A little while ago I wrote about composting toilets, and the lavatorial experiments we carried out before committing to use them. Recently, the Boss read about incinerating toilets and asked me to condider fitting one, because they were "a complete waste solution" and "environmentally friendly". I thought you might like to know the background calculations I did to compare them. After all, we all need to "spend a penny" but I found it cost a little more than that!
I took data from the LeeSan website as they import the popular Cinderella incinerating toilet. These are available as either gas or electric versions, but as Perseverance will have no gas, it's obviously the electric version I did the calculations for.
For this make of toilet, the voltage is 240VAC, which is fine, and the incineration current of 10A is manageable. The Energy consumption is quoted at 0.8-2kWh per incineration. For a worst case calculation, I started with the highest figure of 2kWh.
I’m going to assume we are moored away from a marina, that is, we have no shore power, and I will apply my usual gloomy prediction that the sun doesn’t shine, so we cannot rely on solar power. All the energy will have to come from our generator. I plan to fit a 6kW generator, and this will take 20 minutes to produce 2kWh of energy. Using very rough figures, the generator burns about 3L of diesel an hour. Diesel costs about £1 per litre, so this is £1 per poo.
I don’t know about your lavatorial habits, but let’s say you visit the loo five times a day, once with a full 2kWh/£1 visit and four times at 1kWh/50p. That makes just over £3 (or 3L in diesel) per day per person. More significantly, the generator is running one hour per person each day. Let's think what this means for our cruising experience.
The busy boat
Our boat will sleep six, and assuming four adults and two teenagers, all with large appetites from energetic days on the lock windlasses, we can see the generator running six hours per day to cook their poo and boil their wee. That’s before the boat moves anywhere.
The quiet boat
Let’s extend our calculation to a liveaboard boat with two people on the boat for 300 days a year. (OK, I know there are 365 days in a year, but I like easy numbers to get a feel for things).
Our livaboard couple will burn 1,800L of diesel and spend £1,800 per year. Now, when a litre of diesel is burnt it creates 2kg of CO2 so this is 3.6 tonnes of greenhouse gas.
All this seemed at odds with the ecological image of these toilets. After all, the toilet is manufactured by the Cinderella Eco Group in Norway. To explain where I think the difference lies, please let me take you on a "virtual world tour" to Norway and Australia.
I was fortunate to have a friend who lived in Norway who had a hutte in the mounains, like the one above. It was intended for skiing in the winter, but we crazy Brits went there in the summer for some hiking. The hutte was built on solid rock, and had no drainage. Water came from the local stream. Now, in Norway, electricity is renewable, with 98% of their electricity coming from hydro-electric systems. Interestingly, it is all fed on rather unsightly overhead cables because you don't bury miles of cable in rock.
For Norway, the eco label is justified because they have no drains and it is difficult to dig a hole for a cesspit, but they do have a plentiful supply of 100% renewable electricity.
In Australia, many parts of the outback have a terrible water shortage. They do, however, have a lot of sunshine, and with solar cells providing renewable energy this is an eco-friendly solution to their problem of waste disposal. In fact, the Cinderella toilet won a design award in Australia.
If you live in the Australian outback with no water and loads of solar power, or on a rock in Norway with loads of hydro-electric power but no drainage, an eco-label is justified. However, sitting on a canal and dependent upon a generator that creates a large amount of CO2, I don’t believe the eco label can be justified in this context.
Old folk will remember "spending a penny", but a pound a poo really is too much. So on both cost and environmental impact it's Compoosting for us.
I contacted LeeSan to make sure I was not misrepresenting the incinerating toilet. Their Director was kind enough to reply, and agreed that "the eco credentials must be evaluated for the user". He also said "I wouldn’t use a compost loo on a boat", which is where we have to agree to differ.