Solar panel question

[Elkman]

It is common to have to add a short section of jumper wire to have something that will fit into a connection on a controller. These are not made for an RV with a few panels but for large installations with multiple panels in series that provide higher voltage and so a smaller gauge wire can be used.

The RV solar market is miniscule and so the installers are using bits and bobs designed for other uses. Even with my house the best panels were designated for installers doing large commercial installation and so I found a contractor that did both commercial and residential installations and so could buy the better panels and install them on my house. This was the largest solar installer in the area but even his electrician did not know about dual string inverters and he so wanted to have my two sets of panels providing exactly the same output voltage.

Monocrystalline panels are more efficient at any given size but even these can differ in how they are engineered to deal with shading, which is more of an issue with a RV installation. The solar panel output also can decrease with high temperatures which is one reason to have them mounted with an air gap below them.

An MPPT controller can be 25% more effective than the cheap PWM type and so is equally if not more important than the type of panel that is used.

[AJMike]

Originally Posted by Elkman

An MPPT controller can be 25% more effective than the cheap PWM type and so is equally if not more important than the type of panel that is used.

I have seen that figure in a fair number of posts so I assume it to be correct, but it leaves me asking some questions.

1) How efficient is a PWM solar controller?

2) Is there a difference between the efficiency of cheap and good PWM controllers? If so, how much?

3) Why is it that when I see 15 amps coming in from solar on my Zamp controller I also see 15 amps going to my batteries on my Victron BM if the PWM is so inefficient?

4) How much extra power would a MPPT provide if I see no real difference between the input on the solar controller and the output to the Lithium batteries in my coach?

I really don't understand, and I would like to if it means that my rig could be significantly more efficient, but I would not want to spend the money if it made no real difference. I am trying to understand, not cause an argument.

[creativepart]

Mike, it was explained to me that the PWM controller can only handle 12.X volts from your solar panels and is unable to utilize any voltage above battery voltage. But a MPPT control can take all 20+v from your panels and use all of it to increase charge to your batteries.

That doesn't sound super clear to me. But I do know when I changed from my PWM controller to the MPPT controller it has "seemed" to do a better job recharging the batteries quicker. I quoted seemed because I have no objective proof of this.

I changed my controller out mostly to get the Bluetooth monitoring. Unlike your RV, mine had the Zamp controller buried in a basement compartment where it could not be seen without opening the door, getting down on the ground and looking into the compartment.

I also, hoped that it would improve charging almost as much as adding another 100w panel. I doubt it's done that, but it is either doing a better job, or I think it's doing a better job.

In your Fuse RV, the controller is mounted on the wall in your living area and it would be tough to find a replacement that fit the space and looked good. The Victron is a little larger than the Zamp, it has no display at all, and the wiring is on the bottom not on the back like it is on the Zamp. So, you'd need to take all of this into consideration.

[creativepart]

Try this:

https://www.youtube.com/watch?v=PB6zojol9o0

[DavidM]

Will offered a bunch of opinions in his video, almost all of which I agreed with, but did not offer any theory or test data to back up his assertion that MPPT controllers produce more power than PWM controllers with the same solar panel input.

Creativepart's explanation in his first paragraph above is correct as far as it goes. Bear with me and I will elaborate:

PWM controllers take an input voltage from the solar panels and pulse it for delivery to the batteries. Batteries typically require 13-14 volts while charging and solar panels put out their maximum power at about 17 volts. The PWM's pulsing takes that 17 volts and turns it into 13-14 volts thereby wasting the difference. Well not exactly but close enough.

The MPPT controller has circuitry analogous to an inverter/tranformer/rectifier combination that uses the full 17 volts and converts it to 13-14 volts with little conversion loss, usually a few percent.

So at worst case (for the PWM controller) it takes 17 volts and produces 13 thereby losing 4 or 4/17= 24% whereas the MPPT controller loses less than 5% in its conversion.

He also notes another important fact: PWM controllers generally can only work with 12V nominal panels wired in parallel. If you wire two in series then you waste 34-13= 21 volts or 21/34= 62%. MPPT controllers can either use 24V nominal panels directly or two 12V nominal panels wired in series. Series wiring lets you use smaller gauge wire or with the same wire size as a PWM controller requires, loses less voltage in drop through the wire.

Finally as he notes, RVs usually have limited roof area and you try to get the most out of the available real estate. Besides using more efficient panels, using a MPPT controller will help with total output.

