calling solar experts( questions ??)

[NEWYORKHILLBILLY]

I setting up my casita with solar. My plan is to put 100 watt panel on roof and carry a 100 watt suitcase . My concerns are mixing the 2 panels in parallel
siut case is a renory mono 100 watt (2 50w panels) VMP is 17.6

I looking at several roof mounts but the one that would fit the best is
the sun catcher mony 100 watt panel the VMP is 18.54
.94 volts different about 5%

Both will be attached to controller renogy adventurer 30 amp pvw
the roof panel would be direct wired and suitcase have a plug in at camper shell, controller would be mounted close to battery inside

what will happen to the out put of the roof panel when the suitcase is plugged in? (witch would only be if the roof panel is shaded)

The way i understand it is the VMP should be the same. I could us a regory 100 watt poly panel with VMP of 17.8 witch would be closer to the suitcase VMP but for my mounting location on the casita the sun catcher panlel would work better.

I looking for imput still learning about solar

[RV Doctor]

Hi Mike. Good questions.
You are bound to get more opinions on your questions but I think what you are planning is fine.
Solar in a PWM layout such as your plans are cumulative. Having a roof mount panel is good for constant use and supplementing with your ground panel is good.
More important to consider is matching solar output and requirements to your batteries.
Generally having around 150 watts per two six volt batteries charges well. For a single battery install, two panels will charge quite quickly.
I am in the RV Service business and I usually tell my customers to start with one component, such as the roof panel and then, if required, add the ground panel.
One other point. Do your research on proper and safe mounting of your roof panel.

[gordon2]

I remember reading a lot of good information on this question on the net.
This is one of many good articles, except I think they used the work inverter instead of controller. Other than that, it describes the issues with using multiple panels pretty well.

Mixing solar panels – Dos and Don’ts • SOLAR PANEL SECRETS EXPOSED

[Tom 72]

RV Doctor, your posts are useful and you are generous. Thank you.

I am likely the only one who doesn't know what PWM is. Just in case, I believe this is the reference:

Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by switching the solar system controller's power devices. When in PWM regulation, the current from the solar array tapers according to the battery's condition and recharging needs.

[RV Doctor]

Tom. Thank you!
It seems today that MPPT solar regulation is on everyone’s lips. It is fairly new and I have to confess I haven’t read up enough on it.
Basically running an overall higher panel to controller voltage gives higher charge currents in lower sun locations.
I think that before long MPPT will probably be the standard in solar.

[gordon2]

Originally Posted by RV Doctor

Tom. Thank you!
It seems today that MPPT solar regulation is on everyone’s lips. It is fairly new and I have to confess I haven’t read up enough on it.
Basically running an overall higher panel to controller voltage gives higher charge currents in lower sun locations.
I think that before long MPPT will probably be the standard in solar.

MPPT comes into play more when panel voltages are higher, such as you might have in a home or industrial use where there are long lengths of cable. As usual, when the question is which is better (PWM or MPPT solar controller), the answer is "it depends."

My equipment came from BOGART ENGINEERING and I refer you to their FAQ item C.1. which I will quote here:
---------------------------------

C1. The debate rages: which controller is best PWM (Pulse Width Modulation) or MPPT (Maximum Power Point Tracking). Why did you choose PWM technology instead of MPPT for your SC-2030 Solar Charger?

A very good question! They BOTH have good and bad. Plenty of hype has been written already. Here's my (Ralph's) view:

The "good" for PWM: It is simpler and lower cost technology. Under some common circumstances–it can actually deliver more amps to the battery. That could be when:

(1)days are moderate or warm, with few clouds.

(2) batteries are charging at over 13 volts, (in a 12 battery system) which they almost always are when actually CHARGING.

(3) Panel voltage is properly matched to the battery voltage, for example "12V" panels are being used with a 12V system.

PWM is actually more "power efficient" than MPPT–which means less total power loss in the controller itself. So heat sinks in the design can be smaller (and less expensive). Missing in most analysis of MPPT is that there is always a conversion loss with MPPT, which tends to be higher the greater the voltage difference between battery and panels. That's why PWM can actually beat MPPT under circumstances described above.

