PWM or MPPT controller?

aussie_paul · Guru

PWM or MPPT controller?

meetoo · Guru

Hmmm, Holden or Ford ? What I can tell you Paul is that I have a 30 amp PWM and it works and does it's job well. It didn't cost a lot $79.00 (not why I bought it) It doesn't show all the displays so I don't have to stand there looking at it all the time either. Lol I have a battery monitor for that. But the PWM does show amps in and voltage, and load if you want wire a load through it. Either type will do the job. How big is the pocket?

Cheers, John.

aussie_paul · Guru

meetoo wrote:
Hmmm, Holden or Ford ? What I can tell you Paul is that I have a 30 amp PWM and it works and does it's job well. It didn't cost a lot $79.00 (not why I bought it) It doesn't show all the displays so I don't have to stand there looking at it all the time either. Lol I have a battery monitor for that. But the PWM does show amps in and voltage, and load if you want wire a load through it. Either type will do the job. How big is the pocket?
Cheers, John.

Tightwad John. biggrin Something like this I wonder.

https://www.ebay.com.au/itm/Solar-Panel-Regulator-LCD-10-20-30-40A-12V-24V-MPPT-Charge-Controller-3-Timer-ER/162576900606?ssPageName=STRK%3AMEBIDX%3AIT&var=461581453898&_trksid=p2055119.m1438.l2649

Aussie Paul. smile

Tony Bev · Guru

First solar panel I used was borrowed off the grandson
It was a 180 watt portable fold up with PWM controller, it seemed to work OK

Present solar is a roof top 300 watt, going through a MTTP controller, which seems to work OK

My research told me that MTTP is superior, as it changes any excess voltage to amps
I have proved this to be correct, by placing a clamp amp meter, before and then, after the MTTP controller
I can see the increase in amps, as well as the decrease in volts, when the sun is low in the sky in the morning, which is usually the time the battery is wanting all the amps

But if the battery/s capacity is always more than you use, then if the battery/s do not require full amps
the amount of amps required is usually less than what the controller can produce, if required

Hope that makes sense as English was always my worst subject

Jaahn · Guru

aussie_paul wrote:
Tightwad John. Something like this I wonder.
https://www.ebay.com.au/itm/Solar-Panel-Regulator-LCD-10-20-30-40A-12V-24V-MPPT-Charge-Controller-3-Timer-ER/162576900606?ssPageName=STRK%3AMEBIDX%3AIT&var=461581453898&_trksid=p2055119.m1438.l2649
Aussie Paul.

Hi Paul smile

It has been shown, often, that the cheap MPPT regs like the one above are FAKES ! They may work OK as PWM regs but have no internals to boost the output current. furious There are lots of FAKES on ebay.

When I did my research the Tracer brand, available from a lot of suppliers on ebay and locally were the cheapest ones which actually work. I found mine worked well. They have a front meter to display some details and also have a remote meter available to monitor the functions, for a reasonable price.

Note that poor sized wiring will dissipate the extra power that they can make, in wiring losses. disbelief So if the wiring from the panels is minimal then just use a PWM reg and save the money.

Also note the MPPT reg current rating is based on the full solar power rating not just the panel current rating as the output current will be higher at some times.

Jaahn

PS I bought a cheap PWM reg recently for a simple job. It was advertised as a two stage reg but actually it was just a simple one setting reg with no float. They refunded a small amount to get it "fixed" when I complained. disbelief Plenty of fakes in the cheap end of the market !! I would not trust my expensive batteries to a cheapie.

-- Edited by Jaahn on Monday 20th of November 2017 08:28:56 AM

meetoo · Guru

https://camec.com/solar-charge-regulator-30-amp-12-volt-camec-400-watt-panel-power-max.html

This is branded different but looks the same as I have. The link you supplied Paul is I think you will find is a PWM not a MPPT as it says.

Cheers, John.

