Solar Fixed and portable panels into one MPPT controller

[Just the two of us]

Am considering investing in portable panels for when my fixed panels are working sub-optimally due to shade. As space is limited will be challenged to fit a second MPPT controller into the area where all the other solar gear is stored.

As to my best knowledge all MPPT brands and models only have facility for one input. Not withstanding the voltage limitations of a MPPT controller, am wondering whether I can use a twin to single Anderson Plug lead with the single plugged into the MPPT controller, with one of the two twin ends permanently connected to the fixed panel, with the second of the two twin ends routed to an externally mounted Anderson Plug for the times I connect up a portable panel. Effectively what I seek to do is, occasionally, have one MPPT controller simultaneously receiving input from two solar sources.

 

[Drover]

With my set up the feed from my roof top panels has an Anderson piggy backing on the line before it gets to the Controller where I plug in my portable panel which has its original controller removed, since mine are in parrellel this doesn't cause complications ................... The limitations of the controller in regards to watts/amps is about what is actually coming down the line not the sum total on the label...., ie: if the controller is limited to say 400w and you have 600w of panels it will only clip the supply when its actually producing that much, and since its rarely seen that panels run at max output its not a problem really......... Depending on how its set up having 2 controllers can be problematic ...... Mine has been running this way for a number of years quite well.. and I camp off grid for weeks with no drama, in fact solar is the only way I charge .

I often have my portable out for longer stays as it will catch the morning sun and have the battery at full charge well before the roof tops start to do anything, this then leaves the roof top to be charging phones, laptop, camera batteries etc with the battery staying at charge, it also catches that late bit of sun before night fall.

I have 440w about 24a on the roof and 120w about 6a as a portable, so about 30a depending on the voltage it puts out, in reality the best I have seen is about 16 from the roof and 5 from the portable but not often ....
Of course the secret is to have plenty of storage so that by morning you have only just skimmed the top of the charge, you really need a battery that your normal daily use is no more than 20% of usable power then in the morning charging is quick.

 

[Hitting the road]

I have the one MPPT in my van with max 80v / 40 amp input. The van also has a standard BMPRO BMS where the roof solar panel originally fed in to, only the one standard 160w panel, I have no idea of it's specs as it is ex factory at build, but imagine it must be around 18 odd volt, 160w / 8 amp output. (I am going to replace that panel with a new 200w and add another 200w to the roof shortly)
I also have 400w / 36v of portable panels I put out when parked up. I currently connect the portable panels in series when they are out not parallel as many people do, giving me more usable input in volts rather than amps to the MPPT.

What I have done is disconnected the roof panel from the BMPRO and run that input via an Anderson plug to the MPPT, (piggy backed with the external Anderson plug connection), so that I can unplug it and isolate it from the portable panels when they are out...reason being if I left it connected when the portable panels are out it in series would confuse the MPPT input being it would not be in series with the others but just an additional input in amps.

When I put out the portable panels I plug them in to the van via an external Anderson plug which is hard wired to the MPPT sending volts straight in, while unplugging the roof panel from the MPPT. When I pack the external panels up to hit the road unplugging them from the van / MPPT, I just plug the roof panel back in to the MPPT so it can lazily feed what ever amps it can while I drive...it usually keeps the batteries topped up. I have 2 x 135 amp Lithiums installed.

When I fit the additional panels on the roof I think I will be wiring them in parallel rather than series, and the external then the same, so I can then leave the roof panels plugged in all the time, just plugging in the external panels when I wish to. As Drover wrote above if the input exceeds the capability of the MPPT it will be clipped to what ever it can handle. In my case 4 x 200w panels = 800w, or potentially at best 44 amps, 4 amps above my MPPT's rating...if everything aligned...but that is very unlikely anyhow.

 

[Drover]

I have tossed around the series/parrallel idea but what clinched me to stay with parrallel was a shadow cast from a light pole, the free camp at Wondai has some light poles along the street, while the shadow cast cut my set ups power down , my neighbours series set up really dropped off the map, the shadow was wide and slowly crept across the panels as the sun moved, a cluey fella he just shut it down and plugged in his portable he said its been giving him the *it's for awhile and was seriously thinking of going parrallel as he liked the idea that I just pulled out the portable and plugged it in and more than covered the shadow loss .... I am thinking of moving some of my roof tops so AC doesn't shadow them too much, one day, in the fullness of time, maybe ...

Back on topic................................. The piggy back Anderson I fitted is just one with the 6B&S sockets, thats so the cable from the roof top which is cut and both ends, can be soldered into the socket the tail going to the controller, between the anderson and the roof panels I have a circuit breaker fitted so I can isolate the roof tops easily if needed.....

