RV Solar Installation – Part 1: Planning 2


Last year, after some thought and planning of future trips in our RV, we decided to install solar power on our 29’ Holiday Rambler Traveler class A RV.  This document is going to cover my experience with my DIY installation and the decisions I made in the process.

About me: I have no professional training, but I have been messing about with electrical stuff most of my life. Mostly this seems to have amounted to fixing some hooptie vehicle I own, but it’s been its own reward. I also have a little experience with solar power. For a few years in the 90’s, when I lived in Key West, I owned an electric car that had 240W of panels on a tilting mount on the roof that could slowly charge the car. I also installed a 60W panel and a 7A charge controller in our first camper.

Still, I did a lot of reading, mostly of sources on the Internet. Here are some of the informational resources I used:

http://jackdanmayer.com/rv_electrical_and_solar.htm – Lots of good info.

http://where-rv-now.com/Notes/Solar/ – My brother’s site. Handy solar calculator there, too.

http://h andybobsolar.wordpress.com/2011/01/19/welcome-to-handybob-solar/ – Bob’s kind of a curmudgeon, but a knowledgeable one.

http://www.technomadia.com/solar/ – Technomadia has a lot of good solar and RV power information, including how to do an energy audit, which is very important.

http://roadslesstraveled.us/solar-power-rv-boat-installation/ – Includes tutorials.

http://www.amsolar.com/home/amr/cpage_9/rv_solar_education.html – I bought a lot of my solar components from these guys, but they have some good information, too.

Additionally, almost every manufacturer has a website with technical documents that will be invaluable in planning your installation and in operating it afterwards.

About the RV: Our 2003 29’ Holiday Rambler Traveler came from the factory pretty well equipped for power independence, with a fairly large battery bank of four 6V batteries, a 5.5kW generator and a Xantrex 1500W modified sine wave inverter/charger. The Xantrex works well as a charger, putting out a maximum of 75A back into the batteries, so just a couple of hours of generator operation will bring us back close to full. Our house battery system charges fast from the chassis alternator as well, so if we have a driving day moving from one site to another, it will mean that we’ll arrive with full batteries.  We’ve got a lot of roof space, so large panels are fairly easy to place. Finally, it’s got a fair amount of basement storage, so finding a spot for a controller isn’t a big deal.

Inside the RV, I’ve changed over to LED’s in many of the spots where we had incandescent light bulbs that saw frequent use. I’ve also removed the old 24” tube TV and replaced it with a low power consumption 26” LED 12V TV.  All of our device charging needs are met with 12V chargers, so we don’t need to turn on the inverter to charge a phone or a laptop.

I started by looking over our energy consumption, watching my 12v battery monitor on several trips. In my opinion, the first thing anyone who’s boondocking or concerned about understanding their 12V power situation should do is install some sort of power monitoring system.  This will tell you how many Ah you’ve pulled from your battery system. Simple voltage monitoring is not the same.  Do this BEFORE you buy anything else.

 

I’d suggest either:

LinkPRO or LinkLite from Xantrex ( I have the linkPRO and like it a lot )

 

Trimetric from Bogart Engineering ( I’ve used it and thought it was pretty good )

 

Clipper BM-1 from NASA Marine ( limited to 100 Amps, but they make it in a small surface mount version )

 

All of these will work like a gas gauge for your battery bank, telling you how much power remains in the batteries. They do this by measuring all the current going into and out of your battery pack and comparing it to the known capacity that you program into the unit. Note: Since writing this article I have written a more in depth post on battery meters, giving information on nine different ones.

 

After a few trips doing some dry camping, I’ve come to the conclusion that we can manage pretty happily on about 80Ah per day, as long as cold weather doesn’t force us to run the furnace a lot.

 

Our battery bank is four 6V batteries,  each rated for 235 Ah, wired in series for 12V, with the two 12 sets in parallel for a total of 470Ah @ 12V. If we discharge our batteries to 50% discharged, we have 235Ah of usable capacity. (Note – We upgraded to Lithium in Dec. 2016 and wrote a post about it ).

