Tag Archives: biodigesters

Maintenance of biodigesters and issues surrounding maintenance/service arrangements

Even in the presence of mandated service agreements maintenance for biodigesters can still be an issue. For example, time constraints on private contractors [1] from central government to install and maintain digesters, lead to a slipping in maintenance standards. In a village in Assam interviewed in the paper, no follow up visits from the contractors were had for four years, and a 20% digester failure rate was recorded. Communications issues were a key contributor to this: the fact that a provision of a half of the installation subsidy for maintenance of plants over 5 years old was not communicated to households or the contractors.

broken biogas assam india

A broken biodigester in Assam, India, having not been repaired for 6 months. Source: Raha, Mahanta & Clarke (2014) The implementation of decentralised biogas plants in Assam, NE India: The impact and effectiveness of the National Biogas and Manure Management Programme. http://dx.doi.org/ 10.1016/j.enpol.2013.12.048

One of the more overlooked aspects of biogas digester services and operation is the maintenance requirements of digesters. Older digester designs (for example dome-type biodigesters constructed from brick or earth) require a regular maintenance schedule (monthly to quarterly is common) [2] in order to maintain best performance, including maintaining the chemical balance of the digesting chamber and its structural integrity, repairing cracks in the chamber if necessary. More modern household and collective-scale designs are based off a plastic digesting chamber, usually fibreglass-reinforced plastic (FRP), and as such require less intensive maintenance (annual maintenance visits are sufficient), but still have a maintenance burden to address for peak performance (for example, maintaining the chemical balance of the digester through appropriate feedstock insertion).

However, even in the presence of mandated service agreements for biodigesters, for example delivered through a fee-for-service energy service company (ESCO), maintenance can be overlooked. A useful case study illustrating this can be obtained from India’s National Biogas and Manure Management Program (NBMMP) [1]. The NBMMP relied on local governments in India contracting the private construction sector to construct biogas digesters for rural communities. Time constraints on these contractors on installation, stemming from the prevailing climatic conditions limiting the working period of the year due to monsoons, meant that maintenance standards, for which the contractors under the tender from local government were also responsible, and the overall quality of installation of digesters, slipped drastically. Some contractors reported having to fill an annual allocation of 6,000 digester installations in just three months, at a rate of over 60 digesters per day, often for small companies of just 5-10 technicians. Hence, some digesters were not being maintained for four years or more, and there was a 20% overall digester failure rate. Communication between the public bodies and private contractors was also an issue: the NBMMP made provision of half the subsidy granted to households for purchasing digesters as a maintenance grant over a five-year period, which was barely taken advantage of due to a lack of awareness on the part of households and contractors.

This case study makes clear the necessity of accounting for maintenance arrangements in the design of any biodigester business plan or program. Ensuring the maintenance schedule is followed will extend the life of the biodigester and improve its performance, resulting in greater satisfaction with the system from the point-of-view of end-users. This fact makes biodigesters particularly suited to a fee-for-service business model: regular maintenance can easily be combined with regular payment collection visits, reducing the cost burden on the company/organisation and improving service.

The final post in this series will focus on the recent evolution of the Chinese National Biogas Program, and the lessons to be learned for cross-application in other regions globally.

– Xavier Lemaire and Daniel Kerr, UCL Energy Institute

[1] Raha, Mahanta & Clarke (2014): http://dx.doi.org/10.1016/j.enpol.2013.12.048

[2] Surendra et al (2014): http://dx.doi.org/10.1016/j.rser.2013.12.015


The Challenges and Opportunities of Centralised and Decentralised Biodigesters

The STEPs research project explores the relative benefits and dis-benefits of larger centralised biogas systems at a village scale versus smaller family-scale systems. It also investigates the economic and financing factors (centralisation brings economies of scale but can only really be implemented by organisations/governments, family-scale systems may be out of reach of user capital without financing arrangements), environmental factors, and social and behavioural considerations (do users want to collectively cook, issues with economics of pipe gas supply meaning necessity of group facilities etc) inherent in biodigester development.

Biogas digesters can be a valuable solution to providing thermal energy services to rural and urban households in the developing world. The technology is particularly applicable in rural areas, where access to feed stock for the digesting chamber in the form of agricultural wastes and other organic wastes is greater. In general, digesters fall into two broad categories: household-scale biodigesters, and larger, centralised biodigesters.

Laramee & Davis 2013 Dome Biodigester in Tanzania

Dome-type biodigester in Arusha, Tanzania [1]

Household-scale biodigesters are often seen as the most viable option for rural communities and households. These are generally small, with digesting chambers of volumes in the 4 to 13 cubic metres range. These installations will support the cooking needs of a rural household, as well as providing biogas for heating or lighting if required. Tailoring the size of the biogas system to the availability of feedstock for the household is critical for successful functioning of the system: studies have suggested 4-6 heads of cattle is a sustainable target if using agricultural wastes for feedstock, for an average-sized family of five. Individual biodigesters can produce sufficient gas for a single person on as little as 1 kg/day of feedstock.[2]

However, one of the primary limiting factors in the adoption of household biodigesters is financing and end-user capital constraints. Household-scale systems are still relatively expensive for the majority of rural developing-world users, and experience has shown that without the provision of credit facilities in biodigester programs, or government subsidies, adoption rates remain low.

