A combined heat and power (CHP) unit simultaneously generates electrical energy and usable heat. The decentralized system can supply buildings, commercial sites or industrial processes. Its energy and economic benefits depend largely on how effectively the electricity and, in particular, the generated heat can be used.
CHP at a glance
- A CHP unit converts fuel into electrical energy and usable heat at the same time.
- Possible technologies include internal combustion engines, turbines and fuel cells. The appropriate fuel depends on the system technology.
- Operation can be based on heat demand, electricity demand or a higher-level optimization strategy.
- Thermal storage increases flexibility by partially decoupling heat generation from heat consumption over time.
How does a CHP unit work?
In engine- and turbine-based CHP units, the energy contained in the fuel is initially converted into mechanical energy. A generator then converts it into electricity. The resulting waste heat is recovered through heat exchangers and used for space heating, hot water or industrial processes. Fuel cell CHP units generate electricity electrochemically and also make the resulting heat available for use.
Depending on the system technology, suitable fuels may include natural gas, biogas, biomethane, liquid or solid biogenic fuels and compatible hydrogen blends. Not every CHP unit can process every type of fuel. Fuel quality, manufacturer approvals and the technical system design must be compatible.
The operating strategy determines when and at what output the CHP unit operates. Under a heat-led operating strategy, generation is primarily based on current heat demand. An electricity-led CHP unit is more closely aligned with electrical consumption or specified electrical setpoints.
An EMS can consider both sides and coordinate CHP operation with PV, BESS, thermal storage and flexible loads. Operating decisions can be based on factors such as current and forecast heat demand, the electrical load profile, storage states, generation forecasts, energy prices and the technical operating limits of the CHP unit.
An appropriately sized thermal storage system temporarily stores generated heat. This allows the CHP unit to operate, for example, during periods of high electricity demand, high electricity prices or in response to a corresponding electrical setpoint, even if the generated heat is only needed later. This temporal decoupling remains limited by storage capacity, temperature levels, heat losses and actual heat demand.
Where are CHP units used?
CHP units are particularly suitable for sites with relatively consistent and predictable heat demand. Typical applications include:
- Commercial and industrial sites use the electricity and process heat directly on-site.
- Hotels, hospitals, swimming pools and larger residential buildings cover part of their continuous electricity and heat demand.
- Agricultural operations use biogas and utilize the generated heat for buildings or operational processes.
- Local and district heating networks supply several buildings or consumers through a shared heat generation system.
- Hybrid energy systems combine CHP with PV, BESS and thermal storage to coordinate different generators and storage systems.
Benefits, limitations and technical requirements
When the generated heat is actually used, combined heat and power generation can utilize the fuel more efficiently than separate electricity and heat production. If heat has to be dissipated without being used, the energy benefits and often the economic viability decrease.
Frequent starting and stopping can increase wear and maintenance requirements. Continuous operation under unfavorable partial-load conditions can also negatively affect efficiency and system lifetime. System design must therefore consider time-resolved electrical and thermal load profiles, the required temperature level, fuel availability, minimum operating times and electrical and thermal power limits.
Economic viability depends on factors including fuel costs, avoided electricity procurement costs, potential revenue from exported electricity, annual operating hours, and maintenance and repair costs. A high number of operating hours alone is insufficient if the generated heat cannot be used effectively or electricity is generated under unfavorable economic conditions.
Higher-level control requires the CHP unit to provide a suitable communication interface. Reliable measurements of electrical power, thermal output, temperatures, storage states and consumption are also required. Protection, emergency shutdown and internal control functions must operate reliably and independently of the higher-level optimization system.
How can EcoPhi integrate a CHP unit?
EcoPhi can collect and visualize available measurement and operating data such as electrical power, thermal output, temperatures, operating hours, fuel consumption and fault messages. This requires the CHP unit, connected meters or additional sensors to provide the respective values through suitable interfaces. Depending on the data source, individual values may be measured directly, supplied by the CHP controller or calculated from other measurements.
If a suitable interface is available, the EcoPhi EMS can transmit higher-level operating requests to the CHP unit and coordinate its operation with PV, BESS, thermal storage and loads. The specific control capabilities depend on the CHP controller, the available data points and the approved setpoints. Depending on the device and project, additional integration or engineering work may be required. Engine control, protection, safety and emergency shutdown functions remain within the local CHP controller.
Conclusion: When is CHP suitable?
CHP combines decentralized electricity generation with the use of the resulting heat. It is particularly suitable for sites with sufficiently high and relatively continuous heat demand. Thermal storage and an EMS can make operation more flexible, but they cannot replace appropriate system sizing or reliable local plant control.
Frequently asked questions about CHP
What is the difference between a CHP unit and a boiler?
A boiler primarily generates heat. A CHP unit provides electricity and usable heat simultaneously.
What does heat-led operation mean?
Under heat-led operation, current heat demand determines when the CHP unit operates. Electricity is generated at the same time but is not the primary control criterion.
Why is thermal storage useful for a CHP unit?
Thermal storage temporarily stores generated heat. This means the operating time of the CHP unit does not have to correspond exactly to the current heat demand.
Can an EMS control a CHP unit directly?
If a suitable interface is available, an EMS can transmit approved operating requests or setpoints. Internal control, protection and safety functions remain within the CHP controller.