Some places that analyze MPPT assume that panels with 30V open circuit voltage are being used in a 12V system. Any good MPPT system will easily provide better performance in that case. They also may assume batteries are charging at 12 or even 11 volts, which is unrealistic. Lead acid batteries are typically below 13 volts only when discharging, or perhaps charging with very little charging current–meaning the actual potential gain in amps is not great.

The benefit for MPPT becomes apparent if you use panels not voltage matched for the battery. If they are not, MPPT will utilize more of the potential energy of the panels. For example, if you use 24 volt panels to charge a 12 volt battery system you must use MPPT, otherwise you would be using your panels very inefficiently. If you are trying to use PWM in that case, you are misusing the PWM technology.

Another potential benefit with MPPT is that if distance between panels and batteries is far, smaller wire can be utilized by running panels at higher voltage to the batteries. Running at twice the voltage reduces wire size to 1/4, which for a long run can be a significant saving in copper wire.

If temperatures are low enough, the slightly less power efficiency of MPPT will be compensated by the higher panel voltages, which will result in a little more battery current. But in actual measurements we made using a commonly sold MPPT solar controller, this would occur at temperatures less than 55 F degrees (in full sun, when charging at more than 13 volts), where there is a slight advantage to MPPT in my location (Boulder Creek, near the California coast). As temperature drops below that (in full sun) MPPT will get some advantage, such as could occur at high elevations in Colorado in the winter. Potentially this would be maximum about a 2.5% improvement in amps output for every 10 degrees F lower in temperature (or 4.6% per 10 degrees C colder. I'm using data from Kyocera KD-140 panels.)

There can be theoretically optimal situations (that I don't personally experience where I live) where MPPT could give some advantage: that is when solar current is present, but the batteries are quite low in charge–but because loads are high and even greater than the solar current the batteries are still discharging despite the solar current. Under these conditions the voltage COULD be at 12.5 volts, or even lower. Again, using data from Kyocera panels, ("Normal Operating Conditions") there is a theoretical maximum gain over PWM of 20% current assuming NO MPPT conversion loss and no voltage drop in the wires to the panels, at 20C (68F). With PWM, the voltage drop in the wires in this case would not affect the charging current. Now if in addition you lower the temperature to below freezing at 28 degrees F (while sun is shining) you might actually get up to a THEORETICAL nearly 30% gain while the batteries are discharging.

The only REALLY BAD part of MPPT, is all the hype surrounding it–for example one manufacturer advertises "UP TO 30% OR MORE" power harvested from you panels. If you are using solar panels properly matched to the batteries, 30% ain't gonna happen unless it's EXTREMELY cold. And your batteries have to be abnormally low in charging voltage–which tends not to happen when it's cold (unless you assume the battery is still discharging while solar is happening). Virtually all the analyses I've seen touting MPPT on the Internet ignore the conversion loss, assume really cold temperatures, assume unreasonably low charging voltages, assume no voltage drop in the wires from panels to batteries, use STC conditions for the panels (that the marketing types prefer) rather than more realistic NOCT conditions, and in some cases assume panels not voltage matched to the batteries.

The other thing that is misleading about MPPT, is that some manufacturers make meters that show both the solar current and the battery current. In almost all cases for a well designed MPPT type the battery current will be greater. The engineers making these know better, but it is implied (by marketing types?) that if you were NOT using MPPT you would be charging your batteries with only the SOLAR current that you read on their meters. That's not true, because the PWM BATTERY current should always be higher than the MPPT SOLAR current. It is the nature of the MPPT that maximum power occurs when the current is lower than the maximum, so they must operate there to get the maximum power. So to properly compare the two you need to compare MPPT with an actual PWM controller in the same circumstances.

Finally, the reason we went to PWM is that I was anticipating that panel prices were going to drop (which they certainly have over the last 5-10 years!) and that the small advantage of MPPT (under conditions where the correct panels are used for the batteries) would not justify their additional cost and complexity. So my thinking, for more total benefit per $, put your money in an extra panel rather than a more expensive and complex technology.