Centralised biodigester systems offer a different set of benefits and challenges. Economies of scale are the major advantage: one centralised system can serve a medium-scale settlement or several small settlements, with a reduced burden for upfront capital costs and maintenance compared to the same service with household-scale systems, in the range of US$100 – 500 per household. The Chinese National Biogas Program [which will be the subject of a later blog in this series], has been the major implementer of centralised systems, however experience also exists in other South-East Asian countries. Examples of this can be found in the centralised digesters built near Beijing to service rural villages. For an upfront cost of ~US$1 million, 1900 households are serviced through each centralised digester, with biogas available at a 20% discount compared to market LPG prices, and the additional benefit of organic effluent being made available for sale to the local farms feeding the digester.[2] The major constraint, however, to wider dissemination of centralised systems is the significantly higher up-front capital costs. This puts the systems out of reach for private users in the majority of cases, government-scale implementation is more common.

Socio-political conditions are another factor that has proved a constraint in biogas implementation projects in developing countries. Centralised biogas digesters can have difficulty with biogas supply to end-users, particularly given the poor economics of installing piped gas supply in small rural communities. Communal cooking facilities have been a solution to this problem in theory, however experience from India suggests that collective cooking is not desired by the rural population, and this has impacted upon the success of centralised digester installations. As with dissemination programs for clean cookstoves, biogas installations need to take into account the end-users needs and desires in design and installation for product use and performance.

The other posts in this series will cover the question of why biogas hasn’t succeeded in Sub-Saharan Africa as it has in South-East Asia, the maintenance question for biogas services, and lessons from the Chinese National Biogas Program.

– Xavier Lemaire & Daniel Kerr, UCL Energy Institute

[1] Laramee & Davis (2013) Economic and environmental impacts of domestic bio-digesters: Evidence from Arusha, Tanzania. http://dx.doi.org/10.1016/j.esd.2013.02.001

[2] Hojnacki et al, MIT (2011) Biodigester Global Case Studies. Available at: https://colab.mit.edu/sites/default/files/D_Lab_Waste_Biodigester_Case_Studies_Report.pdf

What Could The Energy Transition Be for Thermal Energy Services in the Global South – Part 2

Following our previous post on cooking, this post will investigate space and water heating/space cooling needs.

Space and water heating/space cooling

Heating can be an important source of energy consumption in a number of developing countries located far from the Tropics. This function is often associated with cooking, where a central heating point is used both to cook meals and heat the house. Bio-digesters in countries like China, India or Nepal have been able to provide heat on top of cooking.

Another energy service which is more widely used – even if often not considered as a priority – is domestic hot water which can be provided with a solar water heater. South Africa has some very large programmes of dissemination of solar water heaters, notably in townships. Half of the population of Barbados has a solar water heater. Solar water heaters are a mature technology, which can be easily manufactured locally and relatively cheaply, most of the time sold on a cash basis or with a consumer credit.

david monniaux 2005 swh

Solar water heater used in the Cirque de MafateRéunion. “Solar heater dsc00632”. Licensed under CC BY-SA 3.0 via Wikimedia Commons – http://commons.wikimedia.org/wiki/File:Solar_heater_dsc00632.jpg#/media/File:Solar_heater_dsc00632.jpg

Cooling renewable energy technologies are less available. For instance solar thermal cooling systems seem to exist mainly as large-scale technology; they tend to be complex to design and generally are quite costly. They are not considered in the STEPs project, which deals with the large-scale dissemination of medium scale collective or individual small-scale mature technologies.

Heat pumps imply dwellings of good quality with good insulation which is not a common occurrence in the case in poor communities.  Nevertheless ground-source heat pump could potentially be used at a larger scale (http://unu.edu/publications/articles/geothermal-energy-in-developing-countries-and-the-mdgs.html).


Energy-efficient insulation and passive housing have traditionally been the preserve of developed nations (for example, the developed German passive housing technology sector). However, the potential for efficient insulation and space temperature management with locally-sourced, low-cost renewable materials has been realised in a number of countries, particularly in Sub-Saharan Africa. This includes both traditional methods for adapting households in temperate developing countries, such as cladding and thatch roofing, as well as the more modern concept of passive housing, where thermal energy inputs (for example, from the sun) are used as part of the building’s thermal energy regime, enabling a reduction in the use of air conditioning methods.

Traditional housing for example in Lesotho is adapted to the variable temperatures of the mountain climate the country resides in, with rondavels (traditional huts) having conical thatched roofs and daubed exterior walls for insulation against the often cold climate, and warm air retention.


By K. Kendall (originally posted to Flickr as Rondavel, Gisela) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)%5D, via Wikimedia Commons

Business model examples and projects for efficient insulation in developing countries are few and far between. For instance, the iShack project in Enkanini, an informal settlement in Stellenbosch, South Africa in partnership with the University of Stellenbosch, is predominantly a fee-for-service solar home system project, where users pay a small monthly fee on top of a fixed installation cost for small (50-80W) solar home systems. However, the organisation is also expanding into sustainable insulation and other household services, particularly sustainable wastewater treatment and household-scale biogas installations for cooking.