 

235Ah ( usable capacity ) divided by 80Ah ( daily usage ) is 2.94 days of power out of the batteries before we’re at 50% discharged. Colder ( requiring the furnace ) or hotter ( requiring the fan-tastic vent fans ) days will require more power and we will get less time out of our batteries.

 

I expect that as we learn more about our usage patterns we’ll get better at conservation, but we’ll probably be using our computers more and that’ll increase the need for power. I’m hoping it’ll balance out somewhat.

 

In the end, I settled for a goal of being able to put back 100Ah per day or better.  If it doesn’t meet its goal every day, that’s OK. More power daily would be better, of course. I figured that a 500 Watt solar installation would work for me.

 

My most challenging issue was how to get the power from the roof to the controller without a long wire run that wastes power, or where I’d go through the interior of the coach. My refrigerator vent is on the side of the coach, so that wasn’t an option, and everywhere else that had a space I could drill through the roof and run the cable didn’t have a good path to the basement compartments. In the end, I decided to run it down alongside the tank vent and use heavy 4 gauge wire to limit voltage drop as much as I could, despite the long cable run.

 IMG_20140316_201417

I found a good deal on a MPPT controller from a company in Canada, so I ordered a Blue Sky Energy Solar Boost 3024iL and the battery temperature sensor so the controller could temperature compensate the charge voltage to the batteries. I chose this controller for several reasons.

 

  • It was in the wattage range I needed, though buying bigger always gives you the option to add more panels, a bigger MPPT seemed to be a jump of about $300.
  • It would fit well in the compartment I planned for it.
  • It had an additional 2A charge port for the chassis battery on the RV, assuring that it would always remain charged when the RV was parked, without any additional circuitry.
  • Good quality and track record, from what I could find on the Internet.

 RV Solar Power Schematic (1)

I liked the idea of being able to tilt my panels and liked the quality of the stainless steel panel mounts from AMSolar, so I ordered three of their 160 watt panel kits with mounts and 10/2 ( 10 gauge, two conductors ) wire. I also ordered a combiner box for the roof, and some 4 gauge wire to go from the combiner to the controller and then on to the battery bank from AMSolar as well.

The folks at AMSolar were very helpful before my purchase, answering questions and helping me understand exactly what I needed for my installation. One of the panels was damaged in shipping ( it looks like UPS punched a bolt-sized hole in it ) and AMSolar was quick to replace it. Also, while I bought three panels, each with 15’ of 10/2 wire, three 15’ segments would have been inconvenient, being too short where I planned to put one panel, and too long for another location. So they let me buy another 10’ of 10/2 cable and sent me a single uncut 55’ length, which I could cut to length as I needed. Very nice.

To max out the capacity of my controller, I decided to add one more panel, so I got a 60 Watt panel from Amazon and some inexpensive aluminum mounts. I knew that I couldn’t tilt it like the other ones, but I couldn’t find a 60W panel that would fit the other mounts. I also ordered some of the other assorted items I would need from Amazon as well, like the panel disconnect switch and the circuit breaker/battery disconnect. I also got cable ends, Dicor roof sealant and 3M VHB ( Very High Bond ) double sided tape for attaching the 60W panel and the junction box to the roof.

This would bring the panel wattage up to 540 watts, the maximum the controller would allow at 12V. Actual wattage will be lower in normal conditions, but I figured this would get me to my 100Ah/day goal.

Using my brother’s solar calculator, I should be able to get 100Ah or more per day ( in sunny conditions ) in any part of the US I’m likely to go in my RV, in any of the seasons that I’m likely to go there. So, while I can’t get 100Ah in Wisconsin in December, I’m unlikely to visit then.  In the south, in the summer, I could get as much as 250 Ah per day. That’ll do.

The calculations don’t take into account the possibility of tilting my panels, so if I’m somewhere for a while during marginal sunlight times, I may be able to adjust my panels to get additional power.

Next: Assembling all the bits and installing the wiring under the RV in part 2.

 


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