-- Edited by meetoo on Monday 20th of November 2017 01:51:17 PM

-- Edited by meetoo on Monday 20th of November 2017 01:53:22 PM

Tony Bev · Guru

Jaahn wrote:
aussie_paul wrote:
Tightwad John. Something like this I wonder.
https://www.ebay.com.au/itm/Solar-Panel-Regulator-LCD-10-20-30-40A-12V-24V-MPPT-Charge-Controller-3-Timer-ER/162576900606?ssPageName=STRK%3AMEBIDX%3AIT&var=461581453898&_trksid=p2055119.m1438.l2649
Aussie Paul.
Hi Paul
It has been shown, often, that the cheap MPPT regs like the one above are FAKES ! They may work OK as PWM regs but have no internals to boost the output current. There are lots of FAKES on ebay.
When I did my research the Tracer brand, available from a lot of suppliers on ebay and locally were the cheapest ones which actually work. I found mine worked well. They have a front meter to display some details and also have a remote meter available to monitor the functions, for a reasonable price.
Note that poor sized wiring will dissipate the extra power that they can make, in wiring losses. So if the wiring from the panels is minimal then just use a PWM reg and save the money.
Also note the MPPT reg current rating is based on the full solar power rating not just the panel current rating as the output current will be higher at some times.
Jaahn
PS I bought a cheap PWM reg recently for a simple job. It was advertised as a two stage reg but actually it was just a simple one setting reg with no float. They refunded a small amount to get it "fixed" when I complained. Plenty of fakes in the cheap end of the market !! I would not trust my expensive batteries to a cheapie.

-- Edited by Jaahn on Monday 20th of November 2017 08:28:56 AM

Jaahn has given some good advice here

The picture below is the profile of the eBay seller above
Note the very last line, where someone had brought the MPPT solar controller, and said that it was not a real MPPT one

MTTP Controller.png

aussie_paul · Guru

Jaahn wrote:
Hi Paul
It has been shown, often, that the cheap MPPT regs like the one above are FAKES ! They may work OK as PWM regs but have no internals to boost the output current. There are lots of FAKES on ebay.
When I did my research the Tracer brand, available from a lot of suppliers on ebay and locally were the cheapest ones which actually work. I found mine worked well. They have a front meter to display some details and also have a remote meter available to monitor the functions, for a reasonable price.
Note that poor sized wiring will dissipate the extra power that they can make, in wiring losses. So if the wiring from the panels is minimal then just use a PWM reg and save the money.
Also note the MPPT reg current rating is based on the full solar power rating not just the panel current rating as the output current will be higher at some times.
Jaahn
PS I bought a cheap PWM reg recently for a simple job. It was advertised as a two stage reg but actually it was just a simple one setting reg with no float. They refunded a small amount to get it "fixed" when I complained. Plenty of fakes in the cheap end of the market !! I would not trust my expensive batteries to a cheapie.

-- Edited by Jaahn on Monday 20th of November 2017 08:28:56 AM

Are there many worthwhile positives to MPPT over PWM?

Aussie Paul. smile

Ron-D · Guru

John is dead right with this panel of mine it came with a cheap PWM it did not work from day one ,the manufacturers sent an updated reg am mppt ,but after reading tons of reviews and doing a lot of research I decided to go with a good brand from Victron, putting them side by side the el cheapo weighs nothing ,the Victron is a lot heavier in weight it has a 20amp fuse on the outside of the unit for easy replacement if needed,the elcheapo states if you misconect it you will ruin the reg, if you miss connect the Victron you will need a 20 amp fuse,honestly seeing them side by side ones definitely garbage in my opinion so be carefull...

rockylizard · Guru

aussie_paul wrote:
Are there many worthwhile positives to MPPT over PWM?
Aussie Paul.

Gday...

Probably, like you Paul, I have gained most (all?) of my knowledge of solar systems, controllers, batteries etc etc from the good folk on this and other forums. The advice, most of the time has been helpful.

Your question is one I have asked and have had some good answers. However, I think this site has a good description of the difference and pro's and con's of both.

http://www.enerdrive.com.au/mppt-vs-pwm-solar-controllers/

If any of the experts on here can find or provide a better source, please straighten me out.

My system uses a PWM controller because when I bought my system, I think (not sure, but think) MPPT were not on the market - or very new on the market. I have never bothered to change/update because my PWM and the whole solar system works very well for me for the past six years and I cannot see an advantage to spend the additional moola.

Cheers - John

aussie_paul · Guru

rockylizard wrote:

Your question is one I have asked and have had some good answers. However, I think this site has a good description of the difference and pro's and con's of both.
http://www.enerdrive.com.au/mppt-vs-pwm-solar-controllers/

Thanks John. Better understood now.

Aussie Paul. smile

meetoo · Guru

Like you rockylizard, my 30amp PWM works very well for me (450 watt solar and 2x120 amp batteries)and I see no reason to change it.

