Roth, Christa

Christa Roth has updated the GIZ HERA Micro-gasification Manual

It is extensively revised, and features good -clear descriptions of essential cooking stove topics, e.g. choosing appropriate fuels, cooking stoves and technologies.

She highlights all of the major micro-gasifier cooking stoves, and includes a new section on biochar, with good, clear graphics and descriptions for how to use biochar.

An essential reference for everyone's cooking stove library, and this is all work supported by the German people through GiZ, we appreciate their support of Christa's amazing work.

Christa Roth's excellent report
Micro-gasification: Cooking with gas from dry biomass

has a new location:

Her comprehensive survey of micro-gasification technology has great technical information and is well worth the read.

thanks to GiZ (the German people) for making it available to all of us.

Christa Roth, January, 2012

To the members of the list who don't know Energypedia yet: it is an online resource created as a Wiki by GIZ . After some years of development as company-interal resource, it was opened to the public energy community late last year. No registration needed to read.

Christa Roth, February, 2011

Dear all, find below the links to new publications by GIZ HERA poverty-oriented basic energy services, among them the manual on Micro-gasification: Cooking with gas from biomass. For queries please refer to the respective authors or Michael Blunck from HERA.

the HERA web site

Micro-gasification: Cooking with gas from biomass

- new link :

Micro-gasifiers: much more than „just another improved cook stove”. In this new HERA handbook, Christa Roth provides an introduction to the concept and the application of wood-gas burning technologies for cooking.

Modern Energy Services for Modern Agriculture. A Review for Smallholder Farming in Developing Countries.
This publication provides an overview on energy inputs required in different steps of the agricultural production chain, such as production, post-harvest and storage, processing, and commercialization.

Small-scale Electricity Generation from Biomass – Part III: Vegetable Oil
In the third and final part of HERA’s paper series on power generation from biomass, GIZ and non-GIZ experience with electricity production from vegetable oils is compiled. While from a technology point-of-view, plant oils constitute a very viable option for off-grid power generation in developing countries, their sustainable application in daily operation for rural electrification projects still remains rare. The paper identifies remaining bottlenecks and provides recommendations for future electrification projects based on plant oil.

Carbon Markets for Improved Cooking Stoves – Revised Edition: January 2011
After receiving a lot of positive feedback for the 2010 edition of the carbon market guidebook for cooking stove projects, HERA has come up with a major revision for 2011. Besides a large number of minor corrections and updates, a new chapter on “Implementing a Carbon-funded Cooking Stove Project” with information on how to practically design a carbon-funded stove project has been added. The chapter includes information on stakeholders’ roles and responsibilities, the CDM-PoA approach, recommendations on the use of carbon revenues as well as an overview on expected costs and revenues from a stove project on the carbon market.

Christa Roth and Christoph Messinger, August 2010

Existing Charcoal Stove

Existing Charcoal StoveImproved Charcoal Stove

Improved Charcoal Stove

Improving the Charcoal Stove for Haiti, Stove Camp 2010 (see the Stove Camp Summary for challenge details)

Main points mentioned at the end of the Stove Camp Workshop

  1. We need a high turn down ratio.

    To bring water and foods fast to the boil, we need high power in the heat-up phase.
    However, thereafter we commonly need low power for simmering. The stove
    therefore needs to offer the opportunity to turn down the power output drastically.

    1. Regulation of primary air supply (e.g. closing door)
    2. The gap between pot and charcoal is increasing over cooking time (shape of char container provides more depth = increased gap to the char)
    3. c) The amount of char available at the end of cooking is reducing (conical shape of char container = less char over time available)
  2. We need to reduce heat losses to the bottom and to the side of the stove.

    A char container radiates heat to all sides – not just to the pot. To reduce the amount
    of char used, it is important to reduce the heat losses to the other directions.

    1. Bottom of stove: rebounding plate (with holes) in between primary air supply
    2. intake and charcoal container. Thus primary air is channeled through the
    3. heated rebounding plate, taking some heat back into the char container.
    4. Side of the stove: double wall with air in between for insulation.
  3. We need to maximize heat harvest from a given amount of charcoal.

    Charcoal burning is mainly influenced by the amount of air available in the char

    1. A vertical spacer in the center of the charcoal container (Lanny Henson’s pig tail”) seemed to increase the availability of air for charcoal combustion.
    2. Additional draft (e.g. forced air) may increase heat generation per time unit. However, this may also increase CO emissions and reduce efficiency of char use.
    3. Secondary air to burn off the CO in a gap between the charcoal and the pot may provide additional heat. However, for this to be beneficial it may not impact on the surface area available for direct radiation from the charcoal to the pot and should not cool down the air in the gap (well preheated secondary air).
  4. We need to maximise heat transfer to the pot.