Source: Frequently Answered Questions - Bogart Engineering
----------------------

[NEWYORKHILLBILLY]

Originally Posted by RV Doctor

Hi Mike. Good questions.
You are bound to get more opinions on your questions but I think what you are planning is fine.
Solar in a PWM layout such as your plans are cumulative. Having a roof mount panel is good for constant use and supplementing with your ground panel is good.
More important to consider is matching solar output and requirements to your batteries.
Generally having around 150 watts per two six volt batteries charges well. For a single battery install, two panels will charge quite quickly.
I am in the RV Service business and I usually tell my customers to start with one component, such as the roof panel and then, if required, add the ground panel.
One other point. Do your research on proper and safe mounting of your roof panel.

So if i understand this if I chose the roof panel that is vmp of 18.54 or the roof panel that is vmp 17.8 . in my install it will make no difference? I was thinking it pull the 18.54 vmp panel down toe the suitcase voltage of 17.6 even if it does i not sure what that would do. Like i say i can choice a different VMP volt panel but it will not fit as well.

Thanks for any help

[John in Santa Cruz]

MPPT costs have come way down in the past year or so, and the efficiency has gone up. this offsets a lot of those arguments.

[Radar1]

I'm certainly not an expert on solar panels. I do have the experience of having bought a 90 watt portable panel and that confirmed that solar was good! There were times and places that I didn't want to place that solar panel out (example is Gettysburg National Park parking lot where we were traveling a short distance between boondocking campsites and having a solar panel out all day while touring would have been nice). I later purchased another 90 watt panel to place on my Scamp roof. It is now my primary solar source and fills my battery (single 155 amp golf cart battery) by noon on most days. I still use the portable panel for winter use, when the sun is low on the horizon, it goes down too soon, and shadows are longer. I also use it if parked directly under a shady tree in the summer.
In those cases where I need to add the portable panel to the circuit because the rooftop isn't getting good sunlight (via a plug on the tongue going to the controller), the amps going to the battery always increase, so having both in the mix helps.
I think a fixed rooftop panel and a portable panel is the best of both worlds, each being able to offset some of the limitations of the other depending on the situation.
One other situation that confirmed the usefulness of the rooftop panel was after boondocking for 4 days, and then having to camp in a hospital parking lot where my wife was another 3 days, and the battery was charged quietly all day long. I would not have wanted to have the portable panel sitting out all day in a parking lot.
I just have a PWM controller and a 30 amp controller, for my needs the MPPT was not needed.

[Raz]

About 5-10 years ago MPPT was the senior project of choice for many E.E. students. As such there were lots of reports/ schematics/ etc. published on line for one to peruse. So when MPPT was mentioned here I did a little studying. I came to the conclusion that if I were building a space station, MPPT would be most welcome. Even a few kilowatt off grid set up would benefit. But for my Trillium with it's group 24 battery using less than 10 amp-hrs/ day, a properly sized panel with a low cost ($25) PWM controller was more than adequate. While MPPT may be more efficient, how would I know? Raz

[NEWYORKHILLBILLY]

Originally Posted by Radar1

I'm certainly not an expert on solar panels. I do have the experience of having bought a 90 watt portable panel and that confirmed that solar was good! There were times and places that I didn't want to place that solar panel out (example is Gettysburg National Park parking lot where we were traveling a short distance between boondocking campsites and having a solar panel out all day while touring would have been nice). I later purchased another 90 watt panel to place on my Scamp roof. It is now my primary solar source and fills my battery (single 155 amp golf cart battery) by noon on most days. I still use the portable panel for winter use, when the sun is low on the horizon, it goes down too soon, and shadows are longer. I also use it if parked directly under a shady tree in the summer.
In those cases where I need to add the portable panel to the circuit because the rooftop isn't getting good sunlight (via a plug on the tongue going to the controller), the amps going to the battery always increase, so having both in the mix helps.
I think a fixed rooftop panel and a portable panel is the best of both worlds, each being able to offset some of the limitations of the other depending on the situation.
One other situation that confirmed the usefulness of the rooftop panel was after boondocking for 4 days, and then having to camp in a hospital parking lot where my wife was another 3 days, and the battery was charged quietly all day long. I would not have wanted to have the portable panel sitting out all day in a parking lot.
I just have a PWM controller and a 30 amp controller, for my needs the MPPT was not needed.

