MPPT Controller Explanation For Dummies

[endoftheroad]

Wikipedia Definition;
Maximum power point tracking - Wikipedia, the free encyclopedia

Can someone simplify?

[MarkJ]

Definition: "an expensive useless piece of equipment you will be told is essential by someone in a chandelry who has no idea how it works, if it did,nor has ever been on a boat where it may be used."

[noelex 77]

Solar panels 98% of the time produce their maximum power at a voltage higher than the battery voltage (in practice about 16.5-17v).

When a panel is connected directly to the battery, or via a simple regulator it has to be at the same voltage as the battery. When the panel is at the battery voltage it will produce less power than at its optimum voltage.

A MPPT controller adds a bunch of electronics that allows the panel to operate at its is optimum voltage and converts this higer voltage to the lower battery voltage. When it lowers the the voltage the current is increased.(electronics can convert a high voltage low current to a low voltage high current. The overall power stays the same)

So more current can be extracted from the panel than the solar panel was forced to be the lower battery voltage.

Unfortunately their are losses in the conversion and the controller has a hard time picking the optimum panel voltage as it is constantly changing. Good circuits that track the optimum panel voltage are complex and the better controllers burn some power tracking this voltage.

The net gain has been debated on CF a few time, but my belief is for the best controllers it is about 5-15% above a non MPPT controller.
For the poor cheap MPPT controllers the gain is less and may be negative.

The expensive controllers that offer MPPT often also offer sophisticated battery management (which is important) and detailed displays of the solar output etc, but these features can also be found on some MPPT controlers

Another way of looking at the controller is to think of like a gearbox. The gearbox in your car allows the engine to spin at suitable revs while the wheels turn at at completely different revs.
A MPPT controller keeps the solar panel at its optimimum voltage no matter what the battery voltage is.


Edit:
I thinks Marks definition is technically more accurate

[btrayfors]

Power = Volts x Amps.

Solar panels vary considerably in their power output, depending on conditions at the time (sun, heat, shadows, resistance, load, etc.).

However, at any given condition solar panels have a "sweet spot", i.e., a place where they have maximum potential power output consisting of a combination of volts and amps into a resistance (load). This is just Ohm's law.

MPPT controllers manipulate the resistance (load) dynamically and calculate the point where the solar panel puts out the maximum power it is capable of.

Then, they process the output of the panel so that it is optimum for multi-stage battery charging. These are very smart puppies...you couldn't do this by hand....at least not on a continuing basis.

Bottom line: MPPT controllers help to get the maximum power out of solar panels, and tailor that power to battery charging needs.

Apologies for this simplified explanation.

Bill

[endoftheroad]

I used a meter yesterday at mid day and my 140 watt panels were 20 volts each entering each mppt controller. Was I seeing things?
The battery was 14.3 volts (if I remember correctly).

My batteries are full mid morning while I'm running refrig, vhf and 12 volt fans.
I'm charging every electronic gadget possible during this 6 or 8 hour period although it's not necessary.
I'm new to solar and mppt, it's been a better than expected experience.

2-Kyocera 140
2-genasun mppt controllers
4-Trojan T-105's in series.

Victron battery monitor soon to be installed.

It's raining here in Key West at 3:00 pm, grey skies and stormy weather and my panels are 14.4 each and the batteries are 12.7 volts.

Looking forward to the Victron.

[noelex 77]

Originally Posted by endoftheroad

I used a meter yesterday at mid day and my 140 watt panels were 20 volts each entering each mppt controller. Was I seeing things?

No. An optimum panel voltage of 20v is on the high side of typical, but is possible. My controller records the maximium panel voltage it selected and today it was 20v.

The controler is hunting for the maximium power that can extracted from the panel, so it will try 20v then go down to 19.9v and see if the power is higher, if it is it will try 19.8v if not it will try 20.1v.
Typically, in practice, for a 12v panel the optimum voltage is 16.5v to 17v, but it can be higher or lower, depending on temperature, light levels, shadows etc.

