My Solar Project

With over 6000 views in just a few weeks to my post "Is solar worth it", many of you have read about my challenges. After many of the helpful replies, personal emails, and an invitation to meet with RC Pilot Jim (we met last weekend), I am convinced that solar will work if sized correctly.

With such an interest in this subject I thought I would start a thread on my plan, build, and results to increase my solar system. This all from someone that still barely knows the difference between watts, volts, amps, draw, shunts, voltage drops, controllers, wire gauge, etc, etc. Hopefully this will help others in similar situations.

With all the feedback from the previous topic and direct communications with Morningstar and Renogy, hours of reading, and meeting with Jim, I think I have a plan that will work, but I welcome practical feedback.

My current system is a factory installed 80W panel, Morningstar SS6 controller, and two camper batteries. This was factory installed during my build in 2012 and I am told by FWC that all solar wiring is 12 AWG. I also had the extra solar plug installed in the back of the camper but was frustrated to learn that I can't even use it without upgrading the controller.

Much of my camping is in the desert in the winter - so short days and low angle sun. I have a compressor frig and need for lots of electronic use for my photography.

My plan is to remove the current 80W panel and install three 100W Renogy bendable panels wired in parallel. One in front of the bed vent, one between the vents, and one behind the kitchen vent. I can either glue them directly to the roof as some here have done successfully, or bolt (there are 6 grommets in each panel)/glue the panels to aluminum platforms and attach those to the full length Yakima tracks. If I go with the aluminum platforms I will add a bunch of cut-outs or drill holes in the aluminum to further reduce weight and allow some air circulation under the panels. I have sent an email to Renogy to ask their opinion. They have been very helpful and responsive to my other questions.

Unless my logic is flawed, another reason I am slightly(?) over engineering this with 300W is this information that I got from Renogy regarding the 12AWG wiring in the camper. From my reading it would be difficult/expensive to rewire and adding another panel is easier and cheaper.
"A 12 gauge is suitable for your system because it can handle 35A, but you
are correct in assuming that there will be a large voltage drop across the
wire. If you are okay with that, then 12AWG wire will work fine."

I will upgrade to a Morningstar SS20L controller.

Finally, I will add a Trimetric. I saw this in action at RC Pilot Jim's, and was immediately convinced of its need.

I still have a few questons out, most stuff is ordered, and I hope to get started next weekend.

Thoughts/comments?

I will do a few posts with parts list, pictures, etc, as I proceed. And of course, information on performance/results after my first trip.

One comment I have, based on your statement " I also had the extra solar plug installed in the back of the camper but was frustrated to learn that I can't even use it without upgrading the controller." This statement is true with your existing setup, because FWC wires the rear-wall plug to the controller they install, and your roof panel used up the amp capacity of the factory controller.

If you are installing a new controller, you may choose to 1) remove the rear-wall plug wiring from the controller and connect it to your battery bank. This will allow you to use a portable solar panel setup that has it's own controller. or 2) re-connect the rear wall plug to the new controller. This will allow you to use a portable panel without it's own controller, if you properly size your new controller to handle the planned roof load of 300W PLUS whatever you plan to use as portable solar.

In addition to changing your controller, be sure to check the in-line fuse size in the factory installed power leads from the solar panel to the controller. Make sure they are sized to handle the current in full sun for all the panels that you parallel before plugging into the factory plug. My fuses are located inside the cabinet directly behind the factory installed controller. I wouldn't have known they were there if I had not been looking at something else inside the cabinet.

I'm very interested in your results. I just received a Renogy 100 watt bendable panel to add to my factory Zamp 100 watt panel. I'm going to see how it works with my Zamp PWM controller with the electrical load I have. If I find I need more solar power, I will go to the MPPT controller so that I can wire panels in series. Voltage drop is less of a issue with the factory wire size by passing the same power at the higher voltage/lower current of series wiring.