But if I just wanted a small panel to keep my batteries charged up, a PWM will work fine and save you a few bucks.

David

[Old Navy]

Originally Posted by AJMike

3) Why is it that when I see 15 amps coming in from solar on my Zamp controller I also see 15 amps going to my batteries on my Victron BM if the PWM is so inefficient?

PWM charge controllers decrease the voltage but do not increase the current. MPPT charge controllers decrease the voltage, but increase the current. V*I=P, so the MPPT typically outputs more power (watts) than the PWM.

Say your panels are operating at 18V and producing 15 Amps. That's 270 watts in to your solar charge controller. Assuming your PWM controller is in bulk charge mode, and putting out 14V at 15A to your battery, thats 210 watts of power out. About 78% efficiency. An MPPT controller can take that same 18V at 15A input and produce 14V at 18A, or 250 watts at it's output. That's 93% efficient. These are not real world numbers, just an example. Actual performance of charge controllers may vary.

In the RV world, this efficiency matters only when the batteries/load can absorb the full output of our charge controller. So, depending on how well matched your solar system and batteries are matched to your load, this efficiency could be meaningless, or critical, and can vary day to day.

[Greg Morrow]

when I realized I would camping more without shore power I wanted a cheap simple way to keep my battery up. I bought a Coleman 100w solar panel/w controller from Costco for $89. I bought 30' of the heavyest 2 pole wire I could find, wired from the panel to battery where I put the controller. I soldered big battery clamps on the controller leads and put pigtails sticking out from the battery box. I connect directly the battery and can move the panel 360 around the trailer. Mixed results at home. Complete failure in Shenandoah NP. However at Assateague Md under bright skies My battery went from 10.5v to 13.5v in about 4 hours. Recovery from lights and water pump were pretty quick, and it more than made up for whatever the fridge uses on gas. It kept me going for 4 days. Too bad ssunshine is not guarandteed. Still need to get a generator.

[creativepart]

Originally Posted by Greg Morrow

My battery went from 10.5v to 13.5v in about 4 hours.

Greg, just a note - when your battery was at 10.5v it was completely dead and doing permanent damage to the battery. You were adding sulfate to the plates and over time this reduces battery effectiveness so much as to shorten its practical life.

And, second, a fully charged battery is 12.7 to 12.8 volts. If you see a reading over that you are not seeing battery voltage but you are seeing the charging voltage.

So, when you saw 13.5v you were not even seeing your battery's voltage - so you really can't be sure it's "fully charged." All you know is the solar charge controller was charging successfully. Because that's all you were seeing.

If you disconnect the solar charge controller, wait an hour or more and then take a voltage reading then you will actually see the state of charge on your battery.

Battery voltage is a difficult thing to measure because to accurately read it the battery must not be charging nor being drawn from for a lengthy period of time. In other words completely at rest. And, normally we are charging or using our batteries.

Whenever I see people posting that their battery is at 13.X volts so it's fully charged I try to remind them that they are not really seeing battery state of charge.

It's also possible that the battery was not really down to 10.5v (hopefully) but that it had a load on it that was depressing the reading you were getting.

Be aware that fully charged is 12.7v and fully discharged is 10.5v:

[Elkman]

With the Victron MPPT charge controller providing Bluetooth connectivity to a smartphone the external display is not needed. 99% of the time my checking the controller is not important.



There is also the simple fact that after the batteries have been charged as much as possible any additional output from the solar panels is of no use. My house system feeds the grid so whatever the panels produce during the day is used somewhere by someone. With the RV it is a matter of whether after a night's drain on the batteries how much time is needed to bring them back to 100% for the next night.



If my panels with the cheap Zamp controller are able to get the house batteries to 100% by the end of the day then any gain from having a MPPT controller is not going to be useful. On the other hand if I have maxed out the real estate on the roof of the RV with solar panels and still have a shortfall then a MPPT controller would be worth considering. Considering that a Victron charge controller would have cost Winnebago only $100 more than the cheap Zamp one they choose to install it is most unfortunate that they made this choice.



In 2015 I added a solar setup to my RV with Blue Sky components for the charge control along with a couple of 100W panels. It took weeks to do it all what with the TPO roof and fabricating a support frame for the panels and having to snake large gauge cable through the cabinets and building a cage for a second AGM battery under the basement. But at least I did not cut corners with the installation as has clearly been done with the Zamp kit installed by Winnebago.



