Technical Summary

Methane Digesters

Project Drawdown defines as large methane digesters, systems associated with agriculture, manure, and wastewater facilities that produce biogas to be used for electricity generation in dedicated biogas or combined heat and power plants. This solution replaces conventional electricity-generating technologies such as coal, oil, and natural gas power plants.

Methane digesters have been installed throughout the world and at relatively high rates in China, the European Union, and Southeast Asia in the past 20 years. Large bio-digesters can be installed at dairy and hog farms, wastewater facilities, and landfills to produce electricity and heat for use on-site, or to provide electricity or gas to the grid.

Methodology

Total Addressable Market[1]

Two total addressable markets were developed for this sector solutions, supported on lower and higher climate emissions mitigation targets linked to different levels of electricity demand and renewable energy sources integration. The total addressable market for large methane digesters with biogas units for electricity generation is based on projected global electricity generation in terawatt-hours from 2020-2050, with current adoption[2] estimated at 0.29 percent of generation (77terawatt-hours) (IRENA, 2016).

Adoption Scenarios[3]

Impacts of increased adoption of large methane digesters 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.

  • Scenario 1: This scenario is based on the yearly average adoption of six ambitious adoption scenarios from the EU project AMPERE,[4] and the 2°C Scenario of the International Energy Agency’s Energy Technology Perspectives (2016), using a medium growth trajectory. In this scenario, biogas represents 1.65 percent of the total electricity generated in 2050.
  • Scenario 2: This scenario is based on the estimated adoption trajectory of biomass and waste from Greenpeace (2015) Advanced Energy [R]evolution scenario, resulting in a lower adoption of this solution due to integration with other electricity generation solutions with higher expectations of increase as wind and solar.

These external sources do not clearly depict biogas technologies for electricity generation adoption pathways: their results combine biomass and waste for electricity generation. Therefore, a few assumptions were considered to obtain future adoption: biogas represents approximately 20 percent of total electricity generation from bioenergy worldwide, and the feedstocks covered within this solution represent 70 percent of total biogas. Landfill methane accounts for the remaining 30 percent (AEBIOM, 2012; WBA, 2013).

Financial Modeling

Several data points were analyzed to determine the average capital cost: it is recognized that costs can vary significantly by region, but exhaustive regional data was not available to calculate an average cost weighted by installation size. Available data points were mainly from Organisation for Economic Co-operation and Development (OECD) countries, reflecting the preponderance of present-day biogas installations in the European Union and United States. The financial inputs used in the model assume average installation costs of US$6,111 per kilowatt.[5]  Due to the maturity of this technology, a learning rate of 2 percent was considered, similar to the one applied to conventional technologies such as coal and natural gas power. An average capacity factor of 92 percent was used for the solution, compared to 57 percent for conventional technologies. An average fixed operation and maintenance cost of US$53.2 per kilowatt, and variable operation and maintenance cost of US$0.05 per kilowatt-hour, were considered for this solution, compared to US$34.7 and US$0.005, respectively, for the conventional technologies.

Integration[6]

Through the process of integrating large methane digesters with other solutions, the total addressable markets were adjusted to account for reduced demand resulting from the growth of more energy-efficient technologies,[7] as well as increased electrification from other solutions like electric cars and high-speed rail. Grid emissions factors were calculated based on the annual mix of different electricity generating technologies over time. Emissions factors for each technology were determined through a meta-analysis of multiple sources, accounting for direct and indirect emissions.

In addition, large methane digesters have a noteworthy impact on methane and nitrous oxide emissions avoidance that would have occurred due to anaerobic degradation, which is also accounted for in the analysis.

Results

Comparing the results from the two modeled scenarios to the Reference Scenario allows us to estimate the climate and financial impacts of increased adoption of biogas units for electricity generation. The Scenario 1 projects 1.7 percent of total electricity generation worldwide coming from biogas by 2050 (i.e. 761 terawatt-hours). In the Scenario 2 the market share is smaller due to an higher total addressable market (i.e. 0.69%) with 487 terawatt-hours of electricity generation.

The climate and financial impacts for the increased adoption of large methane digesters with biogas power plants are both substantial. Scenario 1 adoption avoids a total of 9.8 gigatons of carbon dioxide-equivalent of greenhouse gas emissions from 2020-2050. Large digesters have marginal  first costs of US$284.8 billion; with lifetime operational costs due to feedstock purchase, maintenance, and operational staff salaries of -US$2.83 billion. The Scenario 2 yield results in a small order of magnitude, with reductions in greenhouse gas emissions over 2020-2050 of 6.2 gigatons of carbon dioxide-equivalent.

Discussion

The conversion of waste material in bio-digesters into biogas has several positive financial and environmental impacts for different levels of stakeholders: farmers, industries, municipalities, and governments. These systems enable the capture and use of methane while also addressing waste management and nutrient recovery needs. They can also realize several revenue streams and cost savings for owners.

Appropriate feedstock for electricity-generating biogas plants is available in adequate quantities across the world from sewage sludge and agriculture systems. However, there is significant uncertainty associated with the future adoption of these technologies.

 

[1] For more about the Total Addressable Market for the Electricity Generation Sector, click the Sector Summary: Electricity Generation Sector link below.

[2] Current adoption is defined as the amount of functional demand (i.e. TWh) supplied by the solution in 2018.

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

[4] The adoptions from three AMPERE models (GEM E3, MESSAGE, and IMAGE) on their 450 scenarios were used.

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

[6] For more on Project Drawdown’s Electricity Generation Sector integration model, click the Sector Summary: Electricity Generation link below.

[7] For example: LED lighting and high efficiency heat pumps.