Development of micro-cogeneration with thermogenerators as a modular integrated system for biomass boilers
For the operation of pellet heating systems (boilers, furnaces) electrical energy for fuel transportation, water pumping, control, and induced draft fan is required which is usually taken from the grid. Thus, the heat generation is dependent from the public power supply resulting in a loss of heat and hot water supply during power outages. Biomass boilers have the potential to provide this electrical energy itself via conversion of heat into electrical energy. Thermoelectric generators are suitable to provide this demand due to their properties and are ideal for use in small scale biomass furnaces. The technological advantages are no required working medium, no moving parts and therefore silent and maintenance-free operation.
The result of the project is a validated concept of a heat exchanger element which is aligned with the thermal conditions of a biomass boiler (ash behaviour, temperature range, cleaning, dilatation, …). The optimization variable is the conversion of the largest possible proportion of thermal energy in order to obtain a high yield of electric power while optimizing the material used in the thermoelectric elements in terms of technical parameters (characteristics, load profile, electrical wiring) and costs (power output versus costs of conversion). The overall objective is the design, the construction and evaluation of an energy-supplying and electrical self-sufficient heating system consisting of a biomass boiler and the thermoelectric generator/heat-exchanger. The energy exceeding the self-consumption of the entire heating system incl. pumps shall be stored primarily in a battery to provide the energy for the next start and will be supplied as a surplus for house-internal utilization.
First measurements of open circuit voltage and short-circuit current have confirmed the functionality in an adapted standard pellet boiler with 16 kWth The operating point at 6.3V and about 8A corresponds to about 50W electrical power. An extrapolation with consideration of identified and solvable technical problems shows that it is realistic to reach the planned maximum value of 400 Wel in further development projects.
Klima- und Energiefonds im Rahmen des Energieforschungsprogramms 2016