Choices for 2kw Solar on a RV

TooTall

Hello

Thank you for the great information that you post.

Been lurking here for a while and I'm getting ready to purchase a solar system. I've worked with AC/DC power allot but not solar.

-  It is a stand alone system
-  2kw is a large system for a RV.
-  The primary purpose of the system is to reduced generator time needed to charge batteries in the winter with temps down to 0F.
-  RV furnace typically draw 6-8 amps. 
-  Open wet cell batteries (to start with) are 8 - 6V golf cart. These will be series/parallel = 12V ...OR....series = 48v 
-  Battery temps are never below 32F
-  12v or 48v Inverter/charger

- Shading will be a issue depending on where the RV is parked so there is an advantages to having the panels in parallel.

- Fuses/ breakers in a roof top combiner
- Wire gauge between combiner and controller will be 3x required, probably in conduit
- Over 50VDC is considered hazardous. On layouts 1,2 and 3 I'm considering a remote operated disconnect (rapid shutdown?) for the array.  

Several layouts were done using different panels. The 150w-280w panels were taken off the list as there was no room left to service (remove snow) the panels.

The layouts are composed of 6 of the same size (+/- 39" x +/- 64") 300W- 330W panels. This yields the highest number of watts while still leaving room to move around on the roof. The down side will be the shade loss on a 300W or 600w string.

Layout 1
330W Panasonic
ftp://ftp.panasonic.com/solar/specsheet/n325330-spec-sheet.pdf
 - 2 in series,  3 strings
- Voc = 140VDC x 1.2 = +/-168VDC cold morning wake up
- Midnight Solar Classic 200
- 48VDC battery bank
- This will requires two or  three 48VDC to 12VDC converters

Layout 2
- 330W Panasonic
- Panels in parallel
-  Voc = 70VDC x 1.2 = +/- 84VDC cold morning wake up
-  Midnight Solar Classic 200
- 12VDC battery bank

Layout 3 - 180w less than Panasonic
- 300w SolarWorld
https://www.solar-electric.com/lib/wind-sun/sunmodule-plus-sw-290-300-mono-solar-datasheet.pdf
- 2 in series - 3 strings
- Voc = 80VDC x 1.2 = +/- 96VDC cold morning wake up
- Midnight Solar Classic 200
- 48VDC battery bank
- This will requires two or  three 48VDC to 12VDC converters

Layout 2 - 180w less than Panasonic
- 300W SolarWorld
- Panels in parallel
-  Voc = 40VDC x 1.2 = +/- 48VDC cold morning wake up
- 12VDC battery bank
- Midnight Solar Classic 150

Vic

Hi Too Tall,  Welcome to the Forum.

On Layout 3,  there may be  a typo  --  that configuration should NOT need a Classic 200,   BUT,  the Vmp is really too low for 48 V Flooded batteries,   and probably too low even for cool AGMs.  The customary recommendation for most MPPT Charge Controllers (CCs),   and Classics in particular,   is for the string Vmp to be no less that about 1.3 times the highest battery voltage the system will ever experience.  This is important to allow the CC to find a productive MPP,   and allow EQing cool batteries.

Strings of three SW 300s  would be fine,  but perhaps that is where the Classic 200 came from,  in earlier calculations ...   I have not run Layout 3 through the MidNite String Sizer:
http://midnitesolar.com/sizingTool/displaySizing.php

Just a drive-by comment,   FWIW,   Vic

Estragon

A few thoughts,

- a 70v string with 48v bank can be an issue as hot panels may not give high enough voltage for EQing.
- putting smaller strings in parallel makes sense for expected partial shading. You shouldn't need long wire runs, so the extra cost of heavier wire is not a big issue.
- using a DC/DC downconverter for 12v loads isn't ideal as a potential failure mode apparently can expose the loads to the higher voltage. As with the panel wiring, running heavier wire shouldn't be prohibitive, and presumably the RV is already wired for 12v distibution anyway.

Unless you have large loads (like a big inverter), going with 12v bank looks to make the most sense.

The classic 150 can handle up to 162v with a 12v bank, so the extra cost and slightly lower efficiency for the 200 isn't needed except for layout 1. On a 12v bank, you could the panels all in parallel with no serial strings if you wanted.

