Solar Heated Loo

Michael has developed this simple and elegant solar heated version of Arbor Loo that has many advantages as well as offering a little more comfort on those cold days.

solar heated loo

Full description from Michael below.

Thanks very much to Michael for providing this material!

The Solar Loo

The idea is based on the Arbor Loo concept promoted in Africa/Haiti and other non urbanized parts of the world, which features a portable enclosure over the pit and the plan that as the pit fills, the enclosure is moved to a new pit location, the used pit is then covered with a bit of soil, sometimes rested and then used as a tree planting area. As we are postponing septic, but living on site while constructing a house some sanitary facilities were needed.

First we tried one of the manufactured indoor "composting " toilets with limited success. I would not really advise any one to mess with these. If you are going to be having to deal with the waste, might as well use the Humanure Handbook ( excellent book) idea. If you do not want to handle waste on a frequent basis, and can deal with stepping out to do your business then the Arbor Loo idea seems to be a pleasant and practical solution.  This idea appealed to me for several reasons but primarily no waste handling, efficient recycling of human waste and the savings of thousands of gallons of water. 

solar loo
South side of the loo showing the solar water heating collector and
the PV panel that directly drives the pump that circulates water from
the IBC tank to the collector (no controller or external power needed).

The north side of loo with salvaged door and window!

The one thing I have to add to the Arbor Loo idea is heat, we do have winter. Having some salvaged DHW equipment helped with that.

The solar heating system works like this:

The IBC tank provides heat storage to heat the loo over nights and cloudy days.

This very simple solar heating scheme could be used in other solar heating applications.

The tank is an IBC  (intermediate Bulk Container). The IBC's are often surplus industrial liquid containers which may have contained food syrups and be food grade or may be pesticide/methyl ethyl death grade, they are often available in urban industrial areas as surplus. They hold about 275 gallons. There is a small industry now related to providing these to the secondary market. Google will find them. I have seen these as low as $45.00 in quantity ( not food grade) and as high as $100.00. They may be stacked two high due to the strength of the steel surround. The poly ones ( there are also stainless steel ones $$$$) are almost always translucent white, which means if one wishes to expose to sunlight the light will allow green stuff to grow, I have had good luck with dark green latex paint in my other application as twin storage tanks for solar pumped domestic water. Does not adhere too well, just don't scratch it! 

Having a little backhoe is useful for not only the pit but for relocation. If I were to rebuild this thing I would design an axle under the frame so I could use wheels for the relocation. I do of course drain the IBC before relocation and did insulate the structure and all but one side of the IBC with foam ( mostly scraps) .

I built this for our high dry climate, users in wetter warmer lower locations might not have the same results. 

side view solar loo
The east side during construction. The IBC container stores solar heat and
directly heats the space and also provides a heated backrest.

solar loo vent
This chute made from a section cut from a poly drum
replaced the chute in picture to left that was made from
a 5 gallon bucket, but proved to be to small.

solar loo diagram

Performance and Use

The heating performance is good -- the IBC radiates better than expected, providing a soft comfort at the back. We do have the periodic 3 day storms, and that is about the limit of heat storage. 

We are in the southern mountains of New Mexico at 7150 ft altitude 33 degrees N the latitude. So we have great sun, but also below zero ( not common) temperatures. Lots of wind, not much rain.

As to use, we keep a bucket of aged wood chips ( in abundance due to a fire safety thinning project) and drift a bit of cover over each deposit. Any mulch type stuff could work.  The smell is never bad because of this, although some smell is present at each use. I built in a vent but the resultant chilly updraft in winter means I cap that except for summer, I really do not think it is necessary. The little Rule 24 bilge pump has a temperature rating of 200 F and is doing fine. 

As to time for fill, we built this  two years ago and are nearing fill on the second location with 4 adult users. Obviously this would depend on depth of pit. One chore as things fill is to use a stick/shovel etc. to even the pile out. Since we use about 50/50 chips with waste this is not onerous. The addition of earth worms would be beneficial.

Almost all "composting"  toilet systems as well as our contemporary water flush systems involve what I feel to be the fallacy that humans must somehow intervene in the natural process, which means waste handling, which means eventual errors and occasional disasters. This is human arrogance, nature has been dealing with the waste of billions of creatures for millions of years. The system we evolved with was drop it and move on. The Arbor Loo idea returns to that system. It is not useful for urbanites, but for those who choose non -urban life it is the most simple, most effective and most safe. 



Item Cost
IBC tote $90
Pump (Rule 24 bilge) $20
Framing, skin and screws $150
Insulation (some from scrap) $40
Door (recycled) $0
Collector (salvaged) $0
PV panel (salvaged) $0
Total $300


Michael, February 18, 2014


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