 12V solar panel will give a voltage of up to 18V, and the 130W will give out 130W, based upon 18V and 7.25A max

A pwm charger would limit you to that 7.25A and basically throw away the additional power available, whereas an MPPT charger will maximise the power available and charge at over 9.4A.

Given that there is no reason to lose 25% of charging efficiency just view PWM chargers as simply the old technology, superceded by a better way.

Direct wiring to the battery bank is also inefficient and THEN having to plan and manage what to do when your batteries are charged is more complicated and more risky than simply buying a charger. Your failure modes are still there..just different.

Put it this way, If i am left with a choice of batteries fried from overcharging, or batteries low from a bust charger, with one situation i am totally hosed, the other?.. start the engine and charge the batteries, or carry a spare charger (though i have had zero issues in 8 years).

I am a sailor, and i do not view chargers as expensive or large compared to batteries or panels, and nor do i see them as unreliable. What i do see is that panels are large and the fewer i have the better.
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Old 10-08-2016, 05:23   #6
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Re: MPPT or PWM Solar Charge Controller

A question re 12/24 volt PWM controllers.

Attached is a manual for a ebay one with LCD display plus USB.

It says it can handle up to 50 volts solar input and is self detecting on 12 or 24 volts.

Can I assume that if you connect to 12 volt battery (eg manual says to connect battery first anyway), the unit defaults to 12 volt operation regardless of the voltage of the solar panel ? eg is you have a 36 volt panel the controller will still handle that and still only charge the battery to 12 volts (actually the float at 13.7 volts)

My set up seems to do this okay (albeit I have two controllers feeding off one panel via diodes on the solar inputs, each one charges a 1100CCA battery)

The good thing with these PWM's is that you can always see the voltage on the LCD display and set the charge and cut off voltage (I run some ultrasonic transducers to minimise barnacles).

I've also seen one that shows incoming amps.
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Old 10-08-2016, 05:48   #7
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Re: MPPT or PWM Solar Charge Controller

Get the large arch panel and the two panels for the bimini and install three mppt controllers, one for each panel. This will give you nearly the same output as the five panels would do with one or two pwm controllers and series or parallel connection with less hassle, less weight and probably lesser cost.
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Old 10-08-2016, 07:16   #8
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Re: MPPT or PWM Solar Charge Controller

One think to remember about MPPT and solar panels. The Panels have a negative voltage coefficient. Which means that solar cell temperature looses a volt for roughly every 30 degrees F ish over 60 degrees F. This is why 12V panels output 17V's. In the height of summer that voltage can drop to 15V. Though less of a problem when the underside of the panels are vented / open to air circulation.

Myself, I did add a $100 panel instead of a $240 MPPT controller. More bang for the buck that way.
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Old 10-08-2016, 11:39   #9
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Re: MPPT or PWM Solar Charge Controller

I have 4 220W panels and 2 PWM controllers set up as 2 charging systems with 2 each panels in parallel feeding to each controller. Redundancy is good. I'm with sailorchic34 on the MPPT controllers, the extra cost and complexity does not justify the increase in efficiency compared with putting the money into more panels.

Since I predominantly sail either north or south up the east coast of Australia shading is a problem when going north but with nearly 900W of panels and 4 banks of T105 batteries I seem to get by without abusing the batteries too much.
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Old 12-08-2016, 18:52   #10
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Re: MPPT or PWM Solar Charge Controller

There are choices here

I opted for the most expensive high output panels I could buy to reduce my footprint and fit 2 panels on the back of my cat Bimini.
These panels are the same foot print as most 150-200w panels but put out 340w per panel. So for 2 panels I get 700w. There is place in the future to add another panel to the corner of the Bimini top giving me 1050w.

These panels put out 65v. I like this as I could then run much thinner cables through the Bimini roof down the arch into the back cabin and to the galley cupboard which is where the battery buzz bars for the 3x 210 amp hour batteries are. I ran a red and black dual insulated German certified solar cabling for each panel to this point. I bought 2 good Mppt controllers one for each panel and wired then on and to the buzz bar so it's a parallel system for shading and 100% redundancy.

I have an onboard built in mini pc so usb's go from the each Mppt to the PC. Each Mppt controller gives you live info but also stores the last 30 days info by day. I then also have a battery monitor that gives me a display but also feeds to the pc.


Sun power 340w

Victron 100/30

Battery monitor
Victron 700bmv

I want a no hassle simple don't worry about system. This I now believe I have. Info is at the tap of a button. On a good African sunshine day which is most ;-) I get 1,5Kw hours per panel for the day so that's 3Kw hours in total or 3000/12.8 = 234 amphours

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Old 12-08-2016, 20:00   #11
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Re: MPPT or PWM Solar Charge Controller

Originally Posted by sailorchic34 View Post
Myself, I did add a $100 panel instead of a $240 MPPT controller. More bang for the buck that way.
On land there is an argument for that, but on a boat I think MPPT is usually better. The reason, or at least one of the reasons, is that boats are almost always space constrained when it comes to solar panels. Yes, they are cheap, but once you are out of space to mount them, you are kind of **** out of luck. So most of the time it becomes about getting the most power out of the physical space that you have available.

That said, if you are working with older panels that are 17V or so there is less loss from a PWM charger than with higher voltage panels. But anyone building a system now will almost certainly be using higher voltage panels, and picking them to cram as many watts into the available space as possible. Then you want to extract max power out of those panels, and that means MPPT. It's about watts per sq foot more than anything else, in my experience.

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