Looking for advice on solar to power an Recreational Vehicle (RV)

alansills
By alansills on Sun, Jun 23, 2013 - 8:11pm

I'd love to hear ideas including specifics on how to power an RV with solar power. I'm talking about a 5th wheel - and all the "stuff" inside - electronics; furnace; etc...

5 Comments

DRS78750's picture
DRS78750
Status: Member (Offline)
Joined: Aug 30 2009
Posts: 15
AM Solar - Solar power for RV's

My RV has a 4 panel system from AM Solar (www.amsolar.com). They do have a dealer in CO.

ljhaines's picture
ljhaines
Status: Bronze Member (Offline)
Joined: Apr 23 2009
Posts: 35
Need 12v & 120v Design Engineer in Houston Area

Hi everyone,

I'm building my own on/off grid 20' tiny house on a trailer and need to get with a designer/applications engineer for the RV industry. Here's what I want to accomplish...

1. Calculate loads based on usage so we can size battery bank

2. Find the right solar panels to charge batteries (primary charge when off grid)

3. Incorporate generator with 3 way fuel capability to charge batteries as a back up to solar

4. Use as much low voltage equipment as possible.(i.e.  I have a Sundanzer 12v chest refrigerator)

5. Select optimal equipment to purchase and install along with wiring sizes, breakers, etc.

any help or direction would be beneficial.

silvervarg's picture
silvervarg
Status: Bronze Member (Offline)
Joined: Mar 28 2010
Posts: 57
Self help (knowledge is power)

Calculating the usage or electricity is easy, so that action is something you should do yourself (only you know how much you use each appliance/device).

For constantly connectede devices, like a refridigrator it has an average power usage (like for a refridigrator) of X WattHours per day.

For devices that are just on sometimes you need both the wattage and the number of hours per day you use it.
E.g. One lightsource: 5W * 3 hours = 15 WattHours.

Once you have all that written down just summ up your WattHours to get you total energy need.
This wat your action 1 (Calculate loads).

Now you get to the battery bank.
First the size of the bank.
This just depens on how long you want to be able to run without any charging (e.g. heavy could or night for Y days without giving it a charge from anything).
Lets say you want to go for 3 full days without charging.
That means you need your X WattHours * 3 days = 3X WattHours.
Next is that you normally size your battery bank to only be used to 50% capacity. This both prolongs the life of your batterys a lot and will also enable you to use the batterys even after they have lost some of its original capacity.
This means we now have 3X * 2 = 6X WattHours capacity for the bank.

Batteries are normally sized in Amp-hours and not watt hours, but this is just a simple conversion.
Lets say you go or a 12V system (12V and 24V are common, but you specified that you allready have a 12V chest refridgirator).
The simple formula is: P=U*I
Where P (power) is your watt hours, U is the voltage of your batteries (12) and I is the combined number of Amp-hours of your batteries.

That's actually still number 1 on your list. Battery capacity calculated.

Now you need to size solar panels. I suggest that you want to have your WattHours usage for a day (24hours) and you want to load that in 5 hours (very rare that you don't get 5 hours of effective sun on the panels in a full day).
That means: Your WattHours/5 = Desired total panel wattage.
Now this does not take into account loss in cables and charger, so you might want to add 10% to the panel wattage.
Now to the tricky part:
You typically have only half of the roof that is fairly well turned to the sun, so it is only meaningfull to have solar panels on half the roof. I am assuming you have a "normal" roof shape.
Due to the small size of a Tiny-house you are likely to be limited by the roof size. So, also go the other way. See you much wattage you can fit on one side of the roof.
20 foot is quite long for a Tiny-house, so I think you have a good chance to fit things in.
Thats enough on point 2.

Generator is fairly easy. Noise level varies a lot, so remember to check that. Also decide how long it may take to charge up your battery bank. The longer you can wait the smaller generator you can do with.
Do think if you on occasion want to be able to use machines from the generator, like when you build on the Tiny-house.
Motors tend to want 3-5 times the specified wattage as a spike when they start, and it could be nice if the generator can handle that.
Will you need to be able to carry the generator by yourself or will it be permanently placed on the Tiny-house?

Not much to say on point 4.
In general lights etc draw very little.
Things that sound (radio etc) draw quite little.
Things that move mass uses a lot (e.g. electric chainsaw).
Thing that generate heat or cold uses the most.
Some high efficiency refridirators are a bit of an exeption to the rule, but they still use a substantial amount of power.
So, for heating and cooking you need something else. E.g. propane or alcohol based stove and can be used for heating as well).
If you need lots of heat for longer periods of time you might want to look into pellets or even wood or disel to keep running costs down.

