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Combined heat and power - what is it?
Combined heat and power - what is it?
Video: Combined heat and power - what is it?
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Combined heat and power (CHP) is already being used on a large scale in trade and industry. The technology is now also increasingly being used in private households. Read here how effective the systems are and what advantages they bring for private individuals.

The principle of cogeneration is based on a thermodynamic process in which the energy used is converted into mechanical or electrical energy and usable heat. The heat produced in parallel with the generation of electricity is then used for heating and hot water processing or, for example, in industry for production processes.

Combined heat and power has great potential and is considered a future-oriented solution for your own home. Because in conventional power plants most of the energy used remains unused. Often only 38 percent of the energy used arrives at you. The combined heat and power systems, which you can easily install in your basement, achieve much higher levels of efficiency. In the end, you can also use about 80 to 90 percent of the primary energy, at the same time you make a contribution to greenhouse gas reduction.

This is how the combined heat and power of a CHP plant works

The main components of a combined heat and power plant (CHP) are: an engine or a fuel cell, a synchronous generator to generate electricity and a heat exchanger to recover the thermal energy from exhaust gas, engine waste heat and the oil circuit. In addition, various electrical switching and control devices for power distribution or for engine management and a hydraulic device for heat distribution are required. In the area of ​​space heat supply, the CHP system is supplemented by a top boiler and a heat store.

The motor drives the generator and thereby provides electrical power. The waste heat generated in the engine block is then used to heat the heating water via a heat exchanger. The energy contained in the exhaust gas can be used, for example, to generate steam or as a heat exchanger for heating domestic water.

Good to know: Combined heat and power plants can be based on various technologies: steam turbine, gas turbine, internal combustion engine and steam engine, as well as a Stirling engine, ORC system or fuel cell are drive options. Differences can then be seen, for example, in relation to the electricity key figure and the overall efficiency.

Depending on the type of system, all fuels with a minimum energy content can be used for CHP systems. These include gases, coal, mineral oils, solid and liquid biomass and waste.

The electricity generated can either be used directly or fed into the public grid. However, direct use is more energetic and therefore more sensible from a financial and ecological point of view.

Combined heat and power plants for private households

Due to the positive experience with CHP systems in industry and trade, many manufacturers are now also producing so-called mini CHP systems that achieve an electrical output of up to 20 kilowatts. So far, there have only been units with electrical power that were suitable for larger residential buildings up to apartment blocks or small businesses. It is hoped that cogeneration will also be interesting for private households. Because the small power plants in the house generate heat and electricity very efficiently without enormous transmission losses, as is the case with large power plants.

The German government's National Climate Initiative is planning to reduce CO 2 emissions by at least 40 percent by 2020, so there is now an investment grant for everyone who purchases a CHP plant.

The original hope was to increase electricity generation from cogeneration plants to 110 terawatt hours by 2020 and to 120 terawatt hours by 2025 - the goal for 2020 was already achieved in 2016.

Mini-KWK impulse program: basic and bonus funding

If you meet the funding conditions, you can apply for basic funding. Funding is provided in the form of a one-off grant, the amount of which is determined as follows, depending on the service area:

Min. Performance

Maximum power

Funding amount per kW el

> 0 kW el

<= 1 kW el

1, 900 euros

> 1 kW el

<= 4 kW el

300 Euro

> 4 kW el

<= 10 kW el

100 euros

> 10 kW el

<= 20 kW el

10 Euro

In addition to basic funding, there are bonus grants for "heat efficiency" and "electricity efficiency". Find out more about the CHP promotion programs in your state.

Costs for a CHP plant

As a disadvantage of the micro or nano CHP plants, the acquisition costs of the plants are often mentioned. These are usually twice as high as with conventional boilers and are between 15, 000 and 30, 000 euros. When it comes to costs, it is best to observe the following rule of thumb: the more electricity a system can generate, the lower the investment costs per installed electrical output. So a large system is more expensive, but also more effective. In order for such a power plant to be worthwhile at home, you should therefore have it in operation for as many hours as possible per year - as a guideline we usually give 3, 500 to 5, 000 hours.

Tip: A small system with long run times is more economical than a too large system that operates irregularly.

Before you decide on a combined heat and power plant, it is important to carry out a profitability calculation. Note the connection costs for electricity and water, the acquisition costs, the integration into the heating circuit, the costs of the additional components and all other work involved. Also clarify beforehand whether you use the generated electricity yourself. If you need help, it is best to contact an energy consultant.

Cogeneration plants for the house

Small CHP plants with an electrical output of around one kilowatt (kW) are best suited for single-family houses. Devices that generate more than five kilowatts are better used in apartment buildings. They are usually combined with an additional boiler.

Offsetting the generated electricity?

The CHP Act regulates the remuneration for CHP plants that work with fossil fuels such as natural gas or heating oil. Plants that need renewable fuels such as biogas, rapeseed oil or wood usually receive higher bonuses than fossil fuels and are remunerated according to the rules of the Renewable Energy Sources Act (EEG).

Lea Straub editors

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