The main downside to 12v bank is you would have four stings of batteries in parallel. Ideally it would be better to go with fewer, bigger batteries. 2 strings of L16 size would be similar capacity if you have room for them.

BB.

What voltage and AH battery bank are you looking at?

What average/peak loads from battery?

More or less, a 2kw array and/or peak load works out with 200 AH @ 48v, 400 AH @ 24 volts, or 800 AH 12 volts.

As an RV starting point.

-Bill

littleharbor2

You're going to need 2 classic 150 controllers to handle 2000 watts @ 12 volts

BB.

Another thing to think about... Fans in charge controllers and a.c. inverters.

Mounting on a living area, using fan less devices may be very nice (charge controllers during day, inverters at night).

- Bill

TooTall

Heck....you people are great, fast too....was thinking I'd check back in a day to see if there was a response

VIC
The Classic 200 and the 150 are the same cost so so I've been trading them back and forth not really paying attention to the difference between the two. 

-  What is the lowest VMP that can be used to bulk (lets say AGM) charger 48V? 

-  Want to stay away from stings of 3 for shading issues


Estragon:
- Yes I'm not concerns about some extra $$ for larger wire runs.....time to lay either is the same probaly use conduit. I hate seeing loose wires lying around.  

- The 12v hyd pumps x 4 for the leveling jack can draw 60amp DC ea. Have to test to find the actual draw.

- I read that about the DC-DC converters but haven't found out if it is true of all converters....Law requires the trailer to have a battery  to activate the brakes in case of emergency. Plan (can't remember which one) B, C or D would be to use Group 31 to run the trailer.  

- At some point we'll install a 3kw inverter. I've worked on enough 12VDC to know I don't like 4/0. Smaller wire for 48VDC is what makes it appealing. 

- Agree on the battery connection layout but I already have 4 - golf carts. Was gong to buy 4 more.  My crystal ball tells me I have Lithium in the future but I figure it will be cheaper learning how not to wreck a set of batteries charging off solar than it will Lithium. 


BB
We are currently at (4x6V) 440AH an will double that to (8x6V) 880AH
The system will be built at the front of the trailer away from the living area.


Little harbour2
Yes, money either goes to a:
1.)12VDC bank that needs a 2nd controller
2.) 48VDC that needs DC-DC convert(s) and a battery for E brakes in trailer


I do have room to add 4  smaller 150W at the front of the trailer but I think I'll make these 18V with a PWM controller.

BB.

Generally, the standard minimum/maximum  Vmp-array (standard name platevoltage) voltage for pwm charge controllers is

12v...17.5/19 volts Vmp

24v...35/38 Vmp

48v...70/76 Vmp

-Bill

mike95490

Wire for 48V and use a small Morningstar MPPT controller as a charge controller off the 48V bank, to maintain the 12V trailer brake battery. (Morningstar has a white paper describing this, other controllers can burn up doing this)   Avoid parallel batteries.

Also, the Classic has 3 pretty noisy fans inside it, they kick on about 900W in my system, I'd suggest the Morningstar MPPT 60,

For charging 12V batteries, 60V is the highest panel voltage I would try to use, 30V would be better, MPPT conversion gets lossy the further (higher)  the voltage gets from the battery voltage.  48V battery, I'd use 90V array min.

TooTall

I'd have to call Morningstar to confirm but this looks like the MPPT charger you are referring to.

https://2n1s7w3qw84d2ysnx3ia2bct-wpengine.netdna-ssl.com/wp-content/uploads/2014/02/SSMPPT_ENG10_1111.pdf

Maybe have 2 in parallel

There are these as well but I'd be worried about what Estragon bought up about the 48VDC passing through to the 12VDC side

https://www.amazon.com/uxcell-Step-Down-Waterproof-Converter-Transformer/dp/B01ENGOA4S

Vic

Too Tall,

The MidNite Classics do have fans  --  two inside which are fairly quiet,  and one external,  that generally runs infrequently,   but is fairly noisy.

Of course,   the primary thing that gives the Classics considerably more output current than fanless CCs is just that --  the fan/s.   But for installations in bedrooms,  perhaps using CCs a fanless CC would be best.

