More solar array power with PWM than MPPT. Why?

[dapago]

Hello to everybody,

I have been browsing the web to gather informations for my next solar system and in every forum it is said that MPPT gather more energy from a solar array than PWM. Where I live I can only have access to Morningstar charge controllers and that fine for me as I have read they make very good devices.
The problem is that when I enter their online string calculator

http://string-calculator.morningstarcorp.com/#custom=1&pmax=310&voc=45.9&vmp=37&isc=8.96&imp=8.38&noct=45&tcvoc=-0.31&tcvmp=&tcisc=&tcimp=&coefunit=%25V&product=5&vmin=23&vmax=31&tmin=26&tmax=40&tminunits=c&tmaxunits=c

it shows a result where their TS 60A device allows me to put more panels than the TS MPPT 60A, in either 24v or 48v system.
I don't know if that has to do with the panel characteristics or sth else (and I have tried to enter the only 2 brands panels That I can buy here) but i really don't get it. Somebody can help?

The panels brands and power are 320W Canadian Solar or 310W Jinko. Below are the Jinko characteristics as it is the less expensive one and the one I'd rather buy but the same calculator results I get anyway with the Canadian ones.

Attached the results.

[Mike90250]

If something takes more panels to produce the 60A limit, it is less efficient.

[dapago]

Mike I don't understand. The size calculator do not take in consideration how many panels I would install but just calculate that with the panel specs I entered the MPPT will produce less than the PWM with the same panel, both CC at 60A Can it be the panels specs that do not fit with the MPPT?
Even When I try with the MPPT 45A and the same panels specs, the PWM 45A still give me more power. Should I chose an other panel?

[Sunking]

it shows a result where their TS 60A device allows me to put more panels than the TS MPPT 60A, in either 24v or 48v system..

OK so what is the problem? Easy Peasy to understand. PWM is a Series Voltage Regulator, and MPPT is a Power Converter.

With PWM Output Current = INPUT CURRENT

With MPPT Output Current = Panel Wattage / Battery Voltage

Huge difference

Let's take a single 310 watt Panel and use it on a 12 volt battery. Your 310 watt panel outputs 8.3 amps Imp.So if you used a PWM controller on a 12 volt battery you would have 8.3 amps. At 12 volts is 12 volts x 8.3 amps = 99.6 watts from your 310 watt panel.

Same Panel with a MPPT Controller on a 12 volt battery generates 310 watts / 12 volts = 28.8 amps.

Lets more up to a 24 volt battery. PWM is still 8.3 amps and 199.2 watts from your 310 watt panel. On MPPT is 12.92 amps

Cannot have 48 volts with one panel as it takes at least 2 panels in series. FWIW with MPPT you want to run as many panels wired in series as possible. Avoid Prime Numbers except 1 and 3. Otherwise use 2, 4 or 6 panels.

[dapago]

If I well understood you, an MPPT controller allows me to install less 310W panels than the PWM but will deliver more power to the batteries.

Let's take my particular case here:
Let's say I only need 4 x 310W panels to produce my needs with a PWM controller with a 24V battery bank, I should theoretically only need 3 of those panels with an MPPT controller. Is that correct? But because I can not have Prime numbers I'd need to buy 4 anyway and if I want to expand my solar array, wether it is MPPT or PWM I would have to add panels by pairs. Is that correct? If it is, what is the need for me to invest 3x more in MPPT?
Maybe my location (no shade, full south and an average of 6 sun hours daily all year round with a 5.12 minimum sun hours daily during 3 months of the year) makes MPPT controller not necessary.
You said to avoid Prime Numbers in a 48V system. Is it the same for a 24V system or can I have 5 panels? In that case if I need more than 6 panels in total, I can understand that MPPT can be a cheaper solution in the future but only if I need to install more than 6.
I am very new about solar system sorry if my queries sound naive.

[dapago]

I just realise that in a 24V system (the one I want to implement for my system), I will still need to add panels by pairs (MPPT or PWM) if I want to add power in the future. Unless I can find 24V panels but I am not sure the one I have been proposed (see attached) is a 24V one.

[Sunking]

Prime Numbers only allow you two possible configurations of all in Series, or all in parallel. You controller can only handle a Maximum Voc Input. of 150 volts, So that means you can run 1 or 3 in series before the Voc of the panels is exceeded, So you can work in 1,2,3,4,6,8, or 9 panels. So lets say you use 4 of your 310 watt panels. You wire then 2 in series in parallel with 2 more panels in series aka 2 x 2. With 6 panels 2 x 3

The Tristar 60 amp MPPT has a limit of:

800 watts @ 12 volt battery
1600 Wattts @ 24 volt battery
3200 Watts @ 48 volt battery.

