Could you help a solar newbie with a panel choice and setup?

Audiomaker · January 2015

Solar Newbie, yep...that's me.
I have some inverter/charger/bank time under my belt, but I've never bought a solar panel.

So here's the deal... This is a mobile application (RV), but I'm asking here in the off-grid forum because the system is more something you would find in a home.

The equipment I have so far:

Xantrex XW6048
Xantrex System Control Panel (1050)
Xantrex Automatic Generator Start (1060)
Xantrex MPPT60-150 charge controller
200ah of bank @ 48v (will upgrade to 400+).
No PV's (which is why you're reading this).

Ok, the real estate on the roof of my RV is 8' wide by 28' long... clean. (actually the RV is 40' long, but the other 12' has A/C and other times mounted. I have 28' for solar).
The rig is 13' tall, and I need to stay under 13.5'.

Ultimately (but not right off), I plan to mount the PV's to "speed rail", which is basically a 1.5" aluminum tube used for handrails and other purposes. My intent is to have the panels go from laying flat, to going vertical like a "fence" where you could use the top of the RV for "hanging out" and the PV's become like safety rails (which also allows you to tilt them for collection purposes).

In the short term, I am going to mount them flat however (non moveable) while I work out the fold up design.

My intent is to have 2 rows of PV's laid lengthwise. A driver's side row, and a passenger side row... with a narrow space between them to walk fore and aft.

The PV's I've been looking at are in the 245-320w range.
In the 245-255w range, the length (in my case of stacking lengthwise) is about 66" (usually regarded as the height). The width is apps' 40".
In the 300w panels, the length is appx's 79"

In the space I have available, I can either line up 5 of the 250w'ers per side, or 4 of the 300w'ers, so that's my first question.
Would you do 2400w of 300w panels (4 per side), or 2500w of 250w panels (5 per side). The cost is about the same, although less panels does make the eventual folding framework have less "joints".

The next question... which might have been the first is... Is that a match for the equipment I already have or is it underrated/overkill (Nothing else needs to be on that part of the roof).
Next... how to wire? This is where I go especially newbie on ya...
I know standard electricity pretty well, but all the values on the PV's, and how they fit in a system are new to me. Voc'2...etc.?
I'd really like to get this hooked up an going in less time than it would take me to learn what everything means.
So could you please describe to me how you would hook up (series/parallel) two rows of either 4 or 5 PV's to a MPPT60? The 300w PV's do have the advantage that they are an even number per side.
I am looking for a steady reliable charge vs maximum output since the RV might be parked in many different orientations and shade conditions.
The CC has a maximum input voltage of 140v. As stated, the bank is 48v.

My best guess is that using two rows of 4 300w panels, that it's 2 panels in series x2 , then paralleled per side, then parallel the sides, but that's a guess.
Put another way, for 8 panels that would be 4 sets of 2, or 2 panels in series X 4. How about 5 per side?

And lastly, please tell me about those special connectors on the back of modern PV's? I understand they are quick connect/release, but my CC' simply has bare wire input terminals.
Do you just cut the ends off? Are the paralleling adapters for these connectors? Can this be done without a combiner box (in an RV, you have space for a limited amount of boxes).

Again, sorry for not putting this in the "mobile" section, but I don't think there's a lot of 6048's and MPPT60's rolling around on wheels, I guessed this to be the place.

My goal is to make this until as off-grid as possible and minimize generator use. Assume this will never be hooked to the grid (other than to sell).
I have an average and steady continuous use of appx' 300w, with intermittent loads as high as 3kw (i.e....while cooking electrically or using power tools...etc)
To that end, the system does include a 7k diesel generator, and I apologize for omitting that.

All advice is appreciated
Sean

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

To make this a little more fun, here is the platform being targeted to receive extraterrestrial power:

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

You just had to put up that pic...wife's first question, Where is the living room and bedroom and windows? She wanted pics too...
Pls ? My neck has teeth marks on it already!!

AS far as your question about which PVs to use I suggest you use the Array sizing tool for the specific Charge controller you will use. I am a MidNite name so so not know where they (Schneider) hide their sizing tool. That should tell you if you can use the larger array and the configuration...

hth

ADD found this but don't know if it's the right one... http://solar.schneider-electric.com/product/conext-designer/

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

westbranch wrote: »

You just had to put up that pic...wife's first question, Where is the living room and bedroom and windows? She wanted pics too...

