MPPT vs PWM charge controller in an always cloudy scenario

[Alex9]

I read the Sticky: Off-grid solar charge controllers by Jonathan Cole. He says ho pwm for smaller systems and others say go mppt for 200-300w+. I also read that mppt gives you a distinct power advantage especially on cloudy days.
I live in a part of Hawaii that can be cloudy for >70% of the year. I'm looking to install a 12v system around 500w and we'll adjust our 24hr usage to however much power we can get on a given day. So, hypothetically, if everyday is a cloudy day, will having a good mppt cc like the TriStar TS-MPPT-45 be worth the $400 for me? Will it give me that edge vs pwm?
Any input would be appreciated.

[Mike90250]

MPPT cannot create power out of thin air. It can "tune" the harvest to the maximmum that the panels can produce. But a cloudy day, you cannot expect more than 10% of nameplate from the panels.

[Alex9]

MPPT cannot create power out of thin air. It can "tune" the harvest to the maximmum that the panels can produce. But a cloudy day, you cannot expect more than 10% of nameplate from the panels.

Thanks. On windsun.com there's an article What the heck is an MPPT?? It says
...........
MPPT's are most effective under these conditions:

Winter, and/or cloudy or hazy days - when the extra power is needed the most.
...........

Is that only the case if there iit's only partially cloudy? They're not talking about fully cloudy winter days?

[Alex9]

Another quote from that article
............
You typically get a 20 to 45% power gain in winter and 10-15% in summer.Actual gain can vary widely depending weather, temperature, battery state of charge, and other factors.
...........

[Sunking]

Real gosh darn simple when you your panel wattage goes above 200 wats you have crossed the line from PWM to MPPT>

I had a few stickies on the subject but NUKED them.

[Alex9]

Real gosh darn simple when you your panel wattage goes above 200 wats you have crossed the line from PWM to MPPT>

I had a few stickies on the subject but NUKED them.

Sorry. I don't mean to be redundant. I read that post. I'm just not sure if it applies to my situation being so cloudy all the time. I just want to be sure before I spend that much money.

[billvon]

Is that only the case if there iit's only partially cloudy? They're not talking about fully cloudy winter days?

Any time your panel voltage is above the ideal battery voltage an MPPT will help. This generally means that you get more power when the panels are cool - which means either sunny winter days or cloudy summer days.

However this doesn't "get back" any power that you lost due to clouds. You just operate the panels at a more efficient point. And if you're getting only 10% of the sun due to clouds, you will never get more than 10% of the power from the array, no matter what controller you have.

[Sunking]

Sorry. I don't mean to be redundant. I read that post. I'm just not sure if it applies to my situation being so cloudy all the time. I just want to be sure before I spend that much money.

Once you get above about 200 watts panel wattage, a MPPT charge controller is justified economically.

Example let's say you need to harvest 500 watt hours per day, and your Sun Hours = 3 hours in Winter.

Panel Wattage for MPPT = 250 watts.
Panel Wattage for PWM = 350 watts.

The panel cost for PWM is roughly $200 higher than MPPT. The cost of a MPPT is $100 higher than PWM but total cost is $100 less than PWM.

Any questions?

[Sunny Solar]

You can get as little as 10watts from a 100w panel on cloudy days and no type of charge controller will improve that..and any claims that some types of panels are superior to other types on cloudy days are advertising claims only.
Above about 80% battery charge MPPT and PWM charge batteries at an identical rate.

[Sunking]

Above about 80% battery charge MPPT and PWM charge batteries at an identical rate.

Well that is true if you follow manufactures dumbed down directions for setting the voltage levels for Bulk and Absorb which is stupid for a solar system.

If you set Bulk = Absord = Float = 15 volts all that goes away. There is not enough hours in the Sun to go through an 8 to 10 hours for 3-stage charging. Force the system to become a constant current source and charge time is reduced drastically.

[Alex9]

Well that is true if you follow manufactures dumbed down directions for setting the voltage levels for Bulk and Absorb which is stupid for a solar system.

If you set Bulk = Absord = Float = 15 volts all that goes away. There is not enough hours in the Sun to go through an 8 to 10 hours for 3-stage charging. Force the system to become a constant current source and charge time is reduced drastically.

All of this information is really making me rethink installing a workable system. Sunking can you tell me what the proper 4-stage settings should be on the TriStar MPPT. TS-MPPT-45? I'm thinking about getting that one and maxing out at around 700w on a 12v system.

[epsgunner]

All of this information is really making me rethink installing a workable system. Sunking can you tell me what the proper 4-stage settings should be on the TriStar MPPT. TS-MPPT-45? I'm thinking about getting that one and maxing out at around 700w on a 12v system.

I was looking at the MPPT45 the other day.. (I own the PWM version TS45).. it maxes out at 600 watts of panel at 12v..

I was going to use 5 of my 145W panels and maybe switch up.. but the 580 w limit there calc told me was a downer..

I'm sticking with the PWM TS45 I have..

You may need to go with the Morningstar TS-60 MPPT..

[Mike90250]

As long as you are looking at "full size" MPPT controllers, at least check out the Midnight Classic http://www.midnitesolar.com/
I've got the Morningstar MPPT 60, and you have to buy an optional meter head for it, and at that point, the Classic looks like a good deal, with good reviews

[Sunny Solar]

If you set Bulk = Absord = Float = 15 volts all that goes away.Can you tell me what make and model MPPT controllers can be set like that for a 12v system and can handle 30a charging?

[Sunking]

As long as you are looking at "full size" MPPT controllers, at least check out the Midnight Classic http://www.midnitesolar.com/
I've got the Morningstar MPPT 60, and you have to buy an optional meter head for it, and at that point, the Classic looks like a good deal, with good reviews

Mike I have had in my possession a MNS Classic 150 80 amp for just over a year now the manufacture gave me to play with and use them exclusively now for all my deigns. They are one tough SOB. The input voltage claimed is 150 Voc but not really as it is 150 Vmp + Battery voltage. On a 12 volt battery the thing will pump 93 amps all day long providing you have the wattage to push it and a battery that can take it. Using a 100 volt 50 amp current source into a fixed load box the thing hums for days at 93 amps without a whimper.

The unit will not shut down on a 12 volt configuration to about 190 Voc. Set it for 48 volt config and it can operate up to about 235 Voc well beyond its published spec.

They are expensive and worth every penny of it. You get what you pay for, and tank with heavy Armour to go into battle with. And I do not say that very often now do I?