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Old 01-25-2014, 03:31 PM   #1
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Getting 1 solar panel, should I just get 2 right away?

I'll be picking up my 1990 Airstream Excella 25 in a couple of weeks. The Airstream dealer is going to inspect it, put new tires on, etc. Part of the deal was that they would install a solar panel for me. They were going to put in a 65W panel as part of the deal, but I'm paying a bit extra to upgrade to the biggest panel they have, a 95W panel and also install a second house battery.

I've been going back and forth with the idea of adding a second 95W solar panel so I will have 190W of solar panels. In my research and reading on this forum and elsewhere on the Internet, I'm still not sure how much I really need. Currently there are incandescent lights, but I may change those out for LED later. There's a convection microwave, which I will probably only use (the convection oven part) if plugged into short power. There will be a 19" flat screen TV for occasional use. Having a laptop computer plugged in at all times is essential, as I work from that and may be full timing in this. I might have the Fantastic fans running if warm, but I don't plan to be where it's so hot that I need air conditioning. As for sun, I will be in both sunny and fairly cloudy areas depending on the time of year.

Would it be best to just get the second 95W solar panel now? Partly to ensure that I will have enough electricity when boondocking, and partly since it might be easier for the dealer to just install both panels right now, and ensure adequate space (and prevent having to undo and relocate a panel in the future if I don't add the second panel now)? Thanks!
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Old 01-25-2014, 03:48 PM   #2
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Why can't he obtain a 190 watt now and install it?
I installed a 190watt with two 300 amp AGM 6 volt batteries - on travel days, between the TV and the solar the batteries are 100% by noon when traveling and close to that when boondocking. Haven't had to run the converter/charger yet - makes to much noise when we are sleeping (it's above our beds). Never have we been close to 50% charge.
Thus, It would seem that for supplemental charging, 90watt panel would be enough with two regular batteries.
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Old 01-25-2014, 03:50 PM   #3
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Do both now. Have no regrets.
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Old 01-25-2014, 04:29 PM   #4
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Quote:
Originally Posted by Silver Hawk View Post
Why can't he obtain a 190 watt now and install it?
I think the 95 watt was the biggest they had in stock. I didn't think to ask if they could get a bigger one, but with two weeks before I pick up the trailer, maybe they would have time to order a bigger one in. They're closed now, but I'll call them on Monday to ask.

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Originally Posted by kscherzi View Post
Do both now. Have no regrets.
Sounds like a good plan! That's what I was thinking. The only thing holding me back was the cost, especially with the purchase price of the trailer and a few other upgrades already. It's a bit of a price hit up front, especially with just buying the trailer, but you're right, do it now and have no regrets. Maybe they can get one larger panel, or another 95 watt panel. I may not need that much all of the time, but for those times when I do, I'm sure I'll be glad.

I'm also thinking of buying a portable generator to have when I run down the house batteries, can't wait for them to recharge by solar and don't have shore power (important for me to have power for my computer for working). Since I plan to do some boondocking, this is very possible scenario. But I'd rather use solar power if possible.
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Old 01-25-2014, 07:16 PM   #5
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Quote:
Originally Posted by JustSomeGuy View Post
I'll be picking up my 1990 Airstream Excella 25 in a couple of weeks. The Airstream dealer is going to inspect it, put new tires on, etc. Part of the deal was that they would install a solar panel for me. They were going to put in a 65W panel as part of the deal, but I'm paying a bit extra to upgrade to the biggest panel they have, a 95W panel and also install a second house battery.

I've been going back and forth with the idea of adding a second 95W solar panel so I will have 190W of solar panels. In my research and reading on this forum and elsewhere on the Internet, I'm still not sure how much I really need. Currently there are incandescent lights, but I may change those out for LED later. There's a convection microwave, which I will probably only use (the convection oven part) if plugged into short power. There will be a 19" flat screen TV for occasional use. Having a laptop computer plugged in at all times is essential, as I work from that and may be full timing in this. I might have the Fantastic fans running if warm, but I don't plan to be where it's so hot that I need air conditioning. As for sun, I will be in both sunny and fairly cloudy areas depending on the time of year.

