Help design my solar system for living fulltime in a travel trailer

For smart phones--In the US with standard data plans, (in theory, by law) you can setup your phone as a WIFI station (no extra charge)--And use a tablet or computer. Makes reading long threads a lot easier.

Reading material--You can take a look at this post:

http://forum.solar-electric.com/discussion/comment/99323/#Comment_99323

In general, the quickest way to understanding designing your solar system--Just keep asking questions in your thread (a couple at a time--Do not ask 20 questions at once, it gets confusing really quickly--And a wall of questions is hard to even reply to).

Don't worry about asking too many questions--Everybody here started at ground zero and folks here will help when/where they can.

My suggested way to work through the solar install--Follow the leader... For example, I posted about your (guessing) location, and made some guesses about system size/usage. You want to tilt panels and may be using the system for full time off grid? Verify the numbers (do you have room for xyz watts of solar panels, will your battery bank be large enough for your needs, can you fit your battery bank, can you afford/justify thegenric costs so far, etc.).

Once you have the paper design basics... Then you can start selecting hardware. Solar panels and batteries are pretty generic in pricing. solar Charge controllers have a wide base of pricing/function/costs. I could suggest a $600 full function MPPT charge controller, and you are really looking at a $100 PWM charge controller--Give us some guidance what you are looking for (lots of computer integration, data logging--Or want to try an inexpensive Chinese $100-$200 MPPT controller and see how it works).

Also, there are choices to be made... For example, larger solar panels (say >200 Watts) are 60 or 72 cell panels which cost ~$1 per watt (cheap) and need (expensive) MPPT charge controllers to match Vmp-array to Vbatt voltage.

Or, you can use ~140 Watt panels at ~$2 per Watt (not cheap) with a cheap PWM charge controller. For RV's, because of their small size (not much roof space), the smaller panels may fit better and a cheaper PWM controller is fine (small system). You usually do both paper designs and figure out the total costs and functionality (of charge controller) and decide which is best for you.

So, before I "answer" your charge controller question--Can you tell me how many Watts of solar panels you will be using, what panels you are interested in using (smaller 140 Watt panels or larger 200+ watt panels) to fit your roof/pocket book?

-Bill

Remember that 14.5 volts in the equation is an estimate of average charging voltage over time. Used to estimate solar harvest numbers only.

Not a charging set point.

-Bill

Still looking at a 450 AH @ 12 volt lead acid battery bank?

Vmp=32 volts is not a Panel that can be directly connected to a 24 volt battery bank.

You really need 35-40 volt Vmp panels to do that.

At this point, you want the panels in series (Vmp-array=32 volt) and one or two mppt charge controllers.

That large of wattage array on a 12 volt battery bagel may need two charge controllers. Using one Midnite Classic charge controller may not be enough (running a mppt controller at 100% rated output in hot weather/room is not a first choice).

-Bill

Maximum "cost effective" array on an 855 Watt array (that I would suggest) for a 12 volt battery bank:

• 855 Watt array * 0.77 panel+controller derating * 1/14.5 volts nominal charging = 45 Amps

So a 45 Amp is "close", but a 60-80+ Amp MPPT controller should be fine.

Somewhere in my thinking (and not writing it out)--I thought you were doing a 2x larger battery bank instead of the 450 AH @ 12 volt battery bank....

-Bill

The loads are "what matter"... If the system does not cost effectively power those loads, then it would not meet your needs.

I do not run off grid, and I am not in the solar business--I will leave it to others to comment on good inverter/hardware options. But, from what I have read before on the forum, the Xantrex Prowatt was well liked.

The choice between 12 volt and 24 volt battery banks--Many people here have started at the lower voltage, and then wished they had gone at least one step up--As their loads (and system) kept growing.

Power usage is a highly personal set of choices... I cannot substitute my "beliefs" and choices for your yours. You are the only one, in the end, that can make these decisions.

If you are using a 450 AH @ 12 volt set of flooded cell lead acid batteries--More or less, ~1,000 Watts is about the maximum continuous AC Watts that you can draw from that size bank (minutes to an hour or so--C/5 discharge rate).

• 450 AH * 12 volts * 0.85 AC inverter eff * 1/5 discharge rate = 918 Watts @ 120 VAC (short term max AC load)
  
• 450 AH * 12 volts * 0.85 AC inverter eff * 1/8 discharge rate = 574 Watts @ 120 VAC (suggested multi-hour AC load)
  

If this is your battery bank's maximum planned size (and you don't go to AGM/Li Ion, etc.)--You really only need about a 1,000 Watt maximum inverter. (and not much more than ~1,110 Watts of solar panels either--To much charging current can be a problem for lead acid batteries too, as well as not really cost effective unless you have a lot of day time loads).

-Bill