Micro combined heat and power

The micro combined heat and power ( micro -CHP) is a class of combined heat and power plants ( CHP), which covers the lowest performance segment of CHP. It is especially suitable for building integrated use in single and multi- family houses as well as small businesses.

The micro-CHP is mainly in the boiler room by micro - combined heat and power plants ( micro CHP ) with waste heat recovery for domestic hot water heating and space heating instead. It reduces by decentralized energy conversion electric and especially thermal transmission losses and is characterized by a high exergetic grade compared to pure combustion processes from.

• 4.1 engine
• 4.2 Stirling Engine
• 4.3 steam engine
• 4.4 fuel Cells

Demarcation

Following a three-phase feed into the low voltage network Pehnt et al propose. 2006, a demarcation of <15 kWe ago.

A second possibility is the differentiation according to fed- annual power output, since for small systems usually no performance measurement. On the consumer side network operators have up to one year related work of 100,000 kWh use standardized load profiles ( § 12 StromNZV ).

Third, to offer a two-dimensional criterion: <11 kWe and < 70 kW thermal output. The results from the Gas Appliance Directive 90/396/EEC, which is responsible for issuing a CE certificate in gas units to 70 kWth of importance. The 11 kWe are the lowest common denominator in the European internal market.

Furthermore, the CHP Directive 2004/8/EC restricts the term " micro-cogeneration situation " to a power less than 50 kW el. Also, a further stage in the CHP surcharge can be found in the CHP Act for installations below 50 kWe to the generated electricity from combined heat and power. Also, the " pulse program mini- CHP plants " from the Federal Environment Ministry, the 50 kWe as the upper limit for the granting of an investment grant. Therefore, it makes sense to call this something broader class to 50 kWe micro-CHP.

The difference of micro -CHP to Mini -CHP is that the former is installed predominantly integrated object, in the latter, but also small district heating networks can be supplied already. Both have in common, in contrast to the large CHP and heating plants that they have the potential to reach as a serial product into mass production.

The subclass of the power-generating heating systems for one-and two -family houses is called Nano -CHP ( or nano - CHP ). The electrical power is usually at 1 kW, but there are also other plant sizes available. The borders a single-phase rated current up to 16 A is recommended analogous to EN 50438 ( request to micro-generators ), ie an apparent power 3.68 kVA. The devices are supplied in combination with an integrated or external peak load burners (20-30 kW th ), which provides the maximum heat load in winter.

Technology

In a cogeneration plant (CHP) of energy sources, mostly natural gas, as well as liquefied petroleum gas, fuel oil, vegetable oil or wood is used in a thermodynamic cycle to generate mechanical energy and electrical energy therefrom. The waste heat is coupled into the heating system of the building. The stream itself is used, balanced the balance over the net. In the market overview examples are enumerated, that link to technical details of the various micro-CHP variants. However, still lacks a mass market, which not only promotes technical progress, but also lowers the cost of production as the learning rate.

In order to reach sufficient maturity of the CHP unit, even in summer, it is important that the hot water is generated centrally. In general, the systems are designed so that the base load of heat ( hot water transitional period ) provided by the CHP and the peak heat demand for the cold winter days will be delivered by an auxiliary burner. A heat storage decouples the heat from the power supply and allows overclocking in addition to a poor driving operation at times of high internal current consumption.

Internal combustion engine

The motor CHP is a mature technology, which benefits from the hundred-year history of development of petrol and diesel engines. Even with micro -CHP perennial application experiences are available. In addition to natural gas and LPG heating oil and vegetable oil are used.

In addition to the proven technology at the engine - CHP is the high electrical and thermal efficiency positive aspect (electric 20 and 25%, total about 80 to 90%). Negative to the engine - CHP are the high maintenance costs, which are mainly due to the oil change intervals. In addition to other types of high compared emissions are mentioned, which brings the internal combustion with it. In addition, interfering with the noise and vibrations that can mitigate, through encapsulation to an acceptable level.

Stirling engine

The Stirling engine is older than motor with external heat supply in concept than combustion engines with internal combustion. However, he was driven by their success as a vehicle drive in a niche, because it is unsuitable for rapid load changes. As a machine for use as Heizkraftblock to the energy supply of buildings he is experiencing a renaissance.

