Stacked Use and Transition Trends of Rural Household Energy in Mainland China.

Household energy use is an important aspect of environmental pollution and sustainable development. From a nationwide residential energy survey, this study revealed that household fuel "stacking"-mixed use of multiple fuels-is becoming noticeable over the 20 years from 1992 to 2012, particularly in northern China where space heating is needed in the winter. Approximately 28% of rural households used only one single energy type in 1992, whereas the percentage declined to merely 11% in 2012. The number of energy types correlated positively with the heating degree days and negatively with the household income in areas with limited or no heating requirements. Combined use of biomass and fossil fuels may lead to extra energy use, up to 40% for cooking and 20% for heating. Some fuels, as supplementary ones, are used more often than others, and the energy consumption of coal and honeycomb briquette could be underestimated by 34% and 22% if only the primary energy was accounted for. Generally, household energy is shifting from solid fuels to cleaner ones, such as electricity or gas for both cooking and heating, but with different patterns and transition rates. Transition pathways varied extensively from one region to another due to the imbalanced development. Clean transitions initially occur in well-developed provinces and megacities and then extend to inland provinces approximately 5-10 years later. Rapid energy transitions and urbanization have led to nearly 50% reduction in residential energy consumption over these two decades, consequently resulting in significant declines in emissions of most air pollutants. The updated residential emission of primary PM2.5 was 3100 Gg in 2014. Extensively fuel stacking and rapid energy transitions have led to complex circumstances in energy use.