What is Maximum Power Point Tracking?

If you are thinking about investing in PV panels, it is worth your effort to understand this device. If you are installing a complete Solar system, then it is even more important that you understand some of the methods to save you money, and possibly add to the performance and flexibility of your PV Solar System.

Lower voltages like 12 volt batteries, and 12 volt panel arrays have their problems, there are several reasons to stay away from battery cells  in parallel, and /or PV panels in parallel.

The MPPT (like the Outback MX60) can allow you to configure your panels in series, and it can allow you to increase (augment) your battery string voltage in the future with little effort.

lower voltage means more losses over any given distance, and a need to use much larger wire. at the time of this writing, large wire is expensive!

I bought my MPPT based on the recommendation of a friend, and Solar dealer, but since then, I have been in several discussions with people interested in Solar, and a FEW engineers who are attempting to compare the old style controllers and the MPPT. This has forced me to learn the basics, and I am now confident in my purchase of the MPPT, and I'm sure it will pay dividends in my location and basic design.

I found it interesting that Aero space has been using the MPPT for many many years, Solar Car Racers have found the necessity to deploy this technology to compete, those who pump water with PVs see more water with the addition of a controller with MPPT technology.

So here's what my analogy has become (at the moment), and it is with the help of doubters, and fellow DIYers that I was forced to understand the little I do about this device. KISS is a great concept, but there are times when you see such a large gain to be had that you will cross over that line. The key is to have a fall back plan, and that is easy to implement.

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 Have you ever noticed the difference between crankshaft horsepower and Rear wheel horse power?

Why do people settle for all those losses when they can be so quickly eliminated?

If you look at the losses in the transmission of a truck, and the rear differential, it's really a significant loss. If we eliminate ANY of the losses in the drive train, we effectively end up with more rear wheel horse power. Just Jack up your truck, remove the transmission, attach the drive line to the crank, and to the rear end. Since we still have the clutch, we've pretty much emulated the NON MPPT controller, there's little if any losses there now, and when we need to, we can push in the clutch.

As long as we're moving, and the engine is making good power at constant RPM, we're OK.

Now, let's take two trucks on a trip, one with the common controller (an in out clutch), and one with the MPPT (one with a transmission added).

Sure, we do have some additional losses in the transmission, but I'll bet dollars to donuts as to which truck will likely get the best economy on the long trip.

The PV industry has essentially picked the rear differential gears that will allow the truck to be useful without the transmission, but darned few truck drivers I know will pass on the transmission, especially those who have driven the same route in trucks equipped with either setup.

Don't like transmission losses? Easy to fix, toss it out!

There's one fact to throw in, there are tons of Power Supply Engineers, (there's power supplies in everything, they need lots and lots of these people!) the DC DC converter section is typical and well understood, there is a lot of software in the hands of designers and hobbyists to design same. If the MPPT didn't pay dividends, wouldn't you find at least a few power supply engineers questioning the merits of this investment?

When you catch yourself comparing the losses of one controller over another, Maybe it's time to toss out your auto transmission and save on those  losses too? Best to avoid this comparison, and focus on the real question. How many BTUs will I capture, and how many can I make use of, that is the question that will guide the common DIYer towards reality.

There is a theoretical road where the transmission less truck will perform best:

Your truck is half loaded, the HIWAY is right out front of the warehouse where you depart, you make a right turn, and enter a 4% grade, the grade  deviates less than the percentage of losses equal to the average transmission. There is no traffic, there are no bumps, no need to slow down. If we look for that theoretical road in our world of PV panels, environments, and battery voltage variations, it is likely near the equator, under clear blue skies, but we are allowed the slight deviation.    

 

If Billy is on the playground with his pants down, how long will it be before it's noticed, and how likely is it that only Susie will notice?

(IE: Above comment is about Doubters of MPPT technology, there may be several?)

Remember, the MPPT controller is current limited, doubling the voltage of your PV array and doubling the voltage of your battery string allows you to run twice the power thru the same controller at the same current as before, wire losses go down, and your old inverter could become a backup, just use half the string for 'limp mode' operation. 
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  If you find this page AND have 'hands on' experience upgrading an existing solar install from non MPPT, to the MPPT controller, I'd love to hear about your results.

All the best, George B.