Should i buy mppt controller or stick with pwm? new solar installation

Clarkdale44

Hello

Soon I am finally thinking of buying solar system.

Not that big only 600w max.

So I was thinking of buying 4x 150w panels.

I am confused on how to connect them.
Series or parallel... I have researched a lot on this topic but in the end I always got confused.

The next thing is charge controller.
One costs $30 the other around $200
Pwm vs mppt

I will be using 12v 150 ah battery which requires about 15 amp current to charge.

If I were to connect my PV in series, that would give me around 18.9v x 4 = 75v with 8 amps.

Now if I were to use this setup with mppt controller.. Would the charging current be enough to charge my battery? How much current would I get anyway at peak sun?


And if I connect PV in parallel I would get 12v and 32 amps... I know it would require thicker cable.. But if I were to connect this setup to mppt then how much output current would I get?

And how much current if connected to pwm cc.?

The load I will be running is mostly AC so I will be using DC to ac inverter 230v 50hz. I know there will be losses in the conversation that is why I want to squeeze every last bit of power the solar PV can offer.


So basically I am asking to to tell me what can I do with my 4x 150 w panels?

Any detailed explanations would be appreciated as long as it is understandable.

Regards

Photowhit

Clarkdale44 said:
I will be using 12v 150 ah battery which requires about 15 amp current to charge.

If I were to connect my PV in series, that would give me around 18.9v x 4 = 75v with 8 amps.

And if I connect PV in parallel I would get 12v and 32 amps... I know it would require thicker cable.. But if I were to connect this setup to mppt then how much output current would I get?

Solar panels usually output about 75% of their panel rating. So you could expect about 450 watts on normal days.

MPPT charge controllers convert the incoming wattage to a voltage that your batteries need, they lose just a small fraction of the incoming power as heat, so your 450 watts would be output at about 14.4 volts. We would typically recommend an input voltage about double the output voltage, so running your panels in strings of 2. This makes your loses in converting (heat lose) minimal.

450watts/14.4volts=@31amps (amps x volts = watts)

With an PWM charge controller the voltage must be high enough for the maximum charging voltage. if equalizing you will need as much as 16 volts, so even with voltage drop through wiring and charge controller you should be fine. so with a PWM you should end up with about 450 watts / 18.9 volts = @24amps.

Your system only puts out the full capacity of your array, during bulk charging, once the batteries reach 80-85% full the amperage they accept will drop off. Also the calculation is a bit skewed, since much of the drop from 100%-75% is in a decrease in voltage. I wouldn't expect more than a 10-15% increase in production from a MPPT type charge controller. That said, they have more features (in general) and you should be able to controller the charging amperage with many (perhaps not cheap ones) This may be important since you have the ability to charge your batteries at too  high a rate. I would be sure to get a battery temperature sensor for either one! 

Clarkdale44

Thanks...

I wanna confirm one thing... You said..
450 watts / 18.9 volts = @24amps. i thought in pwm, voltage is dropped to match the voltage of the battery..

Shouldn't the calculation be like this?
450watts / 12.5 volts = 36amps... Is that wrong calculation?

In the above equation, are we using the voltage that is going into the battery or the voltage that is coming out the panals?



And one more thing...
Should i consider investing in mppt at all..? Is it worth it for my setup?
Also i don't want to increase my battery voltage hence i want to use a single 12v 150ah if possible..



Sorry if i am asking too many questions.. i am new to all this...... I never knew we have to plan this much for a single solar installation..

BB.

Questions are why we are here (and to help).

PWM controllers are "simple" On/Off switches. On, the current is passed from the solar array to the battery bank. Off, no current flow. Turn the switch on/off a 100x per second, and the controller gives you "average" charging current. More on time, more current and more off time, less average current--PWM is Pulse Width Modulation.

