Updated on January 20, 2024


Created on May 25, 2016

Flexi Biogas BG5

Upcoming Update

Flexi Biogas BG5 is a system that degrades biological matter into a gas useful for cooking, through a flexible above-ground plastic digestor.

Tested By
  • The International Fund for Agricultural Development (IFAD)
Content Partners


Product Description

Flexi Biogas BG5 developed by Biogas International Limited is a flexible above-ground system that produces biogas. The market name of the BG5 model is Std Domestic. The Flexi system is installed in only a few hours and normally are operational within 7-10 days, is portable and expandable, and runs on any biodegradable matter. Since it is a domestic model, it can supply sufficient cooking fuel for a family of up to around 12 members.

Target SDGs

SDG 7: Affordable and Clean Energy

SDG 8: Decent Work and Economic Growth

Market Suggested Retail Price


Target Users (Target Impact Group)

Household, NGOs

Distributors / Implementing Organizations

Although distribution started as part of an IFAD program, Biogas International Limited is the sole distributor to date. There are a few local and regional agents who market and install systems on their behalf as well.

Competitive Landscape

Manufacturing/Building Method

Locally manufactured with specially treated robust materials designed to withstand all weather conditions in Nairobi, Kenya.

Intellectural Property Type


User Provision Model

Biogas International Limited is the sole manufacturer and distributor.

Distributions to Date Status

500 Flexi Biogas systems were distributed between 2011 and early 2014. This product started as a pilot program launched by the IFAD. The IFAD intended to deploy about 1,000 more systems over the course of 2014–2016.

Output energy product


Average daily biogas production (m3/day)

2 to 3

Description of waste source(s)

Animal and organic waste

Waste input requirements (kg per hour or day)

20 kg of fresh cow dung yields 1,000 litres of cooking gas.

Description of other input requirements

This product requires a 50% water – 50% dung mixing ratio when feeding the digester

Other input requirements (amount per hour)


System dimensions (m)

6 m3

Design Specifications

The Flexi Biogas BG5 includes four key parts: plastic input and output pipes, a reinforced plastic digester bag, plastic piping to transport biogas to home or storage, and a plastic greenhouse covering. The system can run on any biodegradable matter - cow, pig, goat, sheep, rabbit or/and chicken dung, kitchen waste, market waste, grass, water hyacinth, farm weed, and garden clipping.

  • Digestor: 6m x 3.75m plastic bag made of PVC tarpaulin. High cost of good-quality plastic, increasing the price of fabrication.
  • Greenhouse Tunnel: Polyethylene plastic. Trapping heat and keeping the temperature between 25 and 36°C. During the day the tunnel captures solar radiation, increasing the temperature of the organic waste material (substrate) in the digester.
  • Pipeline: gas piped through a PVC tube of 15 meters connected to an appliance or piece of equipment such as a gas stove for cooking.
  • Cross-flow design: prevents overloading of the system and crusting (scum formation). This system does not require agitation.
  • Weight: 10 kg
  • Startup manure required: 1 ton
Process: Flexi Biogas systems perform anaerobic digestions. Anaerobic digestion is the breakdown of organic material by micro-organisms in the absence of oxygen. It produces biogas, a methane-rich gas that also contains carbon dioxide with trace amounts of other gases; and digestate, a source of nutrients that can be used as a fertilizer. The digestion process begins with bacterial hydrolysis of the input material in order to break organic polymers into smaller molecules that finally become methane and carbon dioxide after acidogenesis and methanogenesis.

Product Schematics

Technical Support

Free, provided by Flexi Biogas Solutions. Upon installation, users are trained on how to run and maintain the system, what does and what doesn’t, troubleshooting the system, and how to solve hitches. Technical support to all the clients is offered 24/7 via mobile phone and email.

Replacement Components

1-year warranty on all components against manufacturer defects. Apart from the digester envelope itself, all other components are "off-the-shelf" and are available for replacement in every hardware store.


This product has a lifespan of at least 10 years and it can be enhanced by applying a sunscreen UV block solution every seven years. The greenhouse tunnel requires replacement every 5 years.

