Abstract: To address the inability of conventional toilets in cold regions to operate in winter due to freezing, as well as the difficulty of achieving reliable, continuous, stable, and harmless treatment of feces on site, a multi-functional zero-energy ecological toilet system is developed. The proposed system integrates solar energy collection, power generation, and constant-temperature anaerobic digestion for waste sanitization. Its operational performance is experimentally investigated and comparatively analyzed under three representative weather conditions: sunny, cloudy, and overcast. The results show that the electricity generation under sunny, cloudy, and overcast is 0.9, 0.7, and 0.3 kW·h, respectively, with corresponding photovoltaic conversion efficiencies of 10.9%, 11.2%, and 11.1%. The cumulative power consumption of the system is 1.85 kW·h. Under three working conditions, the effective heat gains of the solar vacuum tube collector are 5.6, 4.6, and 1.8 kW·h, with heat collection efficiency of 50.8%, 54.1%, and 46.2%, respectively. The average temperature of anaerobic fermentation digestion bag is 26.1, 26, and 25.5 ℃, while the average temperature of toilet room is 16.7, 15.9, and 14.6 ℃, respectively. Moreover, the system is estimated to save 1807 kg of standard coal annually, with an investment payback period of 7.6 years. These results indicate that the constructed zero-energy ecological toilet system is suitable for cold areas and can provide a new way for toilet renovation in cold and dry areas.

Key words: zero-energy ecological toilet, antifreezing, heat collection efficiency, photoelectric efficiency, power generation