Small-scale biogas plant made of brick and cement then buried below ground.
Technical Summary

Biogas for Cooking

Project Drawdown defines biogas for cooking as: methane digester technologies that produce biogas for household heating through the anaerobic digestion of organic waste. This solution replaces fuelwood, charcoal, or even fossil fuel-based cookstoves, and helps mitigate their emissions.

Anaerobic digestion is a biological process that produces a gas (biogas) principally composed of methane and carbon dioxide. Methane digesters come in a variety of different tank designs to capture methane and combust it to create heat. This reduces greenhouse gas emissions from the use of fossil fuels or solid biomass fuel, while also mitigating fugitive methane and nitrous oxide emissions from the anaerobic breakdown of manure.

In the Drawdown model, the manure and crop waste fed into digesters is from the cattle and farm owned by the household so there is no fuel cost, but some maintenance is required.

Methodology

This analysis focuses only on three developing regions: Middle East & Africa, Asian sans Japan and Latin America. To derive mitigation impact results and financial considerations for Biogas for Cooking, several steps were taken. First, a forecast was calculated for the total final cooking energy for the included regions from 2014-2050, measured in terawatt-hour therms. Then, current adoption[1] of small methane digesters was determined, future adoption scenarios were forecast for that period based on the availability of waste to feed digesters, an emissions mitigation value was derived in terawatt-hour therms per digester per year, and the emissions mitigation and costs were calculated compared to a Reference Scenario that keeps methane digester adoption at its current percentage of the cooking energy demand.

Total Addressable Market[2]

The total addressable market is defined as the total terawatt-hour therms final energy used for cooking in all regions except OECD90 and Eastern Europe (that is, Middle East & Africa, Asian sans Japan and Latin America). From the literature review, assumptions were derived for population growth, average population per household, average household useful energy use for cooking per capita, a weighted average energy efficiency factor for stove and fuel type mix, and the percentage of the population using solid fuels. These values, along with global data from the International Energy Agency (IEA, 2006 and 2012), were used to develop a composite global market for the period 2014-2050.

Adoption Scenarios[3]                                          

Current adoption and future adoption scenarios for Biogas for Cooking were created by: taking the population of cattle, buffalo, and pigs as well as major crop waste by type (maize, paddy rice, sugar cane and wheat) for each country in Asia (sans Japan), Africa, the Middle East, and Latin America from the Food and Agriculture Organization (FAO)’s most recent database; estimating a certain waste production per day (minus a feasibility factor of what is collectable); then factoring in an average daily waste input requirement for a functioning digester. The result was a total potential capacity for small methane digesters per each region. Current data on the number of installed digesters was used to derive current adoption and indicated that 32.5 percent, 0.3 percent and 0.0 percent of the technical potentials of Asian (sans Japan), Middle East & Africa and Latin America respectively were adopted.

Impacts of increased adoption of Biogas for Cooking from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels. Potential for each region were based on the total potential capacity if waste from all animals and crops were used.

  • Scenario 1: For this scenario, it is assumed that each region in question achieves the current adoption in the region Asia (sans Japan): 32.5 percent of its possible capacity, and Asia (sans Japan) doubled its adoption by 2050 in percent terms.
  • Scenario 2: This scenario assumes that each region achieves the current adoption in China—50 percent of its possible capacity, and Asia (sans Japan) achieves 100 percent of its capacity.

Note that capacity here is limited by availability of animal and plant waste not demand for cooking energy.

Emissions Model

By avoiding methane and nitrous oxide emissions through the use of small methane digesters and the replacement of inefficient fuelwood cookstoves, each digester reduces around 1.25-2.95 tons of carbon dioxide-equivalent emissions per year (Zhang et al., 2013; Izumi et al., 2016). Because of leakages and biogas burning, emissions from small methane digesters amount to around 0.02 kilograms of carbon dioxide per mega joule of cooking energy produced (Zhang et al., 2013). No substantial double-counting or integration effects were factors in generating the results for this solution.

Financial Model

The cost of small methane digesters depends on the country of installation, the size, the design, and the material used, and ranges from US$300 in Costa Rica to US$1200 in Kenya.[4] The operational cost of small methane digesters is very low as the manure is almost free of cost, but there is a need for regular maintenance. Maintenance costs ranging from US$0.01-0.08 per kilowatt-hour (Ghimire, 2005 and Shailendra et al., 2015). High initial capital costs, improper construction leading to high maintenance or repair costs, and inadequate operator training are the main barriers to large-scale adoption of small methane digesters (GACC, 2016).

Most of the cost of traditional stoves has been obtained from sources such as the World Bank and the US Environmental Protection Agency (EPA). Weighting based on cooking fuel mix was applied to all costs.

Results

If 57 million traditional stoves are replaced with small biogas reactors, the total carbon dioxide-equivalent reductions from 2020-2050 in the Scenario 1 would be 4.65 gigatons, with a cumulative first cost of US$23 billion to implement albeit with an increase of $100 billion in lifetime operating costs since traditional stoves have few little financial cost since often women collect firewood over several hours per day for free. The Scenario 2 shows a mitigation of 9.7 gigatons from 2020-2050 with 87 million biogas stoves at a cost of $49 billion.  Again lifetime operating costs are higher by $209 billion.

Discussion

Small methane digesters have the potential to provide reliable, carbon emissions-mitigating household heating across the world for cooking and other uses.  The major risk associated with adoption is disrepair and fugitive emissions. Creative feedstock switching and community-scale aggregating are in development to increase the overall technical feasibility, which is currently the limiting factor for the technology. 

 

[1] Current adoption is defined as the amount of functional demand supplied by the solution in 2018. This study uses 2014 as the base year.

[2] For more about the Total Addressable Market for the Buildings Sector, click the Sector Summary: Buildings link below.

[3] To learn more about Project Drawdown’s growth scenarios, click the Scenarios link below. For information on Buildings Sector-specific scenarios, click the Sector Summary: Buildings link.

[4] All monetary values presented are in US2014$.