Panels Series or Parallell?

CLyndes · June 2012

Folks,

I keep thinking I'm ready to pull the trigger and order a solar system for my RV. Being new to this though I keep finding things I don't understand, and so can't make a good decision.

At this point this is the system I am thinking of;

ET Solar 95 Watt 12 volt Monocrystalline Solar Module ET-M53695 4 $975.00
Z-Bracket RV Mounting Feet (set of 4) Z-BRACKET 4 20 $80.00
Midnite Solar MNPV3 Solar Array Combiner MNPV3 1 63.64 $63.64
Midnite Solar MNEPV 150 VDC Solar Array Breakers 10 Amp MNEPV-10 4 9.3 $37.20
Midnite Solar MNEPV 150 VDC Solar Array Breakers 50 Amp MNEPV-50 1 9.3 $9.30
Morningstar TriStar 45 amp MPPT solar charge controller TS-MPPT-45 1 400 $400.00
Morningstar RM-2 Remote Digital Meter For All TriStar Controllers TS-RM-2 1 116 $116.00
50 Foot MC4 (SolarLine 2) Extender Cable MC4-50-MF 3 50.25 $150.75
15 Foot MC4 Solar Panel Interconnect Extender Cable MC4-15-MF 1 23.22 $23.22
2 Conductor #8 AWG outdoor wiring cable 3G-0802 10 1.75 $17.50
$0.00 $1872.61

I chose the solar panels because of their size. My RV has a lot of stuff on its roof so 22" by 50" works. The panels will be scattered around the top of the RV, so the chances of some being in the shade while others are in the sun is pretty good.

The kind folks at N. AZ Wind and Sun took a look at what I have proposed (thanks Robert Snipes) and suggested I look into connecting the panels in Series, as the MPPT charge controller allows that. It would save me a lot of MC4 wires and I would not have to have as big a combiner box (the one I specified isn't big enough for 4 panels).

What are the pros and cons of connecting the panels in series?

Is there anything else about the system I've proposed that people would suggest changing?

I have 4 6 volt workaholic U2200 232 amp hour batteries (12 volt system). The RV is an '83 Wanderlodge FC 35' and has a horrific parasitic load. My goal is to be able to leave it (empty) indefinitely without draining the batteries. I have calculated I need 360 watts of charging to do that - if I get more and it helps keep up with my use when I am in it, more the better.

Sincerely
Craig Lyndes
Swanton Vermont

Dill · June 2012

Re: Panels Series or Parallell?

connecting them in series runs the string at a higher voltage than parallel connections (you combine the panel voltages) thus allowing you to use less wiring, and smaller wiring. It's a win-win scenario when using an MPPT charge controller like you are proposing.

BB. · June 2012

Re: Panels Series or Parallell?

Looks OK to me too (NAWS is the expert anyway, so they know).

Just a warning, shade is a killer on solar panel performance. If you can do anything to reduce shade/improve angle on the sun, it will increase the available amount of power to harvest a lot (partial shading of one or two panels can kill 25 to 50% of an array' output pretty easily).

Lowering obstructions, raising panels, allowing for panel tilting (more important the farther north you go--especially outside of the summer months), all can help. You can play with PV watts regarding location/angles for your array (use 0.52 as the derating for power generated with an off grid system using an AC inverter).

-Bill

Cariboocoot · June 2012

Re: Panels Series or Parallell?

Welcome to the forum.

The ol' "series vs. parallel" issue.

On an RV, parallel is preferred if there is the likelihood that other roof protrusions will cast shade over some of the panels at various times. Series wiring simplifies installation, but a shadow across even one panel can knock out much of the power. So depending on where the panels have to go and what is likely to shade them when, you might even go with a combination of series/parallel; any two panels in a similar aspect connected as series, and any such strings in a dissimilar aspect connected as parallel.

I'd say those panels are pretty pricey ($2.56 per Watt) and wonder if there isn't a better value in a larger panel that could be fit in the space available. Probably the smallest >100 Watt panel available now is the Kyocera 140 ($2.27 per Watt from NAWS) but this is heavily dependent on panel size and space available. When you have those constraints, you're stuck.

Otherwise the system looks perfectly viable to me.

BB. · June 2012

Re: Panels Series or Parallell?

Craig wanted a physically smaller panel because of a "cluttered" roof--that was his reason for the 95 watt panels (as I understand).

-Bill

Cariboocoot · June 2012

Re: Panels Series or Parallell?

BB. wrote: »

Craig wanted a physically smaller panel because of a "cluttered" roof--that was his reason for the 95 watt panels (as I understand).

-Bill

Understood, hence my comments about constraints. The biggest worry is the other things poking through the roof that will cast shadows on the panels at different times. That's usually why people choose parallel over series on an RV.