Cheers, John.

Jaahn · Guru

Hi Paul smile

That site probably sums it up OK. My experience is the 30% improvement is only likely to be achieved occasionally in certain circumstances, normally perhaps +10- 15%. However with MPPT you do have the option of using house panels which are cheaper or putting some in series, which I do not recommend. With PWM regs you do need 36 cell panels(for 12V) as they have been found to work best for charging LA batteries over the years.

I run a MPPT reg(Victron) and am happy with it and also had one in the last MH(Tracer). If I was setting up a new system on a van I think, if money was tight,(or the owner was !) I might spend the extra money on another 100W panel instead and go for a quality PWM reg. More panels solves most problems. But you do need a quality reg that can be set to correct voltages and has a float setting and can be set and forget in the long run to help the life of the batteries. You might easily find these features in a quality MPPT reg.

Note that I have the old fashioned idea confuse that if I need 20A then I buy a 30A reg. If I need 50V max then I buy 70V. Served me well with electronic gear(and other stuff) over the years.

Jaahn

-- Edited by Jaahn on Wednesday 22nd of November 2017 08:54:09 AM

T1 Terry · Guru

I just finished setting up a 5.6kW off grid battery backed solar set up, 2500w roughly through the quality inbuilt MPPT controller that is part of the 4000w inverter/charger, the rest through solid state relays controlled by a single Plasmatronics Dingo 20/20N.
The MPPT controller takes a while to get going, even though it is being supplied 90v plus from 9 panels in parallel/series configuration the parallel wired PWM controlled panels start producing a lot earlier and continue to supply a lot later. Don't mistake the MPPT controller being actually powered up to mean it is actually producing any charging current, it needs to use some of the solar power internally to make it run, a PWM controller simply passes the solar from input to output until the target voltage is reached. At times the MPPT controller is ahead of the PWM controllers on a work back solar input to output percentage, but these times do not produce enough more charging current to outperform the PWM method over even a 1 hr period so certainly not over a days solar harvest.
The nonsense 70% efficiency limit for a PWM controller is just that, nonsense, battery charge acceptance and cabling has far more effect of charging efficiency and will effect the MPPT controller just as much as the PWM controller, so correct wiring is essential and a far better investment than a rather expensive controller.

Would I use multiple MPPT controller on such a large system in future installs? Only if the owner was happy with the additional costs for linkable MPPT controllers and the extra solar required to equal the output from a well installed PWM system

T1 Terry

meetoo · Guru

T1 Terry wrote:
-snip-
The nonsense 70% efficiency limit for a PWM controller is just that, nonsense, battery charge acceptance and cabling has far more effect of charging efficiency and will effect the MPPT controller just as much as the PWM controller, so correct wiring is essential and a far better investment than a rather expensive controller.

T1 Terry

Terry, if not 70%, what might a more realistic figure be please?

Cheers, John.

aussie_paul · Guru

T1 Terry wrote:

{snip} Would I use multiple MPPT controller on such a large system in future installs? Only if the owner was happy with the additional costs for linkable MPPT controllers and the extra solar required to equal the output from a well installed PWM system

T1 Terry

Thanks Terry.

Aussie Paul. smile

Jaahn · Guru

Hi smile

It is hard to reply to such home grown ideas as Terry puts out to support his methods. I do not intend to write any more on this either.

ALL roof top solar systems that I have seen use MPPT controllers for the solar panels in their grid connect or stand alone systems. Go out and look at the specs of the systems offered. Why Terry is the only person in the world who thinks a PWM system is better and produces more power is a mystery to me. He may be the salvation of the solar world. But obviously there are some who support him. Good luck to them ! confuse

Jaahn

-- Edited by Jaahn on Friday 1st of December 2017 07:36:26 AM

Cupie · Guru

Here are a few references ..

https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/

http://www.enerdrive.com.au/mppt-vs-pwm-solar-controllers/

For those who love Redarc, they seem to talk about MPPT only .. tell you something?

https://www.redarc.com.au/what-is-mppt

If any one wants a spare PWM controller, I have one for free that came with my Panel. I have a MPPT controller built in to my Thunder DC to DC Charger. Just PM me if you want the PWM one.

As for those that are not really MPPT, then that's another argument. More China issues I suspect.

My scant reading lead me to believe that the only way to go was the MPPT solution ... seems like these randomly selected references agree.

