MPPT advice needed (1 Viewer)

[Jaws]

MPPT regulators are obviously better than PWM, but...........
They work better when fed with two ( or more ) panels in series, giving an an open circuit input voltage of approx 40v. there by allowing the controller to utilise the MPPT to track and use the peak power sweet spot..
I have three panels which are in parallel delivering an O/C voltage of about 20v
Unless I go down the route of either replacing the three panels with two, each with a capacity of 150w+, OR get an MPPT unit that can handle ( to be safe ) the 80v input from three by panels wired in series ( expensive !! ) I am stuck with the panels being in parallel
To that end, do the collective brains think it is still worth changing out my extremely costly PWM unit ( it is big, with massive heatsink, auto-detecting etc etc ) with an MPPT unit ?
At the moment the PWM I have regularly delivers 20+ amps if the batteries have taken a hammering and are low

 

[Googlebot]

The problem with panels in series is that a tiny bit of shade on one panel wipes out all the panels output. In parallel this isn’t an issue as it will only affect one panel.

 

[andy63]

At the moment the PWM I have regularly delivers 20+ amps if the batteries have taken a hammering and are low

Hi John...that looks to be a very healthy output from your panels.. you don't say what the wattage of your existing panels are but the nominal output from a 100w panel I usually take to be at best in the region os 5 to 6 amps.. so I'm assuming they are greater than 100w panels..
Is it worth the expense of swapping over to an mppt controller... most probably not if you are happy with your existing system and it does what you want....but I know what its like once you get something in your head...
I reckon an mppt with series wired panels might give a small improvement in poorer conditions...
I've just rejigged my wiring so that it's a couple minutes work on the roof to change my two 140w panels from series to parallel..currently trying series ..but that's just mucking about for fun..the jury is still out ...
Andy..

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[Raul]

You don’t need to wire in series if you have enough voltage above battery voltage, which you do, 20v is still good for a mppt to track in parallel. At the moment with PWM you throw away 30% of panel power.
PWM is amp in- amp out, at battery voltage.
MPPT is power in -power out, nothing is wasted , not even 1w.

 

[68c]

I would suggest if it works leave it alone. Otherwise, to some extent, it depends where you are. The further you move from the equator the lower the sun sits and the longer dawn and twilight last. Anyone who has lived in the tropics will know how quickly it gets dark once the sun reaches the horizon. Near the equator a PWM is acceptable as the light available, and so panel output, is fairly constant. At higher latitudes the MPPT comes into its own as it can better harvest the long dawn and twilight periods with diminished light. I am not convinced the shadow problem has any large effect, otherwise a small shadow would stop a single panel working, most panels have small diodes to bypass a panel section in shadow. Series works well away from the equator as the setup will make even more use of the long dawn and twilight as it will output earlier and later in the day than parallel

 

[Raul]

I would suggest if it works leave it alone. Otherwise, to some extent, it depends where you are. The further you move from the equator the lower the sun sits and the longer dawn and twilight last. Anyone who has lived in the tropics will know how quickly it gets dark once the sun reaches the horizon. Near the equator a PWM is acceptable as the light available, and so panel output, is fairly constant. At higher latitudes the MPPT comes into its own as it can better harvest the long dawn and twilight periods with diminished light. I am not convinced the shadow problem has any large effect, otherwise a small shadow would stop a single panel working, most panels have small diodes to bypass a panel section in shadow. Series works well away from the equator as the setup will make even more use of the long dawn and twilight as it will output earlier and later in the day than parallel

I guess you don’t understand the difference of the two. I gave a simple explanation above. Amp in at battery voltage for PWM vs power in power out for mppt. Light exposure and intensity is true for both cases. The mppt will be ahead by 30% in both cases compared like for like anywhere on earth.

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[cmcardle75]

MPPT regulators are obviously better than PWM, but...........
They work better when fed with two ( or more ) panels in series, giving an an open circuit input voltage of approx 40v. there by allowing the controller to utilise the MPPT to track and use the peak power sweet spot..
I have three panels which are in parallel delivering an O/C voltage of about 20v
Unless I go down the route of either replacing the three panels with two, each with a capacity of 150w+, OR get an MPPT unit that can handle ( to be safe ) the 80v input from three by panels wired in series ( expensive !! ) I am stuck with the panels being in parallel
To that end, do the collective brains think it is still worth changing out my extremely costly PWM unit ( it is big, with massive heatsink, auto-detecting etc etc ) with an MPPT unit ?
At the moment the PWM I have regularly delivers 20+ amps if the batteries have taken a hammering and are low

Are the panels identical? When running in parallel, it is important that the panel voltages are similar. When running in series, it is important that the panel currents are similar. If you have different sized panels, it is far more likely that they will be similar voltages than currents, as the designers will tend to target about 22V open circuit and take whatever current that produces.

