Panel/ system sizing ?

AS Traveler    Quote from previous post.
Do you feel the size of system installed is really providing you results you are happy with considering the out of pocket costs?  Yes, absolutely!  I have a pair of residential solar panels on a 30' Class A (moving to a 36' Class A).  Each panel is 325 watts for a total of 650 watts. 60 amp solar controller, 400AH (Amp Hour) of lithium, and a 2000 watt inverter/charger.

I'm trying to size a system for a 30' class C and I'm overwhelmed with all the info out there. I have read Handy Bob, Jack Danmayer, and Marx. I'm curious about the sizing :
a, of the panels. Did you go with the 325 w for a particular reason? Lack of space, price, ?  What brand did you settle on ? Are the panels 12v?
b. the total array size of 650w. Did you calc all of your loads, monitor battery use, of just go for it.
Are you providing for any unusual needs, loads.  We have nothing unusual but of course the large loads of  microwave, coffeemaker, heat loads and the usual tv, computers, lighting, etc. We will probably be considered liberal users.  I don't even know enough to know what phantom loads to expect. 
I have been thinking of Grape panels  3 @ 180w for total of 540watts.  Not sure how I came up with that. I'm open to larger panels as I feel the less wire/ wiring connections and holes in the roof the better.  There is quite a price difference in panel manufacturers. 

I'm new to this and appreciate any and all info.
Thanks, Pat

Panel sizing:
--  You can't have too much solar. 
--  At least 1 watt to 1AH of battery.  However you will be much happier with 1.5 to 2 watt per AH if space allows.
--  You really need to determine you power usage.  The best way is to install a battery monitor like a Trimetric http://www.bogartengineering.com/products/trimetrics.html and follow your usage over a number of days of usage.  This also shows phantom loads. A good starting point for guesstimating your power needs is in this website  http://www.marxrv.com/12volt/12volt.htm In part 1 or two he lists general info about how much power each device takes.  Some of the amps he provides are outdated, i.e. TV's.  Flat panel LED TV's only pull 1-3 amps of 12V through an inverter.

Which panels. 
--  Higher wattage/voltage panels are cheaper per watt and you can use smaller wire size from the panels to the controller
--  Wire size with voltage drop of less than 1% based on using a wire size calculator is best.  The extra cost of the larger wire is very small compared to the extra power you get.
--  Install panels in series or parallel.  Install three 100 watt panels in series and you get one 300 watt panel at about 49V.  However shade one small corner of one panel you loose output from all 3 panels.  Install 3 of the same panels in parallel you get 300 watts at 12V nominal (really about 17V), but you need much heavier wire to limit the voltage loss.

The concept is simple, but applying it to an individual situation takes analysis that most people are simply too lazy to do.  You need enough battery amp-hours to supply your daily power needs, preferably with some extra reserve in case you are not able to re-charge daily. Then you need enough solar panel to re-charge those batteries each day, given the amount of sunlight available where you will be.  If you have low confidence in your estimates of power usage and sunlight availability, add more battery amp-hours and more panel space, up to the limits of your budget, open space for panels and weight & space for batteries. The only big caveat is that no amount of panels can make up for little or no sun. The hours and intensity of sunlight is much different in the desert Southwest vs New England of the foggy Pacific NW. 

Many people just guess at a battery bank size and then install enough panel watts to hopefully re-charge it, using a rule of thumb such as ASTravelers describes. Then add to it if it comes up short. If you carry a genset as well, you always have a ready reserve anyway.

this will give you a start, you will most likely stick to 12 V so do the calcs for that.
feel free to ask more questions..

http://www.rvforum.net/SMF_forum/index.php/topic,113514.0.html

AStravelers has put it well.

Our install, that made use of high-voltage (40v) residential panels can be found here. You'll see in the pictures that six of them fit on the roof of our 30 foot travel trailer with room to spare.  It is a bit of a long read, but hopefully the pictures will give you some ideas.


http://www.rvforum.net/SMF_forum/index.php/topic,106669.0.html

Thank you Frank, What size wire did you run from the panels to the combiner box? #12 coming out of the panels? I'm spooked over wire size for the longer runs.  I will likely need two panels so I can combine them with heavier wire , #6 or #8 close to the panels then to the controller. I like the conduit. Clean.  How did you make the end at the panel watertight? 
Pat

I think you will get the answers to those questions if you follow the thread down a bit further.  I tried to make the thread as complete as I could. However, do ask if there are questions that are not addressed there.

Wire size is determined by the amps flowing and the distance. There are numerous wire size (gauge) calculators online - use one of them.

Here are a couple:
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html
http://circuitwizard.bluesea.com/