Right behind the roll-up door. Lots of cross ventilation too.

There are a few folks (I am sure more than a few) around here that are living in commercial buildings at $0.50 or less a square foot. Apartments in the big cities her are going for almost $3 a sq foot a month for simple apartment with car port.

The ultimate 1,000 to 3,000 sqft man cave with double bay roll up doors. Costs a bit to heat and light--But less than north of $2,700 a month before utilities.

-Bill

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Well my rig was parked in the lot of a 33,000sqft building that I called my home up until Dec 30 14.

Now it is parked in front of an acre of ashes. A lot of my friends used to joke about my "RV" looking like an apocalypse vehicle, that is how it was being designed, and it has become so.
There are no windows, and in fact, the machine is lined with encapsulated lead sheet (FU Korea...lol). As you can see, I do have one large electric "window"...the door to which weighs hundreds of lbs as it is also lead lined. It has a queen size bed, a full sized jacuzzi tub, a full kitchen... you know.

Anyway...
The roof will hold X panels. Panels aren't very expensive so I might as well fill it. I figure there's enough people on this board who run this type of panel to be able to give me a real world opinion on what to expect with this number and orientation of panels.
In addition, I *think* there is more than one way to wire this as far as series/parallel. Again, I have a 140v max on my charge controller, and I presume I have to make at least 48v to be charging. How would you wire it if it were you? 4 panels per side, maybe 5, and then?

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Ok, pulled this from a 315w "24v" panel on the net...

Rated power Pr SW315
Peak power Pmpp 315W
Peak power voltage Vmpp 36.8V
Peak power current Impp 8.63A
0pen circuit voltage Voc 45.9V
Short circuit current Isc 9.16A
Max Series Fuse* 15A

...and here's my confusion...

First, I don't see 24v anywhere in there?

My charge controller has a 140v maximum continuous rating. I think it shuts down at 150v.
I'm going to steer this discussion towards using 8 panels, 4 per side on this rig.
I'll further narrow that by assuming for the moment that I will parallel the driver's side array with the passenger side array.

Now one could series 4 panels @ 24v and end up with 96v (well under the 140v max), or one could series half and parallel half (2 panels creating 48v paralleled with another 2 panels making 48v), but I'm looking at these panel numbers and seeing a peak voltage of 36.8? If I series 4 panels at that voltage I'd have 147.2v... and that's over my 140v maximum voltage of the CC'.

It seems like when using a down-converting MPPT controller, that it's optimum to series the panels no? In an application where low light is involved, I would be less worried about under voltage if each side were producing 140v peak than half of that (73v). 73v is still above 48v, but that's at peak.

I don't really know how PV's behave electrically? As I said, the spec's above came from a "24v" panel and I'm not making the connection... are they regulated?
Would 4 in series actually ever put 147.2v to my controller?

...and what is this open circuit voltage? 46v? Where does that come from? Do I use that in sizing? Am I assuming incorrectly that if I could get 4 in series that I'd be able to keep my charge controller charging in lower light conditions?

See.. told you I was a newbie.

Edited to add CC spec's
Nominal battery voltage 12, 24, 36, 48, 60 Vdc
Maximum PV array voltage (operating) 140 Vdc
Maximum PV array open circuit voltage 150 Vdc
Array short-circuit current 60 Adc maximum
Maximum and minimum wire size in conduit #6 AWG to #14 AWG
Total power consumption while operating 2.5 W (tare)
Charger regulation method: Three-stage (bulk, absorption, float)
Two-stage (bulk, absorption)

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

This is why it is a "24 volt" panel:

Peak power voltage Vmpp 36.8V

You put 72 solar cells in parallel: 72 volts * ~0.5 Volt Vmp = ~36 volt Vmp for panel.

It is commonly called a "24 volt panel" because it can be used to charge a 24 volt lead acid battery bank... As the panel gets hot, its Vmp will fall. And it takes ~29 volts to fully/quickly charge a typical flooded cell lead acid battery.

In times past, there were "12 volt self regulating panels" that had Vmp~15 volts--These where available decades ago and were used to charge 12 volt batteries for remote equipment (highway signs, etc.). Saved them the cost to design/build a 12 volt regulator.

