We have been living on solar for 6 years now. You will get much confusing info on this topic depending on who you talk to but the previous posting of Handy Bob's blog is a good read. The first I would recommend is take an amp meter and put it on your positive cable on the house battery bank. then one by one put on each item in the coach and record the draw on the meter. Ultimately you want to know what the draw is that you will typically be using daily or nightly.
For instance we pull 23 amps hr. starting from 5pm till around 9:30 or 10:00 pm. This includes the lights we use the tv the slide out freezer the gas fridge which does pull about 2 amps ( it has a circuit board to operate the gas feature), and maybe the gas furnace in the am to take the chill off which we have running as I write this.
Something to understand: what does it mean when something is rated at amps or watts! An item that is rated at lets say 5 amps means it pulls 5 amps per hr. an item that is rated at watts, lets say a 10 watt light bulb is pulling 10 watts per hr. You want to know what your total amp hour draw will be in a 24 hr period or from when the sun goes down to when it rises. Then you need to size your battery bank to meet your need times 2. For instance we have 2 AGM house batteries rated 225 amp hrs each for a total of 450 amp hrs. Rule of thumb is not to go below 50% of your capacity which for this example is 225 amp hrs which will show a reading on your volt meter of 12.2 volts resting, not while something is drawing on the battery bank. A battery monitor is a must if one really wants to know the state of your batteries. A volt meter is not enough. I have a TriMetric battery meter that measures amp hrs in and out and volts in and current volts state of charge. It's like a fuel gage for your batteries. After figuring out your battery needs then you need to size your solar array (panels) This can be complicated but worth taking the time to learn about. The panels can be wired for 12 volts or 24 volts or even 36 to 48. I have ours wired for 24 volts. The advantage is you can get by with smaller wire coming off the roof to the charge controller (we haven't talked about that yet),A wire size chart is necessary to consult for this, then go a the next size larger (trust me on this it is worth it). For a good solar array you should install a bit more than you actually figure you need to make up for cloudy days. Next you need a good solar charge controller. I hane a Morning star 45 amp MPPT ( worth looking into). My mistake on sizing this controller is not understanding what the 45 amps ment which I thought is what the controller would accept, It really mens the capacity that it will put out so for my system in-order to get the maximum I should go up to the next controller which is the 60 amp. But what I have works fine for our needs currently. The controller has an optional remote monitor which I recommend highly. Battery monitors are a must to get the best feel as to what you are doing to your expensive battery bank. You can get twice the life from your batteries if you don't let them go below 12.2 volts. Now to confuse the matter even more you need to understand hoe temperatures shifts effect the batteries. Real cold temps can cut the efficiency as much as 40% but that is only while the temps are low. Here in the desert the temps can get to the 30's over night but when the sun comes up the day time temps warm the batteries just fine back to a good state. A GOOD solar charge controller will have a battery temp sensor to go on the post of one of the batteries which reads the actual temp and adjust the charging capability accordingly. On my controller I have the temp sensor PLUS a voltage sensor which also will adjust the controller based on what it sees for voltage.
With a properly sized system you can enjoy life off grid. There are charts that give average daylight hours based on location in the country. The south west is about as good as it gets. If in more cloudy areas you would have to add more panels.
Have fun.
Brad
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Brad & Karen & Mena
Coach Name BIG BLUE
Coach# 204
1988 40 ft 8v92 TA
2012 Toyota FJ Cruiser,1990 Jeep Cherokee 4/WD now a desert rat
25 ft Haulmark trailer
730 watt solar panels, Full timing.
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