Would it be best to just get the second 95W solar panel now? Partly to ensure that I will have enough electricity when boondocking, and partly since it might be easier for the dealer to just install both panels right now, and ensure adequate space (and prevent having to undo and relocate a panel in the future if I don't add the second panel now)? Thanks!

For sure get the second panel and also make sure you have a good controller and a 1500 watt pure sign wave inverter. He will most likely use 4 gauge wire on the battery and inverter connections so that is about the best you can do without spending a whole bunch of money. You should have adequate power for your needs and you may even be able to run your microwave/ convection periodically. You are getting yourself setup for the most enjoyable type of camping, no tethers. Good luck. Jim
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Old 01-25-2014, 08:55 PM   #6
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From the Magnum Energy owners manual for their 1000 watt sine wave inverter/charger:

Table 1, Recommended DC Wire/Overcurrent Device

Inverter Model
MMS1012
MMS1012-G

Maximum Continuous Current1
200 amps
200 amps

DC Grounding Electrode Wire Size
# 6 AWG
# 6 AWG

Minimum DC Wire Size (90 ̊C rating in free air)
# 1/0 AWG (260 amps)
# 1/0 AWG (260 amps)
Maximum DC Fuse Size
300 amps with time delay
300 amps with time delay

Info: The term “in free air” is defined by the NEC as not encased in conduit or raceway.
If the inverter is expected to operate at a distance greater than three feet from the battery bank, the DC wire size will need to be increased to overcome the increase in resistance – which affects the performance of the inverter. Continue to use the overcurrent device and DC ground wire previously determined from Table 1 and then, refer to Table 2 to determine the minimum DC wire size you need for various distances based on your inverter model.
DC Overcurrent Protection
For safety and to comply with NEC (National Electrical Code) electrical code regulations, you must install a DC overcurrent protection device in the positive DC cable line to protect your DC cables. This DC overcurrent device can be a fuse or circuit-breaker, but must be DC rated. It must be correctly sized according to the size of DC cables being used, which means it is required to open before the cable reaches its maximum current carrying capability, thereby preventing a fire. See Table 1 to select the DC overcurrent device based on the minimum wire size for your inverter model.
Note 1 - Maximum Continuous Current is based on the inverter’s continuous power rating at the lowest input voltage with an inefficiency factor.
Note 2 - Per the NEC, the DC grounding electrode conductor can be a #6 AWG conductor if that is the only connection to the grounding electrode and that grounding electrode is a pipe, rod, or plate electrode.
Note 3 - Wire size is based on the requirements needed to increase efficiency and reduce stress to the inverter.
Note 4 - The next larger standard size overcurrent device may be used if the de-rated cable ampacity falls between the standard overcurrent devices found in the NEC.

They specify 1/0 cable as a minimum for a 1000 watt inverter. I would suggest that 6AWG is a tad took small. Unfortunately, Airstream is famous for installing wire that is either the bare minimum or actually undersized for their battery, inverter and solar connections.

The smallest cable that I use for any inverter or inverter/charger is 2/0 with a 300 amp class 'T' fuse for circuit protection.
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Old 01-25-2014, 09:04 PM   #7
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Thanks for the detailed information! When they open on Monday, I will ask the dealer about the wire size and the inverter. Good thing you told me that or I would have not even known to ask. There used to be at least one solar panel on this Airstream Excella, likely factory installed or dealer installed back in 1990 when this was new. There is an analogue solar panel gage on one of the interior walls. So, my guess is that they were going to reuse this.

I'm excited to get this set up now so that I can live on solar power and boondock or take advantage of RV parks lower rates for unserviced spots. It will be a bit of a financial hit up front, but I'm sure it will be worth it in the long run. I'm thinking 200 watts of solar panels should be OK. It's partly limited by roof space, and partly by how much it costs, otherwise I wouldn't mind a bit of overkill. And the dealer says there's only room for two batteries.
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Old 01-25-2014, 10:45 PM   #8
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Solar power