So, if you have a 180 Watt Pmp panel with 18 volts Vmp and 10 amps Imp--Then the maximum current will be Imp or 10 amps through a PWM controller... Regardless of the battery bank voltage (6 volt, 12 volt, 14.8 volts, will still be, more or less, 10 amps in full sun). A PWM controller is pretty close to 100% efficient (does not use much power for its electronics).

An MPPT type controller is a different animal. It is a (typically) a DC buck mode switching power converter... More or less, it works like you say:

• 18v Vmp * 10a Imp = Power In = 180 Watts = Vbatt * Ibatt =>
• 180 watts * 0.95 typical eff = 171 Watts "available"
• 171 Watts / 12 volt batt = 14.25 to battery
• 171 Watts / 14.5 volt batt = 11.79 amps to battery

Now--In real life, a 180 Watt panel's Vmp will fall in bright/hot sun, as much as 80% of rated Vmp is common (80% of rated power) in hot summer sun. So, your 171 Watts now becomes:

• 171 Watts * 0.80 = 136.8 Watts
• 136.8 Watts / 14.5 volts = 9.43 Amps into 12 volt battery

Because of all of the "deratings" (dust on panels, hot panels, controller losses, etc.)--I have pretty much defaulted to PWM is about the same output as an MPPT controller in spring/summer/fall weather... In cold climates/weather (i.e., freezing or below), you will get ~10% to 15% more with a MPPT controller--But that is not a lot extra--So I would not suggest buying a MPPT controller just to harvest more energy.

However, where MPPT controllers are nice is when you have larger systems and/or with the array many 10's or 100's of feet from the battery shed. You can run a higher voltage solar array (and smaller awg wiring) to the battery shed, and the MPPT controller will efficiently down convert the high voltage/low current of the array to the lower voltage/higher current for the battery bank.

A rough rule of thumb--For typical installations at 400 watts a below, a PWM is usually more cost effective. And for systems >800 Watts, a MPPT controller is usually more cost effective.

To know what is best for your--Have to take the details of your installation and do a couple "simple" paper designs and see what works best for you.

-Bill

jonr

I second the point about controller features.  It's important to treat the battery well and a $30 controller may not do that.

BB.

Note that a 12 volt @ 150 AH battery is relatively small... If I had a choice, I would suggest 2x 6 volt @ ~200 AH batteries instead--Typically it is easier to find "golf cart" batteries which are true deep cycle batteries--Many 12 volt batteries are "Marine/RV batteries" and are not, usually, going to survive deep cycling (taking to near 50% discharge) very well.

A 15 amp (10% rate of charge) MPPT controller tends to be expensive and not really needed if you are going to get one or two ~140 Watt (Vmp~18 volts, Imp~7.8 amp) panels.

Where you can save money with MPPT (or at least break near even) is that 140 Watt "12 volt" panels are almost 2x as expensive at a 280 Watt ~30 volt Vmp panel. -- So you can get 2x the amount of solar panel wattage, and get a true MPPT charge controller (cheaper panels, more expensive controller, cheaper/smaller wiring from array to charge controller) and justify the costs of a MPPT controller.

-Bill

pdh

> 140 Watt "12 volt" panels are almost 2x as expensive at a 280 Watt ~30 volt Vmp panel

Why is that? From a manufacturing perspective, the bill of materials is roughly the same, right? I think the individual cells in the panel are just wired together differently, correct?

Is it a matter of scale? Like, you can sell way more of the 280 watt / 30 volt panels for grid-tie use than you can sell 280 watt / 12 volt panels, so the higher-volume production of 30-volt panels leads to lower manufacturing cost?

BB.

Pretty much high volume and lower production costs ($ per watt).

Down side is shipping a single 300 watt panel is more expensive than shipping a couple 140 Watt panels.

Also panels larger than ~175 watt panels usually takes 2 people to move safely.

-Bill

Clarkdale44

Thanks all of you... I think i got it now...

