Micro-combined heat and power

The micro combined heat and power (micro-CHP) covers the lowermost segment of power cogeneration plants from (CHP). It is particularly suitable for building-integrated use in single and multi-family houses as well as in small businesses.

The micro-CHP takes place mainly in the boiler room through micro- block-type thermal power stations (micro-CHP) with waste heat utilization for domestic water heating and room heating. It reduces electrical and, above all, thermal transmission losses through decentralized energy conversion and is characterized by a high level of exergetic quality compared to pure combustion processes for the provision of useful heat.

Demarcation

Based on a three - phase feed into the low-voltage network , Pehnt et al. 2006 a delimitation of <15 kW _el .

A second possibility is to differentiate according to the annual amount of electricity fed in, since there is usually no power measurement for small systems. On the consumer side, network operators have to apply standardized load profiles up to a related annual workload of 100,000 kWh (Section 12 StromNZV).

The third option is a two-dimensional criterion: <11 kW _el and <70 kW fuel heat output . This results from the gas appliance directive 90/396 / EEC, which is important for the issuing of a CE certificate for gas appliances up to 70 kW _th . The 11 kW _el result as the lowest common denominator in the European internal market.

EN 50438, an electrotechnical standard for microgenerators, is also limited to a nominal value of up to 16 A per phase, i.e. H. three-phase around 11 kVA apparent power , which results in around 10 kW _el effective power with a power factor cos φ = 0.9 .

The sub-class of electricity-generating heating for one and two-family houses is called nano-CHP (or nano-CHP). The electrical output is usually 1 kW, but other system sizes are also available. A single-phase rated current of up to 16 A analogous to EN 50438 (requirements for micro-generators) is recommended as a demarcation. H. an apparent power of 3.68 kVA. The devices are delivered in combination with an integrated or external peak load burner (20–30 kW _th ), which delivers the maximum heat load in winter.

Mini CHP

Furthermore, the CHP Directive 2004/8 / EG limits the term “CHP micro-system” to an output of less than 50 kW _el . There is also a further step in the CHP surcharge on the electricity generated from combined heat and power generation in the CHP Act for systems under 50 kW _el . The first “Impulse program for mini-CHP systems” (September 2008) from the Federal Environment Ministry also had 50 kW _el as the upper limit for granting an investment subsidy. Therefore it makes sense to call this somewhat broader class up to 50 kW _el mini-CHP .

The difference between micro-CHP and mini-CHP is that the former is mainly installed in a building-integrated manner, while the latter can also be used to supply small local heating networks. Both have in common that, in contrast to large CHP and thermal power stations, they have the potential to be mass-produced as series products.

technology

In a block-type thermal power station (CHP), the energy source, mostly natural gas , but also liquid gas, heating oil, vegetable oil or wood, is used in a thermodynamic cycle to generate mechanical energy and from it electrical energy. The waste heat is fed into the building's heating system. The electricity is used internally and the balance is offset via the grid . In the market overview , examples are listed that link to technical details of the various micro-CHP variants. What is still missing, however, is a mass market that not only drives technical progress, but also lowers production costs in line with the learning rate .

In order to achieve sufficient running times for the CHP unit in summer , it is important that hot water is also generated centrally. As a rule, the systems are designed in such a way that the base load of heat (hot water + transition period) is provided by the CHP and the peak heat demand for the cold winter days is provided by an additional burner. A heat storage unit decouples the supply of heat from the supply of electricity and, in addition to low-cycle operation, allows operation at times when there is a high demand for electricity.

Internal combustion engine

The motorized block-type thermal power station is a mature technology that benefits from the hundred-year history of development of gasoline and diesel engines . Experience has also been gained with micro-CHP since the 1990s. In addition to natural gas and liquid gas , heating oil and vegetable oil are also used.

