Generating Electricity from Biogas - Examples
This article summarizes the experience of using biogas to generate electricity in different countries and is a continuation of the article Electricity Generation from Biogas.
The technologies of anaerobic fermentation and electricity generation from the resulting biogas have been well known for a long time. Such plants have been in operation for many years particularly for sanitation purposes. However, power generation from biogas using agricultural feedstock became more common shortly after the introduction of a feed-in tariff. Around 0.11 € per kWh (plus specific bonuses) was the guaranteed base price for plants up to 150 kW.
In 2009, more than 4,500 biogas power plants were in operation in Germany with more than 1,500 MW installed power capacity. Specific know-how and technological solutions are thus available to a very high standard. However, despite the guaranteed feed-in tariff, the profitability of the plants has not always been guaranteed. With fluctuating prices for feedstock, often especially for plants and grains produced specifically for power generation, the profitability of the plants has varied from year to year.
The size of power plants has grown rapidly over the years. While the average size of a biogas power plant was 60 kW in 1999, it was 300 kW only 10 years later (2009). The reason for this lies in the decreasing specific cost of bigger plants - about 50% lower for a 300kW plant than for a 60kW plant.
Today, the profitability of biogas plants in Germany depends greatly on the potential to sell heat as well as producing electricity. The heat output of combined heat and power (CHP) generators is used to provide hot water for community heating systems for households, schools, public swimming pools etc. Furthermore, special bonuses, such as bonuses paid for the use of renewable raw material, are also important for the profitable operation of the plants.
Developing and Newly Industrialised Countries
Millions of biogas plants have been installed all over the world within the last two decades, financed or supported by national and international programmes. It is not possible to give a comprehensive overview of these activities within the context of this paper. However, the following chapter will focus on activities carried out in co-operation or at least in close contact with GTZ as well as selected promising activities that might prove relevant for future approaches.
Since the late seventies, GTZ has launched several projects for the dissemination of biogas technology:
- Bilateral projects with Ethiopia, Cameroon and Lesotho
- The Biogas Dissemination Programme active in Belize, Bolivia, Jamaica, Nicaragua, Burkina Faso, Tanzania, Kenya, Burundi and Thailand
- Special Energy Programmes with Biogas activity in Tanzania, Burundi, Kenya, Ivory Coast, Burkina Faso and Mali.
Most of the plants installed by these programmes were designed for households, hospitals and farmers, mainly using the gas directly as fuel for cooking and lighting. The principal focus of bigger plants constructed for slaughterhouses or similar applications is sanitation.
However, the generation of electricity has also played a role and several pilot plants were installed in the 1980s und 1990s, mostly in the power range 10 kW to 100 kW. Nevertheless, it appears that very few of these plants are still in operation or have worked successfully over the years. Such plants doubtless faced many technical problems as a standard technology for electricity generation from biogas could not be established at the time.
Activity continued, however, and the final conclusions of this paper are based on the following examples of more recent approaches, although it is still very difficult to obtain substantial operational data.
China is the world’s leading country in the application of anaerobic biomass digestion technology in quantitative terms. Besides millions of small biogas plants in farms, there are over one thousand bigger plants, many of which use industrial waste from paper, sugar and the pharmaceutical industry as feedstock. The main purpose of these plants is to reduce waste and slurry problems. The gas is used directly for cooking, lighting or heating purposes and only few of the plants installed in China are destined for electricity production - in general big plants - as only those with capacities higher than 0.5 MW are allowed to connect to the grid. However, power generation from biogas has become the focus of support programmes in recent years. A tenfold increase in electricity generation from biogas is planned between 2005 and 2013.
The GTZ Sino-German Project on Optimisation of Efficient Biomass Utilisation (2009-2013) aims to improve the technical standard and performance of medium and large-scale biogas plants producing energy from biomass. The programme recommends shifting financial sup-port from an investment-oriented to an output-oriented scheme, supported by demonstration projects, policy support and capacity.