I am gonna research a bit more and will take my decision.

softdown

Too tired to say much. I'd go with the PWM charge controller and use the savings on more battery. You may not even be able to laptop/internet well with one battery. $30 may not get a decent charge controller though. I'd be prepared to spend a hundred...or so.

Clarkdale44

Thanks...
I am still thinking.... And taking all that into consideration... I will make my decision soon..

softdown

BB. said:

Pretty much high volume and lower production costs ($ per watt).

Down side is shipping a single 300 watt panel is more expensive than shipping a couple 140 Watt panels.

Also panels larger than ~175 watt panels usually takes 2 people to move safely.

-Bill

Shipping can be important and is rarely mentioned. FedEx/UPS are far cheaper and I forgot their size maximum. I am going to guess ~ 24-30" x 48-60". So....maybe 28"x54"....or so. Feeling too sandy to look it up at the moment. Modern 24 volt panels are simply gigantic. It has been a couple years since new 24 volt panels were easily handled by one sturdy person.

BB.

Very roughly, ~125-140 Watt panels are about the largest that can be shipped with any carrier.

Larger panels usually have to ship by truck (perhaps to a depot, unless you pay for front door delivery, lift gate charge for pallets, etc.).

As Softdown says--Make sure you have cost of packing, insurance, and delivery for your various panel options. Have seen some larger panel cost just about as much to deliver as to buy (i.e., $240 panel and $240 delivery charge).

-Bill

Clarkdale44

Forget shipping... I will be buying everything local...

softdown

Clarkdale44 said:

Forget shipping... I will be buying everything local...

I get the vibe that budget is an issue. I have seen the best prices offered by homeowners who bought a full pallet and wanted to sell the extra panels on....say Craigslist. No warranty when this is done I would expect.

Try to steer away from buying old poly panels. My neighbor did that, their output is next to nothing at this time. Sure...the panels may last 20 years but production declines throughout.

 

Photowhit

softdown said:

Try to steer away from buying old poly panels. My neighbor did that, their output is next to nothing at this time. Sure...the panels may last 20 years but production declines throughout.

I have poly panels that are producing nicely after 5 years, and I'm still friends with the people who purchased my Poly panels from 12 years ago.  Both Evergreen which is no longer in business.

I would stay away from amorphous and thin film panels. Mostly due to longevity issues.

Clarkdale44

By local i meant that from local shops in my city.... I was thinking of going with Poly as they are cheaper compared to mono... What do you think? Or should i buy mono instead?

BB.

In general--Unless you have a space issue (mono-panels are slightly more efficient than poly crystalline panels)--As long as the panels are tempered glass construction(not some sort of plastic/flexible material), just buy on $$$/Watt pricing. Do not pay a premium for mono panels (assuming you are comparing good quality mono vs poly panels).

Some folks say that mono panels have slightly better harvest in overcast conditions (I am not convinced it is worth the added cost--if there is a better harvest). Do your research.

-Bill

Clarkdale44

BB. said:

In general--Unless you have a space issue (mono-panels are slightly more efficient than poly crystalline panels)--As long as the panels are tempered glass construction(not some sort of plastic/flexible material), just buy on $$$/Watt pricing. Do not pay a premium for mono panels (assuming you are comparing good quality mono vs poly panels).

Some folks say that mono panels have slightly better harvest in overcast conditions (I am not convinced it is worth the added cost--if there is a better harvest). Do your research.

-Bill

Thanks... i have got one last confusion about charge controllers doesn't matter whether it is pwm or mppt.
Thing is i have seen many CC with variety of output amps on 12v and 24v with different manufacturers... But they are all different..

Which number in a charge controller defines that how many panals can be connected to it..?