T1 Terry · Guru

Jaahn wrote:
Hi
It is hard to reply to such home grown ideas as Terry puts out to support his methods. I do not intend to write any more on this either.
ALL roof top solar systems that I have seen use MPPT controllers for the solar panels in their grid connect or stand alone systems. Go out and look at the specs of the systems offered. Why Terry is the only person in the world who thinks a PWM system is better and produces more power is a mystery to me. He may be the salvation of the solar world. But obviously there are some who support him. Good luck to them !
Jaahn

-- Edited by Jaahn on Friday 1st of December 2017 07:36:26 AM

Ask Plasmatronics why they do not manufacture an MPPT controller? Ask the most recent product maker on the market, ElectroDacus, why he only uses MPPT for his waste solar energy heat storage bank controller and uses PWM for his solar battery controller specifically designed for lithium battery charging, the first in the world.

Most manufacturers will jump on the band wagon and go with the flow, even the engineers at Morningstar confirmed via a world wide live computer presentation that was open to question time that a country with a climate where solar temps (not ambient) will exceed 50*C that a PWM controller will outperform an MPPT controller over the full days harvest.

Comparing back to grid solar to off grid solar, know of any MPPT controllers that handle 360vdc open circuit designed to charge 12v batteries..... There is no comparison between the 2 systems and attempting to use information gathered from grid connect and use it for battery based off grid systems displays a complete lack of knowledge on the subject so the less said there the better......

You actually need to get your hands dirty and do the real testing before you can comment from a genuine knowledge base, simply reading sales brochures on the internet creates the same level of smarts as the has been seen in the lithium house battery debate. You need to understand the subject before you can analyse any data to weed out the non relevant from the nonsense from the useful information. Remember all the keyboard genius who said lithium batteries were not safe or suitable for RV or off grid use...... seems the SA govt didn't get their info from these people and have actually invested in a working grid back up battery that has actually provided peaking power on its first day of official use.

T1 Terry

El Gringo · Senior Member

I have been involved in a discussion on this subject on a Facebook group.
I too have genuinely wondered what is really best for RV systems.
I have seen the claims and all the people that recon your an idiot if you can't understand why their so much better.
but trying to find the side by side test results to prove it seems almost impossible.

(there are some on youtube etc but I have yet to find one applicable to where we live - tropical/temperate zones, not arctic)

Posted screen capture below shows real time testing done in Australia in a side by side environment.
The PWM was more than 20% better than the Tracer MPPT.

This test was done by a guy who recommends MPPT and uses them on rooftop domestic systems 'all the time'
It therefore seems to me the only benefit from a MPPT controller is when you want to run series connect panels and high voltage.
This will save you some money in copper wire, but does it actually work any better, I certainly can't see it saving any money overall.

Thought provoking result???

Cupie · Guru

After a working lifetime in a technical area I found that for me the best approach was to consult a few 'experts' who had provided me with reliable advice in the past and seek their views.

I then select an advice that seems sound to me and suits my situation. And move on (as I am going to do WRT Solar Controllers ... MPP for me) . You lot can please yourself. LOL

Too much to see & do to waste time arguing about such an insignificant thing as this.

If you have a room full of experts you don't get good advice, you just get an argument.

T1 Terry · Guru

Cupie wrote:
After a working lifetime in a technical area I found that for me the best approach was to consult a few 'experts' who had provided me with reliable advice in the past and seek their views.
I then select an advice that seems sound to me and suits my situation. And move on (as I am going to do WRT Solar Controllers ... MPP for me) . You lot can please yourself. LOL
Too much to see & do to waste time arguing about such an insignificant thing as this.
If you have a room full of experts you don't get good advice, you just get an argument.

:lol: Don't go blinding me with facts, can't you see I've already made my mind up and I'm only looking for people to agree with me it was the right decision.

As I said before, if you are happy to pay the extra and gain nothing or very little then you have every right to do so.... but don't expect me to tell you it was a good decision biggrin

T1 Terry

Cupie · Guru

T1 Terry wrote:
Cupie wrote:
After a working lifetime in a technical area I found that for me the best approach was to consult a few 'experts' who had provided me with reliable advice in the past and seek their views.
I then select an advice that seems sound to me and suits my situation. And move on (as I am going to do WRT Solar Controllers ... MPP for me) . You lot can please yourself. LOL
Too much to see & do to waste time arguing about such an insignificant thing as this.
If you have a room full of experts you don't get good advice, you just get an argument.
:lol: Don't go blinding me with facts, can't you see I've already made my mind up and I'm only looking for people to agree with me it was the right decision.
As I said before, if you are happy to pay the extra and gain nothing or very little then you have every right to do so.... but don't expect me to tell you it was a good decision

T1 Terry

Or I could go & dig out yet another 'expert' who disagrees with your view & away we go.