I hoped with the purchase of a new 2021 Navion that I would avoid having to do this again but I am finding that Winnebago haphazardly installed one of the two 100W panels and so I will be having to move it and to replace the much too long feed cables to the roof port and to make a sealed compartment for the lithium phostate batteries.

[creativepart]

Originally Posted by Elkman

With the Victron MPPT charge controller providing Bluetooth connectivity to a smartphone the external display is not needed.

While this is certainly true, in a Class B or Class C with the Zamp 30-amp controller mounted in a conspicuous location on a main wall inside the living area it's somewhat unsightly to replace it with a big blue box with no display.

Also, all the wiring to the Zamp controller is behind the monitor. So, inside the RV all you see is the face of the controller and the digital display - no wires. Certainly with the Victron Smart Solar and many other solar controllers the wiring is all below the controller where it would all be visible if mounted flush on an interior wall. Again, an unsightly situation.

I mention these things only to give folks considering such a change the full understanding of what they are likely to encounter before they get too far into the change out.

[AJMike]

Originally Posted by creativepart

While this is certainly true, in a Class B or Class C with the Zamp 30-amp controller mounted in a conspicuous location on a main wall inside the living area it's somewhat unsightly to replace it with a big blue box with no display.

Also, all the wiring to the Zamp controller is behind the monitor. So, inside the RV all you see is the face of the controller and the digital display - no wires. Certainly with the Victron Smart Solar and many other solar controllers the wiring is all below the controller where it would all be visible if mounted flush on an interior wall. Again, an unsightly situation.

A couple of comments.

1) I called Zamp today to ask about the PWM and MPPT controllers and the tech pretty much verified what has been written about the PWM controller. He said that it takes only what is needed from the solar panel voltage output, depending upon the charge state of the batteries, and does not use a transformer to step down the voltage (and step up the current). He also said that the actual real world difference between the output of a PWM and an MPPT controller with the amount of solar typically on the roof of an RV is insignificant. I suppose that last statement is in the eye of the beholder.

2) I am not sure that the Zamp controller qualifies as being a "cheap" controller, and I do appreciate the fact that it is made in the US and not in China. Just like the BB batteries, I have some satisfaction in knowing that I am helping employ someone here in the US. On the other hand my Victron Battery Monitor is probably made in the Netherlands, so I need to keep that in mind as well.

3) If I wanted to exceed 500 watts of input solar then I would have to upgrade the controller, but since there is little free space on the roof of the RV that does not seem likely and I am probably safely within limits with the Zamp equipment. I have thought about adding a third Lithium battery but then I probably would not have enough solar to charge all 300 AH with only 400 watts of solar.

4) @creativepart is absolutely correct in saying that trying to mount an MPPT controller on the wall of our Fuse would not be a good solution. It would indeed be ugly with wires sticking out, and since the corridor space in the Fuse is limited it would make walking back and forth more difficult. In addition during the night it might actually be a hazard considering how far out from the wall it would stick.

Putting it under the refrigerator where the other inverter/charger is would work but that is already a rats nest of wires and would make getting to it incredibly difficult.

[Elkman]

It should be understood that the 12 volt solar panels are actually producing over 20 volts output and the charge controller is stepping this down to charge the batteries. With the PWM controller the voltage is clipped and with the MPPT it is down regulated and so less is lost in the feed to the batteries.

When I add a Victron MPPT controller I will manage it from my smartphone and I can leave the Zamp charge controller where it is and ignore it. Not a big deal to me. I do find it odd that Zamp uses such a very large display unit which is not at all necessary. Look at the small displays used by Victron and Blue Sky and others for their MPPT charge controllers.

I did the solar installation on my previous RV and so it is quite apparent the shortcuts taken by Zamp with their 200 Watt kit that is being used by Winnebago. All I gained with the Winnebago factory installation was having the wiring in place from the roof to the controller and from the controller to the batteries.

[AJMike]

Originally Posted by creativepart

Try this:

Very interesting. Thank you for posting the link.

[Old Navy]

Here's a video he did side by side measurements, where the cheap PWM controllers were performing similar to expensive MPTT controllers. There are more factors than just "MPTT outperforms PWM by XX%". I think this is the video he was saying might have mislead people.

https://www.youtube.com/watch?v=kF_cVEYxj3E

Anyway, if you are looking at anything Victron, Inverters R Us has a 15% off coupon code from black friday that still works: RENOVICTRON I just grabbed a SmartSolar 100/30. They also throw in a generic "kill-a-watt" type energy meter if you follow the instructions.