For example..
All are pwm based except F
Charge controller A is 12v 30A and 600Wp panals can be connected. 75% efficiency

Charge controller B is 12v 30A and 500Wp panals can be connected. 90% efficiency

Charge controller C is 12v 40A and 750Wp panals can be connected. 98% efficiency

Charge controller D is 12v 20A and 550Wp panals can be connected. 70% efficiency

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

Charge controller F is 12v 40A and 600Wp panals can be connected. 99.2% efficiency


These are all different brands... I don't understand these numbers... Why are the manufacturers restricting users from adding more panals even though their unit can handle this much current.
For example

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

500/18.9 = 26 Amps... No where near 40.. It can easily handle 600Wp with 31Amps, then why are they restricitng to 500Wp only?

Is it something am i missing?

Please help me understand what's going on here...

Estragon

The anp rating of a charge controller would be at the output voltage of the controller, not the panel. You might initially start charging at 12v with full current, so you're at 500w* .95/12v = about 40A. With a multi-stage controller current will stay at about max until voltage reaches the absorb set point, around 85% SOC, then taper off as the battery reaches full.

Multi-stage charging and ability to adjust charging voltages may be important depending on your application and choice of battery.

Photowhit

Which number in a charge controller defines that how many panals can be connected to it..?

For example..
All are pwm based except F
Charge controller A is 12v 30A and 600Wp panals can be connected. 75% efficiency

Charge controller B is 12v 30A and 500Wp panals can be connected. 90% efficiency

Charge controller C is 12v 40A and 750Wp panals can be connected. 98% efficiency

Charge controller D is 12v 20A and 550Wp panals can be connected. 70% efficiency

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

Charge controller F is 12v 40A and 600Wp panals can be connected. 99.2% efficiency


...I don't understand these numbers... Why are the manufacturers restricting users from adding more panals even though their unit can handle this much current.
For example

Charge controller E is 12v 40A and 500Wp panals can be connected. 95% efficiency

500/18.9 = 26 Amps... No where near 40.. It can easily handle 600Wp with 31Amps, then why are they restricitng to 500Wp only?

Is it something am i missing?

While you are looking at it wrong, something is missing. If you would like to direct us to the charge controller, provide a link. We'll check it out.

With PWM the voltage, so long as it's in the range of the charge controller, doesn't matter. only the amperage. If it can handle 40 amps then 40 amps divided by the amperage output of your panels, about 7.9 = 5... so it should be able to handle 5 panels. It might be that they gave you a maximum wattage that the charge controller can handle if it's a 12/24 volt type. It will handle twice as much at 24 volts. The panels would have to be run in series to reach 24 volts.

The efficiency numbers may be a clue. Internally PWM should be around 98%, but the charging efficiency will be closer to 75% based on VMP and system voltage, real world numbers will be higher, as the voltage reaching the charge controller will be less the panels VMP in all but ideal conditions.

Quality MPPT charge controller can be over paneled and usually over paneling up to 20% is very cost effective, as the panels will only produce 75% of the name plate on typical days.

softdown

Photowhit said:

softdown said:

Try to steer away from buying old poly panels. My neighbor did that, their output is next to nothing at this time. Sure...the panels may last 20 years but production declines throughout.

I have poly panels that are producing nicely after 5 years, and I'm still friends with the people who purchased my Poly panels from 12 years ago.  Both Evergreen which is no longer in business.

I would stay away from amorphous and thin film panels. Mostly due to longevity issues.

I read that mono panels generally last 25-30 years, while poly is rated for 20-25 years. If the panels are 15 years old, (old panels), then the mono may have twice as much life left in them.

It is probably impossible to say exactly what the expected longevity is.  I, like most others, am simply off of personal experience. My neighbors old poly panels produce "next to nothing." We have reached the time when there are a lot of old panels from the 70s and 80s floating around.

