Real world solar power - Fiberglass RV


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Old 09-08-2012, 09:53 AM   #1
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Name: Dennis
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Real world solar power

I've been living full time in my Casita 17SD for about 9 months, but it's been in a RV park. My goal is to get it to where I can make it off the grid when I need to. I've started to do some research (any links you can recommend for setting up solar power are welcome!), but wanted to also get some input from people who've already done it.


My Casita still has the factory battery and charging system. Mine is a 2011 model that has, along with the more power hungry A/C, the "improved" fridge that requires some battery power even when manually set to run off of Propane. No inverter yet, as I'm still not sure which one to get. I've already upgraded to interior LED's, and just got a "Market Umbrella" that shades two of the windows and most of the A/C, so I have a little controllable shade (a necessity in Texas).


I know I'm not going to be able to run the A/C off of any solar system that I can carry around (a 3000 watt generator is on my wish list, but it may be awhile before I can afford one). The factory Fantastic Fan pulls 2 to 3 amps. During the Summer that will probably be needed close to 24/7, and I'd happily add a second 12 volt fan for 100 degree days if I had the power. During the winter, my propane furnace has a 2.8 amp blower motor, but it's on a thermostat so it doesn't run all night.


I have a small net-top PC with a LED TV for a monitor. On paper, it's about 100 watts for the system, or 23 watts for the TV alone (a bit more if I use the factory amplified antenna). I'm a computer geek who would like to run it all day, but I could cut back to a few hours a day. In a pinch I have a little Android tablet that I could get by with. Haven't found any power specs on it, but I'm guessing it takes perhaps twice as much to keep charged as a cell phone? I also have a Smart phone, which tends to need more frequent charges if it is being used as an Internet connection.


My big addition is that I have a small 1.5 cu ft 110 volt electric freezer that is supposed to pull 1.2 amps when running (probably at least twice that when the compressor kicks in?). How much it runs is dependent on the air temperature inside the trailer, although with the A/C on shore power the freezer hasn't affected my electric bill noticeably. Most household freezers don't cycle all that much, but I haven't tried running it in outside temperatures. In a pinch, I could just use the freezer inside the built-in Propane fridge, but the electric freezer is really handy for being able to stock up on groceries. The freezer may sometimes be more important than the PC, depending on how much work I have to do and how much meat I've found on sale. Being able to run both the PC and freezer would be ideal, but may not be realistic (at least with a solar system I can afford).


I'm sure there are some minor battery drains and a whole bunch of other variables, but I guess the main question for you solar experts is, does this sound like a workable one battery system? Casita's don't really have room for a second on-board battery, so adding a second battery presents it's own problems. But if two batteries are necessary to make this work, then I need to start my planing from there. On paper, it looks like it might work on one battery, but I'd rather ask someone who isn't trying to sell me the parts
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Old 09-08-2012, 10:02 AM   #2
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Go to here and start reading, The 12volt Side of Life (Part 1)
parts 1 and 2 and create your own 12v needs schedule. Once you know your daily needs then you will know your daily solar requirements. Double batteries or the biggest group 31 you can find and a 100w solar system should keep you going. Try to convert all your 120 to 12v, like the computer and tv probably already are 12v and you are converting 120 to operate them. Your water and tanks will limit you.
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Old 09-08-2012, 10:08 AM   #3
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There are a lot of good articles on the web concerning this. Example:
Determining How Many Solar Panels You Need For Your RV Getting Started - Solar RV Panels

In every case, you need to make a daily budget of electrical use (amp hours) to size your panel and battery, just like you do a home budget (dollars).

Take the running dialog from your post and turn it in to a column of numbers, each representing amp hours of use per day for each device. Add them up.
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Old 09-08-2012, 10:30 AM   #4
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Name: Dennis
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Originally Posted by cpaharley2008 View Post
Go to here and start reading, The 12volt Side of Life (Part 1)
Try to convert all your 120 to 12v, like the computer and tv probably already are 12v and you are converting 120 to operate them.
Thanks, that's just the sort of link I was looking for.

I realize that 12v appliances are more efficient, but I'm also fighting a limited budget. I looked at 12v "trucker" type freezers, but they cost $600~$800.

I found a dorm room style mini-freezer for less than $200 (that, unlike the trucker freezers, actually holds several pizzas).
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Old 09-08-2012, 10:49 AM   #5
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Originally Posted by colliewagon View Post
Thanks, that's just the sort of link I was looking for.

I realize that 12v appliances are more efficient, but I'm also fighting a limited budget. I looked at 12v "trucker" type freezers, but they cost $600~$800.

I found a dorm room style mini-freezer for less than $200 (that, unlike the trucker freezers, actually holds several pizzas).
You might find this this thread interesting. Topic is making an inexpensive dorm fridge work off solar power and an inverter.

Inverter for dorm fridge online; looks good (so far)
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Old 09-08-2012, 11:11 AM   #6
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Compromise is the word

There's lots of thoughts and ideas about "how to have lots of power via batteries and solar"...
There's a bit more to it than that, at least in my humble opinion.
The first thing to do to live off the grid is to asses each power using device you have as to "REAL" need.
You mentioned a "Fantastic Fan" addition. Consider a 12Volt fan that you can position to blow air across you. Pulling hot air with additional ceiling fan might not do much.
Watch for current draw on each item.
LED lights are another big energy saver.