In addition to the tried and tested technology, the high electrical and thermal efficiency of the motorized CHP unit should be positively emphasized (electrical 20 to 25%, total around 80 to 90%). The negative thing about the engine block-type thermal power station is the high maintenance costs, which are mainly due to the oil change intervals. Also to be mentioned are the high emissions in comparison to other types that result from internal combustion. In addition, the noise and vibrations interfere, which can be contained to an acceptable level by encapsulation.

Stirling engine

As a motor with external heat supply, the concept of the Stirling engine is older than power machines with internal combustion . However, its success as a vehicle drive drove it into a niche existence, as it is unsuitable for rapid load changes. It is experiencing a renaissance as a machine for use as a thermal power unit for supplying energy to buildings.

This is mainly due to the external burn. Continuous combustion can be used here, which results in low exhaust gas emissions due to the stationary flame and also allows a wide variety of gaseous, liquid and solid fuels. Quiet operation is also possible. The maintenance costs are lower compared to the internal combustion engine, because as a hot gas engine it is usually constructed oil-free. The difficulty in production lies on the one hand in the material pairing of oil-free sliding parts (piston / cylinder) and the permanent tightness of the working gas-carrying volumes. On the other hand, the design of the heat exchanger in the head of the working cylinder made of high-temperature and corrosion-resistant materials is a challenge.

In practice, implemented machines only achieve electrical efficiencies of 15-25 percent, which is significantly less than motors with internal combustion. In terms of overall efficiency, however, the Stirling engine achieves over 90 percent, which makes it ideal for nano-CHPs installed in small residential buildings because of the advantages mentioned above.

Steam engine

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

The steam engine works like the Stirling engine with external combustion, is therefore just as flexible in terms of fuel and has similarly good exhaust gas values . However, with the small dimensions of the micro-CHP in the steam cycle, the same electrical efficiency levels cannot be achieved as in the large power plant, but only around 10 to 15%. The low maintenance costs, similar to a condensing boiler, and the overall efficiency of over 90% speak positively for the concept .

Fuel cell

In contrast to the above technologies, the fuel cell does not convert the energy source used into electrical energy via a thermodynamic intermediate step, but directly via an electrochemical redox reaction . Waste heat generated by electrical resistance or by preparatory reforming of the fuel gas can be given off as useful heat. The types PEFC and SOFC are of interest for micro-CHP .

The fuel cell has the highest technical potential with electrical efficiencies of 30–60%. It is the latest technology that has only recently been the focus of development for mass use (10 years). In addition to the technical problems that still exist, such as the service life of the fuel cell stacks that is still too short due to degradation , advances in construction and production technology are still necessary in order to further reduce production costs. When used for domestic energy supply, the fuel cell has further advantages: hardly any moving parts, therefore low-maintenance (similar to a condensing boiler) and almost silent in operation.

economics

A micro-CHP system is a highly efficient heating system with a primary energy factor of the heat supply below one. The standard value from the EnEV is - that is a good third better than the PE factor of a condensing boiler with 1.1. In individual certifications of mini-CHP series, values of 0.6 and below can also be verified. The low PE factors result from being offset against the electricity credit. In the end, you swap a higher purchase price for the micro-CHP system for lower running costs for the energy supply of the building. ${\ displaystyle f _ {\ text {PE, WV}} = 0 {,} 7}$

In addition to the electrical efficiency and the current index as the ratio of electrical to thermal output, the differential efficiency also plays a role in the economic feasibility study. It denotes the quotient of the electricity yield to the additional fuel requirement compared to the reference boiler when supplying the heat load (to simplify the representation, the point is omitted and written below for the heat flow ). Does the reference boiler have the same overall efficiency as the micro-CHP system , i.e. This means that the waste heat losses of both heat generators are comparable, so the following results: ${\ displaystyle \ eta _ {\ text {diff, el}}}$ ${\ displaystyle P}$ ${\ displaystyle \ Delta Q _ {\ text {BS}}}$ ${\ displaystyle Q _ {\ text {Last}}}$ ${\ displaystyle {\ dot {Q}}}$ ${\ displaystyle Q}$ ${\ displaystyle \ eta _ {\ text {Boiler, th}} = \ eta _ {\ text {KWK, th}} + \ eta _ {\ text {KWK, el}}}$