Traditionally, people warning against running in series, due to the shading effect. However, on modern panels, bypass diodes are used which significantly reduce this problem. As you've stated, running in series gives significant benefit in low light conditions, as by increasing the voltage, the total output will be higher than the battery voltage in lower light conditions. It is also is more electrically efficient.

MPPT units are rated for both current and voltage. The majority will accept at least 3 standard panels in series (typically indicated by 75V in the model name). Many take 4 (i.e. 100V) or more. However, you do need to ensure that the current rating is sufficient at 12V for the total output. In some cases (i.e. Victron), any excess is discarded. Other makes may do this, or they might shut down or be damaged. You need to check the specs.

Discarding unwanted power is rarely an issue. Getting enough power in shoulder season is the reason for large panels, not trying to get even more in sunny conditions where you've almost certainly got enough anyway.

 

[cmcardle75]

I guess you don’t understand the difference of the two. I gave a simple explanation above. Amp in at battery voltage for PWM vs power in power out for mppt. Light exposure and intensity is true for both cases. The mppt will be ahead by 30% in both cases compared like for like anywhere on earth.

Well, not anywhere. The MPPT adjusts voltage vs current to find where the maximum power can be extracted. The PWM doesn't. However, the random value it settles on might, in some circumstances, be exactly right and it could potentially extract just as much as an MPPT would. But you need to be lucky and it would likely change due to weather, time of day, state of battery charge etc.

 

[andy63]

I am not convinced the shadow problem has any large effect,

Well in my experience that is not the case..
I've run basic tests with panels..the bypass diodes may allow the panel to produce a bit when shaded but the output can drop rapidly once a panel is part shaded..
Two things which I found really matter..
If the panel can be inclined to face the light it is most probably the single biggest factor in output..
And shading kill the output..
Andy

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[Raul]

Well, not anywhere. The MPPT adjusts voltage vs current to find where the maximum power can be extracted. The PWM doesn't. However, the random value it settles on might, in some circumstances, be exactly right and it could potentially extract just as much as an MPPT would. But you need to be lucky and it would likely change due to weather, time of day, state of battery charge etc.

Yes everywhere as in location. Matching hardware like for like PWM does not track. Mppt will and extract more power from the spare voltage.

 

[Lenny HB]

I certainly noticed the difference when I changed to MPPT biggest difference was on cloudy overcast days and even saw output I didn't expect in thick fog. Although the MPPT regulator I fitted was quite a good one I then upgraded to a much better one (Votronic) and noticed further improved output.
I always wire the panels in parallel on the van because of the shading problem.

 

[the1andonly]

In feb i did a few simple trials with a new 100W panel i had in garden. none of this is scientificaly rigorous. only done because couldn't find it online and bored.
1 for 3 days measured OC voltage @10min intervals (at sunset 4-6 pm). i was looking for the threshold when voltage went bellow 16V and 9V. This was approx 1 hour between these 2. ie (assuming sunrise same) we could get an extra 2 hours collection time per day if used series collection(11 instead of 9 +20%)
2 using a very cheap pwm controller and power meter i played with altering angle to sun and inclination. being upto 20 degrees from optimum inclination reduces power by 5%. (optimum 20% better than flat). A spread of 90 degrees (from directly pointing at sun) was feasible but cut of quickly.
3 On a very cloudy day the best orientation is flat. some collection happens raise it 5 degrees zero collection.
4 sHading a small area is not catastrophic (specific to this panel)
5 for OP in my mind a good compromise would be 2 panels in series on a MPPT controller capable of 50V (eg the votronics) and use the 3rd on the existing pwm controller.
these are just observations and approximate.


as said previously wire 2 panels in series with y connectors (MP4) on roof, this can allow a quick change to parallel configuration.

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[sallylillian]

Really interesting thread. Thanks all.

 

[funflair]

Just my two pence worth then, I have been running basically identical regulators but one PWM and one MPPT side by side with identical panels feeding them, I have taken quite a few clamp meter readings in a variety of conditions and the MPPT is normally 20% ahead on power output even in good sunlight.