India has extensive experience of biogas plants. Over 1.8 million cattle dung digesters had been installed in India by the mid 1990s. However, around one third of these were inoperative by early 2000 and there is little experience of commercial electricity generation at small and medium level.
The GTZ Project Indo-German Energy Programme (IGEN) recently started a rural electrification programme with biogas plants of around 60 kWel output.
More than 25,000 biogas plants have been set up in Bangladesh. However, most of them are family-sized and used only for cooking burners. Over 2,000 of these biogas plants have been constructed on poultry farms. In such cases, the main purpose of the plants is not only the generation of gas; the plants are also necessary owing to the bad odour caused by poultry droppings and for other environmental reasons.
Feasibility studies A feasibility study (GTZ-PURE, 2005) with financial analyses of plants with 100–50,000 birds came to the following conclusions:
- Larger farms may opt for electricity production, but selling gas is more profitable
- Selling electricity is economically viable only with the additional sales of at least one of the other two products: gas or fertiliser (assumption: only 50% of the gas is used for electricity generation).
These feasibility findings from 2005 correspond quite well with actual development as evi-denced by the first examples of electricity generation from biogas in poultry farms.
AAS poultry farm The Advance Animal Science Co. Ltd. (AAS), a dairy and poultry farm in Kashimpur of Ga-zipur district, supported by GTZ, has an electricity grid connection but also generates power from biogas using cow dung and chicken droppings as feedstock. In order to generate power, the biogas is passed through a traditional gas generator set with minor modifications.
Only one-third of the plant’s capacity is used for electricity generation. According to press reports (bangladesheconomy.wordpress.com), this electricity co-generating unit is rendered profitable by the savings involved in reducing the electricity bill. The financial contribution of the by-products, such as bio-fertiliser and the gas provided to some cooking burners in the neighbourhood, is obviously consider-able.
From a financial perspective, certain additional effects are not easily measurable:
- Enhancement of environmental security in the farm area and the removal of bad smells.
- Independence of the erratic power supply from the national grid.
This Advance Animal Co. biogas power plant is the second of its kind, following one from a similar pilot project in Faridpur started two years earlier.
In the wake of these first pilot projects, expectations in Bangladesh are high. AAS estimates that a poultry farm of 5,000 birds could generate 5 kW of electricity. Selling electricity in the neighbouring areas seems to be economically viable from an output of 10 kW.
East Africa, Tanzania and Kenya
In Kenya, Tanzania and neighbouring countries, biogas is traditionally used in small and very small installations for providing household energy and for supplying social institutions with gas as fuel for cooking, heating and lighting. With GTZ support, over 1,000 small and medium-size plants and one bigger digester of over 100m³ have been installed by CARMATEC in Tanzania from 1983 on. However, potentials for industrial biogas and electricity generation in East Africa remain largely untapped.
Hale Sisal Farm, Tanzania
In Tanzania a pilot project managed and partly financed by the United Nations Industrial Development Organisation (UNIDO) entitled 'Cleaner Integral Utilisation of Sisal Waste for Bio-gas and Biofertilisers' involved a biogas pilot plant with a capacity of 150 kWel at the Hale Sisal Estate in the Korogwe District of Tanga region.
According to UNIDO statements, the project showed that sisal residues constitute an efficient substrate for anaerobic digestion, generating gas, electricity, and bio-fertiliser. In 2007, UNIDO announced that the results will be transferred to other interested sisal growing nations for replication.
However, the originally planned second and third phases of plant development were never realised. This can be seen as an indicator of the plant’s potential lack of profitability and confirms the views of experts based in the region that the plant’s design seemed ill-adapted to the required sisal operations, and that its substantial operating problems were due to low quality technical components.
Sisal-cum-cattle farm in Kilifi, Kenya
The biogas plant with electricity generation on a sisal-cum-cattle farm in Kilifi, Kenya is usually referred to as a positive example. It converts agricultural waste such as cow manure and sisal into biogas and produces electricity and heat as end products. The technology is practi-cally the same as that used in Germany.