This is attributable mainly to the outer combustion. Here you can work with continuous combustion, due to the steady flame causes low exhaust emissions and also allows for a wide variety of gaseous, liquid and solid fuels. In addition, a low-noise operation. Maintenance costs are low compared to the internal combustion engine, because it is constructed as a hot- gas engine is usually oil. The difficulty in the production is primarily based on the material combination oil-free funktioniernder sliding parts ( piston / cylinder ) and the permanent sealing of the working gas volumes leading. On the other hand, the design of the heat exchanger in the head of the working cylinder of a high temperature -resistant and corrosion -resistant materials is a challenge.

Running machines only reach electrical efficiencies of 15-25 percent, which is significantly less than internal combustion engines in practice. However, in the overall efficiency of the Stirling engine comes to over 90 percent, making it ideal for the aforementioned benefits for installed in small residential buildings nano- CHPs.

Steam engine

In the steam engine, water is heated in a closed circuit and evaporated. In an expansion module, the water vapor does work, condenses and releases heat to the heating circuit off. It is then pumped back to the evaporator.

The steam engine works like the Stirling engine with external combustion, is therefore similarly flexible in fuel and also comes to similar good exhaust emissions. However, with the small dimensions of the micro-CHP in the steam cycle is not the same electrical efficiencies as in large power plant can be achieved, but only about 10 to 15%. Positive for the concept speak the low maintenance costs similar to a condensing boiler and the overall efficiency of over 90 %.

Fuel cell

The fuel cell does not walk in contrast to the above technologies the energy sources used on a thermodynamic intermediate step into electrical energy, but directly by electrochemical reaction. This waste heat can be released as useful heat by electrical resistance or by preparatory reforming of the fuel gas. For the micro-CHP types PEFC and SOFC are of interest.

The fuel cell has the highest technical potential with electrical efficiencies of 30-60%. She is the youngest technique (10 years) is the focus of development for mass application for only a short time. In addition to outstanding technical problems such as degradation due to too low lifetime of the fuel cell stack design and manufacturing technical progress is still needed in order to reduce the manufacturing costs. When used for domestic energy supply, the fuel cell has other advantages: no moving parts, so maintenance (similar to a condensing boiler ) and almost silent in operation.

Multi -fuel units

While previous CHPs were usually built each for a variety of fuel, the development is towards equipment that can be operated with all common varieties of fuel. This has the advantage that such a CHP unit can also be operated in existing buildings with the existing fuel, such as fuel oil, and must not be changed in a conversion to another fuel such as gas or pellets. Another advantage is likely to lie in the fact that the maintenance personnel or installers must be trained locally on a device.

Economy

A micro - CHP system is a highly efficient heating with a primary energy factor of the heat supply is below one. The default value of the Energy Saving Ordinance is 0.7 - which is about one-third better than the PE - factor of a condensing boiler with 1.1. In individual certifications of micro-CHP - series can also be values ​​of 0.6 and prove below. The low PE factors resulting from the settlement with the current credit. In the end, you exchange a higher purchase price of the micro - CHP system to lower running costs for the power supply of the building.

In addition to the electric efficiency and the power ratio as the ratio of electrical to thermal power and the slope efficiency plays a role in the economic efficiency. It refers to the ratio of power output to the need of additional fuel in comparison to the reference boiler in supplying the heat load ( to simplify the representation is subsequently omitted and written for the heat flow of the point). Has the boiler reference the same overall efficiency as the micro - CHP system, ie, the heat losses of both heat sources are comparable, the result is:

Thus, a CHP unit with condensing technology ( overall efficiency about 90%) also scattering generously the additional required fuel compared to a conventional condensing boilers (thermal efficiency 90 %) with about 90 % efficiency. As variable generation costs thus result, the fuel costs plus maintenance costs. This according to the module size with currently available mini - CHP plants between 2.5 and 5 cents / kWh. A special feature are the micro gas turbines: they are characterized by low maintenance costs, although a lower electrical efficiency exists. The heat from the unit will be assessed according to the residual method with the heat prices, which could provide a reference boiler with condensing boiler technology.

On the income side, therefore, is only the power to look at, the CHP heat and the heat from the reference boiler are assumed to be treated equally. The electrical energy from the cupola process can now be fed to one, whereby the usual price of electricity on the EEX ( baseload average for the previous quarter) plus the avoided grid use fees are added to approach. Secondly, the power in the building itself can be used, whereby the tariff power purchase will be displaced. The latter option is usually more economically attractive, but connected to houses with more units with higher acquisition costs. For both options, the CHP surcharge of 5.11 ct / kWh additionally obtained during the first 10 years.

