For an example, I'll document my own power system, which I've spent the last few years upgrading to a more state of the art system. My double geodesic domes were originally built in 1980, and for that time, it was a pretty standard design. How times change...
For a long time we've limped by on the 20 year old photovoltaic panels that were there when I bought my house. These panels comprised of 8 Arco 16-2000 panels (rated at 35 watts), and 2 Solec Panels (rated at 90 watts) for a grand total of 460 (if running at full efficiency) watts. This isn't much when compared with other fully off-grid houses. We've managed by being heavily propane dependant. I recently installed 16 Evergreen EC-110 panels to reduce my propane dependancy, and switch to more DC devices.
Upgrading the photovoltaic array turned out to be more of a carpentry and ditch digging project than an electrical one. I was working on a 45 degree roof, too steep to stand on, and impossible to get a ladder on. So I was forced to hanging in a climbing harness off of a few climbing bolts I put in. Once I got a few of the footers installed through the wood shake roof, I could then use those for foot rests, tie off points, or directional anchors. It did make things a bit slow though, plus working on flashing and reshingling parts of a wood roof are a major pain in the neck.
When it comes to working on a wood shake roof, you need to buy round standoffs to use instead of the feet that come with the rack. These ate the size of plumbing vent pipes, so you can use standard vent pipe flashing to keep your roof from leaking. I also sealed all the bolt holes with caulk, and tarred the flashing into place.
The slowest part was probably digging the 130 foot trench deep enough. Here in the Colorado Rockies, ditch digging should be an olympic sport. Rather than go through the house, entailing lots of conduit work, and digging some how under my deck without destroying it, I went around the house from the garage (where the new panels are now) to the power shed. About a quarter of the trench was through previous excavated dirt around the septic tank, so digging through that wasn't hard at all. But the other half involved drilling rocks, and lots of sledge hammering. Good exercise, but really slow.
When I bought this place, it came with an ancient Paris Dunn 5kw wind generator that was broken, and a small WhisperLight 430 that soon after I bought this house. I recently installed a recording wind meter on my tower, and the data has been good. At least during this dark time of the fall, we get less than 3 hours of sunlight, but the wind has been blowing about 30mph steadily for weeks! So this summer I plan to install a new Bergey XL-1 1000 Watt wind generator.
My old power system was a joke of homebuilt and ancient electronics. For one thing, it only had a single disconnect for everything, including all the DC and AC circuits. After we suffered through a major crash because of the lack of electrical isolation, I decided to redesign it all. The spontaneously fried Heart inverter was replaced with a Trace 4024 Inverter, and I added all the disconnects required by the NEC code, as well as a few more for ease of maintainance.
The rewiring project of the power center started well, but at this altitude, the weather can change quick. It went from a reasonably warm spring day, to a windy cold one. It took about 3 days, but I replaced everything, brought it up to code, and left room for future expansion as well. It was a bit of a canabalizing project mixed with redesigning, reusing components, and adding more disconnects and a new charge controller.
When I bought this place, it came with 12 Trojan L16 batteries that were about 7 years old. (a little past warrenty). These died a year or so later due to age. I replaced them with a 8 Surette 6CS-25PS batteries (roughly 3 times the storage capacity) I have heard stories the original owners used dozens of car batteries for power.
I've got neighbors with amazingly small systems. My closest neighbor (over the hill) runs on 16 golf cart batteries. Another neighbor ran on 4. It's doable if you don't mind running a backup generator alot, but I prefer sufficient backup storage.
I have a Honda 5000 watt generator that puts out both 120VAC, as well as 240VAC. This is mostly used to run the 240VAC deep well pump. I soon plan to replace that pump with a DC one. This generator has been modified to run on propane, which is much nicer in cold or bad weather than dealing with fuel cans. It does suck quite a bit of propane however.
One day, while I was filling the cistern, the generator caught on fire. If I hadn't been around and had a working fire extinqusher handy, it might have been a disaster. This is one good reason to never have an automatic startup switch for your generator. This day it was particularly stressful, as I was filling the cistern because there was a large forest fire 2-3 miles away.