Ok, I am just delving into my first experience (other than generator) with off-grid power.
Please - before commenting - can I ask that you see what my goals for this system are before commenting, as I think that the objectives inform the method. Thanks.
My goals for this system are very modest, I think. I do NOT want to power the house. I DON'T want to run the furnace, washer, fridge, power tools, welding rig or any such power-hungry device. If I did, I would have chosen an altogether different strategy.
The goal is to provide a very small amount of power for a set of very small devices.
The devices I want to power are things like LED flashlights, cell phones, Kindle reader, a netbook computer, portable DVD player, shortwave radio (receiver only, not HAM), etc. Things that have replaceable/rechargeable batteries which don't draw a lot of current.
My goal in doing this is to always have some power available for these devices, even if there is a reason why the generators cannot or should not be run (noise signature, fuel shortage, etc). After the initial cost of getting set up, the energy should be basically "free" and infinitely renewable.
In pursuit of this modest ambition, I have acquired two 6 volt batteries (Trojan T-105 RE which are basically golf cart batteries that have been beefed up for use with renewable energy applications) which are hooked up in series, and a Harbor Freight 45 watt 3-pannel kit. I've heard some folks are not thrilled with the HF kit, but like I said, I'm not planning to power the house, just "float" a couple of batteries for emergency use. I installed everything last night. Because of the modest ambitions for this kit, I am not concerned about optimal placement of the pannels. Right now I have them propped up in the windowsil, facing due south. I want to see how they perform in this position before taking the experiment further. If needed, they can be mounted outside in a more favorable position. We have a large tree in the west that shades the house after about 3-4 in the afternoon. I am hoping that the pannels will still generate a trickle charge even if they are not receiving direct sunlight.
I like that the regulator unit of the HF kit has several kinds of power outlet - 12v Auto, 5v USB, etc... I have heard people say it is a crappy unit, but never heard anyone say what specifically they didn't like about it. For all I know it could be the color or that they wanted some option that it doesn't offer. I'd consider upgrading the regulator if there was a significant reason to do so. I'm hoping that for what I want to do, it will be sufficient. I actually like the form-factor and it sits on a bookshelf, out of the way yet easily accessible - it doesn't require mounting.
Last night when I got everything connected (after the sun went down) I had a chance to test the system a little bit. The batteries read right at 12.3 v and the two (included) 15 w CFL's worked fine, as expected. When I got up this morning (before sunup) it was still reading 12.3 v and by the time I left for work (8 am) there was a bit of good daylight and I noticed the battery reading was up to 12.4 so it looks like it's taking a charge even with sub-optimal placement of the pannels.
Hopefully this evening I can put up some photos and report on charging performance in this configuration. Total cost of the whole system so far is about $700 which is just under $200 for the HF kit and around $500 for the batteries, cables, battery boxes etc. Yes, I could have gone cheaper with a simple deep-cycle marine battery but I thought it was worth the money to go for a little more capacity and the reliability of the Trojan product. I expect this system to spend much time charging and little time being drained, so hopefully this setup will meet that need.