Biomass refers to renewable organic materials (matter containing carbon and hydrogen compounds) from plants and animals[1]. Biomass energy is generated using these organic materials as either heat, electricity or biofuel etc. Fundamentally, the energy in biomass is from the sun through the process of photosynthesis. Here, sunlight together with water and carbon dioxide synthesize oxygen and glucose as shown in the chemical equation below.

Biomass sources mostly used include:

  • Agricultural crops and waste – hyacinth, corn, soybeans, crop and food processing residues.
  • Wood and wood processing waste – firewood, wood pellet, lumber, sawdust.
  • Biogenic materials – paper, cotton, food waste.
  • Animal manure and human sewerage.

Useful energy is obtained from biomass using any the processes listed below.

  1. Burning- This is what is commonly used especially in developing countries to produce heat.
  2. Thermochemical conversion, through pyrolysis or gasification. In both processes, biomass is heated in an enclosed pressurized container with oxygen supply varied depending on the two processes.
  3. Chemical conversion where vegetable oils, animal fats and greases are converted into fatty acid methyl esters used to produce biodiesels.
  4. Biological conversion where fermentation is used to convert biomass into ethanol and anaerobic digestion to produce renewable natural gas[1].

70% of Kenya’s energy demand is met by biomass. Two thirds of this energy is from firewood while the rest is from charcoal. In rural areas biomass use accounts for up to 90% of the energy used[2]. This highlights the importance of biomass but also shows the level of underdevelopment in the country with little or no adoption of modern clean energy sources in the rural areas.  The total biomass energy in the country is estimated at  GJ annually[3].

In recent years, there has been a growing interest in modern biomass conversion processes. This is both by efficiency improvement as in energy saving jikos, biogas, biofuel and cogeneration plants. The Bio joule Thermal Plant and the Baringo thermal plants use biogas to generate electricity with both having a combined capacity of 12MW[4].  Other cogeneration plants have been developed notably in sugar processing industries. Mumias Sugar Company uses cogeneration and exports 26MW to Kenya Power Company.  

Figure 1: Mumias Sugar Company Substation.

The growth of biomass energy has been fueled by the need to decarbonize the planet. With biomass listed as a renewable source of energy by the UN[5], many companies and countries are increasing their efforts in seeing a growth in the utilization of biomass for energy. Sadly, notable scientists are disagreeing with these developments, with data showing biomass as a worse polluter than fossil fuels in some applications[6]. Proponents on the other hand claim biomass is carbon neutral and renewable. Is biomass then the green energy that might be destroying the planet? Rather is it a green climate solution?

To its advocates, biomass is carbon neutral. Trees take in carbon dioxide from the atmosphere through the photosynthesis process. The trees release the carbon back to the atmosphere when they naturally die or when burnt. If trees are replanted, at a faster rate than they are cut then the carbon cycle will be in balance, hence the carbon neutral consideration. Biomass then becomes important in replacing fossils, which unlike biomass take several years store their carbon. On the other hand, some scientists explain that atmospheric carbon dioxide can only be reduced if fast growing crops (energy crops) are grown in unproductive lands. Cutting forests for biomass energy would release carbon to the atmosphere that would have been stored in the trees if they were not cut, and replanting the trees to recapture the released carbon takes decades and even centuries. Moreover, more carbon is released when the trees are burnt resulting in a net increase in carbon dioxide.

With the incentives offered by governments for biomass energy, the number of biomass plants are growing in the developed nations. The impact of this trend is an increase in global warming CO2. Biomass burning plant produce 65% more CO2/MWh than modern coal plants and up to 285% more than combined cycle plants. Burning wood biomass emits nitrogen oxides, sulfur dioxide, mercury, lead and other hazardous material. The air pollution from biomass burning has been cited by American Lung Association to be a danger to public health. It causes respiratory illnesses, heart disease, cancer and delays development in children.

The harvesting of leaves, plant parts and limbs, which would otherwise recycle nutrients back into the soil as they decompose. This can increase soil erosion as the amount of runoff increases and diminish soil fertility. Removing vegetation from the ground destroys habitat for wildlife on the forest floor.

Figure 2: Deformed trees cut for biomass energy

Another issue that should be addressed is the type of trees that are used for biomass energy. Some trees are used in making boxes, toilet paper, paper etc. therefore increasing the overall demand for wood. This will eventually lead to more logging and trees, which would otherwise have been absorbing carbon will be cut, releasing the stored carbon. Natural forests store carbon in the whole ecosystem not just the trees. It is estimated that about half the carbon stored in natural forest is in the soil[7]. Destroying such forests will release carbon, which will take planted forests centuries to recover.

Figure 3: Natural forests store carbon in the whole ecosystem.

In general the ‘greenness’ of a biomass varies with the specific application, its location, type of biomass used and the conversion process employed. Implementation of biomass projects with the aim of reducing carbon should be considered carefully instead of a blatant declaration of biomass energy as green and renewable. Taking the advice of Bob Perciasepe “People who are very enthusiastic should temper their enthusiasm just as the opponents should probably temper their opposition”[8]. This I think quells the debate on whether biomass is green or not. The caution remains, governments and private organizations should make haste slowly when it comes to biomass. 


[1] “Biomass explained – U.S. Energy Information Administration (EIA).” [Online]. Available: [Accessed: 05-Apr-2021].

[2] “Biomass Energy Resources in Kenya –” [Online]. Available: [Accessed: 05-Apr-2021].

[3]“A biomass energy flow chart for Kenya|INIS.” [Online]. Available: [Accessed: 05-Apr-2021].

[4]“List of power stations in Kenya – Wikipedia.” [Online]. Available: [Accessed: 05-Apr-2021].

[5] A. / 66 and / …… General Assembly, “United Nations ADVANCE UNEDITED COPY Promotion of new and renewable sources of energy Report of the Secretary-General,” 2011.

[6]“Is Biomass Really Renewable?” [Online]. Available: [Accessed: 05-Apr-2021].

[7]D. O. Hall and J. I. House, “Trees and biomass energy: Carbon storage and/or fossil fuel substitution?,” Biomass and Bioenergy, vol. 6, no. 1–2, pp. 11–30, Jan. 1994, doi: 10.1016/0961-9534(94)90081-7.

[8]“The ‘Green Energy’ That Might Be Ruining the Planet – POLITICO.” [Online]. Available: [Accessed: 07-Apr-2021].