Paul

DesertDave said:

One comment I have, based on your statement " I also had the extra solar plug installed in the back of the camper but was frustrated to learn that I can't even use it without upgrading the controller." This statement is true with your existing setup, because FWC wires the rear-wall plug to the controller they install, and your roof panel used up the amp capacity of the factory controller.

Click to expand...

Yes, I understand that now after help from this forum. But FWC recommended and sold this to me and explained the added benefit and flexibility it would give me. They never said I couldn't actually use it without an upgrade to the controller they sized and installed. That would have been a simple 30 second conversation at the time of purchase.

I would go up to a 30 amp controller. The SS20L is a 20 amp controller, if the output from your 300 watt panels fall below 15 volts you will be over 20 amps. If I was going to run 300 watts dedicated I might think about a MPPT controller and run the panels in series, higher voltage and lower amps.

billharr said:

I would go up to a 30 amp controller. The SS20L is a 20 amp controller, if the output from your 300 watt panels fall below 15 volts you will be over 20 amps. If I was going to run 300 watts dedicated I might think about a MPPT controller and run the panels in series, higher voltage and lower amps.

Click to expand...

Morningstar said the SunSaver 20L would handle 300 W, but I'm open to listen. Do you have a recommendation of what would fit in the same space as the SS6?

This is Morningstar's 30 amp MWP controller I can't recommend one as I have the $30.00 Renogy controller. The MPPT controllers go to big bucks. Solar Bob does not recommend mppt under 300 watts.

As you probably now know, volts time amps equals watts.
V x A = W
With some algebra applied:
V = W/A
or
A = W/V

What all of this is saying is that for a given wattage you can have high amperage and low voltage, or you can have high voltage and low amperage. High amperage heats the wires, high voltage does not. Hot wires have a larger voltage drop, which is a loss in efficiency. Which is why Bill suggests wiring the panels in series. You'll only have the amps equal to one panel's output, but at 3 times the voltage of one panel, so Watts going into the controller stays the same but the wires don't get as hot. Good wire is rated for at least 300 volts, so that's not an issue.
A good controller can convert (with minimum loss) that to ~300W at 12VDC nominal.

So the you guys think series would be better? I thought it was implied in another thread that parallel was better. I'm sure "better" is a relative term, but I don't understand all the issues.

I read that doing two 100W panels in series creates a 24v system, does three in series create a 36v system?

Separate your thinking into solar panel power in and battery charging power out.
The controller's task is to transfer the input power into characteristics to properly charge the batteries.

If you look at Renogy's bendable 100 watt panel's specs, you will see that its voltage output is up to 17.7 volts. The rigid panel voltage is 18.9 volts. Either of these without a charge controller would eventually damage your batteries so you use a controller.
http://renogy.com/renogy-solar/pv-modules/

The charge controller must be made or configured for the battery voltage. In our case, that is 12 volts nominal. The actual output voltage must vary according to the battery state of charge. The Morningstar SS12L-12 can handle panels that provide up to 30 volts to charge your 12 volt batteries. See second page of http://www.morningstarcorp.com/wp-content/uploads/2014/02/SunSaverENG_R3_5_12web1.pdf

This isn't enough voltage capacity to handle your panels in series so you must wire them in parallel with this controller. This just means that you have to consider everything as a whole system when you are putting it together.

Paul

According to James Langan, OVERLAND JOURNAL tech editor, writing in the Fall 2014 issue, two 80W panels are more than sufficient for charging and maintaining two Odyssey 31M-PC2150 batteries.

Of course, otimum charging and efficiency is strictly a function of avaialble sunlight and maintaining optimum angle between the panel and the sun. Any deviations in angular relationship or overcast will diminish charging capability.

Paul - I'm trying to consider everything together, but I have a lot to learn.

I'm a little confused by your post. Up thread I identify that I'm looking at the Sunsaver 20L (not SS12) which in a call with Morningstar they said would be fine for 300W in parallel.


From what I've read I'm not really thinking series, but thought I would throw it out there since it was brought up.

DonC said:

So the you guys think series would be better? I thought it was implied in another thread that parallel was better. I'm sure "better" is a relative term, but I don't understand all the issues.

