Before we purchased our property in the woods, my wife said that she hated outhouses and said that she wanted a real toilet. Being a water access only property I was worried about this, and called a few of the local contractors in the area, who all said "no problem." After the deal closed I called them back and they said "Oh, on that lake? there is no barge service there, it is too small, we can't do it." Thus I was involuntarily introduced to the world of alternative toilets.
Not yet particularly concerned about the cost of energy or it's carbon footprint, I liked the idea of the Incinolet, where one drops a sort of melita filter cone into the stainless steel bowl and then press the foot pedal, which drops the whole thing into the combustion chamber below and incinerates it to ash (sort of) in 40 minutes, and sounds like you have a 747 in your cabin. It seemed so clean and neat, incinerating it all, but we got smoke. Flames. Kilowatt-hours galore. A strange smell lingering around the cottage on still days. This hot seat put our kids off potty training for a year.
Taking a less incendiary approach, I bought a Sun-Mar Centrex composting toilet, which separates you from the composter with a ceramic low-volume valve toilet and a flush mechanism, made for boats but married to a composter instead. We churn it, let it bake, follow instructions carefully and yet seem to be constantly removing not compost but a soggy mixture of peat moss and poop. The drain pipe ran almost horizontally to the composter and my children used so much toilet paper that the little bit of water rarely made it to the composter, preferring to clog the pipe so that I was spending my weekends with a wire snake trying to clear it out. Furthermore there is "excess fluid" that does not evaporate and has to be dealt with by constructing a whole other Class II septic system. Not having this, we got closed down by the local toilet police.
Had I used the proper mix of sawdust and peat moss, and trained my kids better about the use of toilet paper, I suspect now that it would have been fine; many people swear by the Sun-Mar. They also advise that Building Code issues regarding the "excess fluid" have been resolved, and I do not want to cast any aspersions on their product, but at the time I was fed up with it and closed it down.
I wanted a unit that did not use water, and that meant losing the china bowl and getting an all-in-one unit that can evaporate the urine. I worried that my new Envirolet might not have the capacity to deal with family and guests so I broke down and built a funky A-frame outhouse up the hill behind the cabin, leaving the composter for nights and visiting moms. In the first year I still had problems with excess toilet paper, but now have a separate wastebasket for toilet paper and the composter is working fine, and even my 89 year old mother has no problem with it.
It is big enough that we only have to empty it once a year, in the spring after it has sat all winter, so it usually is completely innoffensive compost by the time I open the door on the front of the unit. This year was a bit different; the exhaust vent had been broken by the huge snowfall we had this winter, and I had not realized that a lot of water got into the unit. When I opened the watertight door to remove what was supposed to be a nice, dry pan full of compost, I got ten gallons of very disgusting wet stuff all over the floor. Not fun to clean up.
The Envirolet has a very simple operating system, simply a rake that you push back and forth to distribute the compost-to-be. The Sun-Mar has a rotating drum that mixes the compost thoroughly. Both are available in off-grid 12 volt systems to run the fans; the Envirolet even has a solar panel option.
However, if you have a little more money and electricity, have a look at the Swedish Multoa composter, sold in the States as the Biolet. Lifting the lid fires up the fans; sitting on the toilet seat opens the trap doors; putting the lid back down activates the churning motors. It does everything automatically and anticipates your every move and movement.
Now, our neighbours have put in a road to their place, and I could spend a little money and extend it to ours, and bring in the trucks and the backhoes and install a real flush toilet and septic system if I wanted to. But I never would; both the outhouse and the composter have lovely views, maintenance is minimal, impact on the site is almost non-existent and there is less chance of damage to the environment and our lake. I wouldn't change it if it was free.