You will always need more panels than you first thought. Even tho the snow was falling you can tell my home has many solar panels. The row back in the back has twice as many as the row of panels in the front (behind the frost killed banana trees) I installed them in three phases, you see the first phase in this picture, fifteen solar panels, 220 watt per panel. Even tho I do not "work" any more (retired) I travel and help people with their solar power systems. I have been as far as the Bahamas to help an ex-patriot get his solar power problems ironed out. My advice to you is plan for growth. It seems like you are strapped for cash. Do like I did. I planned a three phase system. With proper planning you can grow your system, increasing it's production over time. An MPPT controller allows for smaller wire between the solar panels and controller. The pre-wired 10 gauge wire can actually be okay if using MPPT controller and wiring panels in series, which doubles the voltage hitting the charge controller.
I like dealing with www.solar-electric.com. That is the website for Arizona Wind and Sun. Some of the people on this forum mention another website but I do not recall anybody saying they are using an MPPT charge controller. That is not a brand name but a leading technology. It means Maximum Power Point Tracking.
Message me if you have a particular question about solar. When I bought my 23 ft Flying Cloud I had it on solar within a month. I use panels which can be located wherever the sun happens to be hitting your campsite. My MPPT charge controller is mounted under the front bed near the battery terminal block and the display is mounted inside on the wall of the wardrobe where I can see it. This is where the solar pre-wire was terminated as well.
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Old 01-25-2014, 11:18 PM   #9
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I think I'll spring for the extra solar panel now. I can afford more, but I'm already over budget and didn't want to spend money on something I may not need. But, it sounds like you can never have enough solar panels! At least when considering just two, for around 200 watts. That sounds like the minimum I should go with. In a year, this will probably all seem like common sense, but right now it's all new to me. It seems easier to just get this all set up right now, before I pick up the trailer. I'm not sure how much room will be left on the roof to expand to more panels in the future, but I'll keep in mind that I may need to add more later. I'll see how the two panels do for now. Thanks!
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Old 01-26-2014, 01:32 AM   #10
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It would certainly be more cost effective (labor saving) to have both panels installed at the same time ... also allows for better planning so that one doesn't have to be moved if/when you install two. Two panels are muuuuch better for those cloudy or overcast days... so long as you have adequate storage capacity in your battery bank(s).
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Old 01-26-2014, 06:26 AM   #11
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Some good info here already - as in - you can never have too many panels, although the RV adds space limitation certainly. And - a large number of RV installations done by 'pros' and dealers use wire that is too small or a design that is poor for getting the most out of your panels. They don't put out a lot of power, so you want to maximize it.

Locate the inverter(s) close to the batteries if possible - then if you have to go distance use the 120v output from the inverter to do it, you won't have the same losses there, and you won't need so much heavy wire. I use 1/0 copper for my inverter connections and it's heavy and expensive.

A 95w panel shouldn't cost a LOT more than a 65 either. If you are paying more than $2 a watt for a panel that sounds very suspicious to me. You didn't mention any costs, but cost for a top quality 200watt setup could be around $1k - 2 100w panels, pure sine inverter, 2 deep cycle batteries, charge controller, wiring. And the installation is not rocket science.

I would definitely go with LED lights if possible - it's almost like they use no juice at all when compared to incandescents and even fluorescents.
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Old 01-26-2014, 09:03 AM   #12
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I'll start by saying that with solar getting popular in the RV field for those that boondock, there are loads of misconceptions and misinformation available today. The basis of a quality solar charging system is the cable that carries the electrical current between the various components: solar array, solar charge controller and storage batteries.

ALL of the wiring, and especially the connectors, are highly susceptible to voltage drop. While some voltage drop is tolerable, the less drop you have in your system, the more efficient it is in doing it's job; keeping your batteries properly charged. We (at AM Solar) tolerate no more than a 2% voltage drop in any of our systems. This is the primary reason for utilizing such large capacity cables in our installations.

In our experience of several thousand system installations over the last 27 years (not including the package systems that are sold to the DIY crowd), our minimum recommended wire gauge for a 100 watt panel is 10AWG. This increases to 8AWG for a 200 watt system and goes up from there to 2AWG for larger systems above 800 watts. The longer the wire run, the greater the need for larger cabling to keep the voltage drop at a minimum.