The Morningstar CCs are really naked.  Almost anything that one would expect on a good MPPT CC is MISSING on them,    and,   if available,   are extra cost on Morningstar CCs.   They are a fairly good CC,   but just be prepared to pay extra for almost anything that is standard on the Classics.

The Morningstar use 1960's-era  DIP switches,   and have generally crude,   inflexible  Absorb/Float voltage options from those switches.   You can use their software on a computer for better customization,   but,  you need the computer to be available make even the slightest changes in those settings ...   need an Aux output for some control function (?),   on the Morningstar,   that is only about a $200 option,  including some shipping.

The Classic 150,  and 200  are not identical.   There is a COST for the higher input voltage capability of the Cl 200.   That cost,   is a bit of reduction in the efficiency,   and a reduction in maximum output current capability for the 200.   This results in more heating in the Cl 200,   even it the PV input voltage is in the range that the 150 could handle.  So,  one should specify the Classic 150,  unless one needs to USE the higher input capability of the Classic 200.

But,  you are asking good questions,   and are being analytical.

FWIW,   some opinions,    Vic

Estragon

The plan to install a 3kw inverter at some point does change things some. That's a big inverter to run at 12v. Also, mixing new and old batteries in a bank could be a problem.

It might help if we had a better understanding of loads. For example, what kind of loads would run on the inverter, and at what time of day?

Vic

Well,   there are many tradeoffs,   as you know ...   perhaps a 24 V system with strings of two PVs ...

Four strings of parallel batteries in your 12 v system,  also pushes one's ability to keep them balanced,   particularly  if the battery ages differ by very many months (as Estragon noted).

Get the Dart Board!   Kidding.    Good Luck,    Vic

Marc Kurth

From your original post:
" The primary purpose of the system is to reduced generator time needed to charge batteries in the winter with temps down to 0F"

Depending upon the size of your genset, and how long you run it for other purposes anyway..... A high output battery charger might be a smart move. I have many customers who never run their generator for battery charging only. They have BIG charging capacity on board to use generator run time more effectively.

Remember that some types of batteries can be charged more quickly than others.

I do not know what equipment you have, nor what your usage patterns are - so the approach may not apply. Just food for thought in planning your upgrades.

Marc

Raj174

@TooTall
You might be able to use a 12 volt 250 amp hour AGM battery for the leveling jacks if they don't have to run for too long, if not then maybe two 200 AH AGMs. A 15 to 30 amp hour MPPT charge controller could be installed to step the voltage down from 48 to 12 volts and charge the battery. 

You might also consider a Morningstar Tristar 60 PWM charge controller. (No Cooling Fan)
https://www.solar-electric.com/tr60amp12244.html?gclid=EAIaIQobChMI0LXd_fLk1QIVk4uzCh1RGAKAEAQYAyABEgImh_D_BwE

It will handle up to 12 190 watt mono crystalline solar panels, wired 2 in series. 
https://www.solar-electric.com/solarland-slp190s-24-190-watt-24-volt-solar-panel.html 

Rick

TooTall

VIC
- The electrical panel will be at the front of the trailer under the bedroom. I'm thinking the fans won't be an issue at night??
- A couple sites I've check have the CL50 and the CL200 at the same price.
- I played around with the Classic sting sizing again

5 - 330w (58VMP) panels in parallel into 12VDC will work for one CL150 
   Pros:
       1.) 12 volts make the battery monitoring easier. 
       2.) A 2nd CL150 allows combiner boxes at the front and back of the trailer for up to 5 more panels 
       3.) Don't need DC-DC...one less thing to break down....KISS
       4.) Most of the DC marine electric is rated up to 32VDC not 48VDC
       5.) Continue to use 2-50amp  ProNautic chargers
       6.) Continue to use the Progressive Dynamics 55amp converter 
       7.) Continue to used the 300W Go power inverter for movie nights with the kids
      
Cons
1) 4/0 wire and massive fuses for an inverter  .....other than this no other loads require more than 1 ga.
2) Batteries in parallel is not the best practice.......does this apply to Lithium?


Anything  missed?

12V pro = 7
12V con = 2

I glued the dart board to my forehead. Take a shot


Estragon
     The inverter would be for convenience only.  We try to use the trailer to sleep in only.  It changes with the shorter days in winter but we still don't use much 110VAC. The big use I see for the inverter is popcorn on movie nights.
      Mixing batteries is not the best. The batteries are less than 1 year old. I suspect I'll kill them learning before they wear out from charge cycles.