 

[Just the two of us]

WOW. Thanks guys. This is valuable info for the masses, not just me.

 

[jazzeddie1234]

I better chip in with an over engineered solution...

I have 2 roof panels connected to 2 mppt controllers - mostly because they are very different panels - but I do like seeing what the roof panels are doing.

Then I have a third, basic, pwm controller that connect to andersons on both undersides of the cv for my portable 140w panel. The panel also has andersons on it and I have a couple of short and long anderson extension cables that can be used

I hardly use the portable because the ute also has a solar panel, controller and battery. I use the anderson extension to parallel up the CV and ute second batteries and park the ute in the sun. Most times this is more than adequate to charge everything up.

 

[Boots in Action]

WOW. Thanks guys. This is valuable info for the masses, not just me.

It is always better if all the panels are connected the same method ie in parallel or in series.
If all connected in parallel, voltage at the MPPT controller is the average of all the panels (not the lowest or the highest panel) so the MPPT controller will see somewhere between 16 to 18 volts which limits how much the MPPT controller can convert to extra AMPS. However, you do get the combined total output (amps) of all working panels regardless of some possible shading on some panels, providing BLOCKING diodes prevent power from operating panels to allow current to bleed back into the shaded panels (a resistance) and so reduce total system output. Remember that every silicon diode in the panels in line in panels reduces voltage by up to 0.8 volts. Schottky diodes only have a voltage loss of 0.2 volts but these are not standard!!

If all panels are connected in series, voltage is the total of all the panels, but amperage is limited to the output of the weakest or smallest panel. The MPPT controller therefore has the maximum voltage to convert to extra amps and this is especially beneficial in low light or cloudy changing conditions. All panels require BYPASS diodes which allows current from working panels to bypass or go around the shaded panel and so while overall current is reduced by the loss of output of the shaded panel, the voltage remains high. Even in low light, voltage is still there, just not current output! Once again, the bypass diodes fitted to panels (fixed and portable) are usually the cheaper silicon type and so if you have 3 panels in series you are looking at a voltage loss of approx 2.4 volts by the time the MPPT controller is reached. With Schottky diodes the total voltage loss would only be 0.6 volts approx. Which is what I have on my setup - up to 58.0 volts from 3 X 200w panels at MPPT controller instead of only approx 48 to 54.0 volts or less. So more current (amps) produced by MPPT controller to charge battery/ies.

If you connect up some panels in parallel (say 17 volts each) to the MPPT controller AND also connect up a couple of panels in series (say 35.0 volts total) to the same inputs at the MPPT controller, the controller (always endeavoring to get the the max wattage out of volts in and amps in) will average out the voltage to provide the best amperage at approx 26.0 volts. This is always a compromise between both types. So all depends on siting and conditions!!!

 

[Hitting the road]

Top stuff Boots..very informative post. The old series vs parallel chestnut is a fairly hot topic anywhere. As drover noted when a panel is shaded it will affect output, but really that applies to both series and parallel setups.

I have followed the theory of pushing maximum voltage in to the MPPT to deal with, rather than max amperage with lower voltage.
Correct me if I am wrong...Being an MPPT controller deals well with volts conversion to amps, the more volts going in the better the amps coming out. Plus in low light conditions, any MPPT controller will still need at least 14 volts to keep charge going in to the battery. As most panels are around 18v, if there is less sunlight available the panels are not going to produce max volts, and could fall easily fall to less than 14v therefore not really enough to keep charge flowing to the battery. In series however, even if the two panels are producing only 12 volts each, the input to the controller will still be 24v allowing enough voltage to see conversion to amps so the batteries will still be seeing charge.

In my case in series I can still add additional panels to the array if desired. The other plus from where I sit using external panels in series, is as I often use up to 12 metres of (8awg) cabling to the panels depending where I am parked, there is not too much voltage drop. Where as if I was trying to push amps over the same longer distance I would lose a fair bit being amps just don't travel as well.

I would much prefer to stay with series connections once I add the additional panel to the roof of my van, but, it does becomes complex when adding additional panels via external cabling. It could be done for sure, but, that said I haven't fully explored that option as yet.
Plugging additional panels in in parallel doesn't require as much grey matter activity eitther, as providing they are all similar outputs the benefits will be reaped...

 

[Drover]

Yeah top info Booties ..................................................... Been contemplating, if you have roof top panels in series and want to have a portable so instead of going and throwing mucho $$$ on another MPPT controller wouldn't fitting an MC4 plug in the feed from panel to reg using either POS or NEG line so the portable fitted with MC4 plugs would just plug inline and that would be a much cheaper and easier solution ??????
Of course thats assuming the set up isn't buried in a small cupboard or in the wall ...