The thus obtained contribution margin must refinance the initial investment. Assuming a contribution margin of 10 ct / kWh a 5 kW system per 1000 operating hours 500 euro surplus generated. An initial output of 25,000 euros would thus be refinanced after 50,000 h (without assistance under the War Weapons Control Act ).

Market Overview

Internal combustion engine

Cogeneration plants with a combustion engine are available for some years as the smallest CHP plants.

• Vaillant and Honda presented at a press conference in Dusseldorf on 3 February 2011, the micro - cogeneration plant Vaillant ecoPOWER 1.0. It returns 1 kWe and 2.5 kW of heat ( overall efficiency of 92%). It should be available by mid-year in Germany.
• Honda offers the micro-CHP ECOWILL on, it returns 1 kWe and 3.25 kW of heat ( total efficiency of 85%). In Japan it is sold since 2003, in the spring of 2007, the market launch in the U.S. took place in Europe, the device is still in testing. Mid-2007 were installed in total 50,000 Ecowills.
• KW energy technology provides for multi-family, hotel and industrial companies since 1995 various cogeneration models from 7.5 kWe and 18 kWtherm power for operation with natural gas, LPG, biogas and sewage gas as well as diesel and fuel oil.
• PowerPlus Technologies ( Vaillant ) offers the ecopower 4.7 kWe and 12.5 kWth ( modulating) to.
• Senertec offers its roof since 1996. It delivers 5.5 kWe and provides 12.5 kW of heat.
• Other micro-CHP can be found on the tables of B.KWK, ASUE and ACFA. ( List of 2013)

Stirling engine

The Stirling engine is commercially available as Heizkraftblock.

• In the UK, Stirling engines from Microgen and WhisperGen be tested currently. Take place field tests WhisperGen systems at Gelsenwasser AG and Gasag Also in Germany. The devices are suitable for around one kilowatt of electrical power and 7-14 kW of heat for use in a family house. After the end of 2012 more than 700 Whispergen Stirling engines were sold in Germany, the sales rests due to the insolvency of Efficient Home Energy SL (EHE ) is currently.
• The company Cleanergy AB, Gothenburg, SE (formerly SOLO, or Stirling Systems ) has brought a Stirling CHP to market. Indeed, its performance (9 kWe and 26 kWth ) it is suitable for larger buildings. The machine is characterized by modulation capability on a tight quarters. The working gas helium must be added during maintenance, which increases operating costs.
• The company Sunmachine offered a pellet powered Stirling CHP with an electrical continuous output of up to 3 kWe and 10.5 kWth. but is due to bankruptcy no longer on the German market.
• Another concept for a combination of a pellet heating system with a Stirling generator Stirling Power Module. The project was discontinued in 2010.
• Viessmann offers a small block power plant with a Stirling engine.
• The company Ökofen developed a pellet heating system with integrated Stirling engine. Currently the development is subjected to a practical test.

Steam engine

CHP plants with steam engine are on the way to mass production.

• When the CHP with steam engine, the company OTAG and Enginion be mentioned. Enginion had the development of the so-called SteamCell the goal, but was forced to declare bankruptcy in November 2005. The company OTAG has also provided a preliminary bankruptcy petition on December 8, 2011 - the process is still running. (03/ 2012)
• In addition to the natural gas CHP was developed with the oil -and heat - institute a fuel variant. 2011, a pellet burner was also presented.

Fuel cells

Mini - CHP fuel cells are in many heating appliance manufacturers in the development and field testing. An extensive collaborative projects is the project Callux a nationwide field experiment, collaborate in the energy supplier and developer of fuel cell heating appliances.

• Baxi Innotech: partner companies of the European Commission of the Fuel Cell Initiative ene.field.
• Buderus ( brand of Bosch Thermo Technology ): partner companies of the European Commission of the Fuel Cell Initiative ene.field.
• Ceramic Fuel Cells: Australian SOFC specialist manufacturing in Germany. Production and sale of micro power plant BlueGen based on fuel cells.
• Elcore
• Hexis: The Swiss company is a partner company of the European Commission ene.field the fuel cell initiative and works with the German company Viessmann at a high temperature fuel cell systems Galileo 1000 N -type SOFC.
• Vaillant: partner companies of the European Commission of the Fuel Cell Initiative ene.field.
• Viessmann developed with Panasonic, the heating system Vitovalor 300-P on the basis of a low temperature fuel cell and with the Swiss company Hexis the high-temperature fuel cell heating Galileo 1000 N.