{\ displaystyle {\ begin {aligned} \ eta _ {\ text {diff, el}} & = {\ frac {P _ {\ text {el}}} {\ Delta Q _ {\ text {BS}}}} = {\ frac {\ eta _ {\ text {KWK, el}} \ cdot {Q _ {\ text {KWK, BS}}}} {Q _ {\ text {KWK, BS}} - Q _ {\ text {boiler, BS}}}} = {\ frac {\ eta _ {\ text {KWK, el}}} {1 - {\ frac {Q _ {\ text {boiler, BS}}} {Q _ {\ text {KWK, BS }}}}}} = {\ frac {\ eta _ {\ text {KWK, el}}} {1 - {\ frac {Q _ {\ text {LAST}} \ cdot \ eta _ {\ text {KWK, th}}} {Q _ {\ text {LAST}} \ cdot \ eta _ {\ text {boiler, th}}}}}} \\ & = {\ frac {\ eta _ {\ text {CHP, el} }} {1 - {\ frac {\ eta _ {\ text {KWK, th}}} {\ eta _ {\ text {boiler, th}}}}}}} = {\ frac {\ eta _ {\ text {KWK, el}}} {\ frac {\ eta _ {\ text {Boiler, th}} - \ eta _ {\ text {KWK, th}}} {\ eta _ {\ text {Boiler, th}} }}} = {\ frac {\ eta _ {\ text {KWK, el}} \ cdot \ eta _ {\ text {boiler, th}}} {\ eta _ {\ text {boiler, th}} - \ eta _ {\ text {KWK, th}}}} \\ & = {\ frac {\ eta _ {\ text {KWK, el}} \ cdot \ eta _ {\ text {boiler, th}}} {( \ eta _ {\ text {KWK, th}} + \ eta _ {\ text {KWK, el}}) - \ eta _ {\ text {KWK, th}}}} = {\ frac {\ eta _ { \ text {KWK, el}} \ cdot \ eta _ {\ text {Boiler, th}}} {\ eta _ {\ text {KWK, el}}}} = \ eta _ {\ text {Boiler, th} } \ end {aligned}}}

Thus, a CHP with condensing technology (total efficiency approx. 90%) can convert the additionally required fuel into electricity with approx. 90% efficiency compared to a classic condensing heating system (thermal efficiency approx. 90%). The fuel costs plus the maintenance costs result as variable electricity generation costs. Depending on the module size, these are between 2.5 and 5 ct / kWh for currently available mini CHP systems. The micro gas turbines have a special feature: They are characterized by low maintenance costs, even if the electrical efficiency is lower. The heat from the unit is valued according to the residual value method with the heat prices that a reference boiler with condensing technology could deliver. ${\ displaystyle k _ {\ text {var}}}$ ${\ displaystyle k _ {\ text {BS}} / \ eta _ {\ text {diff, el}}}$

On the income side, therefore, only the electricity needs to be considered, the CHP heat and the heat from the reference boiler are assumed to be treated in the same way. The electrical energy from the coupling process can now be fed in, on the one hand, whereby the usual price for electricity on the EEX (baseload average of the previous quarter) plus the avoided network usage fees are applied. On the other hand, the electricity can be used in the building itself, which displaces the tariff electricity purchase. The latter option is usually more economically attractive, but associated with higher acquisition costs for houses with several residential units . With both options, you also receive the CHP surcharge of 5.11 ct / kWh during the first 10 years.

The contribution margin achieved in this way must refinance the initial investment. The specific module costs in the micro-CHP segment are around 10,000 / √P _el € / kW, plus around 50% for transport, integration and commissioning. With an assumed contribution margin of 10 ct / kWh, a 5 kW system generates a surplus of 500 euros per 1000 operating hours. An initial expenditure of 25,000 euros would thus be refinanced after 50,000 h (without funding under the KWKG ).

