TECHNICAL VARIATIONS OF CHP
The difference in the technical CHP versions is based on the underlying technology used.
The concept of the Stirling engine is older than that of internal combustion engine, although they have struggled to reach the same commercial viability - until now. In fact, it is the success of the internal combustion engine that is to blame for the stall in the development of the Stirling engine. However, the Stirling engine is now experiencing a renaissance; especially with regards to energy supply in buildings.
Principle: In a closed compartment, process gas is heated and cooled externally, resulting in movement of a piston due to the variable expansion of the gas.
Status: Devices for gas as a fuel source are available and ready to go into series production. The advantage of this device is for the generation of low electrical power.
How it works:
Steam, which is produced
by heating up water, drives the piston
of a generator.
Gas-fired steam generators with low
power levels are already available.
However, their acquisition is associated
with high capital costs.
Another disadvantages are the high
maintenance complexity and the related
The fuel cell is a very recent technological
development, which allows production of clean and renewable
electricity if the hydrogen is produced renewably.
Several manufacturers already offer
production-ready fuel cells or have prototypes in the test.
With fuel cells can be generally produced very efficient electricity at low waste heat rate.
Principle: Hydrogen is converted by an electrochemical process directly into electricity.
The steam that is generated along with the production of hydrogen from gas can then be used for heating.
The internal combustion engine is a mature and widely-used technology. For deployment as CHP, the combustion engine has a limited suitability due to its need for maintenance (oil change) and its high emissions and noise levels.
Principle: Fuel is mixed with intake air and is brought to its ignition point. The resulting overpressure due to the "explosion" causes the piston to move.
Status: These CHP systems have been ready for series production for many years and are currently available for combustion of oil or gas. The devices are also available for the low power output.
CHP PERFORMANCE CLASSIFICATION
In the classification in terms of performance of cogeneration systems, the electric power generated is decisive.
Beyond the large-scale power plants, the low power range is mainly divided between "micro-cogeneration" and "mini-CHP".
Micro CHPs are combined heat and power systems with an electrical output of less than 15 kWe and thus cover the lowermost power segment (single-family and multi-family homes). To give an idea of scale, a normal single-family household has a peak demand of around 4 kW of electricity, and a supply of 1 kW can cover 88 percent of the electrical power consumption of an average household.
Mini-CHP are combined heat and power systems that cover a range between around 15 kWe to 50 kWe. These Mini-CHPs are mainly used in larger homes, small district heating networks and larger commercial establishments.
More about the topic
Brennstoffzellen KWK-Info auf bhkw-prinz.de (only available in German)
Technikinfo auf www.waermekraftkopplung.ch (only available in German)
THE STIRLING ENGINE
One solution to implement combined heat and power systems is the use of a Stirling engine, also known as a hot gas engine. Stirling engines are like no other energy converter, as they are capable of converting renewable, low-emission and climate-friendly fuels into kinetic energy, or movement.
Unlike an Otto or diesel engine, where the combustion happens internally, the heat for a Stirling engine is supplied from outside the device. This heat can come from various different energy sources – including wood pellets.
The mechanical energy is generated due to two different temperature zones in the Stirling engine, in which encased process gas is heated and cooled. Due to the differential expansion of the gas, a compression wave is generated, which moves a piston.
USING THE STIRLING ENGINE FOR ELECTRICAL POWER GENERATION
Stirling engines are like no other energy converter, as they are capable of converting renewable fuel sources into kinetic energy, or motion, in a clean, renewable, sustainable and climate-friendly manner.
The Stirling engine is therefore outstanding suitable for electricity generation using wood pellets and is a source of hope for the electricity producing heating.