Click to expand...

I hope I'm not adding to any confusion with this...but I wired my two (120-watt) "12-volt" panels in series so that I could use the existing OEM solar roof wire (as ntsqd remarked, more voltage without taxing the wires with more current), which is fed to the input of my Blue Sky Energy Solar Boost 2512iX-HV charge controller -- an MPPT controller.
Here are the relevant spec of the 2512iX-HV:

SPECIFICATIONS Solar Boost 2512iX-HV
Output Current Limit 25 amp maximum with 36-cell modules
Nominal Battery Voltage 12VDC
PV Input Voltage 50VDC absolute maximum (Recommend maximum VOC at STC ≤ 40VDC)*
PV Input Power Recommended maximum, 340W with 36-cell modules

Since the voltage from each panel can be as high as 20+ volts (Open Circuit, that is), this charger can handle two panels in series but not three.

And the MPPT charge controller magically converts the higher voltage into more current at whatever voltage the batteries need, depending on their state of charge.

I read that doing two 100W panels in series creates a 24v system, does three in series create a 36v system?

Click to expand...

Well, sort of...since my panels are "nominally 12 volt" then two in series are nominally "24-volt" (and 3 in series would be nominally "36-volt"). But it's only higher-voltage between the panels and the MPPT charge-controller. Between the charge controller and the batteries it's not more that 14+ volts, depending on the state of charge of the batteries.
Assuming you have "12-volt" batteries then it's still really a "12-volt system".

Don,

Sorry, I fat fingered the model. Trying to finish the post before the honey-do list creator returned.

Paul

MarkBC said:

...
And the MPPT charge controller magically converts the higher voltage into more current at whatever voltage the batteries need, depending on their state of charge....

Click to expand...

I know this has been covered elsewhere, but just for the sake of complete explanation of my post, here's an example of what I mean by MPPT conversion in my system, which I originally posted here.


The top meter is reading the current and voltage from the 2 solar panels in series going into the MPPT charge controller -- in this photo: 1.26 amps at 38.41 volts. The voltage from two panels in series is so high because it's cold out -- a lot colder than the "STC" condition of 77°F at which they're rated, and panel output voltage increases as temperature decreases (and maybe there's some error in the meters..? ). The bottom meter is reading the current and voltage being fed to the batteries after being processed by the MPPT charge controller: 3.21 amps at 13.93 volts.

(in use is a previous MPPT charge controller, one which I eventually killed by using it beyond its intended range. It was rated for 10 amps and I exceeded that significantly when solar conditions were ideal)

Note that power in is 48.3 watts, power out is 44.7 watts. Difference is 3.6 watts. According to data sheet of the Controller, it consumes 1.0 watt when on, and is 96% efficient. 4% of 48.3 watts is 1.9 watts. 1.0 + 1.9 = 2.9 watts. That leaves about .7 watts to account for.

Don't know how much power the two meters consume. But that's close enough to show that power into the controller from the solar panels is the same as power out of the controller to the batteries even though the voltages & currents are different.

If you get curious about how this works, search for "buck boost voltage regulator" and look at the wiki pages. This can get deep in the weeds fairly quickly.

Paul

PaulT said:

Note that power in is 48.3 watts, power out is 44.7 watts. Difference is 3.6 watts. According to data sheet of the Controller, it consumes 1.0 watt when on, and is 96% efficient. 4% of 48.3 watts is 1.9 watts. 1.0 + 1.9 = 2.9 watts. That leaves about .7 watts to account for.

Don't know how much power the two meters consume. But that's close enough to show that power into the controller from the solar panels is the same as power out of the controller to the batteries even though the voltages & currents are different....

Click to expand...

Yep. And the ~7% loss of power is quite a bit less than would be lost in a non-MPPT controller, which can't make use of input voltage (from the panels) that exceeds the voltage that the battery needs.

Of course, an MPPT controller costs a lot more...and some say that money could be better spent on additional panel area. But I like the idea of what the MPPT controller does, and I like that I can use the existing OEM smaller gauge wire with panels-in-series...and I don't want more panels on my camper roof!