So--We backup to what you need--And then pick the hardware that supports those needs.

MPPT charge controllers make the design process a bit more confusing (and expensive)--But they allow us a lot more options and ways to optimize a solar power design.

Note--Do not use the "24 volt panel" in the design... You need to use actual Imp/Vmp/etc. numbers

For example, using these panels with a Midnite 150 charge controller... Using the Midnite sizing website:

MidNite Solar Classic Sizing Tool

input: 4 series panels x 2 parallel strings and a very wide temperature range of -22 to +104 F on a 48 volt nominal battery bank.

We are basically worried about Voc-cold (voltage open source, very cold weather and high array voltage would over volt charge controller), and Vmp-hot (voltage maximum power hot--depressed voltage would be too low to charge battery bank).

PV Array

Rated PV Array Power:
2520
Watts

Anticipated Array Power @ 104F:
2350
Watts

Rated PV Array Current:
17.26
Amps

Battery Charging Current @ 57.6 V:
43.8
Amps

VMP (Maximum Power Point Voltage) :
147.2
Volts

VOC (Open Circuit Voltage):
183.6
Volts

VMP @ -22 F°:
183.6
Volts

VOC @ -22 F°:
216.8
Volts

Classic & Classic Lite Charge Controller Selection

150
200
250

Max Operating Voltage
150
200
250

Max Non operating VOC (HyperVOC) @ 48V Nominal Battery Voltage
198
248
298

Maximum Number Of Modules In Series
2
3
4

Max Number Of Modules In Series (Using HyperVOC)
3
4
5

Max Allowable Output Current Per Classic
Based On This Current Configuration
76
65
55

Max Allowable Wattage Per Classic
Based On This Current Configuration
4438
3796
3212

Present PV Array Wattage Of This Configuration
2520
2520
2520

Design Check

Max VOC
TOO HIGH
MARGINAL
(HyperVOC)
OK

Temperature The Classic Will
Enter HyperVOC
ALWAYS
28.4 F°
-121 F°

Array Power (Wattage)
OK
OK
OK

Classics Required
0.6
0.7
0.8

NOTE: MidNite Solar recommends a second controller be added after 1.2

... continuted on next post:

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

input: 3 series panels x 3 parallel strings:

PV Array

Rated PV Array Power:
2835
Watts

Anticipated Array Power @ 104F:
2644
Watts

Rated PV Array Current:
25.89
Amps

Battery Charging Current @ 57.6 V:
49.2
Amps

VMP (Maximum Power Point Voltage) :
110.4
Volts

VOC (Open Circuit Voltage):
137.7
Volts

VMP @ -22 F°:
137.7
Volts

VOC @ -22 F°:
162.6
Volts

Classic & Classic Lite Charge Controller Selection

150
200
250

Max Operating Voltage
150
200
250

Max Non operating VOC (HyperVOC) @ 48V Nominal Battery Voltage
198
248
298

Maximum Number Of Modules In Series
2
3
4

Max Number Of Modules In Series (Using HyperVOC)
3
4
5

Max Allowable Output Current Per Classic
Based On This Current Configuration
86
70
55

Max Allowable Wattage Per Classic
Based On This Current Configuration
5022
4080
3212

Present PV Array Wattage Of This Configuration
2520
2520
2520

Design Check

Max VOC
OK
OK
OK

Temperature The Classic Will
Enter HyperVOC
-268.6 F°
-565.6 F°
-862.6 F°

Array Power (Wattage)
OK
OK
OK

Classics Required
0.6
0.7
0.8

-Bill

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

And 2 series x 4 parallel strings:

PV Array

Rated PV Array Power:
2520
Watts

Anticipated Array Power @ 104F:
2350
Watts

Rated PV Array Current:
34.52
Amps

Battery Charging Current @ 57.6 V:
43.8
Amps

VMP (Maximum Power Point Voltage) :
73.6
Volts

VOC (Open Circuit Voltage):
91.8
Volts

VMP @ -22 F°:
91.8
Volts

VOC @ -22 F°:
108.4
Volts

Classic & Classic Lite Charge Controller Selection

150
200
250

Max Operating Voltage
150
200
250

Max Non operating VOC (HyperVOC) @ 48V Nominal Battery Voltage
198
248
298

Maximum Number Of Modules In Series
2
3
4

Max Number Of Modules In Series (Using HyperVOC)
3
4
5

Max Allowable Output Current Per Classic
Based On This Current Configuration
86
70
55

