I've received so much useful information on this forum and figured it's about time I gave something back. I thought a review/starting a discussion on the Sunmar composting toilet we have may be a good start.
The Sunmar Excel NE is a self-contained, waterless composting toilet that doesn't require any electricity and is said to be suitable for full time use for 2-3 people. We chose it for those reasons - it seemed like the best off-the-grid option on the market.
Unfortunately, the information we got with the toilet from the Australian supplier (we got ours from Solazone) said that if the temperature shouldn't be maintained above 14oC for continuous use of the toilet. This wasn't stated anywhere in any of the advertising material (we did our best to research before buying, especially as it cost around three grand).
During Summer it seemed to compost fine and there was no smell, even though where we are nights are regularly below 14oC even in Summer. Now that Autumn has come along composting has pretty much stopped. Winter is going to suck!
We have also had issues with the excess liquid in the bottom of the unit not draining properly. The drain is too high so it excess liquid builds up and even with the toilet sitting up on a pallet we have to tip it back every few weeks for it to drain (we've checked for blockages etc, so that's not the issue).
Anyway, I would definitely not recommend this toilet at this stage. We've emailed the company we bought it from to see if they can provide a solution to the temperature problem, but for three grand you could do a lot better - next time we'd look at building one ourselves.
If anyone else has the same model and has had similar problems, or has a solution I'd love to hear about it, or even information on good composting toilets.