 

[Raul]

In feb i did a few simple trials with a new 100W panel i had in garden. none of this is scientificaly rigorous. only done because couldn't find it online and bored.
1 for 3 days measured OC voltage @10min intervals (at sunset 4-6 pm). i was looking for the threshold when voltage went bellow 16V and 9V. This was approx 1 hour between these 2. ie (assuming sunrise same) we could get an extra 2 hours collection time per day if used series collection(11 instead of 9 +20%)
2 using a very cheap pwm controller and power meter i played with altering angle to sun and inclination. being upto 20 degrees from optimum inclination reduces power by 5%. (optimum 20% better than flat). A spread of 90 degrees (from directly pointing at sun) was feasible but cut of quickly.
3 On a very cloudy day the best orientation is flat. some collection happens raise it 5 degrees zero collection.
4 sHading a small area is not catastrophic (specific to this panel)
5 for OP in my mind a good compromise would be 2 panels in series on a MPPT controller capable of 50V (eg the votronics) and use the 3rd on the existing pwm controller.
these are just observations and approximate.


as said previously wire 2 panels in series with y connectors (MP4) on roof, this can allow a quick change to parallel configuration.

1. Not conclusive on open circuit voltage, means you got voltage, but, without knowing the amp potential, for all is worth, once under load the voltage collapses until has some amps to sustain it. The mppt wakes up at battery voltage plus 5v open circuit, and then it keeps scanning for a power point. As soon as there is some potential it will lock on, and every so often, depending on logarithm, it will keep taking samples to search for more power or to adjust to light intensity.
2 correct , the incidence angle (azimuth) is important to max power of sun is out.
3 very true, the reflection of white clods (albedo), helps on overcast and winter, with panels completely flat.
5 shading a small area of a cell is not going to cause massive drop, depending on witch cell in the string configuration to the diode position. Some panels have more diodes, some to and some none. The more diodes, the more sections are bypassed and allow the rest to work. If a permanent or long time shade, ( clean your panels), then hot spots and diode failure can happen on elevated temps above 40-50 deg.
5 if nothing on the roof in the vicinity to potentially shade, agree a series will be fine. Otherwise parallel will work to.

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[the1andonly]

Raul the point of trying the voltage check was i couln't find any info on the web regarding the posible increase in harvest time using series rather than parallel connection. I used oc voltage as both my mppt controllers were allready installed in van. Have you any data on harvest time increase using series config.

 

[Raul]

I do have, for fixed installations. One in particular is my house. For increased harvest time are two solutions: tracker or multiple orientations. The voltage makes very little difference in staring and finishing charging maybe minutes. The higher voltage will start sooner but the amount of energy harvested it’s not that much. I have south east 6s with south 6s 2p total 4950w with a victron 250/85 and voc 220 ish. This array starts first along with another small 850w 3s facing east. The east is 110 voc on a 150/35 and produces more in the first few minutes, until the 4950w array overtakes. Despite the voltage difference. Next one is south west 3s 4p 3060w on a 150/85. Again this is a 110voc and is the last one to shut down. As you notice orientation beats the voltage on harvest. All this arrays, are charging a 48v battery bank. The 150/85 and the 150/35, always runs cooler than the 250/85. This has a voc in winter of 234-236vdc and converts down to 48v. The others with a cold voc 120v still runs cooler converting to 48v.
Saying that I have on the van a voc of 50vdc plus, but, is out of a single 96 cell panel not series, 2p. I totally agree with you that you should strive for a higher voltage if possible. But not always is going to be a advantage. Long runs of cable with higher battery bank voltage, yes, If series will bring a advantage of higher voltage but with risking shadowing, then that advantage will be eaten away.

 

[the1andonly]

My particular interest is for low season having a 330w 46v panel and 220w in 20v panels, thus in summer im not worried about losing the 220w to shadowing. Boosting the effectiveness in winter is more interesting which is why the 100w panel is tiltable.

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[Raul]

At low sun the best think is as you say tilt to face the sun or manual tracker. But when no sun flat is better in winter. Best of both worlds is have some flat on the roof, and a portable on the ground you can track the sun. It’s not perfect but a good compromise.