Market overview

Internal combustion engine

Combined heat and power plants with combustion engines have been available as the smallest CHP systems for several years.

Vaillant and Honda presented the Vaillant ecoPOWER 1.0 micro-heating power plant at a press conference in Düsseldorf on February 3, 2011 . It supplies 1 kW _el and 2.5 kW heat (overall efficiency 92%). It should be available in Germany by the middle of the year.

Honda offers the mini-CHP Ecowill , it delivers 1 kW _el and 3.25 kW heat (overall efficiency 85%). It has been on sale in Japan since 2003; it was launched in the USA in spring 2007, and the device is still being tested in Europe. In mid-2007 a total of 50,000 ecowills were installed.

KW Energie Technik has been offering various block-type _thermal power station _models from 7.5 kW _el and 18 kW _thermal power for operation with natural, liquid, bio and sewage gas as well as diesel and heating oil for multi-family houses, hotels and industrial companies since 1995 .

PowerPlus Technologies (Vaillant) offers the Ecopower with 4.7 kW _el and 12.5 kW _th (modulating).

Senertec has been offering its badger since 1996. It delivers 5.5 kW _el and supplies 12.5 kW of heat.

Further mini-CHP units can be found on the overviews from B.KWK, ASUE and BAFA. (List from 2013)

Stirling engine

The Stirling engine is commercially available as a heating power block.

The Microgen and WhisperGen brands of Stirling engines are currently being tested in Great Britain. Field tests of the WhisperGen systems are also taking place in Germany at Gelsenwasser AG and Gasag. With around one kilowatt of electrical output and 7-14 kW of heat, the devices are suitable for use in single-family homes. After more than 700 Whispergen Stirling engines were sold in Germany by the end of 2012, sales are currently suspended due to the insolvency of the manufacturer Efficient Home Energy SL (EHE).

The company Cleanergy AB, Gothenburg, SE (formerly SOLO, or Stirling Systems) has brought a Stirling CHP unit to market maturity. With its performance data (9 kW _el and 26 kW _th ) it is suitable for larger buildings. The machine is characterized by its modulation capability to just under a quarter. The working gas helium must be supplemented during maintenance, which increases operating costs.

The Sunmachine company offered a pellet- operated Stirling CHP with a continuous electrical output of up to 3 kW _el and 10.5 kW _th . but is no longer on the German market due to insolvency.

Another concept for a combination of a pellet heating system with a Stirling generator is the Stirling power module. The project was discontinued in 2010.

Viessmann offers a small block power plant with a Stirling engine.

The company Ökofen develops a pellet heating system with an integrated Stirling engine. The development is currently being tested in practice.

With the Dachs Stirling SE, Dachs offers a heating boiler based on gaseous fuels with an integrated Stirling engine. The electrical and thermal output is 1 kW _el and 5.8 kW _th or 18 kW _th through an additional burner.

Steam engine

CHP systems with steam engines are on the way to series production.

The companies OTAG and Enginion should be mentioned for the CHP with steam engine. Enginion's goal was to develop what is known as the Steamcell, but had to file for bankruptcy in November 2005. The company OTAG also filed for preliminary bankruptcy on December 8, 2011 - the proceedings are still ongoing. (Status 03/2012)
In addition to the natural gas CHP, a heating oil variant was developed with the Oel-Waerme-Institut . In 2011 a pellet burner was also presented.

Fuel cells

Mini-CHP units with fuel cells are in the development and field test phase at many heating device manufacturers. An extensive joint project is the Callux project , a nationwide field test in which energy suppliers and developers of fuel cell heating devices work together.

Baxi-Innotech: partner company of the European Commission's fuel cell initiative ene.field .

Buderus (brand of Bosch Thermotechnik): partner company of the fuel cell initiative of the European Commission ene.field .

