How biogas could help Malawians without electricity

In sub-Saharan Africa, more than 600 million people (more than 50% of the population) do not have access to electricity. Malawi has one of the lowest electricity access rates in the world: only 14.1% of the total population has access to the main grid. In rural areas, the access rate to electrification is even lower, estimated at 5.6% in 2021.

Decentralized renewable energy systems at household and community scale, such as biogas plants, can provide a solution. Ehiaze Ehimen and Thomas Robin study energy efficiency and energy poverty in marginalized communities. They explain what they found in their research about the potential role of small biogas plants in meeting rural energy needs.

Why are biogas plants such a good idea?

Biogas plants are easy to install and can be relatively inexpensive. They use readily available materials, such as manure and plant waste, and can be built with cement and bricks. They could potentially be used to meet the electrical needs of homes and small communities, especially in rural areas where connection to the national electricity grid may not be economically viable.

Biogas plants take advantage of the fact that rural communities in countries like Malawi have abundant biomass resources, such as agricultural residues, animal waste, and organic municipal waste (discarded grass and vegetables). Biogas production can therefore provide a decentralized energy solution, where energy is produced close to where it is used.

Compared to other energy sources (especially electricity), biogas production systems can have a relatively low cost to install and operate. This makes them suitable for communities with limited financial resources.

There are also health and environmental benefits: they prevent organic waste from rotting in landfills and releasing harmful methane gas, by converting this waste into a useful energy source. They reduce people’s dependence on traditional biomass fuels, such as firewood or charcoal for cooking; These fuels can cause deforestation and indoor air pollution. This is currently a major problem in Malawi. Between 2002 and 2023, Malawi lost 21% of its primary rainforest due to deforestation. And people are experiencing an increasing number of chronic coughs from cooking over a wood fire.

What is a biogas plant?

A biogas plant is a facility that converts organic waste such as animal manure, agricultural waste, food waste and even sewage sludge into gas. It does this through a process called anaerobic digestion. Here, microorganisms break down organic materials in an oxygen-free environment, such as the inside of a sealed drum.

This produces biogas, which is mainly made up of methane and carbon dioxide. It can be used as a renewable energy source for generating electricity, heating and cooking.

A biogas plant has a useful life of 20 years and could be built in various designs. A common design includes the floor plan composed of:

• A rectangular shaped base.
• On top, a brick and concrete dome and a layer of plastic. This could be above or below ground to keep the temperature uniform in the digester and limit temperature fluctuation.
• The central part of the reactor is located underground.
• There are two auxiliary tanks to store the raw material and the digestate (what is left over)
• A thin concrete slab can be added to prevent leaks into the ground.

What did you find?

Our study was the first to investigate whether it was possible to produce electricity for rural farmers in Malawi using biogas. The only small-scale biogas plants that existed in Malawi before our study were located at Zomba Central Hospital and Mikuyu Prison, but they were used only for cooking needs.

Our research found that building a small community-scale biogas plant with a digester volume of 15 cubic meters in Malawi cost a total of US$1,540. A biogas plant of this size can provide enough energy for a family of up to five people to cook for a month.

The biggest costs—$1,089—were cement and labor: qualified masons who had knowledge of waterproofing and insulation and could guarantee that good quality materials would be used. This was a simplified rectangular-based dome reactor design, which is made primarily of brick and concrete, with a layer of plastic to minimize gas leaks.

The cost can vary depending on the size of the biogas plant, material transportation costs, local regulations, labor costs, and the amount of cow manure and corn or grass residue available to feed it. We use manure collected from six cows every day for a year. 10.8 kg of manure were produced per day. The amount of methane produced is estimated to be significantly improved when cow manure is mixed with grass cuttings and post-harvest corn plants – the leaves and husks left on cropland after harvest.

The digestate left after anaerobic digestion is very rich in nutrients such as nitrogen, potassium and phosphorus and can be spread directly on cropland as fertilizer.

What are the challenges?

Access to finance to build biogas plants is a big problem, especially for small farmers or community initiatives. Malawi is one of the poorest countries in the world and the number of people living on less than $2.15 a day is expected to rise to 72% of the population this year. For a small rural farmer earning an average of $380 a year, the initial cost of building and operating a biogas plant is likely unaffordable.

There is also currently a lack of local capacity and technical expertise to establish and maintain biogas production, especially in some rural areas. Training programs would be necessary.

Our study also showed that building larger biogas facilities would be more expensive and operationally more effective, because they would provide more energy for a greater number of people at a lower cost per person. But transporting huge quantities of biomass feedstock by truck is not planned.

Therefore, financial support from governments, non-governmental and non-profit organizations and international development agencies could be essential to overcome these challenges.