Note: SOLOING is a dangerous activity and really should never be done. Climbing, like most outdoor sports should be done with a partner incase of mishap. The techniques described below should not be done by the inexperienced. If you have never soloed before find out from someone who has. Learning this technique of the Internet is not good for one health.
Being an avid hater of rope work you wouldn't find me caught dead trying to solo myself, and since I'm not an expert I asked around for some advice. Below are the best responses and most detailed I got...
I use a self-belay top-rope set-up several times per week. I started using this system this summer. I use ita lott and like it.
I use the Petzel Ascention handled ascender. My rope is a Sterling V-dry 60m. I use a prussic (6mm. cord, sheath fuzzed a bit) with 3 wraps, above the ascending unit clipped to a leg strap on my harness. The harness is one of those old ones that's all 2 in. webbing, so the leg loops are sewn to the belt, etc. I also have a daisy clipped to the ascender and girthed to my harness to keep me from losing the ascender if dropped. And I carry the second ascender on my harness as well. And sometimes a partial rack.
This link shows the petzel ascender self-belay setups. I prefer the first one , harness only.
I usually set up this way:
Walk to the top of the intended climb, set up anchors/clip into bolts etc. rapell off the top using an extended ATC with prussic back-up off a leg loop. this enables me to lock off the rappell and redirect the toprope with gear or (existing) bolts to follow a less than perfectly vertical line. I realize this allows for a potential drop if the placement blows. The placements need to be bombproof. If a placement fails slack is introduced to the system and may cause the ascender to cut through the sheath or even the rope. The manual/notice that comes with the ascenders describes in 3 languages how the rope can be cut or damaged by slack in the system. A fall factor 1 can sever an 8 mm rope. As little as 4.7 Kn. can badly damage a 10.5.
At the bottom I set up a weight on the line , usually a 1/2 gallon of water is cozy for me. Too much is bad. None is deadly, as the rope will not feed properly for the first 15-20 feet without it. If I'm going to retrieve the line from the top, sometimes I'll tape the rope to a springy branch. That way the tape releases when I pull the rope up. I use gaffer's tape, a heavier form of duct tape.
I set up the ascender and leave the prussic on the line, above the device. I have no illusions that this will stop a fall in the event the ascender fails. It is only handy in the event I need to lower down a bit. I can lock the prussic , release the ascender, move down a bit, re-weigh the ascender, release the prussic and climb again. That is the one drawback I've encountered with the ascender self-belay, the inability to downclimb or generate slack. (Remember, too much slack + fall = DEATH in this set-up)
When I get to the top of the climb, I'll clip in to the anchor with another daisy, lock the prussic, remove the ascender, set up my extended ATC above the prussic, rap down, repeat,etc.
I practiced this set-up on a really easy slab about 10 -15 feet off the ground with nothing to hit if I fell. I took me a while to get used to it. There is little to no redundancy in most parts of this system, and equipment failure could be fatal. I personally don't use a back-up rope. That is because I am a lazy idiot. And I do this in areas that are not well travelled. This is also very foolish.
I have fallen on this set-up several times. The catch is quite soft, like a good top-rope catch with no slack out. I am confident enough to use it at my top-rope limit. I look upon ANY belay system only as a back-up to climbing skill, not a trampoline to jump into if I get tired or over my head.
I haven't yet used this system on big overhangs. Getting back on the climb could be a challenge.
Really, this is only the way I do top-rope solo. I do it because I like to climb alone sometimes. I'm not suggesting anyone else use this set-up. If you fall and your head pops off and your relatives sue me,I have nothing. And I told you not to do it.
The only thing I would add is now I use fishing line instead of tape for tension, I fall more now than when I posted this,( as i am climbing harder stuff,) and I do think the prussic would help in the event of an ascender failure,(since i have found it to have locked up before the ascender several times) hope this helps.
Another way you can solo is explained below.....
Set up a completly bomber anchor with several anchor points
I have used this system several times when I havent been able to get a partner or havent had any faith in my belay partner. and have found it works well and is the safest ive seen so far.
Also believe it or not there is actually a book on the subject...(I've never read it or seen it, someone just told me about it.)
"Himmelsleiter - The Art of Solo Climbing":