Biogas Electricity (Small-scale)

Compiled by:
Niels Sacher (Xavier University), Shierlyn S. Paclijan (Xavier University), Robert Gensch (Xavier University), Dorothee Spuhler (seecon international gmbh)
Adapted from:
TEIXEIRA COELHO, S.; STORTINI GONZALES VELAZQUES, S.M.; STELLA MARTINS, O.; CASTRO DE ABREU, F. (2006)
SCHALLER, M. (2007)
TILLEY, E.; LUETHI, C.; MOREL, A.; ZURBRUEGG, C.; SCHERTENLEIB, R. (2008)
WRAPAI (Editor) (2009)

Executive Summary

Biogas is a mixture of methane, carbon dioxide, water and hydrogen sulphide produced during the anaerobic decomposition of organic matter. Biogas can be recovered and used either directly for cooking, lighting or it can be transformed in any kind of thermal, electrical or mechanical energy. It can also be compressed, much like natural gas, and used to power motor vehicles. Methane is the valuable component under the aspect of using biogas fuel. The calorific value of biogas is about 6 kWh/m3, what corresponds to about half a litre of diesel oil.

In Out

Biogas

Energy

Introduction

Biogas is a combustible gas mixture produced during the anaerobic digestion of organic matter in an anaerobic biogas reactor (e.g. small-scale digester, biogas settler, digestion of organic waste, anaerobic baffled reactor, etc; see also anaerobic digestion, general factsheet). During anaerobic digestion, wastes are treated and degraded and biogas is produced. Anaerobic treatment also has the advantage over aerobic treatment of a smaller emission of greenhouse gases. Therefore, biogas is a renewable green energy source.

Biogas Composition

Biogas consists mostly of methane (CH4, around 65-70%) carbon dioxide (CO2, around 25-30%) and varying quantities of water (H2O) and hydrogen sulphide (H2S) and some trace amounts of other compounds, which can be found, especially in waste dump biogas (e.g. ammonia, NH3, hydrogen H2, nitrogen N2, and carbon monoxide, CO). The amount of each gas in the mixture depends on many factors such as the type of digester and the kind of organic matter. Diverse sludge composition requires diverse/specialised reactor designs to achieve a high conversion.

Methane is the valuable component under the aspect of using biogas fuel. The calorific value of biogas is about 6 kWh/m3, which corresponds to about half a liter of diesel oil and can be utilised directly as a heat source or to produce electricity. In all cases, the biogas must be dehumidified and purified before combustion; otherwise it can damage the gas engine.

Converting Technologies

Various technologies to generate electricity from biogas on a household level are available. In principle, the chemical energy of the combustible gases is converted to mechanical energy in a controlled combustion system by a heat engine. This mechanical energy then activates a generator to produce electrical power. The most common heat engines used in for biogas energy conversion are gas turbines and combustion engines. Combustion engines can be either internal combustion engine (e.g. reciprocating engine) or external combustion engine (e.g. Stirling engine).

For small-size heat engines, combustion engines are popular as they are more efficient and less expensive than small gas turbines. However, gas turbines may be more efficient when operating in a cogeneration cycle producing heat and electricity. Cogeneration or combined heat and power (CHP) describe the simultaneous generation of both electricity and useful heat. Heat engines (also thermal power plants) in general do not convert all of their thermal energy into electricity. In most cases, a bit more than half is lost as excess heat. By capturing the excess heat, CHP use heat that would be wasted in a conventional power plant, potentially reaching an efficiency of up to 89%, compared with 55% for the best conventional plants (WRAPAI 2009). This means that less fuel needs to be consumed to produce the same amount of useful energy. By-product heat at moderate temperatures (100-180°C) can also be used in absorption chillers for cooling (WRAPAI 2009). A plant producing electricity, heat and cold is sometimes called trigeneration or more generally a polygeneration plant.

