Roped soloing is inherently much more dangerous than even normal climbing. Rope soloing truly puts your life in your hands, and you better not biff. Rope soloing is truly for experts who are well versed in all aspects of wall life. Do not rope solo, you'll die.
The basic problem is to inch worm yourself up the wall. You'll need to lead, clean, and haul. Two basic styles exist, one with more risk than the other.
Sequence is to 1) lead the pitch, 2) rap the pitch, 3) clean the pitch, and 4) haul the bag(s).
1) Leading: You'll lead as you would with a partner, however the belay is inverted. Integrating either a screamer or a heavy haulbag into your anchor can significantly reduce the impact of a fall, and the likely hood of Bad Things happening. Your rope will be tied to your Truly Bomber and Multi-Directional anchor, slither through your gear up to you, and attach to you using your favorite self belay device (Silent Partner, Solo-Aid, Gri-Gri, clove hitch, etc.). Of course you'll have upwards of 200' of rope on the other side of the device. Two common options exist.
Option 1 is to carry the slack with you in the form of backup loops, typically 50' or so per loop clipped into a large pear biner. The haul line is stacked at the belay and tied to the back of your harness for later use. The advantages are that you have all the slack near you in case of a snag, and that you have a backup to your solo belay device should it fail/break (and not sever the rope in the process...). The disadvantage is that you have a rats nest of loops hanging 25' below you just waiting to snag or lassoo something.
Note that as you move up there is ever increasing weight on the protection side of your belay device. Unless you use additional means to relieve this weight from the belay deivce it is pretty common for the rope to back feed, or to make it difficult to add slack to the system for moving up. Common solutions include rubber bands, clove hitches, or prussik loops (or equivalent). Back feeding without your knowledge can create a very dangerous situation, turning a one piece fall into a long whipper.
Option 2 is usually referred to the continuous loop system leaves all the extra rope down at the belay. At the beginnig of the pitch the haul and lead rope are both stack or preferably placed in rope bags/buckets in a way that assures easy feeding. The far end of the lead line is tied to the beginning of the haul line. As you move up you will not be supporting any more rope weight than is needed to go from the anchor to you and back. After 100' the lead line will start bringing the haul line along for the ride
One variation uses a tag line to bring up the haul rope (and extra gear). The tag line and gear must then be rehung mid pitch using a fifi hook. Beware that should the tag line come loose the weight of any remaining gear will result in a harsh jolt.
As a soloist you must handle EVERY situation on your own. Be sure you can operate your solo belay system through free climbing sections, lower outs, penjis. Not all self belay systems handle all of these situations equally well, if at all.
2) Rap the pitch
For striaght up and down pitches this is the most straight forward and least gruelling part of the sequence. However a significantly traversing pitch can require gymnasitcs that a team never has to face. You may need to lock off your rap device and jug horizontally along the slack end back to the anchor. Make sure your belay device can be locked off securely.
You can often save yourself much time and hassle by cleaning or partially cleaning wandery pitches on the way down, rather than the way up. Keep this in mind as you descend. Cleaning the wrong pieces can making cleaning impossible, and will result in an offering to the booty gods.
Counter Weighting A major variation exists at this step. If you want to avoid hauling, it is possible to couterweight yourself on the way down. On the positive side you avoid much hauling and misery. On the downside you can loose your haulbag or die.
You must remotely cutting the bags loose, no easy feat. Unless you invent a magic RC caribiner, you be stuck hanging your bags off of a fifi hook (preferably two stacked together). Obtaining a clean release is key. Put a loop of accessory cord throught he eye of the fifi and rig a prussik around the haul line. The end of the haul line is tied to the bags for real, but the idea is to get the line to tension the hook so it lifts off cleanly. Alternately hang a liter water bottle off the eye to that it will unhook once unweighted.
In a worst case scenario the bag can come loose. If you are tied into the haul line at the time, you'll likely be ripped off the wall in violent fashion. If your rigging and some piece of protection holds, you'll still be stuck awkwardly with the haul line and lead line playing tug of war with you. Bad news. Instead affix the haul line to your system with a loop of ~3mm cord. The cord will snap around 500 lbs, hopefully saving you (for the time being anyway).
While counterweight rapping you still need to be rapping. If the bags are equal or more than your weight, you can basically walk down the face, maybe cleaning some gear as you go. If the pitch overhangs, traverses, or the bags are light enough, you'll have to use the lead line to get to the previous station. Variations abound here, but be aware it is possible to hose yourself pretty badly if you try this on overhung or traversing pitches.
3) Clean the pitch
Cleaning the pitch is just like with a partner. However you can often same much time by cleaning some or all of a pitch on the way down to avoid or reduce the hassles of cleaning traversing sections.
4) Hauling the bags
Other than having the counterweight option as before, hauling is just as with a team. If you have very heavy bags, you cannot rely on having a partner for space hauling, so bone up on the 2:1 or 3:1 hauling systems to augment your hauling.
When choosing a belay device several aspects of performance must be accounted for. Big wall soloing requires more techniques to be mastered and maneuvered than say solo free climbing. Not all devices are created equal. Petzl does not advocate using the gri-gri as a self belay device, but nobody should advocate solo climbing anyway. You may opt for a combination of devices on a varied route - a gri-gri for aid with pendulums and a silent partner for free sections, for example.
The gri-gri is probably already part of your big wall rack. As a solo device it has many advantages:
- Lower outs are handled in stride, just cinch up the rope, unclip your daisies, and rap down the free end.
- Allows you to rap the haul line without the need for an extra device.
- Allows a convenient backup while jugging.
It also has some disadvantages:
- It only allows one caribiner, and has been known to twist or cross load biners in a fall and break them.
- It does not self feed, so a modest amount of attention must be spent on it to keep slack in the system for moving.
- Best operated with two hands. Once tensioned from running out of rope (often in a desperate free section) it does not always feed out slack while operating one handed.
- Factor 2 or close falls really wedge the rope in, though it appears no permanent damage is done.
The solo-aid is not the most common, and for some good reasons. It's advantages are:
- Tie in is with rope (or sling) so there is nothing to cross load.
- Bomber contstruction with only 3 parts. Visual inspection is very easy.
- Feeding out slack once tensioned is a little better than with the gri-gri.
For solo aid climbing it does not really live up to it's name:
- Rapping or doing lower outs are a contrivance with this device, and do not work well, it goes from locked up to minimal fraction and back, nothing in between. It's easiest to bring an ATC to lower out or rap with rather than the method prescribed in the user manual.
- Feeding slack is still problematic, and can still require two handed operation if under tension.
- It is a specialty device, unlike the gri-gri it won't be of use on your bolt-clipping or toproping days.
The Silent Partner by Wren Industries is by far the most expensive, and slickest device. It's main advantages are:
- Self feeding, allows you to move up without having to arrange for excess slack ahead of time.
- Can be used as a rap device.
- Clipped in with two biners for redundancy.
However it is still not perfect:
- Rapping and lowering out require a lot of hand tension, as it does not have very much friction
- Self feeding can be problematic with large fuzzy ropes (like any good wall rope after a few pitches of jugging).
- Mechanism is not inspectable.
- The device is large and clunky, and can be a severe impediment in squeeze chimneys.