But this photo is from my solar project, not DonC's, so sorry for the topic diversion.

MarkBC said:

But this photo is from my solar project, not DonC's, so sorry for the topic diversion.

Click to expand...

No problem! We all learn from each other, which is why this forum is so good.

When I started looking into this I was hoping someone could say just do step 1, step 2, step 3 - done. But like most things there are lots of ways to do things, and people like or believe in different ideas, most of which work. Parallel vs series, MPPT vs PWM, propane vs compressor, 12AWG is adequate/not adequate, iOS vs android vs Windows (haha) etc, etc.

There is probably not a single DIY solar install here that is exactly like another, yet they all meet the need of the owner (I hope). I'm just wanting to make sure there are no fundamental flaws in my ideas/plan, even though it may not be exactly how someone else might do it.

This solar panel stuff is a continuing learning experience. And is very complicated. I am far from an expert but have been trying to better understand it myself. So correct me where needed.

I am sure this was posted while I have been typing but MPPT controllers can convert a higher voltage solar configuration to 12 volts.

Series or parallel can get complicated. If your panels are in series, the voltage going to the controller (which should be near the batteries) will be higher. This means the current will be lower so, I think, the power loss, on the wire going from the solar panels to the solar controller will be lower. So, less power loss caused by the small wires. If this is true, you would think putting the panels in series is the solution. So I figured I would buy a 130 watt solar panel and put it in series with my factory 80 watt panel. It turns out, from what I have read, the 80 watt panel would drag the system down. I would pretty much end up with a 160 watt system rather than a 210 watt system.

Typically, if you had three (100 watt) solar panels on your camper in series and one panel was putting out half the power. Your whole system will drop to about half (150 watts) of power. Most solar panels really want total sun with no shade in order for them to operate well. What I have read here and other places is, if even a small part of a solar panel is in the shade, the loss of power can be BIG. So, if one of your solar panels is just slightly in the shade and it drops to half power, your whole system drops to half power. Your 300 watt solar system is now more like 150 watts. Based on this and because I camp very often in forest areas, I am afraid to put the panels in series and I would personally want my panels in parallel. If someone knew that their camper would be used where the panels would never or almost never be blocked by the sun, they would probably seriously consider the series configuration. And I guess someone could even add a switch or two in order to change the configuration between series and parallel.

A question I "don't yet" know the answer to is which controller allows the highest voltage between the solar panels and the solar controller? MPPT or PWM or something else? I would consider using the controller that kept the voltage between my panels and the controller at the highest voltage in order to minimize the power loss over the small wire. Seems like this could help with power loss in a parallel configuration. A 12 volt solar panel will be more like 20 volts with no load. I do know a MPPT controller tries to keep the voltage at the solar panel at a voltage that will give you the highest amount of power from the panels. I have read in a few places that this is around 17 volts. So, at least with a MPPT controller, your voltage on the wire will be around 17 volts. I am not sure about voltages on a PWM controller. But figure if your 300 watt controller is in good sun and charging the battery, the voltage on the wire coming from the panels is going to be at least 14.5 volts. So, yeah, we want a higher voltage on the wires between the solar panels and the controller but is this really enough to make a difference?

I currently have one 130 watt panel on my camper going to a MPPT controller. It seems like I saw here where someone put a PVC pipe going down the side of their camper and I think it had the wires for the solar system in them. I personally really liked that approach because I could run the wires the shortest distance to the controller and batteries. And, of course, I would increase the wire size some. Maybe, one of these days, I will bite the bullet and implement a solution similar to that.

I know I got a little carried away but hope this helps and I am not off in left field.

Steve

NorCalSteve's point about the affect of shade on panels -- and how partial shade on one panel can bring down multiple panels if in series -- is a good one.
I camp most of the time in generally treeless areas of the Great Basin (and other arid, low-vegetation, regions)...but if I camped in/under trees more I might not do an in-series configuration. Definitely worth considering.