Understanding biomass solid fuels as a renewable energy source

Pistachio shells, wood shavings, cow manure — it’s easy to think of such substances as waste. Yet, each is rife with organic compounds that can be converted to energy through processes including hydrothermal carbonization, pyrolysis, and densification.

Luan et al. reviewed more than 150 articles to synthesize known biomass solid fuel sources and their potential for clean energy. They found that fuel quality depends on the match between the biomass source and the processing method, and that different fuel types best serve different purposes.

“We were motivated by a practical problem: there are many types of biomass wastes, and many technologies can convert them into fuel, but it is not always clear which material should be matched with which process,” said author Ping Han. “We wanted to help researchers and engineers see the whole picture more clearly, so they can choose better feedstocks, better processing methods, and better final fuel forms.”

The researchers began by identifying biomass types suitable for solid fuels, including forest and agricultural residues; energy crops; algae; and food, livestock, and municipal wastes. Then, they compared the sources’ fuel-quality indicators, such as moisture, ash, fixed carbon, and volatile matter, as well as the main processing method for each. Finally, the team assessed how changing the processing method changes the fuel’s energy density and combustibility, among other qualities.

The authors revealed that each fuel source has unique properties best suited to specific processing methods and specific applications.

“The meaning is simple: there is no single ‘best’ biomass fuel,” said Han. “The best choice depends on the raw material, the process, and the final use.”

Source: “Sustainable biomass solid fuels: Feedstock sources, processing technologies, densification, additives, hydrochar and circular-economy perspectives,” by Jiyi Luan, Qi Wang, Qiang He, Bo Cui, and Ping Han, Journal of Renewable and Sustainable Energy (2026). The article can be accessed at https://doi.org/10.1063/5.0321225 .