So as you can see by using 310 watt panels do not fit real together. Where as 200 or 400 watt panels work better, At 24 volt with 310 watt panels limits you to five panel and forces you to wire all of the parallel which you want to avoid. .

[dapago]

Thank you Sunking.
Is that why my dealer/installer (who only has 100W and 310W panels) advise me to use PWM because I quote "you can put more panels"? But I can read that the PWM morningstar 60A has a limit of 125V. What happens if the Voc of the panels are exceeded?
What would be then the best configuration ratio controller/panels/budget for future array expansion (regardless of what is available or not). Anticipating a future expansion, I will never use more than 4kw/h per day with maximum 3 days back up and the sun conditions stated in my previous post.
I can start with 3.2KW/h a day with 2 days back up and then may need to extend in 6 months time to 4kw/h per day (if my budget allows me to). Until then I can managed with 3.2 kw/h a day being careful.

Let say I can not get 200W or 400W panels (difficult here to get what is not in stock unless you import them and are prepared to wait a few months) and have to stick with the 310W ones, will it be more convenient (money wise) to use PWM in that case?

Many questions I know but I have heard that many people around me having now problems with their configurations that are not effectives and /or do not allow future expansion unless you have to buy a new controller and rewire the system. We only have 3 suppliers/dealer and for each of them I have heard bad press from different persons.

[jflorey2]

Is that why my dealer/installer (who only has 100W and 310W panels) advise me to use PWM because I quote "you can put more panels"?

You can "put more panels" on an 80 amp PWM controller than you can on a 20 amp MPPT controller. But you will not get as much power from a PWM controller as you will from an MPPT controller, assuming the same array size. In addition, if you're starting to current limit, you can just parallel MPPT controllers.

(Note that MPPT controllers will current limit, so it is safe to go slightly over the current rating. Since in real world applications solar panels put out about 70-80% of their rated STC power, that usually results in no net loss of power. Also note that PWM controllers can NOT current limit without shutting down completely.)

But I can read that the PWM morningstar 60A has a limit of 125V. What happens if the Voc of the panels are exceeded?

You can damage or destroy the controller if the Voc of the panel array exceeds the absolute max voltage limit of the controller. Some controllers (like Midnite) have a "hyperVOC" mode that will give you a significant margin against damage, although the controller won't operate in that state.

What would be then the best configuration ratio controller/panels/budget for future array expansion (regardless of what is available or not).

By far the best choice for future expansion is a larger MPPT controller with a high max voltage. That will allow the maximum flexibility in the number and configuration of panels.

Let say I can not get 200W or 400W panels (difficult here to get what is not in stock unless you import them and are prepared to wait a few months) and have to stick with the 310W ones, will it be more convenient (money wise) to use PWM in that case?

PWM is cheaper in absolute dollars. MPPT is cheaper in terms of dollars per watt.

If you care only about saving money, and not about performance, power or flexibility, go PWM. If you want the most bang for your buck, and the most flexibility, go MPPT.

Many questions I know but I have heard that many people around me having now problems with their configurations that are not effectives and /or do not allow future expansion unless you have to buy a new controller and rewire the system. We only have 3 suppliers/dealer and for each of them I have heard bad press from different persons.

You will almost always have to rewire (and recalculate all your operating current/voltages and max/min voltages) when you add panels. If you find that too onerous, then have a qualified installer install it once and don't touch it again. A solar array is not something you can just bolt one more panel to, splice it in and expect it to work (outside of trivial cases.)

[dapago]

Very clear to me now. I just have to calculate what will be my max power needs in the future (difficult to say BUT I bet on more and more available appliances being energy efficient) and make a choice whether PWM or MPPT in my location and budget. It seems that with 3.2kw/h load a day, PWM sound better MONEY WISE. Above that, MPPT is best.

I have been doing my calculation with a 24V system (because I can have only 4x420Ah L16P batteries to start with). But will charge controller (PWM or MPPT)/panels/budget ratio will be better in a 48V system (not taking in consideration the battery bank that will need to be higher with a 48V system)?
I know I will have to invest first at start in batteries but I will need 8x420Ah batteries in the future so... I am just trying to cash flow the total investment over 12 months because I can not have everything at once.

