Cdash wrote:
So basically, what I am getting from all of this is:
If you get a PWM you are happy with it and if you get a MPPT you are happy with it!
I appreciate the information and opinions, it seems that I can't really go wrong either way. Almost seems like I am better off picking my panels, and then the charge controller.
Yes, it seems overwhelming when researching some of this stuff. I would rule out the comments like you will get 30 % more with mppt or that you are being cheap because you dont buy the more expensive mppt. I would rather have more panels than put the money in mppt. A person can buy an mppt and it works great but another person buys pwm and it works great also. As I said in my last post I compare my pwm to my buddies mppt and he's not doing anything better than I am but he spent more and right now his controller is giving pwm performance.
His system is wired in parallel because he added panels as he went along. His mppt blue sky controller will take about 46 volts when the panels are wired in series. So ideally he could use say four 140 watt panels wired in series/parallel. Two pairs of panels wired in series and those two strings would then be wired in parallel. Mppt controllers give the most amp boost when they see the biggest difference in voltage between the panels and the controller.
If the same four panels were all wired in parallel he wouldn't get much better performance from an mppt because the voltage is low and may as well have an pwm. He started with one 140 watt panel then added a second 140 and then a 3rd 190 watt panel. He has a difference of .9 volts between the 190 and the lowest voltage 140 panel so the mppt cant lock onto the voltage signal. He also cant wire them in series because the total voltage would go over 46 volts. He could use his two 140 panels in series and stay under the 46 volt limit but he would only have 280 watts. Yes, he could add 2 more 140's in series and then parallel them with the old panels but they will probably default to the lowest amperage panel. Again, it's probably more important for mppt to have matched panels for best performance.
It seems like his best improvement would come from getting four new matched panels so as to get the most out of his controller. It's common for people to start out with a couple panels and add more later. This may be easier to do with pwm. As you add mismatched panels to pwm they will be pulled down or default to the lowest voltage of the group but the amps will all add up.
If you are mixing panels in series, the voltage isn't as critical (as long as it's under the controller limit) but the amperage is. If you are mixing panels in parallel, the amperage isnt important but the voltage is. If I was installing mppt I would be sure to fully panel it at the start of the build.
If you look at the difference of an MS mppt for $350 and say a Morningstar PWM for $145 you have enough money to buy 200 more watts of solar panels. There is no way that an mppt controller is going to give you the increased performance of 200 more watts of panels with pwm.
Now, if you want to go with a big system and use large dimension 24 volt panels you will get even more watts for your money but they often times dont fit the roof area as well as narrower 12 volt panels. With that large system you would absolutely go with mppt and get a controller that will run high voltage like over 100 volts. The Morning Star 60 amp mppt will run up to 150 volts. With that high voltage you will have low amperage in the wire so you can run one smaller wire all the way down to the controller and not use a combiner box on the roof to make the parallel connections. If you were doing a home install I cant imagine why they would ever use pwm because of all the long wire runs. Homes use big panels and long wires.
As mentioned above someone had a small roof area so they wanted all the bang they could get so they went mppt. If you have very limited space and can wire two panels in series to run about 40 plus volts that may be a better way to go. It will be more pricey for the given watts but they have no choice with limited roof area. Again, if those same two panels are wired in parallel he would probably get pwm performance. mppt wants to see high voltage and convert it to higher amps.
So it's not a urinating contest or you are being cheap or other bs, it's more about what will work for you and your needs. Mppt probably shines best in larger systems.
Have you done an energy audit?
Will your system grow as you realize how well solar works?
How much battery room do you have?
Do you have another EFFECTIVE source to charge the batteries if you have several bad solar days? What model converter do you have?
Will you invert heavy loads such as toaster, microwave, hair dryer etc?
Do you have a generator.
Will you consider running a generator along with your solar sytem?
NO, you are not a failure or cheap and your solar system is not a failure if you do supplemental generator charging. It's all just part of your choices in your energy management program. It's not one size fits all with many rv issues.
If I'm explaining any of this wrong others please help out.