    Generating as much heat as possible out of a given amount of charcoal is one step.
    But another important step is to make sure that most of this heat actually is
    transferred into the cooking pot.

    1. “Sunken pot” concept seems to provide best results in terms of heat transfer (Henson stove). Unfortunately, in real life this might not be possible in many work environments.
    2. Best heat transfer is NOT achieved if the pot rests on the char. Optimum is about 1inch away from the char, not closer than that. For Simmer, this could increase to 2-3 inches.
    3. A skirt is highly important to shield the gap area between the pot and the char against the influence of wind. The gap between pot and skirt should bedetermined.

Christa’s Summary of the stove camp

Observation and necessary action Derived Design Principles
Charcoal radiates heat to all
sides: as much can radiate
towards the bottom of the stoves
as can radiate upwards towards
the pot.

Avoid loss of radiating and
conducting heat from charcoal
that is not directed towards the

  • Add space between the charcoal grate and other stove parts: Lift the charcoal grate slightly off the bottom of the stove and increase the space to the sides of the stove.
  • Limit the places where the hot grate can conduct heat to other stove parts.
  • Add a deflector plate between charcoal chamber and the stove bottom to radiate heat back upwards.
  • Insulate the stove bottom to prevent heat loss through the bottom.
  • Insulate sides of the stove.
  • Regain heat through air circulation (air cooling of stove) by passing air through heated stove parts thus preheating air entering the combustion system. This can be by passing primary air through the deflector plate below the grate and/or secondary air through a gap between double side walls of the stove.
Charcoal combusts in function of the available oxygen. Thus heat generation is a function of
air supply to the charcoal grate.

Action: get the right amount of air to the charcoal grate. To little will choke the combustion, too much will cool the flue gases.

If power of the stove is too low, increase air supply by

  • making more holes in the grate.
  • adding a ‘Henson pig-tail’ vertical air-pass through the charcoal bed.

Do not pile the charcoal up too high, as this will restrict air flow through the charcoal bed (this is influenced as well by the shape and particle size of the charcoal chunks).

The combustion of charcoal goes from oxidizing C to CO, then in
a subsequent step from CO to CO2.

CO is a toxic gas and has still considerable energy value. Ensuring a complete combustion
will increase energy output and reduce toxic emissions.
Action: avoid CO emissions.

Charcoal radiates heat but there is also considerable convection of hot flue gases.
Optimize transfer of created heat into the pot.
Avoid obstructions between the radiating charcoal bed and the bottom of the pot (increase
the view factor of the charcoal seeing the pot).

Christa Roth, December, 2009

Good question, Tom: while we were with GTZ in Malawi, we did a lot of work on standardising the dimensions of locally produced fired portable clay stoves (model adopted from Practical Action's work in Kenya). Their selling price ranges from 1- 3 $ in the communities. We all agree that stove-wise, they are not the greatest devices, but the most affordable, accessible and convenient ones in this area. As people mostly don't have kitchens, portability ranges high on the priority list of peoples choices, so mudstoves are not an option here.

Thus we had to work with the available material to produce a stove that people wanted and could afford. With the help of simple moulds and measuring tools we worked towards a uniformity of this artisanal product and standardise the crucial points influencing stove
performance: size of the door, height of the fire-chamber, durability and shape of potrests to ensure a standard gap between stove body and pot., to name a few.
I never had a chance to get the stoves tested for emissions, but they do reduce fuel consumption as compared to the open fire, while the amount of reduction depends more on the user than the stove itself.
I can't quantify the change in performance achieved by these quality control measures, but they definitely led to a much better uniformity and acceptance of this artisanal product. A good-looking stove just sells better!

GTZ Probec Protos Stove Tests Tanzania
Christa Roth, GTZ Probec, September 26, 2006

To give feedback on the Bosch-Siemens PROTOS plant oil stove when using Jatropha oil:

To give feedback on the Bosch-Siemens PROTOS plant oil stove when using Jatropha oil:
The long term test of the Jatropha oil being used in the BSH stove is currently under way in Tanzania in cooperation with GTZ-ProBEC. Preliminary tests are giving very positive results, even though with Jatropha oil being produced on small scale. Purity of the oil seems to play a crucial role, but we will be able to tell more early 2007.
The stove is designed for using straight plant oils, no need to convert them into Biodiesel. However, Biodiesel can also be used.

Prototype Staff House Kitchen Assembly Kit Stove with Pot Rests
Christa Roth, GTZ/IFSP Mulanje, Malawi, May 19, 2006

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