For some time, I have been watching videos of people living off-grid. Their civilized living required electricity. They generated electricity using solar panels and gasoline-powered generators. They utilized power management systems and battery packs to supply mains voltage to their remote cabins. These people usually had a redundant supply of wood in their proximity, yet they only used wood for heating. This observation led to the design of an electric generator that operates with combustible resources available in rural areas, utilizing a modular approach to solve the reliable energy supply problem without needing several disconnected systems.
The process of converting thermal energy from burning wood into electricity via a closed-cycle sCO₂ (supercritical CO₂) system operates on a Brayton cycle. Unlike a steam turbine that requires massive water supplies and phase changes, or an internal combustion engine that burns fuel inside the cylinder, this system uses an external heat source to expand a contained gas.
Thermal Intake and Heat Exchange
The wood is fed into the integrated grinder, which reduces it to a consistent particulate size. This biomass is then combusted in an external furnace area. The heat generated by this combustion is transferred to the closed CO₂ loop through a high-temperature heat exchanger.
Supercritical State and Expansion
Inside the closed loop, the CO₂ is maintained at high pressure. As the heat from the burning wood is applied, the CO₂ temperature rises significantly. Because CO₂ at these pressures behaves like a supercritical fluid—possessing the density of a liquid but the expansion properties of a gas—it carries a high amount of energy per unit of volume.
Turbine Kinetic Energy
The high-pressure, high-temperature CO₂ is directed through a turbine. The fluid expands across the turbine blades, causing the shaft to spin at high velocities—in my design, approximately 35,000 RPM. This is the stage where thermal energy is converted into mechanical work.
Electricity Generation
The turbine shaft is coupled to a high-speed permanent magnet generator. As the turbine spins the magnets within the generator’s stator coils, it induces an electrical current. This high-frequency AC power is then processed by the integrated power management system to provide stable electrical output (AC or DC) for the cabin or caravan.
Cooling, Recirculation, and Fuel Conditioning
After exiting the turbine, the CO₂ remains at an elevated temperature despite the drop in pressure. Before being re-compressed, the fluid passes through a multi-stage heat rejection process:
Primary Recirculation: The CO₂ enters a recuperator to pre-heat the high-pressure gas heading toward the furnace, conserving cycle energy.
Active Fuel Pre-heating: A secondary heat exchanger diverts a portion of the remaining waste heat to the wood-processing assembly. This thermal energy is used to dry the moisture out of the freshly ground wood particles and pre-heat them before they enter the combustion chamber.
Combustion Optimization: Dry, pre-heated wood particles ignite faster and burn more completely, reducing tar buildup and increasing the peak temperature of the external furnace. This creates a positive feedback loop: more efficient combustion leads to higher turbine inlet temperatures and greater electrical yield.
Final Cooling and Compression: Once the wood-drying task is complete, the CO₂ is cooled to its maximum density state through the external casing's cooling vents. The integrated compressor then returns the fluid to the start of the high-pressure loop.
This addition transforms waste heat into a functional asset, ensuring the system can handle wood with varying moisture content—a common variable in rural or off-grid environments—without a significant drop in performance. This makes the wood-fired version even more robust compared to traditional generators that cannot adjust to fuel quality.
System Synergy
The lateral mounting of the turbine disks ensures that the gyroscopic effects of the 35,000 RPM rotation do not cause instability. Because the wood is burned externally, the ash and combustion byproducts never touch the sensitive turbine blades or the CO₂ working fluid, significantly reducing the maintenance requirements compared to a standard engine. This modular design provides a comprehensive mobile power plant that integrates generation, management, and storage into a single, high-efficiency architecture.
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