HandsCamping, if your question is what will a 90 watt solar module provide enough battery recharging to run on an ongoing basis I can try to answer that. Battery charge is generally measured in amp hours (AH) so you need to know about how many AH your solar module will produce on a daily basis and compare that to about how many AH you will use in your trailer.
A 90 watt module will produce about 5 amps of charging current under full sun conditions. On a typical day in the spring/summer/fall in the southeast you will get about 5 hours a day of equivalent full sun conditions on a tilted south facing solar module. So, that 90 watt module will typically produce about 25 AH if you keep it in the sun all day, no shading. If you have a really clear day you might get 35 AH and on a really cloudy day you might only get 5 AH out of it.
What will 25 AH a day run? I find with reasonably careful use 25AH is enough to run everything I want to in my rPod as long as I'm not doing any heating or cooling. That includes lights, some 12V TV watching, and water heater and water pump use. YMMV.
If I need to heat or cool then the usage goes up a lot. The fantastic fan on medium and furnace each use about 2 amps when running so if you run either one of them 12 hours a day then you will double your AH requirement, and you'd need about 180 watts of solar to replace that on that typical day.
The other thing to consider is to go to a dual battery setup if you're doing much camping without hookups. That will start you out with about 200 AH stored in the battery. You should avoid going below about 50% state of charge on your battery so think about that as 100 AH available. That would give me about 4 rainy days or days camped under trees without any solar charging, as long as I'm not heating or cooling, or about 2 sunless days if I need to heat/cool.
So, starting with a fully charged large battery will effectively allow you to extend a boondocking trip with a smaller solar system. Even so, here in the east we can never really count on clear weather for very long so for me, having an alternative charging source (generator or tow vehicle) is a must.
I'll add one other unsolicited comment. IMHO, the Zamp kits are way overpriced for what you get. Unless you have your heart set on one, take a look at the options out there before you buy.
Hope that helps.
------------- 1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
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