Many people with RVs are swapping out propane refrigerators and installing residential refrigerators and adding 1.0kw-1.3kw solar. We may install a small 110V fridge in the front storage compartment but I don't see it being big power draw in the winter.


Marc Kurth
    Our combined 110VAC is limited to battery charging and TV/Blueray.  We have 2 -50amp ProNautic + the PD 55 amp converter. A Honda3000 and 2- Honda2000. Bulk charging 440Ah using 2 x 50 amp doesn't do the batteries any good and the absorption adds allot of idle hours on the generator(s).  Lithium would solve the charge rate issue but that is in the future.

mike95490

I would trust the SUNSAVER MPPT wired into the battery, with proper fuses, it's unlikely to die.  But I see it's max voltage is 60V.  I thought it used to be 75v   60v is too low to use with a 48V bank, which can EQ at 64V

You can size your battery box to carry 2V or 4V batteries, to get in a single string, the amp hours you need

https://www.solar-electric.com/residential/batteries-battery-storage/deep-cycle-batteries.html?nav_battery_voltage=4+Volts

littleharbor2

TooTall said:

- A couple sites I've check have the CL50 and the CL200 at the same price.
- I played around with the Classic sting sizing again

Check out the Classic SL (solar only) or Classic Lite (no MNGP, graphics panel).
I've seen The SL version for under $500.00 at times.

Marc Kurth

Now I am wondering what your daily electrical load profile looks like?

Estragon

> @Marc Kurth said:
> Now I am wondering what your daily electrical load profile looks like?

Me too. If the only big AC load is making popcorn on movie night, a 3kw inverter is overkill. Going with a smaller inverter makes 12v likely the better solution.

TooTall

Estragon said:

> @Marc Kurth said:
> Now I am wondering what your daily electrical load profile looks like?

Me too. If the only big AC load is making popcorn on movie night, a 3kw inverter is overkill. Going with a smaller inverter makes 12v likely the better solution.

Sorry guys I should have said inverter charger....(Victron?)  Bigger the inverter the bigger charger which wouldn't go in until the LiPo4 comes along. That won't happen until I figure our what 2Kw of solar will do for us in the winter

littleharbor2 said:

Check out the Classic SL (solar only) or Classic Lite (no MNGP, graphics panel).

I've seen The SL version for under $500.00 at times.

Budget is important but on this project it is not the most important factor. Adaptability would be the most important.

TooTall

I have what I think is a stupid question......can 4 equal 12VDC feeds be taken off a 48VDC battery bank.  I've pulled 12VDC off 24VDC but at the time I didn't care what it did to the batteries.

BB.

In theory, yes, 4 equal 12 volt feeds from a 48 volt battery bank will work fine. If the feeds are equal current/time of operation/etc.

Regarding 2,000 watts of solar panels... Obviously, where you will be camping (and getting full sun) has a lot to do with how much energy you can get from them. But, this can give you some ideas.

Assuming fixed array that can be tilted depending on location (latitude) and season, you can expect something like:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Vancouver
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface (typical RV roof mount):

Jan	Feb	Mar	Apr	May	Jun
1.09	2.00	3.10	4.51	5.39	5.69
Jul	Aug	Sep	Oct	Nov	Dec
6.00	5.15	3.92	2.14	1.27	0.90

Vancouver
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 26° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
1.94	3.05	3.70	4.35	4.32	4.28
Jul	Aug	Sep	Oct	Nov	Dec
4.59	4.64	4.46	3.02	2.17	1.70

A 2,000 Watt array in December, both flat to roof and 64 degrees from horizontal in Vancouver Canada would give you:

• 2,000 Watts * 0.52 off grid system eff * 0.90 hours of sun (flat, December) = 936 Watt*Hours per day
  
• 2,000 Watts * 0.52 off grid system eff * 1.70 hours of sun (near vertical, December) = 1,768 Watt*Hours per day
  

Of course, this all depends on where you will be camping (location) and if you will have an array that can be tilted depending on season (a 2,000 watt array is not small, making a tilt mount on an RV is not easy--plus it has to withstand the wind when going down the highway). And you may want to tilt the array flat if you are in areas of high wind when camping (big sail).