Enkanini, Stellenbosch from the steps of the iShack hub. Image: Daniel Kerr

– Xavier Lemaire & Daniel Kerr – UCL

What Could the Energy Transition Be for Thermal Energy Services in the Global South

The STEPs project (Sustainable Thermal Energy Service Partnerships) funded by Dfid-DECC-EPSRC is about the design of public private partnerships for the provision of thermal energy services targeting the poorest in developing countries.  The STEPs research focuses on thermal energy services for households and small producers.  The following posts describe what the main needs are in terms of thermal energy services, and with which technologies they could be provided.

Households and small producers in developing countries have needs in terms of cooking, heating/cooling, refrigeration and drying which vary according to the geographical, socio-economic and cultural conditions found in their locations, and can be satisfied in a very different manner than in industrial countries.  Not only can the technologies used be different, but the entrepreneurial model which can help to disseminate these technologies is particular to the Global South: social entrepreneurs, cooperatives, informal groups or established small rural companies acting like utilities have to be involved.

The sustainability of their business models implies the need to find the right mix between different technologies and services provision adapted to the context they evolve in.


Currently cooking in developing countries is mainly done using non-efficient cook stoves using traditional biomass (wood, charcoal) or fuels like coal or paraffin. More infrequently efficient cook stoves, bio-digesters or more rarely LPG (Liquefied Petroleum Gas) are used for cooking in rural areas.

Improved cook stoves have been tried to be disseminated for several decades now with mixed results. It seems cook stoves of all kind of shapes and made of all kind of materials have been conceived without being able to reach their intended market. Improved cook stoves fall broadly into two categories – cook stoves that use traditional wood fuels more efficiently, or cook stoves that use improved fuels such as unprocessed charcoal, briquettes or pelletised fuelwood.


A small selection of the diverse design options for clean cookstoves. Image credit: GIZ 

One of the aims of the STEPs project is to understand if public-private partnerships similar to the ones established for rural electrification could facilitate the dissemination on a very large scale of improved cook stoves. This is done by reviewing the (few) successful experiences of large-scale dissemination of improved cook stoves, for example the National Biogas Cookstoves Program (NBCP) in India (http://www.mnre.gov.in/schemes/decentralized-systems/national-biomass-cookstoves-initiative/), and determining how private business can take charge of the distribution and the marketing of improved cook stoves.

Another way of facilitating the energy transition in terms of cooking facilities is to encourage the use of LPG (Liquefied Petroleum Gas). LPG may not be a very low-carbon energy but it is considered a lot cleaner/less damaging for the environment and efficient than the use of traditional fuels. Unfortunately, the logistics of distribution in remote places makes it unaffordable for the poorest unless a program of subsidies is also implemented, which experiences show are difficult to target. For example, the Ghanaian LPG distribution and promotion program started in the 1990s, and continuing today, has experienced difficulties through cross-subsidising LPG, intended for cooking, through gasoline sales. This led to a rise in LPG transport use and conversions, particularly in urban taxis, skewing sales towards transport use and not rural cooking use as intended by the government program.

Bio-digesters can produce methane for cooking. This technology is widely disseminated in few countries like China or India, but not so much in sub-Saharan African countries. Various reasons have been invoked to explain this situation – low density of population/small size of holdings notably. It seems nevertheless than even if conditions may be less favourable in African countries than Asian countries, there could be specific services organised around collective use of bio-digesters (e.g. cooking in a school by collecting waste from a community).

There are two main approaches to household biodigester construction. The traditional technology is a dome-type biodigester, with the digesting chamber constructed from compacted earth or brick. These are cheap and easy to construct, but are prone to failure and require significant maintenance for good efficiencies. Modern household biodigesters are made from prefabricated plastic digesting chambers, which only require maintenance to maintain the digestion process, and are significantly more durable than the traditional type.

biodigester in cantonment

Biogas construction in cantonment (4971874669)” by SuSanA Secretariat – https://www.flickr.com/photos/gtzecosan/4971874669/. Licensed under CC BY 2.0 via Wikimedia Commons

africa biodigester

Prefabricated biodigester being installed in South Africa. Image: popularmechanics.co.za

agama biogas

Prefabricated biogas digester being constructed by AGAMA Bioenergy worker in South Africa. Image: Agama Biogas PRO via Youtube

Solar cooking and solar ovens are another technology that can be used for cooking in rural areas of developing countries. The Global South, and Sub-Saharan Africa in particular, generally has a good level of insolation for the use of solar technologies. Solar cooking technology however has struggled to find a foothold in Sub-Saharan African markets, and is at a low level of dissemination despite the maturity of the technology. A number of factors could be behind this, most notably the lack of convenience associated with solar cooking and the long cooking times and forward planning associated with using the technology.

ikiwaner solar oven 2008

A solar oven being demonstrated in Ghana. Credit: Ikiwaner / Licensed under CC BY 2.0 by Wikimedia Commons

– Xavier Lemaire & Daniel Kerr – UCL