Ceramic Fuel Cells: Australian SOFC specialist with production in Germany. Manufacture and sale of the BlueGen micro power plant based on fuel cells.

Elcore

Hexis: The Swiss company is a partner in the European Commission's ene.field fuel cell initiative and is working with the German company Viessmann on a high-temperature system with fuel cells Galileo 1000 N of the SOFC type .

Vaillant: partner company of the European Commission's fuel cell initiative ene.field .

Viessmann is developing the Vitovalor 300-P heating system based on a low-temperature fuel cell together with Panasonic and the Galileo 1000 N high-temperature fuel cell heating device with the Swiss company Hexis .

Web links

Nano-BHKW market overview (small micro-BHKW up to 2.5 kW el.) , BHKW-Forum eV
Micro-CHP market overview (greater than 2.5 kW el. To 15 kW el.) , BHKW-Forum eV
Funding programs and financing , BHKW-Forum eV
Mini-CHP impulse program - information and facts , BHKW-Infozentrum GbR
6 types of CHP integration in a building Ihr-BHKW.de, accessed on November 20, 2015
Innovation and decentralization: case study micro-CHP (PDF file; 1.8 MB), BMF
Fuel cells x combined heat and power. ene.field, accessed on March 31, 2013 (fuel cell initiative of the European Commission since September 2012).

literature

Steck et al .: Primary energy factors for SenerTec CHP systems (PDF; 338 kB). FfE , Munich, 2006.
Pehnt et al .: Micro Cogeneration . Springer-Verlag, Berlin, 2006, ISBN 3-540-25582-6 .

Individual evidence

↑ https://www.gesetze-im-internet.de/bundesrecht/stromnzv/ overall.pdf

↑ Requirements for micro-generating plants to be connected in parallel with public low-voltage distribution networks; German version EN 50438: 2013

↑ Directive 2004/8 / EC

↑ Correction to Directive 2004/8 / EC of the European Parliament and of the Council of February 11, 2004 on the promotion of cogeneration based on useful heat demand in the internal energy market and amending Directive 92/42 / EEC (OJ L 52 of February 21, 2004)

↑ Gunnar Kaestle: promotion of cogeneration in Germany - The new CHP Act and the mini CHP incentive program . IEWT, Vienna February 2009 ( tuwien.ac.at [PDF; accessed on March 30, 2013]).