With short wire runs and dubious MPPT advantages under the circumstances they usually pick the less expensive PWM charge controller too.

Jim45D · June 2012

Re: Panels Series or Parallell?

Cariboocoot wrote: »

Understood, hence my comments about constraints. The biggest worry is the other things poking through the roof that will cast shadows on the panels at different times. That's usually why people choose parallel over series on an RV.

With short wire runs and dubious MPPT advantages under the circumstances they usually pick the less expensive PWM charge controller too.

Exactly. Which at this point I'd like to post a layout of my proposed RV setup. Panels 1 thru 4 have been in position for a long time, operating off a Solar Boost MPPT controller. Not too bad. But, I've never seen close to anything ever advertised about the possible 10 - 30% increase. The afore mentioned panels have always, from initial installation....been daisey chained in parallel, no fuses, with only two batteries. In my situation, there is room for panel expansion, and one more battery. Please look at the configuration of the way I have decided to do the modification, still all paralled, but two panels to a run. I'd like some input. I have one panel to go, which I cannot order until next month. I won't do anything until I have all necessary modification items in hand. I probably won't even start on the installation until late October.....the heat here dictates when, and if daily work can be performed.

The panels are all tiltable. 1 & 2 as a unit, 3 & 4 as a unit, 5 & 6 likewise. Number 7....thus far, will be on a single separate run. Unless it feasabile that I can parallel it with the 5 & 6 unit. The panels are, and mods., will be attached to 1" sq. aluminum tubing hinged at the bottom. Of course the fuse block will be enclosed in a combiner box. I will include a photo of such here. There are air conditioning units, a evaporative cooler unit, exhaust fan openings, TV antenna.....all will shadow the panels at one point or the other if I were to place them flat on the roof. The way the tilt frames are constructed.....there's no chance of a shadow. When the RV is moved, all the panels are latched in the down position. However, when parked, it is always parked, with the panels faceing roughly 10° south by s.e. Otherwise I won't park until I find a suitable location for placement.

At the present time I'm in the desert heat of HOT. Yesterday, and today it was well above 110°, in the shade. Once this modification is complete we're moving to Ensenada, Baja, Mexico. Why not? Today their temp was a cool 67°. Where I'm located presently the Lat. is 33°, and where we're going is 31° latitude. I won't even have to redrill the tilt arms. Besides, there I will get reflections from the Pacific.

Cariboocoot · June 2012

Re: Panels Series or Parallell?

Jim, in defense of MPPT controllers I have to say you usually do not see much advantage with the panels in parallel. The possible additional charge current comes from the Voltage difference between Vmp and battery. When the panels are "close" to battery (17.5 to 12) there's not much "overhead" to make use of. Double them up and you get the "extra"; basically the "necessary" V-drop from Vmp to battery remains the same, and the additional "extra" Voltage can all be turned into charge current (if needed).

This is the "small" MPPT advantage.

The "large" advantage would be the greater over-all flexibility in array design.
The "medium" advantage would be the cold-weather Voltage increase that not everyone will have.

Jim45D · June 2012

Re: Panels Series or Parallell?

This is the layout of the RV with some dimensions, and specs, and equip. to be used. This is exactly how the panels are to be placed. Spacing between 6 & 7 has to be there due to conflicting spot lights. Otherwise I'd mount the #7 there. #5 has caused the most work, as it has to be elevated on it's tilt mechanism by almost 1.5 foot. Otherwise the A/C unit would block it out. Needless to say this has been a expensive project. But, I'm retired, sold the house, and the wife and I are RV fulltimers. The coast of Mexico sounds nice to us. We've visited many times. Plus 50% cheaper than here....on everything, if one is prudent.

Some of you may remember about two months + ago I was inquiring about posibably using some Siemen's 10 watt panels that I have.....well, I scratched the idea, and will loan, or use them myself for trickle charging extra vehicle batteries. I have more charge controllers than one can shake a stick at. I had forgotton I bought them. Old age is a drag........

Opps; Overlook the 538 watt specs, as at the time I was thinking about just one 140 watter.

Jim45D · June 2012

Re: Panels Series or Parallell?

Cariboocoot: Your defense of MPPT controllers is well noted, and true. However, when I first decided to go with the solar program I was told nothing of the sort. When I inquired as to how it was done, as I was already at the dealers....this is what he said: "Awww, just parallel daisey chain whatever panels together, as long as they're close to one another in voltage until you achieve the output current you need in your RV." That's how he managed to sell me the Heart 458 Combo (2k) inverter I have, the lousy RV Products MPPT charge controller, wiring, and many other extras. I didn't know, and went with word of mouth. Then came to find out that many of the people that had sent me to him in the first place were in the same boat I was. We all ceased buying from this particular dealer. Then I fell for another dealer that told me that the Solar Boost 2025 was a much better controller, and would fit right in with the 25 amps that I wanted to install. He frothed at the mouth too!!! I discovered on this very forum....that it is a two stage charger, and a 20 amper. It's still in the original wrapping.....never installed.