 GTZ Ecosan

Combined heat and power (CHP) unit “micro size” in Germany. Source: GTZ (2009).

Micro cogeneration is a so-called distributed energy resource (DER). Biogas is burned for running a generator (e.g. micro turbine). The installation is usually less than 5 kWe (Kilowatts-electrical, WRAPAI 2009). Instead of burning fuel to merely heat space or water, some of the energy is converted to electricity in addition to heat. This electricity can be used within the home or business or, if permitted by the grid management, sold back into the electric power grid (WIKIPEDIA 2010). 

Mini cogeneration is a DER producing usually more than 5 kWe and less than 500 kWe (WRAPAI 2009) and the excess energy is generally fed into the electricity grid. To be viable a good base load for electrical demand and heat demand must exist (WIKIPEDIA 2010).

Current Micro- and Mini CHP installations use five different technologies: micro turbines, internal combustion engines, external combustion engines (stirling engines), steam engines and fuel cells.

Biogas systems are an environmental friendly way of energy production and have a positive impact on climate change. In fact, the contribution of a methane molecule (CH4) to the greenhouse effect is 21 times greater than that of a carbon dioxide molecule (SUSANA 2009). Therefore burning methane, even though producing CO2, reduces its impact on the environment.

Applicability

The technology is easily adaptable and can be applied at household or community level. To minimise distribution losses, the reactors should be installed close to the CHP where the gas can be used.
Micro cogeneration is a so-called distributed energy resource (DER) useful for a single house or small business because of the low power output. This electricity can be used within the home or business or, if permitted by the grid management, sold back into the electric power grid.
Mini cogeneration DERs supplies electricity for more than one household and if the excess energy can be sold, these installations are generally more viable from an economic point of view. Thus, mini CHPs have a large role to play in the field of carbon reduction in buildings where more than 14% of carbon can be saved by using mini CHPs (WRAPAI 2009).
Biogas cogeneration is extensively used and disseminated in rural China, Nepal, Vietnam, rural Costa Rica, Colombia, Rwanda, and other regions of the world where waste management and industry closely interface.
 

Advantages

  • Generation of renewable, green electricity
  • Low operating costs
  • Underground construction minimizes land use
  • Long life span
  • Reduces greenhouse gases
  • Increases family income by selling back electric energy to the electric power grid
  • On site use of heat

Disadvantages

  • Requires expert design, skilled construction and expert maintenance required
  • Biogas production below 15°C, is no longer economically feasible
  • High capital costs

References Library

MANG, H.-P.; LI, Z. (2010): Technology Review of Biogas Sanitation. (= Technology Review ). Eschborn: Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH. URL [Accessed: 17.06.2013].

ISAT (Editor); GTZ (Editor) (1999): Biogas - Costs and Benefits and Biogas – Programme Implementation. (= Biogas Digest, 3). Information and Advisory Services on Appropriate Technology (ISAT) and German Agency for Technical Cooperation GmbH (GmbH) . URL [Accessed: 19.04.2010].

JENSSEN, P.D.; GREATOREX, J.M.; WARNER, W. S. (Editor) (2004): Sustainable Wastewater Management in Urban Areas. (= Kapitel 4. Kurs WH33, Konzeptionen dezentralisierter Abwasserreinigung und Stoffstrommanagement). Hannover: University of Hannover.

MDC (Editor) (2003): Minnesota's Potential for Electricity Production Using Manure Biogas Resources. Final Report. Minnesota: Minnesota Department of Commerce (MDC) and State Energy Office (SEO). URL [Accessed: 23.04.2010].

REITH, J.H. (Editor); WIJFFELS, R.H. (Editor); BARTEN, H. (Editor) (2003): Biomethane and Biohydrogen. Status and perspectives of biological methane and hydrogen production. Dutch Biological Hydrogen Foundation and the Netherlands Agency for Energy and the Environment (Novem).

