10forty2 wrote:
Curious...for those who dry camp a lot, are you using the solar panels to power the house instead of the house batteries? I would have thought the regular house batteries would run the coach and the solar panels would keep the batteries charged..similar to plugging in to shore power. If so, then why is some much wattage required for the solar panels? I admit to not being up on solar usage, nor do I dry camp, so I'm honestly asking in case I decide to do either!
You kind of power both the house and house batteries. If power is being used, the power your solar produces will supply that fist, with any excess going to charge the batteries. It's all the same DC bus for most users.
Solar is one of those highly variable things, and energy usage can easily be much more than you expect. As for some reasons for needing a fair amount of solar:
Flat mounted panels don't harvest all that is available much of the time. I generally figure I'll get around 75 percent of rated output but it varies a lot with time of year. For a 100 watt panel I plan on 25ah a day captured, again varying widely with time of year. Trees, afternoon thunderstorms etc make a lot of difference. If I go to Southern Utah or Arizona I get a fair bit more, go North it tends to be a little less.
Residential refrigerators use a fair bit of power. When we were last shopping for our RV, most of the ones we were interested in either had 18cf Gas/elect units or 18cf residential units with energy star labels that showed an equivalency of about 95 amp hours of 12vdc use per day. If you figure your inverter efficiency at 85 percent that's around 105ah, or right about half the capacity of 2 golf cart batteries per day. Again, efficiency comes in to play with wet cell batteries only being about 85 percent efficient when charging, so you're looking at 400 to 500 watts of panels to keep up with the refrigerator. All of your other energy use is above and beyond this.
There are also things to consider such as having excess capacity so your can bulk charge as much as possible early in the day in order to try and get the batteries fully charged while the sun is still available, which is something more important to those, full timing, or camping for longer periods of time. You really need to get your batteries fully charged fairly often for maximum battery life.
Energy Audits, conditions you'll be camping in, and willingness/ability to do things like run the generator for a period in the morning for bulk charging are all considerations in figuring out what will work best for your situation.
