Seems like we need to cut to the chase on solar panels. I think its reasonable to expect that your solar panel charges your battery in a day of full sun. That way you can boondock as long as you want.
Here's what you need:
1) 65W (minimum!) Solar panel
2) Sunsaver 10 Solar panel controller
3) #12 wires from the solar panel, to the controller, to the battery
Wait a minute you say, I've been to a bunch of solar web sites and there's charts and graphs and battery sizes and all kinds of stuff. What size panel do I need? Why do I need a controller? How do I wire it? Why did you pick such a small wire, isn't that too small? I have a battery charger, won't that screw things up? And whats that aiming stuff about, don't I have to angle my panel or something?
- Solar Panel Size
Solar panels aren't as efficient as we would hope. You can get a 5W panel because its real cheap but it won't charge your battery, it will just maintain it. Get the largest size you can afford and they aren't cheap. Expect to pay about $6/watt. Don't expect the panel to completely charge the battery in one day (in full sun) if its less than 65W. 85W is better. And don't be a battery hog! Minimize your power usage, treat electricity like water and turn it off as soon as you can. The more juice you use the bigger solar panel you will need. A 65W panel is the smallest you can get and reasonably expect to charge your battery in one day with miserly power usage.
- Battery Size
Wow, there's a lot of debate on this topic. Get a group 27 Deep Cycle
battery if you don't want to think about it. Use an online amp-hour calculator if you want to be more precise and get a more exact battery size. But the bottom line is that a 120 amp-hour group 27 battery is about the best choice when it comes to capacity versus cost.
You need a controller so you don't overcharge your battery and ruin it. Small panels don't need a controller but you don't want a small panel because it won't charge your battery in a day. A Sunsaver 10 is a good compromise between cost and efficiency. It's rated for 10A so you can start with an 65 or 85W panel and add another one in the future if you really get into solar power. If you're sure you won't every get another panel you can go with the Sunsaver 6.
- Wiring a Solar Panel
Its easy to wire a solar panel. Two wires from the panel to the controller. Two wires from the controller to the battery. Stick a 15A fuse on the positive wire between the battery and the controller. Keep the fuse as close to the controller as you can. Read the instructions that come with the panel, controller and battery and make sure you follow the polarity marking ( + and -) on each device.
- #12 wire
The power wasted in voltage drop through a 10' section of #12 wire from an 85W solar panel to your battery is about half a watt. Don't worry about it.
- Battery Charger
The Sunchaser controller "knows" if a battery charger is in use and shuts down the panel. It turns it back on if you turn off the battery charger. If its dark outside the panel won't be working anyways. It also "knows" if your charging the battery off the 12V side of a generator and shuts down the panel.
Okay, here's where you have to make some decisions that will affect how much solar panel you buy. You can expect to gain about 20% extra charging capacity if you're real anal and point the panel right at the sun every 30 minutes or so. If you're lazy like me you can just lay the panel flat where it will get full sun and forget about it. Bump the panel sizes shown above up by 20% if you can't be bothered by angling the panel towards the sun. But watch out for any kind of shade on your panel. Just the tiniest, little bit of shading will cripple your panel's output.
Okay, I've been a bit flip about this but I feel like I can be because my solar panel system has worked like a champ and I don't have to worry about battery capacity anymore. There's a ton of technical items that can be discussed about solar panels, and they're all relevant. BUT, I don't believe that it will change the sizes of the items I've posted above by much. And if you're just trying to get into a solar panel system without having to take an engineering course, you can't go wrong with what I've posted. You just might not like the price, but what are you going to do?