In the far north, with poor weather (if coastal/marine layer camping) in winter--There just is not a lot of sun. And you need sun to make solar power (I would not even suggest looking at a wind turbine).

A Honda eu2000i will give you about 3,600 Watt*Hours per gallon of gasoline (assuming a 400 watt load and 9 hours per gallon). Or about 2-4 days of equivalent sun per gallon of gasoline. Solar in winter to avoid fuel usage/costs--May be difficult to justify.

-Bill

Estragon

If the main idea behind a big inverter is to get a big charger, it may be worth considering separate units?

Photowhit

BB. said:

Generally, the standard minimum/maximum  Vmp-array (standard name platevoltage) voltage for pwm charge controllers is

12v...17.5/19 volts Vmp

24v...35/38 Vmp

48v...70/76 Vmp

-Bill

We have boB from Midnite here from time to time, I've book marked his recommendations for input for the Midnite classics on another computer. From my feeble mind;

For MPPT to work properly you need @30% higher input than output, so a 48 volt system typically charging at 60 volts you would need @88 vmp input.

Photowhit

I don't believe the Midnite sizing tool, represents this, but it is a valuable tool;

http://www.midnitesolar.com/sizingTool/

BB.

I was typing about Vmp-array with a PWM controller... In theory (specifications world), the minimum voltage for a MPPT controller is supposed to be the same, but I would agree that higher Vmp-array is a good thing (30% [1.3x] to 2x Vbatt is typical recommendation unless unusual circumstances such as long cable run from array to charge controller where a higher Vmp-array usually makes more sense to allow smaller diameter array to MPPT charge controller cable diameter/lower cost of installation).

-Bill

Marc Kurth

Bill - That is good and very helpful region specific input. But, without knowing what the daily load profile looks like...............

I strongly agree with your comments about judicious generator usage. Time after time, we find that a blend of solar, batteries and generator work most cost effectively. I sell batteries for a living, but I often show customers how a small amount of annual generator run time can cut their battery bank size in half.

For RV use, I am a fan of the Magnum MS 2000 and MS 2800 intverter/charger package with 100a and 120a chargers. They can be "dialed down" to lower  AC input current to match available generator or other power supply at any time.
 
Marc

BB.

Marc,

Thank you for the kind words...

For an RV, generally space and weight limit the size of things like battery banks and solar arrays. Going dry camping in the far north--There just is not very much sun. I would agree that the RV battery bank + solar array is sized for the "non-winter" loads. And that efficient energy usage (i.e., look at RV heating that does not use a fan) and a genset sized for the load (i.e., a 1,600 Watt genset vs a 4,000+ watt genset--If the high power is not needed).

And besides the point that batteries are heavy, they are also not cheap to replace every 5+/- years.

And Marc, did you intend to type "MS" Magnum series and not the "MSW" series (nothing that I could find) for the AC inverter/chargers?

https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?manufacturer=Magnum+Energy&nav_inv_frequency=60+Hertz&nav_inv_input_voltage=12+Volts

-Bill

Marc Kurth

Bill, Yes!
My mistake - I was going from memory and did not verify the model number.

Vic

Photowhit said:

BB. said:

Generally, the standard minimum/maximum  Vmp-array (standard name platevoltage) voltage for pwm charge controllers is

12v...17.5/19 volts Vmp

24v...35/38 Vmp

48v...70/76 Vmp

-Bill

We have boB from Midnite here from time to time, I've book marked his recommendations for input for the Midnite classics on another computer. From my feeble mind;

For MPPT to work properly you need @30% higher input than output, so a 48 volt system typically charging at 60 volts you would need @88 vmp input.

..whit,

This is what I had tried to note before.

When the MN Parameters are Submitted in the MN Sizer,  there are two Notes at the foot of the Sizer results.  The second Note includes the following:
"   ...    BUT you also have to be careful not to have the input voltage to low. Most all MPPT controllers will want to see a minimum of 130% of the actual high battery voltage. So if we have a 48v battery and it has an Equalize voltage if 62.3 volts than we would multiply that by 130% and we would need a minimum of 81 volts on the input on the hottest day of the year in order to have enough headroom for the MPPT to work   ...   "

FWIW,   Vic