Manufacturer Specified Performance Parameters

The manufacturers specify the following as the system's benefits:

  • Flexi Biogas systems are prefabricated and installed in a few hours.
  • The overflowing bio-slurry from the system is a highly nutritious fertilizer ready for absorption by plants without ”burning the plants”. It can also be applied as a top dressing or sprayed on plants as an effective pest repellent.
  • Flexi systems run on any bio-degradable matter. High calorific feedstock produces larger volumes of gas.
  • FlexiTech employs “True Cross-flow” fermentation, which means that what goes in one end is fully processed before exiting the other. This also means that 100% of the biogas is captured making FlexiTech the GREENEST biogas plant design yet.
  • After installation, the system will have usable volumes of gas within 3 – 5 days and is normally in full production within 7 – 14 days.

Vetted Performance Status

A technical and field performance evaluation of Flexi biogas plants was conducted by the  International Fund for Agricultural Development. As a conclusion on the study, researchers stated:

  • Women can play an effective role in earning their livelihood through Biogas by forming self-help groups that can install and maintain biogas plants.
  • The Flexi biogas BG5 generally meets cooking and heating requirements for a family of 4-6 people.
  • The Flexi biogas system can be recommended to small and poor families as it is easy and quick to install with the temperature-controlled conditions.


There are some dangers associated with biogas digesters: fire hazard, leaks, and negative pressure, but since this is a small/ family size system the hazards are also lower.

Complementary Technical Systems

A BioDC generator can be acquired in order to run  automotive chargers, for powering lights, TV, radio phones, etc.

Academic Research and References

Grist, N., Winkels, A. and Reynolds, J., 2018, Baseline Study: Dunga Beach Biogas Community and Household Pilot, the University of Cambridge Institute for Sustainability Leadership (CISL), 2018.

Benjamin K. Sovacool, Matthew Kryman, Taylor Smith, Scaling and commercializing mobile biogas systems in Kenya: A qualitative pilot study. Renewable Energy, Volume 76, April 2015, Pages 115-125

Sehgal, K., Wanjihia D., Kembe M., Flexi Biogas systems: inexpensive, renewable energy for developing countries. IFAD, 2012 November.

Vijay, V.  Technical and field performance evaluation of Flexi biogas plants. IFAD, 2014.

International Fund for Agricultural Development. n.d. IFAD.

Flexi Biogas. n.d. Biogas International.

Biogas International Limited . 2015. Flexi Biogas Systems Brochure. Biogas.co.ke. Kenya: Biogas International Limited.

Biogas International Limited . 2018. Flexi Domestic Systems. Biogas.co.ke. Kenya: Biogas International Limited.

Rota, Antonio, and Karan Sehgal. 2015. How to Do – Mainstreaming Portable Biogas Systems into IFAD-Supported Projects. Ifad.org. Rome, Italy: IFAD.


Compliance with regulations


Evaluation methods

Field Trials

Other Information

Biogas International Limited also offers other products like gas systems, utilities, bio-slurry systems, and more.

Comments from the Community


  1. David Fulford says:

    The use of flexible biogas plants is very popular in Kenya and other places in East Africa. They are much cheaper than masonry plants, but have shorter lifetimes. Flexible bag plants were first used in Vietnam, but masonry plants became more popular, as they did last much longer. The vary large programmes in Asia (India and China) all use fixed dome plants.

  2. David Fulford says:

    500 plants in three years is seen as a small programme for domestic biogas. It is not clear how it can be patented, as flexible plastic biogas plants have been used for at least 20 years.
    Plastic biogas plants can be made very quickly. Practically, they have a short life-time, unless they are looked after very carefully.

  3. David Fulford says:

    There is a large number of publications on biogas from groups such as SNV. Most of the successful programmes were based on masonry plants, such as fixed dome systems.

  4. David Fulford says:

    All of the biogas programmes that have won Ashden Awards (see http://www.ashden.org) use fixed dome digesters.

Leave a Reply

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