Max Allowable Wattage Per Classic
Based On This Current Configuration
5022
4080
3212

Present PV Array Wattage Of This Configuration
2520
2520
2520

Design Check

Max VOC
OK
OK
OK

Temperature The Classic Will
Enter HyperVOC
-268.6 F°
-565.6 F°
-862.6 F°

Array Power (Wattage)
OK
OK
OK

Classics Required
0.6
0.7
0.8

NOTE: MidNite Solar recommends a second controller be added after 1.2
WARNING: MidNite Solar makes no representation, warranty or assumption of liability regarding the use of the String Calculator. This tool uses data provided by other parties (such as PV module specs) and makes calculations based on assumptions which may or may not prove to be valid.

-Bill

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

AM, that panel could qualify as a "24V" panel even though the specs are a little higher than normal... a 12V NOMINAL panel will put out ~ 17 - 18V Vmp~ 21 - 22V Voc and Imp of ~7 -8A.. 24 = double and 48 = 4 X those numbers..

Please do not plan for voltage at the upper end of the range especially if you will be in colder climes as the VMP can easily exceed the CC's limits, there is a factor listed on the name plate on hoe to determine the effect of colder temps and most good Array sizing programs ask for that factor..

Electronics last longer if not constantly being maxed out... Use the manufacturers calculator!

Down converting, the closer that the PV voltage presented to the CC is to the battery bank the less losses in down converting...

The advantage of putting PVs in series is higher voltage that needs to be sent long distances, read hundreds of feet...

hth

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Ok Thanks!

If I'm reading that correctly, I need to use 2 series X 4 (with 8 panels total) and a 150v max.

I really didn't know how "real" these numbers were and without knowing better presumed that the voltage goes up with higher solar input, meaning that if I could series more panels, that I'd have a workable charge voltage for more hours of the day.

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

This can be an issue with higher voltage Vmp panels... 2 panels are just at the bottom end of being acceptable (Vmp-hot) for your 48 volt battery bank, and just about too high of Voc-cold with 3 panels in series.

If you can find Vmp~30 volt panels instead (for a good price), then 3 of those in series give you a higher Vmp-array voltage that gives you higher voltage and lower current for your array--And can allow you to use a smaller diameter copper wire and/or go longer distances from the array to the charge controller.

One of the problems with low voltage/high current arrays is that you need very heavy gauge (and expensive) copper cables to go longer distances.

So--In your case, the panels are mounted directly to the top of your hauler, and the charge controller is probably 10 feet away (roughly) (one way run).

4x Imp = 4x 8.6 amps = 34.4 amps total Imip-array
2x Vmp = 2x 36.8 volts = 73.6 volts Vmp-array
1% drop = 0.74 volts
3% drop = 2.2 volts

Using a generic voltage drop calculator:

10 AWG:
Voltage drop: 0.69
Voltage drop percentage: 0.94%
Voltage at the end: 72.91

14 AWG:
Voltage drop: 1.74
Voltage drop percentage: 2.36%
Voltage at the end: 71.86

So, for very short runs--The voltage drop is not a big issue. And for the wire rating:

4x Isc = 4x 9.16 amps = 36.64 amps short circuit current

So using NEC table 301.16, you would need around 10-8 AWG wire minimum (depending on wire type and conduit fill, etc.).

Any way, that is the basics of how to pick array configuration and wire requirements... There is a lot more detail to go in the design process--But this is how to go from a paper design to actual hardware.

-Bill

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

BB. wrote: »

This can be an issue with higher voltage Vmp panels... 2 panels are just at the bottom end of being acceptable (Vmp-hot) for your 48 volt battery bank, and just about too high of Voc-cold with 3 panels in series.

-Bill

Ugh. I was afraid of that.

So if I went 4 in series, I couldn't go out on cold days or at high altitudes without risking my controller...

But if I go two in series x 2, then I don't charge my batt's on hot days at low altitude...

But if I go 3 in series, I can't make full use of my roof real estate (ending up with only 6 panels).

Is that what I'm hearing?