Kenya With support of the GTZ Project PSDA, installed two small biogas power plants. However electricity generation could be realised only partly:
The original purpose of the plant in Keekonyokie was to deliver electricity for a refrigerating storage house. The storage house was built and the cooling compressor was purchased but the thermal insulation has not yet been installed. In the meantime, the gas generated from slaughterhouse waste is fed into a mini gas grid and supplied to 6 restaurants. The designated generator set consists of an adapted diesel engine for dual fuel use and a generator with 20kWel output. The estimated cost is €0.14/kWh compared to a grid price of €0.16/kWh.
At the Abdul Sidis farm, vegetable residues are used as feedstock and the (off-grid) electricity generated by a 20 kWel genset is mainly used for a water pump. Estimated costs are again around €0.14/kWh compared to diesel-generated electricity at a price of €0.36/kWh. Daily savings are estimated to reach €10.
Both plants seem to work well in technical terms.
Independent of GIZ activities, the company BME GmbH in Bavaria offers a ‘High Perform-ance, Temperature Controlled (HPTC)’ biogas plant system known as the ‘Rottaler Modell’.
According to company communications, at least 3 of these plants have been installed in Eastern Africa, 3 are under construction and 2 are in concrete planning:
- In Kenya in Mombasa (2007), Murang’a, Homabay, Bungoma (8/2009);
- Further plants are planned in Dagoretti (KE), in Kigoma, Tanzania, in Zanzibar, Uganda, Ruanda and Madagascar.
- Most of these installations were carried out in cooperation with UNIDO.
- The plants of this system have a two-stage digestion system, with separate Hydrolysis and acidification methanisation;
- It has a controlled temperature of 37°C with insulation and solar heating system.
- Due to the design, even high fibrous material can be digested and a high biogas output per m³ digester volume and day is possible.
- The digester and a separate storage are made from plastic bags of a three layer material.
Desulphurisation is achieved exclusively through the addition of a little air into the gas storage tank. Owing to the steady fermentation temperature and constant gas pro-duction and composition, this method seems to work very well.
A typical HTC plant has a 25 m³ digester bag, a 20 m³ biogas storage bag and two 4 m³ hydrolysis units, a bio filtering system for filtering the hydrolysis gas generated in the hydrolysis unit, a desulphurisation pump and a condensation trap.
The first HPTC plants in Africa apparently used diesel engines, replacing up to 80% of the diesel with biogas. In 2009, a 10kWel generator set running only on biogas was developed by modifying a commercially available petrol generator set used on construction sites in Europe.
Most of these plants were set up near slaughterhouses to use the waste and to provide them and neighbouring buildings with electricity.
The company calculates the cost of installing the plant at around €30,000, but emphasises that profitable operation is possible even without special feed-in tariffs in remote areas where electricity generation with small diesel generators is extraordinary expensive. It calculates a payback period of 2.5 years.
However, during discussions with different biogas experts, concerns were raised regarding this expensive model. It remains to be seen whether the higher price for these sophisticated high temperature plants can be compensated for by higher and more stable production.
The planning and construction agency AKUT Umweltschutz in Berlin carried out some feasibility and concept studies for specific biogas plant projects in the agricultural sector of Kenya. All plants were designed to use as much locally available technology and expertise for con-struction as possible.
The studies carried out between 2006 and 2009 came to the following general conclusions:
- Many substrates from typical agricultural production in Kenya can be used for biogas production
- However, the feed-in tariff for electricity that cannot be used in-house is crucial for the economical operation of biogas power plants. Most of the projects are on hold until there are appropriate feed-in tariffs available for the national grid
- In case of exclusive in-house use of electricity, the feasibility studies show that plants can only be operated economically if there is also a profitable use for the thermal en-ergy output of the CHPS. However, in most cases thermal energy demand is insuffi-cient
- Use of slurry is recommended
- Capacity building should be provided for operators.