PIPOLI, T. (2005): Feasibility of Biomass-based Fuel Cells for Manned Space Exploration. In: Proceedings of the Seventh European Space Power Conference, Stresa, Italy. URL [Accessed: 18.01.2011].

SCHALLER, M. (2007): Biogas electricity production hits 17,272GWh a year in Europe. In: Engineer Live, 46-49 . URL [Accessed: 03.05.2010].

SUSANA (Editor) (2009): Links between Sanitation, Climate Change and Renewable Energies. Eschborn. (= SuSanA fact sheet 09/2009). Sustainable Sanitation Alliance (SuSanA) . URL [Accessed: 05.09.2010].

TEIXEIRA COELHO, S.; STORTINI GONZALES VELAZQUES, S.M.; STELLA MARTINS, O.; CASTRO DE ABREU, F. (2006): Biogas from Sewage Treatment used to Electric Energy Generation, by a 30 kW (ISO) Microturbine. (= World Bioenergy Conference & Exhibition). Sao Paulo: Brazilian Reference Center on Biomass (CENBIO) . URL [Accessed: 03.05.2010].

TILLEY, E.; LUETHI, C.; MOREL, A.; ZURBRUEGG, C.; SCHERTENLEIB, R. (2008): Compendium of Sanitation Systems and Technologies. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and Water Supply and Sanitation Collaborative Council (WSSCC). URL [Accessed: 15.02.2010].

See document in FRENCH

WIKIPEDIA (Editor) (2010): Cogeneration. Wikipedia. URL [Accessed: 16.09.2011].

WRAPAI (Editor) (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research. Australia: Waste Refinery Australia Project Association Incorporated (WRAPAI).

Further Readings Library

Reference icon

MDC (Editor) (2003): Minnesota's Potential for Electricity Production Using Manure Biogas Resources. Final Report. Minnesota: Minnesota Department of Commerce (MDC) and State Energy Office (SEO). URL [Accessed: 23.04.2010].

This report is a basic assessment of the feasibility and potential for using animal wastes in anaerobic methane digesters to create electricity in Minnesota. It covers an estimation of the electricity potential, the farm-size thresholds that warrant further investigation for a potential digester system, a quantification of the impact of incentives as well as a financial analysis.


Reference icon

SCHALLER, M. (2007): Biogas electricity production hits 17,272GWh a year in Europe. In: Engineer Live, 46-49 . URL [Accessed: 03.05.2010].

Biogas is a green energy using new technology. Undoubtedly, the produced kW cost is not yet a competitor against nuclear or fossil fuel energies, but the systems installed are more and more efficient, and their financial profitability is increasing. Marc Schaller reports.


Reference icon

WRAPAI (Editor) (2009): Document 8, Data Management Document, Appendix S 06 - Energy Research. Australia: Waste Refinery Australia Project Association Incorporated (WRAPAI).

This document provided by Waste Refinery Australia Project Association Inc. contains information on biogas, different types of cogeneration (CHP) and district heating. Additionally there are also facts and information on hydronics and gas flare.


Case Studies Library

Reference icon

OTTER-WASSER (Editor) (2009): Ecological housing estate, Flintenbreite, Luebeck, Germany - draft. (= SuSanA - Case Studies). Eschborn: Sustainable Sanitation Alliance (SuSanA). URL [Accessed: 25.04.2010].

In the Flintenbreite in Luebeck, Germany, blackwater is collected in vacuum toilets. Together with organic wastes from the kitchen it is converted to biogas. Greywater is treated in a reed-bed filter. The project demonstrated the consistent utilisation of ecological building materials, the use of self-sustaining, integrated energy and wastewater concepts, and the implementation of innovative energy saving technologies, with a minimisation of interference in nature, and a responsible, integrative and active cohabitation of the inhabitants.