As I said, just listen to the views of previously reliable & trusted sources, choose the view that seems sound & is applicable to the (my) situation ...... and away you go.

I evaluate the 'experts' not the arguments or the so called 'facts'.

I have no interest in others opinion of my decision and in this case the decision was made for me as the DC to DC Charger came with an integral MPPT regulator.

El Gringo · Senior Member

Cupie wrote:

Or I could go & dig out yet another 'expert' who disagrees with your view & away we go.
As I said, just listen to the views of previously reliable & trusted sources, choose the view that seems sound & is applicable to the (my) situation ...... and away you go.
I evaluate the 'experts' not the arguments or the so called 'facts'.
I have no interest in others opinion of my decision and in this case the decision was made for me as the DC to DC Charger came with an integral MPPT regulator.

For me personally, facts are way more important than expert opinions.
As you say, for every expert with one opinion you can dig up 2 others with the exact opposite opinion.
Whereas, facts give a definite answer.

Now I have been ridiculed for not just accepting the science /math of the MPPT brigade, but it seems very suspect that no name brand will give the side by side test results of MPPT vs PWM.
So no, I"m not interested in opinions per say - let the facts speak for themselves.

Has anyone got any test results, or can point me to any? (please not in the arctic circle, I don't plan on taking my bus anywhere near there???)
I attached a test result earlier from a man in the industry that seems to show PWM to be superior in some instances at least.

Would really love to see more proper test results though.

Cheers,

Cupie · Guru

ELGringo ..

I had better make this my last comment on this post before we go down the well known path that lots of stuff on the 'Technical' Forum takes. I wouldn't want to contribute to that as I don't really care if the MPPT is superior or not.

Perhaps I haven't previously explained my position very well. Let me try again.

I believe that tests produce Data that may lead us to the Facts/Conclusions.

That being the case then my view is that one needs a good degree of relevant technical expertise & objectively applied analytical ability to interpret the data to determine the facts and reach a conclusion.

That's what I have always used my selected 'Experts' for.

If in this case they were perhaps not correct, then Ho Hum, there you go.

You all have a good day.

El Gringo · Senior Member

My comments weren't meant as an attack Cupie, just a different point of view.
I understand where you are coming from and respect that.

As was stated earlier it's not a huge deal one way or the other, both systems work.

I only get annoyed when people start to attack me for wanting to see the evidence, I don't believe it's stupid to want to see the facts rather than rely on stated theories.
Lots of theories get disproved as we all know.
And there is no way I'm going to be a lemming, no matter what the subject or idea.

Anyway, until further reliable results come in there is no definable answer at this stage - for me at least.
Though from the 1 reliable test it seems that the way I intended going will work fine.

Cheers,

T1 Terry · Guru

Maybe these people could be considered to have some knowledge and expertise in the field. https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-ssl.com/wp-content/uploads/2014/02/Morningstar-Corporation-Traditional-PWM-vs-TrakStar-MPPT-Whitepaper-March-2015.pdf

read page 8 and then ask yourself are you looking for a controller to suit Aust conditions or US/European conditions.

The important part in making any equipment purchase is determining if that equipment was designed to function as claimed in the conditions you plan to use them. One of the all important bits of information is temp. operating range. This is not ambient temp but the temp the actual piece of equipment will be operating at in the cupboard or under the bed or under the bonnet or front van boot. If normal operating conditions, what is the temp in this area and will a piece of equipment that generates heat increase the temperature? Do you consider the temp inside your RV is the same as the ambient temp the weatherman publishes? Do you consider a solar panel mounted in full sun where you plan to use it will remain at 25*C? If you think it will get hotter than 25*C then you need to look at the panel manufacturers chart to see what the Vmp would be at the real panel temperature rather than the light box flash Vmp @ 25*C published on the back of the panel.

