Sol Char Toilet
University of Colorado Boulder
The Sol Char Toilet uses solar power to convert waste into charcoal and fertilizer.
Global; the prototype needs sunlight to function properly, hence regions with high sunlight are mainly targeted. It is constructed to operate off-sewer, to allow functionality in water scarce regions (often coinciding with sunny regions). In prototype phase 1, the toilet was laboratory tested. A field pilot is part of the planned phase 2.
This product has been implemented by the University of Colorado Boulder, Sol-Char research team.
2,600-11,000 USD, depending on the size of the system.
Communities and households without access to adequate sanitation, wastewater infrastructure, or that use charcoal as an energy source; farmers and other users interested in fertilizer and soil amendments; people interested in recycling and sustainable technology.
The Sol-Char Phase I prototype is constructed with industrial-grade materials: aluminum for the metal and optical components, stainless steel for the reactor components, and industrial steel and plastic for the user compartment. However, a functional prototype could be constructed more economically. The fiber optic cables are the most expensive component and outsourcing is currently in development. The majority of the Sol-Char toilet materials could be constructed in a local machine shop using more affordable materials such as concrete, spun aluminum, and injection-molded plastic. For example, the carousel drive that rotates the reactors can be constructed out of recycled bicycle parts and scrap metal.
The Sol-Char Toilet is still a prototype so it is not provided to users yet, but the product characteristics open up for several options of user provision. The toilet could be bought directly from the manufacturer/retailer or rented as a service. In low-income, NGOs or governmental agencies may finance a larger system with several toilets for a community. Another option is that a company provides the toilet to the public and the user pay a fee for each use.
Type of toilet
Method of evacuation
How the fecal sludge is stored
The holding volume of the containment
Time until emptying is estimated to be needed
Processes 2 kg feces in 4 hours sunshine (converts to charcoal)
The prototype was designed to process 2 kg of feces and 4 kg of urine with 4 hours of sunshine (given that fecal char has an energy content of 25.6 MJ/kg). The product concentrates sunlight and transfers energy to fiber optic bundles located at the focus of parabolic concentrators. The concentrated solar power illuminates the containers (both “collection” and “reaction” chambers) and disinfects the waste through conduction, convection, and radiation heat transfer. The reactor is designed to achieve temperatures between 300 °C – 750 °C and produces a safe and usable product.
Technical support is provided directly by the manufacturer, the Sol-Char team.
Replacement components can be hard to find locally in the Global South if the prototype materials are used. There are ways to simplify the construction and use materials available in most contexts such as scrap metal, concrete and bicycle parts. Some parts will need to be specially ordered such as the optic fibers which are the most expensive part of the system.
Performance targets include creating an affordable product that operates off-grid, without piped water or sewage. In addition, the treatment of human waste should create useful outputs. The Sol Char is expected to produce 80 g charcoal/use/day and 1 L of treated urine/person/day.
The product has been tested by the Sol-Char Team at the University of Colorado.
Manual hand cranks can be used if the automated flush mechanism fails so contact with fecal matter is still avoided. Dilution and adsorption is used to reduce human contact to exhausts. Exhausts are done through a pipe 2.5 m above ground. All moving parts are shrouded, and fibers are made so that light only exits within 8″ (fire precautions only have to be taken in this range). Pathogens are killed in the charring process to ensure that the system is hygienic.
Electrical ‘co-generation’ provides up to 15 kW-hrs of electricity with battery backup for offline (cloudy) operation.
Ward, B. J., et al., 2014, “Evaluation of Solid Fuel Char Briquettes from Human Waste“, Environmental Science and Technology, 48, pp. 9852-9858.
2014, “Reinventing the toilet for 2.5 billion in need“, Bulletin World Health Organisation, 92, pp. 470–471.
Garcia-Fine, S., 2015, “Redesign of the Sol-Char Toilet“, Bachelor dissertation, Worcester Polytechnic Institute, Worcester, Massachusetts.
The product has been developed to comply with safety standards and environmental regulations so that it can be implemented in diverse contexts.
The product has been developed and evaluated continuously through iterative prototyping.
Sol-Char sanitation media can be viewed here. In addition, an extensive amount of published articles have covered the Sol-Char project. Several conference posters are also available. The Sol-char sanitation team is exploring a phase 2 design for a field pilot.
Additional research articles and presentations conducted by the University of Colorado research team can be viewed here. Topics include Solar Thermal Design & Modeling, Biochar Fuel & Emissions, Biochar Applications in Agriculture, Odor & Exhaust, and Disinfection.
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