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

You are looking at Midnite's Classic 150... The cold temperatures and hi Voc-cold voltages will not damage your charge controller (basically, over ~150 Volts from the panel, the controller will shut down and be safe to 150v+Battery Voltage (i.e,. 150+48=198 volts)--As I understand.

So, once the sun hits the panels, the will warm up and the controller wills start generating current. Basically, the cells warm to >29F. And the panels really do not produce very much current until there is substantial sunlight (and warming).

However, you can look around for Vmp~30 volt panels, aka 60 Cell panels--These are very common too--You may be able to find other combinations of these panels to fit your roof.

-Bill

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

By the way, we are "focused" on the Classic 150... There is the 200 and 250 too. The 200 is the same price as the 150, and the 250 is $72 more.

Since there is no room to add more panels, a higher voltage controller will still carry the output of all the panels you can fit to your RV. The fact that they have lower rated output current does not really matter to you here (the higher voltage are slightly less efficient--I would guess, but should not be enough to really worry).

That should fix your high voltage in cold weather issue.

-Bill

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Thanks Bill.

I already own the Xantrex MPPT60-150 as I purchased it used along with the XW6048.

They do make a larger charge controller, but it's also larger in size (which is at a premium in an RV), and would also entail selling and purchasing a different charge controller.

So, If I'm getting what you're saying, this Voc-cold is an environmental condition (cold temps, lots of sun input?), and that if I encountered that environment, then the MPPT60 would simply go into safe mode until the conditions changed? Trust but verify...I know, but that would be workable for me. I don't plan on spending much time camping at high altitude, and even if I did, couldn't I just park in the shade or partially cover the panels to get around it?

As long as it's safe and occasional, my larger concern is not making the required voltage to charge or equalize the bank under more normal conditions. I live in Oregon where we have a lot of overcast days, and traveling will be to mostly sea level areas of the country (including deserts like those you'd find in the south).

My choice of approximately 66 or 78" X 40" panels (72 cell) really had to do with availability and the fact that just by chance, I can neatly fill that area you see in the photo below (and have the most wattage output from the space available)

Perhaps I'm misunderstanding some concepts and terms which I should have placed in the "Solar Beginners" forum, but is it true that if I series panels right up to the maximum voltage, that I will be able to harvest useable (to my 48v charger) energy earlier and later in the day? I guess I need to get a handle on that first because if that's true, than I think I'd rather have the system harvesting at maximum in what would be 95% of the conditions I'd actually ever be in, and shut down at solar noon on that mountain trip.

On top of this, I keep reading that PV's normally only produce their rated output to something in the mid-70%, which looks like it would put me back in the game doing 4 series x 2 parallel strings?

Again... as we both know, this is an RV, so if the high volt alarm is going off, I supposed I could pull under a tree in that rare occasion if a rare occasion is what it would really be in reality.

Edited to include that after reading the manual for MPPT60 that it does state that the Voc must *never* be over 150v under *any* conditions. It specifies that it *will* shut down, but also has an equipment damage warning. (ok, that's kinda vague).

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

the Xantrex MPPT60-150 does not as far as I know have the 'Hyper Voltage' safety feature, only the Classic line.

Can you fit 9 panels? 3 x 3?

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Audiomaker wrote: »

Thanks Bill.

I already own the Xantrex MPPT60-150 as I purchased it used along with the XW6048.

They do make a larger charge controller, but it's also larger in size (which is at a premium in an RV), and would also entail selling and purchasing a different charge controller.

Sorry--Got lost in the details. Schneider does make a string tool you can download and do similar calculations (as I understand--Their String Tool has been MIA for a while).

So, If I'm getting what you're saying, this Voc-cold is an environmental condition (cold temps, lots of sun input?), and that if I encountered that environment, then the MPPT60 would simply go into safe mode until the conditions changed? Trust but verify...I know, but that would be workable for me. I don't plan on spending much time camping at high altitude, and even if I did, couldn't I just park in the shade or partially cover the panels to get around it?

The amount of sun does not matter--Any sun/sky scatter that is enough to bring Voc-cold up over Vmax input for the controller is the problem. I believe the input limitations are based on the FETs (switching transistors) and input filter caps. Any voltage exceeding the limits can ruin those parts (very little current required).