I tried to upload a photo of the relevant charts from Kyocera but the NBN has dropped its bundle yet again and can't seem to handle the task

T1 Terry

oldtrack123 · Guru

Jaahn wrote:
Hi
It is hard to reply to such home grown ideas as Terry puts out to support his methods. I do not intend to write any more on this either.
ALL roof top solar systems that I have seen use MPPT controllers for the solar panels in their grid connect or stand alone systems. Go out and look at the specs of the systems offered. Why Terry is the only person in the world who thinks a PWM system is better and produces more power is a mystery to me. He may be the salvation of the solar world. But obviously there are some who support him. Good luck to them !
Jaahn

-- Edited by Jaahn on Friday 1st of December 2017 07:36:26 AM

A BIG DITTO

All the world is wrong according to T1

The full facts of Terry's set ups is that the panels he generally uses have MPPs that are closely matched to the lithium batteries voltage under all SOCs.

I have tried to point this out to him in the past

After many experiments he has a specifically matched set up that does perform well for JUST THAT ARRANGEMENT

They have no real extra output to convert

One needs a fair bit of ELECTRICAL knowledge & theory to understand why that is so, . but some people simply hate Theory

Standards 36 cell panels with higher MPP used with LA Batteries with a substantial range in voltage over SOCs is a totally different situation biggrin

Particularly when most needed ,when the LAs are in a low SOC!!!

THAT is when the greatest advantage occurs.

The often mentioned conversion losses with MPPT regs, is overexaggerated with high quality MPPS.

The real problem is ensuring that you have a REAL MPPT reg

-- Edited by oldtrack123 on Saturday 2nd of December 2017 05:22:21 PM

Peter_n_Margaret · Guru

In some conditions, there may be little difference between MPPT and PWM, but I suggest that a good quality MPPT will always equal or exceed the performance of a good quality PWM controller.
Also, with a PWM controller, you are constrained to a narrow range of voltage inputs to the controller otherwise there will be losses. These constraints do not apply to MPPT controllers which can accept higher voltage inputs (such as those offered by cheap panels designed for grid connect) without the extra losses.

Cheers,
Peter

T1 Terry · Guru

Peter_n_Margaret wrote:
In some conditions, there may be little difference between MPPT and PWM, but I suggest that a good quality MPPT will always equal or exceed the performance of a good quality PWM controller.
Also, with a PWM controller, you are constrained to a narrow range of voltage inputs to the controller otherwise there will be losses. These constraints do not apply to MPPT controllers which can accept higher voltage inputs (such as those offered by cheap panels designed for grid connect) without the extra losses.

Cheers,
Peter

Agree with the first part, but not all of it Peter. A good quality MPPT controller costs a lot more than a good quality PWM controller and is limited to the capacity of that controller. If you need more capacity you need a second MPPT controller identical to the original and they must be of a type that can be linked in a master/slave operating mode. MPPT controllers with this ability are not cheap, up around the $1,000 mark each so a system expansion requires another $1,000 controller plus the linking kit.

Victron do make MPPT controllers that can be linked together, but they are not the cheaper ones, they are the much more expensive units. Midnite solar make linkable units as well but they are both expensive and huge. MPP solar make an inverter/charger/MPPT controller all in one that can be linked to expand the capacity of the inverter as well as the 2 chargers.... but they only come in 24v and 48v designs, the 12v model can't be linked.

Plasmatronics, a great Aust company that build RV solar controllers for Australian conditions have the ability to be expanded by 100 amps capacity by as many times as you want by using solid state relays. One controller at around $350 plus $50 for a solid state relay and you have a controller that can handle 120 amps, add another $50 and it can now handle 220 amps and so on.... you don't need an economics degree to figure out which is the more cost effective.

As for grid connect panels being cheaper than 12v panels, where did you get that notion from, the going price is $1 per watt no matter the voltage output. They only come down in price when the panel size goes well beyond the area the average RV owner has clear to mount a solar panel. Small output 12v panels like the 60w units are more expensive than the $1 per watt, but the advantage is you can fit so many more panels into the available space because they can fit up the sides and between the vents and roof top rattler, big panels won't fit. You can't mix and match panel sizes with an MPPT controller, you can with a PWM controller, you can simply plug in portable solar into the same control system used for the roof top solar, you can't if the roof top solar is a different voltage or series connected to build a higher voltage, the advantages go on and on ..... it really is a no brainer when you compare the flexibility of a quality PWM controller to an MPPT controller when it comes to an RV set up.