Now for my personnel experiences.
Single 74 amp hour battery.
65 Watt Solar Panel.
Battery users... LED Lights, Furnace, and an occasional electronic device recharge. (Most of the time computers, cell phones, etc. are charged from the tow vehicle battery. The thought here the tow generally gets driven every couple days so the battery gets recharged from the little drawn)
Converter turned off.
Most of 90 days off the grid.
When it's really really cold, (teens and below) I have to get out the solar panel about every 3rd day. Worst case.

Speaking worst case, if you're going to do a power budget do it for worst case.

Again, understand what you need and don't need. Do you really need a 12 Volt freezer?
Are there ways to do what you would like without the use of battery energy?
Like I said compromise is the word.

I recommend that anybody that has a desire to live off the grid study a book or two on the subject. Backpacking books are a good place to start. It changes your way of thinking about needs and wants, about how to unencumber yourself with stuff and mental gotta haves.

Good luck and I hope it all works well for you.
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Old 09-08-2012, 12:15 PM   #7
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Compressor

We once had a compressor based refrigerator in an earlier trailer. The compressor running current was about 1 amp. The start up current required at least an 800 watt Inverter, indicating a start up current about 7 amps..

Our experience is that a freezer is not needed for extend RVing. WE have simply learned to give up ice cubes and ice cream.
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Old 09-08-2012, 01:17 PM   #8
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Name: Dennis
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Our experience is that a freezer is not needed for extend RVing. WE have simply learned to give up ice cubes and ice cream.
Yes, I lived full time in my little egg for six months with nothing but the built-in freezer and know that it can be done. But I've also really enjoyed having room for some bulkier things (pizza, ice cream) and also being able to stock up on frozen foods when they're on sale. Always having to buy stuff in the smallest containers in the grocery store is noticeably more expensive, but often that's all that will fit in an RV fridge or freezer.
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Old 09-08-2012, 02:09 PM   #9
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Power hungry and on a budget= lots of compromising. More than 1 battery is likely in the cards. 2- 6V golf cart batteries and a 100-150 watt panel would be a good place to start. A 30 amp solar charge controller with a built in battery monitoring system would give you real world numbers to work with. Then you can size your battery bank and panels as needed. A 30 amp controller will allow a system of up to approx. 450 watts of panels and 400 amp hours of batteries. You probably don't have room for more than that. You can pick up one of these controller monitors for less than $100. Bottom line is you can guesstimate your power needs or monitor your real use and design your system from there.
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Old 09-08-2012, 02:50 PM   #10
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Name: Dennis
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Originally Posted by Thomas G. View Post
You might find this this thread interesting. Topic is making an inexpensive dorm fridge work off solar power and an inverter.

Inverter for dorm fridge online; looks good (so far)
Thanks, that link was extremely useful. As a long term project, it sounds quite possible - but also like it would take several batteries to make it work 24/7. Given my current budget, I think I may just plan to use the electric freezer when I have shore power. Although I now want to select solar components that leave an option for future expansion.

Short term, I think I may try to get a halfway decent ice chest. Especially if I could find some dry ice, that would give me a few days of expanded freezer storage. Although I've gotten by with the tiny built-in freezer, there were lots of times I couldn't quite fit in one or two more frozen items. Compromises, compromises...
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Old 09-08-2012, 03:31 PM   #11
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A 30 amp solar charge controller with a built in battery monitoring system would give you real world numbers to work with. Then you can size your battery bank and panels as needed.
Can I install the charge controller/monitor before adding any panels? That would let balance my current needs and budget before buying the panels (then expand it latter as money allows).
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Old 09-08-2012, 04:29 PM   #12
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Yes you could, Start with the battery you have, add a solar panel and and controller and start monitoring. You will then know precisely what you stand to gain with a bigger battery bank and more panels. It would also be a good idea to use larger gauge wire for the initial installation. Reduce your voltage drop to a minimum and allow for future expansion. Good wire is relatively cheap. When you want to add batteries make sure you go big enough because adding new batteries to older batteries is a bad idea.
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Old 09-08-2012, 04:42 PM   #13
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WIth specific reference to the problem of compressor dorm fridges alone, my experience is that I can pre-cool a 2.7 ft/3 dorm fridge on AC power; add the groceries (also cold) and switch to inverter power on the road and the drawdown on a group 27 battery isn't close to 12.2V after 3 or 4 hrs. on the road. With 80watts of solar and plenty of "shine" I can continue to power from battery with a decreased rate of drawdown but not indefinitely. I have an acceptable method of maintaining operating temperature in a pre-cooled AC fridge for a limited drivetime per day which also allows some daylight hours for solar recharge. I would certainly prefer to have an AC hookup the second nite out as the drawdown is too fast for multiday battery use. If I used the inverter to pre-cool the fridge, the drawdown would be pretty much "instantaneous" (a few mintues) to 12.2V. And 1 amp AC demand from a compressor motor is more like 10DC amps demand by the inverter. NOTE: I have a 6' run of 1/0 power cable from batt. to 1500watt inverter. Also I just finished replacing my converter and ran 6awg battery cable in place of the 10awg original. Certainly nothing wrong with making 12VDC transmission as "strong" as you can make it.

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Old 09-08-2012, 04:42 PM   #14
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Can I install the charge controller/monitor before adding any panels?


You need at least 1 solar panel in order to use the charge controller with monitor. The monitor will not work without it.
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