Midnite is the controller with Hyber Voc function/design (Vmax+Vbatt as safety limit). No other controller has that--As far as I know.

As long as it's safe and occasional, my larger concern is not making the required voltage to charge or equalize the bank under more normal conditions. I live in Oregon where we have a lot of overcast days, and traveling will be to mostly sea level areas of the country (including deserts like those you'd find in the south).

So--No, your standard 60 amp Schneider would not work in this application as it may sustain damage (and probably logged in the controller as a warranty disqualification).

Schneider does make a 600 VDC limit input controller that may work (put all panels in series). Need to check the specifications/use the string sizing tool to be sure. The 600 volt controller is way more expensive:

Conext XW MPPT 80 Amp 600VDC Solar Charge Controller

My choice of approximately 66 or 78" X 40" panels (72 cell) really had to do with availability and the fact that just by chance, I can neatly fill that area you see in the photo below (and have the most wattage output from the space available)

Yep--Fitting panels in a tight space can be a real pain.

Perhaps I'm misunderstanding some concepts and terms which I should have placed in the "Solar Beginners" forum, but is it true that if I series panels right up to the maximum voltage, that I will be able to harvest useable (to my 48v charger) energy earlier and later in the day? I guess I need to get a handle on that first because if that's true, than I think I'd rather have the system harvesting at maximum in what would be 95% of the conditions I'd actually ever be in, and shut down at solar noon on that mountain trip.

No--There is no advantage in power collection by having a higher Vmp-array voltage configuration (other than less current, less copper in wire back to controller).

Basically, a solar panel will not output any useful current until there is weak direct sun on the panel (i.e., enough to cast a shadow). You can get some power (a hand full of watts) from back scatter from the sky. And it does not really matter if the Vmp-array is near the bottom of the Vmp range of the controller or near the top--Similar power collection will result.

The thing that can cause sigificant losses is very high Vmp-array and a 12 volt battery bank. Not all vendors list the Vmp-array vs battery bank voltage, but MorningStar (or example) MPPT TS controller will run from 97% efficiency with low Vmp-array relative to battery voltage and down towards 92% for high Vmp/low voltage battery bank.

On top of this, I keep reading that PV's normally only produce their rated output to something in the mid-70%, which looks like it would put me back in the game doing 4 series x 2 parallel strings?

We use 77% as a derating for solar panels+charge controller losses. For MPPT type charge controllers it is because Vmp-array falls as the array cells get hot in full sun. Much hotter than the ~75F that the panel name plate wattage/Vmp is rated at (call it ~81% of factoring Vmp rating durign summer and some dust on the panels). And allows for ~95% MPPT efficiency.

During cold weather/winter, you can get better (or even much better)--And of course high altitude help too.

Again... as we both know, this is an RV, so if the high volt alarm is going off, I supposed I could pull under a tree in that rare occasion if a rare occasion is what it would really be in reality.

No--Won't work. Takes Microseconds for the damage to be done to the electronics. With electronics, never exceed their design ratings/specifications. There is rarely a lot of wiggle room in the specifications.

-Bill

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

I don't believe I can fit 9 panels without overhanging fore or aft.

I'm a bit aggravated that this MPPT60-150 is right outside the border on what is safe. The next step up from Xantrex (MPPT80-600) would easily handle it, but it's big.

I think my solution is going to be this...

Purchase 8 of these: http://www.solarworld-usa.com/~/media/www/files/datasheets/sunmodule-pro-series/sunmodule-pro-series-solar-panel-xl-320-mono-33mm-frame-ds.pdf

I will go ahead and wire for 2 series X 4 parallel and hope that the higher voltage ratings (45 open circuit) help it produce usable charging currents at lower light than the 60 cell (37v open circuit) panels would.

I'll just keep an eye out on eBay for a used MPPT80-600 which would allow me to re-wire those same panels 4 series X 2 Parallel (or even 8 series).

Maybe I'll luck out and it will be more than I need in the first configuration (and safe for the controller).

Thoughts?

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

I'll just keep an eye out on eBay for a used MPPT80-600 which would allow me to re-wire those same panels 4 series X 2 Parallel

Or sell the one you have and get a Classic 150 or 200

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Audiomaker wrote: »

I will go ahead and wire for 2 series X 4 parallel and hope that the higher voltage ratings (45 open circuit) help it produce usable charging currents at lower light than the 60 cell (37v open circuit) panels would.