The use of MPPT (Maximum Power Point Tracking) technology has allowed for a boost in the charging amperage that the batteries 'see' from the charge controller over what the solar array is sending to that charge controller. in the right conditions (low battery voltage and bright sunshine), this boost can be as high as 30-40%. MPPT technology has nothing to do with allowing you to use smaller wire sizes in your system. As stated above, The 10AWG solar pre-wire that Airstream includes in their trailers is woefully inadequate for any solar array larger than 100 watts (12VDC nominal system voltage. Larger voltage systems like 24VDC or 48VDC can utilize smaller wire sizes successfully).

Use properly sized cables, keep your connections to a minimum, place the charge controller (and inverter) as close to the batteries as possible and route the cables from your solar array as directly (short) as is feasible to the controller and you will have minimized your voltage drop and maximized the charging efficiency of your system.
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Old 01-26-2014, 09:51 AM   #13
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Thanks again! I'm armed with a lot of good information now so that when I talk to the dealer tomorrow, they'll know I have an idea of what I'm talking about. If they are too pricey, or don't agree or want to do certain things, like use or change existing wire to thicker wire, I'll get it done elsewhere.
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Old 01-27-2014, 12:08 AM   #14
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lewster,

This explains why when using 10 gauge wire you are better off using an MPPT charge controller.

The smallest, well designed, MPPT charge controller I am aware of is the MorningStar 15 amp 12/24 volt MPPT controller. I use two of these if I want 30 amp of charge power or one could use a TriStar 45 amp MPPT charge controller which provides 150 volts of panel voltage. Sometime the space to mount the controller(s) dictates which is best.

15 amps * 14.5 volts charging * 1/0.77 derating = 282 watt solar array @ 12 volts

So, for a smaller 200 watt array--you do have a very nice controller available for $245 vs an inexpensive 20 amp PWM controller down to $90 or less.

You could spend the $155 difference and throw another 50 watts or so of solar wattage out there... if you have the space on your roof.

The advantages to MPPT (in my humble opinion by order of importance):

Ability to run "high" Vmp-array for using smaller cable from the array to the charge controller.
  1. Ability to run in wide temperature extremes efficiently. Hot Vmp=17.5 volt solar panels and cold battery banks means you may not get full voltage/current when charging/equalizing your battery bank. Run Vmp=35 volts on a 12 volt battery bank--and you have no worries about voltage drop (temperature, wiring, controller, or cold batteries requiring higher voltages to recharge).
  2. In cold weather (subfreezing), they can collect around 10-15% extra energy from Vmp increasing because of cold panels.

MPPT controllers cost more and typically have more logging functions and computer interface options. Also, Remote Battery Temperature Sensors are usually an available options for MPPT controllers (monitoring battery temperature can optimize battery charging too).

However, those options do cost money too--MorningStar probably makes a lot of money selling LCD displays for their units (Rogue offers theirs in the base unit).

Instead of getting the extra LCD display option--I would consider spending that money towards a Battery Monitor. I believe, a much more useful piece of gear.

Or put another way:

An area that is enhanced by an MPPT charge controller is power loss. Lower voltage in the wires running from the solar panels to the charge controller results in higher energy loss in the wires than higher voltage. With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v. Using an MPPT controller allows much higher voltages in the wires from the panels to the solar charge controller. The MPPT controller then converts the excess voltage into additional amps. By running higher voltage in the wires from the solar panels to the charge controller, power loss in the wires is reduced significantly and the option to use smaller wire.

Myself, I generally use a grid-tie type solar panel or I will combine two nominal 12 volt panels in series to feed an MPPT charge controller.

MPPT charge controllers are more expensive that PWM charge controllers, but the advantages are worth the cost.
If you can
afford it, you should definitely use an MPPT charge controller.

Or explained another way:
MPPT controllers down-convert the panel voltage, to the battery voltage. This accomplishes 2 things.

1) Higher array voltages have less wire loss, or copper expense, using smaller wire, for same wattage.

2) Adds the temperature advantage of cooler panels produce slightly higher voltage, and therefor, more power in cold weather.

A third thing , could be, for equal systems, you can get a bit higher wattage, into a low battery with MPPT, than with PWM. As Battery voltage rises to normal full charge, the MPPT advantage fades, as it throttles back
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