With this I think you have at least can go a bit on the way. Just write here how far you have come and we wil be glad to help you with more information.

metalmongrel's picture
metalmongrel
Status: Bronze Member (Offline)
Joined: Oct 7 2008
Posts: 38
For any solar system for an

For any solar system for an RV (or even a small house), I highly recommend reading the following blog first:

https://handybobsolar.wordpress.com/ 

HandyBob is very knowledgeable, is frequently correcting bad work done by RV dealer-installed solar systems, and lives off of solar entirely without a generator.  In other words, he walks the walk and lives on only 350W of panels with plenty of reserves.  He may seem a little cranky, but he knows his stuff.  I know there's alot of info on his site, but it's all worthwhile.

Here are some highlights to his writings:

1.  Use the largest and shortest cables you can afford between the charge controller and your batteries.  Sufficiently large cabling between the panels and the charge controller are also recommended.  (10-12 gauge is not big).  He uses 2, 1, 0/4, 0/2 gauge where possible and has his charge controller within 6' of his batteries.  

2.  Get a good battery monitor like a Bogart Engineering TriMetric for analyzing your charging, battery state/levels, and keeping an eye on power draw.  Without this, it's nearly impossible to charge batteries correctly and to know how to develop power usage patterns.

3.  Understand the difference between PWM and MPPT charge controllers, what your budget can afford, and what your charging needs are (12V, 24V, 48V system, AGM/Wet Cell batteries, etc).  Read his section about charging at the proper voltage for your batteries since undercharging them can damage them and ultimately give you less charging power.  Some PWM's cap the incoming voltage at too-low voltages for alot of batteries and you cannot adjust it, so select your charge controller carefully per the types of batteries that you'd like to run.  Bob recommends 14.8V charge for his type of batteries, which may be too much for other types of batteries, but maybe not enough for other batteries at certain temperatures.  Some MPPT's (and some PWM's) allow you to adjust the incoming voltage and some even have a temp sensor so that your incoming voltage varies with temperature.  

DC charging systems can be complex, but I've found that the best way to learn is to read enough not to injure yourself :) then proceed with the understanding that this is a learning process that may require some trial and error.  Good luck.

 

alfrede's picture
alfrede
Status: Member (Offline)
Joined: May 15 2013
Posts: 20
Metalmongrel nails it! Bob is cutting edge good!

Yeah a little cranky..but within reason. But info I found nowhere else. great summary of the important points I know of on important stuff if limited to solar.

ea

metalmongrel wrote:

For any solar system for an RV (or even a small house), I highly recommend reading the following blog first:

https://handybobsolar.wordpress.com/ 

HandyBob is very knowledgeable, is frequently correcting bad work done by RV dealer-installed solar systems, and lives off of solar entirely without a generator.  In other words, he walks the walk and lives on only 350W of panels with plenty of reserves.  He may seem a little cranky, but he knows his stuff.  I know there's alot of info on his site, but it's all worthwhile.

Here are some highlights to his writings:

1.  Use the largest and shortest cables you can afford between the charge controller and your batteries.  Sufficiently large cabling between the panels and the charge controller are also recommended.  (10-12 gauge is not big).  He uses 2, 1, 0/4, 0/2 gauge where possible and has his charge controller within 6' of his batteries.  

2.  Get a good battery monitor like a Bogart Engineering TriMetric for analyzing your charging, battery state/levels, and keeping an eye on power draw.  Without this, it's nearly impossible to charge batteries correctly and to know how to develop power usage patterns.

3.  Understand the difference between PWM and MPPT charge controllers, what your budget can afford, and what your charging needs are (12V, 24V, 48V system, AGM/Wet Cell batteries, etc).  Read his section about charging at the proper voltage for your batteries since undercharging them can damage them and ultimately give you less charging power.  Some PWM's cap the incoming voltage at too-low voltages for alot of batteries and you cannot adjust it, so select your charge controller carefully per the types of batteries that you'd like to run.  Bob recommends 14.8V charge for his type of batteries, which may be too much for other types of batteries, but maybe not enough for other batteries at certain temperatures.  Some MPPT's (and some PWM's) allow you to adjust the incoming voltage and some even have a temp sensor so that your incoming voltage varies with temperature.  

DC charging systems can be complex, but I've found that the best way to learn is to read enough not to injure yourself :) then proceed with the understanding that this is a learning process that may require some trial and error.  Good luck.

 

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