Got no power or minimal power on site? No worries - a composting toilet is still an option! While composting toilets do have a small fan for ventilation, in the right conditions and with the correct setup, you can run a composting toilet completely power-free! The only limitation on this is that you cannot run heated models as these require constant power to run the heating elements and evaporate liquids. However, there are passive heating options which are beneficial to both power-free and low-power setups. A leachate drain is required for both for effective management of liquid discharge.
Below, are some recommendations for running a composting toilet on a zero power or minimal power setup. If you're in a pickle and would like some further advice, custom design services can be provided by WCTNZ®.
Total off-grid (TOG) - zero power
This is a total off-grid setup, where there is no power on site and all systems are essentially nature based. This setup requires passive ventilation and leachate drainage. Heated composting toilets are ruled out and passive heating of compost is beneficial.
Passive ventilation
In the right conditions, a composting toilet can be equipped with a wind-driven vent to allow for passive ventilation in place of fan-forced ventilation. For this to be an effective solution, the site should ideally be in a location with consistent high-winds. This is usually seen in coastal and mountain locations. However, in low wind locations, such as valleys and tall forests, a wind-driven vent can still be effective if a high solar-thermal index exists. In this case, you can build a passive solar-thermal vent stack. These are best built in conjunction with high-winds, but if sufficiently sized in length and width, can do the job regardless. There are also ways in which you can maximize the efficacy of passive ventilation - see How to Build Resilience for Passive Ventilation.
See product as example:
Passive heating of compost
To keep your compost pile at an optimum composting temperature, it is beneficial to the compost to passively maximize heating of the composting chamber. To do this, simply place the toilet/composting chamber in a sunny location. For split systems, you can also insulate your chamber - read how to do this here.
Liquid discharge (leachate) management
In power-free setups, it is not possible to have a system that can effectively evaporate all the leachate consistently. Some options exist for solar-thermal evaporation, but are not reliable enough to manage leachate on their own. Properly placed drainage is required for power-free sites.
Minimal power - power present in the form of solar (system under 1KVA)
This is a minimal power setup for those using a small solar array, charge controller and batteries (under 1KVA). You can run the composting toilet fan on solar, but heating is still ruled out. Passive heating of compost is beneficial and a leachate drain is required.
Passive heating of compost
To keep your compost pile at an optimum composting temperature, it is beneficial to the compost to passively maximize heating of the composting chamber. To do this, simply place the toilet/composting chamber in a sunny location. For split systems, you can also insulate your chamber - read how to do this here.
Liquid discharge (leachate) management
In low-power setups, it is not possible to have a system that can effectively evaporate all the leachate consistently. Some options exist for solar-thermal evaporation, but are not reliable enough to manage leachate on their own. Properly placed drainage is required for low-power sites.
Bucket Systems
If you're wanting to forgo the drain and ventilation altogether, you can opt for the good ol' bucket system. Bucket systems are easily installed, and require no power or drainage. While they act as more of a composting toilet commode, bucket systems are a solution proven by time. Keep in mind these are small capacity systems that require secondary treatment of materials in an onsite Secondary Treatment System.
See product as example:
Need help choosing a system? Call WCTNZ® on 0800 022 027 for free advice on system specification and setup. Advanced design consultancy services are also available.
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