Key support to the development of the Kenyan biogas sector was earlier provided through GTZ’s bilateral Programme for Private Sector Development in Agriculture (PSDA). GTZ has recently been commissioned to implement the ‘Project Development Programme – East Africa’ (PDP) on behalf of the German Ministry of Economics and Technology under the ‘Re-newables Made in Germany’ initiative. The programme aims to build partnerships between German and East African companies in the field of renewable energy. Biogas has been iden-tified as one of the priority areas. The PPP lessons have now been integrated into the various follow-up activities of this programme, and the information presented below has been com-piled in the context of the PDP.
After the positive experience with the pilot plant in Kilifi, investors and government have ex-pressed increasing interest and asked GTZ to make recommendations.
Study on agro-industrial biogas potential, Kenya GTZ commissioned the DBFZ (Deutsches Biomasse Forschungs Zentrum) to undertake a study on ‘Agro industrial Biogas in Kenya’ examining the theoretical potential of 13 types of biomass from agro-industrial businesses in Kenya to municipal waste in Nairobi. The report concludes that the potential electric capacity of generated biogas is high. Biogas from all examined subsectors could cover up to 16% of the total Kenyan electricity production as of 2007/08.
Municipal solid waste, sisal and coffee production are the most promising sectors with the greatest potential. However, specific electricity production costs for small plants (50kWel) range between 0.11 and 0.29 US$/kWh. A basic feed-in tariff for small plants of about 0.20 US$/kWh was therefore proposed, but the implementation of such a prohibitively high tariff seems unrealistic. It seems probable that only bigger plants with a profitability at a lower tariff of around 0.15 US$ will be able to take advantage of this.
Based on the ‘hard facts’ of this study’s recommendations, follow-up is currently taking place under the PDP, focusing on targeted advice and cooperation with policymakers and investors on the tariff framework.
Brazil is one of the countries whose biomass energy market is the most advanced. Biofuels are produced from sugar cane and hundreds of power plants use the remaining sugar cane bagasse as fuel. Most of these plants use direct combustion and have capacities far over 1 MW.
However, a number of small and medium sized biogas power plants also exist, mostly in-stalled in agro-industrial settings. The main purpose of these plants (using the waste of a slaughterhouse or animal production facility) is sanitation and environmental protection. The second important benefit is gas and electricity production for in-house use in the companies.
There are probably large numbers of biogas plants in farms or small industries using the gas for individual power generation, as suggested by the provision of a specific biogas motor programme by the Brazilian company Branco. It provides small motors, motor pumps and a generator set of 3.6 kW, especially for Biogas use (branco.com).
However, hardly any electricity provision from biogas for basic public energy needs has so far been realised. A programme for the support of alternative energy resources, designed to feed-in more biomass energy into the national grid, was already approved in Brazil back in 2002. However, implementation met with delays, and only big power plants with direct combustion of the biomass were able to benefit from the programme.
Feed-in Agreement in Parana Since 2009, in the southern state of Parana (PR), 5 biogas power plants have become the very first small plants to feed their power into the public grid.
These plants, with capacities of 20 – 160 kWel, won a tender to sell their electricity to the pub-lic energy provider Copel Distrubuicao SA in the southern Brazilian state of Parana. The feed-in tariff corresponds roughly to 0.05 EUR / kWh.
This price is not high enough to guarantee the profitable operation of biogas power plants in Brazil. It is nevertheless an important step forward, as it can help make the plants more prof-itable. Only the excess electricity is sold at the fixed feed-in tariff.
The GTZ Energy Programme (‘Programa Energia’), on behalf of German Federal Ministry of Economic Cooperation and Development, supports the use of renewable energy and energy efficiency in Brazil and hence also the appropriate production and use of biogas. The pro-gramme aims to improve framework conditions for the sustainable use of biogas, the analysis of experience and know-how transfer between German and Brazilian partners. In October 2009, the GTZ Energy Programme entered into a partnership with the public energy utility Eletrosul, subsidiary of Eletrobras, the national electricity provider, focusing on know-how transfer in the field of biogas. Eletrosul aims to construct biogas power plants for electricity generation in the South of Brazil.