That should be fine. In my humble opinion, don't worry about low light. On a 2kWatt array, will it make much difference if you get 20 watts vs 10 watts early morning/late evening for an extra 20 minutes (made up numbers)? Not enough to spend much extra time/money to achieve such results (in my humble opinion).

I'll just keep an eye out on eBay for a used MPPT80-600 which would allow me to re-wire those same panels 4 series X 2 Parallel (or even 8 series).

I think it would be 8 series only--4 would not be high enough voltage to turn on the controller (I think). Your only advantage with this configuration--On the floor of Death Valley with a cold battery bank (low Vmp-array, cold battery below freezing needing higher Vmp-array for full charging current). Not likely to happen very often.,

Maybe I'll luck out and it will be more than I need in the first configuration (and safe for the controller).

You should be fine. It is unlikely it would be worth stripping off the old panels and MPPT controller to get those extra few watts vs just running a cup of fuel through a small genset a hand full of times a year.

-Bill

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

BB. wrote: »

Bill writes...
No--There is no advantage in power collection by having a higher Vmp-array voltage configuration (other than less current, less copper in wire back to controller).

-Bill

Of course you understand that this is a hard concept to wrap one's head around when you have a non-solar based working electrical knowledge.

My way (and supposedly the wrong) way of thinking is that a panel that supplies a higher voltage per sq ft is able to make the nominal voltage with a lower amount of sun energy vs the lower voltage panel.

Put another way, that the higher voltage panel will trigger the minimum required by the CC' earlier and later in the day (even if only by a percentage of hours), or that it might produce that minimum voltage on slightly more overcast days.

You can understand why I would think that right?

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

PV's are a different animal as the voltage comes first , early morning and no AMPS.... then the amps come, it is that high Voltage that is the problem..
I will let BB deal with the why of your position.. he has the electrical engineering background...

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

westbranch wrote: »

PV's are a different animal as the voltage comes first , early morning and no AMPS.... then the amps come, it is that high Voltage that is the problem..
I will let BB deal with the why of your position.. he has the electrical engineering background...

I'm sure I'll learn "why" in time. My house burned to the ground the day before New Year's and I'm now living in this RV until further notice, so my goals are very much time constrained.

To answer your earlier question, I am sticking with the Xantrex (Schneider) products because they all communicate and are configurable via it's System Control Panel. I'm too much of a newbie to start mixing brands at this point.

You guys have been a HUGE help here. It's so much more useful to gather people's real world knowledge than to look at a PV sizing chart...etc.

When you're diving in, and drilling holes, it's all attached to a wallet at some point and confidence is everything.

I think I have a workable solution, and there's real cash on the line (which is in short supply for me).

gww1 · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Put another way, that the higher voltage panel will trigger the minimum required by the CC' earlier and later in the day (even if only by a percentage of hours), or that it might produce that minimum voltage on slightly more overcast days.

It might produce the requred voltage before it even sees light but won't help if it produces no amps to go with it. Mine on cold days will show 90 volts and the cc will still be sleeping due to low light.

Once you start getting enough amps the voltage goes down ergo the term voc which is basically voltage not under load.
gww
gww

gww1 · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

The zantrax is more expencive and has its own draw backs. Having to convert from a higher voltage down to the battery and shade in one little area affecting all the panels outputs.
gww

BB. · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Yes... But it is because we are not used to how solar panels work.

Batteries--We understand. The idea battery holds 12 volts and outputs zero to full rated current--And at that point, the output voltage collapses (over current, battery dead, etc.).

Solar panels are current sources.... The output current is proportional to the amount of sunlight hitting the panels. 1% sun light, 1% of Imp. 50% light, 50% of Imp, 100% of light, 100% of Imp (more or less).

So the panel will output (for example) 5 amps from zero volts to Vmp (at a fixed temperature). Above Vmp to Voc, current falls dramatically to zero amps.

At low light levels, the panel does have internal leakage current (solar panels are just giant diodes). And don't really produce useful output current until Vmp is reached (the low sun light is consumed by internal leakage current).

It is sort of like a car engine... The engine consumes a certain amount of fuel just because it is turned on and running. If you try to move the car at any speed, the engine will stall unless you supply more gas/air for more power.