↑ ASUE: CHP characteristics 2014–2015 ( memento of the original from November 20, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / asue.de
↑ http://www.honda.de/content/news/common_news_70828.php
↑ http://www.honda.de/content/news/17506_30135.html
↑ http://world.honda.com/news/2007/c070717Compact-Household-Cogeneration-Unit
↑ Archived copy ( memento of the original dated November 25, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ http://www.vaillant.de/heizung/produkte/mini-kwk-systeme-ecopower-3-0-4-7-1792.de_de.html
↑ Archived copy ( memento of the original dated August 31, 2005 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ MICRO CHP PLANTS. (PDF) Bundesverband Kraft-Wärme-Kopplung eV (B.KWK), March 2008, archived from the original on September 13, 2008 ; accessed on January 28, 2014 .
↑ Device overview of the electricity generating heaters. (PDF) Working Group for Economical and Environmentally Friendly Energy Consumption eV (ASUE), November 2011, accessed on January 28, 2014 .
↑ Mini-CHP systems: List of eligible CHP systems up to and including 20 kW _el . (PDF) Federal Office of Economics and Export Control , November 17, 2015, accessed on November 20, 2015 .
↑ List of general decrees for granting approval for small CHP systems with an electrical output of up to 50 kilowatts
↑ General decree - for issuing approval for small CHP systems with an electrical output of up to 50 kW
↑ http://www.microgen-engine.com/
↑ http://www.whispergen.co.uk/content/library/AC_specBase.pdf ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2
↑ http://www.gelsenwasser.de/de/unternehmen/presse/pressmektiven/2006/02/miniblockheiz.php
↑ http://www.baulinks.de/webplugin/2007/1frame.htm?0447.php4
↑ The manufacturer of the WhisperGen has to file for bankruptcy. Retrieved December 3, 2012 .
↑ http://www.pressebox.de/pressemitteilung/bhkw-infozentrum-gbr/Verkauf-von-Whispergen-Stirlingmotoren-wegen-Insolvenz-vorlaeufig-eingendet/boxid/559712
↑ Archived copy ( Memento of the original dated August 12, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ Archived copy ( memento of the original dated August 6, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ http://www.bhkw-prinz.de/sunmachine-gmbh-insolvent/1160
↑ http://www.stirlingpowermodule.com/
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↑ http://www.viessmann.de/de/ein-_zweifamilienhaus/produkte/mikro-kwk.html Micro-CHP based on Stirling
↑ http://www.bhkw-infothek.de/bhkw-dienstleistungen-und-steller/nano-bhkw-ubersicht/okofen-pellematic-smart_e/
↑ Archived copy ( memento of the original dated June 30, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2
↑ http://www.dachsheizung.de/der-dachs/stirling-se//
↑ http://www.bosy-online.de/Mini-Dampftriebwerk.pdf
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↑ http://www.bhkw-forum.info/nachrichten/7104/2012-02-20-wie- geht-es-weiter-beim-bhkw-steller-otag /
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↑ Devices - Models. (No longer available online.) Initiative-Brennstoffzelle.de, archived from the original on March 5, 2016 ; accessed on March 31, 2013 (overview: Baxi Innotech, Buderus, Ceramic Fuel Cells, Elcore, Hexis, Vaillant and Viessmann): "Various manufacturers are currently testing the use of fuel cell heating devices." Info: The archive link has been inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.

↑ http://www.callux.net/

↑ The fuel cell heater for the home. BAXI INNOTECH GmbH, accessed on March 31, 2013 .

↑ Electricity and heat from the fuel cell. With the Logapower FC10 energy center, Buderus is presenting an electricity-generating heating system based on fuel cells. Bosch Thermotechnik GmbH, accessed on March 31, 2013 : "As part of the ene.field project, the largest European demonstration program for fuel cell-based solutions for decentralized power and heat generation, Buderus will install energy centers from 2014 and thus prepare for the market launch."

↑ Inexpensive power generation on site from fuel cells. (No longer available online.) Ceramic Fuel Cells BV, formerly the original ; accessed on March 31, 2013 (production and sale of the BlueGen micro power plant based on fuel cells.). ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.

↑ Markus Gailfuß: Fuel cell company Ceramic Fuel Cells files for bankruptcy. CHP information center, accessed on March 5, 2015 (insolvency of a fuel cell supplier).

↑ ^a ^b Innovations from Viessmann for a secure energy supply. (PDF) (No longer available online.) In: Press release. Viessmann Werke, March 2013, formerly in the original ; accessed on March 31, 2013 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.

↑ ^a ^b Galileo - Intelligent Heat. Clean electricity. Accessed March 31, 2013 (production and sale of the fuel cell-based micro power plant Galileo 1000 N ).

↑ fuel cell. In: Research & Development. Vaillant, accessed March 31, 2013 .

[1] ttps://www.gesetze-im-internet.de/bundesrecht/stromnzv/ overall.pdf

[2] Requirements for micro-generating plants to be connected in parallel with public low-voltage distribution networks; German version EN 50438: 2013

[3] Directive 2004/8 / EC

[4] Correction to Directive 2004/8 / EC of the European Parliament and of the Council of February 11, 2004 on the promotion of cogeneration based on useful heat demand in the internal energy market and amending Directive 92/42 / EEC (OJ L 52 of February 21, 2004)

[Kaestle_2009-5] Gunnar Kaestle: promotion of cogeneration in Germany - The new CHP Act and the mini CHP incentive program . IEWT, Vienna February 2009 ( tuwien.ac.at [PDF; accessed on March 30, 2013]).