On a normal day though if your batteries aren't charged up by 0800 something is wrong really, the rest of the day the panels run the van with the battery just sitting by doing nothing .... same as household solar the panel should run the house during the day and battery/grid during the night.... well thats how I look at it all.

 

[Boots in Action]

Top stuff Boots..very informative post. The old series vs parallel chestnut is a fairly hot topic anywhere. As drover noted when a panel is shaded it will affect output, but really that applies to both series and parallel setups.

I have followed the theory of pushing maximum voltage in to the MPPT to deal with, rather than max amperage with lower voltage.
Correct me if I am wrong...Being an MPPT controller deals well with volts conversion to amps, the more volts going in the better the amps coming out. Plus in low light conditions, any MPPT controller will still need at least 14 volts to keep charge going in to the battery. As most panels are around 18v, if there is less sunlight available the panels are not going to produce max volts, and could fall easily fall to less than 14v therefore not really enough to keep charge flowing to the battery. In series however, even if the two panels are producing only 12 volts each, the input to the controller will still be 24v allowing enough voltage to see conversion to amps so the batteries will still be seeing charge.

In my case in series I can still add additional panels to the array if desired. The other plus from where I sit using external panels in series, is as I often use up to 12 metres of (8awg) cabling to the panels depending where I am parked, there is not too much voltage drop. Where as if I was trying to push amps over the same longer distance I would lose a fair bit being amps just don't travel as well.

I would much prefer to stay with series connections once I add the additional panel to the roof of my van, but, it does becomes complex when adding additional panels via external cabling. It could be done for sure, but, that said I haven't fully explored that option as yet.
Plugging additional panels in in parallel doesn't require as much grey matter activity eitther, as providing they are all similar outputs the benefits will be reaped...

You seem to be all over it @Hitting the road. Just confirming the benefits of a MPPT controller over the PWM type. The former can utilize the extra input voltage and convert that to extra amps, something the PWM type cannot do. A PWM type controller pulls down the input voltage from panel/s to just above the current battery voltage, any excess voltage is just wasted. Another advantage of series connection is that the current generated by the solar panels is transferred to the MPPT controller at a higher voltage. This means that there are less losses in wiring. It also means that you can use thinner cable between panel/s and controller without the losses associated with longer runs at lower voltages. Grid power lines are able to transfer AC current very long distances with minimum losses at very high voltages - 200,000 volts or similar - without resorting to extremely heavy wiring, something that would be prohibitively expensive and very heavy on the towers. But as @Drover said, shade on panels is a problem whether connected in Series or Parallel and there are only limited ways of reducing this problem. And, yes, connecting extra panels in parallel is easier than joining up several panels in a string for a series connection, especially if you have only limited electrical knowhow.

 

[Boots in Action]

Yeah top info Booties ..................................................... Been contemplating, if you have roof top panels in series and want to have a portable so instead of going and throwing mucho $$$ on another MPPT controller wouldn't fitting an MC4 plug in the feed from panel to reg using either POS or NEG line so the portable fitted with MC4 plugs would just plug inline and that would be a much cheaper and easier solution ??????
Of course thats assuming the set up isn't buried in a small cupboard or in the wall ...

On a normal day though if your batteries aren't charged up by 0800 something is wrong really, the rest of the day the panels run the van with the battery just sitting by doing nothing .... same as household solar the panel should run the house during the day and battery/grid during the night.... well thats how I look at it all.

Correct stuff Ian @Drover. If you had fixed panels on roof connected in SERIES with MC4 plugs, then connecting another panel in series would be an easy matter. Disconnect string somewhere between roof panels and controller and connect in extra panel/s with MC4 plugs. This will certainly increase the voltage in the string, but may not increase current significantly. Remember, series output (current AMPS) is limited to the output of smallest/weakest panel. But if the extra panel is placed in good sun, it could be replacing the weakest panel which may be in shade.

 

[Drover]

. And, yes, connecting extra panels in parallel is easier than joining up several panels in a string for a series connection, especially if you have only limited electrical knowhow.

I don't know just so long as you plug the right ends together in both cases not that hard though if adding a portable, well at least using MC4 plugs it either fits or it doesn't................. but your right I have seen some horrible set ups .......... Also been noting temps the last week or so, interestingly these summer temps are showing that lithium technically isn't much chop for around here if charging temp is supposed to be below 30c, my battery has been showing 30c plus for much of the time and inside cupboards in van the same so I wonder how sensitive these things are in the real world ????? My rudimentary tests show that not much temp variation if its fitted outside, in its own compartment or under the bed hate to think what it would get to if a cover over rig ............. mine is in sleep mode with solar shut down so no charging taking place, seems to sit happily at 75% for ages....