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.

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

Second STEPs Network Meeting – KwaMbonambi, South Africa, 28-30 October 2014

The second STEPs network meeting was held in KwaMbonambi, South Africa from the 28^th – 30^th October 2014. The purpose of the meeting was to address the current status of the project and determine next steps, as well as take the opportunity to both meet local representatives from South African electricity and thermal off-grid concessionaires, and visit the operations of local concessionaires for fieldwork, which will be described in a later post on this blog.

The first day of the meeting saw a great deal of discussion among project partners as to the way forward for the STEPs project. Primary discussion focused around the construction of the STEPs model, focusing on five main aspects: institutional arrangements, business/enterprise models, financing, technology options, and policy/regulation. The project will look to test a number underlying assumptions for the sustainability of thermal energy service businesses, for example operating margins (in the 50-70% range), and the importance of using public sector clients as anchor consumers in a thermal energy business customer base.

Discussions were had on the most relevant technologies to target with STEPs. Key technologies are improved cookstoves, LPG for cooking/refrigeration, and household biogas installations, primarily for the successes seen in previous projects using these technologies. These include the Ghanaian experience in LPG stove dissemination via the government, and the vast scale of the Chinese domestic biomass gasifier program. However, challenges exist to the uptake of all these, including cultural contexts for cooking (meaning stove design needs to take social factors into account), as well as the difficulty in acquiring biomass feedstocks in some country contexts, for example Sub-Saharan/Southern Africa.

Discussion was also had about the most relevant financial and management models to target under the STEPs model, as well as which technologies these models applied best to. For example, outright/financed purchase models under a concession contract are most relevant for improved cookstoves, whereas fee-for-service and progressive purchase models are more relevant for LPG and biogas systems.

Binu Parthan presenting to the STEPs team – 2^nd Steps meeting network – KwaMbonambi, South Africa – 28th – 30th October 2014.

The second day saw representatives from local utility concessions in KwaZulu-Natal attend the STEPs meeting. The concessions represented were KES, with their CEO Vicky Basson attending, active in the Durban and central KwaZulu-Natal region, and Nuon-RAPS (NuRa), with MD Sifiso Dlamini, active in Northern KwaZulu-Natal up to the Mozambican border. The KES utility was founded in 1997, and currently services over 28,000 customers with solar home systems on a fee-for-service basis in and around the Durban area. Tariffs are set at 96ZAR/month for a solar home system, with six lights (2 outdoor, 4 indoor), and a 9V and 12V DC connection point. The company has provided LPG services, both in LPG bottles and integrated stove systems (notably the Shesha stoves from Totalgaz). Their concession is granted via a bidding process by the KZN state government and local municipalities on a yearly basis.

Questions were answered by the concessionaires that added context to the construction and future work of STEPs. These included revisions of assumptions for sustainable operating margins, insight into the regulatory framework in South Africa for LPG financing, and particularly the barriers to the use of mobile money in South Africa, due to transaction regulations in the financial sector and a lack of culture for mobile payments. Subsidy positioning from the government was also identified as a key barrier in South Africa to thermal energy use, with subsidies moving between thermal energy sources frequently.

Both concession representatives stated a desire to expand their thermal energy services business, and stated the criticality of tailored solutions to national and local contexts for technologies, an aspect of the thermal energy market that is core to the development of the STEPs model.

Discussion between the STEPs team and Vicky Basson (KES, far left) and Sifiso Dlamini (NuRa), middle – 2nd Steps meeting network – KwaMbonambi, South Africa – 28th – 30th October 2014.

A number of conclusions were drawn from the meeting. Given the ongoing political difficulties in Lesotho, a reorientation of project objectives was proposed to take into account the changing landscape in which the project operates. Current goals are to construct the STEPs model as a resource across all sectors, being relevant to governments and policy-makers, as well as the private sector and SMEs/entrepreneurs wishing to enter the thermal energy services market.

– Daniel Kerr, UCL Energy Institute