[dapago]

An other question:My choice will be triggered by max future load needs and the main reason I will have to expend to 4kw/h per day are the future ceiling fans in the bedrooms I will have to install. I will need 5 of them running for about 6 hours a day during the night. That makes a lot of power (5x75Wx6=2.2kw/h per day). I was thinking of going 12V or 24V on those fans but I will have to run a new wiring just for them and the distance between each bedroom and the battery bank is around 15m. Will it be possible to power them with the 120AC wiring and transform the 120AC to 12V just for the fans?

[Sunking]

PWM is more expensive them MPPT silly. Quit looking at the price of the controllers. It takes a minimum of a 300 watt MPPT system to equal a 200 watt MPPT system. You do not understand:

PWM Output Current = Input Current
MPPT Output Current = Panel Wattage / Battery Voltagge

Uou are not getting that. Example take one of your 310 watt panels to a 12 volt battery. Your Panel has a Vmp = 37 volts, and Imp = 8.38 amps (37 volts x 8.38 amps = 310 watts) If you use a PWM controller on a 12 volt battery you get 8.38 amps of charge current and not any more than that. Do the math 8.38 amps x 12 volts = 100 watts.

Use a MPPT controller and you get 310 watts / 12 volts = 25.83 amps. Do the math. 12 volts x 25.83 amps = 310 watts.

If you use those panels on a 24 volt battery with a PWM controller you must wire them in PARALLEL. Example if you take two panels in series you have 74 volts @ 8.38 amps. Than means with your 620 watts of panels 8.38 amps x 24 volts = 201 watts. GET IT? You would have to wire them in parallel which gives you 37 volts @ 16.76 amps or 400 watts out of your 620 watts.

So now tell me which is a less expensive system?

6200 watt PWM
4000 watt MPPT

They both deliver the exact same amount of power. Quit looking at the price of the controller.

[Sunking]

Always use the higher voltage battery system. It is less expensive and more efficient. If you buy a 80 amp MPPT Controller the maximum wattage input vs battery is:

1000 watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts.

So you want a 4000 watt 12 volt battery system stupid?

That means you need 4 very expensive $600 80 amp MPPT controllers. A smart many would run 48 volts and use 1 80 amp controller. As a dealer I think you should go with 12 volts. What do you think? Are you stupid? If you use 12 volt battery with PWM it means you must use 12 volt battery panels which cost 2 to 5 times more then Higher voltage Grid Tied Panels.

So how stupid are you and how much money does the fool have to spend?

[dapago]

I am a artist painter/sculptor and I participate in a few forum (as Moderator) ON MY SPECIALITY and I never had to insult nobody. "Silly" "GET IT", "STUPID" (in CAP)?
If somebody ask me something EVEN IF THEY MAKE THE SAME MISTAKE OVER AND OVER or have difficulty to understand (newbies always do) I try again to explain or I just pass on BUT NEVER INSULT!

LET ME remember you THAT YOU DO NOT HAVE TO ANSWER MY QUERIES if it bother you. MY QUERIES ARE NOT ONLY MADE FOR YOU TO ANSWER. ONE THING IS SURE, YOU DO NOT INSULT OTHERS (SPECIALLY HIDDEN BEHIND YOUR SCREEN) UNLESS PARTICIPATING IN A forum is YOUR WAY TO COMPENSATE THE FRUSTRATION CREATED BY WHAT YOU,VE MADE OF YOUR REAL LIFE!
I maybe a fool on solar matter (total newby) but YOU are definitively the IDIOT.!
My advice? Ignore this post and take that time to make your day, watch porno and try to relax.

[dapago]

Morningstar Corp. Tech Supportvia 2isxwz4yimt5l6sd.tncf8291yjaqxqbd.3a6vrl.3-oneaeai.na13.bnc.salesforce.com

Hello Sir,

Having MPPT is not necessary in your case but it does provide some benefits where PWM cannot. I have attached a few documents below which may help guide you.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/Morningstar-Corporation-Traditional-PWM-vs-TrakStar-MPPT-Whitepaper-March-2015.pdf

http://www.morningstarcorp.com/wp-co...ogy-Primer.pdf

In your situation (location, temperature, panels available, etc) I would say staying with PWM will likely be more than fine. If the system is sized appropriately and you are able to reach absorption and float everyday than having MPPT may is not necessary, you may just get into regulation a little sooner in the day.

SUNKING (what a pedant & ridiculous pseudo to take anyway), here is an answer ADAPTED TO MY QUERIES (the same I actually made here, just a copy/paste of my post here)! Take note. Be confident, you will prevail in your struggles with life.