I feel the same way You end up with the best of both worlds. Plus teh portable size has come way down. I ordered a renory 100 watt suit case that fold to 21x21 and will fit in casita closet . I also just ordered my rooftop panel Lightcatcher 100 mono.. I wanted to get my panels before the 30% tariff raised prices. I haven't look at solar in a few years, but i was surprised how much prices have come down.

[Huck]

Why get a suitcase instead of just a solar panel? That way you could get identical panels and use y cables to connect to controller.

[sokhapkin]

Originally Posted by Huck

Why get a suitcase instead of just a solar panel? That way you could get identical panels and use y cables to connect to controller.

You want the trailer be in the shade but the panel in the full sunshine.

[NEWYORKHILLBILLY]

Originally Posted by Huck

Why get a suitcase instead of just a solar panel? That way you could get identical panels and use y cables to connect to controller.

The size of the suit case has a big advantage 21.5x21.5 . plus you can move it around

[gordon2]

Originally Posted by Huck

Why get a suitcase instead of just a solar panel? That way you could get identical panels and use y cables to connect to controller.

In fact I have two Renogy 50 watt panels arriving tomorrow. I'll put a hinges and a handle on it an have my DIY suitcase that plugs into my camper where the controller is housed. I used to have a single alum frame 100 watt panel but it was very unwieldy so I am building a more transportable unit of equal wattage. Its about having it easy to carry and set-up. If you have to buy wiring, connectors, etc. to build a comparable suitcase, then the pre-made ones turn out to be a fair price. I also have a flexible 50 watt panel that weighs next to nothing. It is so light it can blow away in the wind. It is very easy to use, but I'm not sure how long it will last.

PS, I agree with the "best of both worlds" statements, but I would suggest that if you are only doing roof OR portable, start with a portable.

[Raz]

Originally Posted by gordon2

In fact I have two Renogy 50 watt panels arriving tomorrow. I'll put a hinges and a handle on it an have my DIY suitcase that plugs into my camper where the controller is housed. .

I did the same with a pair of Renogy 30 watt panels. It worked out well. The only odd thing was that my panels were not square so they don't quite line up when folded. Not a big deal, just odd. I'd be curious what you find.

http://www.fiberglassrv.com/forums/f95/t!ime-for-new-solar-68977.html

[NEWYORKHILLBILLY]

I needed a controller so i ordered the renorgy 100 watt suitcase, i will relocate the controller inside. The controller is not water proof. I not sure why they would make a portable unit with out a waterproof controller .

this is the one i ordered they had them on eBay for 209 a few days back
https://www.renogy.com/renogy-100-wa...-box-like-new/

[Jon Vermilye]

Originally Posted by NEWYORKHILLBILLY

So if i understand this if I chose the roof panel that is vmp of 18.54 or the roof panel that is vmp 17.8 . in my install it will make no difference? I was thinking it pull the 18.54 vmp panel down toe the suitcase voltage of 17.6 even if it does i not sure what that would do. Like i say i can choice a different VMP volt panel but it will not fit as well.

Thanks for any help

You are correct. The 1 volt difference will mean a bit less power from the rooftop panel. That is why it is best to match Vmp when paralleling panels. That said, the amount of power lost with a 1V difference is going to be negligible. I wouldn't worry about it. If you have a choice when purchasing a portable panel, it is best to match voltages, but again, not critical.

[NEWYORKHILLBILLY]

Originally Posted by Jon Vermilye

You are correct. The 1 volt difference will mean a bit less power from the rooftop panel. That is why it is best to match Vmp when paralleling panels. That said, the amount of power lost with a 1V difference is going to be negligible. I wouldn't worry about it. If you have a choice when purchasing a portable panel, it is best to match voltages, but again, not critical.

Jon how will it work if the roof top panel is shaded and suitcase is in full sun?
would the suit case still work to its maximum being wired to same controller?

another question is what would you recommend for connectors and extension cord for the portable panel ?
I know you spend more time boondocking than most

[John in Santa Cruz]

parallel wired panels that aren't in the sun just don't contribute to the current. they don't leak any power, its just like they aren't there.