Anthracite is a high-carbon solid fossil coal with very low moisture and volatile matter content, high density, and high lower heating value. It has a hard, glossy structure and burns slowly and steadily with a high flame temperature and relatively low smoke and soot levels compared with other coal types. These characteristics make anthracite suitable for use in energy systems and industrial processes that require intense and stable heat, as well as in plants designed for controlled combustion of solid fuels.

Biomass pellets are a solid biofuel in the form of cylindrical granules produced by compressing milled organic feedstock under high pressure. The feedstock can be various types of biomass: woody biomass (sawdust, shavings, wood residues), agricultural biomass (straw, husks, cobs, stalks), energy crops, and selected biodegradable waste streams. Compared with raw biomass (chips, baled straw), biomass pellets offer more uniform particle size, higher bulk and energy density, and lower moisture content, which simplifies storage, transport, and automated combustion in larger boilers and furnaces. Fuel quality (moisture, ash content, chemical composition) depends on the biomass type and target application (energy systems, industrial plants) and is matched to the combustion equipment and technology.

Bituminous coal is a solid fossil fuel with medium to high carbon content, moderate volatile matter, and relatively low moisture. It has a high lower heating value compared with lignite and sub‑bituminous coal, making it suitable for use in large power and industrial boilers and furnaces. Bituminous coal provides relatively stable combustion, can be finely milled for pulverized firing, and is widely applied in thermal power plants, large district heating plants, and process industries that require a reliable source of process steam and heat.

Peat briquettes are a solid fuel produced by mechanical processing and pressing of dried peat into compact shapes. They feature uniform size and shape, lower moisture content compared with raw peat, and more stable combustion behavior. Peat briquettes have a medium lower heating value, lower than coal but higher than wet raw biomass, and are used as a locally available fuel for heat, steam, and, in certain systems, electricity generation. Due to their compact form and easier handling compared with loose peat, they are suitable for small and medium boiler plants designed for solid fuels.

Sawdust is a solid wood biomass generated during cutting, sawing, and processing of wood in sawmills, furniture factories, and other wood-processing plants. It consists of fine wood particles with relatively uniform grain size and variable moisture content, depending on whether it originates from green or kiln-dried wood. In energy applications, sawdust is used as a fuel for direct combustion in industrial biomass boilers, either alone or blended with wood chips and shavings, as a feedstock for pellet and briquette production, and in biomass-based cogeneration plants. It requires suitable storage systems, protection against moisture and self-heating, and automated feeding into the combustion chamber.

Straw bales are solid agricultural biomass formed by pressing cereal crop residues (wheat, barley, rye, oats, etc.) into rectangular or round bales of various sizes. They are a bulky, fibrous fuel with a stable lower heating value typical of cereal straw. In energy applications, straw bales are used for direct combustion in dedicated bale-fired boilers and furnaces, where the bales are fed into the combustion chamber manually or by mechanical systems. Due to higher ash content and greater slagging tendency compared with woody biomass, they require boilers specifically designed for agro biomass, with controlled furnace temperatures and efficient ash handling. Straw bales are most commonly used in local and regional energy systems and industrial facilities located in agricultural areas.

Sunflower husk is a solid agricultural biomass originating as a by-product of sunflower processing (oil extraction, feed production). It is a light, fibrous material with a relatively high lower heating value compared with many other agricultural residues. In energy applications it can be used in loose form but is far more often briquetted or pelletized to facilitate handling, transport, and automatic feeding. Due to its higher ash content and specific ash behavior prone to slagging, it requires boilers and furnaces designed for agro biomass, with appropriate ash removal and combustion temperature control. It is predominantly used in energy systems and industrial boiler houses integrated with oil mills and processing plants.

Wood briquettes are a solid biofuel in the form of compressed cylinders or blocks produced by high‑pressure compaction of dry wood residues (sawdust, shavings, wood dust), typically without chemical binders. Under high pressure, natural lignin in the wood softens and acts as a binder, providing mechanical strength. Wood briquettes feature uniform geometry, low moisture content, and relatively high energy density, making them suitable for small commercial boiler rooms and household heating appliances. They burn with a stable flame and usually generate less ash compared with many agro biomass fuels and coal.

Wood chips are a solid wood biomass produced by chipping wood into pieces of defined size, usually in chippers or shredders. They consist of irregular, medium-sized wood particles with controlled dimensions, enabling reliable transport and combustion in boilers and energy plants. In energy applications, wood chips are used as a main fuel for district heating systems, cogeneration plants, and larger biomass boiler houses, thanks to their favorable balance between cost and energy content, suitability for automated handling, and the possibility of using local forest and wood resources. Moisture content and quality of wood chips are key parameters for efficient and stable combustion, therefore standardized wood chips with defined classes are often used.

Wood pellets are a solid biofuel in the form of small cylindrical granules, typically 6–8 mm in diameter, produced by high‑pressure compaction of milled and dried wood residues (sawdust, shavings, wood dust) without chemical binders. During pelletizing, natural lignin in the wood softens and binds the particles, ensuring mechanical strength and durability. Wood pellets feature very low moisture content, high and consistent energy density, and a stable lower heating value, making them suitable for fully automated boilers and stoves in commercial buildings and households. Their uniform size and flow properties enable easy mechanical or pneumatic transport and automated feeding, combined with low ash content and relatively clean combustion.