Then I found NAWS, this forum, and started paying better attention to what I bought. The rest is history. Now, I dream of solar.....when I can sleep! There's a old saying here, mabey it's the same in B.C., "There's a fool born every minute." I changed that several years ago. Now there's 10 born a second.......and the unscrupulous dealers are squirming to get one, or all of them. Especially some I know in Western Az. Some of them come to Az. every winter from the west coast peddling their solar wares at triple prices. During that time, the snowbirders from the mid east, and the east coast flocking here for the warm winters get taken hand over fist. Many lawsuits prevail, most are elderly men, and sometimes just women. I'm afraid to tell my wife what money I've spent because I was a fool.

Cariboocoot · June 2012

Re: Panels Series or Parallell?

Jim, you are no fool. We make our decisions based on the information available to us at the time. Later we learn that info was wrong, and make a new decision. This is called "education".

The appalling large number of crooks, liars, and other fraudsters that infect the solar industry is one of the reasons for this forum: to have at least one source of info that's as accurate as possible. It's why there's a whole section of the forum devoted to such garbage. Even so, info from the forum changes over time as new products replace old, new technologies become prevalent, and all of us learn and discover more about RE.

O brave new world, that has such people in't!

ggunn · June 2012

Re: Panels Series or Parallell?

Cariboocoot wrote: »

Jim, you are no fool. We make our decisions based on the information available to us at the time. Later we learn that info was wrong, and make a new decision. This is called "education".

All decisions are made with insufficient data; if there were sufficient data, a decision would be unnecessary.

westbranch · June 2012

Re: Panels Series or Parallell?

Or as an old boss of mine always said ...I reserve the right to be smarter tomorrow than I am today...

Jim45D · June 2012

Re: Panels Series or Parallell?

Would someone look over the layout posting I made on number 7. I'd like to get some input. Is it ok? Should I make any changes. Unfortunately, as someone posted not long ago, "I have painted myself into a 12 volt corner!" This is where I'm financially stuck for many moons. Will this fly, is the fuseing alright, switching, etc? Is it alright to run the #7 panel by itself, should it be paralled to the 140's. Clues please. Thanks.

Cariboocoot · June 2012

Re: Panels Series or Parallell?

Disclaimer first: I have difficulty seeing images on here so I may not see them right.

You seem to have three instances of two panels in parallel on one fuse. This is a no-no. The reason being if one of those panels fails the fuse can pass enough current (especially in conjunction with the remaining panel of the pair) to exceed the defective panel's Isc. In other words, the 10 Amp fuse can let 10 Amps flow to a panel with an Isc of 4.97 (one of the 80 Watts) and the other panel can add 4.97 more Amps, making 14+ Amps flowing through a shorted circuit capable of handling 4.97 Amps max. Ever parallel connection must be protected separately.

Each 140 Watt should have a 10 Amp fuse. The 80 and 87 Watt panels should each have 7.5 Amp fuses.

In addition, there must be circuit protection on the output of the charge controller. It would be best if each of those three batteries in parallel had a fuse too, just in case. The full battery bank output must be protected at the very least.

That's all I see that's wrong.

Jim45D · June 2012

Re: Panels Series or Parallell?

Cariboocoot: Thanks for you input. What I was attempting was to eliminate excessive wire runs. Hence, the reason for daisey chaining two panels to a run. It's back to the drawing board. The only way that these can be fused properly is to simply use individual runs from each panel. I don't see any other way. Which brings me to the final question......why would any dealer suggest that any panels, series or paralled be daisey chained? There is no possible way to attain individual panel protection at the fuse block if ran as such. Or am I missing something here?

Cariboocoot · June 2012

Re: Panels Series or Parallell?

The only thing you're missing is that a lot of people who sell electrical equipment actually know diddly-squat about electricity.
Solar electric is still relatively new, and the nuances of things like panel fusing are often still debated among people who do know what they're talking about.

Now, about this daisy-chaining; how are you making the parallel connections between two panels? There is need for weather-tight connections here, so that usually means inside a box. Inside a small box without fuses can also be inside a larger box with fuses. At each of these connection points you could add circuit protection along with the junctions and up to a larger wire size until all come together and down to the charge controller. Since these junctions should be accessible, there should be no trouble replacing a fuse if one goes. And rarely will one go; solar panels are amazingly dependable.