Also, another analogy--Think of a MPPT controller as being an automatic transmission (or even gears on a bicycle)... The output (torque to the wheels at X RPM) is fixed for your needs--The input RPM/Torque can be "optimized" by using a transmission. First gear, high RPM/low torque from the engine. 5th gear, low RPM/High Torque from the engine--And you are still moving at 25 MPH in both cases.

Power = Voltage * Current...

For an MPPT controller Voltage is Vmp -- And Current is the amount of sunlight. Yes, you can run at 1/2 Vmp (maybe, if controller/array configuration allows it)--But there is almost no difference in current (made up numbers--but probably close to real world):

72 Volts Vmp * 0.1 amps = 7.2 watts
36 Volts Vmp * 0.12 amps = 4.32 watts

So, even if you got slightly more amps at much lower array voltage--The actual power gain may be minimal or even negative.

I have watched my MPPT based 3 kW GT solar charge controller--The array voltage is already at Vmp-array well before the GT inverter can output any useful energy to the grid--The first 20-40 watts or so is consumed by the MPPT controller's electronics.

All MPPT type charge controllers have significant "tare losses" (energy used just because the "electronics" are "turned on"). I do not believe you will see any advantage to trying to figure out how to harvest energy early AM or late PM (or during heavy cloud cover)--At best you are looking at a couple of percentage points of improvement from worst case to best case.

And, remember that there are other loss mechanisms... Remember that running 96 volts into a MorningStar MPPT TS controller will give you ~92% efficniecy into a 12 volt battery bank. Run the same thing down towards 18 volts Vmp, and you are looking at >96% efficiency.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/150V-TS-MPPT-Operators-Manual.pdf (page 61)

4% spread in Vmp-array * 500 watts = 20 Watts "lost" to higher voltage array

Not saying there is anything wrong with the MorningStar MPPT controller (it is a very good controller)--It is just the nature of the beast. Stray capacitance in the high voltage FETs is the physics of the design.

So, to get 20 watts early/late in the day for a fraction of an hour--Costs you 20 watts for many hours during the day. "Penny wise, pound foolish" comes to mind here.

Rarely does it make sense to skew a design towards one extreme or the other. Trying to optimize one small corner of the operating range de-optimizes (is that a word?) another operating corner.

Sort of makes sense?

-Bill

Ethan Brush · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Another reason to stick with the Schneider controller for your application is it has no cooling fan. Many/most controllers would (IMO) be super annoying in a small space like an RV or tiny house. The noise issue is often overlooked, although you have other stuff that has fans so maybe its not an issue.

westbranch · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

I am sticking with the Xantrex (Schneider) products because they all communicate and are configurable via it's System Control Panel.

I know you are going at this asap but , as GWW1 indicated a search here on the model you decide on may inform you on some of the peculiarity of different "X" products and follow up support and customer service....

Audiomaker · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Bill, yes that makes complete sense and I can see why there's no point to OCD about it.

I just had to check, because a purchase will follow soon. I really thank you.

Ethan, the only thing that has a fan is the XW6048 and I have yet to have that come on in my 10 days of owning it. Judging from my power requirements, and the bank I am able to fit in the RV, I think it will be a rare occasion that I pull enough to kick the fans on because I think I'd be out of bank before the inverter reached temperature, so yes... it's nice that the MPPT60 doesn't add one.

I only have one more question at this time...

Because I will have 8 wires coming from the solar array (2 panels series X 4 parallel), is there a way to do this paralleling without a combiner box at the panels so I only have 2 wires off the array to the controller?

inetdog · January 2015

Re: Could you help a solar newbie with a panel choice and setup?

Audiomaker wrote: »

I only have one more question at this time...

Because I will have 8 wires coming from the solar array (2 panels series X 4 parallel), is there a way to do this paralleling without a combiner box at the panels so I only have 2 wires off the array to the controller?

Whenever you parallel more than two strings of panels you are required to have a fuse (or circuit breaker) in each separate string. This is to protect the panels if there is a malfunction. If you can find suitable inline fuse holders you can do the splicing inside a simple junction box instead of an official combiner.
But do not try to get by without fuses.

Could you help a solar newbie with a panel choice and setup?

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