Guess a lot depends on ones definition of "old". A 15 year old panel is old in my book.

mike95490

I cannot answer why some controller mfg's impose lower limits on their controllers.  Reading the manual may explain it,
For a Well Designed and Constructed PWM controller, there is no valid reason to not connect 40A of array to a 40A controller.
 Lesser models may not have thermal foldback controls and could overheat, but to me, that is a flawed design and should be called a 30A controller.
MPPT controllers are rated at their output terminal, regardless of the input voltage/amps (within wide limits)  They nearly universally include thermal foldback to protect themselves and publish a derate curve for different thermal enviroments. The possible output amps can easily be calculated from the input wattage and battery voltage

Photowhit

  It is probably impossible to say exactly what the expected longevity is.  I, like most others, am simply off of personal experience. My neighbors old poly panels produce "next to nothing." We have reached the time when there are a lot of old panels from the 70s and 80s floating around.

Guess a lot depends on ones definition of "old". A 15 year old panel is old in my book.

I don't know your neighbors or if they know enough to tell what the problem is...

I haven't heard that there is a problem from a reputable source.  Amorphous panels use to be made in larger sizes and they had problems with longevity. I know Al's Simpler Solar Systems had a large set of amorphous and took them down. I have some cut round, French Photowatt panels from 1980 that still work well. Likely the low iron prism glass would cost more than a 55watt panel today.

softdown

The information data has faded so bad that it is illegible. Looking at them, I would guess they were made around 1985....just going from looks.

Perhaps my information is flawed...it is simply what I read. Not a big difference until the panels reach ~ 20 years of age. In my world, the years fly by so I look at longevity pretty hard.

Did a little web searching and found:
Even though a monocrystalline panel has the potential to last up to 50 years, most warranties only go up to 25 years which polycrystalline panels are able to reach just fine.

Poly-crystalline cells are known to function better than mono-crystalline under high-heat circumstances (This claim is disputed by others) however less efficient in low light conditions.

Monocrystalline solar panels live the longest. Most solar panel manufacturers put a 25-year warranty on their monocrystalline solar panels.

If the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down. (refers to mono)

• Polycrystalline solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels. This technically means that they perform slightly worse than monocrystalline solar panels in high temperatures. Heat can affect the performance of solar panels and shorten their lifespans. However, this effect is minor, and most homeowners do not need to take it into account.

Longevity

25+ years

25+ years This source rates them the same

Solar cell type

	Output loss in percent per year
	Pre	Post
Amorphous silicon (a-Si)	0.96	0.87
Cadmium telluride (CdTe)	3.33	0.4
Copper indium gallium selenide (CIGS)	1.44	0.96
Monocrystalline silicon (mono-Si)	0.47	0.36
Polycrystalline silicon (poly-Si)	0.61	0.64

The above source favors mono longevity by a significant amount.

***It appears that mono costs a little more and is a little better. If space is not a concern, the value is pretty much a toss up at this time.

Poly panels are very good. Nothing to be ashamed of. Evergreen was showing a lot of promise with their thin ribbon technology before they went down.

I would likely change poly longevity to 30+ years and mono longevity to 40+ years....after more study.

706jim

I'm running an old Trace C40 pwm controller. It has performed faultlessly for 20 years. My question would be for anyone who has run this unit at or near capacity at 24 volts input. Obviously, it should be able to take 40 amps, but is there any safety factor built in for a modest overload? We all recognize that panels rarely develop their rated output. I'm just wondering how many watts I can put into this puppy without having to upgrade to a larger controller.

softdown

706jim said:

I'm running an old Trace C40 pwm controller. It has performed faultlessly for 20 years. My question would be for anyone who has run this unit at or near capacity at 24 volts input. Obviously, it should be able to take 40 amps, but is there any safety factor built in for a modest overload? We all recognize that panels rarely develop their rated output. I'm just wondering how many watts I can put into this puppy without having to upgrade to a larger controller.

Subscribing because I have the exact same question about the C40. How many watts can it handle. Mine overheats with maybe 600 watts and I can't find a wiring error. The panels read about 42 volts at the charge controller.

DConlyGuy

i have the c35 model and i was told 400 watts for 12 volts and 800 watts of panels for 24 volts. i figure with your c40 you can go up another 100 watts for the each 12 and 24 volts