 

[sallylillian]

I do have, for fixed installations. One in particular is my house. For increased harvest time are two solutions: tracker or multiple orientations. The voltage makes very little difference in staring and finishing charging maybe minutes. The higher voltage will start sooner but the amount of energy harvested it’s not that much. I have south east 6s with south 6s 2p total 4950w with a victron 250/85 and voc 220 ish. This array starts first along with another small 850w 3s facing east. The east is 110 voc on a 150/35 and produces more in the first few minutes, until the 4950w array overtakes. Despite the voltage difference. Next one is south west 3s 4p 3060w on a 150/85. Again this is a 110voc and is the last one to shut down. As you notice orientation beats the voltage on harvest. All this arrays, are charging a 48v battery bank. The 150/85 and the 150/35, always runs cooler than the 250/85. This has a voc in winter of 234-236vdc and converts down to 48v. The others with a cold voc 120v still runs cooler converting to 48v.
Saying that I have on the van a voc of 50vdc plus, but, is out of a single 96 cell panel not series, 2p. I totally agree with you that you should strive for a higher voltage if possible. But not always is going to be a advantage. Long runs of cable with higher battery bank voltage, yes, If series will bring a advantage of higher voltage but with risking shadowing, then that advantage will be eaten away.

That is a very informative summary, thank you. I have 6 by 130w panels on my van. They are paralleled in pairs at individual buses that the factory installed. (Morelo). Originally the regulators were 3 off Buttner PWM, read Votronic with a different badge. I changed the 3 to Votronic MPPT and achieved a meaningful improvement. Unfortunately I do not have the exact numbers to hand and wished I had been as scientific as you. However from memory I saw a maximum of 43 amps from the MPPT Votronics (6 panels). The Buttner PWM with 4 panels were maxing at about 25amps. There was a factory upgrade during the process to add confusion.

My progressive conversion to Victron led me to sell the 3 Votronics after one trip so as to get a complete Victron solution on the van. I installed a
SmartSolar Charge Controller MPPT 150/85-MC4 and took the 3 panel feeds from the buses into the 3 MC4 connections. I have now seen 53amps max on a sunny cool day and often exceeding the rated panel output.

So preamble over, I have been debating the option of putting each pair into series to get a higher voltage on the 3 feeds so 3 by 2 panels in series then paralleled at the regulator. Not too much hassle just a rejig of the wiring at each bus and the regulator can handle that with ease. However your post has convinced me that this would likely be fruitless when including the risk of panel shading. I do see in my hutch over the winter that the Victron is showing harvesting from a couple of roof lights, admittedly only in the single digit watts, but it led me to assume that increasing the voltage would increase the harvest early and late in the day due to the 5v differential that is required. Clearly not so and better to remain in parallel. Thank you. Michael

 

[Raul]

Your 6 panels are configured 6s at the moment. If you would get more out of 2s 3p ( 2 series 3 parallel) as 3 strings coming in, it’s down to shade. If you have no shade risk, access to plug 3 Y mc4 splitters I would try it. You will be running at double the voltage per string at the same amps as now, so same cable used. If one sting gets a minimal shade, the other two will chug away. It will wake up sooner due to higher voltage, but without amps, it’s going to idle until about 5w available. Wheather that comes from 6s or 2s 3p, it’s still the same source. The only difference you will se is higher conversion step down, and ability to carry longer smaller cable per string. The only way to fi d out is try it, maybe your wire configuration will benefit of the higher string voltage, maybe not.

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[mitzimad]

John ask your self if what you have is working?have you run out of power at any time if the answer is no go and find something else to play with if yes stick another panel on the roof instant 33percent improvement

 

[sallylillian]

So marginal benefit that only really becomes clear if you have a permanent installation in a static location, which of course a motorhome for the most part is not. I feel very comfortable with your persuasive presentation that I may only achieve a marginal gain which is likely to be more hassle than its worth in a mobile environment. The real benefit being MPPT. Thanks.

 

[jongood]

Ive also been watching with interest wondering if I could do something clever using the 24v chassis batteries and a b2b but here in Spain I'm regularly seeing 30 and briefly (very) saw 41amps yesterday out of my 600 watts.

(Apart from the one you know about) Your old votronic setup is working very well for me Michael sallylillian

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[sallylillian]

Ive also been watching with interest wondering if I could do something clever using the 24v chassis batteries and a b2b but here in Spain I'm regularly seeing 30 and briefly (very) saw 41amps yesterday out of my 600 watts.

(Apart from the one you know about) Your old votronic setup is working very well for me Michael sallylillian

Good to hear Jon.

 

[Jaws]

Well I have made a purchase
It is ne of the CPK series.. handles up to 100v input or 960w of panels, max output 80 amps

 

[Raul]

What is a CPK if you don’t mind?

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[Richard n Ann]

What is a CPK if you don’t mind?

Looks like a Chinese make

 

[Robert Clark]

 

[Jaws]

Yup, thats the one

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