Jim45D · June 2012

Re: Panels Series or Parallell?

OK. I have simply connected + to + and - to - within each junction box to each panel to get the parallel connection. Now, I could possibably install a fuse of the proper size within each box according to it's ISC, but haven't. With the daisey chaining, as it is now, and has been for years on the 80 watters.......it's + to - at each panel all the way to the controller. Yes, these boxes are weatherproof so Kyocera say's. If I did it that way then there wouldn't be any need for the end fuse block. Thus still eliminiating excessive wire runs. Please advise. Thanks.

I'd just have to purchase 7 fuse holders along with the appropriate fuse size rating for each individual panel. That would work.

Cariboocoot · June 2012

Re: Panels Series or Parallell?

It comes down to: is there room enough in those junction boxes for a couple of fuses, or will you need to add a bigger box to hold all the connections?

At any rate they wouldn't be daisy-chained anymore; they'd be 'Y'ed, with a fuse on each panel (+) before they join into one. No need for lots of wires running into the RV or a fuse block inside. Just be sure that as more panels are added in to the wiring the remaining wire is able to handle the increasing current.

Jim45D · June 2012

Re: Panels Series or Parallell?

Yes, there's room for a fuse per panel inside the attached junction box. Let me get this straight........I open each JB, as I have to anyway to go from #10 wiring to #8. There I install a fuse holder within the box with the appropriate sized fuse. From that panel's JB to the next JB it's + to - with another fuse holder w/fuse on each + side. (Incidently, these panels are from JB to JB approximately 2') From the second panel output wiring to the combiner box, (already have, but will have to install a + and - buss bar) to accomondate the wire runs. Once all wiring is attached from the panels.......one #4 wire from the combiner box via the roof to the CC. This will eliminate the fuse block, and I will still only have 4 separate wire runs to the combiner box. Am I on track?

Cariboocoot · June 2012

Re: Panels Series or Parallell?

If you're going to open each junction box anyway, give each panel its fuse at the panel. When you connect one to the next, make sure it's on the "outgoing" side of the next one's fuse (so you don't run the current of both panels through one fuse).

Panel - Fuse - junction
Panel - Fuse - junction

Just keep on that track and you should be all right. But oh how I wish I could draw a schematic of it to be sure!

CLyndes · June 2012

Re: Panels Series or Parallell?

Cariboocoot,

Thank you for your reply! My first try at designing this system for my RV included using 3 Kyocera 140 panels to generate more potential watts at a lower cost. Then I went up on the roof and measured.... The only way I could use the larger panels is if I installed them in a manner like is depicted in the attached picture.

Attachment not found.

This would also help the shading by other equipment on the roof that mounting the panels directly on the roof (well with a small gap for cooling) would allow.

The down side is that the larger panels would extend 3" beyond the goat rail on the outside - becoming the furthest thing towards the edge at that height on the roof - and would be touching the air conditioners towards the center - blocking all access to storage pods and devices further forward on the roof. I'm also really unsure about the wind while driving down the road and what effect it would have on the panels. Note they are only attached on the ends.

I met the person who took this picture and he said he has had no problems.

Does anyone have an opinion about a mounting setup like this as opposed to mounting directly on the roof?

Can anyone suggest a mounting strategy that would allow me to release the inside edge of the panel, both front and back and tilt it out of the way so I could walk past the array towards the front of the RV roof?

Craig Lyndes
Swanton Vermont

ps - I am following and learning a lot from the conversation about daisy chaining panels in parallel and fuses...

Cariboocoot wrote: »

Welcome to the forum.

The ol' "series vs. parallel" issue.

On an RV, parallel is preferred if there is the likelihood that other roof protrusions will cast shade over some of the panels at various times. Series wiring simplifies installation, but a shadow across even one panel can knock out much of the power. So depending on where the panels have to go and what is likely to shade them when, you might even go with a combination of series/parallel; any two panels in a similar aspect connected as series, and any such strings in a dissimilar aspect connected as parallel.

I'd say those panels are pretty pricey ($2.56 per Watt) and wonder if there isn't a better value in a larger panel that could be fit in the space available. Probably the smallest >100 Watt panel available now is the Kyocera 140 ($2.27 per Watt from NAWS) but this is heavily dependent on panel size and space available. When you have those constraints, you're stuck.

Otherwise the system looks perfectly viable to me.

Cariboocoot · June 2012

Re: Panels Series or Parallell?

Another strategy many RVers use is to put some small panels on the roof, and then put together a "portable" panel set with a couple of bigger panels that get stowed when not in use and can be put in the sun (and kept aimed at it) when parked. There are concerns about damage and theft this way, but it can be done.

Panels Series or Parallell?

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