[sailorchic34]

Originally Posted by noelex 77

No. An optimum panel voltage of 20v is on the high side of typical, but is possible. My controller records the maximum panel voltage it selected and today it was 20v.

EOTR's batteries were pretty much already at float when he measured voltage so the controller had backed to float PWM, which in theory would allow the panel voltage to float higher to near voc.

[btrayfors]

Open circuit (OC) panel voltage ranges from about 17VDC for a "12-volt panel" to 70VDC for some of the larger panels found on boats these days.

It is ONE of the jobs of the MPPT controller to convert this voltage down to the 14.6VDC or so needed to charge batteries.

Bill

[endoftheroad]

Noelex quote;
The net gain has been debated on CF a few time, but my belief is for the best controllers it is about 5-15% above a non MPPT controller.
For the poor cheap MPPT controllers the gain is less and may be negative.




Well wouldn't it be simple to hook up a non-mppt temporarily and evaluate the stats on a battery monitor?

As I mentioned I'm a greenhorn regarding solar and electrical but it seems my Genasuns mppt's each dedicated to a sole panel are rockin the house (boat).

[sailorboy1]

For me it was so I could use a 24V panel on my 12V system which allowed a larger less expensive panel (seems to keep the panel output voltage at 36V, which is what the panel manufacturer said was the max point). In the end to only cost $100 more than using smaller panels and a PWM controller.

On a clear day getting am getting 7amps into the battery at 7am in Mass. Don't know if this in the end is more power, but it sure is working.

But I really got it for the programing and other features and am glad I didn't cheap out (saving $100 was never the goal) .

[tartansail]

Originally Posted by endoftheroad

Noelex quote;
As I mentioned I'm a greenhorn regarding solar and electrical but it seems my Genasuns mppt's each dedicated to a sole panel are rockin the house (boat).

+1

I'm a month into using my 2X125 watt Solbian panels, each with a Genasun GV-10 and 4 Sam's Club EGC-2 6V Duracells golf cart batteries. I am in awe of the juice flowing silently through the system. Fridge on constantly for cold beer. Check. Running whatever needs to be run without worry. Check. Batteries > 14V by midday. Check. As someone who fretted and wondered if solar was going to be useful in New England, I'm more than convinced.

[SVNeko]

Now, what if you wanted later to change to a lithium house bank? Are MPPT controllers programmable for the different charging profile of LifePo batteries?

[Maine Sail]

Originally Posted by SVNeko

Now, what if you wanted later to change to a lithium house bank? Are MPPT controllers programmable for the different charging profile of LifePo batteries?

The Genasun controllers can be re-programmed (you need to send them into Genasun however) and many better quality MPPT's can be programmed and tailored to Li as well.

The most critical aspect is to be sure that temp compensation has been 100% disabled. Some cheaper MPPT's used "ambient" temp sensing of the air around the controller even without an external temp sensor connected. This needs to be able to be turned off if charging Li banks...

[foggysail]

Benefits of an MPPT controller were discussed often here in the forums. The most basic answer was always..."if you have room for additional panel/panels, that is the least costly route and one that will yield the greatest output"

Others will share knowledge on this...

[sailorchic34]

I should note that my $26 PWM controller also charges my batteries by noon in the summer. 230 watts solar and 65 ish amps a day, including a 3 cf 120V fridge. To me the added cost of a MPPT controller was not justifiable for my small loads.

I should note that we did have a blue sky controller on the Florida boat, but I generally only saw 10 ish percent gain. When panels were $600 each it made sense to go mppt. But with cheap panels its not always the best bang for the buck. Least wise for the $500- $600 a month people anyway.

As to lithium,to my mind using a battery material that burns / explodes er.. that is highly reactive with water vapor contact, may not be prudent in a marine environment. Look at the fun the 787 had. The USPS will NOT ship lithium phone batteries by air anymore. Something about a fire on a 747 cargo plane or two...