Help understanding MPPT controler and watt output

Re: Help understanding MPPT controler and watt output

Welcome to the forum Ggiesler.

ggeisler wrote: »

I currently have a small system with 3 12v 100 watt panels

"12 volt panels" really have Vmp (voltage maximum power) around 17.5 to 18.6 volts or so to properly charge a 12 volt lead acid battery over most conditions (hot solar panels/cool battery bank).

this is connected to a 30A PWW charge controller

this is connected to 6 35AH 12V Sealed Batteries connected together in parallel giving me a total of 210 AH at 12V

You really do not want to parallel that many lead acid batteries together if you can avoid it. I prefer a single battery (12 volt 210 AH) or a pair of 6 volt 210 AH batteries in series for 12 volts at 210 AH. If you have paralleled batteries, 2-3 strings in parallel is about the typical maximum that works well for most people. If paralleling batteries, review this website.

now i am looking into getting a MPPT charge controller and ultimately increasing the number of PV's.

MPPT controllers are more expensive and will "match" the Vmp/Imp of your array to your battery bank's working voltage... Sort of like the DC version o a variable transformer (technically a switching down converter or DC switching power supply inside the MPPT controller).

While a MPPT controller can increase current in very cold weather with a "12 volt" array (by 10-15% in subzero weather)--Where they really work will is when you run a Vmp-array 2x or more battery voltage. Allows you to use much smaller gauge copper wire (save money) and/or install the solar array much farther away from the charge controller+battery bank.

MPPT controllers also allow you to use GT solar panels with "non-standard" Vmp ratings (typically around 30-40 volts) and efficient take high voltage/low current of the array to the low voltage/high current needed to charge the battery bank.

Those >200 Watt GT Panels are usually much cheaper (and larger wattage)--And you can save money overall (cheaper panels+more expensive MPPT controller) vs a "12 volt"+PWM system (12 volt panels are usually more expensive vs GT panels).

There are some other advantages too--MPPT controllers can have many more optional connections and various software configuration choices.

As I understand it my current system as it stands is pretty much maxed out. If i were to add one more panel (12V 100 Watt) it would effectively put my Amperage to 33.3A Maxing out my charge controller

You need to look at the Manual for your controller and the Vmp/Imp of your array. I am not sure I understand the 33.3 amps for your array--But really need the exact ratings/configuration of your array to be sure.

Now this is one of the reasons I want to go to MPPT. but am a bit confused.

the MPPT controller i have been looking at states it is a 40A 12v a 500W charge current at 12V and 1000W for 24Volt

Need to know which controller you are looking at... There are many choices--But usually you get what you pay for... $300 to $600 for a full featured/larger MPPT controller. There are some import "MPPT" controllers that are very cheap and either do not work well are are sometimes really PWM controllers inside.

I am assuming that if i keep everything at 12V i could have a total of 5 panels and the controller would be maxed out. (5*100/12=41.66)

The Vmp of your panels is probably around 17.5 volts:

500 Watts / 17.5 volts Vmp = 28.6 amps

Just under the maximum rating of your PWM controller (check the manual--Sometimes there are other limits/deratings used).

Now if i change the panels to series / parallel to a 24 volt system this would effectively drop my wattage in half.

4x100 watt "12 volt" solar panels in parallel:

17.5 Vmp * 5.7 amps Vmp (for 100 watt panel)
4*5.7 amps = 22.8 Amps @ 17.5 volts Vmp

2 panels in series then two strings in parallel:

2*17.5 volts = 35 volts Vmp array
2*5.7 amps = 11.4 amps Imp array

Note that Power = Voltage * Current. If you have 2x the voltage and 1/2 the current, you still have the same power.

In order to receive the same amperage on 24 volt i would need 20 panels (20*50/24=41.66)

Same amperage * 2x 12 volts = 2x the Wattage from the array.

Now Here is where my confusion is.

As I understand the way MPPT controllers work it will sense my 12V battery system and down convert the voltage to the optimum voltage for my system. taking the 24V to somewhere more acceptable for my bank. By doing this will it increase the wattage?

Configuring 4 panels in parallel vs 4 panels in series/parallel (2 series, 2 parallel strings)--Does not really change anything between PWM and MPPT. Still about the same amount of power (unless you are talking about sub freezing weather, where the very cold panels and Vmp can extract 10% more power or so).

The advantage is you can have an array with 2x the voltage and 1/2 the current and basically use 1/4 the diameter (minus 6 AWG sizes) smaller copper wire from array to charge controller. Depending on size of system and distance covered--This may or not be a "big deal" to you.

so if i were to take my above example, would it take the 24V input, drop it down to 12V and double my Watts?

No.

If you put a "24 volt" array on a PWM controller charging a 12 volt battery bank, the PWM+battery will use only about 1/2 the wattage of the array (because of the way a PWM controller works).

If this were true would my maximum wattage be 2000 Watts? or would the maximum 24V wattage of 1000 limit my setup to 10 Panels?

If limited to 10 panels on a 24V system i would still get double the amount of wattage from this configuration correct?

This is all speculation and I'm sure not very clear so if anyone could help clear this up for me I would greatly appreciate it.

You have asked a lot of questions, and made some assumptions that are not really correct. It makes a bit difficult to give you "the right answer" because of the differences in the way MPPT vs PWM controllers work.

If you want more information on MPPT vs PWM controllers--We can do that.

Or, you can tell use about your needs (what loads you are powering, Watts or Amps peak at what voltages, Watt*Hours or Amp*Hours per day, etc.) and where it will be installed (how many hours of sun per day by season). And we can help you design a system that will meet those needs (on paper). Then, at that point, we can start talking about hardware choices.

The hardware between a "small" DC only solar power system and a "large" AC+DC off grid power system can be quite different... Sort of like talking about choosing options for a truck--Without knowing if the parts will be for a compact pickup or an 18 wheel semi-tractor+trailers.

If we size the system first--Then we have a better idea of what components to pick for your installation. And it limits the scope of the discussion to those things of interest for your application--And not the theory of the universe type discussions.

-Bill