Reference icon

TEIXEIRA COELHO, S.; STORTINI GONZALES VELAZQUES, S.M.; STELLA MARTINS, O.; CASTRO DE ABREU, F. (2006): Biogas from Sewage Treatment used to Electric Energy Generation, by a 30 kW (ISO) Microturbine. (= World Bioenergy Conference & Exhibition). Sao Paulo: Brazilian Reference Center on Biomass (CENBIO) . URL [Accessed: 03.05.2010].

The sewage treatment process at SABESP (Basic Sanitation Company of Sao Paulo State, Brazil) has until now burnt some of the biogas produced in the anaerobic digester to enhance the process temperature and the other part was burnt in order to limit impact of emission. The transformation of this excess biogas into electricity would be a sustainable solution generating even additional income. An alternative to burn it in flare is the biogas conversion into electricity through engines or microturbines. This paper describes the proposed system to convert biogas in electricity and heat using microturbines (30 kW ISO).


Awareness Raising Material Library

Reference icon

SUSANA (Editor) (2009): Links between Sanitation, Climate Change and Renewable Energies. Eschborn. (= SuSanA fact sheet 09/2009). Sustainable Sanitation Alliance (SuSanA) . URL [Accessed: 05.09.2010].

This factsheet of Sustainable Sanitation Alliance describes the impact of greenhouse gases on climate change and focuses on the advantages of renewable energies. Therefore many different technologies like production of biogas or short-rotation-plantations are mentioned.


Training Material Library

Reference icon

MITZLAFF, von, K. (1988): Engines for biogas. Eschborn: German Appropriate Technology Exchange (GATE), German Technical Cooperation (GTZ) GmbH. URL [Accessed: 06.01.2011].

The aim of this publication is to build a bridge between the elaborate literature and information on the biogas production side and the existing technical and scientific know-how on the side of internal combustion engines. An engine fuelled by biogas shall become understandable as a core module in a system of energy supply, energy transformation and a demand of energy for a useful purpose. This publication attempts to provide a source of essential information for decision-making, planning, modification and operation of biogas engines within this system.


Reference icon

NAVICKAS, K. (2007): Biogas for Farming, Energy Conversion and Environment Protection. Rakican, Lithuania: Lithuanian University of Agriculture, Department of Agroenergetics. URL [Accessed: 03.05.2010].

This presentation gives information on the agricultural aspects of biogas production and focuses on the process of digestion and fermentation. But it also provides knowledge about different ways of using biogas including cogeneration and fuel cells.


Important Weblinks

http://en.wikipedia.org/ [Accessed: 26.04.2010]

This link to Wikipedia provides information on cogeneration. There are many existing further links explaining the technologies of engine or generator types.

http://www.mrec.org/anaerobicdigestion.html [Accessed: 10.05.2010]

The webpage of Midwest Rural Energy Council (MREC) provides a wide range of information on implementing small- and mid-scale biogas plantations in order to produce electricity.

http://www.snvworld.org/en/Pages/re-Publications.aspx [Accessed: 28.04.2010]

The Netherlands Development Organisation (SNV) library hosts an extensive choice of domestic biogas reports from around the world domestic biogas.

http://www.appropedia.org/Category:Biogas [Accessed: 28.04.2010]

Appropedia is the site for collaborative approaches to sustainability, poverty reduction and international development. This article is about simple and sustainable biogas production and use.

http://www.unapcaem.org/act_detail.asp?id=311 [Accessed: 26.04.2010]

This webpage presents the proceedings of the International Seminar on Biogas Technology for Poverty Reduction and Sustainable Development, jointly sponsored by the United Nations Economic and Social Commission for Asia and the Pacific (UNESCAP) and the Ministry of Agriculture of China (MOA) (18 to 20 October, 2005, Beijing). Utilisation of household biogas systems and large-scale biogas systems as a means to boost rural economy, while contributing to rural poverty reduction and sustainable development are discussed.

http://en.wikipedia.org/ [Accessed: 26.04.2010]

This link to Wikipedia provides information on cogeneration. There are many existing further links explaining the technologies of engine or generator types.