[backtrack15]

Any concerns mounting either a PWM or MPTT controller in the Micro Minnie front storage bay? That is where Winnebago expects it to be mounted (10 AWG wires from roof already there and labeled, as well as wires to battery). I’m thinking 100W or maybe 200W max. I’m just not sure how much heat these controllers generate. That storage area is spacious but not ventilated. I can see it getting pretty hot sitting at the storage unit in full sun on 107F days.

[Elkman]

The heat from the charge controller is negligible and tiny compared to what an inverter produces. If the heat was great there would be very large heat sinks to dissipate the heat and protect the electronics inside.

Test indoors are not relevant when comparing a MPPT versus a PWM controller. What needs to be measured is the total output for a full day of solar collection outdoors which is where these devices are actually used. I would not expect a candid response from someone whose company only sells PWM charge controllers.

There is a reason why installers recommend and people pay the extra dollars for a MPPT charge controller.Adding $200 to the cost of an installation with a MPPT controller is trivial. The installation labor is 75% of the cost if one is paying for a system to be configured and installed. Paying $130 for a Zamp ZS-30Aversus $300 for a Victron 100/50 should not even be up for discussion.

It is like the panel tilt discussions that make a lot of assumptions and then provide calculated results that have litte semblance to real world solar installations and their performance.

[AJMike]

Originally Posted by Elkman

Paying $130 for a Zamp ZS-30Aversus $300 for a Victron 100/50 should not even be up for discussion.

Why not?

It may not be important to you, or to a group of users with specific needs, but it surely is important to some other group of users with different needs. If a Zamp PWM solar controller is enough to take care of some user's needs why in the world should the cost difference between the PWM and the MPPT not be up for discussion for them?

[Elkman]

The limitation on motorhomes and most travel trailers is the amount of space available for installing solar panels and in particular higher output panels. If it takes 4 panels with a PWM controller to provide the charging output of 3 panels with a MPPT controller, most people would choose to purchase the MPPT controller.

I installed two 100W solar panels and a MPPT controller and battery temp monitor and remote display and control unit on my last RV in 2015. It was obvious even then that the MPPT would provide maximum output to charge my two house batteries. With my current Navion there is barely room for 4 panels and so I want to have as much output to charge my two house batteries as well.

There is usually a choke point in any system and with solar it is the wiring gauge and the MPPT controller that determine how much of the available current from the solar panels makes its way to charge the batteries. And it can make a big difference in how much one needs to run a generator to charge the batteries fully. With my previous RV the solar was so effective that I did away with the generator and this provided more space and more load capacity for our other gear.

[Old Navy]

Originally Posted by AJMike

If a Zamp PWM solar controller is enough to take care of some user's needs why in the world should the cost difference between the PWM and the MPPT not be up for discussion for them?

Like you said, if the PWM system meets your solar production requirements, there is little point in spending more money to increase efficiency or production.

If you are designing a NEW solar system and want maximum efficiency, or you want some of the extra features or integration some MPPT controllers offer, then MPPT would seem like an easy decision. But for many RV owners, the PWM controller is already there and panels are wired for a 12V system. If these folks have a 200W system, they can spend a couple hundred dollars to install an MPPT controller and increase production by 10%-15%, or they can add one or two panels and increase production by 50%-100%. It's definitely "up for discussion". In fact, adding panels rather than upgrading to MPPT has been common practice for quite a while.

From another angle, it my 200W array is producing 1000 Wh a day, and I need 1500 Wh, a new charge controller isn't going to get me there. Another panel will.

[AJMike]

Originally Posted by Elkman

There is usually a choke point in any system and with solar it is the wiring gauge and the MPPT controller that determine how much of the available current from the solar panels makes its way to charge the batteries. And it can make a big difference in how much one needs to run a generator to charge the batteries fully. With my previous RV the solar was so effective that I did away with the generator and this provided more space and more load capacity for our other gear.

I am not questioning that a PWM controller is not up for discussion for you. I am only saying that for some people there is no reason for the price difference not to be up for discussion.

If the extra 15-20% or so of power is not needed for some people, then there is no reason for them to spend the extra money.

If the extra 15-20% or so of power is not enough to make up the difference for them, then they can put the money toward another solar panel that might make the difference.

People's needs are different and it seems to me that when trying to solve a problem pretty much all options should be up for discussion, including PWM or MPPT.